1. Characteristics of the anodic process

The anodic process has different laws in different potential ranges. As the potential changes, the dissolution rate of the anode changes. When the critical passivation current density is reached, the anode will be passivated and the dissolution rate will decrease. The passivation process is a special law of the anode process. It can be activated and returned to normal by adjusting the process in electroplating production.

2. Factors Affecting the Anode Process

(1) Metallic nature

Some metals are easier to passivate, such as chromium, nickel, titanium, etc.; some metals are not easy to passivate, such as copper, silver, etc.

(2) Plating solution composition

Some components in the plating solution can activate the anode and promote the dissolution of the anode; while some components can passivate the anode, such as carbonate in the cyanide plating solution.

(3) acidity and alkalinity

Generally, metal anodes are not easily passivated in acidic baths.

(4) Working conditions

Increasing the current density can accelerate anode dissolution, but when it is greater than a critical value, it will significantly accelerate anode passivation. When the temperature is low, the anode is easily passivated. The anode area is small and easy to be passivated.

3. Anode Control and Maintenance

(1) Rolled anodes with high purity should be selected, which can not only increase the anode current density, but also achieve the uniformity of anode dissolution, reduce the generation of anode slime, and make the anode difficult to be passivated.

(2) The main surface of the plated part should be parallel to the anode, and the distance between different parts of the cathode and the anode should be reduced. If necessary, pictographic or auxiliary anodes can be selected.

(3) The layout of the anode is determined according to the cathode current density and the area ratio of the cathode and anode in production. The anode is used to improve the distribution of the current density in the cathode, so as to keep the plating solution reasonably stable. Generally, the anode area of ​​the plating species should be larger than the cathode area.

(4) The area ratio of the soluble anode and the insoluble anode is an effective method to ensure the normal dissolution of the anode, prevent anode passivation and keep the plating solution stable.

(5) Eliminate bad phenomena such as hooks, and strengthen the cleaning and maintenance of the anode plate and the electrode bag is an important measure to ensure the normal operation of the anode.

4. Methods of Preventing and Discriminating Anode Passivation

(1) Grasp the area ratio of cathode and anode and the current density. This is an effective measure to prevent anode passivation and ensure the normal dissolution of the anode. Only when the area ratio of the cathode and anode and the current density are compatible with the process specification, can the anode be dissolved normally and passivation can be prevented.

(2) Anode passivation can be detected from a sudden rise in rectifier voltage. In the same tank, if the tank voltage suddenly rises, it indicates that the electroplating is abnormal. After excluding the poor contact of the conductive rod, it can be inferred that the anode is passivated.

(3) Identify passivation from the surface condition of the anode. For example, the galvanized anode zinc plate should be gray-black, and white is passivation; acid tin plating passivation is black film gray; nickel is gray-white when it is normal, and reddish-brown after passivation.

(4) Various electroplating processes have different temperature requirements. Too high or too low temperature will have a direct impact on the dissolution and passivation of the anode, which should be controlled within the working range.

(5) Select the high-purity rolling anode, and select the alloy anode according to the process requirements.

The behavior of the anode in the electroplating production process is much more complicated than that of the cathode. The production process should be reasonably controlled to ensure the specification of the plating solution process, and the area and quantity of the cathode and anode should be reasonably arranged. According to different process requirements, using anode characteristics to stabilize the process is also an effective way to improve the quality of electroplating and reduce failures and losses.