Dissertations / Theses on the topic 'Tungsten carbide cobalt'

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1998.<br>Includes bibliographical references (p. 69-70).<br>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.<br>(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.<br>by Andrew Kelley, III.<br>S.M.

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.

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.

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.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2004.<br>Includes bibliographical references (p. 119-120).<br>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<br>(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.<br>by David Guo.<br>S.M.

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.

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.

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

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 tunnelier<br>The 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

<p>The object of this work is to obtain a fundamentalunderstanding of the principal issues concerning the handlingof an aqueous WC-Co powder suspension.</p><p>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.</p><p>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.</p><p>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.</p><p>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.</p><p><b>Key words:</b>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.</p>

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 &#947;H2AX.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 différentes<br>Nanomaterials 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 &#947;H2AX 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

Este trabalho apresenta o estudo da Retificação de Ultraprecisão de ligas de carbeto de tungstênio-cobalto (WC-Co) com diferentes microestruturas. A motivação para este estudo foi o grande potencial desta liga para a fabricação de componentes que requerem materiais de alta dureza e resistência à fratura. Devido à combinação dessas características, esses materiais vêm sendo usados na fabricação de moldes para injeção de lentes ópticas de dispositivos eletrônicos e ópticos. Assim, amostras de carbeto de tungstênio-cobalto foram submetidas a vários testes para determinação da correlação entre os parâmetros de corte e parâmetros estruturais (tamanho de grão e teor de cobalto) com o regime de remoção de material. As amostras foram polidas e posteriormente microendentadas com cargas variadas para pré-avaliar a ocorrência de formação de microtrincas. Testes de usinagem foram conduzidos em uma retificadora de ultraprecisão, usando rebolos de diamante e posteriormente a rugosidade e os danos da superfície (microtrincas e crateras) foram avaliados. Para melhor entendimento da influência dos parâmetros estruturais e dos parâmetros de corte sobre os resultados de rugosidade foi realizado um teste ANOVA. As forças de usinagem foram medidas durante os ensaios usando um microdinamômetro piezelétrico com objetivo de estimar a temperatura na zona de retificação. Os resultados obtidos indicam que tanto os parâmetros estruturais como os parâmetros de corte influenciam na rugosidade, microdureza e temperatura na zona de retificação das ligas de carbeto de tungstênio-cobalto. Amostras com maior tamanho de grãos apresentam as menores rugosidades e altas temperaturas na zona de retificação. A velocidade de avanço (Vf) mostrou-se mais influente que a profundidade de corte (ap). Menores velocidades de avanço aumentam a temperatura na zona de retificação e a microdureza na camada superficial. Entretanto, verificou-se que as maiores temperaturas obtidas nos ensaios não foram suficientes para promover alteração metalúrgica no material. Algumas condições de corte combinadas com parâmetros estruturais levam a remoção de material em regime dúctil, resultando em superfícies com qualidade óptica. A porcentagem de cobalto e a velocidade de avanço (Vf) têm forte influência na alteração da microdureza da camada superficial das amostras retificadas. A diminuição da velocidade de avanço tende a aumentar a microdureza na camada. Há aumento de microdureza de até 200 kgf/mm2, sugerindo a ocorrência de encruamento por tensões compressivas. Com base nestes resultados, acredita-se que a retificação de ultraprecisão apresenta-se como uma opção viável para a manufatura de componentes de carbeto de tungstênio com acabamento submicrométrico, possibilitando a eliminação dos processos tradicionais de manufatura óptica, tais como a lapidação e o polimento.<br>The ultraprecision grinding of different tungsten carbide-cobalt microstructures (WC-Co) were investigated. The motivation for this study is the materials high hardness and potential application for micromolds. These materials have been used as optical inserts in glass injection molding processes for optical and electric devices, due to their excellent combination of high hardness, ductility and fracture toughness. Tungsten carbide samples were subjected to tests to determine the correlation between cutting parameters and microstructures to achieve the ductile regime of material removal. Polished surfaces of carbide samples were indented using varying loads to evaluate the microcracks formation. The machining tests were conducted using an ultraprecision grinding and A V-shaped metal-bond was used. Surface roughness was investigated as functions of the grinding conditions by means Analysis of Variance (ANOVA). The tangential force was measured using a piezoelectric dynamometer to estimate the grinding zone temperature. The results indicate that structural parameters (grain size and cobalt content) and cutting parameters have a significant influence on surface roughness, micro-hardness and grinding zone temperature for tungsten carbide-cobalt alloys.Tungsten carbide-cobalt samples with the larger grain size presented lower surface finish results and high grinding temperatures. The feed rate (Vf) showed greater influence that the in-feed (ap). The grinding zone temperature and the hardness are increased when speed rate is reduced. However, it was found that the highest temperature achieved did not reach a critical temperature for phase transformation. Some cutting parameters combined with structural parameters lead to ductile mode grinding mechanism, and as consequence, high optical quality surfaces are obtained. The micro-hardness of layer is extremely influenced by cobalt content and speed rate. Lower feed rate tends to increase the micro-hardness up to 200 kgf/mm2, suggesting that the compressive stress occurs. Considering the results presented it is believed that the Ultraprecision grinding showed to be a viable option for the fabrication of components made of tungsten carbide-cobalt with nanometer surface finish possibly eliminating traditional optical manufacturing processes such as lapping and polishing.

L'objectif de cette thèse était de trouver des traitements de surface adéquats pour adapter les propriétés physico-chimiques du carbure de tungstène fritté cobalt (WC-Co) au dépôt de diamant par CVD. Sans traitement, des couches composées de graphite et non de diamant sont obtenues. La première partie de ce travail a consisté à étudier le dépôt par électrochimie des alliages nickel-tungstène sur le WC-Co. Puis, une phase d'étude sur le comportement chimique et électrochimique des ions tungstates a été effectuée. Ces travaux ont montré, en particulier, une réduction en deux étapes monoélectriques pour mener à l'oxyde de tungstène V. Ce dernier matériau possède des propriétés catalytiques vis-à-vis de la réduction du proton. Avec cette phase d'optimisation, la teneur de 20 % at. En tungstène a été atteinte. Néanmoins, les couches de diamant obtenues sur des substrats de carbure de tungstène fritté avec 16 % de cobalt, recouvert de Ni-W, sont de faible qualité, avec une importante présence de carbone graphitique. Le dépôt diamant par HFCVD a montré que la couche la plus adéquate était le niture de titane. Puis par une phase d'étude sur les traitements de surface du substrat et de la couche intermédiaire, des couches de diamant de très bonne qualité ont été obtenues. Enfin, une méthode de brasage de pastilles de diamant a été développée. Avec une brasure Ag-Cu-Ti, le diamant, de 0,5 mm d'épaisseur, adhère très bien au substrat. Les tests tribologiques sur ce composite ont révélé l'inadéquation du diamant type CVD à l'abattage des roches. Par opposition, des tests complémentaires sans choc ont montré la possible utilisation du diamant CVD pour l'usinage des matériaux non ferreux.

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 proposé<br>WC-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

Nouveau modele de phase active obtenu par interpretation des resultats de rmn du **(59)co et de microscopie electronique haute resolution pour des catalyseurs d'hydrotraitement a base de sulfure de molybdene et de cobalt. Application a d'autres systemes : nire, core, rhre et rhmo. Etude de l'empoisonnement par la porphyrine de catalyseur nimo/al::(2)o::(3)

博士<br>國立臺灣海洋大學<br>材料工程研究所<br>98<br>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.

碩士<br>國立臺灣海洋大學<br>材料工程研究所<br>99<br>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.

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.<br>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.<br>GR 2016

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.

RESEARCH PROJECT SUBMITTED FOR MASTERS DEGREE IN ENGINEERING<br>The 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.

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.

碩士<br>國立虎尾科技大學<br>機械與電腦輔助工程系碩士班<br>104<br>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.

碩士<br>修平技術學院<br>精密機械與製造科技研究所<br>97<br>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.