Preparation of hydroxyapatite fibre composites by hot isostatic pressing

Abstract

Hot isostatic pressing (HIPing) has the potential to fully densify ceramics, provided that they are surface-sealed prior to HIPing. Surface sealing generally involves one of the following: presintering to a closed porosity density level; glass encapsulation (glass of appropriate consistency at the HIPing temperature); metal encapsulation (metal chemically compatible with the sample and suitably soft at the HIPing temperature). Hydroxyapatite fibre composites can not be presintered to a closed porosity density level owing to the additive-induced decomposition phenomenon. Glass encapsulation was shown to be problematic owing to severe HAp volatilisation catalysed by the reinforcement fibres at elevated temperatures. Therefore a specialised metal encapsulation process was developed, which enabled the production of fully dense fibre reinforced HAp, with no cracking on capsule removal. The result was near-fully dense, decomposition-free, fibre-reinforced HAp with a toughness comparable with cortical bone.