Particle contact before firing

Abstract

If our picture of the unfired ceramic body is of the classical three-sphere sintering model repeated in space we have deployed the fallacy of composition. Most fabrication routes can produce non-uniform density and regions of reduced coordination which will mature into defects under conditions of differential or restrained shrinkage. Injection moulding and the related plastic forming processes are particularly vulnerable because of the almost complete absence of particle contact during shaping which is essential for the flow of suspensions. Between the end of shaping and the beginning of sintering a series of mechanisms can lead to heterogeneity and anisotropy in the arrangement of particle contacts. These include the relaxation of stress and of orientation in the organic vehicle, flocculation and the non-uniform loss of organic vehicle from junctions.