Copper anode passivation of electric heating tubes

Copper anode passivation of electric heating tubes

Monovalent copper exists

The presence of monovalent copper in acidic bright copper plating solution will cause the coating to not shine. Because during electrodeposition, monovalent copper always precipitates first than divalent copper, it is easy to cause roughness and burrs in the coating, especially in low current density areas where the plating is not bright and the leveling ability is poor. In addition, if there is an excess of Cl - in the plating solution, copper monovalent and Cl - will also form cuprous chloride precipitates, making the plating solution turbid and deteriorating the quality of the coating. Monovalent copper is produced due to the introduction of certain reducing agents, and sometimes copper anode passivation also produces monovalent copper. To eliminate the influence of monovalent copper, H2O2 can be diluted with a volume fraction of 0.25mL/L before each shift and added to the plating solution; Sometimes an appropriate amount of sulfuric acid can be added based on the anodic dissolution, which can also eliminate the influence of monovalent copper. It is best to use continuous filtration production method to make the plating solution cleaner and maintain a fine and bright coating.

Copper anode passivation

The presence of anode copper powder and monovalent copper is usually due to the high current density of the anode used or the unsuitable phosphorus content of the copper anode, resulting in passivation of the anode and a lack of brightness of the coating. The mass fraction of phosphorus in acidic bright copper plating anodes should be within the range of 0.02%~0.07%. During electrolysis, it is beneficial for the anode surface to be covered by a soft black film to reduce the generation of anode sludge and avoid direct contact between the plating solution and the anode metal surface. This not only prevents the formation of pitting on the coating, but also avoids the adsorption and oxidation decomposition of the brightener on the anode mud. If the mass fraction of phosphorus in the anode is less than 0.02%, the black film formed in electrolysis is difficult to prevent the production of monovalent copper, resulting in an increase in copper powder in the plating solution. If the mass fraction of phosphorus exceeds 0.1%, it will seriously affect the dissolution of the anode, cause anode passivation, reduce the mass concentration of divalent copper in the plating solution, and generate a large amount of anode mud, affecting the brightness of the coating. Therefore, it is best to use brushed polypropylene fabric as the anode bag to prevent anode mud from contaminating the plating solution.

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