LAUSR

Alumina based ceramics used as insulators for extremely cold areas were fabricated via pressureless sintering technique from α-Al2O3, PSZ, MgO, and TiO2. The effects of MgO, TiO2, zirconia on physical properties, phase transformation, microstructure and freeze-thaw resistance of the composite ceramics were investigated. The results indicated that the composite ceramics exhibited the excellent physical properties. The addition of MgO and TiO2 promoted the sintering process, improved the strength and decreased the sintering temperature by at least 140 °C when comparing with the sintering of pure alumina. The increase in the content of zirconia improved the bulk density and bending strength at the same sintering temperature. Especially, sample A5 (80 wt% α-Al2O3, 20 wt% PSZ, additional 1 wt% MgO and 1 wt%TiO2) sintered at 1580 °C exhibited the optimum freeze-thaw resistance after 30 freeze-thaw cycles (from −50 °C to 40 °C) with a bending strength decreasing rate of 13.82%, which reduced 37.38 MPa. Even so, it still maintained the high strength and dense structure. The strength loss after freeze-thaw could be attributed to the phase transformation of tetragonal zirconia to the monoclinic zirconia and the increase in the number and size of pores. It is believed that alumina based ceramics can be promising candidate materials to be used as insulators for extremely cold areas.