Thermal behavior of apatitic calcium phosphates synthesized from calcium carbonate and orthophosphoric acid or potassium
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Thermal behavior of apatitic calcium phosphates synthesized from calcium carbonate and orthophosphoric acid or potassium dihydrogen orthophosphate Doan Pham Minh • Marta Galera Martı´nez Ange Nzihou • Patrick Sharrock
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Received: 2 July 2012 / Accepted: 7 September 2012 Ó Akade´miai Kiado´, Budapest, Hungary 2012
Abstract The synthesis of calcium hydroxyapatite powder (Ca-HA) from orthophosphoric acid or from potassium dihydrogen orthophosphate and calcium carbonate was carried out under moderate conditions. A better dissolution of calcium carbonate and a complete precipitation of the orthophosphate species were obtained with orthophosphoric acid, indicating that it may be of interest as a phosphate source compared with potassium dihydrogen orthophosphate. The influence of calcination treatment on the physico-chemical properties of the solids is discussed in this paper. Different characterization techniques such as specific surface area (SBET), true density, particle size distribution, thermo-mechanical analysis, simultaneous thermogravimetry and differential scanning calorimetry analysis, X-ray diffraction and infrared were performed to understand the phase changes during thermal treatment. Specific surface area decreased while true density and particle size increased with the rise in the calcination temperature, due to the sintering of particles and the chemical reactions occurring at high temperatures. Mixtures of well-crystallized Ca-HA and tricalcium phosphate (TCP) or well-crystallized Ca-HA, CaO, and TCP were obtained after calcination at 800–1,000 °C of the solid products starting from orthophosphoric acid or potassium dihydrogen orthophosphate, respectively.
D. Pham Minh (&) M. Galera Martı´nez A. Nzihou Universite´ de Toulouse, Mines Albi, CNRS, Centre RAPSODEE, Campus Jarlard, 81013 Albi Cedex 09, France e-mail: [email protected] P. Sharrock Universite´ de Toulouse, SIMAD, IUT Paul Sabatier, Avenue Georges Pompidou, 81104 Castres, France
Keywords Apatite Calcium hydroxyapatite Calcium carbonate Thermal treatment
Introduction Calcium orthophosphates form a large family of chemical compounds including dicalcium phosphate dihydrate (DCPD, CaHPO42H2O); dicalcium phosphate anhydrous (DCPA, CaHPO4); octacalcium phosphate (Ca8(HPO4)2(PO4)45H2O); b-tricalcium phosphate (b-TCP, Ca3(PO4)2); or calcium hydroxyapatite (Ca-HA, Ca10(PO4)6(OH)2). In this family, Ca-HA seems to be the most widely studied, because of its excellent properties, such as biocompatibility, bioactivity, and osteoconductivity [1], and its high-potential application in different fields such as catalysis, heavy metal removal, gas sensors, or chromatography [2]. Generally, low-crystallinity Ca-HA is prepared by the precipitation of calcium cations with orthophosphate anions under mild conditions [3, 4]. In the biomaterials field, low-crystallinity Ca-HA is usually converted into pure and well-crystallized Ca-HA by a calcination step at high temperature [5, 6]. Ca-HA used in gas sensors is also treated by a thermal proce
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