Effect Of Citrate On Electrolytic Deposition Of Hydroxyaptite Coating On Ti Surface

Inspired by adding modifiers into electrolyte in plating process to improve the quality of the coating, we conducted the investigation on the effect of citrate in the electrolyte on the electrolytic deposition of HA on the titanium substrate in a hope to improve the uniformity and adhesion strength of electrolytically deposited hydroxyapatite (HA) coating on Ti surface.Generally, electrolytic deposition of HA involves two successive reactions: first reaction is hydrogen evolution on cathodic surface; second one is supersaturation of calcium and phosphate ions and precipitation on Ti surface because of the pH increase near the Ti cathode. Analysis on the effect of citrate on this two steps is the key to understand the whole process. In the present study, we focused firstly on theoretical analysis of the citrate adsorbed on Ti electrode surface and its effect on the hydrogen evolution. The experimental results show that the hydrogen evolution rate decreased and the size of the hydrogen bubbles decreased and distributed evenly on the Ti surface. This may help deposition current uniformly distributed and reduce the bubble erosion on coating surface. Secondly, we use spectrophotometer to test the coating weight increment, SEM to observe the crystal morphology changes, electrochemical workstation to record the deposition current. Based on the above information we divided the whole deposition process into 5 phases: absorption period, incubation period, eruptive growth period, extra layer growth period and balanced growth period. We made micro-mechanism and thermodynamic explanations for every period and hypothesized a growth model of HA crystal.Finally, the physical and biological characterization (including adhesion strength, contact angle, roughness and biological activity) of the coating was carried out. The results show that the adhesion strength, smoothness and biocompatibility were improved by the addition of citrate.