Dense β-SiAlONs consolidated by a modified hydrolysis-assisted solidification route

Dense beta-Si4Al2O2N6 materials were fabricated by a modified hydrolysis-assisted solidification (HAS) route from aqueous slurries containing 48-50 vol.% solids, in which 5-22 wt.% of the required alpha-Al2O3 was replaced by equivalent amounts of unprotected aluminium nitride (AIN) powder to promote consolidation via AIN hydrolysis. A fixed amount (9.37 wt.%) of AIN passivated against hydrolysis with a coating phosphate layer was also added to all the samples consolidated by the modified HAS method. The aqueous slurries were cast in non-porous moulds, allowed to set and dried before sintering at 1675 degrees C for 4 h. For comparison purposes, ceramics with the same predicted final composition (having 64.33% alpha-Si3N4, 23.36% alpha-Al2O3, 9.37% AIN and 7% Y2O3 as starting materials) were also consolidated by a conventional dry-powder pressing (CDPP). The beta-Si4Al2O2N6 ceramics consolidated by the modified HAS route exhibited superior outstanding properties (bulk density, apparent porosity, water absorption capacity, hardness and fracture toughness) in comparison to the traditional dry-powder pressing route. (c) 2007 Elsevier Ltd. All rights reserved.