Development of Corrosion Diagnosis Method for Copper with Carbon Film by Potential Difference Measurement

Abstract

Listen

Translate article

Copper is widely used in the heat exchangers of air conditioning systems because of its high thermal conductivity and good workability. Although copper shows a good corrosion resistance in the fresh water, the occurrence of pitting corrosion is strongly related to the carbon films on copper 1,2. It has been reported that the pitting corrosion was observed in the inner surface of copper tubes due to the carbon films on copper 2,3. In this case, the carbon films were produced by the influence of undergoing an oil and heat treatment. Yamada et al.2 investigated the factor of the pitting corrosion on copper by field test of air conditioning systems in Japan. They indicated that the occurrence of type Ⅰ pitting corrosion was affected by the water quality and carbon films on copper. Iyasu et al.3 reported a method to estimate the residual amount of carbon on the inner surface of the carbon tube by electrochemical measurement. In this method, the corrosion potentials related to the inner and outer of copper tube were measured to estimate the corrosion potential difference from both corrosion potentials at arbitrary measurement time. They demonstrated that the residual amount of carbon on the inner surface of the carbon tube was correlated to the corrosion potential difference estimated from the corrosion potentials of the inner and outer of copper tube. Though they implied that their proposed method can be applied the corrosion diagnosis method for copper tubes, the dissolution mechanisms of copper with carbon films were still unclear.In the present study, we investigated the dissolution behavior of copper with carbon films in the fresh water based on the air conditioning systems. To estimate the corrosion potential difference, the corrosion potentials related to the inner and outer of copper tube were measured in the different compositions of electrolyte solution. The inner surface of copper tube with different residual carbon contents was employed for the measurement. To develop the corrosion diagnosis method of copper, the suitable conditions involving compositions of electrolyte solution for the corrosion potential measurements were discussed.References F. J. Cornwell, G. Wildsmith, P. T. Gilbert, ASTM STP (1976). Y. Yamada, K. Mizutani, and Y. Inoue, Zairyo-to-Kankyo, 63, 158-162 (2014).T. Iyasu, M. Kuratani, I. Ikeda, N. Tanaka, Y. Yamada, O. Sakurada, Open J. Compos. Mater., 11, 12-22 (2021).