The fabrication of near net-shaped hydroxyapatite ceramics by the oxidation of solid, metal-bearing precursors

摘要

Near net-shaped bodies of hydroxyapatite (HA),Ca_10(PO_4)_6(OH)_2, have been fabricated by a novel process:the oxidation of solid, metal-bearing precursors. High-energymechanical alloying was used to produce an intimate powdermixture of metallic calcium and calcium pyrophosphate, #beta#-Ca_2P_2O_7, that possessed an overall stoichiometry consistentwith HA (molar Ca:Ca_2P_2O_7 ratio = 4:3). The milled Ca-Ca_2P_2O_7 mixtures were sufficiently malleable as to allow forcompaction and forming (pressing, machining) into shaped greenbodies with relatively high densities (80-86percent). The greenbodies were converted into phase-pure HA through heat treatmentsat 500-600beg C in dry oxygen (for Ca oxidation), 850beg C inmoist oxygen or air (for HA formation), and 1100-1150beg C inmoist oxygen or air (for sintering). The offsetting volume changesassociated with calcium oxidation (V_m(CaO) 4V_m(CaO) +3Vm(Ca_2P_2O_7)) resulted in HA bodies that retained theshapes and dimensions (to within a few percent) of the metal-bearing precursors.