Synthesis of aluminium borate–boron oxide and binary titanium–boron and zirconium–boron oxides from metal alkoxides and (MeO)3B3O3 in non-aqueous solvents

Abstract

The reaction of metal alkoxides M(OR)₄ (M = Ti, Zr; R = organyl) with (MeO)₃B₃O₃ (1 : 0.67) in dry propan-2-one at room temperature led to gels which when dried and calcined in air for 24 h at 500–1000 °C afforded bi-phased mixed-oxide materials formulated as 4TiO₂·3B₂O₃ and ZrO₂·B₂O₃ in high ceramic yields and purity; the B₂O₃ phases of these materials were amorphous. The materials remained amorphous upon calcination at lower temperatures. The TiO₂ phase of the 4TiO₂·3B₂O₃ was crystalline when calcined at higher temperatures with either anatase (600 °C) or rutile (>800 °C) being obtained. The ZrO₂ phase of the ZrO₂·B₂O₃ was crystalline when calcined at higher temperatures and was obtained as a metastable tetragonal phase (<700 °C) or baddeleylite (>800 °C). In a similar reaction, Al(OⁱPr)₃ (2 : 1) gave a bi-phased aluminium borate–boron oxide (Al₁₈B₄O₃₃·7B₂O₃) after calcination at >700 °C. The dried gels and oxide materials were all characterized by elemental analysis, TGA–DSC, and powder XRD.