Copper sulphate, also known as alum, blue enamel, copper enamel, is widely used in mordant printing and dyeing of cotton and silk fabrics, producing green and blue pigments, used as insecticide, water fungicide, wood preservative, tanned leather, copper Electroplating, batteries, engraving and manufacturing catalysts. At the same time, it is widely used in the non-ferrous metal beneficiation (flotation) industry, the ship paint industry and other chemical raw materials. Blue transparent crystals, gradually weathered in dry air.
In the early days, copper sulfate electroplating used electrolytic copper or oxygen-free copper as the anode, and its anode efficiency was as high as 100% or even more than 100%, which caused a series of problems: the copper content in the bath liquid increased continuously, and the additive consumption was accelerated. The copper powder and the anode mud in the bath increase, the anode utilization efficiency is lowered, and the plating layer is highly susceptible to burrs and rough defects.
In 1954, the study of anodes by Neverse et al. found that a small amount of phosphorus was added to the anode and electrolytic treatment was carried out after a period of time (electrolytic anodic black film is very important for electroplating. Therefore, it is recommended to use electrolytic drag plate/false plate / Wave plate is electrolyzed at a current density of 2-3 ASD for 4-10 hours), a black phosphorus film is formed on the surface of the copper anode, and the main component is copper phosphide Cu3P. This black film has metal conductivity, which changes the steps of some reactions in the copper anode dissolution process, effectively overcomes some of the above defects, and plays an important role in copper quality and process stability.
The dissolution of the copper anode is mainly the formation of divalent copper ions. The experimental results prove that (rotating ring disk electrode and constant current method): the dissolution of copper in the copper sulfate solution is carried out in two steps.
Cu-e-→Cu+ elementary reaction 1
Cu+–e-→Cu2+ elementary reaction 2
The oxidation of cuprous ions to divalent copper ions under the action of an anode is a slow reaction, and it can also form divalent copper ions and elemental copper by disproportionation, as in the chemical copper precipitation reaction. The generated copper element is deposited in the plating layer by electrophoresis to produce copper powder, burrs, roughness, and the like. When a small amount of phosphorus is added to the anode, a black phosphorus film is formed on the surface of the anode by electrolytic treatment (or dragging), and the dissolution process of the anode undergoes some changes:
1. The black phosphorus film has a significant catalytic effect on the elementary reaction 2, which greatly accelerates the oxidation of cuprous ions, makes the slow reaction become a fast reaction, and greatly reduces the accumulation of cuprous ions in the bath. At the same time, the phosphor film on the surface of the anode can also prevent cuprous ions from entering the bath, causing it to oxidize and reduce the cuprous ions entering the bath. The standard anode black phosphorus copper film has a conductivity of 1.5×104Ω-1CM-1, has metal conductivity, does not affect the conductivity of the anode, and the anode polarization of the phosphor copper anode wall copper anode is small, and the Da is 1ASD. When the phosphorus anode is 0.02—0.05%, the anode potential of the copper anode is 50-80 mv lower than that of the oxygen-free copper anode. The black anode phosphor film does not cause passivation of the anode at the allowable current density.
2. The black phosphorus film on the surface of the anode causes the anode to be abnormally dissolved, the phenomenon of the fine particles falling off is greatly reduced, and the utilization efficiency of the anode is greatly improved. When the anode adopts a current density of 0.4-1.2 ASD, the amount of phosphorus contained on the anode is linear with the thickness of the black film. In the anode, the phosphorus content is 0.030-0.075%, the utilization efficiency of the anode is the highest, and the anode black phosphorus film is the best.
Anode material distribution% electrolytic copper fired copper air agitated phosphorus-containing copper air stirring
Air stirring stationary tank
Cathode deposition 85.5185.5997.9098.36
Mud and attached film 6.8113.610.150.04
Increase in copper content of electrolyte 7.600.801.951.60
Cuprous ions are also produced during cathodic deposition:
Cu2++e-→Cu3
Cu2++e-→Cu+ slow reaction 4
Cu++e-→Cu fast reaction 5
The cuprous ion in the plating solution is mainly produced by the anode reaction and the reaction 4. Although the content is very small, the plating quality can be affected by a small amount. The cuprous ion entering the bath will cause the following damage to the cathode plating:
1. The coating burr is rough. During the electroplating process, the copper powder is deposited on the cathode coating by electrophoresis. In the case of low current density and high temperature, the cathode current efficiency decreases, and hydrogen ions discharge, causing the acidity to decrease. The direction of hydrolysis reaction proceeds in the direction of favorable copper powder formation, and the phenomenon of burr will be aggravated.
2. The cuprous ion will cause the coating to be non-bright, the leveling property is poor, the plating solution is turbid, etc. This is also because the copper powder is finely dispersed on the cathode plating layer, resulting in poor compactness and dullness of the deposited layer. In the low current region, the influence More serious. At this time, the effect of adding the light agent is not great. Adding hydrogen peroxide to remove the copper powder, driving away the complete hydrogen peroxide, and supplementing the light agent, the regional brightness and leveling will be improved. At the same time, the reaction will consume a part of the acid, and should be supplemented appropriately. sulfuric acid.
The phosphorus content of the anode is mostly 0.3% in China. Foreign studies have shown that the phosphorus content in the phosphorus copper anode reaches more than 0.005%, and the black film is formed, but the film is too thin and the bonding force is not good; the phosphorus content is too high, the black film Too thick, too much anode sludge, poor anode solubility, resulting in a decrease in copper content in the plating solution. The anode phosphorus content is preferably 0.030—0.075%, preferably 0.035-0.070%. The domestic production equipment and process are backward, stirring Uneven, can not guarantee the even distribution of phosphorus content, usually increase the phosphorus content to 0.1–0.3%; foreign use of electrolytic or oxygen-free copper and phosphorus copper alloy as raw materials, smelting with medium frequency induction furnace, high purity of raw materials, easy to control phosphorus content It adopts medium frequency induction, magnetic stirring effect is good, copper phosphorus is melted and stirred evenly, and it is automatically controlled. The copper anode produced in this way has uniform distribution of phosphorus, uniform dissolution, fine crystals, fine crystal grains and high anode utilization rate, which is beneficial to smooth and bright coating. Burr and rough defects.