Analysis of problems in plastic plating-trivalent Chromium plating.
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Trivalent chromium plating still has many weaknesses, such as unstable bath, sensitivity to impurities, high production cost, dark color of the coating, etc., especially the following aspects must be considered in research, development and production.
1 it is difficult to thicken the coating.
The thickness of trivalent chromium coating can only reach a few microns, so it can only be used in decorative coating. This is mainly because the electroplating conditions have changed with the increase of electroplating time: in the electroplating process, the cathodic current density and time can be controlled, while the pH value and temperature of the solution will change. Therefore, pH value and temperature are the main reasons why the coating can not be further thickened.
(2) difficulty in anode selection.
Because the trivalent chromium plating bath is still unstable and sensitive to impurities, it is generally impossible to choose soluble materials as anodes, while trivalent chromium in insoluble anodes is easy to be oxidized to hexavalent chromium, which accelerates the instability of the plating bath. At present, graphite anode is used in almost all kinds of trivalent chromium plating processes studied in China. The main disadvantages of graphite anode are:
(1) the electrode is not stable enough under the working conditions in the bath solution, and the electrode is continuously oxidized to form CO;2.
(2) the carbon powder formed by the collapse of the anode will pollute the plating bath.
(3) the electrode becomes thinner after oxidation, which leads to the increase of internal resistance and the distance between cathode and anode, which leads to the increase of slot voltage.
(3) the composition of solution is complex.
Domestic scholars have proposed a kind of plating bath system-oxalate-ethylenediamine tetraacetic acid system, the formula of this system is very complex, and the range of temperature and current density is too narrow. In the process of use, because of the complex components, it is very difficult to manage and maintain.
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