Main features of chrome plating

Main features of chrome plating
Compared with other single metal plating baths, although the composition of the commonly used chromic acid plating bath is simple, the chromium plating process is quite complex and has the following characteristics.
① The main component of chromium plating solution is not metal chromate, but the oxygen-containing acid of chromium - chromic acid, which belongs to strong acidic plating solution. During the electroplating process, the cathode process is complex, and most of the cathode current is consumed by two side reactions: hydrogen evolution and the reduction of hexavalent chromium to trivalent chromium. Therefore, the cathode current efficiency of chromium plating is very low (10%~18%). And there are three abnormal phenomena: the current efficiency decreases with the increase of chromic anhydride concentration, and decreases with the increase of temperature; As the current density increases, it increases.
② In the chromium plating solution, a certain amount of anions, such as SO42-, SiF62-1, F-1, etc., must be added in order to achieve normal deposition of metal chromium.
③ The dispersion ability of chromium plating solution is very low. For parts with complex shapes, pictorial anodes or auxiliary cathodes need to be used to obtain a uniform chromium plating layer. The requirements for hanging tools are also quite strict.
④ Chromium plating requires a high cathode current density, usually above 20A/dm2, which is more than 10 times higher than ordinary plating. Due to the large amount of gas released from the cathode and anode, the resistance of the plating solution is high, and the tank pressure increases. Therefore, a power supply greater than 12V is required for electroplating, while a power supply below 8V is sufficient for other plating types.
⑤ Chromium plated anodes do not use metallic chromium, but use insoluble anodes. Lead, lead antimony alloy, and lead tin alloy are commonly used. The chromium consumed in the plating solution due to deposition or other reasons needs to be supplemented by the addition of chromic anhydride.
⑥ The operating temperature of chromium plating and the cathode current density have a certain dependence, and changing the relationship between the two can obtain chromium coatings with different properties.

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