Creation and investigation of chitin/HA double-layer coatings on AZ91 magnesium alloy by dipping method
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Seyed Rahim Kiahosseinia) Department of Engineering, Damghan Branch, Islamic Azad University, Damghan 3671639998, Iran (Received 6 April 2017; accepted 24 May 2017)
In this study, chitin was deposited on AZ91 magnesium alloy at room temperature for 180 min, and then HA coating was applied as second layer for 180, 240, 300, 360, and 420 min by dipping method. The layers were analyzed by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and field emission-scanning electron microscopy (FE-SEM), as well as adhesion, nanohardness, and potentiodynamic polarization tests. XRD results analyzed by Williamson–Hall method revealed residual tensile and compressive strains in the chitin and HA coatings, respectively and with prolonged deposition time to 420 min, coating adhesion decreased. FTIR results indicated the presence of the chemical factors affecting the chitin and HA coatings. FE-SEM results indicated that prolonged deposition time resulted in increased coating density and formation of a porous structure of HA coating. Overall, the optimum corrosion resistance was observed for the sample with 300 min deposition time.
I. INTRODUCTION
Magnesium and its alloys have been extensively used as biodegradable implant materials for medical applications,1,2 because of their good mechanical and biocompatible properties.3 Although the absorption rates of magnesium alloys, such as AZ31, AZ91, and MgCa, are less than that of pure magnesium, their corrosion rates must still be controlled.4,5 Using biocompatible coatings, such as calcium phosphate materials, on magnesium alloy surfaces can significantly reduce the corrosion rate of biodegradable implant in the body environment.4,6 Hydroxyapatite (HA) is a bioactive material with Ca10(PO4)6(OH)2 chemical composition7,8 that has been widely used in dental9 and orthopedic applications to enhance biocompatible implant materials.10–14 HA coating can be used for increasing biocompatibility,15,16 and it prevents implant metal corrosion during the initial stages after implants. HA coating can create acceptable mechanical properties and elastic moduli that are close to the bone of the human body.11,12,17 Considering the HA brittleness, researchers have used a combination of alternative apatite that has a similar chemical composition and inorganic phase to the bone.18 HA nano-coating is a promising solution not only for delaying the biodegradation of magnesium alloys but also for promoting biomimetic behavior, which improves the effectiveness of orthopedic implants. In addition to Contributing Editor: Lakshmi Nair a) Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2017.231
controlling magnesium corrosion, HA nano-coating provides a desirable environment for rebuilding bone tissues.19 Previous studies have utilized different coating methods, such as dipping method, plating, cathodic arc technique, chemical solution deposition, cold spray deposition, plasma electrolytic oxidation, and a deposition process involving sound accelerati
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