Date of Award

1986

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Abstract

The atmospheric corrosion mechanisms of weathering steel have been investigated through the use of both field and laboratory techniques. Laboratory techniques included time-transformation studies of the oxide-hydroxides (gamma)-FeOOH and (beta)-FeOOH under controlled temperature conditions in air and in vaccum, as well as electrochemical testing for the characterization of the dissolution and film formation kinetics. Potentiostatic tests with set potentials in the immediate vicinity of the open circuit potential of the weathering steel were found to simulate very well the conditions of atmospheric exposure. 0.1% NaCl solutions as well as other concentrations were generally used for comparison purposes. The specific adsorption of chloride ions from the solution were found to have a significant influence on the rate of dissolution of the steel. The rate of change of the current with time(m) was determined at various settings. Potentiodynamic tests were done to verify the dissolution mechanism of weathering steel in chloride media. The effect of the surface treatment of the phosphoric acid inhibitor was also investigated using the same techniques. The infrared spectroscopic technique was successfully utilised to follow the phase transformations of the Fe-H(,2)O system both in the laboratory and in field exposure testing. The transformations of akagaenite and lepidocrocite to haematite were confirmed but a previously unreported intermediate, the hydrated maghamite, was found. Ferrihydride was found to occur in rural atmospheres.

Pages

205

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