Preparation, characterization and thermochemistry of magnesium carbonate co-substituted fluorapatites

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• 作者：Houda Chihi ; Ismail Khattech ; Mohamed Jemal
• 关键词：Magnesium carbonate co ; substituted fluorapatites ; Calorimetry ; Heat of solution ; Enthalpy of formation
• 刊名：Journal of Thermal Analysis and Calorimetry
• 出版年：2017
• 出版时间：March 2017
• 年：2017
• 卷：127
• 期：3
• 页码：2427-2438
• 全文大小：
• 刊物类别：Chemistry and Materials Science
• 刊物主题：Physical Chemistry; Analytical Chemistry; Polymer Sciences; Inorganic Chemistry; Measurement Science and Instrumentation;
• 出版者：Springer Netherlands
• ISSN：1588-2926
• 卷排序：127

文摘

Magnesium carbonate co-substituted fluorapatites with similar Mg/(Ca + Mg) atomic ratio and different amount of carbonate were prepared by the precipitation method. X-ray diffraction, Fourier transform infrared spectroscopy, and chemical and thermogravimetric analyses were used to characterize the obtained powders. The results showed that the compounds are pure B-type carbonate apatites with the general chemical formula Ca_10−x+u−yMg_y(PO₄)_(6−x)(CO₃)_xF_2−x+2u, 0 ≤ x≤2, u ≤ x/2 and y = 0.90 ± 0.01. Simultaneous incorporation of CO₃ and Mg ions into the fluorapatite (Fap) induced a decrease in “a” parameter, a slight increase in “c” parameter, and a decrease in crystallinity associated with reduction in crystallites size. Using an isoperibol calorimeter, the heat of solution of the products was measured at 298.15 K in 3 mass% hydrochloric acid solution. Thermochemical cycle was proposed and complementary experiences were performed in order to get the standard enthalpy of formation of these compounds. This quantity increases when magnesium is incorporated in Fap, and it carries on increasing when the apatite becomes more carbonated. The result could be correlated with the modification of magnesium environment when the amount of carbonate increases.