Abstract
The thermal decomposition of calcium phosphates prepared in a medium with a dielectric constant less than that of water and characterized by a Ca/P atomic ratio of 1.33 were studied. After drying by lyophilization the phosphate is amorphous by X-ray diffraction, whereas it is apatitic when it is oven dried at 80°C. Their thermal decomposition was carried out by thermogravimetric analysis. Phosphate samples were heated to different temperatures and examined by X-ray diffraction, IR spectroscopy and chemical analysis. This study showed that the composition of phosphates depends on the drying method used: it can be written as Ca 8(PO 4) 4(HPO 4) 2· xH 2O and Ca 8(PO 4) 3.5(HPO 4) 2.5OH 0.5· xH 2O for the lyophilized and oven-dried phosphates respectively. This difference of composition results from an internal hydrolysis of PO 4 3− ions into OH − and HPO 4 −- ions during the drying at 80°C. This hydrolysis leads to the crystallization of the phosphate in apatitic structure.
Published Version
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