THERMODYNAMIC EFFECTS ON THE KINETICS OF VACANCY-GENERATING PROCESSES

Abstract—The inhibiting eect of vacancies on the very process in which they are generated is considered from a thermodynamic viewpoint. Examples of such processes treated here in some detail are grain growth and pore dissolution. It is shown that these processes are inhibited due to vacancy generation. A particular scenario discussed implies intermittent ‘‘locking’’. After a period of uninhibited kinetics the process comes to a halt due to a thermodynamic back force ‘‘locking’ ’ it. It can only re-start once the vacancies produced are removed by diusion. This repetitive cycle leads to an overall reduction in the rate of the kinetic pro-cess in question. Specific predictions with regard to grain growth in fine-grained (particularly nanocrystal-line) materials and void dissolution kinetics in sintering are made. A third example considered is vacancy drag on a moving individual grain boundary. The magnitude of the drag is re-assessed by taking int