Phase transformation and sintering behavior of Ca2P2O7

The phase transformation and sintering behaviors of Ca2P2O7 with different phase composition were investigated by using X-ray powder diffraction (XRD), dilatometery and scan electron microscopy techniques in this paper. It is found that although α-Ca2P2O7 (high-temperature form) could be kept during its cooling process, it is metastable and retransformed into β-Ca2P2O7 (low-temperature form) at about 950 °C during its reheating process. This reversible phase transformation was discussed from the point view of polyhedral distortion. The sample from β-Ca2P2O7 calcined at 1000 °C/2 h densifies much faster than that from α-Ca2P2O7 and α+β mixture, and bulk density as high as 98% TD can be obtained as it is sintered at 1150 °C. A dense α-Ca2P2O7 free of micro-crack could not be obtained whatever from the powder of β-Ca2P2O7 or α-Ca2P2O7 or α+β mixture. Such different sintering behavior was explained in related to the reversible phase transformation between α- and β-Ca2P2O7.