Abstract
Two kinds of commercial, submicron-grained, nondoped α-alumina powders were cold-isostatically pressed and then sintered at a constant heating rate. Before the sintering, pre-treatments were executed at 820 or 920 ° C for 50 h. The effects of the pretreatments on the densification behavior and the microstructural development are discussed. The powders contained some nano-sized alumina particles about 10 nm in diameter as well as sub-micron-sized primary particles about 0.1 μm in diameter, which agglomerated in packs of 0·2–0·4 μm diameter. The densification rate curves showed a low temperature shoulder during sintering attributed to these nano-sized particles. After pretreatments, the nano-particles disappeared, resulting in disappearance of the shoulder in the subsequent densification rate curves. These treatments, however, caused little change in the apparent activation energy in the intermediate stage sintering. For the weakly agglomerated powders, the bodies sintered with pre-treatments had coarser final microstructures.
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