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There are mainly two kinds of trivalent chromium plating process systems currently used in production: chloride system and sulfate system.
The two systems have their own characteristics. The solution of the chloride system has good conductivity, the coating is white, and the graphite is used as the anode, and the slotting cost is low. But compared with the sulfate system, there are obvious following defects:
(1) In the electroplating production process of chloride system, chlorine gas which is harmful to human body will be generated, causing secondary pollution;
(2) Using graphite as the anode, because graphite has a high oxygen evolution overpotential, it is easy to produce hexavalent chromium, and the production of hexavalent chromium not only affects the stability of the plating solution, but also has a negative impact on the harmful substances in the plating solution. Strictly limited concentrations exist;
(3) After the graphite is used for a long time, the anode is deformed due to corrosion, and the area of the anode changes, resulting in unstable manufacturing process and at the same time producing sediment to pollute the plating solution;
(4) Chloride has a strong corrosive effect on electroplating equipment;
(5) A special system is required to purify the plating solution, and the maintenance cost is high.
Therefore, more and more trivalent chromium plating processes use sulfate systems, and insoluble noble metal-coated titanium anodes are used as anodes, which are basically insoluble during the electroplating process. Therefore, they are also called “dimensionally stable anodes”.