4. Local measurement of corrosion rates

The electrochemical techniques generally used to study corrosion lead to surface-averaged values of corrosion processes, and in particular corrosion rates. However, numerous heterogeneities in the metal - intermetallic precipitates, inclusions, grains, etc. - make the corrosion rate non-uniform across the sample surface. Corrosionists have therefore proposed techniques for determining the corrosion rate at each point on the surface. Local measurements of potential, current and impedance were thus developed, giving access to the distribution of these quantities on the electrode surface. Techniques such as the Kelvin probe can be used to obtain microgalvanic activity at the surface of a sample in the presence of a film or drop of electrolyte, or in humid air. However, the examples presented here will be limited to techniques for locally obtaining the characteristics of a corrosion process...