Factors influencing the kinetics of electrochemical reactions in milling

Input of mechanical energy at a high rate can drive a system and induce phase transformations and chemical reactions away from equilibrium. The evolution of such a change depends on both thermodynamic as well as kinetic factors. Besides the microstructural changes like attainment of nanostructure, which alters the overall free energy, the high rate of mechanical energy input also changes the kinetics by influencing the mass transport and related processes. In order to understand these factors, we have recently started a programme of looking at the influence of mechanical energy on driving simple chemical reactions in solid state. In this presentation we shall present and discuss the results of two kinds of situation that we have studied. The first one is simple electrochemical replacement reactions between metals and metal sulphates in solid state. We show that the mechanical milling alters the kinetics of these reactions, which can be rationalized by considering the phenomena taking place at the microscopic level. For example we will show that the crystal structure of the sulphate and the nature of the reaction product at the interface influence the mechanochemistry significantly. It is even possible in some special cases to alter the direction of the chemical reaction. In the second set of results we shall present the effect of mechanical milling on the site occupancy in ferrites, which can lead to a significant change in magnetic behaviour