Preparation of ultrafine particles of refractory metal carbides by a gas-evaporation method

Abstract

In an atmosphere of rarefied inactive gas a carbon rod is mounted vertically with its bottom end touching the top surface of a block of refractory metal. By applying a heavy electric current through the carbon-metal junction, a smoke of metal carbide is produced. The smoke particles are examined by electron microscopy and electron diffraction. The particle diameter is always less than 1 μm. In the case of Si, particles of β-SiC (cubic type) are mixed with those of pure Si. For Ti, V and Zr, Debye rings shows that the particles are of NaCl-type. The lattice parameter is 4.27 Å for Ti and 4.21 Å for V, each of which roughly agrees with that of the stoichiometric carbide. The lattice parameter for Zr is found to be 4.47 Å, which is several percent lower than that of stoichiometric ZrC. Particles of chromium carbide have a complex structure which is analysed to be of the form Cr 7 C 3 with hexagonal structure. For Hf, Nb, Mo, Ta and W, crystalline carbide particles are not yet obtained.