Corrosion Estimation of Stainless Steel in Nitric Acid by an Optoelectronic Instrument Based on Diffuse Light Scattering Pattern Measurement

This paper presents the design and implementation of an optoelectronic instrument for measuring corrosion of metal surfaces, based on measurement of lightwave scattering pattern. The instrument consists of a thin beam light emitting diode (LED) that illuminates a tiny spot on the metal surface, and an array of photodiodes spread over a hemispherical structure covering the surface to record the light scattering pattern. A mathematical model of light scattering by a corroded metal surface is constructed in which a newly defined corrosion factor is correlated to light scattering pattern. The corrosion factor derived from the scattering pattern gives a measure of the degree of corrosion in a scale from 0 to 100. The temporal behavior of corrosion of stainless steel samples immersed in nitric acid of various concentrations is presented graphically. A semi empirical mathematical model describing the corrosion and dissolution processes in terms of the well-known bilogarithmic laws fits very well with the experimental results. The measured corrosion factor and the corresponding roughness factor as measured by an atomic force microscope are compared to show the relation between the two.