The Effect of Microwave Settings on HAp Sintering

Hydroxyapatite (HAp, Ca10(PO4)6(OH)2), a calcium phosphate bio ceramic which is chemically similar to natural bone mineral, is widely used as a scaffolding material in bone tissue engineering. In this study, Hydroxyapatite (HAp) ceramics were sintered using microwave in one- and two-step heat treatment. The sintering temperatures in the first heat treatment step were in the range of 965-1000 °C without isothermal holding, and the power levels of the microwave were set at 600, 750, and 900 W. The temperatures in the second heat treatment step were 600, 735, and 860 °C. Of note, HAp-to-Tricalcium phosphate (TCP) phase transformation was not detected at 1000 °C; instead, the preferred growth of (211) planes corresponding to the circular morphology was observed. As observed in the XRD images, crystallite degradation occurred in two-step sintered samples. In addition, the SEM micrographs indicated that the open porosity in the two-step heat treated samples was more than that of samples which were heat treated in one step. In case the sintering temperature was set at 1000 °C, the maximum density values of 92 % and 95 % were obtained for one- and two-step sintered samples, respectively.