In situ IR-RAS Investigation of Surface Layers Initially Formed on Metal Surfaces in Atmospheric Corrosion Environments

Abstract

An in situ infrared reflection absorption spectroscopic technique was developed to investigate metal surfaces during atomospheric corrosion. Sufficient purging of the whole measurement systems with nitrogen gas, strictly constant flow rates of corrosive gases, and reciprocal measurements with p- and s-lights, together with careful optical arrangements, have enabled acquisition of spectra of water and corrosion products from thin surface layers. Pure copper and low carbon steel were tested at room temperature. The corrosive gases containing water vapor with 65% and 80% relative humidities and 10ppm SO₂ were introduced into the test cell by nitrogen gas or air synthesized from nitrogen and oxygen. The measurements were carried out under the passage of the gases over the specimens. In using nitrogen as a carrier, only water layer was recognized on copper and the thickness attained a constant value within 30 minutes, whereas in corrosive gases with air as a carrier, sulfite and sulfate together with water bands were observed. On low carbon steel, sulfite and water layers were detected in the nitrogen carrier, and in using air as a carrier, bands attributed to sulfate and probably due to Green Rust II were observed together with sulfite and water bands. These layers grew obeying the parabolic rate law.