Surface reactions on hydroxyapatite in the presence of fluoride ions 1. Saturated and congruent conditions

✍ Scribed by P. Gasser; J.C. Voegel; Ph. Gramain

• Book ID: 103966828
• Publisher: Elsevier Science
• Year: 1993
• Tongue: English
• Weight: 912 KB
• Volume: 74
• Category: Article
• ISSN: 0927-7757
• DOI: 10.1016/0927-7757(93)80271-f

✦ Synopsis

The adsorption of fluoride ions onto hydroxyapatite powder from aqueous solutions is studied as a function of the concentration of fluoride ions and the amount of powder, in well-equilibrated congruent solutions and in the absence of any dissolution at neutral pH. The exchange kinetics of fluoride, calcium and protons are continuously followed with use of ion-selective electrodes. Neither the desorption of phosphate nor hydroxyl ions is observed during the fluoride adsorption process. For low fluoride ion concentrations, Langmuir-type adsorption of fluoride occurs together with the adsorption of H,PO, and H' ions. For higher fluoride concentrations, once the solubility product of CaF, is well exceeded, this phase is deposited. When a further increase in the fluoride ion concentration occurs, the solutions remain supersaturated with respect to CaF, and only fluoride ions are adsorbed. The observed adsorption of protons and H,PO, ions at the interface excludes the formation of fluorapatite or fluorinated apatite but it may lead to the formation of brushite.