Macrokinetics of mechanochemical synthesis in heterogeneous systems: Mathematical model and evaluation of thermokinetic constants

Abstract

The paper introduces the concepts of the new macrokinetic theory of mechanical activation and mechanochemical synthesis, focusing on three main factors of acceleration of mechanochemical reactions: kinetic, structural and thermal. Based on the macrokinetic theory a mathematical model is proposed for quantitative evaluation of kinetic and thermophysical constants that characterize the stage of mechanical activation in the systems Ti–Ni, Ni–Al and titanium powder, as well as determine two-stage mechanochemical synthesis in the Nb–Al system. The role of the main factors of mechanical activation in the acceleration of synthesis of niobium aluminide is shown. It is revealed that with increasing the time of preliminary mechanical activation of the Nb+Al powder mixture, the ignition temperature and the total synthesis time of final product decrease, while the thermal reaction effect increases due to additional heat release caused by normalization of the substance structure during chemical conversion. The leading role of the structural factor, determined by the formation of the interface, for the synthesis of aluminide from mechanically activated compositions has been revealed.