title: The effects of magnesium and fluoride on the hydrolysis of octacalcium phosphate.
abstract: The adsorption of Mg ions on octacalcium phosphate (OCP) and its effect on OCP hydrolysis, with and without F, were studied. The Mg adsorption isotherm was fitted by the Langmuir model with an affinity constant of 0.74 ml/mumol and maximum number of sites, 31.19 mumol/g. The hydrolysis rates were measured in a pH stat by titration of base and were strongly temperature dependent. The products were examined by X-ray diffraction and chemical analysis. OCP hydrolysis takes place in two stages: the fast initial process, which is attributed to the surface topotactical conversion, followed by the main, slower process, which involves the nucleation and crystal growth. Mg ions, as 1 mmol/l MgCl2, prevented the initial surface reaction and decreased the nucleation rate dramatically and the growth rate slightly; F increased the rates of surface reaction and both the nucleation and crystal growth processes. The Ca/P ratio (1.53) and the line broadening in the X-ray diffraction patterns of the apatitic products were not significantly affected by the F. Mg also did not affect the Ca/P ratio and the line broadening at (002) diffraction, but decreased the line broadening at (310) diffraction.
authors.affiliation: American Dental Association Health Foundation Paffenbarger Research Center, National Institute of Standards and Technology, Gaithersburg, MD 20899.
authors.forename: M S
authors.initials: MS
authors.lastname: Tung
authors.forename: B
authors.initials: B
authors.lastname: Tomazic
authors.forename: W E
authors.initials: WE
authors.lastname: Brown
mesh_terms: D000327:Adsorption; D002130:Calcium Phosphates / Q000737:chemistry*; D003460:Crystallization; D003461:Crystallography; D005459:Fluorides / Q000737:chemistry*; D006868:Hydrolysis; D006878:Hydroxides / Q000737:chemistry; D008274:Magnesium / Q000737:chemistry*; D011188:Potassium / Q000737:chemistry; D017680:Potassium Compounds; D012995:Solubility; D013997:Time Factors
chemical_list: D002130:Calcium Phosphates; D006878:Hydroxides; D017680:Potassium Compounds; C022045:octacalcium phosphate; D008274:Magnesium; D005459:Fluorides; D011188:Potassium; C029943:potassium hydroxide