Investigation of copper and zinc alloy surface exposed to corrosion environment by digital image processing

Abstract

Usually, corrosion processes on brass, which are manifested by discoloration of the metal or alloy surface, are a little destructive and slow in natural environment or non-acid solutions. In this context, investigation of the corrosion process under the above conditions can be a research area of great relevance because standard analysis such as weight loss and electrochemical techniques can not be applied. Here, we report on a digital image processing analysis of the evolution of copper and zinc alloy surfaces corrosion due to exposure to air, alcohol-aqueous solutions, and sugarcane liquor. For our analysis, we investigated 2D image produced by a confocal microscope from a topographic surface survey, by calculating parameters such as correlation coefficient, Hurst exponent, and bright/dark ratio to follow the early stage of the corrosion process evolution due to exposure to several conditions for different periods of time. The best fits are presented together with the image processing data to show the evolution of the surface characteristics as a function of time and treatment. We show that digital image of rough surfaces that have undergone early stage of the corrosion processes can be used to monitor surface changes. For all tested solutions, the changes in the surface can be better sensed by using the B/D ratio due to the large vertical scale but the fit was better for the correlation coefficient. Particularly for sugarcane liquor and 100% C2H5OH alcohol solution, B/D ratio varies slower than for the other solutions, thus, suggesting an inhibitory effect of this solution.

Keywords

• Corrosion
• Image processing
• Correlation
• Hurst exponent
• Bright/dark ratio
• Cu–Zn alloy