THE CHEMICAL-KINETICS OF MECHANICAL ALLOYING

The chemical kinetics of a mechanically induced double displacement reaction exhibiting a self-sustaining combustion event have been investigated using differential thermal analysis. In particular, the effect of milling time on the activation energy for the reduction of cupric oxide by iron has been evaluated. It has been shown that the activation energy decreases from 575 kJ/mol at the start of milling to 199 kJ/mol at combustion. This is an indication that the rate-controlling step changes during milling from intrinsic ionic diffusion initially to diffusion down short-circuit pathways prior to combustion. It is suggested that this is dependent on the rate at which strain accumulates in milled powders and is hence a consequence of the mechanical alloying action.