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Gerald S. FrankelProfessor,
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Dr. Frankel's primary interests are in the fields of corrosion and electrochemistry. He has focussed on localized corrosion, passivation, coatings, inhibition, corrosion of electronic and magnetic materials, X-ray absorption studies of electrochemically-formed films using synchrotron radiation, behavior of anodes used in electrodeposition applications, and electrodeposition of magnetic materials.
The current activities in Dr. Frankel's group are focused largely on the corrosion and protection of Al and Al alloys. He is leading a large Multidisciplinary University Research Initiative funded by the Air Force Office of Scientific Reasearch. This is a team effort with seven other co-principal investigators focused on addressing the mechanism of corrosion inhibition of Al alloys by chromate.
Localized corrosion is being studied in Dr. Frankel's group by a variety of techniques. Pit growth in thin film metal samples (hundreds of nm thick) is of interest because of the nature of the pits that form. Pits in thin metal films deposited onto an inert substrate such as glass are 2-D in nature. They penetrate quickly to the substrate and then grow outward with vertical active side walls. These pits grow with a constant and quite large pit current density. The pit current density can be determined by image analysis of the growing pits with no assumptions needed. An example of an image of a growing pit in a thin Al film is shown below.
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| Video image of a pit growing in a 209 nm thick Al film in 1.0 M NaCl at an applied potential of -450mV SCE |
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| Corrosion sensing paint |
A corrosion-sensing paint has been developed and is under investigation. This work has received recognition in a number of different magazines, including Business Week. As seen in the figure on the right, the paint changes color in spots where corrosion occurs.
The idea behind the work is to sense the pH change associated with the cathodic reaction that accompanies corrosion, since this reaction should occur at more accessible locations that the anodic dissolution reaction. Cathodic reactions typically result in an increase in pH, so pH-sensing compounds have been added to the paint's organic matrix.
Pitting and protection by inhibitors is also studied by atomic force microscopy, making use of two novel techniques: in situ AFM scratching and Scanning Kelvin Probe Force Microscopy (SKPFM). SKPFM is a new technique, and the work here is the first application of it to corrosion. Using a metal-coated AFM tip as a Kelvin Probe, it is possible to map the Volta potential across a sample surface with resolution of at least 0.1 micrometer.The surface topographic and Volta potential maps are obtained at the same time. Below is an image of an AA2024-T3 sample. The SKPFM potential map on the right side provides clear indication of the location of the intermetallic particles, while the topographic map on the left provides little information.
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| Left, topograhy of Al alloy surface determined by atomic microscopy. Right, Volta potential distribution of the same area measured simultaneously by Scanning Kelvin Probe Force Microscopy (SKPFM) |
