Ghahari, Seyed Majid (2012)
Ph.D. thesis, University of Birmingham.
Pit propagation in stainless steels under electrochemical control was investigated using in situ synchrotron X-ray microtomography, which was used to confirm that the lacy covers commonly found for pits in stainless steels grow through perforation of the metal surface by upward growth of rapidly dissolving lobes from the main pit. In situ synchrotron X-ray radiography has been used to observe the evolution of 2D pits growing at the edge of stainless steel foils under electrochemical control in chloride solutions. Pit growth shape, kinetics and stability under current and potential control at various bulk chloride concentrations have been studied. It was found that the pit depth tends to grow under diffusion control, whereas lateral development is influenced by solution conductivity. The impact of the perforated cover on the pit growth and stability was examined and its formation was found to be similar to the observations from 3D by X-ray microtomography. A method for extracting the key dissolution kinetic parameters from radiographs has been developed. The local anodic current density along the boundary of a pit was directly measured from the rate of advance of the pit into the metal. Then the local metal ion concentration and potential drop inside the pit cavity was back-calculated using transport equations and the requirement to maintain charge neutrality, establishing the relationship between local current density, interfacial potential and metal ion concentration in the solution. The predictive model for pit propagation in stainless steel developed by Laycock and co-workers was examined, its sensitivity to key growth parameters was evaluated, and a modified version of the model was developed based on the kinetic parameters extracted from the radiographic measurements.
|Type of Work:||Ph.D. thesis.|
|Supervisor(s):||Davenport, Alison and Rayment, Trevor|
|School/Faculty:||Colleges (2008 onwards) > College of Engineering & Physical Sciences|
|Department:||School of Metallurgy and Materials|
|Subjects:||T Technology (General)|
TN Mining engineering. Metallurgy
TP Chemical technology
|Institution:||University of Birmingham|
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