Synchrotron XPS and Electrochemical Study of Aging Effect on Passive Film of Ni Alloys

Abstract

To investigate the aging effect on a passive film of Ni23Cr15Mo and Ni22Cr9Mo3Nb, synchrotron-based X-ray photoelectron spectroscopy (XPS) was used to analyze the structure and composition of the air-formed passive film on the alloys. The corrosion resistance of the two Ni alloys in 1M NaCl solution was evaluated with electrochemical cyclic polarization measurement. The synchrotron XPS measurement provided detailed information about chemical states of alloying elements in the surface layer, showing that the passive film consists of an inner oxide layer and an outer hydroxide layer. The XPS data allowed precise determination of the chemical composition and the thickness of the outer hydroxide layer, the inner oxide layer, and the underlying subsurface alloy layer. The Cr-oxide in the inner layer grows thicker with aging time, leading to Cr-depletion in the subsurface region. Mo and Nb in the alloy form mixed oxides and hydroxides, and aging in air leads to transformation of the lower valence oxides into higher valence oxides. The freshly formed oxide film exhibits similar barrier properties as the aged oxide film. The stability of the passive film formed on Ni22Cr9Mo3Nb seems to be better than that on Ni23Cr15Mo.

The Oxygen Evolution Reaction Drives Passivity Breakdown for Ni–Cr–Mo Alloys

“…[32] NiO and MoO 2 are good catalysts for the oxygen evolution reaction (OER), [33][34][35][36][37][38][39] which adds another dimension of complexity to understanding the degradation of Ni-Cr-Mo alloys since OER is known to be coupled with dissolution and degradation in other related materials. [40][41][42][43][44][45] The oxidation and corrosion of Ni alloys have previously been studied with electrochemical measurements, [20,31] X-ray photoelectron spectroscopy (XPS), [23,[27][28][29][46][47][48] scanning tunneling microscopy, [21,30,49] time-of-flight secondary-ion mass spectrometry, [50,51] transmission electron microscopy and energy loss spectroscopy, [52,53] operando neutron reflectivity, [54,55] and inline inductively coupled plasma mass spectrometry. [56,57] providing valuable information of the electrochemical behavior, the passive film, and metal dissolution.…”

Reports From the Frontier: The Need for a Better Understanding of Passive Films

“…In this scenario, conducting in-situ film composition analysis is crucial, as exposure to air and dehydration have the potential to induce alterations in composition via phase transformations. Therefore, in-situ methods, including synchrotron X-ray techniques for film composition analysis, 40,41 ASEC for dissolution kinetics, 42,43 and liquid-cell TEM for spatially resolved compositional and structural insights, 30 employed either individually or in combination, hold promise for advancing corrosion science beyond its current boundaries (Fig. 2b).…”

Operando Surface Optical Reflectance Microscopy Study of Corrosion Film Growth on a Ni–Cr–Mo Alloy During Anodic Polarization

“…Metallic materials are used everywhere in our modern society, and the corrosion of these essential materials results in an annual cost of around 3–4% of each nation’s gross domestic product, − leading to a significant environmental footprint. , The reliance on structural materials that are thermodynamically prone to oxidation is made possible due to the presence of stable, passive oxide films that form spontaneously at the surface of many metals and alloys, − for example, stainless steel, aluminum, and Ni alloys. − In some harsh environments, especially low pH and high chlorine content, the corrosion resistance of stainless steel is insufficient; instead, Ni-based alloys are used to ensure the safety of the installations. − …”