The study of electrodeposition of hydroxyapatite-ZrO2-TiO2 nanocomposite coatings on 316 stainless steel

Abstract

In this research pure HA and HA-ZrO2-TiO2 nanocomposite coatings (named HZT coatings) were successfully synthesized by merging two usual electroplating methods. In order to deposit pure HA coating a particular saline solution of Calcium and Phosphate was prepared with pH = 4.2, thermodynamically rich of hydroxyapatite. XRD and FTIR studies prove the synthesis of hydroxyapatite during electrodeposition process. To synthesize composite coatings with rational molar ratios of composite agents to matrix, two different concentrations of ZrO2-TiO2 suspensions were added to Ca-P solution at the pH = 4.2 and electrodeposition process done similar to pure HA sample. XRD, FTIR and FESEM (EDS) analyses prove that composite coatings electrodeposited successfully too. The effect of ZrO2-TiO2 composite agents on the characteristics of the coatings were investigated using X-ray diffraction (XRD), Fourier transform infrared spectra (FTIR), Field emission scanning electron microscopy (FESEM) and energy dispersive spectroscopy. Polarization test was carried out to evaluate corrosion behavior of the coatings. In-vitro test was done in SBF solution and bioactivity of coatings was evaluated using FESEM observation.Adding ZrO2-TiO2 nanoparticles makes different changes in the coating specifications. In composite coatings hydroxyapatite has higher crystallinity (92%) rather than pure HA (80%). FESEM observations reveal new morphologies of electrodeposited HA, such as micro-nanorods of HA formed in composite coatings that are not mentioned before in the literature. EDS results show that adding more nanoparticles to the solution results in more nanoparticles deposition in composite coating.The minimum corrosion current density (icorr.) of coatings was for HZT2 composite coating equal to 0.01 μA/cm2 while icorr. of bare substrate was 1.5 μA/cm2 (it means that icorr. of composite coating is 0.007 icorr. of bare substrate.). As a result of nanoparticles addition, porosity is decreased from 46% for HA coating to 6% for HZT2 coating. EIS results show that corrosion resistance of coating increased as a result of adding nanoparticles and HZT2 coating has largest charge transfer resistance among the prepared coatings.The FE-SEM observations suggest that the coatings would demonstrate bioactive behavior because natural hydroxyapatite (deposits formed during immersion) is formed during immersion.