Atomic origins of water-vapour-promoted alloy oxidation

• Published in: Nature materials 2018-06, Vol.17 (6), p.514-518
• Main Authors: Luo, Langli, Su, Mao, Yan, Pengfei, Zou, Lianfeng, Schreiber, Daniel K., Baer, Donald R., Zhu, Zihua, Zhou, Guangwen, Wang, Yanting, Bruemmer, Stephen M., Xu, Zhijie, Wang, Chongmin
• Format: Article
• Language: English
• Subjects: 639/301/1023/1026; 639/301/930/12; 639/925/930/328/2082; Alloys; Anions; Biomaterials; Boilers; Catalysis; Cations; Chemical reactions; Chromium; Clustering; Condensed Matter Physics; Density functional theory; Diffusion barriers; Environmental Molecular Sciences Laboratory; Free energy; Fuel cells; Heat of formation; High temperature; Laboratories; Lattice vacancies; Letter; Materials Science; Nanotechnology; Nickel; Nickel chromium alloys; Optical and Electronic Materials; Oxidation; Protons; Theoretical physics; Transmission electron microscopy; Turbine engines; Turbines; Vapors; Water vapor
• ISSN: 1476-1122; 1476-4660
• DOI: 10.1038/s41563-018-0078-5

The presence of water vapour, intentional or unavoidable, is crucial to many materials applications, such as in steam generators, turbine engines, fuel cells, catalysts and corrosion 1 – 4 . Phenomenologically, water vapour has been noted to accelerate oxidation of metals and alloys 5 , 6 . However, the atomistic mechanisms behind such oxidation remain elusive. Through direct in situ atomic-scale transmission electron microscopy observations and density functional theory calculations, we reveal that water-vapour-enhanced oxidation of a nickel–chromium alloy is associated with proton-dissolution-promoted formation, migration, and clustering of both cation and anion vacancies. Protons derived from water dissociation can occupy interstitial positions in the oxide lattice, consequently lowering vacancy formation energy and decreasing the diffusion barrier of both cations and anions, which leads to enhanced oxidation in moist environments at elevated temperatures. This work provides insights into water-vapour-enhanced alloy oxidation and has significant implications in other material and chemical processes involving water vapour, such as corrosion, heterogeneous catalysis and ionic conduction. In situ transmission electron microscopy observations reveal atomistic mechanism of water-vapour-enhanced oxidation of Ni–Cr alloys. Protons derived from water promote vacancy formation, migration and clustering.