Phase and melting relationships of beta, alpha and alpha '-Ca-3(PO4)(2) polymorphs in the Ca-3(PO4)(2)-Zn-3(PO4)(2) system

摘要

In order to provide an exact knowledge of the phase transitions and melting relationships of Ca-3(PO4)(2) (TCP) in the presence of zinc, a revisited version of the rich-Ca-3(PO4)(2) region of the phase diagram of the system Ca-3(PO4)(2)-Zn-3(PO4)(2) has been established in the present work. Experimental determination of this diagram was carried out by solid-state reactions of samples prepared from pure NH4H2PO4, CaCO3 and ZnO raw materials. X-ray Diffraction, Differential Thermal Analyses and Field Emission Scanning Electron Microscopy studies allowed to revise the alpha, beta, alpha+beta-TCP phase stability fields, delimitating for. the first time the biphasic alpha + alpha'-TCP field and the melting relationships in the high temperature region of the system. The results allowed to determine two peritectic invariant points, at approximate to 1400 degrees C for 95 mol% Ca-3(PO4)(2) and at approximate to 1490 degrees C for approximate to 99.5 mol% Ca-3(PO4)(2). (C) 2016 Elsevier Ltd. All rights reserved.