PARTICLE CONTACT BEFORE FIRING

If our picture of the unfired ceramic body is of the classical three-s phere sintering model repeated in space we have deployed the fallacy, of composition. Most fabrication routes can produce non-uniform densit y and regions of reduced coordination which will mature into defects u nder conditions of differential or restrained shrinkage. Injection mou lding and the related plastic forming processes are particularly vulne rable because of the almost complete absence of particle contact durin g shaping which is essential for the flow of suspensions. Between the end of shaping and the beginning of sintering a series of mechanisms c an lead to heterogeneity and anisotropy in the arrangement of particle contacts. These include the relaxation of stress and of orientation i n the organic vehicle, flocculation and the non-uniform loss of organi c vehicle from junctions. (C) 1996 Elsevier Science Limited.