12 - Sintering Additives and Defect Chemistry

Abstract

Sintering additives are usually added to powders in an attempt to enhance the sinterability and to control the microstructure. For the most part, the roles of sintering additives are only known empirically and their mechanisms are not well understood. This chapter considers the point defects formed by the addition of sintering additives in ionic compounds with low-defect concentrations. For a low concentration of point defects, it is assumed that the matrix atoms and point defects form an ideal solution with no interaction between defects. It may also be assumed that the concentration of matrix atoms is 1. In this case, the estimate the concentration of point defects caused by dopant addition can easily be calculated. Therefore, in the case of lattice-diffusion controlled sintering, the estimation can explain the change in sinterability with dopant addition. The concentrations of point defects in ionic compounds vary with the concentration of dopants. The defect concentrations can be predicted using defect chemistry, where each defect species is considered to be a chemical species and the reactions among defects are expressed as chemical reaction equations.