Variations of structure and composition in magnesium incorporated hydroxyapatite/β-tricalcium phosphate

The phase evolution of magnesium incorporated hydroxyapatite/β-tricalcium phosphate (HA/β-TCP) ceramics of high purity prepared by solid-state reaction was investigated with the aid of x-ray diffraction and infrared spectroscopy (IR) in transmittance mode analysis. The dependence of the microstructure on the phase evolution of biphasic ceramics during natural sintering was also investigated as a function of Mg content. When sintered at 1100 °C, Mg is preferentially incorporated into the β-TCP phase rather than the HA phase. This Mg incorporation into the β-TCP effectively suppresses the phase transition from β- to α-TCP. With increasing sintering temperature, the solubility limit of the Mg in the β-TCP decreases and Mg starts to be either incorporated into the HA phase or segregated as free MgO. The decreased Mg content in the β-TCP facilitates the phase transition from β- into α-TCP, at 1300 °C or higher. Different processing methods on Mg addition show that the retarded phase transition from β- to α-TCP is the inherent property of Mg-doped HA/TCP. The variations in processing parameters mainly affect the microstructure instead of the phase evolution, leading to highly densified HA/β-TCP ceramics.