Pulse Electric Current Sintering and Strength of Sintered Alumina Using Transition Alumina Powders Prepared from Polyhydroxoaluminum Gel.

Alumina ceramics were densified by pulse electric current sintering (PECS) using transition alumina powders at temperature range of 1250-1550°C for holding time of 3 min under uniaxial pressure of 30 MPa. The transition alumina powders used for PECS were prepared from polyhydroxoaluminum(PHA) gels, which were calcined at 800-1000°C and then ground by planetary ball mill. Optimization of calcination temperature of PHA gels and sintering conditions of PECS were investigated. The PHA gels were transformed into transition aluminas consisted of γ- and χ-alumina at 800-950°C and partly into α-alumina at 1000°C. The sintered compact obtained by PECS at 1400°C using the sample powders thus prepared had an advantage of a higher density of more than 99% of theoretical density, as compared with that using commercially available γ-alumina powders. Densification of the sintered compacts depended on the calcination temperature of the powder samples; the sintered compacts were more densified as the calcination temperature increased. The inclusion of fine α-alumina particles, which were derived from wet grinding abrasion powders with wearing in planetary ball milling, had a significant effect on densification due to the seeding effect, decreasing the γ- to α-alumina transformation temperature. The bending strength of sintered compact fired at 1400°C reached a value as high as 740 MPa using the sample powders calcined at 900°C.