Dehydroxylation of hydroxyapatite in dense bulk ceramics sintered by spark plasma sintering

Dense transparent hydroxyapatite (HAp) nanoceramic samples were prepared by spark plasma sintering of a commercial available granulated nanopowder. This made it possible for investigating the dehydroxylation behaviours of HAp in fully dense bulks. Post-SPS thermal annealing was performed in a temperature interval of 800 to 1100 °C in air. The phase analysis and microstructural characterization revealed that the dehydroxylation in fully dense HAp was initiated above 900 °C and its kinetics seems to be determined by the water vapour diffusion. Accordingly, a gradient structure consisting of porous interiors and a peculiar surface topography reflecting the water vapour escaping patterns were observed in samples experienced severe dehydroxylation.