On the removal of organic vehicle from moulded ceramic bodies

Abstract

The origin of defects in moulded ceramic bodies during pyrolytic removal of the organic vehicle is predicted. The kinetics of thermal degradation of the polymer are combined with a nonlinear, numerical model for the unsteady-state diffusion of degradation products in solution in the parent polymer. The resulting centre concentration of monomer in an infinite cylinder is used to predict the incidence of boiling which results in the formation of internal defects in the ceramic body. The calculation, which incorporates the concentration dependence of the diffusion coefficient based on free volume theory, reveals the outcome of the competition between degradation and diffusion and thus allows the influence of material, geometric and process variables to be explored.