OVERALL SHAPE OF SINTERED ALUMINA COMPACTS

The extent of the thermally induced shrinkage during sintering of nomi nally homogeneous ceramic compacts depends upon the green density; com pacts with a low green density shrink more than those with a higher de nsity. Therefore, shape distortions of compacts with variable density during their sintering is inevitable. The overall shapes of various si ntered alumina compacts, prepared using different types of alumina agg lomerates, is described. The agglomerates were prepared using organic polymer [poly(vinyl alcohol) (PVA) and poly(ethylene glycol) (PEG)] bi nders and the influence of the particle agglomerates size and the wate r content in the agglomerates is considered. The extent of the shape d istortions in the cylindrical sintered compacts were reduced with the application of lubricants to the die walls. The agglomerate properties are shown to affect the overall shape of the sintered compacts signif icantly. The compacts, produced using the wet (plastisized) agglomerat es, have the smallest shape distortions. A prediction of the sintered shape evolution is obtained using a first order model. The model predi cts that the shape distortions in the sintered compacts increase with the increasing of the sintered density and a good agreement between th e predicted and measured data is demonstrated. (C) 1997 Elsevier Scien ce Limited and Techna S.r.l.