Phase Relation in the System Ca₃(PO₄)₂-CaMg(SiO₃)₂-MgSiO₃-SiO₂

Abstract

The phase diagram in the system C3P-CMS2-MS-S was studied because it corresponds to a composition region for manufacturing fused calcium magnesium phosphate fertilizer and for corrosion of refractories. In the quaternary system, phase diagrams of C3P-CMS2-S and C3P-MS were reported already. In this report, the phase relation in the system C3P-CMS2-MS and a part of the quarternary system were investigated. The former ternary system has a β-C3P (whitlockite), diopside solid solution (ss.) and pigeonite-protoenstatite ss. fields covering a wide region of the ternary diagram. In the quarternary system, ternary eutectics among β-C3P, diopside, tridymite continues from 1277°C in the system C3P-CMS2-S to 1245°C in the system C3PMS-S. This composition of the lowest eutectic temperature corresponds to the fertilizer composition and it gives a suggestion for the manufacture of apatite ceramics as biomaterials. The pigeonite ss. and protoenstatite ss. exist at a higher temperature region in contact with the diopside ss. field, but the phase boundary between pigeonite ss, and protoenstatite ss. has not been clearly determined.