In Operando Analysis of Passive Film Growth on Ni-Cr and Ni-Cr-Mo Alloys in Chloride Solutions

Abstract

The instantaneous kinetics of oxide formation and growth, in competition with passive film dissolution and breakdown, were investigated for Ni-22 Cr and Ni-22 Cr-6 Mo (wt%) during single step passivation at +0.2 V SCE . Experiments were conducted in selected acidic and alkaline chloride-containing environments using simultaneous AC and DC electrochemistry; including on-line Inductively Coupled Plasma-Mass Spectrometry (ICP-MS). In parallel experiments, in-situ neutron reflectometry (NR) and ex-situ X-ray photoelectron spectroscopy (XPS) were utilized to characterize the formation of surface oxide films as a function of time. The specific roles of pH and Mo during passivation and breakdown kinetics are highlighted, providing an insight into the fate of the elements which comprise the alloys, and their effects on passivation behavior. It was observed that early oxidation of both Ni and Cr-species occurred in acidic electrolyte. Preferential dissolution of Ni 2+ at later times enabled gradual Cr 3+ enrichment within the surface film. However, greater relative stability of NiO and Ni(OH) 2 was observed in the alkaline condition. Upon alloying Ni-Cr with Mo, Cr 3+ became increasingly enriched in the surface film during anodic polarization. Oxides were interpreted to consist of non-stoichiometric solid solutions formed via solute capture.

Potential-pH diagrams considering complex oxide solution phases for understanding aqueous corrosion of multi-principal element alloys

“…To evaluate the current thermodynamic analysis with an experiment, the atomic emission spectroelectrochemistry (AESEC) [49][50][51][52] was introduced to measure the total quantity of dissolved alloy components in aqueous solution, which was shown to be consistent with the 3D-APT and XPS analysis 36,37,52,53 . AESEC measurements of dissolved alloy components were performed in 0.1 M (i.e., mol per liter or molarity) NaCl, pH = 4 solution at applied potentials from 0.00 to 0.34 V vs. SHE.…”

Atomic Emission Spectroelectrochemistry: Real-Time Rate Measurements of Dissolution, Corrosion, and Passivation

“…For steady-state corroding systems, the EIS spectrum may in some cases be used to estimate the corrosion rate without significant electrochemical perturbation, and the EIS spectrum itself is often considered a fingerprint for specific mechanisms revealing different kinetic processes over a wide range of time constants. It is straightforward to perform EIS simultaneously during an AESEC experiment and Cwalina, et al, 87 used high-frequency AC electrochemical measurements to follow the growth of oxide films for the Ni-Cr-Mo system during conventional DC experiments coupled with ICP-MS measurement of elemental dissolution rates.…”

Recent Advances in Corrosion Science Applicable To Disposal of High-Level Nuclear Waste

“…Oxide formation at an applied potential in the passive range was extremely rapid and efficient, with lower quasi-steady-state passive current densities than for the commercial alloy C-22. Oxide thickness at the quasi-steady-state condition was in the nanometer range and consistent with logarithmic or reverse-logarithmic growth . XPS analysis of a sample polarized at a potential in the passive region indicated that all elements in the alloy were oxidized.…”

“…Oxide thickness at the quasi-steady-state condition was in the nanometer range and consistent with logarithmic or reverselogarithmic growth. 397 XPS analysis of a sample polarized at a potential in the passive region indicated that all elements in the alloy were oxidized. Using APT, the oxide was found to be a nonstoichiometric solid solution closely resembling a highly disordered corundum structure with significant enrichment in Cr and Ru, Mo and W near their bulk composition, and depletion of Fe and Ni (Figure 28).…”