Reaction sintering of ZnO-Al2O3

The reaction sintering of equimolar mixtures of ZnO and Al2O3 powders was investigated as a function of primary processing parameters such as the temperature, heating rate, green density, and particle size, The powder mixtures mere prepared by two different methods, In one method, the ZnO and Al2O3 powders were ball-milled. In the other method, the ZnO powder was chemically precipitated onto the Al2O3 particles dispersed in a solution of zinc chloride, The sintering characteristics of the compacted powders prepared by each method were compared with those for a pre-reacted, single-phase powder of zinc aluminate, ZnAl2O4. The chemical reaction between ZnO and Al2O3 occurred prior to densification of the powder compact and was accompanied by fairly large expansion, The mixing procedure had a significant effect on the densification rate during reaction sintering, The densification rate of the compact formed from the ball-milled powder was strongly inhibited compared to that for the single-phase ZnAl2O4 powder. However, the densification rate of the compact formed from the chemically precipitated mixture was almost identical to that for the ZnAl2O4 powder. The difference in sintering between the ball-milled mixture and the chemically precipitated mixture is interpreted in terms of differences in the microstructural uniformity of the initial powder compacts resulting from the different preparation procedures.