Effect of NaOH(aq) treatment on the phase transformation and morphology of calcium phosphate deposited by an electrolytic method

Calcium phosphates deposited by an electrochemical deposition process (ECD) have been prepared in the 0.04 M Ca(H2PO4)2H2O (MCPM) solution at 10 V, 60 °C and 80 Torr for 1 h. Subsequently, the deposits have been treated in various concentrations of NaOH(aq) solutions at different temperatures for 1 h. When excess OH− is present in the ECD process, hydroxyapatite (HAP) referred to as pre-HAP is deposited on the Ti-6Al-4 V substrate. After NaOH(aq) treatment, all deposits are converted to the HAP phase. The treatment in 1-2.5 M NaOH(aq) solution at over 60 °C offers a more proper environment for the HAP conversion, referred to as post-HAP, and has an average crystallite size of about 21 nm. For more than 5 M NaOH(aq) treatment, both pre- and post-HAP show a reduction of 5-20 nm in particle size.