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 a s 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 dispe rsed 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. Th e chemical reaction between ZnO and Al2O3 occurred prior to densificat ion of the powder compact and was accompanied by fairly large expansio n, 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 r ate of the compact formed from the chemically precipitated mixture was almost identical to that for the ZnAl2O4 powder. The difference in si ntering between the ball-milled mixture and the chemically precipitate d mixture is interpreted in terms of differences in the microstructura l uniformity of the initial powder compacts resulting from the differe nt preparation procedures.