CONSOLIDATION OF ALUMINA ZIRCONIA MIXTURES BY A COLLOIDAL PROCESS

The relationship between the dispersion of colloidal powder particles in Al2O3-ZrO2 suspensions and the microstructures of consolidated compacts was examined. Suspensions were prepared from Al2O3 powder and ZrO2 sol with average particle sizes of 390 and 62 nm, respectively. The dispersion was controlled by pH and salt concentration adjustments. The compacts composed of completely separated Al2O3 and ZrO2 layers were obtained from well-dispersed suspensions with pH values below about 4 and salt concentration of 0.0527M. An increase in pH or salt concentration resulted in macroscopically uniform compacts. The compacts made from suspensions with pH values above about 7, however, were composed of a mixture of Al2O3 and ZrO2 agglomerates, with one acting as a matrix and the other a dispersed phase. Suspensions with a pH value of 4.5 and optimum salt concentrations resulted in compacts with microscopically uniform microstructure. Above or below these salt concentrations, ZrO2 agglomerates were distributed in an Al2O3 matrix. The optimum concentration was dependent on solid content. In addition, the dispersion of mixed suspensions was compared with those of single-component suspensions. The ZrO2 particles formed three-dimensional networks during agglomeration, which reduced the component separation in suspensions and during consolidation.