Mechanism of the solid-state transformation of a calcium-deficient hydroxyapatite (CDHA) into biphasic calcium phosphate (BCP) at elevated temperatures

Three types of poorly crystallized calcium-deficient hydroxyapatites (CDHA) with Ca/P molar ratios 1.50, 1.58, and 1.67 were prepared from CaHPO4.2H(2)O and KOH. These were sintered at 1050 degreesC for 4 h. Well-crystallized beta-tricalcium phosphate (beta-TCP), biphasic calcium phosphate (BCP), and stoichiometric hydroxyapatite (HA) were produced, respectively. The sintered and unsintered calcium phosphates were studied by X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy. In addition, Ca/P molar ratios were determined by a chemical analysis. Thermogravimetric analysis (TGA) revealed a loss of water for the period of sintering. On the basis of the experimental data, a structure of BCP was suggested. After applying the numerical values of ionic (OH-, Ca2+, and PO43-) diffusion coefficients at 1000 degreesC, the solid-state transformation mechanism of CDHA into BCP was proposed.