Formation of the monoclinic zirconia phase by heating from hydrous zirconium oxide

Abstract

The X-ray amorphous hydrous zirconium oxide (ZrO2 . nH2O) obtained by precipitation is an interesting substance because it is the precursor for the technically important pure and doped ZrO2 materials [1]. The crystallization of ZrO2 . nH2O to the metastable tetragonal ZrO2 phase (t-ZrO2) takes place during heating at approximately 400 8C. The t-ZrO2 phase transforms itself, by appropriate heat treatment, to monoclinic zirconia (m-ZrO2), which is thermodynamically stable up to 1200 8C. The martensitic t-ZrO2 ! m-ZrO2 phase transition of powdered materials has been discussed extensively in the literature [1±11]. The role of the surface energy of both phases or the strains [1, 2], the cationic [3, 4] and anionic impurities [5±8], the structural similarity of t-ZrO2 and ZrO2 . nH2O [9] and the precipitation and=or heating conditions [10, 11] have been described in detail. The complicated processes accompanying the formation of the monoclinic zirconia phase by heat treatment of ZrO2 . nH2O, however, disturb its quantitative description. The aim of the present investigation is: