Formation and Sintering of Alkoxy-derived Al₂O₃-TiO₂ Composite Powders

Abstract

In the Al₂O₃-TiO₂ system, solid solutions of AIO(OH) gel are formed between 5 and 20 mol% TiO₂ by the simultaneous hydrolysis of aluminium and titanium alkoxides, followed by washing and drying. After dehydration γ-Al₂O₃ solid solutions crystallize slowly from amorphous materials. At higher temperatures, rutile (TiO₂) is formed directly with the transformation of γ-Al₂O₃ phases into corundum. Corundum-rutile composite ceramics with dispersed fine pores generated from the decomposition of Al₂TiO₅ have been fabricated as follows:(1) hot pressing for 2 h at 1350°C under 35 MPa using γ-Al₂O₃ solid solutions, (2) heating for 1 h at 1500°C to achieve the complete formation of Al₂TiO₅, and (3) annealing for 7 h at 1000°C to decompose of Al₂TiO₅ into corundum and rutile. Their mechanical properties have been examined. The bending strength yields the maximum value of 365 MPa with 15 mol% TiO₂ content whereas the fracture toughness increases from 4.7 to 6.2 MPam^1/2 with increasing TiO₂ content.