Application and latest Research trend of trivalent decorative Chromium plating

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Application and latest Research trend of trivalent decorative Chromium plating.
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1 hexavalent chromium plating has excellent corrosion resistance even if it is only 0.1-0.3 μ m, and it has good decoration after chromium plating on nickel layer, so it is widely welcomed as the final coating on automobiles, electrical appliances, daily hardware and other products. Up to now, it is still the main method of decorative electroplating. In addition, hard chromium with a thickness of more than several μ m is also widely used in industry, from automobiles, hydraulic devices to tools, moulds and so on. According to the current technical level, it is impossible to cancel chromium plating completely, so there are a variety of low concentration chromium plating and trivalent chromium plating technology. Among them, trivalent chromium plating is eye-catching because it avoids the pollution of hexavalent chromium.
2 general situation of trivalent chromium plating.
In fact, the earliest reports about chromium plating appeared in the form of trivalent chromium. In 1854 Mr.Bunsen adopted chromium plating in the form of chromium chloride. Two years later, Mr.Geuther carried out hexavalent chromium plating with potassium dichromate. In the 1920s, Mr.Sargent and Dr.Fink developed the chromium plating technology based on chromate. Through the efforts of many developers and researchers, the chromium plating system with standard solution and fluoride additive was formed. That is, the current chromium plating bath is mainly chromic acid, plus sulfuric acid, silicon fluoride and other catalysts. However, hexavalent chromium plating has a large amount of hydrogen in the cathode and a large amount of oxygen in the anode, which causes chromium fog spatter and causes environmental pollution in production. On the other hand, the hexavalent chromium in a large amount of wastewater pollutes the ecological environment.
Trivalent chromium plating has single-slot mode and double-slot mode, and the anode material in single-slot mode is graphite rod, and the other is the same as ordinary plating. In the double trough mode, the inner anode slot is used, which can be placed with lead-tin alloy anode, and dilute sulfuric acid is used as the anode base solution.
Compared with hexavalent chromium plating, trivalent chromium plating is easy to operate, safe to use and no environmental problems. However, there are some shortcomings such as large investment and high cost of primary equipment. There is also because users are accustomed to the color of hexavalent chromium, there is an adaptation process in chromaticity. However, trivalent chromium plating not only has no environmental pollution, but also has some remarkable advantages, such as good dispersion ability and high corrosion resistance in low current area. The comparison of the specific properties of trivalent chromium plating and hexavalent chromium plating is shown in Table 1, and the typical process of trivalent chromium plating is shown in Table 2.
Taken together, trivalent chromium plating has the following advantages:
(1) the production efficiency is improved, the loading capacity of the hanger is increased, the plating speed is increased, and the average plating capacity is good.
(2) there are few electroplating faults, such as coke burning, milky white coating, poor dispersion and so on, and there will be no color chromium film.
(3) the current utilization ratio is improved, the current resistance is small, the current efficiency is high, and the current utilization rate is greatly improved.
(4) the cost of de-plating and re-plating is reduced.
(5) the cost of wastewater treatment is reduced without the cost of reducing hexavalent chromium, which is reduced due to the low concentration of chromium.
(6) the working environment is improved without the use of chromic acid, chromium fog does not occur, and the problem of operator poisoning is avoided.
Although the cost of chemical raw materials for trivalent chromium plating has increased and the equipment investment has increased, from the above advantages, the favorable factors can fully offset the increased costs.
Trivalent chromium plating is different from hexavalent chromium plating in that it is easily affected by a small amount of copper, zinc, nickel and other metal impurities, so proper bath management is necessary. Trivalent chromium plating system is equipped with a small ion exchanger system, which can selectively and effectively remove metal impurities in order to operate stably.