In vitro corrosion of pure magnesium and AZ91 alloy—the influence of thin electrolyte layer thickness

In vivo degradation predication faces a huge challenge via in vitro corrosion test due to the difficulty for mimicking the complicated microenvironment with various influencing factors.A thin electrolyte layer(TEL)cell for in vitro corrosion of pure magnesium and AZ91 alloy was presented to stimulate the in vivo corrosion in the micro-environment built by the interface of the implant and its neighboring tissue.The results demonstrated that the in vivo corrosion of pure Mg and the AZ91 alloy was suppressed under TEL condition.The AZ91 alloy was more sensitive than pure Mg to the inhibition of corrosion under a TEL thickness of less than 200 mm.The TEL thickness limited the distribution of current,and thus localized corrosion was more preferred to occur under TEL condition than in bulk solution.The TEL cell might be an appropriate approach to simulating the in vivo degradation of magnesium and its alloys.

Corrosion behavior of pure zinc and its alloy under thin electrolyte layer

The corrosion behavior of zinc and its alloy under thin electrolyte layers （TEL） in 0.1M NaC1 solution was investigated by cathodic polarization curves and EIS. There was only one phase in pure zinc while zinc alloy consisted of eutectic phase and primary phase. Corrosion rate of zinc alloy was faster than that of pure zinc due to the effect of the micro-galvanic couples between the primary phase and the eutectic phase. The results indicated that corrosion rate of zinc alloy was greatly enhanced under TEL than that in bulk solution. Pure zinc exhibited minimum corrosion resistance as TEL decreased to 198 #m. Zinc and its alloy exhibited localized corrosion under TEL while it was more uniform in bulk solution. There were two capacitive loops in high frequency （HF） and middle frequency （MF） respectively, with finite length diffusion in low frequency （LF） presented in EIS. For pure zinc under TEL below 300 pm an additional inductive loop presented in MF-LF. The corrosion products and morphology were respectively examined by X-ray diffraction （XRD）, FTIR （Fourier Transform Infra Red） and SEM-EDS. FTIR micro spectroscopy results indicated that the component of the corrosion products was similar at different section of the specimen surface but different in content.