Phase Transformations in the Al₂O₃/TiO₂ System and Metastable Phase Formation at Low Temperatures

摘要

In this work we studied the phase formation in the Al₂O₃/TiO₂ system using amorphous powders with a high degree of chemical homogeneity and prepared by co-precipitation of inorganic salts. The aluminum tialite (Al₂TiO₅) phase of the Al₂O₃/TiO₂ system is of considerable technological interest due mainly to its thermal properties. This phase is thermodynamically stable only at temperatures above 1280 °C; below this value it decomposes into the starting oxides rutile and corundum. The formation of tialite in temperatures bellow 1280 °C is possible using chemical methods of powder synthesis like co-precipitation. In this work, the gel obtained by co-precipitation of inorganic salts was calcined at different temperatures and dwell times. The formation of metastable tialite under a number of temperature conditions and dwell times below its stable formation temperature was observed. Results showed strong dependence not only on calcination temperature, but also on dwell time. The cooling rate did not significantly alter the conversion or reverse conversion of tialite into rutile and corundum.