Phase Transformation and Morphology of Calcium Phosphate Prepared by Electrochemical Deposition Process Through Alkali Treatment and Calcination

The phase transformation and morphology of calcium phosphate prepared by the electrochemical deposition (ECD) process through alkali treatment and calcination have been characterized using X-ray diffraction (XRD), thermogravimetry and differential thermal analyses (TG/DTA), and scanning electron microscopy (SEM). At the ECD process, when the excess OH⁻ was produced, the reaction of 10Ca²⁺+6PO ₄ ³⁻ +2OH–→Ca₁₀(PO₄)₆(OH)₂ takes place on the Ti-6Al-4V and the HA is deposited. The XRD results reveal that the as-deposit was mostly composed of dicalcium phosphate dehydrate (Ca₂H₄P₂O₉; DCPD) and the minor phase of hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂; HA). After NaOH treatment, all DCPD were converted to HA. Moreover, the content of HA phase increases with ECD potential. After being calcined at 673 K and 873 K (400  °C and 600  °C) for 4 hours, the phase of HA maintained the major phase for an alkali-treated deposited sample. After being calcined at 1073 K (800  °C) for 4 hours, some HA decomposed and caused the minor phases of β-tricalcium phosphate (β-Ca₃(PO₄)₂; β-TCP), calcium pyrophosphate (Ca₂P₂O₇; CPP), and calcium oxide (CaO) formation. The β-TCP becomes the major phase with residual HA and CaO after being calcined at 1273 K (1000  °C) for 4 hours. The crack forms due to the release of absorbed water from the interior to top surface of sample. For the as-alkali treatment samples, the microstructures were affected by ECD potentials; when the deposited samples after alkali treatment and calcined at 1073 K (800 °C) for 4 hours, the microstructure presents the need-like “preforming HA” (pre-HA) from the matrix of plate-like postforming HA (post-HA).