Phase transformation behaviour of hydroxyapatite foams subject to heat treatment

This study examined the relationship between sintering and phase transformation behaviour in hydroxyapatite (HA). Pellets and replicated foams were sintered at five different temperatures ranging from 1350 degrees C to 1550 degrees C. Hydroxyapatite remained as the major phase in all the samples studied. In the pellets, sintering took place prior to the phase transformation which occurs primarily at the surface. This created damage that extended into the interior of the pellet above 1400 degrees C. In contrast, the foams transformed at lower temperatures due to the higher surface area. This did not create damage in the foam. The differences in the foams and the pellets are discussed in terms of sintering and phase transformation behaviour.