Electrodeposition of hydroxyapatite coating on CoNiCrMo substrate in dilute solution

In the present work, calcium phosphate coatings on CoNiCrMo substrate were prepared by electrodeposition at different voltages (− 1.4,−1.6,−1.8,−2.0 and − 2.2 V versus Ag/AgCl) in the mixed solution of 0.6 mM Ca(NO3)2·4H2O and 0.36 mM NH4H2PO4 at 80 °C. The electrocrystallization process of the moderate potential (− 1.8 V) was addressed. To investigate the role of pH on HA formation during electrodeposition, different kinds of uncharged substrates (including CoNiCrMo, non-conducting polyethylene, Ti substrate and glass) were placed close to the cathode separately in some of the electrodeposition experiments at − 1.8 V. Moreover, the effect of pH on saturation indexes with respect to hydroxyapatite, octacalcium phosphate and dicalcium dihydrogen phosphate of this dilute solution were calculated by a computer program PHREEQC. The results showed the moderate potential sample (− 1.8 V) exhibited a uniform coating consisted of fine crystallized hydroxyapatite with hexagonal prism shape. It was also found the local pH value plays a crucial role in the formation of HA during the electrodeposition.