Investigating the kinetics of layer development during the color etching of low-carbon steel with in-situ spectroscopic ellipsometry

Color etching is a useful corrosive process, widely applied in metallography to study the microstructure of metals. To prove the existence of the previously hypothesized steady-state etching rate, in-situ investigations were performed with spectroscopic ellipsometry during the color etching of ferritic materials. Kinetic information regarding the refractive index, extinction coefficient, and layer thickness were used to calculate the steady-state layer buildup rate, which was 1.90 +/- 0.15 nm/s for low-carbon steel and 0.99 +/- 0.06 nm/s for cast iron owing to its better corrosion resistance. The presented methodology and findings could help understanding other processes that involve the development of layers on metallic surfaces.