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1
Kelley, Andrew III. "Tungsten carbide-cobalt by Three Dimensional Printing." Thesis, Massachusetts Institute of Technology, 1998. http://hdl.handle.net/1721.1/32316.
Full textAbstract:
Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1998.Includes bibliographical references (p. 69-70).
Three Dimensional Printing is an additive manufacturing process for rapid prototyping ceramic and metallic parts [Sachs, et al, 1990]. Green (not sintered) tungsten carbide-cobalt parts must have a density greater than 50% of the theoretical density, 14.9 g/cc, for proper sintering and post-processing. Two approaches were assessed for feasibility and robustness: printing slurry into tungsten carbide-cobalt spray dried powder and printing a solvent in spray dried tungsten carbide powder that readily dissolves. For slurry administered to a powder bed of solid, spherical particles, it has been found that the resulting packing primitive packing fraction increases almost linearly with the volume loading of the slurry over a range of powder size. The increase in density is approximately half what would be calculated by assuming that the slurry fills all the porosity in the powder bed. The maximum green density achieved by printing slurry into a spray dried tungsten carbide-cobalt bed was 41%, midway between the lower bound calculated by assuming the vehicle in the slurry infiltrates only the large pores between the spray dried power and the upper bound calculated by assuming that the vehicle of the slurry also infiltrates the find pores within a spray dried granule. A re-dispersible spray dried powder (38-53 micron size range) was fabricated using only the Duramax 3007 dispersant as the binder. This powder redisperses in water. Administering a drop of water to this powder resulted in primitives with 47% packing density, but which had significant quantities of 80 micron voids.
(cont.) Several lines of evidence pointed to the hypothesis that the voids were the result of trapped air. Two methods were successfully employed to nearly eliminate such voids. In one approach, the droplet of water wvas administered to the powder bed under a vacuum of between 25 and 40 torr and air was admitted to the chamber to 1 atmosphere after different intervals of time ranging from 30 seconds to 10 minutes. In another approach, the ability of water to absorb CO₂ was used to "getter" any trapped gas into the liquid. Water was administered to a powder bed under a CO₂ environment at room temperature. After a 2 minute period, intended to allow the spray dried powder to substantially re-disperse, the temperture of the powder bed was lowered to 0-5 degrees Centigrade in order to increase the amount of CO₂ which could be absorbed in the water and "switch on" the gettering of the trapped gas.Controls were run with the same procedure in air. The primitives made under CO₂ were nearly void free and had densities as high as 52%, while the controls were not significantly different than primitives made at room temperature in air.
by Andrew Kelley, III.
S.M.
2
Huba, Zachary. "Synthesis and characterization of cobalt carbide based nanomaterials." VCU Scholars Compass, 2014. http://scholarscompass.vcu.edu/etd/3320.
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Permanent magnets are used heavily for multiple applications in industry and current electronic technologies. However, the current permanent landscape is muddled by high cost of materials and insufficient magnetic or thermal properties. The primary focus of this dissertation work is the synthesis and optimization of a new permanent magnetic material, in the form of cobalt carbide nanomaterials. The optimization revolved around controlling the crystal phase and particle shape of synthesized cobalt carbide particles; these parameters have significant impact on the observed magnetic properties of magnetic nanoparticles. Co3C was identified to be the preferred crystal phase, leading to better magnetic properties. Cobalt Fumarate was found to be the ideal precursor to synthesize anisotropic Co3C particles and enhance magnetic properties of the synthesized cobalt carbide particles. Lastly, an ethanol based reduction system was employed to develop the greener synthesis of Co and Ni magnetic particles.
3
Archer, M., RI McCrindle, and ER Rohwer. "Analysis of cobalt, tantalum, titanium, vanadium and chromium in tungsten carbide by inductively coupled plasma-optical emission spectrometry." The Royal Society of Chemistry, 2003. http://encore.tut.ac.za/iii/cpro/DigitalItemViewPage.external?sp=1001953.
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Summary
Inductively coupled plasma optical emission spectroscopy (ICP-OES) was used to measure the concentrations
of cobalt, tantalum, titanium, vanadium and chromium in solutions of tungsten carbide. The main advantage
of the method described here lies in the speed, convenience and effectiveness of the dissolution procedure.
Aliquots of powdered tungsten carbide were dissolved in a solution of 5% aqua regia in 30% hydrogen
peroxide. Complete dissolution was usually achieved within 10 min. The accuracy of the method was assessed
by the analysis of certified reference materials, secondary reference materials and matrix spiking. The method
was successfully applied to commercial type samples with differing compositions. Slightly more emphasis was
placed on the measurement of vanadium, since no information on the measurement of this element in solutions
of tungsten carbide, by ICP-OES, has been published. Investigation of the interference effects of the elements in
the sample matrix on each other was essential for accurate results comparable to other published analytical
methods.
4
Crause, Chantelle. "Synthesis and application of carbene complexes with heteroaromatic substituents /." Access to E-Thesis, 2004. http://upetd.up.ac.za/thesis/available/etd-05252005-145146/.
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Oliveira, Mark A. (Mark Anthony) 1977. "Slurry based Three Dimensional Printing (S-3DP tm) of tungsten carbide cobalt." Thesis, Massachusetts Institute of Technology, 2002. http://hdl.handle.net/1721.1/109638.
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Almugaiteeb, Turki I. "OPTIMIZING COBALT CARBIDE BASED NANOMATERIALS BY USING NUCLEATING AGENTS AND STATISTICAL ROUTES." VCU Scholars Compass, 2016. http://scholarscompass.vcu.edu/etd/4310.
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The continuous high demand on permanent magnets in industries opened new research plateau to develop alternative magnetic material. The current used permanent magnet materials in the market still suffer from high cost and insufficient magnetic or thermal properties. The central focus of this dissertation work is the optimization of cobalt carbide based nanomaterial by means of modifying polyol synthesis assisted by nucleation agent and systematic statistics using JMP software tool. In most existing literatures, producing cobalt carbide (Co2C or Co3C) lack reproducibility and consistency resulting in nonsolid magnetic properties results. The practical requirements for cobalt carbide to be used as permanent magnet are high coercivity (Hc), high magnetization (Ms), resulting in a high-energy product (HcxMs). Previous literatures have shown coercivities of 1.5 to 2.5 kOe for cobalt carbides under aggressive temperatures conditions (300oC) or after aligning the particles under magnetic field.
A statistical guided method performed a sequence of experiments toward producing high coercivities using surface response design. Primarily, the statistical study to optimize cobalt carbide was made by analyzing experimental condition to fulfill high magnetic properties with tuned conditions as much as possible. Therefore, having the advantage for superior control on process variable when shifting cobalt carbide for scale up production in flow chemistry set up using microreaction system (MMRS). The optimization is based upon selecting the most important conditions in polyol reaction to produce cobalt carbide (Co2C or Co3C) and feed JMP software model e.g. reaction temperature, reaction time, and or precursor concentration…etc. These factors called (effects) used to design experiments and generate tables to run minimum experiments. Points of each effect (levels) are selected based on previous knowledge and experience with the synthesis. The output called (response) can be any of the magnetic properties of our interest e.g. magnetization (Ms), coercivity (Hc), or energy magnetic product (HcxMs). In the first model fit of cobalt carbide magnetic was studied in a polyol reaction to increase its magnetic energy product and optimize the experimental conditions. The results disclosed increase in magnetic energy product (6.2 MGOe) when validating the prediction model conditions suggested by JMP: shorter reaction time, and lower precursor concentration conditions at maximum reaction temperature.
Finally, to my knowledge studying the effect of the nucleating agent to alter cobalt carbide growth have not been studied so far. Therefore, statistical study design using central composite design (CCD) to investigate the nucleating agent effect of silver nitrite on cobalt carbide coercivity was made. The importance of nucleating agent on coercivity is vigorous to attain and control the growth direction of cobalt carbide nanoparticles. This is due to the shape anisotropy contribution to enhance coercivity unlike weak shape anisotropy attributed to agglomeration of nanoparticles demonstrated in previous studies. Enhancement of coercivity reached 3 kOe with aspect ratio control as a function of silver nitrite concentration under lower reaction temperature.
The continuous high demand on permanent magnets in industries opened new research plateau to develop alternative magnetic material. The current used permanent magnet materials in the market still suffer from high cost and insufficient magnetic or thermal properties. The central focus of this dissertation work is the optimization of cobalt carbide based nanomaterial by means of modifying polyol synthesis assisted by nucleation agent and systematic statistics using JMP software tool. In most existing literatures, producing cobalt carbide (Co2C or Co3C) lack reproducibility and consistency resulting in nonsolid magnetic properties results. The practical requirements for cobalt carbide to be used as permanent magnet are high coercivity (Hc), high magnetization (Ms), resulting in a high-energy product (HcxMs). Previous literatures have shown coercivities of 1.5 to 2.5 kOe for cobalt carbides under aggressive temperatures conditions (300oC) or after aligning the particles under magnetic field.
A statistical guided method performed a sequence of experiments toward producing high coercivities using surface response design. Primarily, the statistical study to optimize cobalt carbide was made by analyzing experimental condition to fulfill high magnetic properties with tuned conditions as much as possible. Therefore, having the advantage for superior control on process variable when shifting cobalt carbide for scale up production in flow chemistry set up using microreaction system (MMRS). The optimization is based upon selecting the most important conditions in polyol reaction to produce cobalt carbide (Co2C or Co3C) and feed JMP software model e.g. reaction temperature, reaction time, and or precursor concentration…etc. These factors called (effects) used to design experiments and generate tables to run minimum experiments. Points of each effect (levels) are selected based on previous knowledge and experience with the synthesis. The output called (response) can be any of the magnetic properties of our interest e.g. magnetization (Ms), coercivity (Hc), or energy magnetic product (HcxMs). In the first model fit of cobalt carbide magnetic was studied in a polyol reaction to increase its magnetic energy product and optimize the experimental conditions. The results disclosed increase in magnetic energy product (6.2 MGOe) when validating the prediction model conditions suggested by JMP: shorter reaction time, and lower precursor concentration conditions at maximum reaction temperature.
Finally, to my knowledge studying the effect of the nucleating agent to alter cobalt carbide growth have not been studied so far. Therefore, statistical study design using central composite design (CCD) to investigate the nucleating agent effect of silver nitrite on cobalt carbide coercivity was made. The importance of nucleating agent on coercivity is vigorous to attain and control the growth direction of cobalt carbide nanoparticles. This is due to the shape anisotropy contribution to enhance coercivity unlike weak shape anisotropy attributed to agglomeration of nanoparticles demonstrated in previous studies. Enhancement of coercivity reached 3 kOe with aspect ratio control as a function of silver nitrite concentration under lower reaction temperature.
7
Woolmore, Nicola J. "The failure of a tungsten carbide-cobalt cored projectile penetrating a hard target." Thesis, Cranfield University, 2010. http://dspace.lib.cranfield.ac.uk/handle/1826/4657.
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Experimental results are presented from an investigation of the parameters of a ceramic-faced armour system that are required to induce damage in a tungsten carbide - cobalt (WC-Co) penetrator. A WC-Co material model has been successfully developed and implemented within the numerical hydrocode AUTODYN 2D. The understanding of penetration mechanisms was used to guide a parametric investigation, validating the WC-Co material failure model with experimental results. A series of experiments has been conducted firing the Russian 14.5 mm BS41 WC-Co cored projectile into various thicknesses and types of alumina (Al2O3) and silicon carbide (SiC), backed by aluminium alloy or mild steel semi-infinite witness blocks. Results demonstrated that SiC B out-performed standard monolithic armours and a selection of other armour ceramics including PS 5000 SiC and Sintox-CL. After comminution, the SiC B consisted of particles of closely interlocked grains. These appeared to provide considerable resistance to deviatoric stresses. Results suggest that it is not only increased hardness but also the nature of the fracture of the ceramic ahead of the penetrator that improves the armour’s ballistic performance at defeating WC-Co penetrators. If such superior ballistic response can be controlled and incorporated into practical armour systems, it will provide the basis for an advance in armour protective capability against WC-Co penetrators. In addition, a numerical material model derived from experimental data was developed to provide a preliminary tool to study the WC-Co failure. It was demonstrated that the numerical estimation of WC-Co behaviour using a shock Equation Of State (EOS), a piecewise linear strength model and a principle stress failure model provides a good method to estimate spall behaviour under dynamic loading in AUTODYN 2D. Successful numerical simulation of the material model used demonstrated the future potential of the technique.
8
Woolmore, N. J. "The failure of a tungsten carbide-cobalt cored projectile penetrating a hard target." Thesis, Engineering Systems Department, 2010. http://dspace.lib.cranfield.ac.uk/handle/1826/4657.
Full textAbstract:
Experimental results are presented from an investigation of the parameters of a ceramic-faced armour system that are required to induce damage in a tungsten carbide - cobalt (WC-Co) penetrator. A WC-Co material model has been successfully developed and implemented within the numerical hydrocode AUTODYN 2D. The understanding of penetration mechanisms was used to guide a parametric investigation, validating the WC-Co material failure model with experimental results.
A series of experiments has been conducted firing the Russian 14.5 mm BS41 WC-Co cored projectile into various thicknesses and types of alumina (Al2O3) and silicon carbide (SiC), backed by aluminium alloy or mild steel semi-infinite witness blocks. Results demonstrated that SiC B out-performed standard monolithic armours and a selection of other armour ceramics including PS 5000 SiC and Sintox-CL. After comminution, the SiC B consisted of particles of closely interlocked grains. These appeared to provide considerable resistance to deviatoric stresses. Results suggest that it is not only increased hardness but also the nature of the fracture of the ceramic ahead of the penetrator that improves the armour’s ballistic performance at defeating WC-Co penetrators. If such superior ballistic response can be controlled and incorporated into practical armour systems, it will provide the basis for an advance in armour protective capability against WC-Co penetrators.
In addition, a numerical material model derived from experimental data was developed to provide a preliminary tool to study the WC-Co failure. It was demonstrated that the numerical estimation of WC-Co behaviour using a shock Equation Of State (EOS), a piecewise linear strength model and a principle stress failure model provides a good method to estimate spall behaviour under dynamic loading in AUTODYN 2D. Successful numerical simulation of the material model used demonstrated the future potential of the technique.
9
Liu, Yuefeng. "Silicon carbide and nano-carbons containing cobalt catalysts for the Fisher-Tropsch synthesis." Thesis, Strasbourg, 2013. http://www.theses.fr/2013STRAF024/document.
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La Synthèse Fischer-Tropsch (SFT) est une technologie clé pour transformer le gaz de synthèse (CO + 2H2) en hydrocarbures liquides, matières premières pour la chimie de base. Il s'avère que les catalyseurs à base de cobalt sont les plus performants et leur développement dans l'industrie impose au matériau support de posséder une conductivité thermique élevée et une structure ouverte. Dans ce travail, un nouveau support hiérarchisé constituée deα -Al2O3, recouvert homogènement de nanotubes de carbone, a été préparé pour supporter des catalyseurs au cobalt. Ces derniers montrent une très grande sélectivité en hydrocarbures liquides ainsi que de meilleures activités catalytiques. Les performances obtenus ont pu être améliorées en déposant une fine couche de TiO2 sur la surface des nanotubes de carbone, améliorant considérablement la dispersion du cobalt et l'activité. Le TiO2, également introduit dans la matrice de β-SiC lors de la synthèse, interagit fortement avec les sites actifs de cobalt, conduisant ainsi à sa grande dispersion et à une meilleure activité et stabilité dans la réaction de SFT. Parallèlement, un catalyseur à base de β-SiC de haute porosité, recouvert d'une couche de dioxyde de titane monocristallin a été développé et testé. Un taux spécifique de 1,2 gC5+. gcat -1. h-1 et une sélectivité en C5+ de 86% ont été obtenus. Ces performances sont les plus élevées signalées jusqu'à présent sur des catalyseurs sans cobaltThe Fischer-Tropsch synthesis (FTS) is a key technology to transform the synthesis gas (2H2 + CO) into liquid hydrocarbons as the basic chemical feedstock. It can be found that the cobalt active sites supported on the materials with high thermal conductivity, opened structure is necessary to accelerate FTS synthesis process in the development of industry catalysts.In this work, a new hierarchical support consisting of α-Al2O3, which is homogeneously covered by a layer of carbon nanotubes, is successfully prepared to support cobalt catalyst. The supported cobalt catalysts show extremely high selectivity towards liquid hydrocarbons along with the better catalytic activity. The FTS performance obtained on this support can be further improved by coating a thin layer of TiO2 on the CNTs surface which significantly improve the cobalt dispersion and in turn,the FTS activity.The TiO2 is also successfully introduced into the matrix of β-SiC during the synthesis process which strongly interacts with cobalt active sites, leading to high dispersion of cobalt, accounting for the better activity and stability in FTS reaction. In the mean time, a highly activity Fischer-Tropsch catalyst based on single crystalline titanium dioxide coated high porosity β-SiC was also developed. The FT specific rate of 1.2 gC5+·gcat -1·h-1 and a C5+ selectivity of 86 % are obtained,which are among the highest FT performance reported up to now on cobalt noble-free catalyst
10
Guo, David 1976. "Vector drop-on-demand production of tungsten carbide-cobalt tooling inserts by three dimensional printing." Thesis, Massachusetts Institute of Technology, 2004. http://hdl.handle.net/1721.1/27064.
Full textAbstract:
Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2004.Includes bibliographical references (p. 119-120).
Three Dimensional Printing (3DP) is a solid freeform fabrication process used to generate solid parts directly from three-dimensional computer models. A part geometry is created by selectively depositing binder into sequentially spread layers of powder. In slurry-based 3DP, a suspension of powder in a solvent is used to form the powderbed layer. This slurry-based powderbed yields higher green density and part resolution than dry powder-based 3DP because of smaller particle size. Vector printing requires that the printhead trace and define the external geometries of a part before raster filling the interior, a new approach in comparison to conventional, raster-only printing. Drop-on-demand (DOD) printheads allow binder droplets to be ejected when needed rather than relying upon charge-and-deflect mechanisms used in continuous jet printheads. Integrating these concepts for vector, DOD printing has the potential to enhance the 3DP process by providing greater part resolution and surface finish. The 3DP slurry-based process and vector, drop-on-demand printing are examined as potential methods to produce Tungsten Carbide-Cobalt (WC-Co) tooling inserts. The research focuses on three fundamental process steps: (1) development of a stable slurry, (2) determination of jetting parameter values for optimal powderbed deposition, and (3) implementation of vector, DOD printing for the binder. Due to unforeseen circumstances, the first two objectives are only briefly introduced in Chapter 1 and summarized in Chapter 3. Further details may be found in the Diplomarbeit document of Olaf Dambon. Two approaches are explored to develop a stable, jettable slurry. One method involves using a water-based Tungsten Carbide slurry and a
(cont.) Cobalt Acetate binder; the other method utilizes an alcohol-based Tungsten Carbide-Cobalt slurry and an organic binder. Various suspension properties, such as sedimentation density and viscosity, are measured to assess the degree of slurry stability. After adequate slurry formulations are developed, an investigation of powderbed formation is conducted. Due to the low solubility limit of the Cobalt salt in water and the persistent defects in water-based slurry powderbeds, the alcohol-based approach is pursued and, because of its greater efficacy, is used for optimizing powderbed jetting parameters. An effective combination of line spacing, flow rate, and drying time is determined for producing powderbeds with minimal surface roughness and high packing density. Experiments are subsequently conducted in vector DOD printing of various geometries using a piezo-actuated, drop-on-demand printhead and Bridgeport three-axis milling machine. A Hewlett-Packard inkjet cartridge is initially used for vector testing of the milling machine; a Siemens PT-88S printhead is used to assess and optimize binder droplet formation parameters, such as voltage waveform and fluid properties. Functional conditions for vector printing and DOD droplet generation are developed and deliver acceptable performance. Successfully printed geometries with high-definition lines (140-170 [mu]m line width) and smooth surface finish are produced using sanded, jetted alumina slurry powderbeds. Following necessary refinements in slurry redispersion and slurry-binder compatibility, the same vector process can be repeated with jetted WC-Co slurry powderbeds.
by David Guo.
S.M.
11
Coulson, W. "Characterisation of coatings deposited by the high velocity oxygen fuel process." Thesis, University of Nottingham, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.260773.
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Tymowski, Benoît de. "Fischer Tropsch synthesis on conductive silicon carbide based support." Thesis, Strasbourg, 2012. http://www.theses.fr/2012STRAF019/document.
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La synthèse de Fischer-Tropsch (SFT) permet la transformation d'un mélange de gaz de synthèse, i.e. H2 et CO, issu des différentes matières premières (charbon, gaz naturel ou biomasse) en hydrocarbures synthétiques. Les catalyseurs généralement utilisés en SFT sont à base de fer ou de cobalt supporté sur alumine ou silice. Dans ce travail, le carbure de silicium (SiC) a été proposé comme nouveau support de remplacement pour la SFT. Les résultats obtenus ont montré que les catalyseurs à base de cobalt supporté sur du SiC, contenant essentiellement des mésopores, sont actifs et sélectifs pour la réaction de SFT par rapport aux catalyseurs traditionnels supportés sur alumine ou silice. L'activité en SFT peut être améliorée en utilisant de l'éthanol comme solvant d'imprégnation ou en ajoutant un promoteur tel que le ruthénium. Le dopage du support de départ par du Ti02 contribue également à une forte augmentation de l'activité en SFT grâce à la formation de petites particules de cobalt présentant une activité en SFT plus élevée. La forte interaction entre le Ti02 et le cobalt permet également d'améliorer d'une manière considérable la stabilité du catalyseurThe Fischer-Tropsch synthesis (FTS) allows the transformation of a mixture of synthesis gas, i.e. H2 and CO, into valuable liquid hydrocarbons. The catalysts generally used in FTS are based on iron or cobalt supported on alumina or silica. ln the present work, silicon carbide (SiC) has been proposed as a replacement media to traditional supports. The results obtained indicate that the mesoporous SiC containing cobalt catalyst exhibits a good FTS activity and an extremely high selectivity towards liquid hydrocarbons compared to other FTS catalysts supported on alumina or silica. The FTS activity on the Co/SiC catalyst can be improved by changing the impregnation solvent or by promoting the cobalt phase with trace amount of noble metal. The doping of the SiC support with Ti02 phase also significantly improves the FTS activity keeping a similar high selectivity thanks to the formation of small cobalt particles in contact with the Ti02 phase
13
Ndlovu, Siphilisiwe. "The wear properties of tungsten carbide-cobalt hardmetals from the nanoscale up to the macroscopic scale." kostenfrei, 2009. http://d-nb.info/999595199/34.
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Bastian, Susanne. "Neuro- und Gliotoxizität von Wolframcarbid-basierten Nanopartikeln in vitro." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2011. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-77170.
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Die Anzahl neurodegenerativer Erkrankungen nimmt in unserer Gesellschaft stetig zu. Obwohl inzwischen eine Reihe genetischer Ursachen identifiziert worden sind, wird auch der Einfluss von Umweltfaktoren bei der Pathogenese dieser Erkrankungen zunehmend in Betracht gezogen. Der Beitrag von ultrafeinen Partikeln aus Industrie und Umwelt auf neurodegenerative Erkrankungen steht daher zunehmend im Fokus der Forschung. Die Translokation von ultrafeinen Partikeln bzw. Nanopartikeln ins Gehirn ist bekannt. Die Charakterisierung neuro- und gliotoxischer Wirkungen von Nanopartikeln in einem in vitro System war deshalb Ziel dieser Arbeit. Untersucht wurden Wolframcarbid-Partikel mit und ohne Cobalt, die im Herstellungsprozess von Hartmetallen von Bedeutung sind.
Die meisten toxikologischen Daten wurden bisher mit mikrokristallinen WC-Pulvern an Lungenzellen bzw. -gewebe erhoben. Da aber die Verarbeitung von nanoskaligen Partikeln bessere Eigenschaften der Hartmetalle bewirkt, nimmt das Interesse an toxikologischen Studien mit WC-Nanopartikeln zu. Da die Gefahr der Translokation und Akkumulation im Gehirn beim Einatmen von Stäuben am Arbeitsplatz besteht, wurde erstmalig die Toxizität von WC-NP mit und ohne Cobalt auf Zellen des Gehirns untersucht. Für die Durchführung wurden primäre Neuronen, Astrozyten und Mikroglia sowie die Oligodendrozyten-vorläuferzelllinie OLN-93 der Ratte eingesetzt. Alle untersuchten Partikel konnten mittels Elektronenmikroskopie, ICP-Massenspektrometrie und Durchflusszytometrie in den verschiedenen Zelltypen nachgewiesen werden. Untersuchungen mit Cytochalasin D (Inhibitor der Aktinpolymerisation) deuteten auf zell- und partikelspezifische Aufnahmemechanismen hin.
Experimente mit Cobaltchlorid und Natriumwolframat konnten beweisen, dass nicht die gelösten Ionen für die Toxizität von WC-Co ursächlich waren, sondern die Partikelform von entscheidender Bedeutung ist. Es zeigte sich jedoch, dass einige der WC-Co verursachten Effekte vermutlich auf dem Cobaltanteil beruhen. Offensichtlich dienen WC-Co-NP als Vehikel, um Cobalt in die Zellen einzuschleusen. Zur toxischen Wirkung trägt auch das Reaktionsvermögen von WC und Cobalt an der beiderseitigen Grenzfläche bei, denn dadurch können in der Zelle vermehrt reaktive Sauerstoffspezies gebildet werden.
Im Rahmen der Untersuchungen wurden die zeit- und konzentrationsabhängigen Effekte der Nanopartikelexposition auf die Vitalität, die Proliferation, das Adhäsionsverhalten, das mitochondriale Membranpotential und die Induktion apoptotischer und nekrotischer Zelluntergänge untersucht. Dabei wurden verschiedene Vitalitäts- und Proliferationstests angewendet, um die häufig beobachteten Wechselwirkungen zwischen Reagenzien und Nanopartikeln auszuschließen.
Nicht alle untersuchten Nanopartikel erwiesen sich in den durchgeführten Experimenten als akut toxisch. Nur eine Exposition mit WC-Co-NP führte nach 72 h zu einer deutlich verringerten Vitalität und Proliferation bei Astrozyten und OLN-93 Zellen. Eine Exposition mit WC-Co-NP zeigte des Weiteren eine geringe Induktion von Apoptose und Nekrose bei Astrozyten, nicht aber bei OLN-93 Zellen. Neurone wiesen nach einer Exposition mit NP eine wenig verringerte Vitalität auf. Es wurde festgestellt, dass erst die primäre Schädigung von Astrozyten zu einer sekundären Neuronenschädigung führt. Bei der Bewertung der NP-Toxizität müssen daher unbedingt die Wechselwirkungen der Zellen bedacht werden.
Die Exposition mit WC- und WC-Co-NP beeinflusste das mitochondriale Membranpotential und das Adhäsionsverhalten der untersuchten Zellen. Neuronen und OLN-93 Zellen zeigten nach NP-Exposition eine verminderte Adhäsion. Auch physiologische Kalziummessungen lieferten einen Hinweis für die veränderte Funktionalität glialer Zellen nach einer NP-Exposition. Des Weiteren wurde die Expression einiger Gene, bedeutend für Adhäsion und extrazelluläre Matrix, mit realtime RT-PCR bei OLN-93-Zellen und Astrozyten überprüft. Es konnte eine Regulation von Mmp9, Timp1, Lama3, Tgfbi, Col8a1 und Hmox1 gezeigt werden.
Zusammenfassend lässt sich feststellen, dass die ausgewählten Nanopartikel nicht per se neuro- und gliotoxisch wirkten. Die Partikel können anhand abnehmender Toxizität wie folgt geordnet werden: WC-Co > WC 100na > WC 10n. Auch die Reaktionen der Zellen fielen unterschiedlich aus: die Astrozyten erwiesen sich als die sensitivsten Zellen.
Eine Exposition des Gehirns mit WC-Co-NP in hohen Konzentrationen oder über einen längeren Zeitraum könnte also weit reichende Folgen haben, angefangen bei einer gestörten Signalweiterleitung über eine erhöhte Permeabilität der Blut-Hirn-Schranke bis hin zu neurodegenerativen Veränderungen.
Diese und weitere Untersuchungen könnten bei der Erstellung von Arbeitsrichtlinien im Umgang mit Hartmetallen, deren Ausgangsmaterial nanoskalige Pulver sind, hilfreich sein und damit einen Beitrag zum Schutz der Arbeiter liefern.
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Hönig, Richard [Verfasser], Carsten [Akademischer Betreuer] Westphal, and Markus [Gutachter] Betz. "Photoemission microscopy and spectroscopy of cobalt-intercalated graphene on silicon carbide / Richard Hönig ; Gutachter: Markus Betz ; Betreuer: Carsten Westphal." Dortmund : Universitätsbibliothek Dortmund, 2019. http://d-nb.info/1199106429/34.
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Hewitt, Stephen A. "Consolidation of WC-Co nanocomposites synthesised by mechanical alloying." Thesis, University of Wolverhampton, 2009. http://hdl.handle.net/2436/106834.
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The influence of mechanical alloying (MA) milling time, temperature, sintering method and microstructure on the mechanical properties of a tungsten carbide-cobalt (WC-Co) hardmetal, based on 10wt% Co, has been established. The effects of high-energy milling for 30, 60, 180 and 300 min and the interrelation between milling time and powder properties, and the resultant effects on the mechanical properties of the consolidated WC-10Co material, has been obtained for a horizontally designed ball mill. Nanostructured WC-10Co powder was synthesised after 60 min cyclic milling at room temperature with an average WC domain size of 21 nm. In direct comparison, a WC-10Co composition MA at -30°C for 60 min produced an average WC domain size of 26 nm with a higher lattice strain. WC domain size showed a slight increase with milling time, measured at 27 nm after 300 min ball milling. Extended ball milling (300 min) reduced the mean particle size from 0.148 μm for 60 min milling to 0.117 μm. Thermal analysis showed that the onset temperature of the WC-Co eutectic was related to particle size with increased milling time reducing the onset temperature from 1344°C after 60 min milling to 1312°C after 300 min milling. Onset temperature was further reduced by the addition of vanadium carbide (VC), reducing the onset temperature to 1283°C after 300 min milling. Powder contamination increased with increased milling time with Fe content measured at ~ 3wt% after 300 min ball milling. Milling at -30°C reduced Fe contamination to an almost undetectable level. Increased ball milling time resulted in decreased levels of green density with the powders milled for 30 and 300 min achieving 62.5% and 59.5% TD, respectively. Relative density increased for the powder milled at -30°C compared to the RT milled powder due to its flattened, slightly rounded morphology. A large difference in VC starting particle size compared to WC and Co led to non-uniform dispersion of the inhibitor during milling. Densification and hardness reached optimum levels for the 60 min milled powder for both pressureless sintering and sinter-HIP. Both properties decreased with increased milling time, regardless of the sintering method. Low temperature milling resulted in a higher hardness value of 1390 HV30 compared to 1326 HV30 for the 60 min, RT milled material after pressureless sintering. Densification levels of the doped materials were restricted to < 90% TD for both sintering methods due to inhomogeneity in the microstructures. Palmqvist fracture toughness (WK) of the RT milled powders increased with increased milling time and increasing WC grain size for both sintering methods. WK reached 11.6 MN.m3/2 with 300 min milling after pressureless sintering but reached 16.1 MN.m32 for the same material after sinter-HIP due to the effect of mean WC grain size and binder phase mean free path. The -30°C milled powder exhibited higher fracture toughness for both sintering methods than the 60 min, RT milled material. Spark plasma sintering (SPS) showed that the onset of densification was dependent upon particle size with the powder from 300 min milling showing an onset temperature of ~ 800°C compared to ~ 1000°C for the 60 min milled powder. The low temperature milled powder showed an onset temperature of ~ 980°C, which suggested that low temperature milling provided enhanced densification kinetics.
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Parker, Donald Scott. "Fracture and residual-stress characterization of tungsten-carbide 17%-cobalt thermal-spray coatings applied to high-strength steel fatigue specimens." [Gainesville, Fla.] : University of Florida, 2003. http://purl.fcla.edu/fcla/etd/UFE0000763.
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Moche, Hélène. "Utilisation du carbure de tungstène-cobalt (WC-Co) comme témoin positif génotoxique nanoparticulaire et étude de la génotoxicité de candidats nanovecteurs de médicaments." Thesis, Lille 2, 2014. http://www.theses.fr/2014LIL2S024/document.
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Les nanomatériaux sont utilisés dans de nombreux secteurs industriels, et plusieurs produits de consommation contenant des nanomatériaux sont d’ores et déjà commercialisés. Dans ce contexte d’exposition humaine croissante aux nanomatériaux, l’évaluation de leur potentiel génotoxique est d’une importance significative. Cependant, la pertinence des tests classiques de génotoxicité, développés pour des produits non nanoparticulaires, est fréquemment remise en question pour l’évaluation des nanomatériaux. Un témoin positif de référence sous forme nanoparticulaire pourrait donc constituer une avancée importante pour l’évaluation de la génotoxicité des nanomatériaux, permettant de s’assurer que les systèmes d’essais sont appropriés et/ou d’en valider de nouveaux.Dans un premier temps, nous avons étudié la possibilité d’utiliser des nanoparticules de carbure de tungstène – cobalt (WC-Co) commerciales, préalablement caractérisées sur le plan physico-chimique (distribution de taille et charge dans les milieux utilisés), comme témoin positif dans trois essais de génotoxicité in vitro. Le test de mutations géniques au locus thymidine kinase sur cellules de lymphome de souris, le test des micronoyaux étudiant les dommages chromosomiques et le test des comètes détectant les dommages primaires à l’ADN ont ainsi été réalisés, les deux derniers essais dans deux types cellulaires, la lignée de lymphome de souris L5178Y et des cultures primaires de lymphocytes humains. Nos résultats montrent que les nanoparticules de WC-Co pourraient être utilisées comme témoin positif dans ces essais de génotoxicité in vitro, selon le type cellulaire et le schéma de traitement.Nous avons ensuite étudié les mécanismes d’action impliqués dans la génotoxicité des nanoparticules de WC-Co. Le marquage des centromères dans les micronoyaux grâce à la technique d’hybridation in situ en fluorescence (FISH) montre l’implication d’évènements clastogènes et aneugènes. Ces résultats ont été confirmés par un essai d’aberrations chromosomiques sur lymphocytes humains bloqués en métaphase, avec l’observation de cassures de chromatides et de cellules polyploïdes. Par ailleurs, les mécanismes oxydants étant les plus décrits pour les nanomatériaux, nous avons étudié les lésions oxydatives à l’ADN en utilisant le test des comètes in vitro modifié avec l’enzyme de réparation de l’ADN formamidopyrimidine DNA glycosylase (FPG). Nous avons également détecté par résonance paramagnétique électronique une production de radicaux hydroxyles après mise en suspension des nanoparticules de WC-Co en présence et en absence de cellules. Dans le cadre d’études haut-débit des nanoparticules de WC-Co réalisées dans trois lignées cellulaires humaines correspondant aux principaux organes cibles pour les nanomatériaux (la lignée pulmonaire A549, la lignée hépatique Hep3B et la lignée rénale Caki-1), il a été confirmé que le stress oxydant joue un rôle important dans la toxicité des nanoparticules de WC-Co. En effet, la production d’espèces réactives de l’oxygène dans les cellules traitées avec les nanoparticules de WC-Co était corrélée avec l’observation d’une cytotoxicité et de génotoxicité, étudiée à l’aide du test de détection des foyers γH2AX.Finalement, nous avons appliqué les tests de génotoxicité les plus pertinents à l’étude de nanodiamants et de nanocapsules lipidiques, qui constituent des candidats prometteurs pour la vectorisation de principes actifs. Les tests des comètes et des micronoyaux in vitro ont ainsi été réalisés sur d’autres types cellulaires mimant des organes cibles : la lignée intestinale T84 et la lignée bronchique 16-HBE exposées à des nanodiamants de trois tailles différentes et des lymphocytes humains exposés à des nanocapsules lipidiques de 3 tailles et 3 charges différentesNanomaterials are used in many industrial sectors, and many nanomaterial-containing consumer products are already available. In this context of increasing human exposure to nanomaterials, the evaluation of their genotoxicity is of significant importance. However, the relevance of routinely used genotoxicity assays, developed for non-nanoparticular products, is often questioned for the evaluation of nanomaterials. A nanoparticulate reference positive control would therefore constitute an important step to a better testing of nanomaterials genotoxicity, ensuring that test systems are actually appropriate and/or allowing the validation of new ones.Firstly, we studied the possibility of using commercially-available tungsten carbide-cobalt (WC-Co) nanoparticles, previously characterized for physicochemical properties (size distribution and charge in used media), as positive control in three in vitro genotoxicity assays. The mouse lymphoma thymidine kinase gene mutation assay, the micronucleus assay studying chromosomal aberrations and the comet assay detecting primary DNA damage were performed. The last two assays were realized in two cell types, the mouse lymphoma cell line L5178Y and primary cultures of human lymphocytes. Our results show that WC-Co nanoparticles could be used as positive control in these in vitro genotoxicity assays, according to cell type and treatment schedule.Secondly, we investigated the mechanisms of action involved in WC-Co nanoparticles genotoxicity. Detection of centromeres in micronuclei using fluorescence in situ hybridization (FISH) show the involvement of both clastogenic and aneugenic activities. This was correlated with the results of a chromosome aberration assay on human lymphocytes blocked in metaphase, showing chromatid breaks and polyploid cells. Moreover, as oxidative mechanisms are the most described for nanomaterials, we studied oxidative DNA damage using the modified in vitro comet assay with the DNA repair enzyme formamidopyrimidine DNA glycosylase (FPG). We also detected a production of hydroxyl radicals using electron paramagnetic resonance in suspensions of WC-Co nanoparticles with and without cells. While performing high-throughput assays on WC-Co nanoparticles in three human cell lines corresponding to the main target organs for nanomaterials (A549 lung cell line, Hep3B liver cell line and Caki-1 kidney cell line) it was confirmed that oxidative stress play a significant role in the toxicity of WC-Co nanoparticles. Indeed, the production of reactive oxygen species in cells exposed to WC-Co nanoparticles was correlated to the observation of cytotoxicity and genotoxicity, studied using the detection of γH2AX foci.Finally, we carried out the most relevant genotoxicity assays to study nanodiamonds and lipid nanocapsules, which constitute promising nanovectors for drug delivery. The in vitro comet and micronucleus assays were performed on other cell types mimicking target organs: the T84 intestinal epithelial cell line and the 16-HBE bronchial epithelial cell line exposed to nanodiamonds of three different sizes, and human lymphocytes exposed to lipid nanocapsules of three different sizes and three different charges
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Prno, Peter. "Obrábění kobaltové slitiny UmCo50." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2021. http://www.nusl.cz/ntk/nusl-444280.
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The diploma thesis deals with the topic of machinability of materials. The theoretical part describes the aspects according to which machinability can be evaluated. The material side of the thesis is focused on various types of difficult-to-machine materials. The cobalt alloy UmCo50 belongs to the group of difficult-to-machine materials and it is the subject of the experimental part. UmCo50 is an alloy for high temperature use. The primary aim of the thesis was to monitor the wear of the selected cutting tool when turning this alloy. Other aspects of the selected machining process were also monitored, such as force effects or the quality of the machined surface. Despite the fact that machinability of tested materials cannot be expressed in terms of the absolute value of a quantity, it is necessary to compare the various aspects of the machining processes by reference materials. However, certain conditions of this comparison must be met. Based on this, a comparison of tested and reference material was performed.
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Lawson, Thomas Ryan. "Micro-Raman spectroscopy and dry turning evaluations of nanostructured diamond films deposited on tungsten-carbide lathe inserts." Birmingham, Ala. : University of Alabama at Birmingham, 2008. https://www.mhsl.uab.edu/dt/2008m/lawson.pdf.
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Andersson, Karin M. "Aqueous Processing of WC-Co Powders." Doctoral thesis, KTH, Chemistry, 2004. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3725.
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The object of this work is to obtain a fundamentalunderstanding of the principal issues concerning the handlingof an aqueous WC-Co powder suspension.
The WO3 surface layer on the oxidised tungsten carbidepowder dissolves at pH>3 with the tungsten concentrationincreasing linearly with time. Adding cobalt powder to thetungsten carbide suspension resulted in a significant reductionof the dissolution rate at pH<10. Electrokinetic studiesindicated that the reduced dissolution rate may be related tothe formation of surface complexes; the experiments showed thatCo species in solution adsorb on the oxidised tungsten carbidepowder.
The surface forces of oxidised tungsten and cobalt surfaceswere investigated using the atomic force microscope (AFM)colloidal probe technique. The interactions at various ionicstrengths and pH values are well described by DLVO theory. Theadsorption of cobalt ions to tungsten oxide surfaces resultedin an additional non-DLVO force and a reduced absolute value ofthe surface potential. It was shown that the adsorption ofpoly(ethylene imine) (PEI) to the WO3 surfaces induces anelectrosteric repulsion.
The properties of spray-dried WC-Co granules were related tothe WC primary particle size, and the poly(ethylene glycol)(PEG) binder and PEI dispersant content in aqueous WC-Cosuspensions. The granule characterisation includes a new methodfor measuring the density of single granules. The increase inthe fracture strength of granules produced from suspensionsthat were stabilised with PEI was related to a more densepacking of the WC-Co particles.
The AFM was used to study the friction and adhesion ofsingle spray-dried WC-Co granules containing various amounts ofPEG binder. The adhesion and friction force between two singlegranules (intergranular friction) and between a granule and ahard metal substrate (die-wall friction) have been determinedas a function of relative humidity. The granule-wall frictionincreases with binder content and relative humidity, whereasthe granule-granule friction is essentially independent of therelative humidity and substantially lower than the granule-wallfriction at all PEG contents.
Key words:Hard Metal, Cemented Carbide, WC-Co, TungstenCarbide, Cobalt, Oxidation, Dissolution, Surface Complexation,XPS, AFM, Colloidal Probe, Hamaker Constant, Cauchy, WO3,CoOOH, ESCA, Zeta-Potential, Surface Potential, Poly(ethyleneimine), PEI, Suspension, van der Waals, Steric, Spray-Dried,Poly(ethylene glycol), Strength, Density, Friction, Adhesion,Granule, PEG, Pressing, FFM.
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Okatsu, Hiroko. "New synthetic methods to alter catalytic properties of supported K/MoS₂ catalysts for syngas conversion to higher alcohols." Thesis, Georgia Institute of Technology, 2012. http://hdl.handle.net/1853/48996.
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The purpose of this study is to develop catalysts for conversion of synthesis gas (H₂ and CO) to higher alcohols, primarily ethanol and propanol. Crude oil is consumed at a rate of more than 20 million barrels a day in the United States, mainly for producing fuels and chemical feedstocks. However, the total amount of crude oil is limited, and alternative ways of producing alcohols as precursors for chemical feedstocks are desirable. In this study, using a known K/MoS₂/metal oxide catalyst as the starting point, two different approaches were explored to improve catalytic properties: 1) Co promotion on K/MoS₂/mixed metal oxide (MMO) catalysts, and 2) Preparation of K/MoS₂/metal oxide catalysts with molybdenum carbide as a precursor, instead of molybdenum oxide. With respect to Co promotion on K/MoS₂/MMO catalysts, the effect of varying the Co content in the K/Mo-Co/MMO catalysts prepared by a co-impregnation method did not produce significant changes in catalytic acitivities or selectivities. It was due to the premature precipitation of cobalt molybdate during synthesis. Cobalt molybdate precipitation can generally be prevented by using water as a solvent, but this approach is not appropriate for this study because of the use of hydrotalcite-derived mixed metal oxide as the support. Co loadings on K/Mo/MMO-Co catalysts did not change selectivities significantly, either. However, they changed catalytic activities, represented by gas hourly space velocity (GHSV) required to obtain 8% conversion while maintaining high selectivities for higher alcohols. As a result, C ₂₊ alcohol productivities reached 0.01g(alcohol)/g(catalyst)/hr with Co loadings higher than 8%. With respect to using Mo2C as the precursor of Mo species instead of MoO3, comparisons between catalysts with different precursors for Mo species and different pretreatments were investigated. In this study, both K/Mo catalysts supported on MgO and α-Al₂O₃ showed similar tendencies of catalytic activities and selectivities. The highest C₂₊ alcohol selectivities and productivities were obtained on presulfided MoO₃ catalysts on both supports. In comparison of K/Mo ₂C catalysts with different pretreatments, higher C₂₊ alcohol selectivities and lower MeOH selectivities were obtained on presulfided catalysts compared to non-pretreated catalysts.
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Marou, Alzouma Ousseini. "Durabilité tribologique de matériaux pour insert de dents de tunnelier." Thesis, Ecully, Ecole centrale de Lyon, 2015. http://www.theses.fr/2015ECDL0042.
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La fréquence des opérations de maintenance lors de l’excavation du sol par les tunneliers est problématique pour les entreprises de travaux publics. Ces opérations de maintenance engendrent des temps morts onéreux et nécessitent l'intervention d'opérateurs dans des conditions de travail hyperbares. Une des raisons aux nombreuses interventions humaines pour la maintenance est l’endommagement des outils racleurs du sol excavé (dents) qui sont placés sur la tête du tunnelier. Ces outils sont sujets à l’usure compte tenu de l’abrasivité des différents milieux qu’ils rencontrent. Le but de cette thèse est de contribuer à augmenter d’au moins 20% la durée de vie des matériaux constitutifs de ces outils, afin de réduire les différentes opérations de maintenance qui exposent les opérateurs à des risques importants. Pour atteindre cet objectif, les investigations menées dans ce travail ont porté sur plusieurs axes. Dans un premier temps, une expertise est menée pour identifier les modes d’endommagement prédominants sur les inserts à base de carbure de tungstène placés sur les dents ; ensuite, de nouveaux matériaux avec des propriétés mécaniques et des microstructures optimisées, développés dans le cadre du projet européen NeTTUN, sont caractérisés sur des bancs d’essais représentatifs. Ces essais ont permis de bien comprendre les mécanismes d’usure des nouveaux matériaux à base de carbure de tungstène. Les résultats de ce travail peuvent ensuite donner lieu à de nouvelles orientations en matière de choix de matériaux pour renforcer les dents de tunnelierThe frequency of maintenance operations during the excavation of the ground by the tunnel boring machines (TBM) is problematic for civil engineering companies. These maintenance operations provoke expensive timeouts and they bring in excavation operators in risky hyperbaric work conditions. One of the reasons which leads to the numerous human interventions for the maintenance is the damage of drag bits located on the cutting wheel of the TBM. These drag bits undergo wear due to the abrasiveness of the various media they meet. The purpose of this thesis is to contribute to increase by 20 % at least the lifetime of the materials of the dag bits, in order to reduce the various maintenance operations which expose the operators to important risks. To achieve this goal, the investigations led in this work concerned several axes. At first, an expertise is led to identify the wear modes prevailing on the carbide inserts located on the drag bits; then, new materials with enhanced mechanical properties and optimized microstructures, developed in the framework of the European project NeTTUN, are characterized on representative lab testing devices. These tests allowed us to understand well the wear mechanisms of the newly developed grades of tungsten carbides. The results of this work can lead to new strategies for the selection of materials to reinforce the drag bits
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Pellan, Maxime. "Développement des joints de grain et des joints de phase dans les carbures cémentés WC-CO." Thesis, Université Grenoble Alpes (ComUE), 2015. http://www.theses.fr/2015GREAI121/document.
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Le carbure cémenté (WC-Co) est un système biphasé constitué de grains de carbure de tungstène enrobés dans un liant à base de cobalt. Dans ce matériau composite, qui allie donc la dureté du carbure à la résilience du cobalt, la maîtrise de la microstructure est un paramètre clef pour l’optimisation des propriétés mécaniques.Le but de ce travail est de mettre au jour les mécanismes régissant le développement des joint de grain et des joints de phase lors du frittage. L’effet de la teneur en liant, du taux de carbone et du temps de frittage ont été particulièrement étudiés.Ce travail est basée sur la caractérisation du matériau par EBSD (Electron BackScattered Diffraction), une méthode qui facilite la séparation des grains et donc l’utilisation de techniques d’analyse d’image pour étudier la microstructure. En outre un programme basé sur les données d’orientation des grains collectées par EBSD et permettant l’analyse de la texturation des joints de grain et des joints de phase a été développé pour cette étude.L’étude de la contiguité montre qu’elle ne dépend pas du taux de frittage ni de la teneur en carbone du liant, mais essentiellement de la fraction volumique de liant. Cela implique que l’encombrement et l’imbrication des particules sont les principaux paramètres entrant en compte dans l’établissement de la contiguité. Un grossissement plus rapide et plus marqué a été observé dans les échantillons riches en carbone, ainsi que dans ceux présentant un fort taux de liant. Un grossissement anormal a été observé dans les échantillons riches en carbone et à fort taux de liant. La désorientation aux joints de grains est caractérisée par un couple axe/angle décrivant la rotation liant les deux cristaux. L’étude de la distribution des axes a révélé que trois rotations sont particulièrement abondantes : celles autour de [101 ̅0], [21 ̅1 ̅0] et [0001]. Elles représentent environ 30% de la surface totale des joints de grains. Pour chacune des rotations particulières ont été détectées : [101 ̅0]/90°, [21 ̅1 ̅0] / (48°- 60°- 90°) et [0001]/90°. L’étude de la géométrie de ces joints suggère que leur remarquable stabilité est due au fort taux de cohérence dans le plan de joint. L’analyse statistique des plans de joint de grain et de joint de phase montre que la plupart d’entre eux correspond à un plan basal ou prismatique pour au moins l’un des deux grains (70% environ de la surface totale de joint de grain, et 50% environ de la surface totale de joint de phase). Sur la base de ces résultats, un scénario décrivant l’évolution de la microstructure durant le frittage est finalement proposéWC-Co cemented carbide is a two phase system constituted of a cobalt based binder matrix embedding hard tungsten carbide grains. This material is especially used in fields such as metal cutting or mining, where high mechanical properties are required. Therefore, the microstructure is a key parameter to control to optimize the mechanical properties of the alloy.This work aims at understanding the mechanisms of grain boundary and phase boundary development during sintering, and how they may influence the final microstructure. The effect of the binder content, carbon content and sintering time was especially investigated.Electron BackScattered Diffraction characterization was chosen to conduct this study. First because the precise separation of grains in the resulting images makes possible automation of the measurements, and thus allows a statistical analysis of several microstructural parameters (as grain size, contiguity) on numerous samples. Secondly because orientation data collected by this way make possible the analysis of grain boundary and phase boundary texture. To this end, an automated method was developed for analysis of grain boundaries and estimation of remarkable boundary planes fraction from 2D EBSD measurements.The study of contiguity shows that it does not depend on sintering time or carbon content in the binder, but essentially of the carbide grain volume fraction. This result implies that impingement is the first order parameter in the evolution of contiguity. Grains appear to grow faster and in a larger extent in samples with a carbon rich binder, as well as in high binder content samples. Abnormal grain growth seems to be favored by high binder content in carbon rich samples. All grain boundaries were characterized by a couple of rotation axis and misorientation angle. Three particular rotation axes were identified: [101 ̅0], [21 ̅1 ̅0] and [0001]. They represent around 30% of the total grain boundary surface area. In addition, specific rotations were found to be particularly abundant in the microstructure: [101 ̅0]/90°, [21 ̅1 ̅0] / (48°- 60°- 90°) and [0001]/90°.A study of their geometry suggests that their stability would be due to a particularly coherent boundary plane. A statistical analysis shows that most grain boundaries and phase boundaries have a habit plane parallel to a basal or prismatic plane (about 70% of the total grain boundary surface area and 50% of the total phase boundary area. Finally, a scenario is proposed for the microstructure development model during sintering of cemented carbides on the basis of the results
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Roure, Sophie. "Densification des mélanges de poudres WC-Co : de la compression au frittage." Grenoble INPG, 1996. http://www.theses.fr/1996INPG0222.
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Ce travail a pour objectif de prevoir le comportement des melanges wc-co lors du compactage et leur evolution au cours du frittage, en s'interessant particulierement a l'influence de la geometrie des microstructures sur la densification du materiau. Lors de l'etude macroscopique de la compression a froid, un test de compressibilite est etabli pour caracteriser l'aptitude de ces melanges a se comprimer selon les parametres de la poudre et les conditions de l'essai. Ce test fournit une loi de compressibilite intrinseque du melange et un coefficient relatif a la fluidite de la poudre et a son frottement aux parois. Les resultats des essais effectues sont interpretes a l'aide d'une analyse micromecanique du comportement d'empilements composites de particules. Au cours du frittage, l'etude macroscopique de la densification par dilatometrie determine l'evolution du retrait en fonction des parametres du procede, des caracteristiques du melange et de la densite a vert. Un interet particulier est porte a la part de densification realisee en phase solide. On montre que celle-ci est reliee a un rearrangement des grains wc qui se poursuit jusqu'a la formation d'un empilement stable de ces grains. En parallele, une etude microscopique quantitative par analyse d'images caracterise les etats comprime et fritte et l'evolution d'un etat a un autre. Elle permet d'etablir qu'en phase solide l'ecoulement du liant et le rearrangement des grains wc sont deux phenomenes simultanes. Finalement, une modelisation de la densification des melanges wc-co est proposee, qui integre les caracteristiques geometriques instantanees de l'empilement, propres au systeme etudie, au sein d'une approche cinetique globale simple
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Jacobson, Felix. "Wear and degradation of Co, Fe and Ni-based cemented carbides against sandstone and granite." Thesis, Uppsala universitet, Tillämpad materialvetenskap, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-365746.
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This diploma work is performed at Sandvik Mining and Rock Technology, Rock Tools division, a world-leading mining equipment manufacturer. The aim is to study the wear of cemented carbide rock drill inserts worn against granite and sandstone countersurfaces, with focus on the impact of binder phase composition and flushing agent chemistry. A brief introduction to rock drilling, cemented carbides and the wear and degradation mechanisms of cemented carbides in rock drilling is given. Wear is induced in a lab test by sliding cemented carbide inserts against granite and sandstone countersurfaces while flushing with deionized water or synthetic mine water. The wear is quantified by measuring material weight loss, and worn inserts are studied by SEM. All wear marks feature crushed, fragmented and heavily deformed WC grains and cavities left after individually removed WC grains. Rock adhere strongly on inserts worn against both granite and sandstone, and adhered material from both rock types sometimes endure the mechanical contact between insert and rock without significant spalling. Inserts tested with deionized water against sandstone wear 2.2 - 5.1 times more relative to against granite, and the only distinct difference observed is the distribution of adhered rock. The use of synthetic mine water relative to deionized water impacts the wear of all inserts, though corrosion products are only found on some of them. Further, the tribological contact greatly impacts the corrosive attack. The relative wear difference using different water chemistries is larger for inserts with a smaller relative amount of binder. In most cases, increased wear is measured for inserts tested with synthetic mine water. For reasons yet unknown, this trend is reversed for inserts with a high relative amount of binder tested against sandstone, where a decrease in wear is measured instead.Detta examensarbete har utförts åt Sandvik Mining and Rock Technology, Rock Tools avdelningen, som är en världsledande utrustningstillverkare inom gruvindustrin. I arbetet undersöks nötningen av så kallade bergborrstift av hårdmetall. Berg är generellt ett mycket hårt och sprött material, och borrning i berg går därför i huvudsak ut på att krossa och spola bort krossad sten. Längst fram på bergborrar sitter borrkronor som till största del är gjorda i stål. Då stål är för mjukt för att effektivt kunna avverka berg monterar man in stift av hårdmetall längst fram på borrkronan. Hårdmetall är ett kompositmaterial av mycket hårda men spröda wolframkarbidkorn (WC) som hålls ihop av en, jämfört med WC, mjuk och formbar metall som kallas bindefas. Resultatet är ett mycket hårt men fortfarande relativt segt material som dessutom klarar de mycket höga temperaturer som uppstår vid bergborrning. Traditionellt används kobolt som bindefas, men nu tros det finnas hälsorisker med kobolt och dessutom sker en stor del av världens koboltutvinning under oetiska förhållanden i konfliktländer i Afrika. Detta i kombination med att koboltpriserna ökat dramatiskt de senaste åren leder till att man nu söker efter alternativa bindefaser. Bland annat undersöker man olika legeringar av nickel och järn. I detta arbete jämförs nötningen av stift med nickel-, järn- och olika koboltbindefaser. I ett labtest fås nötning genom att stiften trycks mot en roterande stencylinder av antingen granit eller sandsten. I verkliga förhållanden används ofta så kallat gruvvatten som sipprar in i gruvan som spolvatten för att ta bort stenkrosset och kyla borrkronan. För att se hur kemin i spolvattnet påverkar nötningen spolas kontaktytan mellan stift och stencylinder med antingen avjoniserat vatten eller syntetiskt gruvvatten under testerna. Stiftens materialförlust under provningen beräknas genom att mäta deras vikt innan och efter. För att se om skillnader i nötningshastighet mellan olika stifttyper eller testvillkor avspeglas i olika utseenden på slitytorna undersöks stiften med hjälp av ett svepelektronmikroskop (SEM). Från SEM-bilderna ser man att alla stift från alla testvillkor har krossade och fragmenterade WC-korn på ytan och att stora delar av slitytorna täckts av påkletat berg. Bergpåsmetningarna är ibland mycket tunna (< 1 μm) och delvis inblandade i bindefasen, och ibland betydligt tjockare (flertal μm). De tjockare påsmetningarna är bundna så pass hårt till ytan att de kan upprätthålla delar av kontakten mellan stiftet och berget under testningen utan att lossna. Huruvida detta skyddar hårdmetallen från att nötas eller om det påkletade berget reagerar med, och därmed ökar den kemiska nedbrytningen av stiftet är inte utrett. Berget skyddar dock den underliggande hårdmetallen mot den korrosion som uppstår i kontakt med spolvattnet. Resultaten visar att stiften nöts betydligt mer mot sandsten än mot granit. Förutom att bergpåsmetningarna har en annan fördelning över ytan så syns inga tydliga skillnader mellan stiften testade mot de båda bergarterna. De flesta stiften nöts mer när de testas med gruvvatten än med avjoniserat vatten. Detta gäller alla stift utom de som har hög relativ mängd bindefas och som testats mot sandsten. Dessa stift nöts tvärt om mindre när de testas med gruvvatten än med avjoniserat vatten. Hittills har ingen anledning till denna konsekventa avvikelse hittats.
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Fry, Peter Ryan. "Fatigue crack growth behaviour of tungsten carbide-cobalt hardmetal alloys." Thesis, 2015. http://hdl.handle.net/10539/17280.
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GUO, QING-SHENG, and 郭慶生. "On the electrodeposited composite coating of cobalt and silicon carbide." Thesis, 1991. http://ndltd.ncl.edu.tw/handle/64161363934454800424.
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黃成顯. "On the Elextrodepsited Composite Coating of Cobalt and Silicon Carbide." Thesis, 1990. http://ndltd.ncl.edu.tw/handle/15911573429820916561.
Full textAbstract:
碩士國立臺灣科技大學
工程技術研究所
78
The model of the Co-SiC electro-codeposition was investigated. A new electro-codeposition model involving the deposition of particles and metallic ions was proposed. Effects of the current density, the particle loading, the stirring rate and pH value on the percent weight of partcle on the composite coating and the polarization curve were also studied. The resuits indicated that the rate of particle deposition was controlled only by the reduction of the adsorbed H+ ions on particle surface at low current density. When the current density is high, the rate of particle deposition was governed by reduction of both the adsorbed H+ ions and Co+2 ions on particle surface. The metallic deposition rates increased linearly with the current density but were independent of the particle loading. The weight percent of particle on the composite coating can be predicted by the proposed model. The experimental results are consistent with the prediction of the proposed model.
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Lin, Bo-Lu, and 林栢祿. "Diffusion barrier characteristics of TaN thin film on cobalt cemented tungsten carbide." Thesis, 2010. http://ndltd.ncl.edu.tw/handle/66234581999559070656.
Full textAbstract:
博士國立臺灣海洋大學
材料工程研究所
98
To prevent the diffusion out of cobalt from cemented tungsten carbides at high working temperature, TaNx coatings were prepared as a diffusion barrier by direct current magnetron sputtering using a Ta target in an argon-nitrogen atmosphere. The nitrogen flow ratio, N2/(N2+Ar), in the sputtering process varied from 0.05 to 0.4. The deposition rate reduced as the nitrogen flow ratio increased. Silicon wafers and 6wt% cobalt cemented tungsten carbide were used as the substrates. Effects of nitrogen flow ratio on crystalline characteristics and mechanical properties of the TaNx coatings were examined by X-ray diffraction. The TaNx coatings were annealed at 500, 600, 700, and 800oC for 4 hours in air, respectively. The diffusion barrier performance was evaluated by Auger electron spectroscopy depth profiles and X-ray diffraction. Oxidation resistance of the TaNx coatings was also investigated. Orthorhombic Ta2O5 was observed after annealing above 600oC. If the 6wt% cobalt cemented tungsten carbide was used as the substrates, the WO3 oxide compound was found when the annealing temperature was over 600 oC in air. When the oxide appeared, the thin film surface become more rougher. The TaNx deposited on cemented tungsten carbides played the role of diffusion barrier for Co at 600oC for 4 hours in air. But the diffusion barrier was not effective under high temperature in air due to the oxidation problem, which was transferred from TaN to Ta2O5. If the diffusion barrier was used under low vacuum environment, such as, at 600 oC for 4 hours, the TaNx coating should be successful to play the role of diffusion barrier for Co diffusion.
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Lin, Yu-Ting, and 林育廷. "Diffusion barrier characteristics of CrTaN thin film on cobalt cemented tungsten carbide." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/16377992891784606267.
Full textAbstract:
碩士國立臺灣海洋大學
材料工程研究所
99
To prevent the diffusion out of cobalt from cemented tungsten carbides at high working temperatures, CrTaN coating were prepared as a diffusion barrier by reactive direct current magnetron co-sputtering onto 6 wt.% cobalt cemented tungsten carbide substrates, using Ta and Cr targets in an argon-nitrogen atmosphere. The nitrogen flow ratio, N2/(Ar+N2), during the sputtering process was set at 0.4. The deposition rates of CrTaN coatings varied from 23 to 27 nm/min. The CrTaN coatings crystallized into a columnar structure, without heating the substrates during the sputtering process and exhibited surface hardness and Young's modulus values of 16–27 and 211–383 GPa, respectively. The annealing treatments were conducted at 500 and 600oC for 4 hours in air and 600oC for 4 hours in 50 ppm oxygen with balanced nitrogen gas. The diffusion barrier performance was evaluated by Auger electron spectroscopy depth profiles (AES), and X-ray diffraction (XRD). Oxidation resistance of the CrTaN coatings was also investigated. Orthorhombic L-Ta2O5 and rhombohedral Cr2O3 was observed after annealing at 500 and 600oC for 4 hours in air. When the oxide appeared, the thin film surface become more rough, the surface hardness and Young's modulus values decreased. Annealing in 600oC for 4 hours in a 50 ppm O2-N2 atmosphere, surface not oxide phase was observed. The hardness and Young's modulus values was increased. We also investigated oxidation resistance of the CrTaN coatings under a 50 ppm O2-N2 atmosphere, to assess the fabricated layers effectiveness as a protective coating for glass molding dies. Next carbon nitride films were deposited on the CrTaN films, to increase the surface wear property, because carbon nitride film has a batter wear resistance. The films were annealing in 50 ppm O2-N2 environment to simulate the glass molding environment, to observe the adhesion of CrTaN, surface roughness and hardness.
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Sufianu, Adeleke Wasiu. "A Mossbauer Spectroscopy Investigation of Fe enriched WC-Co." Thesis, 2016. http://hdl.handle.net/10539/21292.
Full textAbstract:
A dissertation submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of requirements for the degree of Master of Science. May 2016.Tungsten carbide cobalt (WC-Co) cemented carbides are widely used for cutting, drilling, machining and as wear resistant materials due to the combination of high hardness and fracture toughness. In this work, we report on as-milled and as-sintered WC-10Co-20Fe samples which were ball milled for 15 hrs and sintered using liquid phase sintering (LPS). These samples were investigated by Vickers hardness test, microstructural analysis, X-ray diffraction (XRD), transmission Mössbauer spectroscopy (TMS) and conversion electron Mössbauer spectroscopy (CEMS) techniques. A mean hardness value of 1160 ± 42 HV was obtained for WC-10Co sample while a value of 776 ± 35 HV was determined for the WC-10Co-20Fe using the Vickers hardness tester. The lower hardness value for WC-10Co-20Fe is attributed to the high volume of the binders (10% Co and 20 %Fe) incorporated in the sample. The microstructural analysis of the as-sintered WC-10Co and WC-10Co-20Fe samples reveals that the light regions represent the WC phases and the dark regions signify the presence of the Co and CoFe phases in the as-sintered WC-10Co and WC-10Co-20Fe samples, respectively. The energy dispersive spectroscopy (EDS) of the as-sintered samples shows the presence of the starting powders used (WC, Co and Fe) and some Cr contamination resulting from either the production process or the starting powders.
GR 2016
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Mabhali, Luyolo Andrew Baxolise. "Effect of SiC abrasive breakdown on the wear rate of WC-12wt%Co alloy." Thesis, 2008. http://hdl.handle.net/10539/4982.
Full textAbstract:
This research project is a preliminary investigation of the effect of SiC abrasive
breakdown on the wear rate of a WC-12wt%Co mining alloy. Wear tests were
carried out on a two body-sliding wear apparatus under (a) “Ideal” (replacing the
SiC paper periodically to ensure continual exposure to fresh abrasives), (b) “No
debris” (removing the wear debris periodically) and (c) “With debris” (retaining
the wear debris for the entire wear test) wear conditions. The WC-12wt%Co
specimens and SiC abrasive grits were examined before and after the wear tests
using optical, stereo and electron microscopy.
As wear progressed, the SiC abrasives blunted thereby increasing the
abrasive/specimen contact area, resulting in a reduction in the WC-12wt%Co
wear rate. Wear debris clogging the interstices between the abrasive grits caused a
further reduction in the WC-12wt%Co wear rate by adding to the
abrasive/specimen contact area already created by blunting. Increasing the applied
load resulted in an increase in the WC-12wt%Co wear rate under “Ideal” wear
conditions. Under the remaining wear conditions, the increased load resulted in a
faster deterioration of the SiC grits. The dominant wear mechanisms under all
conditions are characterized by hard abrasive wear that caused extensive
grooving, Co binder extrusion and cracking and fragmentation of WC grains.
34
Peng, Yang-Ching, and 彭揚景. "Investigation of the effect of cobalt concentration on the grindability of cemented carbide." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/36712686547623951853.
Full textAbstract:
碩士淡江大學
機械與機電工程學系碩士班
100
Glass molding process (GMP) is regarded as a very promising technique for mass producing high precision optical components such as spherical/aspheric glass lenses and free-form optics. However, only a handful of materials can sustain the chemical reaction, mechanical stress and temperature involved in the glass molding process and almost all of these mold materials are classified as hard-to-machine materials. This makes the machining of these materials to sub-micrometer form accuracy and nanometer surface finish a rather tough and expensive task. Amongst those handful choices, tungsten carbide (WC) is by far the most commonly used mold material in GMP industry. WC, also known as sintered/cemented WC with cobalt (Co) binder, is a metal matrix composite of WC particles and Co matrix. Cobalt concentration plays an important role in shaping mechanical properties of the obtained WC/Co materials. This research aimed to investigate the effect of Co concentration on the grindability of WC/Co materials. Efforts have been made to correlate grinding parameters such as spindle speed, cut depth and feed to the obtained surfaces. It is found that, despite of higher hardness values, better surface finish can be achieved on WC/Co specimen of lower Co concentration. In the present study, surface roughness (Ra) values better than 5nm and 10nm were obtained on WC/Co specimens of 0~3% and 6~13% Co concentrations respectively.
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Yi-HengLin and 林奕亨. "Highly active electrocatalyst cobalt-carbide nanoparticles synthesized by wet-chemistry method for hydrogen evolution reaction." Thesis, 2019. http://ndltd.ncl.edu.tw/handle/b9acf9.
Full textAbstract:
碩士國立成功大學
材料科學及工程學系
107
Hydrogen is a promising alternative energy without greenhouse gas emissions. Since the transition metal carbides (TMCs) exhibited similarly electronic properties with noble metal platinum, they are considered sustainable alternatives to noble metals in catalysis. Among the TMCs, CoxC (x=2,3) nanoparticles (NPs) can act as an excellent electrocatalyst for hydrogen evolution reaction (HER) by water splitting. In our report, CoxC nanocomposites were synthesized by wet chemistry method using Cobalt (II) acetate, sodium hydroxide as precursors and triethylene glycol (TEG) as solvent. In addition, Co2C NPs were synthesized by similar wet chemistry method using Cobalt (II) acetate as precursors and TEG, oleylamine (OAm) as solvent. The cobalt carbide NPs exhibited high electrocatalytic activity. CoxC nanocomposites performed a -0.33V onset potential and 91mV/dec tafel slope, while the Co2C NPs exhibited a better performance of -0.27V and 60mV/dec respectively.
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Archer, Marcelle. "Analysis of cobalt, tantalum, titanium, vanadium and chromium in tungsten carbide by inductively coupled plasma - optical emission spectrometry." Diss., 2004. http://hdl.handle.net/2263/24896.
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Chun-KaiChang and 張鈞凱. "Properties Improvement with Laser Remelting for Tungsten Carbide-Cobalt Film Coating Sprayed by High Velocity Oxygen Fuel." Thesis, 2019. http://ndltd.ncl.edu.tw/handle/y65t6g.
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Su, Jiunn-Cherng, and 舒圳晟. "Optimization of mechanical properties of cemented carbide: influence of grain size, cobalt content, and grain growth inhibitors." Thesis, 2017. http://ndltd.ncl.edu.tw/handle/72987828195677809766.
Full textAbstract:
碩士國立臺灣科技大學
材料科學與工程系
105
Tungsten carbide particles are difficult to joint to each other if there are no intermedia in between. Researchers have found that cobalt’s liquid phase has ability to reinforce the microstructure of tungsten carbide. Thereby, the most widely used tungsten carbide rods usually contain 10wt% of cobalt. This composition has characteristic of high wear-resistance, high impact strength, and high tolerance of chipping because the amount of cobalt provides sufficient toughness and tungsten carbide grains maintain the hardness. Tungsten carbide plays an important role in terms of industrial development. However, commonly used solid tool blanks with 10wt% cobalt is not suitable for all kinds of tasks, since end user’s working environment is becoming more and more difficult with rising industrial requirements, especially in the aerospace industry. Therefore, researchers tend to satisfy the working condition by means of promoting mechanical properties which are governed obviously by grains size of tungsten carbide and the proportion of cobalt. Generally, tungsten carbide’s toughness and hardness are inversely proportional to each other if we merely alter those two parameters mentioned above. According to articles, carbon content indeed influences mechanical properties a lot due to percentages of carburization and wetting angle during sintering process. Therefore, carbon balance control is a crucial factor all over the processes. Wear resistance would greatly reduce if carbon content is over the limit, while insufficiency in carbon content will lead to brittleness and shorten tool’s life time. Tungsten carbide products are often used in the environment with high risks. If the quality is not stable, it is impossible to ensure the security to user and even harmful for the machines where the products being installed in. Through the cooperation of National Taiwan University of Science and Technology(NTUST) and CB-CERATIZIT group(CBCT), experiments have been conducted mainly on the influences of mechanical properties and microstructure of tungsten carbide after doping with varied amount of cubic carbide, such as chromium carbide and vanadium carbide. In order to achieve further improvements, other researchers have started to dope different kinds of carbides, such as titanium carbide, chromium carbide, tantalum carbide, vanadium carbide, etc. Taking the advantage of chemical interaction between those carbides and tungsten carbide or cobalt, people have been trying to enhance mechanical properties of tungsten carbide and pushing the boundary in various applications.
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Freinkel, D. M. "Experimental investigation into the wear resistance of tungsten carbide-cobalt liners in a full scale pneumatic conveying rig." Thesis, 2015. http://hdl.handle.net/10539/16761.
Full textAbstract:
RESEARCH PROJECT SUBMITTED FOR
MASTERS DEGREE IN ENGINEERINGThe purpose of the investigation was to compare the relative wear resistance of various grades of sintered tungsten carbide liners against a mild steel standard in a full scale oneumatic conveying testing rig. Specimens ranging in cobalt content from 6i to 30% and in grain size from 0.56 to 2.98 micrometers, including a mild steel standard, were placed on a specially designed holder which fitted into a tee type 100 mm Jjureter bend. The specimens were tested under various operating conditions i.e. air velocity ranging from 28 m/s to 52 m/s, impact angles of 30° to 70°, mass flow rates of 35 kg/min to 83 kg/min and phase densities of 1.2 to 2.9, using a 4 mm nominal size crushed granite rock. The experimental results show that the ultrafine grained, low cobalt (6%) tungsten carbide displays little sensitivity to varying velocities, impact angles, mass flow rates or phase densities, and consistently gave the best wear resistance under all testing conditions. The coarse grained high cobalt (30%) tungsten carbide's wear resistance was found to be the most s e n s i t v re to ant * increase in conveying air velocity * decrease in phase density * decrease in solids mass flow rate * decrease in impact angle. This material consistently showed the least wear resistance under all testing conditions and performed only slightly better than mild steel. The effect of the carbide grain size was found to be small. However, the medium grained alloy displayed a higher erosion resistance than the fine grained alloy. This is due to the effect of plastic deformation, which determines the WC grain size that yields optimum erosion resistance, (if one excludes the ultrafine grained alloy which is expensive to produce). The effect of cobalt content was such that the lower cobalt specimens (6% range) consistently performed better than the higher cobalt contents (10%, 15%, 30%) under all testing conditions; the wear resistance decreasing with increasing cobalt content. Microstructurally it has been shown that there is a definite relationship between erosion resistance and the inverse of the magnetic coercivity of the tungsten carbide alloys. Maximum erosion occurring below 90° has been explained in terms of a combination of three energy mechanisms i.e. removal of cobalt, plastic deformation of the target specimens and fracture of the erodant particles.
40
Ndlovu, Siphilisiwe [Verfasser]. "The wear properties of tungsten carbide-cobalt hardmetals from the nanoscale up to the macroscopic scale / by Siphilisiwe Ndlovu." 2009. http://d-nb.info/999595199/34.
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Bastian, Susanne. "Neuro- und Gliotoxizität von Wolframcarbid-basierten Nanopartikeln in vitro." Doctoral thesis, 2010. https://tud.qucosa.de/id/qucosa%3A25777.
Full textAbstract:
Die Anzahl neurodegenerativer Erkrankungen nimmt in unserer Gesellschaft stetig zu. Obwohl inzwischen eine Reihe genetischer Ursachen identifiziert worden sind, wird auch der Einfluss von Umweltfaktoren bei der Pathogenese dieser Erkrankungen zunehmend in Betracht gezogen. Der Beitrag von ultrafeinen Partikeln aus Industrie und Umwelt auf neurodegenerative Erkrankungen steht daher zunehmend im Fokus der Forschung. Die Translokation von ultrafeinen Partikeln bzw. Nanopartikeln ins Gehirn ist bekannt. Die Charakterisierung neuro- und gliotoxischer Wirkungen von Nanopartikeln in einem in vitro System war deshalb Ziel dieser Arbeit. Untersucht wurden Wolframcarbid-Partikel mit und ohne Cobalt, die im Herstellungsprozess von Hartmetallen von Bedeutung sind.
Die meisten toxikologischen Daten wurden bisher mit mikrokristallinen WC-Pulvern an Lungenzellen bzw. -gewebe erhoben. Da aber die Verarbeitung von nanoskaligen Partikeln bessere Eigenschaften der Hartmetalle bewirkt, nimmt das Interesse an toxikologischen Studien mit WC-Nanopartikeln zu. Da die Gefahr der Translokation und Akkumulation im Gehirn beim Einatmen von Stäuben am Arbeitsplatz besteht, wurde erstmalig die Toxizität von WC-NP mit und ohne Cobalt auf Zellen des Gehirns untersucht. Für die Durchführung wurden primäre Neuronen, Astrozyten und Mikroglia sowie die Oligodendrozyten-vorläuferzelllinie OLN-93 der Ratte eingesetzt. Alle untersuchten Partikel konnten mittels Elektronenmikroskopie, ICP-Massenspektrometrie und Durchflusszytometrie in den verschiedenen Zelltypen nachgewiesen werden. Untersuchungen mit Cytochalasin D (Inhibitor der Aktinpolymerisation) deuteten auf zell- und partikelspezifische Aufnahmemechanismen hin.
Experimente mit Cobaltchlorid und Natriumwolframat konnten beweisen, dass nicht die gelösten Ionen für die Toxizität von WC-Co ursächlich waren, sondern die Partikelform von entscheidender Bedeutung ist. Es zeigte sich jedoch, dass einige der WC-Co verursachten Effekte vermutlich auf dem Cobaltanteil beruhen. Offensichtlich dienen WC-Co-NP als Vehikel, um Cobalt in die Zellen einzuschleusen. Zur toxischen Wirkung trägt auch das Reaktionsvermögen von WC und Cobalt an der beiderseitigen Grenzfläche bei, denn dadurch können in der Zelle vermehrt reaktive Sauerstoffspezies gebildet werden.
Im Rahmen der Untersuchungen wurden die zeit- und konzentrationsabhängigen Effekte der Nanopartikelexposition auf die Vitalität, die Proliferation, das Adhäsionsverhalten, das mitochondriale Membranpotential und die Induktion apoptotischer und nekrotischer Zelluntergänge untersucht. Dabei wurden verschiedene Vitalitäts- und Proliferationstests angewendet, um die häufig beobachteten Wechselwirkungen zwischen Reagenzien und Nanopartikeln auszuschließen.
Nicht alle untersuchten Nanopartikel erwiesen sich in den durchgeführten Experimenten als akut toxisch. Nur eine Exposition mit WC-Co-NP führte nach 72 h zu einer deutlich verringerten Vitalität und Proliferation bei Astrozyten und OLN-93 Zellen. Eine Exposition mit WC-Co-NP zeigte des Weiteren eine geringe Induktion von Apoptose und Nekrose bei Astrozyten, nicht aber bei OLN-93 Zellen. Neurone wiesen nach einer Exposition mit NP eine wenig verringerte Vitalität auf. Es wurde festgestellt, dass erst die primäre Schädigung von Astrozyten zu einer sekundären Neuronenschädigung führt. Bei der Bewertung der NP-Toxizität müssen daher unbedingt die Wechselwirkungen der Zellen bedacht werden.
Die Exposition mit WC- und WC-Co-NP beeinflusste das mitochondriale Membranpotential und das Adhäsionsverhalten der untersuchten Zellen. Neuronen und OLN-93 Zellen zeigten nach NP-Exposition eine verminderte Adhäsion. Auch physiologische Kalziummessungen lieferten einen Hinweis für die veränderte Funktionalität glialer Zellen nach einer NP-Exposition. Des Weiteren wurde die Expression einiger Gene, bedeutend für Adhäsion und extrazelluläre Matrix, mit realtime RT-PCR bei OLN-93-Zellen und Astrozyten überprüft. Es konnte eine Regulation von Mmp9, Timp1, Lama3, Tgfbi, Col8a1 und Hmox1 gezeigt werden.
Zusammenfassend lässt sich feststellen, dass die ausgewählten Nanopartikel nicht per se neuro- und gliotoxisch wirkten. Die Partikel können anhand abnehmender Toxizität wie folgt geordnet werden: WC-Co > WC 100na > WC 10n. Auch die Reaktionen der Zellen fielen unterschiedlich aus: die Astrozyten erwiesen sich als die sensitivsten Zellen.
Eine Exposition des Gehirns mit WC-Co-NP in hohen Konzentrationen oder über einen längeren Zeitraum könnte also weit reichende Folgen haben, angefangen bei einer gestörten Signalweiterleitung über eine erhöhte Permeabilität der Blut-Hirn-Schranke bis hin zu neurodegenerativen Veränderungen.
Diese und weitere Untersuchungen könnten bei der Erstellung von Arbeitsrichtlinien im Umgang mit Hartmetallen, deren Ausgangsmaterial nanoskalige Pulver sind, hilfreich sein und damit einen Beitrag zum Schutz der Arbeiter liefern.
42
Sacks, Natasha [Verfasser]. "The wear and corrosive-wear response of tungsten carbide-cobalt hardmetals under woodcutting and three body abrasion conditions / by Natasha Sacks." 2004. http://d-nb.info/971984166/34.
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43
Wu, Yu-Ru, and 吳育儒. "The Analysis of Cutting Performance in the Plastic Materials for the Grinding Precision and the Cobalt Content of Tungsten Carbide of End Mills." Thesis, 2016. http://ndltd.ncl.edu.tw/handle/382a75.
Full textAbstract:
碩士國立虎尾科技大學
機械與電腦輔助工程系碩士班
104
Since the plastic material itself has good toughness, so when cutting plastic materials, in the past are adjusted for tool geometry or machining parameters, thereby reach to enhance tool life, but with the advances in technology, in addition to the plastic composite material increase their own strength plastic material, the plastic material of the cutting cutting more difficult, but now in terms of cutting the plastic rarely for precision grinding tools and tungsten carbide cobalt content to explore research, so this study end precision grinding and milling of tungsten carbide cutting analysis of cobalt content on the plastic material. In this study, the impact tool edge precision grinding process parameters were cutting surface grit size, cutting surface feed rate, cutting surface speed, relief surface grit size, relief surface feed rate and the relief surface speed, use Taguchi experiment Planning Act, the analysis of L36 (22 × 34) orthogonal table to find the best, the worst and moderate three levels of precision grinding, precision grinding and then in accordance with each grinding tungsten carbide rods with different cobalt content, total available nine different tool characteristics to a series of cutting analysis. The experimental analysis showed that cutting blue PC material (EXL14414) to the tool component cobalt content of 8% of its edge polishing accuracy 1.095μm has better tool life quality; cutting white material PC (EXRL2031) to the tool component cobalt content 8% of its edge polishing accuracy 1.095μm has better tool life quality; cutting black PC glass material (Kalix 9950) to the tool component cobalt content of 9% of its accuracy 1.095μm edge grinding tool life with better quality.
44
Yeh, Po-Cheng, and 葉柏成. "Modeling and analysis of surface roughness and electrode wear on the wire electrical discharge machining of cobalt-bonded tungsten carbide using the response surface methodology." Thesis, 2009. http://ndltd.ncl.edu.tw/handle/92352988685852175596.
Full textAbstract:
碩士修平技術學院
精密機械與製造科技研究所
97
In this paper, the predictive model of surface roughness (SR) and wire-electrode wear (WW) in the Wire Electrical Discharge Machining (WEDM) process of cemented tungsten carbide using the response surface methodology had been carried out. The cemented tungsten carbide P10 grade, which is widely used in mould and tool applications, was adopted as the workpiece material to explore the performance characteristics of WEDM process. The first and second order models were developed to study the effect of four processing parameters, pulse duration, open discharge voltage, peak current and wire speed on the surface roughness (SR) and wire-electrode wear (WW). The experiment plan adopts the centered composite design (CCD). The predictive models proposed in this study were investigated by the analysis of variance (ANOVA). The second order model in this study have been proved to fit and predict values of the performance characteristics close to those readings recorded experimentally with a 95% confidence interval.