Sintering of high alumina ceramics with ZrO2 inclusions

Abstract

High performance technical ceramics of high alumina are used in several applications such as mechanical seals, thread guides, pulleys, cylinder jackets, pistons, among others. They are usually produced with alumina powders obtained by the Bayer process and sintered with additives that forms vitreous phases. The composites of alumina-zirconia belong to a class of higher performance stands products. The ZrO2 added in small amount to high alumina ceramics, as a insoluble second phase in the grain boundaries, acts during sintering as a grain growth inhibitor and accordingly, they are additives of sintering that improve final densification to near the theoretical density. This work aims to obtain alumina composites with zirconia inclusions in order to improve the performance of conventional technical ceramics of high alumina. Two commercial alumina powders were used in the experimental work, one of then obtained from a coarse normal soda calcined Bayer alumina by milling to increase sinterability and the other a reactive low soda alumina. Compositions were prepared with talc (1%) and zirconia (2 and 5%) additions and sintered at 1500, 1550 e 1600oC. The samples were characterized by density measurements and microstructure analyses. It was shown that the beneficial effects of each type sintering additive are complementary and that a small amount of zirconia is effective in prevent grain growth and increase final densification.