DETERIORATION OF A CLASSICAL FINAL-STAGE MICROSTRUCTURE - A STUDY IN ALUMINA

Classical final-stage microstructures have been obtained in an ultra-high-purity alumina by a latex sphere impregnation and burnout technique. The isolated equilibrium-shaped pores produced by the latex spheres deteriorated during long-term, high-temperature annealing under reducing atmospheres to produce a cracklike interconnected pore network. Several mechanisms of degradation are considered, including (i) the influence of entrapped gases, (ii) the effect of stresses produced during differential sintering, and (iii) the kinetics of competing mass transport mechanisms. Results suggest that the degradation is an inherent microstructural instability promoted by enhancing the ratio of coarsening rate/densification rate. Furthermore, it is shown that magnesia additions inhibit the process of microstructural deterioration.