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.

Crystal growth and morphology of the nano-sized hydroxyapatite powders synthesized from CaHPO4·2H2O and CaCO3 by hydrolysis method

“…Ando and Matsuno [19] have investigated the Ca 3 (PO 4 ) 2 -CaNaPO 4 system and confirmed that the structure of Ca 20 Na 2x (P 2 O 7 ) 1Àx (PO 4 ) 12+2x can be formed. These products are stable under the condition of preparation in the range 0pxp1, which is equivalent to the synthesized product from DCPD in this study.…”

“…(2) is supposed to have a slow reaction rate which starts at 650 C and continues even above 1000 C. In this study, b-TCP is not found in the sample after annealing above 600 C, which means that b-TCP is excluded by some other reactions. Ando and Matsuno [19] have investigated the Ca 3 (PO 4 ) 2 -CaNaPO 4 system and claimed that at high temperatures CaNaPO 4 dissolves large amounts of Ca 3 (PO 4 ) 2 . In the Ca 3 (PO 4 ) 2 -CaNa-PO 4 system, b-TCP disappears during heating between 650 C and 980 C, containing CaNaPO 4 from 50.5% to 97% to form an a-rhenanite solid solution.…”

Immobilization of sodium and phosphorus-bearing PW-7a waste in SYNROC. Progress report. [SYNROC C]

“…X-ray diffraction confirmed that this complex phosphate is isostructural with Ca^a-tPO. ), -phase 'A' described by Ando and Matsuno (1968). These authors note that phase 'A' is soluble in weak citric acid solutions.…”

“…The phase equilibria defined by Ando and Matsuno (1968) reveal that at 1200-1300°C, there is substantial mutual solid solution between…”

Transitions solide-solide dans le systeme CaO-Na2O-P2O5 sous-systeme Ca3(PO4)2-CaNaPO4 Etude par diffraction de rayons X à température variable

“…This study was limited to that of mixtures in a temperature range determined by previous results. The pcesent work confirms the existence of two metastable diagrams which are superimposed on the stable diagram.The experimental conditions leading to the formation of the metastable phases on cooling (cooling rate and highest temperature reached before cooling) and to the different types of metastability were determined from the differential X-ray diffraction spectra.L'dtablissement du diagramme de phase des dquilibres solide-solide du syst~me Ca3(PO4)2-CaNaPO4 par analyses thermiques directe et diffdrentielle coupldes a fait I'objet d'une premiere sdrie d'~tudes [1][2][3].Diff~rents diagrammes de phase avaient auparavant dtd proposals pour ce syst~me [4,5]. Ces diffdrences, portant sur les limites du domaine d'existence d'une phase non stoechiom6trique (phase A) stable ~ haute temp6rature, ont pu ~tre expliqu6es par la mise en 6vidence de deux diagrammes mdtastables pouvant ~tre d~crits au refroidissement.…”