Abstract
Ultrafine (< 100 Å) and high purity (99.99%) powders of mullite (3 Al203 · 2 Si02), Zyttrite ® (Y203 stabilized Zr02), and alumina-zirconia (58 wt. % Al203) were prepared from appropriate organo-metalllic precursors. The materials were dried at 125°C and then calcined at 550°C for 112 to 3 hours and cooled in desiccators in order to minimize the absorption of moisture. The calcined mullite and Zyttrite® and noncalcined alumina-zirconia powders were isostatically pressed up to 60,000 psi (4222.2 kg/cm2) and sintered at up to 1500°C using two different sintering pathways: (1) one-step sintering at up to 1500°C and (2) multi-step sintering (sintered at 1100°C, cooled, resintered at 1300°C, cooled, and finally sintered at 1500°C). Results show that these ultrafine powders sinter to 95% + theoretical density at 1500°C, irrespective of sintering pathways. Sintered materials showed a uniform grain size and change in the sintering pathways from one-step to multi-step has little or no effect on the grain size or microhardness. Surface reactivity of these powders is neither diminished nor increased by variation in the sintering pathways and thus the densification is dependent mainly on the final sintering temperature.
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