Sintering Behavior and Microwave Dielectric Properties of Tricalcium Phosphate Polymorphs

Abstract

The phase transformation and sintering behavior of tricalcium phosphate polymorphs [β- and α-Ca3(PO4)2] are investigated using differential thermal analysis, X-ray powder diffraction, and dilatometry. The low-temperature phase, β-Ca3(PO4)2, can be sintered at 1125 °C prior to phase transformation to α-Ca3(PO4)2. However, it is difficult to obtain dense α-Ca3(PO4)2 samples owing to volume expansion and subsequent microcrack formation during the transformation of β-Ca3(PO4)2 to α-Ca3(PO4)2. Herein, we develop α-Ca3(PO4)2 with a density higher than 97% by microwave heating α-Ca3(PO4)2 without any reversible phase transformation. Also, we initially explore the microwave dielectric properties of tricalcium phosphate. Both tricalcium phosphate polymorphs show dielectric constants lower than 10. Of importance is the fact that a dense α-Ca3(PO4)2 sample has a high quality factor of 22,000 GHz.