Characteristics of Al2O3/ZrO2 Ceramics by the Dispersion Process of ZrO2 Particles

For the homogeneous dispersion of ZrO2 particles in Al2O3/ZrO2 ceramics, Zr-precusors were mixed with oxide Al2O3 powders by chemical routes such as partial precipitation or partial polymerization of Zr-nitrate solutions. In case of the mechanical mixing of ultrafme Al2O3 and ZrO2 oxide powders, relatively homogeneous dispersion was difficult to achieve so that the particle size and distributions of ZrO2 were relatively inhomogeneous after sintering at high temperature. But when the Zr-Y-hydroxide were co-precipitated to ultrafme Al2O3 oxide powders followed by calcinations, homogeneous dispersion of nano-sized ZrO2 particles in Al2O3/ZrO2 composite ceramics were obtained. But because of the coalescence of dispersed ZrO2 particles, dispersed ZrO2 was grown up to more than 0.2 mu m (200 nm) when sintered at the temperature of higher than 1500 degrees C. But when the sintering temperature was kept to lower than 1400 degrees C by using nano-sized alpha-alumina, the particle size of dispersed ZrO2 could be sustained below 0.1 mu m. But the coalescence of dispersed ZrO2 between Al2O3 particles could not be avoided so that the mechanical properties were not enhanced contrary to the expectations. So Zr-polyester precursors were precipitated and coated to the surface of ultrafine alpha-alumina powders by the polymerization of Ethylene Glycol with Citric Acid and Zirconium Nitrate. By this dispersion much more uniform dispersion of ZrO2 was achieved at 1450 similar to 1600 degrees C of sintering temperature ranges. And due to especially discrete dispersion of ZrO2 between Al2O3 particles, their mechanical strength was more enhanced than mechanical mixing or hydroxide precipitation methods.