Understanding Surface Reactivity of Bimetallic Alloys

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Corrosion is a crucial concern in applications involving metals, such as nuclear reactor vessels, pipelines, ship hulls, jet engine turbines blades, bio-metallic implants, and bridges. A longstanding challenge in corrosion science is the need to predict accurately the degradation of a given alloy or coating based on its composition and the exposure conditions. The formation of a protective oxide scale layer is a common mechanism by which metals achieve corrosion resistance, but the formation of these scales is not well understood. Factors such as chemistry, surface conditions, and material sensitivity control oxidation behavior, but classical oxidation models lack the ability to predict whether a given alloy composition can form a continuous protective scale for a specific service environment. A primary reason for this gap in knowledge is the lack of experimental tools capable of observing the earliest stages of oxidation. This award supports the fundamental research into the atomic- and nano-scale process of alloy oxidation needed to develop practical, predictive models. The scientific understanding will accelerate materials innovations relevant to many technological areas that require sustained corrosion resistance at elevated temperatures, including energy generation, materials processing, and chemical conversion processes. This research program will contribute to national economic competitiveness through the development of novel materials and technologies, and to the development of a competitive STEM workforce through training and mentorship of graduate students and postdocs, interdisciplinary courses, and an emphasis on the participation of women and underrepresented minorities.The evolutionary processes leading to the establishment of protective oxide scales during corrosion are critically important but depend on many intrinsic and extrinsic variables, including temperature, total pressure, nature and abundance of the reacting species, structural and chemical factors, and competitive nucleation and interfacial phenomena. This research will systematically assess the relationships among these variables to develop a detailed understanding of the establishment of protective scale formation in harsh environments including environments of high temperature and multiple oxidizing gases. The metal oxide nucleation and growth will be visualized at the atomic level using in situ environmental transmission electron microscopy. The growth kinetics and structure of the scales that eventually form will be characterized using thermal gravimetric analysis and a variety of electron microscopy techniques. These key experimental efforts, enhanced by complementary theoretical calculations, will explicate the atomic origins and critical parameters affecting the reaction pathways of protective oxide-scale formation in service-relevant environments. This combination of in situ and ex situ characterizations bridges large temporal- and spatial-scale ranges, from initial-stage oxidation to the development of the thermodynamically stable oxide. The knowledge resulting from the methodologies developed will lead to new paradigms in this important field of gas-solid surface reactions.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.