Carbides of tungsten

Carbide-based cermets have particles of carbides of tungsten, chromium, and titanium. Tungsten carbide in a cobalt matrix is used in machine parts requiring very high hardness such as wire-drawing dies, valves, etc. Chromium carbide in a cobalt matrix has high corrosion and abrasion resistance it also has a coefficient of thermal expansion close to that of steel, so is well-suited for use in valves. Titanium carbide in either a nickel or a cobalt matrix is often used in high-temperature applications such as turbine parts. Cermets are also used as nuclear reactor fuel elements and control rods. Fuel elements can be uranium oxide particles in stainless steel ceramic, whereas boron carbide in stainless steel is used for control rods. 

Similar results were found for the decomposition on surface carbides of tungsten. The W(IOO) surface reconstructs to form a W(IOO) (5 x 1)C structure, as shown in Fig. 2. This structure has been interpreted to be a hexagonal layer of W2C on top of the (100) surface 110) with the carbon atoms in interstitial positions under the first layer of tungsten atoms 111). The presence of the carbon atoms strongly modified the reactivity of the surface. Rather than dissociating formic acid completely like W(IOO), the carbide surface selectively formed the formate. The decomposition proceeded at 540 K with... 

Carbides of tungsten, titanium, tantalium Manufacture of cutting edges on tools Pulmonary fibrosis... 

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. 

C) and carbon (3600° C). The carbides of tungsten and vanadium are not appreciably softer than diamond itself. The compositions of the more stable carbides generally approach M1C1 (where M is the metal). However, as with the interstitial hydrides, the solid phase may appear homogeneous even though less than the stoichiometric amount of carbon is present. 

Thermally sprayed and hot isostatically pressed (HIP) coatings, including nickel and iron-base materials, with a high content of the carbides of tungsten, chromium, and titanium, deposited 5 mm (0.2 in.) or more thick... 

Besides the material based characteristics, the difference of density of the used particle/substrate combination is a very important criterion. The difference of density influences the contrast of the radiographic tests. Tungsten carbides were used as mechanically resistant particles and titanium based alloys as substrate. The substrate material is marked by an advantageous relation of strength to density. This material is often used in aeronautics, astronautics, and for modification of boundary layers. The density of tungsten carbide (15.7 g/cm ) is about 3.5 times higher than the density of titanium (4.45-4.6 g/cm ). 

Nitrogen and carbon are the most potent solutes to obtain high strength in refractory metals (55). Particulady effective ate carbides and carbonitrides of hafnium in tungsten, niobium, and tantalum alloys, and carbides of titanium and zirconium in molybdenum alloys. 

A wide apphcation of electrochemical grinding is the production of tungsten carbide [12070-12-1] cutting tools (see Carbides Tool materials). ECG is also useful in the grinding of fragile parts such as hypodermic needles and thinwaH tubes. 

Ha2ards encountered with tungsten may be caused by substances associated with the production and use of tungsten, eg. As, Sb, Pb, and other impurities in tungsten ores, Co aerosols and dust in the carbide industry, and thoria used in welding electrodes. Lanthanum is being promoted as a substitute for thoria in this appHcation. 

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