Low temperature synthesis of hydroxyapatite from CaHPO4·2H2O and Ca(OH)2 based on effect of the spark plasma system (SPS)

A mixture of 6 mol of CaHPO4·2H2O and 4 mol of Ca(OH)2 was reacted to produce hydroxyapatite (HA) by spark plasma system (SPS). The reaction was carried out at 300–1200 °C under pressure of 20–670 MPa for 10 min in a vacuum. HA formation started at 300 °C at 600 MPa and was completed at 500 °C at 670 MPa, the same product being obtained at 1200 °C in air using a furnace. The temperature of the HA formation increased with decreasing pressure and was 1150 °C under 20 MPa. There was a linear relationship between the reaction temperature and pressure. The crystal size of the HA prepared at 500 °C at 670 MPa and that at 600 °C at 600 MPa by SPS were less than 1 and 2 μm, respectively.