SYNTHESIS AND ISOMORPHOUS SUBSTITUTION REACTIONS OF SOME HYDROXYAPATITES

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Date
1992-12
Authors
INIKORI, GODWIN O.
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Abstract
ABSTRACT Cation exchange reactions in calcium, strontium and lead hydroxy apatites have been carried out by the method of co-precipitation in aqueous ammonia and acidic media. Solid state synthesis was applied in some cases. Products of the substitution reactions were analysed by atomic absorption spectrometry, infra-red and ultraviolet/visible spectrophotometry and in some cases by X-ray powder diffractometry. Magnesium formed solid solutions of calcium-magnesium hydroxyapatite in the entire composition range at pH 12. Solid solutions of calcium-zinc hydroxyapatite in the whole series were also obtained in both basic (pH = 10.5) and acidic (pH 5.0 -6.0) media. It is the first time that the formation of calcium-zinc hydroxyapatite solid solutions in the entire range is being reported. Calcium-lead hydroxyapatites in the entire series were obtained by solid state synthesis at 900°C. Formation of solid solutions between Mg2+ and Ca2- appears to be dependent on the pH of the precipitating medium. Replacement of Ca2+ by Mg2+ in the apatite lattice resulted in enhancement of peak intensity and sharpening of X-ray powder diffraction peaks. Expansion of lattice parameters was observed when Pb2+ substituted Ca2+ in hydroxyapatite. Infra-red frequencies for the OH and P04 groups were shifted to lower values in calcium-magnesium, calcium-lead and calcium-zinc 4 with increasing replacement of Ca2+
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SYNTHESIS, ISOMORPHOUS, SUBSTITUTION, REACTIONS, HYDROXYAPATITES
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