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Effect of temperature variation on the corrosion behaviour and semiconducting properties of the passive film formed on chromium oxide coatings exposed to saline solution Oje, A.M.; Ogwu, A.A.; Rahman, S. Ur; Oje, Alex I.; Tsendzughul, Nathaniel AbstractThe corrosion behaviour of chromium oxide coatings and semiconducting properties of the passive film formed on the surface of the coated samples when exposed to saline solution at a temperature range 25°C to 65°C was investigated. The cyclic polarisation results revealed that the coatings tested at an electrolyte temperature range 25°C to 35°C possess superior resistance to pitting corrosion when compared to coatings tested at higher temperatures. Our Mott-Schottky analysis suggests that this variation in corrosion resistance can be linked to the increase in the amount of the defect density present in the films and enhanced diffusion at higher temperatures.

Chromium oxide coatings prepared by radiofrequency reactive magnetron sputtering on stainless steel substrates were exposed to Ringer's physiological solution and tested for their electrochemical corrosion stability using an open circuit potential measurement, potentiodynamic polarization, electrochemical impedance spectroscopy and Mott–Schottky analysis. The coatings were found to be predominantly Cr2O3, based on the observation of the dominance of A1normalg and Eg symmetric modes in our Raman spectroscopic investigation and the Eu vibrational modes in our Fourier transform infrared spectroscopic measurements on the coatings. We investigated for the presence of chromium ions in Ringer's solution after all of the above electrochemical tests using atomic absorption spectroscopy, without finding a trace of chromium ions at the ppm level for coatings tested under open circuit and at the lower potentials implants are likely to experience in the human body. The coatings were further exposed to Ringer's solution for one month and tested for adhesion strength changes, and we found that they retained substantial adhesion to the substrates. We expect this finding to be significant for future orthopaedic implants where chromium ion release is still a major challenge.

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