Tungsten carbon black

The Atmosphere. Industrial carburization of tungsten powder is commonly carried out in hydrogen or hydrogen-containing gas mixtures. Hydrogen reacts with the solid carbon in the W -H C mixture to form methane (at temperatures <1600°C) or acetylene (>1600°C), which transport the carbon in tungsten-carbon black mixes over larger... 

Figure 3.21 shows the change of the product composition with carburization time in hydrogen for a tungsten-carbon black mixture at 1119°C. After only 10 minutes at this temperature most of the metal was transformed to W2C, which was ffien only slowly converted to WC. This result is characteristic for the temperature range of 1050 to 1850 °C and W particle sizes of 1.3 to 20 pm [3.71]. It is remarkable that W2C forms during carburization even at 900 °C, which is well below its eutectoid decomposition teniperature of 1250°C. 

It was found in the 1960s that disperse platinum catalyst supported by certain oxides will in a number of cases be more active than a similar catalyst supported by carbon black or other carbon carrier. At platinum deposits on a mixed carrier of WO3 and carbon black, hydrogen oxidation is markedly accelerated in acidic solutions (Hobbs and Tseung, 1966). This could be due to a partial spillover of hydrogen from platinum to the oxide and formation of a tungsten bronze, H WOj (0 < a < 1), which according to certain data has fair catalytic properties. 

Titanium carbide, TiC, is made by the action of carbon black on titanium dioxide at 2000 °C. It is the most important hard metallic material after tungsten carbide, and in fact is the hardest of all the metal carbides with a hardness rating of 9 on the Mohs scale - diamond is 10. In itself it is too brittle to be used pure but when mixed with the carbides of tungsten, tantalum and niobium it delivers great strength. 

The parameters of the electrical oxidation of hydrogen and reduction of oxygen were compared using the materials like AD-100 hydrophobic carbon-black, ASM 1/05 grade statically synthesized diamond submicron powders, tungsten and vanadium carbides. 

After tungsten carbide, titanium carbide, TiC, is the most important metallic hard material. It is manufactured from pure Ti02 and carbon black in induction furnaces at 2000 to 2200°C ... 

The reduction of tungsten oxides by carbon or carbon-containing compoimds can be easily performed. Statements about the starting temperature for the reaction between WO3 and solid carbon (carbon blacks, graphite) vary in the current literature between 655 °C and 783 °C. Differences in WO3 and C properties (particle size of the powders, preparation history, crystallinity, etc.) as well as in atmospheres may be responsible for that. The temperature range coincides with the begirming of self-conductivity and sublimation of WO3. Carbon monoxide starts to react witii WO3 at 535 °C (reduction pressure 1 bar, PcoJPco equilibrium ratio 8.52) [3.45]. 

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. 

Tungsten, chromium, molybdenum, nickel, and carbon black powders from Atlantic Equipment Engineers were between 1 and 5 p in diameter. Bulk MOjC from Sigma-Aldrich had a 44 p nominal diameter. Cu-Zn-Al was purchased from Sud-Chemie. 

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. 

Tungsten pentachlofide [13470-13-8], WCl, mp 243°C, bp 275.6°C, is a black, crystalline, deHquescent soHd. It is only slightly soluble in carbon disulfide and decomposes in water to the blue oxide, 200 2. Magnetic properties suggest that tungsten pentachlofide may contain trinuclear clusters in the soHd state, but this stmcture has not been defined. Tungsten pentachlofide may be prepared by the reduction of the hexachloride with red phosphoms (9). 

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