Analysis of the Application of Rare Earth Elements in the Electroplating Techniques

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Rare earth element has unique properties: high corrosion resistance, high wear resistance, high magnetism, superconductivity, high catalytic activity and high hydrogen storage, etc., is an integral part of modern science and technology in functional materials. It is renowned as the “Industrial Monosodium Glutamate” with very wide range of uses. China is blessed with its abundance of rare earth element resources, with rare earth reserves accounted for about 80% of the world.

In the early 1980s, Chinese scientists introduced the rare earth elements into the field of electroplating. Add rare earth additives into the chrome electrolyte and replace Cr3+ with RE3+. In this way, the performance of plating solution is greatly improved and the deposition rate of chromium is accelerated. By improving the cathode current efficiency, both the coverage ability and dispersion ability of the bath are also improved, thus reduces the operating temperatures of the cell voltage and the plating solution as well as the mass concentration of chromium trioxide. This is a big step forward for the traditional chrome plating technique, setting a precedent for the application of rare earth element in the electroplating field.

Since then, the study of rare earth elements in the electro-deposition process has become one of the focuses of the electrochemical workers. New achievements continue to emerge, a variety of rare earth additives have come out, and its applications are becoming increasingly widespread. To sum up briefly, the following aspects:

a. In single metal plating, except chromium plating, adding rare earth additives into zinc, copper plating electrolyte allows fine grain density and improves its anti-corrosion performance; adding cerium compounds into tin plating not only makes the coating bright and delicate, improves welding ability and oxidation resistance ability, but also prevents the occurrence of “tin pest”. Thus, the safety and reliability of tin coatings in the use of electronic components can be guaranteed.

b. In alloy plating, a small amount of scandium, praseodymium and neodymium compounds is added into the widely used alkali film Ni-Fe alloy electroplating. In this way, the stability of the bath can be enhanced, the cathode current efficiency improved, making the coating fine, uniform, smooth and bright; adding cerium into the Zn-Ni alloy plating solution can increase the mass fraction of nickel and improve the coating properties; in addition, the 0.1% to 0.5% mass fraction Sn-Ce alloy clad layer obtained by the electro-deposition method is not only of excellent anti-discoloration performance and welding performance, but also prevents the formation of “tin whisker” effectively.

c. Brush electroplating add different kinds of rare earth ions into its plating solution, can act as a catalyst to accelerate the electrode reaction speed, improve wear resistance and corrosion resistance of the coating. It is applied into the remanufacturing project and achieved good results.

d. Chemical plating adds rare earth additives into the chemical plating crafts. It can increase the deposition rate, enhance the stability of the bath, and extend life cycle. One prominent example is the application of cerium-containing additives in the nickel powder chemical plating. It improves the performance of Ni-P alloy coating. The coating hardness can reach more than 1000HV after heat treatment.

e. Composite plating is a new surface treatment technology in recent years. Studies have shown that: in some chemical composite plating techniques, adding small amount of rare earth compounds into the bath can promote the co-deposition of the insoluble solid particles and metal ions, which is a unique advantage. Not only helps to increase the mass fraction of the solid particles in the coating, but also to improve its hardness and abrasion resistance. For example, adding rare earth accelerant into chromium plating solution. The wear resistance of the electro-deposition Cr-SiC composite coating is 60% higher than the chromium plating layers; electrodeposited Ag-La2O3 silver-based composite coatings used for the manufacture of electrical switch contacts can replace silver contacts and greatly improve the ability of anti electric corrosion and burns.

f. In the crafts of electroplating diamond tools, adding lanthanum and cerium rare earth elements into diamond tools, can improve the adhesion of the carcass and the diamonds, reinforce cutting characteristics of the tools.

In short, the application of rare earth element in electroplating technology has achieved remarkable results in China. The characteristic of rare earth element is small dosage but huge effects. This is of great benefits to the resource conservation and environmental protection. It can be predicted that the application of rare earth elements is of great promise and potential in China’s electroplating technology, especially in the development and application of some functional coatings.