Fabricating densified hydroxyapatite ceramics from a precipitated precursor

A fine hydroxyapatite precursor was prepared by reacting calcium hydroxide and an orthophosphoric acid solution. To fabricate sintered hydroxyapatite ceramic, the resulting precursor was not calcined in powder form. Instead, it was compacted in a uniaxial die, followed by thermal treatment of the powder pellets at various temperatures, prior to being sintered at a high temperature. A sintered density of 98.15% theoretical was obtained at a sintering temperature as low as 1000°C. Prolonged dwelling at 1200°C, up to more than 20 h, did not affect the phases present in the sintered hydroxyapatite, although it resulted in a slight fall in sintered density due to the grain coarsening. The increase in average grain size leads to a noticeable improvement in fracture toughness of the sintered hydroxyapatite.