Synthesizing and comparing HA–TiO2 and HA–ZrO2 nanocomposite coatings on 316 stainless steel

Abstract

In this research, hydroxyapatite coating and composite hydroxyapatite coatings containing nanoparticles were fabricated using a single step electrodeposition method. To investigate the effect of compositing agent type on hydroxyapatite structure, two different compounds (titania and zirconia) were used. Each compound was used at two different concentrations to observe the effect of compositing agent content on matrix structure. Pure hydroxyapatite was deposited with a water based Calcium–Phosphate (Ca–P) solution with pH = 4.2. To deposit composite coatings, a merged solution was prepared by merging Ca–P solution with aqueous TiO2 (ZrO2) suspension. Prepared coatings were analyzed using thickness measurement, XRD, FTIR, FESEM, polarization test and immersion in SBF solution. In the first step, XRD, FTIR and FESEM results proved the formation of hydroxyapatite using Ca–P solution and analysis of composite coatings proves the existence of nanoparticles in the coatings as compositing agent and the coating procedure was successful. Thereafter, polarization and immersion results indicate that composite coatings show superior properties than pure hydroxyapatite. The properties of hydroxyapatite matrix are influenced not only by the type of the compositing agent but also by the content of the additive. Adding nanoparticles changes different characteristics of pure HA, such as (1) decreasing the thickness of the coating, pure hydroxyapatite was 5.5 µm and the thickness of HA–ZrO2 (ZrO2: 6 mM = HZ2) composite coating was 4.4 µm; (2) increasing the crystallinity (Xc), Xc for HZ2 coating is 86% and Xc for pure HA is 80%; (3) obvious changes in morphology has occurred and new morphologies of HA are observed which has not been mentioned in the literature previously; (4) composite coatings have more positive Ecorr than pure HA, Ecorr. of HZ2 coating is − 0.23 which is the most positive one and Ecorr. of HA is − 0.41; (5) composite coatings have smaller porosity ratio than pure HA; (6) Pure and composite coatings are bioactive, but composite coatings show different bioactivity behavior.