Electrochemical Determination of Residual Carbon in Copper Pipe Using Gel Electrolyte

Abstract

Copper tubes are widely used as heat transfer tubes for air conditioners and heat exchangers due to their excellent corrosion resistance, heat transfer, and workability. However, carbon film is formed on an inner surface of copper tube by the burning of the lubricating oil used in the annealing after drawing process during copper tube manufacturing. This causes pitting corrosion of copper tubes and increases the risk of leakage accidents. General method to quantify the amount of residual carbon includes collecting the amount of residual carbon by acid treatment and measuring the amount of residual carbon by infrared absorption method. In this study, as a simpler method to measure the amount of residual carbon, we used a gel electrolyte whose shape can be easily controlled and measured the potential difference (hereafter ΔE) between pure copper and carbon-attached copper. As a result, an increasing trend of ΔE value with increasing residual carbon was the most observed in the 0.5 mol L⁻¹ Na₂SO₄ gel electrolyte adjusted to pH 6.5.

 

This Paper was Originally Published in Japanese in J. Japan Inst. Copper 64 (2025) 214–218.

Fig. 1 Schematic diagram of a working electrode (copper tube), a reference electrode (copper film), and a measuring instrument in ΔE measurement with gel electrolyte.