What are the factors that cause the acidic bright copper coating of electric heating tubes to not shine?

What are the factors that cause the acidic bright copper coating of electric heating tubes to not shine?

1. Electrolyte impurity

The ordinary copper sulfate and sulfuric acid used in the new plating solution are impure, such as industrial sulfuric acid with a mass fraction of ≥ 92.5%, which contains a lot of iron and organic impurities. If not treated, the plating will not be bright. Even with reagent grade sulfuric acid, this situation can occur without treatment, as copper sulfate also has impurities to some extent. Before adding sulfuric acid, a 30% mass fraction of H2O21~2mL/L and activated carbon 0.5~1.0g/L can be added to the dissolved copper sulfate solution (pH value 4) for joint treatment. Remove iron impurities by utilizing the easily precipitated nature of trivalent iron hydroxides; Adding activated carbon adsorption can simultaneously eliminate the influence of organic impurities. Starting electroplating in this way will result in a bright copper layer. The metal and organic impurities generated by long-term use of the plating solution will accumulate more and more, indicating that the plating solution is impure. If regular treatment is not carried out according to the process requirements, the current efficiency and coating brightness will significantly decrease when the mass concentration of iron impurities reaches 10g/L.

For example, in a certain factory, the current of a plating bath is not high, the coating is thin and not bright, and the edges and corners of the plated parts are prone to burning, which once prevented normal production. At the suggestion of the author, sampling and analysis were conducted, but due to the high concentration of iron in the solution, which interferes with the analysis of copper sulfate and sulfuric acid endpoint, the data cannot be displayed. Therefore, the analysis of iron ions reached as high as 40g/L. According to observation, the color of the plating solution is light. After confirming that the mass concentration of each component in the plating solution is low, supplement 40g/L copper sulfate and 15g/L sulfuric acid to reduce the impact of iron impurities; Then, the conventional treatment was carried out to restore the plating bath to normal and produce a fully bright copper layer.

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