Nano-beta-tricalcium phosphates synthesis and biodegradation: 1. Effect of microwave and SO42− ions on β-TCP synthesis and its characterization

Nano-sized calcium deficient hydroxyapatite (CDHA) powders with an average particle size less than 100 nm were prepared by a co-precipitation method at low temperature. The initial Ca/P molar ratio was chosen to be less than the stoichiometric ratio of ?-TCP (1.5). Additionally, lowering the temperature and pH values accelerated HPO42? incorporation in the CDHA structure. HPO42? is considered as an essential source for ?-TCP formation. Sulfate ion doping during the maturation period is proved to be an effective step to eliminate the pyrophosphate P2O72? phase that results during the calcination of CDHA with Ca/P < 1.5. Furthermore, the heating effect of microwave irradiation resulted in an increase in Ca ion concentration and lowered the CDHA deficiency which affected ?-TCP purity despite its ability to reduce the particle size. A purity of 99.32% ?-TCP with respect to the P2O72? phase was achieved by increasing the sulfate ion concentration from 2% to 3% and the calcination temperatures from 900 ?C to 1100 ?C.