Dissertations / Theses on the topic 'Metallurgical'

The MAX phases constitute a group of ternary ceramics which has received intense attention over the last decade due to their unique combination of properties. The Ti3SiC2 is the most well studied MAX phase to date and it has turned out to be a promising candidate for high temperature applications. It is oxidation resistant, refractory and not susceptible to thermal shock, while at the same time it can be machined with conventional tools which is of great technological importance. Most attempts to synthesize bulk Ti3SiC2 have involved pure titanium in the starting powder mixtures, but Ti powder is oxidising and requires an inert atmosphere throughout the synthesis process which makes the procedures unsuitable for large scale production. The aim of the first part of this study was to delineate the influence of sintering time and temperature on the formation of Ti3SiC2 from a starting powder which does not contain pure titanium. Titanium silicon carbide MAX phase was synthesised from ball milled TiC/Si powders, sintered under vacuum for different times and temperatures. After heat treatment the samples were evaluated using scanning electron microscopy (SEM) and x-ray diffraction (XRD). This study showed that TiC was always present in the final products whereas TiSi2 was an intermediate phase to the Ti3SiC2 formation. The highest amount of Ti3SiC2 was achieved for short holding times of 2-4 hours, at high temperatures, 1350-1400¢ªC. More elevated temperatures or extended times resulted in silicon loss and decomposition of Ti3SiC2. In the second part of this study the sintering reactions and the mechanisms of formation of Ti3SiC2 were investigated by x-ray diffractometry, thermodilatometry, thermogravimetry, differential scanning calorimetry and mass spectrometry. TiC/Si powders of the different ratios; 3:2 and 3:2.2, were heated to different temperatures under flowing argon gas in a dilatometer and examined by XRD. The TiC/Si powder samples of the ratio 3:2 were further investigated by the other thermal analysis methods. The results confirmed the presence of the intermediate phase TiSi2. From 1500¢ªC silicon evaporation and MAX phase decomposition were observed, and the results show that the MAX phase formation may be concurrent with the melting of silicon. TiC was always present in the final products, either as a reactant or as a decomposition product. The extra silicon of the 3:2.2 TiC/Si powder significantly increased the Ti3SiC2 conversion and no intermediate phases were observed for this powder mixture. The Si of these samples did not melt or evaporate, and only minor decomposition was observed even at 1700¢ªC. These results indicate that the silicon content of the initial powder mixture is decisive to the reaction mechanisms of the sintering process.

Godkänd; 2007; 20070523 (ysko)

In mineral processing, one of the most important and versatile separation methods is flotation. Flotation utilizes the different surface properties of the valuable minerals in the ore to separate them from the less valuable gangue material in the ore. Crushed and ground ore is mixed with water and fed into flotation tanks. In the flotation tanks, the particles of valuable mineral are made hydrophobic. That way, they can be floated by attaching to air bubbles and gather on top of the flotation tank as froth. This froth, containing higher concentrations of valuable mineral, is recovered and then processed further. The flotation circuit is controlled and maintained using measurements on the mass flows and grades of different materials. Due to economical, practical, and technological limitations, these measurements are performed at a chosen number of points in the circuit and at discrete points in time. Poor measurement data can have devastating consequences if the operators are left with limited information and errors in the circuit remain undetected. The accuracy of the acquired measurements is improved by performing mass balance and reconciliation. Traditionally, mass balance uses the sum of the total mass flows and the average grades over long times to avoid including the internal mass of the circuit in the calculations. It is desirable to perform mass balance directly to allow for faster intervention if any failures occur in the circuit during the on-line process. This report describes an on-line dynamic approach towards mass balancing and reconciliation of the mass flows and grades in a flotation circuit. Here, physical models of the flotation circuit are used to construct mass balance constraints using interpolation and test functions and the mass balance problem is posed as an optimization problem. The optimization problem is to adjust the assay such that the residual, the difference between the measured and the adjusted assay, is minimized while maintaining mass balance. An implementation in MATLAB and tests on synthetic data show that the dynamic formulation of mass balance does adjust 'erroneous' measurements such that mass balance is fulfilled. Given this result, there are still important aspects of the implementation that have to be addressed. The model uses the unknown and cell specific parameters flotation rate and recovery. Thus, these must be found or properly modeled. This report proposes a possible model for flotation rate as well as a strategy to find the recovery. The requirements of accuracy and speed of the implementation are also discussed. Possible next steps of this project is to further confirm a time effective implementation using synthetic data. Consequently, the implementation can be adapted for natural data in order to verify correctness of models.
I malmanrikning, är flotation en av de viktigaste och mest mångsidiga metoderna. Flotation utnyttjar de fysikaliska ytegenskaperna som partiklar av värdemineral har för att separera dessa från det mindre värdefulla gråberget i malmen. Krossad och mald malm blandas med vatten och matas in i flotationstankar. I flotationstankarna görs partiklarna av värdemineral hydrofobiska. På så vis kan de fästa sig vid luftbubblor och flyta till ytan och bilda ett skum. Detta skum samlas sedan ihop och behandlas vidare eftersom det innehåller en högre koncentration av värdemineral. Flotationskretsen styrs och underhålls med hjälp av mätningar av massflödena och halterna av de olika ämnena som finns i kretsen. På grund av ekonomiska, praktiska, och teknologiska hinder kan dessa mätningar bara göras på ett utvalt antal punkter i kretsen samt bara vid diskreta tillfällen. Felaktigt data kan ha förödande konsekvenser om operatörerna lämnas med begränsad information och processen fortlöper med oupptäckta fel. Mätsäkerheten kan förbättras med hjälp av massbalansering och haltjustering. Traditionellt görs massbalansering genom att summera den totala massan som löpt genom kretsen samt medelvärden av halterna över lång tid för att undvika att räkna in den interna massan i systemet. Det är önskvärt att utföra massbalansering direkt för att möjliggöra snabbare ingrepp ifall fel uppstår i kretsen under den fortlöpande processen. Denna rapport beskriver en dynamisk lösning för massbalansering och justering av massflöden och halter i en flotationskrets. Här används fysikaliska modeller av kretsen för att konstruera bivillkor för massbalans med hjälp utav interpolation och testfunktioner och massbalanseringsproblemet ställs upp som ett optimeringsproblem. Optimeringen sker genom att justera mätserien så att residualen, skillnaden mellan det uppmätta värdet och det justerade värdet, minimeras under uppfyllande av mass balans. En implementation i MATLAB och tester på syntetisk data visar att den dynamiska formuleringen av massbalans justerar de felaktiga mätvärdena så att massbalans uppfylls. Med det resultatet i åtanke, finns det fortfarande viktiga aspekter av implementationen som bör tas hänsyn till. Modellen använder de okända och cellspecifika parametrarna flotationshastighet och utbytet och dessa måste kunna bestämmas för att denna modell ska kunna användas. Ett förslag på modellering av flotationshastigheten föreslås i rapporten. Dessutom ges förslag på strategier att hitta utbytet. Kraven på noggrannhet och snabbhet diskuteras också. Möjliga nästa steg för projektet är att vidareutveckla en tidseffektiv implementation genom att använda syntetiska data. Därefter kan en implementation för naturligt data verifiera modellerna.

The increase in industrial activities has contributed towards an increase in environmental pollution problems. Many ecosystems have deteriorated as a result of an accumulation of pollutants including heavy metals contained in effluents discharged from various industrial processes. Legislative standards require that pollutant levels be controlled to fall within set limits. The World Health Organisation (WHO) states that the following metals: aluminium, chromium, manganese, iron, cobalt, nickel, copper, cadmium, mercury and lead are a concern. The research has focussed on the removal of heavy metals from industrial waste water. This was achieved by investigating, characterising and quantifying pollutants within a metallurgical industry environment resulting from applied operations technology and then looking into abatement measures that can be put in place.The study was done and conclusions are discussed below. Analysis of samples indicated the presence of heavy metals with varying concentrations at different sampling points. D1 borehole is found to have higher chromium levels because ferrochrome was once stored in that catchment area. The dam and road bridge sites manganese content is higher due to suspended particulates settling on the ground and being washed down by water streams . Raw materials from mines contain heavy metals which are transferred to water systems during handling. In this research the toxic metal ion biosorption on an inexpensive and efficient biosorbent from agricultural waste materials has been investigated as replacement strategy for existing conventional systems. The study was conducted by using eucalyptus leaves powder for sequestering heavy metal ions from waste water. The metal uptake from an aqueous solution is facilitated by functional groups in the ligno-cellulosic material Many solids are capable of adsorbing ions and molecules from solutions . The removal of heavy v metals from aqueous solution using eucalyptus leaves has been investigated under different experimental conditions viz. initial metal concentration and adsorbent mass. Results obtained indicated a decrease in metal concentration due to biosorption of a known elemental concentration per known volume by a known mass of sorbent over a specific time. Sorption is found to be dependent upon contact time, initial concentration, sorbent dose of small quantities of wastewaters containing heavy metals. In the event of high levels of heavy metal being experienced, ground eucalyptus leaves can be used for heavy metal recovery from wastewater. A procedure covering the sorbent mass required per average specific pollutant concentration over a specific time frame can be compiled to optimise sorption. The advantage of biosorption compared to conventional treatment methods are low cost, high efficiency, minimisation of chemical and biological sludge as well as the regeneration of biosorbents and a possibility of metal recovery. vi

Current water-cooling technology used in the metallurgical industry poses a major safety concern. In addition, these systems are expensive to operate and result in significant energy losses.
The purpose of the research presented in this thesis was to develop a viable cooling system based on novel heat pipe technology which addresses these problems. This technology employs boiling as the means to store and transfer heat energy. The large heat extraction capacity of the device is owed to two design features: firstly, a separate return line that generates a column of liquid working fluid which drains into the evaporator by gravity, and secondly, a helical flow modifier in the evaporator that stabilizes annular two-phase flow.
A full-scale copper tapblock and launder were designed with water-based heat pipe cooling systems. These systems were successfully tested under industrial heat loading conditions, using a gas burner to simulate the heat loads.
The tapblock cooling system was able to dissipate 142 kW per heat pipe, at heat fluxes as high as 2.4 MW/m2. These values are the largest to date using the novel water-based heat pipe technology. The launder system was the first to incorporate horizontal heat pipes, as well as have multiple evaporators feeding a single condenser.
The cooling systems used in both experiments were fundamentally safer than watercooling systems, being operated at low pressures and with only several kilograms of water exposed to the heat source. The cooling water requirements of these systems represent a reduction of 80-95% compared to conventional water-cooling, with increased potential for energy recovery.
During the testing, dry-out and film boiling were identified as the main limitations. It was found that film boiling occurs when the flow in the evaporator is not great enough to generate a helical motion. The dry-out limitation was achieved when the velocity of the flow within the evaporator was too great, causing a large pressure gradient that opposes the gravity head of the return line.
Both of these limitations are related to the configuration of the evaporator, i.e. the return line and the flow modifier. A methodology was developed to model the evaporator numerically using computational fluid dynamics. This methodology can be used to understand how the design parameters of the evaporator affect the flow patterns during operation.

This study aimed to investigate the relationship between the tensile strength of metallurgical coke and both the textural composition of the carbon matrix and the porous structure of the coke, and further to assess the use of these structural features as bases of methods of coke strength prediction. The forty-four cokes examined were produced in a small pilot-oven from blended-coal charges based on six coals differing widely in rank. Their textural composition was assessed by incident polarized-light microscopy while pore structural parameters were measured by computerized image analysis allied to reflected light microscopy. The tensile strength of coke could be related to textural data with accuracy using several relationships, some of which were based on a model for the tensile failure of coke. Relationships between tensile strength and pore sturctural parameters were less successful, possibly because of difficulties associated with the measuring system used. Neverthless relationships involving combinations of pore structural and textural data were developed and investigated. It was shown that relationships between tensile strength and calculated textural data had promise as the basis of a method of coke strength prediction. Also, tensile strengths could be calculated from the blend composition and the tensile strength of the coke produced from component cokes. Both methods have value in different situations.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2003.
Vita.
Includes bibliographical references.
Airborne particles fall into one of three size ranges. The nucleation range consists of nanoparticles created from vapor atom collisions. The decisive parameter for particle size and composition is the supercooling of the vapor. The accumulation range, which comprises particles less than 2 micrometers, consists of particles formed from the collision of smaller primary particles from the nucleation range. The composition of agglomerates and coalesced particles is the same as the bulk vapor composition. Coarse particles, the composition of which is determined by a liquid precursor, are greater than 1 micrometer and solidify from droplets whose sizes are controlled by surface, viscous, and inertial forces. The relationship between size and composition of airborne particles could be seen in welding fume, a typical metallurgical aerosol. This analysis was performed with a cascade impactor and energy dispersive spectrometry with both scanning electron microscopy (SEM-EDS) and scanning transmission electron microscopy (STEM-EDS). Other methods for properly characterizing particles were discussed. In the analysis, less than 10% of the mass of fume particles for various types of gas metal arc welding (GMAW) were coarse, while one-third of flux cored arc welding (FCAW) fume particles were coarse. Coarse particles had a composition closer to that of the welding electrode than did fine particles. Primary particles were not homogeneous. Particles larger than the mean free path of the carrier gas had the same composition as that of the vapor, but for particles 20 to 60 nanometers, smaller particles were more enriched in volatile metals than larger particles were. This was explained by the cooling path along the bubble point line of a binary phase diagram.
(cont.) Particles were not necessarily homogenous internally. Because nanoparticles homogenize quickly, they may form in a metastable state, but will not remain in that state. In this analysis, the presence of multiple stable immiscible phases explains this internal heterogeneity. The knowledge contained herein is important for industries that depend on the properties of nanoparticles, and for manufacturing, where industrial hygiene is important because of respirable particle by-products, such as high-energy-density metallurgical processing.
by Neil Travis Jenkins.
Ph.D.

The work presented in this thesis aims at furthering the understanding of the microtexture of metallurgical cokes with regard to the interfacial properties of their optical components. Metallurgical coke, on the scale considered, can be understood as a composite of unfused carbon embedded in a porous matrix of fused material. The matrix is composed of textural units varying in size and shape depending on the rank of the coal or blend of coals carbonised. The quality of the interfaces between them and of those they form with the unfused material can reasonably be expected to influence macroscopic coke properties such as mechanical strength.

The reactivity and micro-structure of three coals and two cokes used in iron and steel manufacture have been studied by a variety of techniques, including gas sorption analysis, thermal analysis and microscopy. Changes in surface areas and porosities of the coals and cokes during combustion have been determined by a gravimetric nitrogen sorption technique at 77K. The cokes and coals have been studied by thermal analysis under isothermal and dynamic conditions in different gas atmospheres. Rates of reaction have been correlated with surface area changes. Attempts have been made to calculate activation energies from Kissinger plots of DTA data. Microstructural changes in the cokes and coals during carbon burn-off have been investigated by electron microscopy. Relative porosities have been estimated by image analysis. Mechanical strengths of the cokes have been measured and correlated with porosity data. Selected metals in the carbons have been determined by flame photometry, atomic absorption spectroscopy and Mossbauer spectroscopy. The composition of residual mineral matter (ash) has been investigated by X-ray diffraction. The chemical compositions of the coal distillates have been characterised by ir/uv spectrosopy, NMR spectroscopy and by GC-MS techniques. Calorific values of the carbons have been determined. Results are discussed in relation to previous work and to applications 1n blast furnace practice. In coal combustion the surface areas increase during the initial stages of carbon burn-off, reaching maximum at about 50% burn-off before decreasing. The increases are considerably higher at 400° and 500° C than at 300° C for all three coals. Hysteresis data from the sorption isotherms show that the coals develop full ranges of mesa-porosity and some micro-porosity during burn-off at the higher temperatures. However, the coal oxidation is only slightly accelerated, since most of the new surface is located in the micro- and meso- pores where access to atmospheric oxygen is restricted by slow diffusion, so that the earlier stages of oxidation are approximately linear with time. This improves our knowledge of current empirical industrial carbon solution tests. There is comparatively little change in surface during the coking of the Coals at 1000° C and only restricted sintering of the coal ashes at 300- 500° C. In the combustion of the cokes in carbon dioxide at 1000° C the maxima in surface areas occur within 25% burn-off. However, one of the cokes shows a second maximum at later stages of burn-off, ascribed to the European component in the parent coal blend. This gives a more uniform rate of burn-off which is advantageous industrially.

The thesis describes economical and political situation in the foreign markets that are significant to Ukrainian steel producers. As an example of Ukranian steel maker I have introduced the enterprise JSC "Zaporizhstal" which is a steel giant of Ukraine. Th thesis desribes the plant, its development, its competitive advantages, its product portfolio and the quality of metal products produced. The paper also discusses some of the main problems of Ukrainian steel makers and the suggestions for further improvements. In the main part the thesis analyses the export markets of "Zaporizhstal" such countries as Russia, China and Turkey. It discusses the development of their steel-consuming industries such as machinery industry, and construction sector and shows all the benefits and risks that are associated with the export to those markets.

The pyrometallurgical processing of copper concentrates produces SO₂-bearing offgas. SO₂ in the offgas is catalytically oxidized to SO₃ and absorbed into a ∼98.5% H₂SO₄-H₂O mixture in a sulfuric acid plant. This research provides an analysis of a copper smelter sulfuric acid plant and discusses the control and optimization necessary to attain the following goals: (a) minimize smelter SO₂ emissions; (b) maximize acid plant capacity and availability. The objectives of this work are to: (a) prepare mathematical descriptions of sulfuric acid plant operations; compare the mathematical predictions with plant data; (c) use the mathematical descriptions to: (i) predict acid plant behavior with varying feed SO₂ strengths and gas flow rates; (ii) determine control strategies to minimize smelter SO₂ emissions; (iii) evaluate requirements for an existing acid plant to accommodate future increased feed gas flows and SO₂ strengths.

The size distribution and strength of metallurgical coke are factors vital for the steady and high-efficiency operation of a blast furnace, since these factors govern stack penneability. Coke strength influences the size of lump coke not only because of size degradation by impact and abrasion during transfer to and descent in the blast furnace, but also because of its influence on the fracture which takes place in the coke layer during carbonisation and the effect this has on the initial mean size and size distribution of the feed coke. Therefore, the elucidation of the relationship between coke strength and the fissure fonnation phenomena is significant. In this study, therefore, the coke strength development during carbonisation has been examined in conjunction with various parameters, such as the degree of carbonisation of the coal, namely the extent or fraction of pyrolytic reaction, and the degree of graphitisation of the coke, as well as carbonisation temperature and heating regime. The porous structure of coke has also been examined with a view to establishing a relation between the porous structure and the coking properties of the coal carbonised. The quality of coke porous structure was evaluated by parameters introduced in this study, i.e., the pore size distribution and pore rugosity factors. A poor porous structure is shown to be associated with high proportion of small pores and pores with a rough surface. These features are considered to stem from poor coking properties and the consequent poor adhesion between coal particles. An attempt has also been made to establish a mathematical model capable of predicting the degree of fissuring of coke during carbonisation by utilising the understandings obtained in this study of the coke strength development during carbonisation and the effect of coal properties on coke strength. Coke samples large enough to facilitate the observation of the degree of fissuring in relation to various coal properties and heating conditions, were made to evaluate the mathematical model and introduce the concept. The concept that fissuring takes place when developing thennal stress exceeds the developing coke strength is demonstrated to be capable to evaluate the effects of coal properties and heating conditions on the degree of fissuring observed.

Lo scopo della presente tesi di dottorato è lo studio di vari sistemi metallurgici mediante l’utilizzo di tecniche di analisi della superficie: X-ray Photoelectron Spectroscopy (XPS), Auger Electron Spectroscopy (AES) and Scanning Photoemission Microscopy (SPEM). Mediante tali tecniche, è stato possibile ottenere informazioni sulla composizione chimica, stechiometria, stato di ossidazione e distribuzione laterale (mappe chimiche) degli elementi che compongono i campioni analizzati. Il lavoro è suddiviso in tre argomenti: (i) effetto dei due trattamenti di carbo-cementazione dell’acciao inossidabile a bassa temperatura; (ii) investigazione micro-chimica di rivestimenti spessi a base di tungsteno su un acciaio inossidabile martensitico AISI 420; (iii) studio della disomogeneità micro-chimica in una lega eutettica di Pb-Bi allo stato liquido. Grazie alla loro grande versatilità e flessibilità, le tecniche XPS e AES sono utilizzate per l’investigazione di materiali che trovano applicazione in vari campi tecnologici quali metallurgici, materiali compositi, ceramici, ecc. In futuro, il potenziale delle tecniche di analisi della superficie sarà esplorato per lo studio di differenti sistemi metallurgici.
The aim of this work is to investigate the metallurgical systems by using the surface characterization techniques: X-ray Photoelectron Spectroscopy (XPS), Auger Electron Spectroscopy (AES) and Scanning Photoemission Microscopy (SPEM) at the ELETTRA synchrotron (Trieste, Italy). By using this type of surface-sensitive techniques on metallurgical systems, it is possible to obtain the information on the materials chemical composition, stoichiometry, chemical states and electronic configuration of constituent elements and surface chemical maps. This work can be subdivided into three topics that are linked by the use of the same experimental techniques. These topics are the following: (i) comparison of two different low temperature carburizing treatments of the steel, (ii) micro-chemical investigation of tungsten thick coatings on AISI 420 martensitic stainless steel, (iii) study of micro-chemical inhomogeneity in eutectic Pb-Bi alloy quenched from melt. Thanks to the wide range of variety and flexibility of applications of XPS and AES, these techniques can be used for the investigation of various systems, such as metallurgical, composite materials, ceramics, etc. In future, the potential of surface analysis techniques will be explored for application in different metallurgical systems.

Naturally occurring cellular materials are always optimized in terms of morphology, structural resistance, and functionality. The use of cellular materials is based on the application as well as the loading condition. Cellular materials are composed of an interconnected network of struts, plates, or repeating unit cells, forming edges or faces. The properties of these structures can be tailored according to the requirements by changing one or more of the parameters mentioned above. This makes cellular materials suitable for various applications ranging from aerospace to biomedical. In biomedical applications, these cellular materials can be used to manufacture porous implants to match the properties of the surrounding bone. They can also be used as coatings on solid implants to promote bone tissue ingrowth for better implant fixation. The production of these complex, porous implants using traditional manufacturing methods is a difficult task. However, the development of additive manufacturing processes such as Laser Powder Bed Fusion (LPBF) has made it possible to manufacture complex and intricate shaped cellular materials with minimum material wastage and considerable accuracy. Therefore, with the combination of the LPBF process and cellular materials design, it is possible to produce a wide range of cell topologies with customized mechanical properties depending on the implant location, material, and the needs of the patient. Titanium and its alloys such as Ti6Al4V have been used in biomedical applications due to their high strength to weight ratio, corrosion resistance, and good biocompatibility. Also, the LPBF process has been used to produce various Ti6Al4V components for various applications including cellular materials. The development of cellular materials for implants is dependent on the relative density, response of the unit cell to loading conditions, and the optimal pore size for bone ingrowth. Studies have been carried out to understand the behavior of the cellular materials under compressive loads since most of the implants experience compression loads during their operation. Nevertheless, the implants also undergo fatigue loading due to day-to-day activities and tensile loads when the implant is loose or when the host performs an extensive physical activity. Therefore, designing and studying the cellular materials for these loads is necessary to completely understand their behavior. Considering the pore size, studies have suggested that a pore size of ~ 800 µm is suitable to induce bone ingrowth after implantation. The cellular materials can be broadly classified into stretching and bending dominated. Stretching dominated cellular materials are characterized by high strength and stiffness while bending dominated structures are high compliant. This behavior of cellular materials is dependent solely on the unit cell topology. Therefore, the development of different types of cell topologies and their characterization is required to produce optimized fully porous implants. Also, the effect of the LPBF process on the designed parameters of the unit cell alters the obtained mechanical properties from the desired values. The present work aims at developing different Ti6Al4V cellular materials that can be potentially used for application in implants. A combination of different cellular materials can be used to develop completely porous implants or single cellular materials can be used as coatings for solid implants to induce osseointegration. A major portion of the work is focused on the mechanical properties of LPBF manufactured cellular materials characterized using static and fatigue tests. The study also investigates the discrepancy between the as-designed and as-built geometrical parameters of these cellular structures. Finite elements analysis and the Gibson-Ashby modeling has been employed to understand the difference between the as-designed and as-built properties. Another part of the study was focused on the effect of designed geometrical parameters on the as-built geometry of cellular materials. The aim was to develop a relationship between the as-designed and the as-built parameters. This thesis covers all the aspects mentioned in the above paragraph in detail. The research work has been provided in three different chapters (Chapter 2, 3, and 4) which are well connected to each other. Each chapter is composed of an abstract, introduction, materials and methodology, results and discussion, and conclusion. A conclusion on the complete research and the future scope is provided at the end. The first chapter introduces all the aspects concerned with the development of cellular materials for biomedical applications. Literature review on all aspects have been provided, ranging from the properties of the bone, cellular materials, manufacturing process for cellular materials, and the properties of bulk materials suitable for biomedical applications. In chapter 2, Ti6Al4V cellular materials with three different cell topologies namely cubic regular, cubic irregular, and trabecular have been investigated. The irregular specimens are obtained by skewing the junctions of the cubic regular configuration. Trabecular specimens are designed by randomly joining 4-6 struts at a node to mimic human trabecular bone. The three cell topologies were manufactured at three different porosity levels by changing their strut thickness and pore size. The cubic regular cells are considered due to their stable and simple configuration, while irregular and trabecular based specimens have shown promising results in the osseointegration according to the partner company. However, the mechanical properties of irregular and trabecular specimens play an important role in implant design. Therefore, all the specimens were subjected to compression test and as well as a novel tensile test under two different types of loading conditions, monotonic and cyclic to obtain their strength and stiffness. However, a misalignment in the struts with the loading direction in compression led to an asymmetric behavior between tensile and compression. Higher strength and stiffness values were observed under tensile loading, the results of which were in conjunction with the theoretical prediction from the Gibson-Ashby model. The experimental results indicated the irregularity tends to reduce the strength, stiffness and induce bending dominate behavior. Morphological analysis was carried out to obtain the discrepancy between the as-designed and the as-built thickness values. This led to the FE analysis of as-designed models to obtain the difference in the properties of as-designed and as-built cellular materials. Furthermore, as-built FE models were generated using morphological data to study the effect of strut defects and compare them with the experimental results. The next step involved comparing the experimental results with the FE analysis carried out tomography-based FE models. The last part of the study involved obtaining a relation between the as-designed and as-built Young’s modulus for cubic regular, cubic irregular, and trabecular specimens to create a reference database. The mechanical properties from the compression and tensile test of the highest porosity specimens were closer to the properties of human bone. The tensile tests were successful in predicting the mechanical properties accurately. These observations were the motivation to further study the effect of irregularity on various cell topologies, by subjecting them to static and fatigue loads. In chapter 3, seven different types of unit cells, three regular configurations, three irregular configurations, and one trabecular based unit cell. The unit cells used in the study consisted of regular and irregular configurations of the cubic-based, star-based, and cross-based specimens. These specimens were selected to have a comparison of properties from stretching dominate cubic specimen to bending dominated cross-shaped specimens and to study the effect of irregularity. Therefore, the specimens were subjected to and mechanical characterization using compression, tension, and compression – compression fatigue tests along with porosity and morphological analysis. The tensile specimens in this chapter were designed with a thicker transition at the ends, while compression specimens had uniform configuration throughout the specimen. FE analysis was carried on the as-designed configuration of these specimens to study the effect of transition and to compare the as-designed and tensile experimental results to understand the effect of decreased porosity on the failure mechanisms. Fatigue tests were carried under compression-compression load and failure mechanisms in different unit cells were captured. The results of the study indicated that the irregularity has a greater effect on the strength and stiffness of stretching-dominated cellular material and has a negligible effect on bending-dominated cross-based specimens. The trabecular specimens display excellent mechanical properties under static load with good strength, stiffness and sustain high strain values. The normalized S-N curves indicate a clear demarcation between the bending and stretching-dominated cellular materials. The FE analysis showed a similar failure location as compared to the experimental results despite the decrease in the porosity due to manufacturing. The morphological analysis showed the effect of strut orientation of the as-built thickness. The morphological analysis and the difference between the as-designed and as-built geometrical parameters show that an in-depth study on the geometrical deviation due to the LPBF process is necessary. The next chapter focuses on the geometrical deviation in LPBF manufactured cellular specimens and the parameters influencing this deviation. In chapter 4, cubic regular cellular materials with filleted junctions are studied for geometrical deviation and to obtain a relationship between the as-designed and as-built geometric parameters. Initially, nine different specimens with different strut thickness, fillet radius, and unit cell size were manufactured at three different orientations with respect to the printing plane. The main aim of this study was to devise a compensation strategy to reduce the geometrical deviation due to the LPBF process. A linear relation between the as-designed and as-built geometrical values is obtained, which is used for compensation modeling. Struts perpendicular to the building plane were uniform in cross-sections while horizontal and inclined struts had an elliptical cross-section. The internal porosity analysis has been carried out which indicates that the porosity at the junctions is lesser than the porosity at the junctions. The compensation strategy worked well for the second set of specimens produced using the same parameters, thereby reducing the geometrical deviation between the as-designed and the as-built parameters. Finally, the effect of filleted junctions, building directions, and compensation modeling on fatigue properties have been studied. Specimens with load-bearing struts printed parallel to the building plane had the lowest mechanical properties, while the specimens with struts inclined to the loading direction and building plane displayed excellent static and fatigue properties. The fillets at the junctions improve the fatigue resistance of the specimen by reducing the stress concentration. The printing direction and the presence of fillets influence the fatigue failure locations as well. Therefore, filleted junctions that can be reproduced well by the LPBF process can be used to reduce the stress concentration in cellular materials.

Naturally occurring cellular materials are always optimized in terms of morphology, structural resistance, and functionality. The use of cellular materials is based on the application as well as the loading condition. Cellular materials are composed of an interconnected network of struts, plates, or repeating unit cells, forming edges or faces. The properties of these structures can be tailored according to the requirements by changing one or more of the parameters mentioned above. This makes cellular materials suitable for various applications ranging from aerospace to biomedical. In biomedical applications, these cellular materials can be used to manufacture porous implants to match the properties of the surrounding bone. They can also be used as coatings on solid implants to promote bone tissue ingrowth for better implant fixation. The production of these complex, porous implants using traditional manufacturing methods is a difficult task. However, the development of additive manufacturing processes such as Laser Powder Bed Fusion (LPBF) has made it possible to manufacture complex and intricate shaped cellular materials with minimum material wastage and considerable accuracy. Therefore, with the combination of the LPBF process and cellular materials design, it is possible to produce a wide range of cell topologies with customized mechanical properties depending on the implant location, material, and the needs of the patient. Titanium and its alloys such as Ti6Al4V have been used in biomedical applications due to their high strength to weight ratio, corrosion resistance, and good biocompatibility. Also, the LPBF process has been used to produce various Ti6Al4V components for various applications including cellular materials. The development of cellular materials for implants is dependent on the relative density, response of the unit cell to loading conditions, and the optimal pore size for bone ingrowth. Studies have been carried out to understand the behavior of the cellular materials under compressive loads since most of the implants experience compression loads during their operation. Nevertheless, the implants also undergo fatigue loading due to day-to-day activities and tensile loads when the implant is loose or when the host performs an extensive physical activity. Therefore, designing and studying the cellular materials for these loads is necessary to completely understand their behavior. Considering the pore size, studies have suggested that a pore size of ~ 800 µm is suitable to induce bone ingrowth after implantation. The cellular materials can be broadly classified into stretching and bending dominated. Stretching dominated cellular materials are characterized by high strength and stiffness while bending dominated structures are high compliant. This behavior of cellular materials is dependent solely on the unit cell topology. Therefore, the development of different types of cell topologies and their characterization is required to produce optimized fully porous implants. Also, the effect of the LPBF process on the designed parameters of the unit cell alters the obtained mechanical properties from the desired values. The present work aims at developing different Ti6Al4V cellular materials that can be potentially used for application in implants. A combination of different cellular materials can be used to develop completely porous implants or single cellular materials can be used as coatings for solid implants to induce osseointegration. A major portion of the work is focused on the mechanical properties of LPBF manufactured cellular materials characterized using static and fatigue tests. The study also investigates the discrepancy between the as-designed and as-built geometrical parameters of these cellular structures. Finite elements analysis and the Gibson-Ashby modeling has been employed to understand the difference between the as-designed and as-built properties. Another part of the study was focused on the effect of designed geometrical parameters on the as-built geometry of cellular materials. The aim was to develop a relationship between the as-designed and the as-built parameters. This thesis covers all the aspects mentioned in the above paragraph in detail. The research work has been provided in three different chapters (Chapter 2, 3, and 4) which are well connected to each other. Each chapter is composed of an abstract, introduction, materials and methodology, results and discussion, and conclusion. A conclusion on the complete research and the future scope is provided at the end. The first chapter introduces all the aspects concerned with the development of cellular materials for biomedical applications. Literature review on all aspects have been provided, ranging from the properties of the bone, cellular materials, manufacturing process for cellular materials, and the properties of bulk materials suitable for biomedical applications. In chapter 2, Ti6Al4V cellular materials with three different cell topologies namely cubic regular, cubic irregular, and trabecular have been investigated. The irregular specimens are obtained by skewing the junctions of the cubic regular configuration. Trabecular specimens are designed by randomly joining 4-6 struts at a node to mimic human trabecular bone. The three cell topologies were manufactured at three different porosity levels by changing their strut thickness and pore size. The cubic regular cells are considered due to their stable and simple configuration, while irregular and trabecular based specimens have shown promising results in the osseointegration according to the partner company. However, the mechanical properties of irregular and trabecular specimens play an important role in implant design. Therefore, all the specimens were subjected to compression test and as well as a novel tensile test under two different types of loading conditions, monotonic and cyclic to obtain their strength and stiffness. However, a misalignment in the struts with the loading direction in compression led to an asymmetric behavior between tensile and compression. Higher strength and stiffness values were observed under tensile loading, the results of which were in conjunction with the theoretical prediction from the Gibson-Ashby model. The experimental results indicated the irregularity tends to reduce the strength, stiffness and induce bending dominate behavior. Morphological analysis was carried out to obtain the discrepancy between the as-designed and the as-built thickness values. This led to the FE analysis of as-designed models to obtain the difference in the properties of as-designed and as-built cellular materials. Furthermore, as-built FE models were generated using morphological data to study the effect of strut defects and compare them with the experimental results. The next step involved comparing the experimental results with the FE analysis carried out tomography-based FE models. The last part of the study involved obtaining a relation between the as-designed and as-built Young’s modulus for cubic regular, cubic irregular, and trabecular specimens to create a reference database. The mechanical properties from the compression and tensile test of the highest porosity specimens were closer to the properties of human bone. The tensile tests were successful in predicting the mechanical properties accurately. These observations were the motivation to further study the effect of irregularity on various cell topologies, by subjecting them to static and fatigue loads. In chapter 3, seven different types of unit cells, three regular configurations, three irregular configurations, and one trabecular based unit cell. The unit cells used in the study consisted of regular and irregular configurations of the cubic-based, star-based, and cross-based specimens. These specimens were selected to have a comparison of properties from stretching dominate cubic specimen to bending dominated cross-shaped specimens and to study the effect of irregularity. Therefore, the specimens were subjected to and mechanical characterization using compression, tension, and compression – compression fatigue tests along with porosity and morphological analysis. The tensile specimens in this chapter were designed with a thicker transition at the ends, while compression specimens had uniform configuration throughout the specimen. FE analysis was carried on the as-designed configuration of these specimens to study the effect of transition and to compare the as-designed and tensile experimental results to understand the effect of decreased porosity on the failure mechanisms. Fatigue tests were carried under compression-compression load and failure mechanisms in different unit cells were captured. The results of the study indicated that the irregularity has a greater effect on the strength and stiffness of stretching-dominated cellular material and has a negligible effect on bending-dominated cross-based specimens. The trabecular specimens display excellent mechanical properties under static load with good strength, stiffness and sustain high strain values. The normalized S-N curves indicate a clear demarcation between the bending and stretching-dominated cellular materials. The FE analysis showed a similar failure location as compared to the experimental results despite the decrease in the porosity due to manufacturing. The morphological analysis showed the effect of strut orientation of the as-built thickness. The morphological analysis and the difference between the as-designed and as-built geometrical parameters show that an in-depth study on the geometrical deviation due to the LPBF process is necessary. The next chapter focuses on the geometrical deviation in LPBF manufactured cellular specimens and the parameters influencing this deviation. In chapter 4, cubic regular cellular materials with filleted junctions are studied for geometrical deviation and to obtain a relationship between the as-designed and as-built geometric parameters. Initially, nine different specimens with different strut thickness, fillet radius, and unit cell size were manufactured at three different orientations with respect to the printing plane. The main aim of this study was to devise a compensation strategy to reduce the geometrical deviation due to the LPBF process. A linear relation between the as-designed and as-built geometrical values is obtained, which is used for compensation modeling. Struts perpendicular to the building plane were uniform in cross-sections while horizontal and inclined struts had an elliptical cross-section. The internal porosity analysis has been carried out which indicates that the porosity at the junctions is lesser than the porosity at the junctions. The compensation strategy worked well for the second set of specimens produced using the same parameters, thereby reducing the geometrical deviation between the as-designed and the as-built parameters. Finally, the effect of filleted junctions, building directions, and compensation modeling on fatigue properties have been studied. Specimens with load-bearing struts printed parallel to the building plane had the lowest mechanical properties, while the specimens with struts inclined to the loading direction and building plane displayed excellent static and fatigue properties. The fillets at the junctions improve the fatigue resistance of the specimen by reducing the stress concentration. The printing direction and the presence of fillets influence the fatigue failure locations as well. Therefore, filleted junctions that can be reproduced well by the LPBF process can be used to reduce the stress concentration in cellular materials.

Thesis (MScIng)--University of Stellenbosch, 2003.
ENGLISH ABSTRACT: The pneumatic injection of reagent powder into molten iron has become the preferred way to carry out iron and steel desulphurisation. It is therefore essential to not only understand the thermodynamic implications, but also the kinetic principles that govern the desulphurisation process. Key variables that influence the kinetics of the procedure are the condition and composition of the top slag and the melt as well as the injection conditions. Notable injection parameters include reagent flowrate, injection-lance depth and carrier gas flowrate. Owing to sampling restrictions, the subsequent data from Saldanha Steel®, South Africa does not provide adequate insight into the kinetic behaviour of the desulphurisation process and it was therefore the focus of this research to provide an improved quantitive comprehension of the calcium carbide injection procedure at Saldanha Steel. For this purpose a one-dimensional quasi-steady state model for momentum, heat- and mass transfer in rising gas-liquid-powder plumes has been developed for conditions relevant to the Saldanha Steel refining process. Combined with a model predicting the contribution of the topslag to the process, the overall rate of desulphurisation as a function of time can be determined, thus affording the ability to quantitatively explore and analyse the influence of the afore-mentioned injection parameters, as well as the nature of both the topslag and the melt, on the kinetics of the desulphurisation process. Sensitivity analyses concluded that individual increases in the calcium carbide flowrate, the depth of injection and the amount of carry-over slag will result in a reduction in the injection time, while a decrease in the reagent particle diameter and the initial mass of iron in the ladle will have the same effect. Molten iron temperature losses brought about by prolonged injection needs to be electrically recovered within a steelmaking furnace at a high cost. Owing to the high cost of the desulphurising agent, any reduction in the required injection time, while still maintaining product specifications, will therefore result in diminishing overall production costs. Although all the results contained in this study is of particular interest to the Saldanha Steel scenario, it also provides invaluable information and insights into the important variables and parameters playing a role in injection desulphurisation processes in general, along with the influence that changing conditions can have on the end result of such a procedure.
AFRIKAANSE OPSOMMING: Die pneumatiese inspuiting van reagentpoeier is die populêrste ontswawelingsmetode in die yster- en staal bedryf. Dit is dus van groot belang dat die gepaardgaande termodinamiese en kinetiese beginsels betrokke by die ontswawelingsreaksies baie goed verstaan word. Die kondisie en samestelling van die bo-slak en die vloeibare yster, asook die inspuitingkondisies is twee van die belangrikste veranderlikes wat die kinetika van die ontswawelingsproses beïnvloed. Beperkte monsternemingsgeleenthede het veroorsaak dat die relevante data, soos voorsien deur Saldanha Staal®, nie die nodige kinetiese insig in verband met die ontswawelingreaksie weergee nie. Dit is dus die doel van hierdie werkstuk om ‘n verbeterde kwantitatiewe begrip van die ontswawelingsproses by Saldanha Staal daar te stel. Vir hierdie doeleinde is ‘n een-dimensionele, kwasi-gestadigde toestand model vir stygende gas-vloeistof pluime ontwikkel. Die model inkorporeer momentum-, hitte- en massaoordragsprinsiepe en is verteenwoordigend van die ontswawelingsproses by Saldanha Staal. ‘n Tweede model simuleer die bydrae wat die bo-slak tot die algehele ontswawelingsproses maak en saam gee hierdie twee modelle die algehele ontswawelingstempo weer as ‘n funksie van tyd. Die modelle word ook gebruik om die invloed van die bogenoemde inspuitingsveranderlikes op die proses te ondersoek. Deeglike sensitiwiteitsanalise het gewys dat ‘n verhoging in die kalsium karbied vloeitempo, asook die inspuitingsdiepte van die lans en die hoeveelheid slak wat vanaf die boogoond na die ontswawelingseenheid oorgedra word, ‘n vermindering in die vereisde inspuitingstyd te weeg bring. Verkleining in die kalsium kardied partikels se gemiddelde diameter en vermindering van die hoeveelheid yster in die torpedokarre aan die begin van die proses, het dieselfde uitwerking op die vereisde inspuitingstyd. Geweldig baie geld moet aan elektrisiteit spandeer word om die temperatuur wat verlore gaan as gevolg van onnodige lang inspuitingstye, in die staalmaakoonde te herwin. Gekombineerd met die feit dat die kalsium karbied reagent baie duur is, beteken dit dat reduksies in die vereisde ontswaweling inspuitingstyd groot besparings te weeg kan bring. Alhoewel die saamgevatte resultate van spesifieke belang is vir die Saldanha Staal proses, verskaf hierdie studie waardevolle informasie oor die belangrikheid van verskeie veranderlikes, asook die rol wat veranderende toestande op die eindresultate van die ontswawelingproses kan hê.

Thesis (MScIng)--University of Stellenbosch, 2003.
ENGLISH ABSTRACT: This thesis investigates the control of calcium and magnesium in a base metal sulphate leach solution containing nickel and cobalt. The presence of calcium and magnesium in the hydrometallurgical processing of base metals, result in a number of difficulties. These problems range from the contamination of the final product, to high energy consumption and large bleed streams during electrowinning. Calcium poses a greater problem in sulphate solutions due to the low solubility of its sulphate salts. No conventional method exists for the control of calcium and magnesium. As part of this study a review of possible control methods was conducted, which is listed within. From this list the precipitation of fluorides was selected for further investigation. The results showed that it is possible to control calcium and magnesium through the precipitation of their respective fluorides, without the co-precipitation of nickel and cobalt. For 10% stoichiometric excess of fluoride 96.5% calcium and 98.5% magnesium were removed during batch experiments. It is known that mixing and hydrodynamics plays an important role on the characteristics of the formed precipitate, making these processes inherently difficult to scale-up. To evaluate these effects on a continuous process, the three-zone model proposed by Gösele and Kind (1991) was used. A precipitate with consistent characteristics was produced while varying the mixing on the macro, meso and micro scale. Additionally, methods were investigated for the removal or possible recycling of the unreacted fluoride, for which activated alumina was identified. It was observed that activated alumina could adsorb fluoride to low levels in the presence of the base metal solution, after which it could be regenerated again. The activated alumina (AA) had a capacity of 8.65 gF/lAA at a 10 mg/l fluoride breakthrough level during column tests. Based on the experimental results a conceptual process was devised whereby only a portion of the leach stream is subjected to the fluoride precipitation process, after which it is returned to lower the overall calcium and magnesium concentrations. This method would reduce the effect of the observed dominance of magnesium precipitation, in processes where the maximum removal of both elements is not required. The fluoride precipitation process consisted of three steps being precipitation, solid-liquid separation and adsorption of the unreacted fluoride. Sufficient information is provided on the process for a cost estimation to be carried out. Should this found to be feasible, a continuation of the project is recommended. Different reactor configurations could be evaluated for precipitation. The scaling observed during the continuous experiments should also be investigated to minimise its effect. The investigation of activated alumina was only a secondary project and more work is required on optimisation, particularly for the desorption cycle to enable the recycling of the unreacted fluoride.
AFRIKAANSE OPSOMMING: Saamgestel in hierdie tesis is 'n studie van die beheer van kalsium en magnesium in 'n basismetaal-sulfaatoplossing, bevattende nikkel en kobalt. Die teenwoordigheid van kalsium en magnesium in dié oplossings veroorsaak 'n verskeidenheid van probleme, wat wissel van produkkwaliteit verlaging tot hoë energieverbruik en groot bloei strome tydens platering. 'n Groter probleem word ondervind met kalsium as gevolg van die lae oplosbaarheid van sy sulfaatsoute. Geen konvensionele metode kon gevind word vir die beheer van kalsium en magnesium gedurende die oorsig van moontlike metodes nie. Hierdie moontlike metodes is geïdentifiseer en kortliks bespreek in die tesis. Van die moontlike metodes is die presipitasie van fluoried-soute gekies vir verdere eksperimentele ondersoek. Die ondersoek het getoon dat dit moontlik is om kalsium en magnesium te beheer deur die presipitasie van fluoriede sonder om die basismetale saam te presipiteer. Vir 'n 10% oormaat fluoried toevoeging is 96.5% van die kalsium en 98.5% van die magnesium gepresipiteer gedurende die enkelladingstoetse. Dit is bekend dat vermenging en hidrodinamika 'n groot rol speel in die kwaliteit van die presipitaat wat gevorm word. Dit bemoeilik die opskalering van presipitasie prosesse. Vir die ondersoek oor die invloed van vermenging op 'n kontinu proses is die drie-sel model van Gösele en Kind (1991) gebruik. Dit is gevind dat die karakter van presipitaat relatief konstant gebly het vir variasies van vermenging op die makro, meso en mikro skaal, wat opskaling behoort te vergemaklik. Addisioneel is die verwydering of moontlike hersirkulasie van die ongereageerde fluoried ondersoek, en geaktiveerde alumina is geïdentifiseer as 'n moontlike adsorbeermiddel. 'n Eksperimentele ondersoek het getoon dat geaktiveerde alumina fluoried tot lae vlakke kan adsorbeer in die teenwoordigheid van die basismetale, waarna dit weer geregenereer kan word. Die kapasiteit van die geaktiveerde alumina (GA) was bereken as 8.65 gF/lGA by 'n 10 mg/l fluoried vlak gedurende die kolom toetse. 'n Konsep-proses is opgestel na aanleiding van die eksperimentele resultate, waarvolgens slegs 'n gedeelte van die logingstroom na die fluoried presipitasie proses gestuur word, waarna dit weer teruggevoeg word om die algehele kalsium en magnesium konsentrasie te verlaag. Dié metode sal voorkom dat magnesium presipitasie domineer vir 'n toepassing waar slegs 'n gedeelte van kalsium en magnesium verwyder word. Die fluoried presipitasie proses behels drie stappe waarvolgens die fluoriede eers gepresipiteer word, waarna dit geskei word, en dan die ongereageerde fluoried geadsorbeer word. Genoeg inligting is versamel sodat 'n kosteberaming van die proses gedoen kan word. As die koste van die proses aanvaarbaar is, word dit voorgestel dat die ondersoek voortgesit word. Verskillende reaktor konfigurasies kan vir die presipitasie stap getoets word en daar moet ook ondersoek ingestel word hoe om die korslaag wat gedurende die kontinu eksperimente geobserveer is, te verminder. Die ondersoek van geaktiveerde alumina was ondergeskik in die projek en nog werk sal gedoen moet word om dit te optimiseer, spesifiek gedurende die desorpsie siklus vir die hersirkulasie van die ongereageerde fluoried.

Thesis (PhD)--University of Stellenbosch, 2004.
ENGLISH ABSTRACT: The objective of this work was to achieve a completely automated fire assay system for the analysis of process control samples on a flotation plant in less than 120 minutes. With this in mind, a systems engineering approach was undertaken. The physical and chemical characteristics of the technology for each subsystem were investigated in turn and the critical factors that influenced accuracy, precision and analysis time were identified and optimised. Some of the key developments achieved during this work were: · Existing technology for the sampling, filtering, drying and grinding of flotation plant samples were evaluated and where necessary, modified for this application. · The fusion system was totally re-designed with a bottom-loading configuration called FIFA (Fast In-line Fire Assay) to make automation with a central robot possible. With the fast fusing flux developed, a quantitative collection of the platinum group elements with a fifteen-minute fusion was achieved compared to an hour for the classical method. · A robust automated separator system was developed to isolate the lead collector from the fusion in the molten state thereby separating it quantitatively from the slag. This allowed the automation of the entire fire assay process. · Methods to prepare lead standards for calibration were developed. These were used to optimise analytical protocols for the analysis of platinum group elements in lead using a spark optical emission spectrometer. This made it possible to accurately determine the quantities of platinum group elements in lead samples prepared by the automated fire assay system. · A fully automated system was developed that could meet the accuracy and precision requirements for the analysis of tailings and feed grade samples in concentrator slurry streams in less than one hour compared with the 24-72 hours required when using classical methods. The new fire assay technology including flux, FIFA system, oxygen lance and separator were all patented along with the automation vendor. This technology has made the first fully automated fire assay system a reality.
AFRIKAANSE OPSOMMING: Die hoofoogmerk van die studie was om ‘n totale geoutomatiseerde vuuressaieering stelsel te ontwerp vir die ontleding van prosesbeheermonsters van ‘n flotasieaanleg in ‘n bestek van 120 minute. Gedurende die ontwerp is ‘n ingeneursstelselbenadering gebruik. Die fisiese en chemiese kenmerke van elke deel van die tegnologie is eers afsonderlik en dan as ‘n geheel ondersoek. Die bepalende faktore wat akkuraatheid, presisie en ontledingstyd beinvloed het was geidentifiseer en geoptimeer. Die hoofpunte van die werk behels onder andere die volgende: · Bestaande tegnologie vir monsterneming, filtrasie, droging en vermaling van flotasiemonsters was ondersoek en is, waar nodig, aangepas vir die finale stelsel. · Die smeltingsisteem was in geheel herontwerp om monsters van onder in die FIFA (Fast In-line Fire Assay) sisteem te laai en sodoende die outomatisering met ‘n sentrale robot te vergemaklik. ‘n Vinnig smeltende vloeimiddel was ontwikkel wat ‘n kwantitatiewe versameling van die platinum groep elemente binne ‘n tydsduur van vyftien minute moontlik gemaak het, in vergelyke met die oorspronklike duur van die klassieke smelt metode van een uur. · ‘n Outomatiese skeier was ontwikkel waarmee die gesmelte loodversamelaar geskei kon word van die slakfase. Met die nuwe stelsel kon die hele vuuressaieerproses outomaties verloop. · Metodes is ontwikkel om loodstandaarde vir kalibrasie doeleindes te berei. Die standaarde is op hulle beurt weer gebruik om ‘n ontleding protokol daar te stel vir die analiese van die platinum groep elemente in lood, met behulp van ‘n vonkontlading-optiese-uitstraling-spektrometriese instrument. Ten einde was dit moontlik om outomaties klein hoeveelhede van die platinum groep elemente in monsters akkuraat te bepaal, na voorbereiding met behulp van die geoutomatiseerde vuuressaieering stelsel. · Die volle geoutimatiseerde stelsel was ontwikkel wat aan die akkurate en noukeurige vereistes voldoen het vir die ontleding van flotasie-uitskot-envoergraad monsters van die konsentraataanleg binne die bestek van ‘n uur. Die nuwe vuuressaieer tegnologie, insluitend die vinnig smeltende vloeimiddel, FIFA en skeier stelsels, asook die suurstof lanset is gepatenteer met die vervaardiger. Die studie het gelei tot die eerste volle geoutomatiseerde vuuressaieering stelsel wat tans gebruik word in die industrie.

Thesis (MScIng)--University of Stellenbosch, 2004.
ENGLISH ABSTRACT: This thesis details results obtained in an experimental study conducted to determine the effects of operating temperature, oxygen partial pressure, bulk chromium oxide content and bulk FeOx/MgO ratio on the solubility of chromium oxide in melter type slags in the platinum industry. Two PGM-containing layers in the Bushveld Complex in South Africa, the Merensky and UG2 reefs, are currently being mined for the extraction of base metals and platinum group metals (PGM). While the Merensky reef is a pyroxenitic layer, the UG2 reef is a platiniferous chromitite seam. Due to a gradual depletion in Merensky ore reserves, platinum producers have been moving towards the processing of more UG2 concentrates, which are higher in chromium oxide content. The technical difficulties associated with the smelting of concentrates with high chromium oxide contents is a matter of concern. The formation of chromite spinels in melts increases liquidus temperatures and viscosities and subsequently hampers tapping of slags and mattes from furnaces. Bottom build-up from the smelting of high chromium oxide containing concentrates could reduce effective furnace volume. From the literature reviewed it was found that very few published investigations covered melt compositions and oxygen partial pressures similar to those encountered in the platinum industry. Relevant studies were found to deal with significantly lower bulk chromium oxide and iron oxide contents. It became clear that a need exists for information on the behaviour of chromium oxide and its effects on phase chemistry and stability in melter slags. It was decided to study the phase equilibria through drop-quench experiments using six synthetic slags with bulk FeOx/MgO ratios between 0.6 and 1.9 and bulk chromium oxide contents between 1.2 and 7 wt%. Temperatures investigated were 1400, 1500 and 1600°C. The oxygen partial pressure was varied between 6.8x10-10 atm at 1400°C to8.3x10-5 atm at 1600°C. Experiments were conducted in a sealed vertical tube furnace and the required oxygen partial pressure in the furnace tube was maintained by controlling the flow rates of purified CO and CO2 gas mixtures through the tube. Reaction products were quenched after a reaction time of between 20 and 24 hours, depending on temperature, and the phase compositions were analysed by microprobe. The experimental study revealed that chromium oxide partitions very strongly into the spinel phase relative to the liquid phase, especially at lower temperatures, and higher oxygen partial pressures and bulk chromium oxide contents. The solubility of chromium oxide in the liquid phase was found to increase with increasing temperature and decreasing oxygen partial pressure. An increase in bulk chromium oxide contents of 1 wt%, under otherwise constant conditions, resulted in an increase in slag liquidus temperature of approximately 100°C over the range of temperatures investigated. At 1500°C and bulk chromium oxide contents of 3.7 and 6.4 wt% a reduction in oxygen partial pressure from 1.1x10-5 to 1.1x10-7 atm resulted in increases in soluble chromium oxide of 0.9 and 2.0 wt%, respectively. A further decrease in oxygen partial pressure to 6.7x10-9 atm resulted in increases in soluble chromium oxide of 2.8 and 4.7 wt%, respectively. Experimental results were compared to values predicted by the multi-phase equilibrium (MPE) model developed by CSIRO, and found to agree well. Slag basicity was not varied experimentally and therefore the model was used to predict its effect on the solubility of chromium oxide in the liquid phase and the stability of crystalline phases. At constant temperature, an increase in basicity resulted in a decrease in the solubility of chromium oxide in the liquid phase as well as stabilisation of the spinel phase. It was concluded that practicable combinations of one or more of four main factors, namely increased operating temperature and decreased bulk chromium oxide content, slag basicity and oxygen partial pressure, should be applied and evaluated in a plantenvironment to optimise furnace operation. The MPE model would be a valuable tool in predicting the outcomes of such investigations.
AFRIKAANSE OPSOMMING: Hierdie tesis detaileer die resultate wat verkry is uit ‘n eksperimentele studie uitgevoer om die effek van bedryfstemperatuur, die parsiële druk van suurstof, die algehele chroomoksied inhoud en die algehele FeOx/MgO verhouding op die gedrag van chroomoksied in smelter slakke in die platinum industrie te bestudeer. Twee PGM-bevattende ertslae in die Bosveldkompleks in Suid Afrika, die Merensky en UG2 riwwe, word huidiglik gemyn vir die ekstraksie van basismetale en platinumgroep metale (PGM). Die Merensky rif is ‘n piroksenitiese laag terwyl die UG2 rif ‘n platinumbevattende chromitiet laag is. As gevolg van ‘n geleidelike afname in reserwes van Merensky erts beweeg platinumprodusente al meer na die verwerking van groter hoeveelhede UG2 erts. Die tegniese probleme wat gepaard gaan met die smelting van konsentrate met hoë chroomoksied inhoud kan ‘n rede tot kommer wees. Die vorming van chromiet spinelle in die slak- en matfases verhoog likuidus temperature en viskositeite en bemoeilik die tap van hierdie fases uit oonde. Die opbou van soliede fases verlaag ook die effektiewe oondvolume. Uit die literatuurstudie is gevind dat gepubliseerde studies waarin slak samestellings en parsiële suurstofdrukke wat betrekking het op die platinumindustrie bespreek is, baie beperk is. Dit is gevind dat relevante navorsing gedoen is met aansienlik laer algehele chroom- en ysteroksied konsentrasies. Gevolglik het dit duidelik geword dat ‘n behoefte bestaan vir inligting oor die gedrag van chroomoksied in oonde en die effekte daarvan op fasechemie en –stabiliteit in smelter slakke. Daar is besluit om eksperimente uit te voer deur die gebruik van ses sintetiese slakke met algehele FeOx/MgO verhoudings tussen 0.6 en 1.9 en algehele chroomoksied konsentrasies tussen 1.2 en 7.0 % (op ‘n massabasis). Temperature van 1400, 1500 en 1600°C en suurstof parsiële drukke tussen 6.8x10-10 atm by 1400°C en 8.3x10-5 atm by 1600°C is ondersoek. Eksperimente is uitgevoer in ‘n geseëlde vertikale buisoond en dievereiste suurstofdruk in die oond is gehandhaaf deur beheer van die vloeitempos van gesuiwerde CO en CO2 gas deur die oond. Reaksieprodukte is in water geblus na ‘n reaksietyd van tussen 20 en 24 ure, afhangende van die reaksietemperatuur. Fasesamestellings is bepaal deur mikrosonde analises. Die eksperimentele studie het bewys dat chroomoksied baie sterk in die spinelfase konsentreer relatief tot die vloeistoffase, veral by laer temperature, suurstofdrukke en algehele chroomoksied konsentrasies. Dit is gevind dat die oplosbaarheid van chroomoksied in die vloeistoffase toeneem met toenemende temperatuur en afnemende suurstofdruk. ‘n Toename in die algehele chroomoksied konsentrasie van 1 massa%, onder andersins onveranderde toestande, het ‘n toename van ongeveer 100°C in likuidus temperature veroorsaak tussen 1400 en 1600°C. By 1500°C en algehele chroomoksied konsentrasies van 3.7 en 6.4 massa%, het ‘n verlaging in suurstofdruk vanaf 1.1x10-5 tot 1.1x10-7 atm respektiewelike toenames in die chroomoksied oplosbaarheid van 0.9 en 2.0 massa% veroorsaak. ‘n Verdere verlaging in suurstofdruk tot 6.7x10-9 atm het respektiewelike toenames in chroomoksied oplosbaarheid van 2.8 en 4.7 massa% veroorsaak. Eksperimentele resultate is vergelyk met waardes wat voorspel is deur die multifase ewewigsmodel (MPE), ontwikkel deur CSIRO, en goeie ooreenstemming is gevind. Verskillende slak basisiteite is nie eksperimenteel ondersoek nie en daarom is die model gebruik om die effek daarvan op die oplosbaarheid van chroomoksied in die vloeistoffase asook die stabiliteit van kristallyne fases te bepaal. By konstante temperatuur het ‘n toename in slak basisiteit ‘n afname in chroomoksied oplosbaarheid veroorsaak en die spinelfase gestabiliseer. Die aanbeveling is gemaak dat ‘n kombinasie van een of meer van vier hooffaktore, naamlik hoër bedryfstemperature en laer algehele chroomoksied konsentrasies, slak basisiteit en suurstofdruk, in die praktyk toegepas en geëvalueer moet word om sodoendeoptimum bedryfkondisies te bepaal. Die multifase ewewigsmodel is ‘n nuttige instrument wat gebruik kan word om die resultate van sulke ondersoeke te voorspel.

The present work represents a study of the mixing and slag entrainment behaviour of metallurgical processes. Two immiscible fluids were mixed in a model reactor, equipped with a single centrally located tuyere, through which air was blown.
For low energy input systems, it was found that the thickness of the second liquid phase can significantly affect the mixing time of the bulk phase by altering the fluid flow pattern of the liquid. The entrainment of the upper phase into the lower phase was also affected by the thickness of the upper phase, as well as by the intensity of bath agitation. At low flowrates, the number density of entrained droplets was constant with time, increasing with increasing agitation and thickness of the layer. The air flow required for the transition in the entrainment behaviour increased with an increase in the thickness of the upper phase.

Cleanness and uniformity in steel properties are important for high quality steel. Physical and/or mathematical models can be used in order to achieve optimum conditions for the clean steel during steelmaking processes. In the present study, important metallurgical transport phenomena in steelmaking ladles and tundishes have been investigated using both mathematical and physical (water) models.
Through appropriate solutions of the Navier-Stokes equations, the intermixing of fluid within gas-stirred ladles can be modelled quite satisfactorily. It is shown that off-centered bubbling gives the most consistent results in terms of minimising mixing times, since angular velocity components intermix fluid across the width of a ladle. Comparisons between mathematical and experimental data are presented.
Fluid flow, heat transfer and inclusion flotation have been modelled mathematically for testing the behaviour of several tundish designs. Computations are presented to illustrate the importance of thermal natural convection currents in mixing the upper and lower layers of steel. Particle removal rates are also experimentally studied with the aid of the novel E.S.Z. (Electric Sensing Zone) system, and compared with computational results.

The use of composites materials in aerospace applications can provide significant weight reduction. However, in airframe designs composites are frequently required to be joined to metal components, which is a challenging issue owing to the very different thermo-physical properties of the two classes of materials. In many cases adhesive bonding has insufficient durability and the requirement for large lapped areas and mechanical fasteners adds considerable weight, reducing the mass savings associated with the introduction of composite structures. A promising approach for improving joint performance is to surface engineer locking features on to the metal part which then integrate with the composite laminate to increase shear load transfer, both via better adhesion and also by mechanical "fit" throughout the thickness of the composite. Such hybrid joints are known as "hyper-joints". For this work, three main techniques are currently being investigated for generating the required surface features. These are; (i) sculpting surfaces using power beam local surface melting techniques (Surfi-Sculpt), (ii) building surface protrusions by additive layer manufacturing (AM) and (iii) arc percussive welding process. The present work aims to provide understanding of the critical metallurgical interactions during the growth/production of the surface engineered features and how some build parameters might affect the eventual joint integrity, durability and performance. To enable the use of the arc-percussive welding process as a viable manufacturing route for these hyper-joints, optimisation of its process parameters were studied in the course of this work. Further work on the effect of process parameters such as voltage, travel velocity, gap setting and time delay on the quality of the weld were also investigated in this study. Of the above mentioned process parameters, the voltage across the capacitor and travel velocity of the actuator have been found to have far greater effect on the weld quality. More importantly, the travel velocity of the actuator was also found to help determine the shape, size and distribution of the melt pool. Based on the systematic study and analysis of all of the process parameters involved, an optimised process window has now been proposed. Microstructural characterisations of hyper-joint samples made via the three manufacturing routes were performed in the course of the work. The observed microstructures were related to the process history and the process parameters. Most importantly it was for found that in common with most welding and AM processes, columnar prior β grains developed in all the samples studied by epitaxial-regrowth either along the build or weld directions. It was also found that the fusion zone of the similar titanium alloy (Ti-6Al-4V to Ti-6Al-4V) arc-percussive welded samples were characterised by extremely fine acicular alpha' martensitic platelets formed as a result of the high cooling rate associated with the process. On the other hand, the fusion zone of the dissimilar titanium alloy (Ti-6Al-4V to β21S) arc-percussive welded samples was characterised by an extremely fine cellular structure prompted by constitutional supercooling. Finally the microstructures observed in the Surfi-Sculpt samples were found to be dependant on the swipe pattern and duration. In order to assess the performance of hyper-joints made via two of the candidate manufacturing routes, tensile testing of standard and modified tensile samples was performed. The result indicated that on average the strength of these hyper-joint pins were within nominal values expected of the Ti-6Al-4V and β21S alloys. It was also found that with optimum weld conditions, failure occurred only along the gauge length for the arc-percussive welded samples whilst the strength of the AM samples degrade as the gauge diameter decreases as the effect of surface defects became prominent. Results are also reported on a novel method for testing the shear strength and properties of individual hyper-pins manufactured via this process. Interpretation of the shear test was assisted by finite element modelling. The shear test results indicated that the arc-percussive welded samples outperformed the SLM-AM samples thereby giving credence to the process as a viable means for making the pins.

This research project investigated the option of steelmaking with the ESS furnace by using computational modelling to estimate steady state decarburisation rates. It focused on understanding metallurgical phenomena that would dictate refining rates of molten pig iron with iron ore. The results obtained are aimed at designers and potential users of the furnace technology to improve their understanding of the expected steady-state process behaviour. A mass-and-energy-balance model with a decarburisation sub-model was developed to estimate feed material requirements for steady state operation. Modelling and simulation results suggest that it may not be possible to produce steel under the conditions proposed. However, the furnace still holds potential if ideal operational conditions are understood and applied. Modelling also gave insight into which areas areas of concern, such as bubble formation in the furnace’s channel induction heaters, and necessity for a well designed refractory lining to contain heat and allow the process to operate at a stable condition under the conditions proposed. Keywords: ESS furnace, steelmaking, metallurgical analysis, modelling, mass and energy balance, decarburisation kinetics
Dissertation (MEng)--University of Pretoria, 2020.
Materials Science and Metallurgical Engineering
MEng
Unrestricted

Ce travail de recherche a été réalisé dans le but de développer une technologie pour démontrer le potentiel des résidus métallurgiques comme une source secondaire de métaux lourds (Cu et Zn). Trois résidus de lixiviation de zinc différents (en fonction de leur âge de génération et de dépôt) (ZLR1, ZLR2 & ZLR3) et des résidus d'épuration de zinc (ZPR) ont été recueillis sur un site industriel de la métallurgie du zinc localisé au Brésil. Les échantillons de ZLRs et ZPR ont été analysé pour déterminer leurs caractéristiques minéralogiques et physico-chimiques. Le fractionnement de métaux lourds par extraction séquentielle et leur mobilité en fonction du pH ont été déterminés. La modélisation géochimique a été réalisée pour déterminer les mécanismes qui affectent la mobilisation des métaux lourds à partir de ces résidus. Ensuite, les résidus ont été soumis à des tests de lixiviation afin d’optimiser l'extraction de métaux lourds. La récupération sélective de métaux à partir des lixiviats acides a été obtenue par précipitation de sulfure métallique (MSP). Enfin, des séquences de procédés pour la récupération sélective de Cu et Zn ont été proposées. Les résultats révèlent que ZLRs contient une concentration importante de Zn (2,5% à 5%), Pb (1,7% à 2,3%) et des métaux tels que Mn, Cu, Al dans des fractions détectables. Les ZPRs contiennent une forte concentration de Cu (47%), Zn (28%), Cd (9%) et Pb (5%). Le fractionnement à l’aide d’acide acétique ou d’acide nitrique suggère que les résidus de lixiviation et de purification sont des déchets dangereux, qui libèrent une concentration de plomb et de cadmium dans l'environnement supérieure à la concentration admissible proposée par l’USEPA. La lixiviation des métaux à partir des résidus est très dépendante du pH. La lixiviation des métaux lourds (Zn & Cu) est élevée à pH acide et la libération des métaux diminue avec l'augmentation du pH. Les phases minérales sulfatées et carbonatées ont été identifiées comme celles contrôlant la solubilité des minéraux. La lixiviation de Zn à partir de ZLRs est fortement influencée par la température et la concentration en acide. La cinétique de lixiviation des ZLRs indique que plus de 92%, 85% et 70% du zinc peut être extrait de ZLR1, ZLR2 et ZLR3 par lixiviation à l’aide de H2SO4 (1,5 M). Les cinétiques de lixiviation de ZLRs avec l’acide sulfurique suivent le modèle cinétique à cœur rétrécissant. L'énergie d'activation nécessaire pour lixivier le zinc contenu dans ZLR1, ZLR2 et ZLR a été estimées à 2,24 kcal / mol, 6,63 kcal / mol et 11,7 kcal / mol, respectivement, à l’aide de l'équation d'Arrhenius. Les ordres de la réaction par rapport à la concentration en acide sulfurique ont également été déterminés comme étant respectivement de 0,2, 0,56, et 0,87 pour ZLR1, ZLR2 et ZLR3. La précipitation sélective du zinc (comme sphalérite) à partir des lixiviats a été obtenue par la combinaison d'une co-précipitation avec de l'hydroxyde et du sulfure. La lixiviation de Cu à partir de ZPR a été fortement influencée par le rapport solide-liquide et la vitesse d'agitation, ce qui suggère que le transfert de masse est contrôlé par la diffusion. Plus de 50%, 70% et 60% de Cd, Cu et Zn peuvent être lessivés à partir de ZPR en utilisant de l’H2SO4 1M . La covellite a été récupéré sélectivement à partir des lixiviats acides multi-métalliques (Cd, Cu et Zn) et les lixiviats ont été étudiés en optimisant le pH initial et le rapport massique Cuivre-sulfure. En conclusion, ces résidus métallurgiques dangereux peuvent être considérés comme une ressource alternative potentielle de Zn et Cu. Non seulement les coûts d'investissement et les questions environnementales liées au stockage / élimination de ces ZLRs & ZPR mais aussi à l'épuisement progressif des minerais sulfurés de haute qualité (pour Zn et Cu) peuvent être abordés. L'étude ouvre aussi une perspective de valorisation de ZLR & ZPR lessivés, pour la lixiviation sélective et de récupération de Pb
This research was carried out in order to develop a technology to demonstrate the metallurgical residues as a potential secondary source for heavy metals (Cu and Zn). Three different (based on their age of generation and deposition) zinc leach residues (ZLR1, ZLR2 & ZLR3) and zinc purification residue (ZPR) were collected from a Zn-metallurgical industry located in Brazil. The characterization of ZLRs and ZPR were examined for their mineralogical, physico-chemical, bulk chemical features. Fractionation of heavy metals and liquid-solid partitioning with respect to pH were also determined. Geo-chemical modelling was done to understand the mechanisms affecting the mineral solubilities of these residues. Following the above, the residues were subjected to (bio) leachability tests to optimize the maximal extraction of heavy metals. Later, the recovery of Zn (ZLRs) and Cu (ZPR) from the polymetallic acidic leachates were investigated. Finally, hydrometallurgical flow charts for the selective recovery of Cu and Zn were proposed. The results reveal that the ZLRs contain significant concentration of Zn (2.5% to 5%), Pb (1.7% to 2.3%) and metals such as Mn, Cu, and Al in detectable fractions. The ZPRs contain high concentration of Cu (47%), Zn (28%), Cd (9%) and Pb (5%). Fractionation with acetic and nitric acid suggest that both the leach and purification residues are hazardous wastes, releasing higher concentration of Pb and Cd into the environment, than the permissible concentration suggested by U.S. EPA. Leaching of metals from the residues is highly pH dependent. Heavy metals leaching (Zn & Cu) is high at low pH and the release of metals was decreased with increase in pH. Sulfated and carbonated mineral phases were predicted to be the solubility controlling minerals. The leaching of Zn from ZLRs was highly influenced by temperature and acid concentration. The results of the optimization of leaching parameters state that more than 92%, 85% and 70% of zinc can be extracted from ZLR1, ZLR2 and ZLR3 by H2SO4 (1.5 M) leaching (at 80 °C for 6 hours with a pulp density 2%, while the agitation speed was maintained 250 rpm). The sulfuric acid leaching of ZLRs follows the shrinking core diffusion model. The activation energy required to leach zinc from the ZLR1, ZLR2 and ZLR were estimated to be 2.24 Kcal/mol, 6.63 Kcal/mol and 11.7 Kcal/mol respectively, by Arrhenius equation. Order of the reaction with respect to the sulfuric acid concentration was also determined as 0.2, 0.56, and 0.87 for ZLR1, ZLR2 and ZLR3, respectively. Selective precipitation of Zn (as sphalerite) from the leachates was achieved by the combination of hydroxide and sulfide precipitation. Biohydrometallurgy is also as effective as the chemical hydrometallurgy for the selective Zn recovery from the ZLRs. Cu leaching from ZPR was highly influenced by solid to liquid phase ratio and agitation speed, suggesting that the mass transfer depends on the diffusion. More than, more than 50%, 70% and 60% of the total Cd, Cu and Zn can be leached from ZPR by 1M H2SO4 with 2% pulp density continuously shaken at 450 rpm at 80 °C. Covellite was selectively recovered from the acid multi-metallic (Cd, Cu & Zn) leachates were investigated by optimizing the initial pH and Cu to sulfide ratio. In conclusion, these hazardous metallurgical residues can be seen as potential alternative resource for Zn and Cu. Not only the capital costs and environmental issues associated with the storage/disposal of these ZLRs & ZPR but also the gradual depletion of high grade sulfidic ores (for Zn and Cu) can be addressed. The study also leaves a perspective of investigating the leached ZLR & ZPR, for the selective leaching and recovery of Pb

Les principaux objectifs étaient d'évaluer la stabilité de l'environnement des scories métallurgiques de Cu résultant de différentes périodes d'activités industrielles et de différentes technologies de fusion. Parmi les scories étudiées, on retrouve: les scories historiques cristallines (SH) ainsi que modernes: les scories de four vertical (SFS), les scories granulées (GS) et les scories de plomb (LS). Les différentes approches adoptées dans ce travail de thèse ont tenu compte de: i) la composition chimique et la phase minérale des scories, ii) la sensibilité à la lixiviation des scories sous l’exposition à différentes conditions de pH en mode statique, iii) l’altération des scories sous exposition aux acides organiques couramment trouvés dans l'environnement du sol, iv ) la bio-altération des scories par les bactéries (Pseudomonas aeruginosa) et v) l’application future de la récupération des métaux provenant des scories étudiées en mettant en œuvre la méthode de lixiviation biologique. Résultats cruciaux: Les résultats des tests de lixiviation dépendant du pH ont montré une libération de métal plus élevée dans des conditions fortement acides (pH 2 et 4), alors que la lixiviation dans des conditions alcalines (pH 10.5) était moins importante pour toutes les scories analysées. L'effet de l’altération par le sol a été démontré, la dissolution des scories est notamment sensible à la présence d'exsudats racinaires artificiels (ARE), d’acides humiques (HA) et d’acides fulviques (FA), la contribution des ARE étant la plus forte. Selon les données recueillies, la dissolution relative des scories est strictement liée à leurs caractéristiques (composition chimique et minéralogique) en fonction des différentes conditions étudiées. L'étude concernant l’effet de l’altération biologique a révélé que Pseudomonas aeruginosa améliore considérablement la libération des éléments majeurs (Si et Fe) et métalliques (Cu, Zn, Pb) par rapport aux effets des facteurs abiotiques, indépendamment de la chimie et de la structure des scories. En outre, une récupération élevée (jusqu'à 90%) des métaux (Cu, Zn, Fe) pourrait être obtenue grâce à la lixiviation avec Acidithiobacillus thiooxidans dans des conditions de laboratoire. Conclusions générales : La stabilité des scories dans l'environnement dépend à la fois des caractéristiques chimiques et de la minéralogie. Cependant, les phases minérales hébergeant les métaux sont les facteurs les plus déterminants concernant l'intensité de la lixiviation des métaux. Pour cette raison, l'examen individuel du comportement des scories est important pour empêcher la contamination de l'environnement et devrait être considéré comme une priorité pour la gestion durable des scories. L’optimisation des paramètres de fonctionnement pour le biolessivage et le développement de la technologie à l'échelle industrielle pourrait permettre une bien meilleure gestion (voir l’exploitation) des scories métallurgiques de Cu
Problem statement: Copper pyrometallurgical slags are inevitable waste by-products of Cu smelting operations. These waste are considered to be important due to their production volume and high residual metal content that are inefficiently recovered during industrial process. Due to the lack of sustainable practices in the past, tremendous volumes of Cu-slags have been disposed in many industrial districts, regardless of the weathering and associated environmental risk. Consequently, there are many areas where slags have been proven to be a source of metallic pollution for the surrounding environment. At the present time, the outstanding contradiction between the sustainable development and environmental pollution encourages to undertake the action regarding this aspect. For this reason, slags are currently being used as supplementary materials for civil engineering purposes (e.g. cement and concrete additives, road bed filling materials, hydraulic construction materials) rather than disposed. Additionally, modern-day management strategies require slags to be thoroughly evaluated with respect to their environmental stability prior undertaking any reuse action. Main objectives were to evaluate environmental stability of Cu-metallurgical slags resulting from different periods of industrial activities and different smelting technologies. Those included: historical crystalline slag (HS) as well as modern: shaft furnace slag (SFS), granulated slag (GS) and lead slag (LS). Different approaches undertaken in this PhD work considered: i) chemical and mineral phase compositions of slags, ii) leaching susceptibility of slags under exposure to different pH-stat conditions, iii) slags weathering under exposure to organic acids commonly found in soil environment, iv) bacterially (Pseudomonas aeruginosa) mediated weathering of slags and v) future application of studied slags for metal recovery by implementing the bioleaching method. Crucial results: The results of the pH-dependent leaching tests showed a higher metal release in strong acidic conditions (pH 2 and 4), whereas leachability at alkaline conditions (pH 10.5) revealed a lower importance for all the slags analyzed. The study considering soil weathering scenario demonstrated that Cu-slags are susceptible to dissolution in the presence of artificial root exudates (ARE), humic (HA) and fulvic acids (FA), whereby ARE were found to have stronger contribution than HA and FA. According to data collected, the different behavior of individual slags is strictly related to their characteristics (chemical and phase composition) reflecting various susceptibilities to dissolution under the investigated conditions. The study considering bio-weathering scenario revealed that Pseudomonas aeruginosa considerably enhances the release of major (Si and Fe) and metallic (Cu, Zn, Pb) elements compared to the effects of abiotic factors, regardless of the slags chemistry and structure. Furthermore, a high gain (up to 90%) of metals (Cu, Zn, Fe) could be credited to bioleaching with Acidithiobacillus thiooxidans under laboratory conditions. General conclusions: The environmental stability of slags depends on both, their bulk chemistry and mineralogy. However, mineral phases harbouring the metals are the key players in metal leachability intensity. For, this reason consideration of individual slags behaviour is important for preventing environmental contamination and should be regarded as priority branch of sustainable slag management. Optimization of operating parameters for bioleaching following development of industrial scale technology is an incentive scheme for future management of Cu-metallurgical slags

Dissertação (mestrado) - Universidade Federal de Santa Catarina, Centro Tecnológico, Programa de Pós-Graduação em Ciência e Engenharia de Materiais, Florianópolis, 2015.
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Abstract : Biodegradable metal alloys are a new class of implant materials suitable for implants such as stents, bone plates and screws. The corrosion of magnesium alloys might provide a new mechanism where they could be used as degradable metal implants to be applied in musculo-skeletal surgery. In this case, a secondary surgery for implant retrieval is not needed. For that, magnesium alloys with controlled in vivo corrosion rates need to be developed. There is a high demand to design magnesium alloys with adjustable corrosion rates and suitable mechanical properties. An approach to this challenge is a magnesium metal matrix composite (Mg-MMC) composed of the magnesium alloy ZK60 and hydroxyapatite (HA) particles for tailoring its properties such as mechanical properties and corrosion resistance. The composite was produced by mechanical alloying followed by hot extrusion. HA in contact with molten magnesium releases toxic gases like phosphine (PH3), so solid-state processing such as mechanical milling and extrusion is feasible. This work presents the influence of different amounts of HA on the degradation behavior and mechanical properties, which shows that the HA addition has a substantial increase in the compression strength (up to 14% for 20 wt.% HA addition) and no negative effect on the controlled degradation behavior of this biomaterial.

Ligas metálicas biodegradáveis são uma nova classe de materiais de implante adequados para a cirurgia óssea. A corrosão de ligas de magnésio pode proporcionar um novo mecanismo onde tais ligas podem ser utilizadas como implantes metálicos degradáveis a serem aplicados em cirurgia músculo-esquelética. Nestes casos, a segunda cirurgia para retirada do implante não seria necessária. Para isso, ligas de magnésio com taxas de corrosão in vivo controladas precisam ser desenvolvidas. Há uma grande procura para projetar ligas de magnésio com taxas de corrosão ajustáveis e propriedades mecânicas aplicáveis. Uma abordagem a este desafio é um compósito de matriz metálica (CMM) composto pela liga de magnésio ZK60 e hidroxiapatita (HA) para aperfeiçoar suas propriedades como resistência mecânica e resistência à corrosão. O compósito é produzido via moagem de alta energia seguida de extrusão à quente. Uma vez que HA em contato com magnésio líquido libera gases tóxicos como fosfina (PH3), esta é a melhor forma de sua produção. Este trabalho mostra a influência de diferentes quantidades de hidroxiapatita na taxa de degradação e propriedades mecânicas do compósito, as quais evidenciam um aumento substancial na resistência à compressão com a adição de HA (até 14% para o compósito com 20% de HA), sem detrimento às propriedades de degradação controlada do biomaterial.

Le Silicium est le deuxième élément le plus abondant dans la croûte terrestre après l’oxygène. Il est produit par voie métallurgique dans un four à arc électrique, le quartz est réduit en présence de réducteurs (charbon de bois, houille et coke de pétrole). Le silicium métallurgique est principalement utilisé dans la métallurgie comme élément d’alliage, dans la chimie et l’industrie solaire. Le prix du Silicium est fonction de sa pureté. Les travaux de cette thèse se divisent en deux parties l’utilisation du Silicium Métallurgique (99% Si) pour le stockage de l’hydrogène, et la photoluminescence du ferrosilicium (disiliciure de fer) de qualité métallurgique. Des substrats de silicium métallurgique ont été soumis à une anodisation électrochimique dans une solution à base d’acide fluorhydrique. Le silicium poreux nanostructuré obtenu est légèrement différent du silicium poreux issu de substrat de silicium de qualité électronique de même résistivité. L’influence des principaux paramètres sur la génération de l’hydrogène : la porosité, la concentration, le volume et la température ont fait l’objet d’une étude détaillée. Le silicium poreux produit à partir de silicium métallurgique est un matériau de stockage d’hydrogène. Des substrats de disiliciure de fer de qualité métallurgique ont été soumis à une anodisation électrochimique. Le composé obtenu est du disiliciure de fer nanostructuré avec du silicium résiduel, ce produit est recouvert de fluorosilicate de fer hexahydraté qui a la particularité d’être luminescent. Il s’agit à ce jour de la première anodisation du disiliciure de fer, un mécanisme de gravure a été proposé et l’influence des principaux paramètres d’anodisation sur les propriétés de photoluminescence a été évaluée
Silicon is the second most abundant element in the Earth crust after oxygen. Its use in metallurgy, building and electronic industry requires a huge fabrication level. Depending on the contamination level allowed, the price of this material varies in the orders of magnitude. This thesis focuses on the use of dirtiest metallurgical grade silicon and iron disilicide substrates for hydrogen storage and photoluminescence applications. The initial substrates were subjected to electrochemical etching in hydrofluoric acid-containing solutions. Anodization of metallurgical grade silicon substrate produces nanostructured porous silicon with somewhat shifted parameters (comparing with electronic grade porous silicon with the same resistivity), as it was studied in this thesis in details. It was shown, that metallurgical grade porous silicon can be applied as hydrogen storage material. Hydrogen generation is studied here based on the influences of some technically critical parameters: porosity, alkali concentration, volume and temperature. Electrochemical treatment of metallurgical grade iron disilicide substrates produces luminescent iron fluorosilicate hexahydrate, covering the residual nanostructured iron disilicide/silicon. Here, the influence of anodization parameters on photoluminescent properties is studied. Also, etching mechanism is proposed as for the new material never anodized

There are a number of impurity elements present in sulphide ores that can have a deleterious effect on the properties of the final copper metal product. In this thesis, an equilibrium distribution technique was used to determine the thermodynamic behaviour of selenium and tellurium in molten slags used in copper production. Calcium ferrite based slags and copper or silver alloy were equilibrated in magnesia crucibles at temperatures of 1200 to 1400 °C and oxygen partial pressures of 10-11 to 10-0.68 atm. Under conditions typical of those employed during copper converting, the minor elements were found to enter the slag as negatively charged species. The partitioning of selenium and tellurium to the slag was greatest at high temperature, low oxygen partial pressure and at highest concentration of basic oxide (CaO or BaO). The experimentally derived data were combined with published information to calculate the selenide and telluride capacities of the slag, and also to generate fundamental thermodynamic activity data for selenium and tellurium in the slag phase. It was found that the activity coefficients of selenium and tellurium were independent of their concentration in the slag over the range studied, but were strongly dependent on the temperature, slag chemistry and oxidation state of the slag. Experiments were also designed and carried out to determine what effect the presence of iron oxide and its oxidation state has on the behaviour of selenium in the slag. A series of experiments involving iron oxide additions to a calcium aluminate slag was conducted under increasingly oxidising conditions to assess the effect of total iron on the selenide capacity as the dominant oxidation state of iron in the slag changed. It was shown that at a constant ratio of CaO:Al2O3, the selenide capacity increased with total iron in the slag. However, the effect on the selenide capacity did not appear any more significant as the Fe3+:Fe2+ ratio changed in a particular direction. 4 Another series of experiments was carried out with iron calcium silicate slags to determine the stability of phases within the slag, and how this affected the equilibrium distribution and activity coefficient of selenium in the slag. A number of solid phases were identified and their composition determined by scanning electron microscopy, energy dispersive spectroscopy and electron microprobe analysis. The composition and minor element content of the remaining liquid was calculated using a thermodynamic model. From this it was found that the capacity of the liquid slag has a region of independence against slag chemistry, before increasing strongly with increasing lime content to the calcium ferrite composition. Some of the implications of this work are discussed with reference to the practicality of adjusting the process variables in a large-scale industrial process for the purpose of managing minor element content of the molten phases. Considerations include the effect on copper recovery and rate of wear of furnace refractory materials.

Work was undertaken to establish whether microstructural changes during high-speed deformation could explain the inferior crash performance of mild steel compared to carbon-manganese grades, which in turn are deemed inferior to dual phase steel grades. This thesis correlates the relationship between the mechanical properties of commercial sheet steel and crashworthiness of steel structures. In order to deliver the correlation a research project was undertaken that included quasi-static tensile testing and dynamic tensile testing, following by a study of box section testing using quasi-static crush testing and dynamic axial impact testing. The results of the present study identified that the dual phase steel grades with the lowest volume fraction of additional non-martensitic second phase constituents, displayed an increase in energy absorbed, as strain rate increases, that appears to be linear up to and including 100s^-1 strain rate. Finally, this study involved the production of dual phase microstructures in low carbon strip steels, via a modified steel-processing route, with the subsequent determination of the dynamic properties of the strip steels. Two dual phase commercial trial grades with compositions 0.094%C-0.155%Si-1.48%Mn-0.96%V and 0.096%C-0.13%Si-1.15%Mn-0.096%V respectively, were studied. The results showed that the yield/proof strength and tensile strength increased with increasing volume fraction of martensite and increasing strain rate. Steels with a predominantly ferrite-martensite microstructure showed improved performance, in terms of the strain rate sensitivity and work hardening properties up to strain levels of 10% compared with microstructures with additional non-equilibrium constituents, characterised mainly as bainite.

Thesis (PhD)--Stellenbosch University, 2008.
ENGLISH ABSTRACT: The growing need to improve accounting accuracy, precision and to standardise generally accepted measurement methods in the mining and processing industries has led to the joining of a number of organisations under the AMIRA International umbrella, with the purpose of fulfilling these objectives. As part of this venture, Anglo Platinum undertook a project on the material balancing around its largest smelter, the Waterval Smelter. The primary objective of the project was to perform a statistical material balance around the Waterval Smelter using the Maximum Likelihood method with respect to platinum, rhodium, nickel, sulphur and chrome (III) oxide. Pt, Rh and Ni were selected for their significant contribution to the company’s profit margin, whilst S was included because of its environmental importance. Cr2O3 was included for its importance in as far as the difficulties its presence poses in smelting of PGMs. The objective was achieved by performing a series of statistical computations. These include; quantification of total and analytical uncertainties, detection of outliers, estimation and modelling of daily and monthly measurement uncertainties, parameter estimation and data reconciliation. Comparisons were made between the Maximum Likelihood and Least Squares methods. Total uncertainties associated with the daily grades were determined by use of variographic studies. The estimated Pt standard deviations were within 10% relative to the respective average grades with a few exceptions. The total uncertainties were split into their respective components by determining analytical variances from analytical replicates. The results indicated that the sampling components of the total uncertainty were generally larger as compared to their analytical counterparts. WCM, the platinum rich Waterval smelter product, has an uncertainty that is worth ~R2 103 000 in its daily Pt grade. This estimated figure shows that the quality of measurements do not only affect the accuracy of metal accounting, but can have considerable implications if not quantified and managed. The daily uncertainties were estimated using Kriging and bootstrapped to obtain estimates for the monthly uncertainties. Distributions were fitted using MLE on the distribution fitting tool of the JMP6.0 programme and goodness of fit tests were performed. The data were fitted with normal and beta distributions, and there was a notable decrease in the skewness from the daily to the monthly data. The reconciliation of the data was performed using the Maximum Likelihood and comparing that with the widely used Least Squares. The Maximum Likelihood and Least Squares adjustments were performed on simulated data in order to conduct a test of accuracy and to determine the extent of error reduction after the reconciliation exercise. The test showed that the two methods had comparable accuracies and error reduction capabilities. However, it was shown that modelling of uncertainties with the unbounded normal distribution does lead to the estimation of adjustments so large that negative adjusted values are the result. The benefit of modelling the uncertainties with a bounded distribution, which is the beta distribution in this case, is that the possibility of obtaining negative adjusted values is annihilated. ML-adjusted values (beta) will always be non-negative, therefore feasible. In a further comparison of the ML(bounded model) and the LS methods in the material balancing of the Waterval smelter complex, it was found that for all those streams whose uncertainties were modelled with a beta distribution, i.e. those whose distribution possessed some degree of skewness, the ML adjustments were significantly smaller than the LS counterparts It is therefore concluded that the Maximum Likelihood (bounded models) is a rigorous alternative method of data reconciliation to the LS method with the benefits of; -- Better estimates due to the fact that the nature of the data (distribution) is not assumed, but determined through distribution fitting and parameter estimation -- Adjusted values can never be negative due to the bounded nature of the distribution The novel contributions made in this thesis are as follows; -- The Maximum Likelihood method was for the first time employed in the material balancing of non-normally distributed data and compared with the well-known Least Squares method -- This was an original integration of geostatistical methods with data reconciliation to quantify and predict measurement uncertainties. -- For the first time, measurement uncertainties were modeled with a distribution that was non-normal and bounded in nature, leading to smaller adjustments
AFRIKAANSE OPSOMMING: Die groeiende behoefte aan rekeningkundige akkuraatheid, en om presisie te verbeter, en te standardiseer op algemeen aanvaarde meetmetodes in die mynbou en prosesseringsnywerhede, het gelei tot die samwewerking van 'n aantal van organisasies onder die AMIRA International sambreel, met die doel om bogenoemde behoeftes aan te spreek. As deel van hierdie onderneming, het Anglo Platinum onderneem om 'n projek op die materiaal balansering rondom sy grootste smelter, die Waterval smelter. Die primêre doel van die projek was om 'n statistiese materiaal balans rondom die Waterval smelter uit te voer deur gebruik te maak van die sogenaamde maksimum waarskynlikheid metode met betrekking tot platinum, rodium, nikkel, swawel en chroom (iii) oxied. Pt, Rh en Ni was gekies vir hul beduidende bydrae tot die maatskappy se winsmarge, terwyl S ingesluit was weens sy belangrike omgewingsimpak. Cr2O3 was ingesluit weens sy impak op die smelting van Platinum groep minerale. Die doelstelling was bereik deur die uitvoering van 'n reeks van statistiese berekeninge. Hierdie sluit in: die kwantifisering van die totale en analitiese variansies, opsporing van uitskieters, beraming en modellering van daaglikse en maandelikse metingsvariansies, parameter beraming en data rekonsiliasie. Vergelykings was getref tussen die maksimum waarskynlikheid en kleinste kwadrate metodes. Totale onsekerhede of variansies geassosieer met die daaglikse grade was bepaal deur ’n Variografiese studie. Die beraamde Pt standaard afwykings was binne 10% relatief tot die onderskeie gemiddelde grade met sommige uitsonderings. Die totale onsekerhede was onderverdeel in hul onderskeie komponente deur bepaling van die ontledingsvariansies van duplikate. Die uitslae toon dat die monsternemings komponente van die totale onsekerheid oor die algemeen groter was as hul bypassende analitiese variansies. WCM, ‘n platinum-ryke Waterval Smelter produk, het 'n onsekerheid in die orde van ~twee miljoen rand in sy daagliks Pt graad. Hierdie beraamde waarde toon dat die kwaliteit van metings nie alleen die akkuraatheid van metaal rekeningkunde affekteer nie, maar aansienlike finansiële implikasies het indien nie die nie gekwantifiseer en bestuur word nie. Die daagliks onsekerhede was beraam deur gebruik te maak van “Kriging” en “Bootstrap” metodes om die maandelikse onsekerhede te beraam. Verspreidings was gepas deur gebruik te maak van hoogste waarskynlikheid beraming passings en goedheid–van-pas toetse was uitgevoer. Die data was gepas met Normaal en Beta verspreidings, en daar was 'n opmerklike vermindering in die skeefheid van die daaglikse tot die maandeliks data. Die rekonsiliasies van die massabalans data was uitgevoer deur die gebruik die maksimum waarskynlikheid metodes en vergelyk daardie met die algemeen gebruikde kleinste kwadrate metode. Die maksimum waarskynlikheid (ML) en kleinste kwadrate (LS) aanpassings was uitgevoer op gesimuleerde data ten einde die akkuraatheid te toets en om die mate van fout vermindering na die rekonsiliasie te bepaal. Die toets getoon dat die twee metodes het vergelykbare akkuraathede en foutverminderingsvermoëns. Dit was egter getoon dat modellering van die onsekerhede met die onbegrensde Normaal verdeling lei tot die beraming van aanpassings wat so groot is dat negatiewe verstelde waardes kan onstaan na rekosniliasie. Die voordeel om onsekerhede met 'n begrensde distribusie te modelleer, soos die beta distribusie in hierdie geval, is dat die moontlikheid om negatiewe verstelde waardes te verkry uitgelsuit word. ML-verstelde waardes (met die Beta distribusie funksie) sal altyd nie-negatief wees, en om hierdie rede uitvoerbaar. In 'n verdere vergelyking van die ML (begrensd) en die LS metodes in die materiaal balansering van die waterval smelter kompleks, is dit gevind dat vir almal daardie strome waarvan die onserkerhede gesimuleer was met 'n Beta distribusie, dus daardie strome waarvan die onsekerheidsdistribusie ‘n mate van skeefheid toon, die ML verstellings altyd beduidend kleiner was as die ooreenkomstige LS verstellings. Vervolgens word die Maksimum Waarskynlikheid metode (met begrensde modelle) gesien as 'n beter alternatiewe metode van data rekosiliasie in vergelyking met die kleinste kwadrate metode met die voordele van: • Beter beramings te danke aan die feit dat die aard van die onsekerheidsdistribusie nie aangeneem word nie, maar bepaal is deur die distribusie te pas en deur van parameter beraming gebruik te maak. • Die aangepaste waardes kan nooit negatief wees te danke aan die begrensde aard van die verdeling. Die volgende oorspronklike bydraes is gelewer in hierdie verhandeling: • Die Maksimum Waarskynlikheid metode was vir die eerste keer geëvalueer vir massa balans rekonsiliasie van nie-Normaal verspreide data en vergelyk met die bekendde kleinste kwadrate metode. • Dit is die eerste keer geostatistiese metodes geïntegreer is met data rekonsiliasie om onsekerhede te beraam waarbinne verstellings gemaak word. • Vir die eerste keer, is meetonsekerhede gemoddelleer met 'n distribusie wat nie- Normaal en begrensd van aard is, wat lei tot kleiner en meer realistiese verstellings.

Complex heat treatments and manufacturing processes such as welding involve a wide range of temperatures and temperature rates, affecting the microstructure of the material and its properties. In this work, a diffusion based approach to model growth and shrinkage of precipitates in the alpha + beta field of Ti-6Al-4V alloys is established. Experimental heat treatments were used to validate the numerical predictions of the model for lamellar shrinkage, whilst data from literature have been used to evaluate the numerical model for the growth of equiaxed microstructures. The agreement between measurements and numerical predictions was found to be very good. Experimentally-based approaches were used both to describe the growth of alpha lamellae and martensitic needles while cooling down from temperatures above the beta transus, and beta grain growth for temperatures remaining above the beta transus. Such models were coded in the commercial FE software Visual-Weld for the prediction of microstructure evolution during welding simulations. Experimental welding tests were carried out to validate the predictions. The metallurgical models developed were linked with a mechanical physically based model to predict the flow properties and the initial implementation of the coupled models in Visual-Weld is discussed.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Nuclear Engineering, 2005.
Includes bibliographical references (p. 276-279).
Eight heats of material with base alloy chemistries of Alloys 800 HT or 617 with platinum additions of 2, 5, 15, or 30 wt% have been characterized according to their microstructural features. The goals of characterization were to determine metallurgical stability for service as self-catalytic structural materials. The results presented herein will be useful to the development of a material for the construction of a heat exchanger designed for sulfuric acid decomposition. This type of heat exchanger is a key component to hydrogen generation by the thermochemical sulfur-iodine water-splitting process, a future technology that promises efficient hydrogen production if coupled to a Generation IV nuclear reactor heat source. Characterization of each material was carried out in the cast and wrought conditions with optical and SE microscopy, electron dispersive spectrometry, chemical composition analysis, and thermodynamic modeling. Materials have been characterized according to grain size and morphology, precipitate features, twinning characteristics, and platinum composition effects. Results indicate that platinum and carbon compositions have the greatest effect on the development of microstructural features.
(cont.) Increasing platinum compositions in both base alloy chemistries fosters the presence of annealing twins, which indicates that platinum additions reduce stacking fault energy within the alloy systems. Platinum additions appear to cause the development of larger grain structures as well as increase corrosion resistance. With the exception of the Alloy 800 HT - 30 wt% Pt system, the alloy systems characterized herein were melted with carbon contents between 1.2 - 3.6 times higher than the maximum specified compositions for the base chemistries. Excessive inter and intra-granular carbide precipitation resulted, which leads to compromised corrosion resistance and mechanical properties. Inter-granular attack due to sensitization is observed in the Alloy 800 HT - 2, 5 wt% Pt systems. SEM micrographs of the Alloy 617 - Pt systems show that these systems are less prone to inter-granular attack. The grain structures of each base alloy - Pt system are much finer than those of the respective base alloy systems included for comparison. Fine grain structures are detrimental to overall ductility and high temperature creep strength. On average, the Alloy 800 HT - Pt systems developed larger grains than the Alloy 617 - Pt systems.
(cont.) A two phase microstructure that resembles pearlite developed in the Alloy 617 - 30 wt% Pt system. This alloy system will be excluded from further characterization for self catalytic structural application due to expected poor mechanical and corrosion resistance properties. The most important microstructural improvements for the development of a self-catalytic structural material include a reduction of carbon content and an increase in grain size. Further characterization of catalytic, corrosion resistance, and mechanical properties are required for selection of the optimum platinum addition to the base chemistries of Alloys 800 HT and 617 for sulfuric acid decomposition service.
by David Andrés Rigual.
S.M.

The development of CAPP (Computer Aided Process Planning) systems promises improvement to the design efficiency and quality of process plans, whilst maintaining knowledge for future developments. Although considerable progress has been made in Computer Aided Process Planning, most of the systems developed or under development so far are limited to one manufacturing operation and to planning for an individual part design. The systems lack an overall structure for real manufacturing practice. This thesis examines the problems involved in the planning of an extensive manufacturing task involving many different processes including chemical and thermal treatments. On the basis of the evaluation of the manufacturing system in the collaborating company, an intelligent database system has been designed to solve metallurgical process planning problems involved in the manufacture of large steel forgings. In this CAPP database system, two hierarchy control levels involving a number of local planning areas have been adopted to allow the development of process sub-plans as well as supporting engineering data. All the process sub-plans have been integrated into a single system rather than isolated as separate entities within the overall metallurgical process planning system together with quality assurance control and other functions. These sub-plans, however, are planned and modified in the separate planning areas, the development being conducted on facsimile data records. Only when each sub-plan has reached a satisfactory state of development is it issued - made available to the overall system - by transferring the facsimile records into the system data files, the facsimile records then being discarded. Metallurgical process knowledge and rules have been incorporated into the database. These allow the system to assist users to make decisions and achieve final desired process plans. A versional approach has been developed to organise and control the stage by stage evolution of issued process plans within this complex steel forging environment. The use of separate planning areas and local facsimile records allows the modification of sub-plans already issued to be undertaken on a step by step but secure basis. A fully operating authorisation system controlling access to the data and the deletion or modification of records has been achieved. This is essential in a CAPP system of this type in which historical decisions, or approved rules based on historical experience, are presented to the users as the basis to make new decisions. The work has been extended to explore external enhancement of the central database system with an expert system and with specially written C ++ programmes. The system architecture needed to support this link is described, and issues raised by the enhancement that relate to the overall control are then addressed. The final part of the thesis examines the limitations of the method that has been developed and discusses difficulties involved in implementing a CAPP system in a large concern involved in the 'bespoke' manufacture of complex engineering artifacts on a one-off design basis.

Ternary transition metal cubic carbides have high hardness and are potential carbides in cemented carbide and cermet tools, as well as hard coatings used to improve metal cutting performance. In the present work, (Ti,Zr)C, (V,Nb)C, and (V,Ta)C ternary cubic carbides were synthesized using traditional powder-metallurgical methods. The effect of synthesis temperature and starting materials on synthesis is investigated, and the microstructure evolution during aging is studied. (Ti,Zr)C was found to decompose into lamellae upon aging at the temperature range from 1150 to 1800 °C. A similar microstructure was observed in (V,Ta)C and (V,Nb)C- 0.5 wt% Fe. All of these structures were found to form through discontinuous precipitation.The grain misorientation distribution of (Ti,Zr)C aged at 1400 °C is investigated. It was found that decomposition tends to occur at high-angle grain boundaries above 25°. The hardness of as-synthesized (Ti,Zr)C powder was found to be 41±6 GPa. Fully decomposed (Ti,Zr)C particles were found to be slightly harder than the undecomposed counterpart. On the other hand, in (V,Nb)C-0.5 wt% Fe, the decomposed structure formed upon aging at 1200 °C was found to have a hardness of 26±2 GPa, which is basically the same as the unaged alloy.Furthermore, the sintering behavior of (Ti,Zr)C with WC-Co is investigated. There are two γ-phases in the final microstructure, one TiC-rich and one ZrC-rich. (Ti,Zr)C was found to decompose at an early stage of sintering, and the final grain size of WC and the two γ-phases was found to be 10% smaller than that in a reference WC-TiC-ZrC-Co composite.

QC 20170529