Effect of surface passivation on corrosion of a cobalt-chromium dental alloy: surface morphology and chemical composition studies

Biocompatibility in some respects depends on the corrosion behavior of dental alloys. The purpose of this study was to investigate the effect of surface passivation of a cobalt chromium alloy on corrosion behavior.

In this experimental study, 20 samples of Flexicast dental alloy were prepared according to ADA97 standard and after casting, the samples were polished to the mirror surface. Electrolytic passivation was employed by immersion of one first series of samples in Na2SO4 solution for 24 hours at room temperature. The second series of specimens was not passivated. Surface morphology and chemical composition before and after passivation studied by scanning electron microscopy and energy-dispersive X-ray spectroscopy were used to investigate the corrosion behavior in saline solution. Corrosion test was conducted for 4 weeks and surface of specimens were monitored each week. The chemical composition results were analyzed by Kruskal-Wallis and Mann-Whitney tests using SPSS17 software.

The passivated specimens exhibited higher corrosion resistance while pitting corrosion was detected in all specimens. Kruskal-Wallis test showed a significant difference between the two groups of passivated and non-passivated samples. The Mann-Whitney test showed that the cobalt, chromium and oxygen ions were significantly different between the two groups (P <.0.05).

The rate of corrosion and formation of pits were significantly reduced by surface passivation.