A metallurgical approach to civil- and mechanical-engineering corrosion problems

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The proposed program addresses two major problems: (i) the corrosion of reinforcing steels in concrete and (ii) the corrosion and stress corrosion cracking behaviour of aluminum alloys for structural automobile components. In both cases, the corrosion is predominantly caused by exposure to de-icing salts. While these are practical engineering problems in need of effective solutions, a basic understanding of the mechanism of corrosion is required to optimise the solutions. The mechanisms are influenced by the composition, microstructure and surface condition of the alloys, and the in-service environmental conditions. The anti-icing agents applied to Ontario highways are no longer simply "rock salt" but are concentrated brines of different chloride salts: calcium chloride, magnesium chloride as well as sodium chloride and a mixture of all three chlorides. The goal of the proposed program is to develop an understanding of the influence of the different salts on corrosion behaviour of metals and alloys both in the highway infrastructure and automobile components. This will enable the most appropriate anti-icing agents to be selected for specific applications. During the current Discovery Grant period, the development of the passive films in concrete and their breakdown by sodium chloride on both carbon and stainless-steel reinforcement have been studied using the Mott Schottky analysis. It is anticipated the application of calcium chloride and magnesium chloride as anti-icing agents will be even more deleterious than sodium chloride to the reinforcement. We have already shown the calcium-and magnesium-based salts affect the mechanical properties of concrete: they reduce the compressive strengths of concrete by as much as 30% over a period of five years. In the proposed program, these effects will be further investigated. Since highway structures are required to provide service over many decades, this will include thermodynamic calculations to provide expected functionality in the long-term. Most corrosion studies of aluminum alloys have been in sodium chloride environments but it is expected that the corrosion can will be influenced by the different de-icing agents. The general corrosion behaviour will be investigated by conventional electrochemical techniques, while the localized corrosion of individual phases will be studied by scanning electrochemical microscopy. X-ray photoelectron spectroscopy and Mott-Schottky analysis will be used to study the structure, semiconducting properties and composition of the passive films formed before and after exposure to the salts. During the course of the program, two doctoral students and three master's students will be conducting their research on these topics. There is a demand for engineering graduates with a knowledge of corrosion, as evidenced by the multiple offers of employment received by my recent graduates.