Initial Events during the Passivation of Rapidly Dissolving Aluminum Surfaces

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Tak, Yongsug
Hebert, Kurt
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Hebert, Kurt R
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Chemical and Biological Engineering

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.

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)

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The early stages of oxide film passivation of corroding surfaces in aluminum etch tunnels and pits were investigated. Passivation was initiated by step reductions in applied current. A mathematical model for passivation was used to predict experimentally measured potential transients during the first millisecond after the current step. The experimental transients had a characteristic potential undershoot at about 70 μs after the current step; according to the model, the undershoot was directly related to the partial coverage of the corroding surface with an oxide layer. The time and extent of the undershoot were in quantitative agreement with the theoretical predictions, suggesting that the fractional actively dissolving area in the pit at these times is a linear function of potential and adjusts rapidly to changes of the potential. This reconfiguration of the active area occurs at times when the extent of passive film formation is still small. A chemical mechanism for passivation which is consistent with the model is one in which the fractional active area is controlled by the coverage of specifically adsorbed chloride ions. Agreement between experimental and predicted potential transients was also observed at room temperature, where no tunnels are found, but only corrosion pits with irregular shapes.


This article is from Journal of the Electrochemical Society 141 (1994): 1453–1459, doi:10.1149/1.2054945. Posted with permission.

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Sat Jan 01 00:00:00 UTC 1994