Kinetic Model for Oxide Film Passivation in Aluminum Etch Tunnels
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The function of the Department of Chemical and Biological Engineering has been to prepare students for the study and application of chemistry in industry. This focus has included preparation for employment in various industries as well as the development, design, and operation of equipment and processes within industry.Through the CBE Department, Iowa State University is nationally recognized for its initiatives in bioinformatics, biomaterials, bioproducts, metabolic/tissue engineering, multiphase computational fluid dynamics, advanced polymeric materials and nanostructured materials.
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The Department of Chemical Engineering was founded in 1913 under the Department of Physics and Illuminating Engineering. From 1915 to 1931 it was jointly administered by the Divisions of Industrial Science and Engineering, and from 1931 onward it has been under the Division/College of Engineering. In 1928 it merged with Mining Engineering, and from 1973–1979 it merged with Nuclear Engineering. It became Chemical and Biological Engineering in 2005.
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1913 - present
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- Department of Chemical Engineering (1913–1928)
- Department of Chemical and Mining Engineering (1928–1957)
- Department of Chemical Engineering (1957–1973, 1979–2005)
- Department of Chemical and Biological Engineering (2005–present)
- College of Engineering(parent college)
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Abstract
Aluminum etch tunnels are micrometer‐wide corrosion pits with large length‐width aspect ratios, in which dissolution proceeds from the tip or end surfaces, while the sidewalls are covered by oxide films. The dynamics of oxide film passivation in etch tunnels has been investigated using decreasing current ramps superimposed on the otherwise constant applied current during anodic etching in 1 N HCl at 70°C. The ramps cause the dissolving area on the tip to be continuously reduced by passivation around its perimeter. Analysis of potential transients along with tunnel width profiles shows that two additive processes contribute to the passivation rate, expressed as the rate of decrease of actively dissolving area: a potential‐dependent Tafel‐type kinetic expression and a term proportional to the time derivative of the potential. The potential driving force is the “repassivation overpotential,” the difference between the potential at the dissolving surface and the repassivation potential there. The kinetic model for passivation is consistent with both potential transients and tunnel width profiles, over a range of current ramp rates. The rate‐controlling step of passivation is considered to be potential‐dependent removal of chloride ions from the dissolving surface.
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This article is from Journal of the Electrochemical Society 147 (2000): 4111–4119, doi:10.1149/1.1394027. Posted with permission.