Sintering behavior and microwave dielectric properties of tricalcium phosphate polymorphs

The phase transformation and sintering behavior of tricalcium phosphate polymorphs [beta- and alpha-Ca-3(PO4)(2)] are investigated using differential thermal analysis, X-ray powder diffraction, and dilatometry. The low-temperature phase, beta-Ca-3(PO4)(2), can be sintered at 1125 degrees C prior to phase transformation to alpha-Ca-3 (PO4)(2). However, it is difficult to obtain dense alpha-Ca-3(PO4)(2) samples owing to volume expansion and subsequent microcrack formation during the transformation of beta-Ca-3(PO4)(2) to alpha-Ca-3(PO4)(2). Herein, we develop alpha-Ca-3(PO4)(2) With a density higher than 97% by microwave heating alpha-Ca-3(PO4)(2) without any reversible phase transformation. Also, we initially explore the microwave dielectric properties of tricalciurn phosphate. Both tricalciurn phosphate polymorphs show dielectric constants lower than 10. Of importance is the fact that a dense alpha-Ca-3(PO4)(2) sample has a high quality factor of 22,000 GHz.