Since the plating solution of trivalent chromium plating is unstable and sensitive to impurities, it is generally impossible to select a soluble material as an anode; in the insoluble anode, trivalent chromium is easily oxidized to hexavalent chromium, which accelerates the instability of the plating solution. . At present, almost all kinds of trivalent chromium plating processes studied in China use graphite anodes. The main disadvantages of graphite anodes are:
There are still many weaknesses in trivalent chromium plating, such as unstable plating solution, sensitivity to impurities, high production cost, and dark color of coating. In particular, the following aspects must be considered in research, development and production.
1. The coating is difficult to thicken
The thickness of the trivalent chromium plating layer is generally only a few microns and can only be applied to decorative coatings. This is mainly because the plating conditions change as the plating time increases: during the electroplating process, the cathode current density and time can be controlled, and the pH and temperature of the solution change. Therefore, pH and temperature are the main reasons why the coating cannot be further thickened.
2. Anode selection is difficult
Since the plating solution of trivalent chromium plating is unstable and sensitive to impurities, it is generally impossible to select a soluble material as an anode; in the insoluble anode, trivalent chromium is easily oxidized to hexavalent chromium, which accelerates the instability of the plating solution. . At present, almost all kinds of trivalent chromium plating processes studied in China use graphite anodes. The main disadvantages of graphite anodes are:
(1) It is not stable enough under the working conditions in the bath, and the electrode is continuously oxidized to generate CO2;
(2) The carbon powder slag formed by the collapse of the anode may contaminate the plating solution;
(3) The electrode becomes thin after oxidation, causing an increase in internal resistance and an increase in the spacing between the anode and the anode, resulting in an increase in the groove pressure.
3. The composition of the solution is complicated
Domestic scholars have proposed a liquid plating system, oxalate-ethylenediaminetetraacetic acid system. The formulation of this system is very complicated, and the temperature and current density range are too narrow. The use of graphite in the anode also has the aforementioned disadvantages. In the process of use, due to the complex composition, management and maintenance is very difficult.
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