Electrochemical Corrosion and Surface Analyses of a Ni-Cr Alloy in Bleaching Agents

The aim of this study was to evaluate the corrosion behavior of a Ni-Cr dental casting alloy subjected to 10% hydrogen peroxide (HP) and 10% carbamide peroxide (CP) bleaching solutions, as well as to determine the composition of the surface oxide layer formed on the alloy specimens. Ten cylindrical specimens (4 mm in diameter × 25 mm in height) were cast from a Ni-Cr alloy (Wiron 99) and divided into two groups (n = 5). A potentiodynamic polarization test was employed to compare the corrosion rates of specimens in HP and CP (pH = 6.5). The alloy specimens were allowed to reach a steady open circuit potential (E_corr) for a period of 1 hour before initiating tests at 100 mV versus standard calomel electrode (SCE) below E_corr, scanning at a rate of 1 mV/s in the anodic direction up to 1000 mV over E_corr and then returning to E_corr. The open circuit potentials (E_corr) and current densities (I_corr) were determined from the anodic Tafel regions extrapolated from the curves, with differences in E_corr and I_corr analyzed through one-way ANOVA (α = 0.05). Corrosion rates were calculated from these curves and surface morphology was examined using scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy (EDS) before and after polarization tests.