Tungsten Carbide Powder

Tungsten carbide powder can be prepared from different raw materials and by various production methods, as outlined in Fig. 9.3. Only methods used today on a technical or pilot plant scale are considered. The conventional procedure covers the widest range of powder qualities in regard to particle size (0.15 12 pm), and consequently the biggest 

As carbon source, high-purity carbon black is mostly used and, more rarely, graphite, due to its higher price and lower reactivity. Thermal carbon black is preferred to flame 

FIGURE 9.3. Routes of WC powder production conventional manufacture and alternative processes, including WC/Co precursors. 

In any case, carbon black is always more impure than tungsten powder, particularly in regard to the alkali metals, Ca, Si, Mg, and S. Part of these trace elements are volatilized during carburization (the percentage depending on temperature). This is why finer WC powders (lower carburization temperature) are usually more impure than coarser powders. 

The two components (W and C) must be blended thoroughly prior to carburization. This is done in different types of equipment, like V or double cone blenders, mixing ball mills, or high-energy mixers. An even blend is of importance because, during carburization, carbon atoms can only move via diffusion or as methane molecules over very short distances. Pelletizing or compacting enhances diffusion and increases the furnace capacity. 

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

Included in tungsten carbide powder cutting and wear-resistant materials. 

Maroglou A, Nienow AW. Fluidized bed granulation technology and its application to Tungsten Carbide. Powder Metallurgy 1986 29(4). 

Maroglou, A., and Nienow, A. W. Fluidized bed Granulation Technology and its application to tungsten carbide. Powder Metallurgy 29(4) 1986. 

Mixtures of powders of two materials sinter very rapidly if one of them melts at the sintering temperature. Initially capillary action causes the liquid phase to rapidly wet the solid phase, causing an initial contraction. Then as the solid phase dissolves in the liquid it is rapidly transported to locations that decrease the pore volume. Carbide tool material is made from a mixture of cobalt and tungsten carbide powders sintered below the melting point of cobalt. The volume fraction liquid must be limited so capillarity can retain the shape during sintering. 

Preparation of Coarse Tungsten Carbide Powder in an Auxiliary Melt... 

The Rapid Carbothermal Reduction (RCR) Process (The Dow Chemical Company) [9.19,9.20], In principle, the patented RCR process is another type of direct carburization. The tungsten carbide powder is continuously synthesized by an extremely rapid carbothermal reduction of WO3 in a graphite transport reactor. Calculated heating rates are in the range of 100 million K per second by thermal radiation. The WO3/C mixture during this process is converted to a tungsten carbide precursor (WCi c) within seconds. 

Conventional tungsten carbide powder. The particle size range of these qualities is between 1 and 10 pm (the majority between 1 and 2.5 pm). The average particle size has to be met usually within the limits of +10% relative. Particle size distributions for a given average particle size can be adjusted within certain limits already during tungsten powder reduction (see Section 5.4.4). 

Submicron tungsten carbide powder. In principle, every WC powder having an average particle size below 1 pm can be regarded as submicron. However, it has become common practice to further classify these powders into the following three groups ... 

Coarse tungsten carbide powder. Coarse WC powders are available in the particle size range of >8 to 50 pm. Their crystallite sizes vary from <10 pm up to about 50 pm and mainly depend on the carburization temperature (strictly speaking, the maximum crystallite size is determined by the particle size). 

Cobalt-tungsten Carbide Powders and Hard Metals... 

Low Surface Area, Reducing Sintering Atmosphere The material selected for this formulation was a relatively coarse tungsten carbide powder. The binder system was a standard acrylic polymer. Since the WC was very coarse (16 pm average particle size) and had such a high density (15.7 g/cc), the formulation was difficult to prepare. The tape casting had to be done immediately after the slurry was poured from the preparation jar. 

Demirsk) D, Ragulya A, Agrawal D. Initial stage sintering of binderless tungsten carbide powder under microwave radiation. Ceramics International 2011 37 505-12. 

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