SOLUBILITY OF beta -Ca3(PO4)2 IN THE SYSTEM Ca(OH)2-H3PO4-H2O at 5, 15, 25, and 37 degree C.

Abstract

Solubility isotherms of beta-tricalcium phosphate, beta -Ca//3(PO//4)//2, prepared by heating mixtures of CaCO//3 and CaHPO//4 above 800 degree C, were determined in the ternary system Ca(OH)//2-H//3PO//4-H//2O at 5, 15, 25, and 37 degree C in the pH range 6. 0 to 7. 5 by equilibration with dilute H//3PO//4 solutions. The results indicate that beta -Ca//3(PO//4)//2 has a negative thermal coefficient of solubility. The solubility product was determined as a function of temperature. Thermodynamic functions for the dissolution of the salt at the four experimental temperatures are reported. The computed isotherms at 25 degree C for several calcium phosphates are compared. Related compounds are an important constituent of dental calculus and may occur in carious lesions and calcified aortas.