The effect of chemical passivation on the corrosion of a commercial cobalt-chromium alloy

Abstract

Introduction:One of the important factors in the biocompatibility of alloys used in manufacturing of dental prostheses is their corrosion resistance. Lack of this property reduces the thickness of the metal, and as a result causes the prosthesis to break down and tissue damage. The aim of this in vitro study was to examine the corrosion resistance of a type of cobalt-chromium alloy after chemical passivation. passivation develops a surface layer on the metal and establishing conditions where corrosion and ion solubility are significantly reduced.

Materials and methods:Twenty Flexicast alloy samples were prepared. They were polished after casting. A group was placed in solution Na2SO4 × 10H2O (PH = 7) + graphite for 24 hours in order to be passived and then exposed to resin and then in normal saline. The second group was immersed in normal saline without passivation. Corrosion tests were performed as weight loss for 4 weeks. To compare the corrosion rate at 4 different times, Kruskal-Wallis test and Mann Whitney test was used to compare the two groups. Significance level p <0.05 was considered.

Results:Kruskal-Wallis results showed that in the non-passived samples, the corrosion level was similar in 4 studied times (during 4 weeks). Significant differences were observed in passived samples during 4 weeks, so that corrosion rate in the first and second weeks was similar and significantly lower than the third and fourth weeks. Comparison of corrosion rate in two groups with the Mann-Whitney U test showed that in 1,2,3,and 4 weeks the corrosion rate in the passived samples was significantly lower than the non-passived samples (P<0.05).

Conclusion:The corrosion rate of the passived samples at all 4 times was not significantly lower than the non-passived samples. Chemical passivation of Flexicast alloy significantly reduced corrosion over time.