Study on the Reduced Powders of W and Mo by Electronmicroscope

By carbon replica method, an observation was made, under electron microscope, of the shape, surface condition and the state of aggregation of the particles of W and Mo powders prepared by hydrogen reduction.As a result, it wass observed that the primary particles of W less than 0.2μ in diameter were of sphere form and, of larger diameter, of well developed crystal form. On particles of over 2μ in diameter, a lot of octahedral and rhombic dodecahedral particles were observed and some of them looked like cubic particles. At high reduction temperature, dumbbell-shaped particles were observed, primary particles of Mo also showed similar crystal shape when the particle diameter exceeded 1μ.Immediately after the powder is being reduced, the surface of particle was relatively smooth, but when oxidized, small projections or needle oxide were observed on it. On the surface it was also observad that the doping materials were deposited.When the primary particles were small they were linked with each other, resulting formation of aggregates, which resembled in shape with original crystals of their mother salts. As the size of the primary particles increased over 2μ, the aggregate lost their original shape.Doping materials affect the growth of particlces, and as a result of observation it was found that the size of undoped particles is almost uniform and that KC1 has little effect on the size of particles but K2O⋅2SiO2 doped particles results in large and small particle sizes and Al2O3 or TnO2 retards the particle growth. When KCl, K2O⋅2SiO2 and Al2O3 are used at the same time that cause spread in the distribution. It was learned by etching the particles that primary particles observed by electron microscope were substantially single crystals.