Calcium deficient hydroxyapatites were impregnated to varying degrees with fluoride in very dilute solutions of NaF at room temperature. Ca/P ratios were determined before and after fluoridation. Phosphate loss upon fluoridation was consistent with an initial mechanism of OH− vacancy filling by F−, with equivalent amounts of PO43− ions escaping to restore charge balance. Infrared measurements confirmed previous evidence of OH/F exchange and the formation of [Formula: see text] hydrogen bonds, which increased with progressive thermal activation, considerable exchange having occurred already at 120 °C and possibly below. The first signs of lattice collapse occurred near 600 °C, with the fluorided sample exhibiting somewhat better stability.
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Amberg et al. (1974) studied this question.
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