Understanding mechanical energy driven nonequilibrium processing: some results

A large number of nonequilibrium processes for synthesizing metastable materials use mechanical energy for driving the process. The mechanical energy can also alter chemical reactions in a significant manner. In order to understand the role of mechanical energy we have initiated a program of research to explore basic processes behind the mechanical energy induced changes by designing experiments using simple systems. We show that milling leads to both the enhancement of the thermodynamic driving force and the transport kinetics. The former is achieved through reduction in length scale and possible breaking of the bonds. The defects also enhance kinetics. The relative importance of these two factors depends on the system being studied. Analysis of mechanochemical reactions using simple electrochemical replacement reactions involving ionic bonds elucidates the roles of thermodynamics and kinetics. Finally, it is shown that under certain conditions, it is possible to induce reverse reaction by mechanical milling. (C) 2003 Elsevier B.V. All rights reserved.