Optimal Densification of Ceramics by Rate Controlled Sintering

The rate controlled sintering behavior of approximately 99.9% Al2O3 has been studied in comparison with conventional firing methods. Several lots of (a) chemically prepared and (b) superground aluminas (with and without MgO doping) were carefully characterized by transmission electron microscopy, spectrochemical, x-ray, sedimentation and residual gas analyses, surface area determinations and dynamic differential calorimetry. Process steps which preceded firing exerted important influences upon densities, microstructures and strength levels attained after densification by conventional or rate controlled sintering regimes. Investigations and sequential optimizations of a number of process steps, including milling, binder addition, remilling, granulation, dry pressing, and binder burnout are described. Under rate control, grain growth in the intermediate sintering range was found to be a function only of fractional density.