Combustion synthesis of heterogeneous calcium phosphate bioceramics from calcium oxide and phosphate precursors

Abstract

The solid-state reaction of combustion synthesis has been demonstrated to be capable of rapidly producing materials for biomedical applications. Reactant powders of CaO and P2O5 were pressed into cylinders and reacted by heating a tungsten filament in either an argon, CO2 or N2 atmosphere. Reaction systems examined were: (1) 3CaO + P2O5 → Ca3(PO4)2 (TCP) and (2) 4CaO + P2O5 → Ca4P2O7 + O2 (TTCP). The product pellets were bright white with a thin glassy appearing outer layer observed with a very porous interior (range of 5–1000 μm pore diameter) regardless of reaction atmosphere. No evidence of sintering is apparent such as intact precursor particles or necking between particles. In the TCP system characteristic XRD peaks for crystalline β-, α-TCP, and HA are noted while in the TTCP system tetracalcium phosphate, α-TCP, and HA are present. DSC analysis indicates the ignition temperature 450°C when P2O5 decomposes to PO3 to react with CaO. SHS is a viable method to manufacture heterogeneous calcium phosphates from CaO and P2O5 precursors. The formation of HA and TCP, regardless of stoichiometry or atmosphere is due to thermodynamic energies of the products while other phases are preserved due to limited kinetics in the system’s rapid heating and cooling.