New aspects in processing of hydroxyapatite ceramics

Sintering of hydroxyapatite ceramics has been a challenging topic for decades since the material has good bioactivity, proven biocompatibility, low cost, and high availability. Besides its biomaterial applications, hydroxyapatite has been used so far as a catalyst support, sensor material, etc. For improvements in its functional properties, new synthesis and processing routes are certainly required. This work will present current achievements in new processing routes of hydroxyapatite ceramics. In the first part, sintering of hydroxyapatite in the presence of lithium iron phosphate will be presented. Such composition induces formation of liquid phase during sintering and interaction between materials that provides decreasing of the processing temperature and formation of reinforcing Fe-rich phase located along the grain boundaries of the matrix material. Furthermore, an influence of heating rate on pure hydroxyapatite sintering will be presented showing that conventional processing with high heating rates can be beneficial for microstructural refinement without any drawbacks regarding the final density of sintered ceramics. This will be discussed regarding the chemical changes induced due to release of hydroxyapatite structural ionic species