Heterogeneous Metal Surfaces and Local Elements

respectively. Inset shows current flow = x b from sites A to B in the external circuit (short circuit), (b) Same as (a) with low-conductivity electrolyte causing ohmic drops Alf between sites A and B. 

These potential profiles may be measured with two REs, one with a fixed position and the other scanning parallel to the surface. With increasing distance to the surface, it may also scan the profile perpendicularly. A variation of this method uses two scanning REs with their FIL capillaries close to each other. One may also use two small isolated Ft tips, which allow a smaller set-up. This scanning reference electrode technique (SRET) samples 

Current lines (arrows) and lines of equal potential within the electrolyte in front of a corroding metal surface consisting of local elements with metals A and B working as local anodes and cathodes, respectively potential profile for electrolytes with low (1), medium (2), and high (3) conductivity. 

A technical application of potential measurements is the detection of corrosion damages of underground metal constructions like gas or water pipes. Two electrodes are put to the wet ground, one of them changes place to detect sites of intense dissolution currents and the related ohmic drops. These sites are the locations of corrosion damage. 

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