Optical detection of corrosion products exhibiting corrosion inhibition

Corrosion products including passive film work as physical barrier and thus can protect the substrate metals against corrosion attack. The detail measurement may be important in corrosion protection. In this review, in-situ optical technique for the measurement of passive oxide is presented. 3-parameter ellipsometry in which the ordinary ellipsometry is combined with reflectometry can characterize the passive oxide quantitatively on the thickness and optical property. By using Raman scattering spectroscopy with combination of improved collection system of scattering light, composition of the thin passive oxide film may be determined under in-situ condition. Potential modulation reflectance(PMR)exhibits almost same response to frequency and potential as the complex capacitance. The PMR applied to the iron passive oxide film can describe the light-absorption edge from wavelength dependence of the PMR. For iron passive oxide film, the absorption edge was estimated to be about 2.5 eV. From spectrum of luminescence induced by uv light irradiation, the band-gap energy can be estimated; for example, the ban-gap energy of the anodic oxide film on titanium was determined at about 3.1 eV.