Tungsten metal powder properties

The capability of retaining water vapor within the layer is to a certain extent the reason why it can be used as a steering parameter for the final tungsten metal powder properties. The water vapor retention capacity of the layer depends on the layer height and its porosity. The layer height can be chosen within limits in connection with the temperature. The porosity depends on the oxide powder properties. The macroporosity is a consequence of the agglomerate size of the oxide powder (which is related to the size of the crystallized APT particles prior to decomposition) and the microporosity is due to... 

One important class of particulate composites is dispersion-hardened alloys. These composites consist of a hard particle constituent in a softer metal matrix. The particle constituent seldom exceeds 3% by volume, and the particles are very small, below micrometer sizes. The characteristics of the particles largely control the property of the alloy, and a spacing of 0.2-0.3 tim between particles usually helps optimize properties. As particle size increases, less material is required to achieve the desired interparticle spacing. Refractory oxide particles are often used, although intermetallics such as AlFes also find use. Dispersion-hardened composites are formed in several ways, including surface oxidation of ultrafine metal powders, resulting in trapped metal oxide particles within the metal matrix. Metals of commercial interest for dispersion-hardened alloys include aluminum, nickel, and tungsten. 

The oxide hydrate is responsible for the chemical vapor transport of tungsten, which occurs throughout the reduction sequence, a"d which decisively codetermines the physical and chemical properties of the metal powder. Its actual partial pressure during reduction will depend on both the temperature and the prevailing humidity. It will be lower toward the end of reduction, due to the steady decrease in the oxygen partial pressure (humidity) of the system as the reduction proceeds. 

Che] Chemienko, V.V., Martyukhin, I.D., Effect of Niobium, Molybdenum, and Tungsten on Some Properties of Iron-Boride Materials , Sov. Powder Metall. Met.Ceram., 19(2), 135-138 (1980) (Experimental, 5)... 

Kiparisov, S.S., Shvetsova, G.A., Lobova, T.A., Sergeeva, L.M., Pimenova, A.Z. and Volodina, G.A., Structure and Properties of a Self-Lubricating Material Based on Tungsten Diselenide, Soviet Powder Metallurgy and Metal Ceramics, 17, 399, (1978). 

The most important property of tungsten carbide in its utilization in cemented carbides is its ability to dissolve partially in compressed powder mixtures of WC and ferrous metals, particularly cobalt, at 1300 to 1500°C. In the case of sintering with a liquid phase, WC partly crystallizes out of the binder phase of the WC-Co-alloy upon cooling. It becomes embedded in the tough but hard (not brittle) binder phase. 

A further characteristic of metals that is usually given is that, in the solid state, they are malleable (easily hammered into sheets) and ductile (easily drawn into wires). By contrast, nonmetals in the solid state are brittle and easily powdered. In practice, however, while the majority of elements that are metallic according to the above criteria are indeed malleable and ductile, there are a few that do not have this property, even when ultra-pure. (Slight traces of impurity can produce brittleness in metals. Thus, ordinary commercial tungsten is so brittle that it can only be worked with difficulty, whereas the ultra-pure metal can be cut with a hacksaw, turned, drawn, or extmded.) Since the exceptional elements include some whose metallicity has never been questioned - e.g. manganese, cobalt, and zinc - it seems better not to make malleability and ductility a characteristic of metals, but rather a property possessed by most of them. 

Molybdenum is a metal with chemical properties similar to those of chromium but, unlike chromium, it is soluble in dilute nitric acid. The metal is used chiefly for alloying of steel. Wire made from the pure element is used to carry the glowing tungsten filament in incandescent lamps. MoS is a black powder that crystallizes Hke graphite and is, because of that, an essential component in solid lubricants, which can be used at much higher temperatures than conventional lubricants. 

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