Influence of water vapour and tin additive on the stabilization of zirconia phases and on its densification by sintering

By sintering has been prepared pure and compact monoclinic zirconia treated with steam. The perfecting of the treatment of this powder has required a preliminary study of the influence of the three following parameters: 1)the calcination temperature 2)the duration of the heat treatment 3)the atmosphere of steam. These three parameters have an effect on the evolution of the crystal size but on the ratio of the monoclinic and quadratic phases of the zirconia too. A particular pressure and temperature cycle has been used for sintering in an inert atmosphere, following by a post-treatment by hot isostatic compaction. 97% densification sintered products have been obtained by this method. The presence of tin in the sub-stoichiometric thermal zirconia obtained by zircaloy-4 oxidation, has been connected to those of the quadratic phase. The different amounts of tin (0.78 to 1.58% of tin) tested in Zy-4 correspond to about 5% of quadratic phase bound to the sub-stoichiometric monoclinic phase. The sintering in an inert atmosphere of fragments of these products leads to dense products having a relative density of 98%, and whose mechanical properties are very similar to those of the pure stoichiometric zirconia treated with steam. (O.M.)