Strontium hydroxyapatite and strontium carbonate as templates for the precipitation of calcium-phosphates in the absence and presence of fluoride
The heterogeneous precipitation of calcium phosphates on calcium hydroxyapariLe (Ca-10(PO4)(4)OH)(2) or HAP) in the presence arid absence of fluoride is important in the formation of bone and teeth, protection against tooth decay, dental and skeletal fluorosis and defluoridaLion of drinking wafer. Strontium hyclroxyapariLe (Sr-10(PO4)(6)(OH)(2) or SrHAP) and strontium carbonate (SrCO3) were used as calcium free seed templates in precipitation experiments conducted with varying initial calcium-Lophosphate (Ca/P) or calcium-Lo-phosphaLe-Lo-fluoride (Ca/P/F) ratios. Suspensions of SrHAP or SrCO3 seed templates (which were calcium limited for both templates and phosphate limited in the case of SECO3) were reacted at pH 7.3 (25 degrees C) over 3 days. The resulting solids were examined with Scanning Transmission Electron Microscopy (STEM), X-ray Diffraction (XRD), Fourier Transform Infrared (MR), and X-ray Photoelectron Spectroscopy (XPS), X-ray Absorption Near Edge Structure (XANES), and Extended X-ray Absorption Fine Structure spectroscopy (EXAFS). Calcium apatite was the predominant phase identified by all techniques independent of the added Ca/P ratios and of the presence of fluoride. It was not possible to make an unambiguous distinction between HAP and fluorapatite (Ca-10(PO4)(6)F-2, FAP). The apatite was calcium-deficient and probably contained some strontium. (C) 2014 Elsevier B.V. All rights reserved.