Other Carbide Powders

The following carbide powders are used in hardmetal manufacture WC-TiC, WC-TiC-TaC(NbC), TaC, TaC(l%C), as well as M02C, Cx C2, and VC (the latter are used in small concentrations as WC grain growth inhibitors). 

FIGURE 9.22. Ultiafine WC powders produced by conventional (reduction/carburization) manufacture 40,000 X. The size of the spheres emphasizes the degree of fineness of the development grade. By courtesy of Wolfram Bergbau und Huttenges.m.b.H., Austria. 

The powder properties are either directed by powder milling of coarser powders (high-temperatm-e carburized), or by steering the particle size through the oxide precursor and subsequent soft carburization (lower temperature, but longer carburization times). 

WC-TiC-TaC(NbC) mixed crystal carbides (solid solutions). The raw materials are the same as for WC-TiC grades, with addition of Ta20s. Any furnace equipment capable of producing a good quality of WC-TiC is suitable. Total reduction and complete diffusion can only be reached by high temperature, good vacuum, and long exposure time. Carburization temperatures are about the same as for WC-TiC. 

which is a natural companion of Ta, can be tolerated up to 30%, but the exact content must be known for optimal carbon adjustment. Typical grades contain 33-50 wt% WC. 

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Ferro tungsten Tungsten metal powder Tungsten carbide powder Tungsten e scrap Other tungsten materials Total... 

Other linear polysilanes can also be used as ceramic precursors. Solid objects of silicon carbide are manufactured by Nippon Soda Co. from polysilastyrene and finely divided silicon carbide powder.133 These materials are blended, injection molded to the... 

Use of a steel chisel to open a drum of carbide caused an incendive spark which ignited traces of acetylene in the drum. The non-ferrous tools normally used for this purpose should be kept free from embedded ferrous particles [1]. If calcium carbide is warm when filled into drums, absorption of the nitrogen from the trapped air may enrich the oxygen content up to 28%. In this case, less than 3% of acetylene (liberated by moisture) is enough to form an explosive mixture, which may be initiated on opening the sealed drum. Other precautions are detailed [2]. Use of carbon dioxide to purge carbide drums, and of brass or bronze non-sparking tools to open them are advocated [3]. The dust explosion characteristics of calcium carbide powder in air have been studied [4]. 

Other Metal Carbides A host of other metal carbides are used in ceramic formulations. These include TaC, TiC, Cr3C2, VC, M02C, B4C, WC, and ZrC. These metal carbide powders are produced by car-bothermal reduction of the relevant metal oxide or reaction of the relevant metal with carbon in CO or an inert atmosphere. These metal carbides are used as abrasives and in hig -temperature wear applications. 

Carbides of metals and other elements have been produced by this approach, including carbides of boron, silicon, titanium, zirconium, hafnium, vanadium, niobium, molybdenum, tungsten, tantalnm, and thorium (Funke, Klementiev, Kosukhin, 1969 Sheppard Wilson, 1972 MacKinnon Wickens, 1973 Chase, 1974 Steiger Wilson, 1974 Swaney, 1974 MacKinnon Renben, 1975). The produced caibide particles are very small their diameter is usually about 20-200 mu. Halides are mixed with hydrocarbons, usually in a ratio H2 Me = 2-30. The gas mixture is heated up in plasma to temperatures of 1300-4000 K time of synthesis exceeds 50 ms. As an example, production of submicron boron carbide powder from gaseous boron trichloride and methane occurs in the strongly endothermic process ... 

The reaction of UC and UC2 powders with Fe as well as stainless steel at 1000°C was studied by [1962Kat] and [1963Nic]. [1974Mat] studied the influence of Fe on the self-diffusion of C in UC. [1988Jon] determined the products of acid hydrolysis of UFeC2 and some other carbides as a tool for determining whether C atoms form chains. 

In such a process, zinc metal is added and melted with clean cemented carbide scrap cobalt is dissolved in the molten zinc, zinc is distilled off, leaving a spongy cake easily crushed, milled and screened to separate the cobalt metal powder and the hard carbide (tungsten, tantalum and other carbides) grains. 

Considering the final part to be manufactured (the whole reason why the tape is cast), consideration must be given to the firing atmosphere. It would not serve to use an excellent air burnoff binder for casting silicon carbide if the SiC will be fired in a reducing atmosphere. This is an especially important consideration when casting metal powders or other nonoxide powders. 

A very important and technically advanced use of carbon black is as a raw material for making hard carbides in the manufacture of hard metals. Powders of tungsten or of other carbide-forming metals are weighed together very carefully to stoichiometric mixtures, which are heated to a very high temperature. The intended carbide is formed. 

M Yoshida, M Nishioka, S Somiya. Rapid preparation of titanium and other transition-metal nitride and carbide powders by a carbo-reduction method using arc-image heating. In Ref. 8, p 406. 

Cermets on the basis of TiC and other carbides of refractory metals, as well as SiC, B4C, their alloys with oxides for the protective coating of rocket elements, including jets of powder rocket engines and nose parts of rockets ... 

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