In vitro corrosion behavior of cast iron–platinum magnetic alloys

Objective: The objective of this study was to investigate the corrosion resistance of cast Fe–Pt alloys of varying compositions for use as attachment keepers and to make a comparison with the corrosion resistance of magnetic stainless steel. Methods: The corrosion behavior of cast Fe–Pt alloy keepers (Fe–40 at%Pt, Fe–38 at%Pt, Fe–37 at%Pt and Fe–36 at%Pt) was evaluated by means of an immersion test and an anodic polarization test. The solutions used were a 1.0% lactic acid aqueous solution (pH=2.3) (10 ml) and 0.9% NaCl solution (pH=7.3) (10 ml). As a control, the corrosion resistance of a magnetic stainless steel keeper (SUS 447J1: HICOREX) was also measured. Results: Chromium and platinum ions were not detected in either the 1.0% lactic acid or 0.9% NaCl solutions. The only released ions detected were the Fe ions in the 1.0% lactic acid solution. The amounts of Fe ions released from the Fe–40 at%Pt and Fe–38 at%Pt alloys were significantly (p<0.05) lower than from the Fe–37 at%Pt, Fe–36 at%Pt and SUS 447J1 alloys. In the anodic polarization test, the potentials at the beginning of passivation for the four Fe–Pt alloys were higher than for the SUS 447J1 alloy in both solutions. Significance: The Fe–Pt alloys, especially the alloys with higher Pt percentages (Fe–40 and 38 at%Pt), indicated a high corrosion resistance compared to the magnetic stainless steel keeper. A reduction in the Pt percentage may decrease the corrosion resistance in the oral environment.