Abstract
The sintering of the α-alumina powder derived from aluminum sulfates which were precipitated from the solution containing 0.01 and 1mol% of sulfates of Sn, Mn, Ti and Cu was studied. The sinterability of these samples decreased in the following order;Sn>Mn>Ti>Cu>free from additives.The sinterability was little affected by the amounts of additive. By the SEM and porosimetry, it was proved that the differences in the sinterability of these powders were attributed to the differences in the structure of the green compacts. The powder compacts containing hard secondary particles have typical double structure which consists of small pores in a secondary particle and large pores between secondary particles.The samples with Cu and no additives had such a double structure, and showed a low sintered density. Such welldefined double structure was not observed in the compact of the powder containing Sn, which showed a higher sintered density. The formation of hard secondary particles can be ascribed to the strong bond of inner-particles. The bond strength may be affected by the following two factors; nucleation rate of γ→α transformation and the degree of interruption of contact between particles by the adhesion of additives on the particle surface.
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