Phase stability and microstructure development in hydroxyapatite–mullite system

We report here the results of a transmission electron microscopy (TEM) study of hydroxyapatite (HAp)–mullite composites. TEM analysis, in combination with selected-area diffraction pattern analysis, confirms the decomposition of HAp to tricalcium phosphate, irrespective of mullite content. Importantly, the presence of sintering liquid residue of tetragonal gehlenite as well as cubic CaO and rhombohedral Al2O3 has been observed in the investigated HAp composites. Based on the microstructural characterization, the possible sintering reactions are discussed.