Preparation of Al₂TiO₅-ZrO₂ mixed powders via sol-gel process

Abstract

Sol-gel routes in the ternary system Al₂O₃-TiO₅-ZrO₂ were investigated to prepare Al₂TiO₅-ZrO₂ mixed powders. The preparation of ZrTiO₄ and Al₂TiO₅ was studied before going on with the ternary system. Zirconium titanate precursor gels were prepared from Ti(OPrⁱ)₄ and Zr(OPrⁿ)₄ mixtures. The crystallization of ZrTiO₄ develops at T<700°C. Al₂TiO₅ was prepared by different ways, using mixtures of Al(OBu^s)₂(C₆H₉O₃) with Ti(OPrⁱ)₄ (i), or with acetic acid addition (ii). Route (i) leads to a separate crystallization of TiO₂ and α-Al₂O₃, with subsequent formation of β-Al₂TiO₅ at T≈1360°C. Although the pseudobrookite β-Al₂TiO₅ is thermodynamically unstable below 1280°C, route (ii) leads to the crystallization of metastable β-Al₂TiO₅ at T≈800°C. At increasing temperature, β-Al₂TiO₅ decomposes into TiO₂ and α-Al₂O₃, then the two compounds react to form stable β-Al₂TiO₅. For the ternary system, all the preparation routes which were studied lead to ZrTiO₄ and α-Al₂O₃ with subsequent reaction (at T≈1500°C) to give β-Al₂TiO₅ and ZrO₂.