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Why does the copper strip change color during the production process

Update:20-05-2019
Summary:

1. The most direct cause of discoloration of the copper […]

1. The most direct cause of discoloration of the copper strip is the residual acid on the surface of the copper strip.

2. The soft copper strip is more discolored than the hard copper strip. Because the soft copper strip is annealed at a high temperature, it is easy to dezincify, and after pickling, multi-quality copper appears on the surface to form a so-called copper skeleton. Especially because the copper strip becomes soft, after pickling and brushing, the surface appears to be printed, and the microscopic state is concave and convex. After washing with water with residual acid, the soft copper strip is more easily adhered by residual acid and water film, so Soft copper strips are more susceptible to discoloration than hard copper strips.

3. The external environment also has a certain impact on discoloration. First, the corrosion of copper by the residual acid attached to the surface of the copper strip must be carried out with a water film on the copper surface; on the other hand, CO2, SO2, NH3, H2S, etc. in the air and some solid sediments are soluble. In the water film, it becomes an ion conductive liquid, which provides conditions for electrochemical corrosion.

4. The impact of washing water quality. The washing water is made of tap water, so it generally contains chloride ions, especially in coastal cities. The salt concentration in tap water during seawater reversal is higher. On the one hand, as the salt content increases, the electrical conductivity increases, the resistance polarization decreases, and the corrosion rate increases. On the other hand, the chloride ion has a strong oxidizing power when it is at the microscopic defect of the copper surface. When concentrated, it will become a cause of dot-like discoloration.

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