Calcium phosphate apatites with variable Ca/P atomic ratio I. Synthesis, characterisation and thermal stability of powders.

Single phased apatitic calcium phosphate powders Ca(10-x)(PO4)(6-x)(HPO4)x(OH)(2-x) with Ca/P molar ratio ranging from 1.5 to 1.667 (0 < or = x < or = 1) were synthesised using wet method. Outside this compositional range the powders were biphasic mixtures composed of a calcium phosphate apatite and CaHPO4 (Ca/P < 1.5) or Ca(OH)2 (Ca/P > 1.667). Temperature and pH of synthesis were the preponderant parameters for the control of the precipitate composition. The precise determination of the chemical composition requires the use of several complementary techniques and thermal treatments of powders. These techniques include high resolution and high temperature X-ray diffractometry and FTIR spectroscopy and show that very small variations of the Ca/P molar ratio of the powder lead to great changes in powder composition and characteristics after thermal treatment.