Synthesis of nanocrystalline molybdenum by hydrogen reduction of mechanically activated MoO3

Nanocrystalline molybdenum with a mean crystallite size of 50 nm was synthesized by mechanical activation of MoO3 powder and its subsequent hydrogen reduction. MoO3 powder was severely activated in a high energy planetary ball mill under a pure argon atmosphere. Temperature-programmed reduction (TPR) by hydrogen was used to investigate hydrogen reduction behavior of the powder samples activated for 5 and 20 h. It was found that by increasing the activation time, the peak temperature for the reduction was shifted slightly to lower temperatures and the peak for the reduction of MoO3 to MoO2 was completely separated from the one for the reduction of MoO2 to molybdenum. In order to evaluate the effect of mechanical activation on the reduction behavior of MoO3, the initial micron-sized powder and the sample activated for 20 h were reduced at similar conditions. It was found that the activated sample with finer particles was reduced faster than the un-milled sample. Hydrogen reduction of the non-activated MoO3 produced a very fine grained molybdenum powder but the crystallite size changes of the sample activated for 20 h was negligible during reduction. (C) 2011 Elsevier Ltd. All rights reserved.