Sintering of naturally derived hydroxyapatite using high frequency microwave processing

The sinterability of naturally derived hydroxyapatite (HA) materials using 30 GHz high frequency microwave (MW) was explored and compared to conventional sintering. The progress of the MW sintering process of die-pressed HA compacts was investigated via in-situ MW dilatometry measurements. The linear shrinkage, microstructure, porosity and microhardness of the MW sintered naturally derived HA samples were investigated and compared with the conventionally heat-treated samples. The results revealed that the application of high frequency MW allows production of a more porous HA compact with increased microhardness as compared to conventional sintering. In addition, the MW sintering process was successfully performed without the need of hybrid heating and in a relatively shorter time compared to conventional heating. The MW-induced porosity, achieved using millimeter wave MW sintering conditions, can be considered as another added value to the prepared naturally derived HA for drug delivery and bone grafting applications.