Mechanism of solid-state conversion of non-stoichiometric hydroxyapatite to diphase calcium phosphate |
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Authors: | Dorozhkin S. V. |
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Affiliation: | (1) Nicol Hall, Queen"s University, 60 Union Street, Kingston, ON, K7L 3N6, Canada |
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Abstract: | Two non-stoichiometric hydroxyapatites (n-HA) with Ca/P molar ratios of 1.50 and 1.58 and one stoichiometric hydroxyapatite (s-HA) with Ca/P = 1.67 were prepared from chemically pure CaHPO4·2H2O and KOH. After sintering at 1050 °C for 4 h, n-HA with Ca/P = 1.50 was transformed into -Ca3(PO4)2, n-HA with Ca/P = 1.58 was converted to diphase calcium phosphate (DCP), while s-HA underwent no chemical transformations. The sintered and unsintered samples of hydroxyapatite were studied by IR spectroscopy, chemical analysis, and X-ray diffraction analysis. The crystallite dimensions were calculated, and a model for the DCP structure was proposed. The mechanism of the solid-state n-HA to DCP conversion was proposed on the basis of this model and published values of the volume diffusion coefficients of the OH–, Ca2+, and PO43– ions at 1000 °C. |
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Keywords: | hydroxyapatite calcium phosphate solid-state reactions X-ray diffraction analysis IR spectroscopy |
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