Effects of Sintering Processes on Microstructure Evolution, Crystallite, and Grain Growth of MoO₂ Powder

MoO2 micro-powders with a mean pore size of 3.4 nm and specific surface area of 2.5 g/cm(3) were compacted by dry pressing, then pressureless sintered at a temperature of 1000-1150 degrees C for 2 h or for a sintering time of 0.5-12 h at 1050 degrees C in an N-2 atmosphere. Then, their microstructure evolution for morphology, crystallite, and grain growth were investigated. By sintering at a certain temperature and times, the irregular shape of the MoO2 powders transformed into an equiaxed structure, owing to the surface energy, which contributed to faster grain growth at the initial stage of sintering. The crystallite and grain sizes exponentially increased with the sintering time, and the growth exponent, n, was approximately 2.8 and 4, respectively. This indicates that the crystallite growth is governed by dislocation-mediated lattice diffusion, and the grain growth is determined by surface diffusion-controlled pore mobility. The increase in sintering temperature increased both crystallite and grain size, which obeyed the Arrhenius equation, and the activation energies were determined to be 95.65 and 76.95 kJmol(-1) for crystallite and grain growths, respectively.