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Precipitation of calcium phosphates from electrolyte solutions—IV

1975; Pergamon Press; Volume: 37; Issue: 10 Linguagem: Inglês

10.1016/0022-1902(75)80827-x

1878-1225

H. Füredi‐Milhofer, E. Oljica-Žabčić, B. Purgarić, B. Kosar-Grašić, Neven Pavković,

Crystallization and Solubility Studies

The precipitation of calcium phosphates from solutions containing 0·15 M sodium chloride has been studied in a wide concentration range of calcium chloride and sodium phosphate solutions (concentrations ranging from solubility up to 0·1 M). Twenty four hour precipitation diagrams of systems prepared at constant initial pH 7·4 (25°C and 37°C), 6·5 (37°C) and 6·0 (37°C) are represented. The diagrams show the respective positions of the precipitation boundaries, the distribution of calcium ionic species in solutions at these boundaries and the approximate positions of the concentration regions, within which octacalcium phosphate (OCP), calcium deficient hydroxyapatites (DA), dicalcium phosphate dihydrate (DCPD) and/or mixtures of these compounds have been found to prevail. Sodium ions (∼0·5 wt%) were irreversibly incorporated into the precipitates. Kinetic experiments indicate that at low supersaturations precipitates were formed by direct crystal growth, while at medium and high supersaturations precipitation proceeded in more than one step involving the formation of one or more precursor phases.