Phase Transformation of Calcium Phosphates by Electrodeposition and Heat Treatment

The effect of heat treatment on the calcium phosphate deposited on Ti-6Al-4V substrate using an electrolytic process is investigated. The calcium phosphate was deposited in a 0.04 M Ca(H₂PO₄)₂·H₂O (MCPM) solution on a Ti-6Al-4V substrate at 333 K (60 °C), 10 V, and 80 Torr for 1 hour, and calcined at various temperatures for 4 hours. The X-ray diffraction (XRD) results demonstrate that the phases are dicalcium phosphate (CaHPO₄, DCPD) and hydroxyapatile [Ca(PO₄)₆ (OH)₂, HAP] for the as-deposited samples. When the deposited sample was calcined at 873 K (600 °C) for 4 hours, the XRD results show that the transformation of DCPD to HAP occurs. Moreover, HAP converts to β-TCP, CPP, and CaO. For the sample calcined at 1073 K (800 °C) for 4 hours, the scanning electron microscopy (SEM) micrograph reveals that the crack of the calcined sample propagates with a width of about 3 μm. This result is due to HAP becoming decomposed and converting to β-TCP, CPP, CaO, and H₂O. The vaporization of H₂O within the calcined sample promotes the crack propagation and growth.