Abstract
The solubilities of synthetic calcium hydroxyapatites [Ca(OH)A], Ca5(PO4)3OH, are determined in the ternary system Ca(OH)2+ H3PO4+ H2O at 25°C in the pH range 5–7 by equilibration with dilute H3PO4 solutions. The thermodynamic solubility product Ksp of precipitated Ca(OH)A, prepared by titrating a boiling aqueous suspension of Ca(OH)2 with H3PO4, is (3.25± 0.29)× 10–58 mol9 dm–27. Ca(OH)A prepared by solid state reaction of CaCO3 and CaHPO4 and precipitated Ca(OH)A heated at high temperatures in a water vapour atmosphere showed no constant Ksp. After being washed, these samples equilibrate according to the usual solubility product principles with a Ksp value of (3.44± 0.36)× 10–59 and (2.60± 0.21)× 10–59 mol9 dm–27, respectively.The influence of heat treatment and washing on the solubility behaviour is discussed. Deviations from solubility behaviour which accords with the usual solubility product principles are caused by reactions occurring at the surface of the solid. The latter are induced by a high free energy of the solid and/or the presence of a fraction with high solubility associated with the Ca(OH)A sample.
Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
