There are two main trivalent chromium plating process systems currently used in the production of PI PET: chloride system and sulfate system.
Both systems have their own characteristics. The chloride system has good conductivity in the solution, a whiter coating, uses graphite as the anode, and has lower slotting costs. However, compared with the sulfate system, there are obvious defects as follows:
(1) The chloride system produces harmful chlorine gas during the electroplating production process, causing secondary pollution to the human body;
(2) Using graphite as the anode, due to its high oxygen evolution overpotential, it is prone to produce hexavalent chromium. The production of hexavalent chromium not only affects the stability of the plating solution, but also has strict limitations on the concentration of this harmful substance in the plating solution;
(3) Due to long-term use, graphite corrodes and deforms the anode, causing changes in the area of the anode and resulting in unstable manufacturing processes, as well as sediment pollution of the plating solution;
(4) Chloride has a strong corrosive effect on electroplating equipment;
(5) A dedicated system is required to purify the plating solution, which incurs high maintenance costs.
Therefore, an increasing number of trivalent chromium plating processes use sulfate systems and use insoluble precious metal coated titanium anodes as anodes, which are essentially insoluble during the electroplating process and are therefore also known as "size stable anodes".
en 
