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 alpha-Ca2P2O7 (hightemperature form) could be kept during its cooling process, it is metastable and retransformed into beta-Ca2P2O7 (low-temperature form) at about 950 degreesC during its reheating process. This reversible phase transformation was discussed from the point view of polyhedral distortion. The sample from beta-Ca2O7 calcined at 1000 degreesC/2 It densifies much faster than that from alpha-Ca2P2O7 and alpha + beta mixture, and bulk density as high as 98% TD can be obtained as it is sintered at 1150 degreesC. A dense alpha-Ca2P2O7 free of micro-crack could not be obtained whatever from the powder of beta-Ca2P2O7 or alpha-Ca2O7 or alpha + beta mixture. Such different sintering behavior was explained in related to the reversible phase transformation between alpha- and beta-Ca2P2O7. (C) 2003 Elsevier B.V. All rights reserved.