Effect of ZrO2 types on ZrSiO4 formation

The effect of various types of ZrO2 on ZrSiO4 formation was evaluated by the calcination of three types of nanosized ZrO2 (unstabilized ZrO2, 3Y–ZrO2, and 8Y–ZrO2) and amorphous SiO2 powders. Reaction was conducted in vacuum and air atmosphere. Results indicated that under a vacuum atmosphere, the yield of ZrSiO4 during synthetic reaction markedly varied when different types of ZrO2 were used. When 3Y–ZrO2 was used, the reaction reached equilibrium after only 6 h. This occurrence was facilitated by the stabilized ZrO2 tetragonal structure. ZrSiO4 synthetic mechanism by which SiO2 diffuses into a t-ZrO2 crystal structure and then ZrSiO4 nucleates and grows along on t-ZrO2 (101) planes was confirmed. That is, t-ZrO2 acts as a host for ZrSiO4 formation. However, the investigation under air atmosphere demonstrated that ZrSiO4 could be synthesized using unstabilized ZrO2 as previously reported; meanwhile, ZrSiO4 formation was nearly suppressed in samples containing Y2O3-stabilized ZrO2. This suppression was attributable to the oxygen absorption of Y2O3-stabilized ZrO2, affecting its internal micro-chemical environment and impeding ZrSiO4 nucleation.