JOURNAL OF MATERIALS SCIENCE-MATERIALS IN MEDICINE, vol.22, no.4, pp.809-817, 2011 (SCI-Expanded)
The effects of solid state synthesis process parameters and primary calcium precursor on the cement-type hydration efficiency (at 37A degrees C) of alpha-tricalcium phosphate (Ca-3(PO4)(2) or alpha-TCP) into hydroxyapatite (Ca10-xHPO4(PO4)(6-x)(OH)(2-x) x = 0-1, or HAp) have been investigated. alpha-TCP was synthesized by firing of stoichiometric amount of calcium carbonate (CaCO3) and monetite (CaHPO4) at 1150-1350A degrees C for 2 h. Three commercial grade CaCO3 powders of different purity were used as the starting material and the resultant alpha-TCP products for all synthesis routes were compared in terms of the material properties and the reactivity. The reactant CaHPO4 was also custom synthesized from the respective CaCO3 source. A low firing temperature in the range of 1150-1350A degrees C promoted formation of beta-polymorph as a second phase in the resultant TCP. Meanwhile, higher firing temperatures resulted in phase pure alpha-TCP with poor hydraulic reactivity. The extension of firing operation also led to a decrease in the reactivity. It was found that identical synthesis history, morphology, particle size and crystallinity match between the alpha-TCPs produced from different CaCO3 sources do not essentially culminate in products exhibiting similar hydraulic reactivity. The changes in reactivity are arising from differences in the trace amount of impurities found in the CaCO3 precursors. In this regard, a correlation between the observed hydraulic reactivities and the impurity content of the CaCO3 powders-as determined by inductively coupled plasma mass spectrometry-has been established. A high level of magnesium impurity in the CaCO3 almost completely hampers the hydration of alpha-TCP. This impurity also favors formation of beta- instead of alpha-polymorph in the product of TCP upon firing.