Investigation of the sintering of zirconia

Abstract

We investigated the sintering of zirconium dioxide as a function of the activity of the starting material. It was shown that preliminary firing or stabilization of zirconium dioxide reduces its capacity for densification at temperatures of up to 1500°C, while stabilizing it directly during sintering intensifies this capacity. The prestabilized zirconia has the lowest sintering rate. Introducing monoclinic unfired zirconia into the prestabilized material intensifies sintering; the optimal addition is 30%. It is established that the zirconia is sintered by volume diffusion of vacancies. We investigated the sintering of active zirconia obtained by decomposing zirconium nitrate. The greatest degree of densification is obtained with a preliminary short heat processing of the nitrate at 400°C. Activation is connected with the formation of metastable tetragonal and cubic modifications with defect crystal lattices. Increasing the heat-process temperature of the nitrate or prolonging the soak at 400°C, leading to the formation of stable monoclinic ZrO2 with an ordered crystalline lattice, impairs sintering. Incorporating small additions of active ZrO2 in the industrial material, and providing rapid firing in an oxidizing atmosphere, greatly increases the degree of sintering. Introducing stabilizing additives intensifies sintering. The maximum densification is obtained by the formation of 60–70% solid solution. Further increase in these additions reduces the shrinkage and densification of the specimens.