Nano-beta-tricalcium phosphates synthesis and biodegradation: 1. Effect of microwave and SO ₄ ²⁻ ions on β-TCP synthesis and its characterization

Abstract

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 beta-TCP (1.5). Additionally, lowering the temperature and pH values accelerated HPO(4)(2-) incorporation in the CDHA structure. HPO(4)(2-) is considered as an essential source for beta-TCP formation. Sulfate ion doping during the maturation period is proved to be an effective step to eliminate the pyrophosphate P(2)O(7)(2-) 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 beta-TCP purity despite its ability to reduce the particle size. A purity of 99.32% beta-TCP with respect to the P(2)O(7)(2-) phase was achieved by increasing the sulfate ion concentration from 2% to 3% and the calcination temperatures from 900 degrees C to 1100 degrees C.