Lime–alumina–silica vitreous ceramic processing incorporating wollastonite

Abstract

Improvements in mechanical and physical properties of advanced ceramics have been undermined by high processing costs and the reputation of unpredictable reliability. One potential technique to address this situation is to use a naturally occurring mineral to develop new ceramic microstructures using a simple processing technique. The system chosen for potential development was an alumina ceramic modified using 20 wt-% wollastonite (CaSiO₃ ). Green body production was carried out by wet processing optimised by rheological measurements. The best conditions were found to be a pH of 3 using 1500 ppm BETZ (dispersant) processed at ∼0·35 volume fraction of solids in a water based suspension. Thermal analysis revealed that the optimum sintering procedure involved vitreous composite sintering for 15 min at 1500°C followed by an air quench. This glass ceramic was then devitrified using a heat treatment at 1032°C (4 h) followed by 4 h at 1200°C. The final material of 68 wt-% alumina, with anorthite and gehlenite, had a high indentation toughness (6·2 MPa m^1/2 ) and an improved thermal expansion coefficient. Thus, the new material should be attractive as a low cost material for anti-abrasion applications at elevated temperatures.