In vitro corrosion resistance of titanium in fluorinated environment

The aim of this study was to evaluate the resistance to initial and ongoing corrosion of titanium samples in a fluorinated environment, according to specification G5/95 of the American Society for Testing and Materials (A.S.T.M.). Commercially pure titanium was used in the experimental tests. This was a grade 4 titanium in accordance with A.S.T.M. F67-89 Gd 4 (Fe 0.20, O 0.34, C 0.01, N 0.012, H 0.0006, Ti 99.4374). Three cylindrical samples with 6.35 ± 0.003 mm diameter and 20.00 ± 1 mm length were utilized in every solution. The potentiodynamic cyclic polarization tests were performed in two different solutions: 1) Fusayama artificial saliva 2) fluorinate solution with 0.5% NaF. The “ex novo” prepared solutions before each measurement were preserved at 37.5° C temperature and deaerated through azote gurgling, 24 hours before the experiment. 1 hour before polarization the samples were immersed in the electrolyte for recording and stabilizing corrosion potential. This operation simulates potentiometric test to measure the loss potential of the examined material. Afterwards, potentiometric tests, according A.S.T.M. G5/95 rule, were performed. The results indicate that the titanium resting potential becomes anodic in fluorinated environment and in such solution corrosive phenomena of titanium are facilitated. The exposure of titanium in artificial saliva with 0.5% NaF determines a radical reduction of breakdown and repassivation potential of titanium, making it more easily exposed to beginning and spreading of the pitting and crevice corrosion.