The plasmochemical method has provided the means for developing an original technology of preparing nanometric powders, using installations processing from 5 to 80 kg/h of the raw material.

In the installation the reactants are fed into a stream of gas with a definite chemical potential and heated to a high temperature: in most cases >3000 K. The physical and chemical phenomena constituting the process transpire during a period <0.1 s. The particles range in size from 10 to 100 nm.

The installation provides for a whole series of technological processes producing nanometric powders of metals, refractory compounds, and complex metal - refractory compound compositions. The processes carried out include the preparation of tungsten by reducing tungsten oxide in hydrogen. The same installation can also serve to prepare molybdenum powders. It can just as readily reduce oxides of nickel and cobalt to prepare polydisperse spherical powders.

Powders from a number of other rare metals and refractory compounds have been obtained by using their chlorides as raw materials. Original metering pumps for liquid and gaseous chlorides, with a capacity of up to 10 kg/h, have been developed for feeding the chlorides into the high-temperature zone.

The nanometric powders of Та, Nb, W, Mo, Ni, Co, and other metals, prepared from chlorides, have a high degree of purity, a low scatter of particles in size (monodispersity), and an average particle size of 15 to 80 nm. In addition to this, a modification of the process developed for Ni and Co has yielded whiskers of metals up to 10 m m long and from 0.1 to 0.2 m m thick. Such metals have a specific surface of 100m²/g and more.

The mean size of the obtained refractory compounds - carbides, nitrides, and oxides of rare metals, aluminum, silicon, and boron - ranged from 6 to 50 nm. These compounds included WC, TiC, TaC, ZrC, HfC, B₄C, SiC, TiCN, NbN, HfN, Si₃N₄, and AIN. Photo are available of: Niobium carbide.

Nanometric powder compositions of the refractory compound - metal type, with varied proportions of the components, can also be prepared.

The low apparent mass of the nanometric powders (from 0.1 to 0.3 g/cm³) makes it possible to obtain powder compacts having a density no more than 0.2-0.4 of the theoretical. The caking temperatures of nanometric powders are 500 to 800° С lower than those of conventional-granularity powders, and the caking proceeds very quickly: in approximately 5 min. Thanks to the choice of caking modes, the porosity and the pore size of the caked material can be regulated with due account for the initial dispersity of the powder and the density of the mold. Thus, in the case of metal (Ni, Nb, Ta and W) and ceramic (NbC and B₄C) powders, the porosity was regulated in the range from 75% to <1%; the pore size, from 0.03 to 1-2 m m and more. Practically pore-free materials have been prepared by the method of hot pressing in a vacuum at temperatures several hundred degrees lower than in caking micron-size powders. Materials caked from nanocrystalline powders have a grain size of 80 to 300 nm and are therefore distinguished by superior mechanical properties. In the case of metals (Nb, Ta, and W), refractory compounds (TiC, NbC, TiCN, and Si₃N₄), and compositions (WC-Co).the set of mechanical properties is far superior to those of conventionally produced materials; for example, the s prod of NbC or hot-pressed Nb or Та is 3 to 4 times higher.

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