Preparation of ultrafine/nano Mo particles via NaCl-assisted hydrogen reduction of different-sized MoO2 powders

Abstract

The current study investigated the effects of the amount of NaCl addition, particle size of MoO2, temperature (under isothermal condition) and heating rate (under non-isothermal condition) on the morphology, particle size and dispersivity of prepared Mo by hydrogen reduction of MoO2. The formation of sufficient dispersed Mo nuclei and their controllable growth were crucial for transforming the large MoO2 particles to dispersed ultrafine/nano Mo particles. It was found that in the absence of NaCl, it was hard to control the nucleation and growth of Mo grains, and the morphology and particle size of products still retain those of the raw MoO2 in the temperature range of 840–1000 °C. However, as the amount of NaCl addition was above 0.05%, it was successful to control the nucleation and growth of Mo. Ultrafine/nano Mo powders with the average particle size from 100 nm to 800 nm were successfully prepared via adjusting the particle size of MoO2 and temperature under isothermal condition. The use of MoO2 with small particle sizes can increase the reaction rate and the number of Mo nuclei number, thus improve the particle dispersivity and decrease the particle size. Additionally, after reaction at 900 °C and 1000 °C, the residual Na was reduced to 140 ppm and 33 ppm from the initial value of 380 ppm, respectively. Under non-isothermal condition, the temperatures for the nucleation and growth could be adjusted by changing heating rate and particle size of raw MoO2 particles. Mo nanoparticles with smaller particle size and better dispersivity were successfully prepared, and the average particle size can decrease to about 80 nm.