Pulse Electric Current Sintering and Strength of Sintered Alumina Using .GAMMA.-Alumina Powders Prepared by the Sol-Gel Method

Alumina ceramics were densified by pulse electric current sintering (PECS) using γ-alumina powders prepared from polyhydroxoaluminum-polyvinylalcohol(PHA-PVA) composite gels at sintering temperatures of 1250-1550°C under uniaxial pressure of 30 MPa. The γ-alumina powders used for PECS were calcined at 800-1000°C and then ground by planetary ball milling. Optimization of calcination temperature of the composite gels, densification and bending strength of sintered aluminas were investigated. The sintered compact obtained by PECS at 1350°C using the sample powders thus prepared had the advantage of a high density of more than 99% of theoretical density. The use of a single phase of γ-alumina powders made the densification temperature shift to lower temperatures, as compared with the use of sample powders consisting of γ- and χ-alumina. Aggregates of γ-alumina showed no preferential crystallographical orientation between their primary particles while those of γ- and χ-alumina showed the existence of a strong orientation among their primary particles, despite their mixed phases. This difference in both powders might have an influence on sinterability of the transition alumina powders. The inclusion of fine α-alumina particles, which were derived from wet grinding abrasion powders with wearing in planetary ball milling, had also a significant effect on densification due to a seeding effect, lowering the γ- to α-alumina transformation temperature. The bending strength of sintered compact fired at 1350°C reached a value as high as 850 MPa using a sample powder calcined at 950°C.