A thermoanalytical study of synthetic carbonate-containing apatites

This study explores the synthesis and thermoanalytical properties of two series of carbonate-apatites, represented as Ca10(PO4)6 x(CO3)2(F,OH)2, derived from aqueous solutions at temperatures of 20 and 80°C. The initial solutions included a mix of Ca2+, Mg2+, NH4+, PO43-, F-, CO3, and NO3- ions, with Na+ introduced in the second series. Despite low crystallinity, the synthesized apatites exhibited characteristic structures confirmed through X-ray diffraction (XRD) and infrared (IR) analyses. Their thermal degradation was evaluated using simultaneous thermogravimetric analysis/differential thermal analysis (TG/DTA) and evolved gas analysis (EGA) techniques. The distinct thermal behavior of samples containing NH4+ and Na+ at varying temperatures was analyzed in detail. Notably, gas release at elevated temperatures indicated significant thermal rearrangements, leading to stable hydroxy-fluorapatite structures post 1000°C. The results underscore the lability of the precipitated apatite crystalline structure before forming a more stable crystalline phase after volatile release. A comprehensive understanding of the synthetic conditions and thermal responses of these apatites is crucial for their applications in biological and material sciences.