Ca3(PO4)2 - CaNaPO4 System

Abstract

As a fundamental research of a calcined defluorinated phosphate containing a small amount of sodium, the system Ca3(PO4)2(tricalcium phosphate, T) - CaNaPO4(Rhenanite, R) was studied by high temperature X-ray diffraction, differential thermal analysis, etc., and the phase diagram determined. During heating, T inverted from β to α at 1180°C, and then possibly from α to α′ at 1280°C. R inverted from β to α at 690°C. In the composition range containing R from about 10 to 98% by weight, (βT+βR), the stable phase at room temperature, inverted to (βT+αR) at 650°C. The (βT+αR) changed at 980°C to form a compound “A” Ca5Na2(PO4)4 for the sample containing 50.5% R, and (“A”+βT) for samples containing a smaller amount of R. The (“A”+βT) then changed to “A” solid solution at elevated temperatures. The crystals of “A” consisted of a superlattice of αR. “A” and the solid solution changed to αR solid solution at higher temperature. By quenching the samples containing 35 to 50.5% R from 1400°C, a single phase “A” or “A” solid solution was obtained at room temperature. The “A” solid solution was the major phase of the calcined defluorinated phosphate. During heating of samples containing more than 50.5% R, (βT+αR) changed to αR solid solution at or below 980°C; during cooling of the solid solution (“A”+βR) formed at 650°C.