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J Mater Sci: Mater Med (2014) 25:12271237 DOI 10.1007/s10856-014-5161-0
Electrochemical characteristics of calcium-phosphatized AZ31 magnesium alloy in 0.9 % NaCl solution
Branislav Hadzima Mansour Mhaede
Filip Pastorek
Received: 26 September 2013 / Accepted: 21 January 2014 / Published online: 30 January 2014 Springer Science+Business Media New York 2014
Abstract Magnesium alloys suffer from their high reactivity in common environments. Protective layers are widely created on the surface of magnesium alloys to improve their corrosion resistance. This article evaluates the inuence of a calcium-phosphate layer on the electro-chemical characteristics of AZ31 magnesium alloy in0.9 % NaCl solution. The calcium phosphate (CaP) layer was electrochemically deposited in a solution containing0.1 M Ca(NO3)2, 0.06 M NH4H2PO4 and 10 ml l-1 of H2O2. The formed surface layer was composed mainly of brushite [(dicalcium phosphate dihidrate (DCPD)] as proved by energy-dispersive X-ray analysis. The surface morphology was observed by scanning electron microscopy. Immersion test was performed in order to observe degradation of the calcium phosphatized surfaces. The inuence of the phosphate layer on the electrochemical characteristics of AZ31, in 0.9 % NaCl solution, was evaluated by potentiodynamic measurements and
electrochemical impedance spectroscopy. The obtained results were analysed by the Tafel-extrapolation method and equivalent circuits method. The results showed that the polarization resistance of the DCPD-coated surface is about 25 times higher than that of non-coated surface. The CaP electro-deposition process increased the activation energy of corrosion process.
1 Introduction
Orthopaedic devices required for the immobilization and xation of bone fractures are conventionally metallic as they need to maintain mechanical integrity and biocompatibility for the duration of the bone healing period. Traditionally these metallic implants have consisted of titanium alloys and stainless steel. Metallic alloys of cobalt, chromium and nickel base are also well utilized biomaterials. Upon immediate assessment, metallic materials such as these meet the criteria mentioned above; however, closer inspection reveals there are many disadvantages in regard to their use. The mentioned metallic alloys have demonstrated the release of toxic corrosion products [14] and allergens [5]. The elastic modulus of unalloyed commercially pure titanium has been documented as being between 103 and 107 GPa [6, 7], whilst that of trabecular/cancellous and cortical bone have been documented as 314.8 and 18.627 GPa, respectively [811]. The greater elastic modulus of titanium...