Exploring nucleation mechanisms in the hydrogen reduction of MoO2 to Mo

The nucleation of various MoO 2 starting materials was investigated on a laboratory scale during the second reduction step from MoO 2 to Mo of the two-step reduction process from MoO 3 to Mo. It was found that a certain proportion of γ -Mo 4 O 11 or a higher potassium content in the MoO 2 samples as well as the addition of water to the hydrogen gas stream led to a shift from the pseudomorphic transformation towards the CVT process at a low reduction temperature of 900 °C. Not only spherical/polyhedral Mo nuclei but also rod-shaped nuclei were detected for the first time using the γ -Mo 4 O 11 containing MoO 2 starting material after a short reduction time and subsequent cooling in Ar gas flow. The influence of an increased potassium content in the γ -Mo 4 O 11 containing MoO 2 samples on the nucleation was also investigated. Additionally, a mechanism for the formation of the rod-shaped nuclei is proposed. • Investigation of the nucleation behaviour and influence on the grain transformation mechanism of different MoO 2 starting materials during the second reduction step from MoO 2 to Mo. • Detection of unknown rod-shaped nuclei and detailed investigation of their formation and chemical composition. • Proposal of a mechanism for the formation of the rod-shaped nuclei.