Microwave sintering of calcium phosphate ceramics

Microwave sintering of hydroxyapatite (HAP) and tri-calcium phosphate (TCP) ceramics were studied using a commercial 2.45 GHz, 3 KW fully automated microwave system. Four different powder compositions, apart from pure HAP and TCP, were prepared with small amount of different oxide additives e.g., magnesium oxide, zinc oxide and titanium oxide. All samples were densified at 1250 °C for 30 min. Sintered samples had high density and homogeneous microstructure for all compositions. Phase analysis using XRD showed no major variations from starting materials. Presence of additives increased compressive strength between 100 and 200%. Fractured surfaces showed clear signs of intergranular fracture in undoped HAP and TCP while in doped samples, fracture modes were either transgranular or mixed mode. In comparison to conventional sintering, microwave sintering of calcium phosphate ceramics was found to be economically exciting due to substantial reduction in processing time and energy expenditure due to volumetric heating of samples.