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Investigating the in vitro corrosion behaviour of four as-cast magnesium-zinc alloys for orthopaedic applications in Simulated Body Fluid

University of British Columbia

The use of metallic biomaterials, such as titanium alloys, stainless steels and cobalt-chromium alloys in bone implant devices is indispensable to support the bone during the healing period. However, prolonged use of implantation devices made of these inert biomaterials may lead to stress shielding due to their high elastic moduli resulting in the loss of bone density during the remodeling process. Therefore, magnesium is being investigated as a possible biomaterial for temporary fixation devices as it has low elastic modulus close to that of the human cortical bone in addition to being biocompatible and biodegradable in the aqueous chloride environment of the human body. However, the high corrosion rates of magnesium due to its low standard electrode potential compromise the mechanical integrity of the implant during the bone healing process. This thesis involved the fabrication of four magnesium-zinc alloys with 1, 1.5, 2 and 5 weight percent Zn in Mg in an attempt to tailor the corrosion rate of the alloy. The hardness and densities of the alloys were determined. The microstructure of the alloys was characterized by chemical analysis both before and after corrosion experiments. Both gravimetric and electrochemical studies were used to understand the in vitro corrosion behaviour of the alloys in static Simulated Body Fluid (SBF). The weight loss measurements after immersion tests indicated that the as-cast Mg-2.0Zn alloy had the lowest corrosion rate owing to network-like second phase precipitations. The potentiodynamic polarization experiments yielded extremely low corrosion rates for all the alloys, and were correlated to the microstructures of the corroded surfaces. Electrochemical Impedance Spectroscopy (EIS) was conducted to study and model the interface between the sample and the SBF. The electrochemical test results indicated that the Mg-1.0Zn exhibited the highest polarization resistance leading to the decreased corrosion rate of the alloy. The corrosion products consisted of magnesium carbonates, magnesium hydroxides and calcium phosphates as indicated by Fourier Transform Infrared Spectroscopy (FTIR), X-Ray Diffraction (XRD) and X-ray Energy Dispersive Spectroscopy (X-EDS). Results were suggestive that, Mg-Zn alloys with ≤2 wt. % Zn were promising as a suitable metallic biomaterial for orthopaedic applications and should be considered for further in vitro and in vivo studies.

Text

2015-08-31

Attribution-NonCommercial-NoDerivs 2.5 Canada

http://hdl.handle.net/2429/54705

Mechanical Engineering

University of British Columbia

UBCO

http://creativecommons.org/licenses/by-nc-nd/2.5/ca/