Preparation and characterization of biphasic calcium phosphate ceramics of desired composition

A modified processing route for fabricating dense and porous biphasic calcium phosphate (BCP) ceramics of desired and reproducible phase composition (hydroxyapatite (HA)/β-tricalcium phosphate (β-TCP) ratio) has been developed. The principal idea of the route was combining a precipitation and a solid phase methods. First, a nonstoichiometric (slightly carbonated calcium-deficient) HA (CdHA) precipitate was synthesized by mixing a calcium carbonate (CaCO3) water suspension with an orthophosphoric acid (H3PO4) solution in abundance (related to the amount resulting in a stoichiometric HA) under definite conditions, and a powder of the precipitate was prepared and calcinated in air (860°C, 1.5 h). In the second stage, a BCP ceramics of the composition determined by the calcium-deficiency in a calcinated powder (the acid abundance in a mixture) was processed by sintering powder compacts with or without a porosizer under appropriate conditions (1,200°C, 2h). A calibrating dependence of the HA/β-TCP ratio in the ceramics on the acid abundance has been plotted which enabled a controlled preparation of BCP ceramics. A correlation based on unresolved bands in ν4-PO43− domain in IR-spectra of nanostructured BCP materials was found. Using the correlation, the process of CdHA → β-TCP transformation could be easily monitored. The density and microhardness of the BCP ceramics neglectly depended on the composition, however, the compressive strength did: the lower the HA/β-TCP ratio, the higher the strength in the dense materials.