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Carbide Powders (carbide + powder)
Selected AbstractsPressure Effect on the Homogeneity of Spark Plasma-Sintered Tungsten Carbide PowderJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 10 2009Salvatore Grasso A combined experimental/numerical methodology was developed to aid full densification of pure ultrafine tungsten carbide powder by means of Spark Plasma Sintering (SPS) operating in Current Control mode. Applied pressure ranged from 5 to 80 MPa while the current intensity was set and held constant at 1400 A. The developed SPS model used a moving-mesh technique to account for the electrothermal contact resistance change during both shrinkage and punch sliding follow-up. The pressure dependence on the electrothermal contact resistance was also taken into account by the model. The experimental and numerical results showed the effects of pressure on grain growth, residual porosity, and hardness observed along the sample radius. Upon increasing sintering pressure, complete densification was obtained by reducing the peak temperature measured at the die surface. By combining experimental and modeling results, a direct correlation between compact microstructure homogeneity and sintering parameters (i.e., temperature and applied pressure) was established. [source] Effect of Aluminum Doping on Microwave Permittivity of Silicon Carbide PowdersJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 12 2008Fa Luo The permittivity and structure of commercial SiC powders before and after thermal diffusion of aluminum were explored in this study. The X-ray diffraction analysis and permittivity results show that heat treatment at 2000°C for 1 h has no influence not only on the structure of the SiC powders but also on the permittivity. Thermal diffusion of aluminum at 1800°, 1900°, and 2000°C was carried out for 1 h at 5 Pa in Ar atmospheres, respectively. A graphite die with two chambers was used during the experiment to separate the aluminum powders from the SiC powders. Aluminum vapor at high temperatures passes to the upper chamber through holes and diffuses into the SiC powders. The permittivities of the as-received SiC powders at 8.2,12.4 GHz were measured, and the results indicate that the real and imaginary parts of permittivity are improved much more than those of the original SiC powder. Both the real and the imaginary parts of the doped SiC increase with the diffusion temperatures, which could be attributed to defects from thermal diffusion of aluminum. [source] Spheroidization of Titanium Carbide Powders by Induction Thermal Plasma ProcessingJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 9 2001Ya-Li Li Highly spherical particles of titanium carbide (TiC) have been produced by in-flight heat processing of irregularly shaped TiC powders in an aerosol reactor under argon-hydrogen and argon-helium induction thermal plasma. The spherical powders obtained by the plasma treatment consist of unagglomerated and uniform particles with mean diameters between 25 and 28.5 ,m, which is smaller than the original TiC particle mean diameters (29.5 ,m) because of partial evaporation of the particles during the plasma treatment. The spheroidization ratio of the treated TiC powders increases with the increase of hydrogen flow rate in plasma gases and the reduction of powder feeding carrier gas flow rate. Under certain processing conditions, the TiC powders have been completely spheroidized. The morphology and structure of individual spherical particles were examined and their formation mechanism was discussed based on calculation of heat transfer kinetics of the particles in the thermal plasma. [source] Pressure Effect on the Homogeneity of Spark Plasma-Sintered Tungsten Carbide PowderJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 10 2009Salvatore Grasso A combined experimental/numerical methodology was developed to aid full densification of pure ultrafine tungsten carbide powder by means of Spark Plasma Sintering (SPS) operating in Current Control mode. Applied pressure ranged from 5 to 80 MPa while the current intensity was set and held constant at 1400 A. The developed SPS model used a moving-mesh technique to account for the electrothermal contact resistance change during both shrinkage and punch sliding follow-up. The pressure dependence on the electrothermal contact resistance was also taken into account by the model. The experimental and numerical results showed the effects of pressure on grain growth, residual porosity, and hardness observed along the sample radius. Upon increasing sintering pressure, complete densification was obtained by reducing the peak temperature measured at the die surface. By combining experimental and modeling results, a direct correlation between compact microstructure homogeneity and sintering parameters (i.e., temperature and applied pressure) was established. [source] Plasma Synthesis of Tungsten Carbide Nanopowder from Ammonium ParatungstateJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 3 2009Taegong Ryu A thermal plasma process has been applied to the synthesis of nanosized tungsten carbide powder with ammonium paratungstate (APT) as the precursor. The reduction and carburization of vaporized APT produced nanosized tungsten carbide (WC1,x) powder, which sometimes contained a small amount of W2C phase. The effects of reactant gas composition, plasma torch power, the flow rate of plasma gas, and the addition of secondary plasma gas (H2) on the product composition and particle size were investigated. The produced tungsten carbide (WC1,x) powder was <20 nm in particle size. The synthesized powders were also subjected to a hydrogen heat treatment to fully carburize the WC1,x and W2C phases to the WC phase as well as to remove excess carbon. Finally, WC powder of particle size <100 nm was obtained. [source] Fabrication of High-Purity Ti3SiC2 Powders by an In Situ Reaction of Polycarbosilane and Metal TitaniumJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 8 2010Jinshan Yang High-purity titanium silicon carbide powders were fabricated by an in situ reaction of polycarbosilane and metal titanium. The effects of the starting reagents and the pyrolysis temperature on the fabrication of high-purity Ti3SiC2 were studied. The results showed that high-purity Ti3SiC2 could be obtained when the atomic ratio of Ti:Si was 3:1.5 and the effect of the temperature of pyrolysis on the purity of the powders was insignificant. The atomic ratio of Ti:Si was calculated on the basis of the empirical formula of SiC2.5H7. [source] Relative viscosity models and their application to capillary flow data of highly filled hard-metal carbide powder compoundsPOLYMER COMPOSITES, Issue 1 2005Tomas Honek The rheological behavior of highly filled polymer systems used in powder injection molding (PIM) technology strongly influences the final properties of the products. In this study, the capillary flow data of multi-component polymer binders,based on polyethylene, paraffin, ethylene-based copolymers, and polyethylene glycol,compounded with three various hard-metal carbide powders were employed. The rheology of such highly filled (up to 50 vol%) multiphase systems is necessarily a complex phenomenon characterized by strain dependent, non-Newtonian properties complicated by flow instabilities and yield. Over 15 mathematical models proposed for highly filled systems were tested, some of them calculating the maximum filler loading. Due to the complex structure of the filler (irregular shape, particle size distribution) and a multi-component character of the binder, the applicability of these models varied with the powder-binder systems studied. However, the particular values of maximum loadings are in good accordance with the predictions based on powder characteristics. Simple modification of Frankel-Acrivos model to the systems containing unimodal hard-metal carbide powders with particles of an irregular shape and broad particle size distribution gave precise agreement between experimental data and model prediction. POLYM. COMPOS., 26:29,36, 2005. © 2004 Society of Plastics Engineers. [source] | ||||||||||