What Is Nickel Plating?
Nickel is widely used as a plating metal because it is rust-resistant and chemically very stable. Nickel plating is often used to protect the surface of electrical components and decorative objects.
There are two main types of nickel-plating methods.
The first is called electro-nickel plating, which uses electricity to cause an oxidation reaction on the nickel anode and a reduction reaction to deposit nickel on the cathode (the material to be plated).
The second method is called electroless nickel plating, which uses chemicals instead of electricity to cause a chemical reaction to deposit nickel on the plated material.
Electrolytic nickel plating has a long history and was first developed in the 1830s. In Japan, the first nickel plating is said to have taken place in 1892. In the early days, electrolytic nickel plating did not have a shiny surface, and polishing was performed after the plating process to give it a shiny surface.
Principles, Types, and Uses of Different Nickel Plating Methods
Nickel plating methods include electrolytic nickel plating and electroless nickel plating.
Principles of Electro-Nickel Plating
Electrolytic nickel plating is a plating method in which electricity is passed through a solution to electrolyze nickel, the plating metal, causing a chemical reaction.
The plated object (material to be plated) is immersed in a nickel sulfate solution with the cathode and the nickel plate as the anode. When the nickel plate is energized, an oxidation reaction occurs and nickel ions dissolve into the solution, combining with electrons in the solution to cause a reduction reaction, depositing nickel on the surface of the plated material at the cathode and forming a film.
Types and Applications of Electrolytic Nickel Plating
Electrolytic nickel plating is used in a wide range of plating processes, from artistic to electrical components. There are three types of electrolytic nickel plating: bright nickel plating, semi-bright nickel plating, and matte nickel plating.
Typical applications for bright nickel plating include surface treatment of household electrical outlets and connectors.
Semi-bright nickel plating is mainly used for soldering and welding.
Matte nickel plating is less shiny and less attractive than bright nickel plating, but unlike bright nickel plating, it does not require additives to make it shiny. Therefore, a very stable and dense nickel plated film can be obtained without being affected by additives, making it suitable for plating internal components.
Principle of Electroless Nickel Plating
Electroless nickel plating is a method of forming a film on the surface of the plated object by depositing nickel through a chemical reaction between two chemicals in a plating solution.
The plated object is immersed in the plating solution. The plating solution consists of nickel sulfate, sodium hypophosphite, pH buffer, complexing agent, stabilizing agent, etc. Nickel ions in the plating solution cause a reduction reaction, depositing nickel on the surface of the plated object and forming a film.
About Nickel Chromium Plating
What Is Nickel-chrome Plating?
Nickel chrome plating is a silver-colored, slightly bluish-white plating often used for water faucets. Nickel-chrome plating is also known as decorative chrome plating. It is often used as a finish on top of nickel plating because of its good corrosion resistance, hardness, weather resistance, and good light and heat reflectivity.
Naturally, nickel-chrome plating is more resistant to impact and corrosion than nickel plating alone, and an oxide film forms on the surface of the chromium in the atmosphere, protecting the interior from corrosion while at the same time preserving its appearance.
Nickel-chromium plating is a treatment method widely used in addition to the above-mentioned water faucets, etc. because the luster of nickel plating combined with the silvery-white metallic appearance of nickel-chromium plating is popular as a decorative feature.
About Chromium
Chromium is classified into trivalent chromium and hexavalent chromium depending on the oxidation number. Hexavalent chromium is a substance whose use is prohibited by the RoHS and RoHS2 directives due to its reported environmental pollution and toxicity to the human body. Although plating with hexavalent chromium has been the mainstream plating process in the past, in recent years, due to its toxicity, plating with trivalent chromium has been widely used. The trivalent chromium plating process is superior in uniformity and has been developed to have the same corrosion resistance as the conventional process. In addition, it is a plating method that is harmless to the human body and easy to use in terms of workability, etc.
Corrosion of Electroless Nickel Plating
As a method to improve the resistance of nickel plated film to the salt air in the sea, etc., hypophosphite is used as a reducing agent during electroless nickel plating to deposit the plating.
This nickel plating film is called electroless nickel-phosphorus plating, but the major problem with this electroless nickel-phosphorus plating film is that the film is damaged in a short period when sea salt in the atmosphere is relatively low, leaving the metal bare and rusting.
Research has shown that when sulfate ions derived from sulfurous acid gas in the atmosphere come into contact with the surface nickel layer, a hydrate of nickel sulfate is formed, which is the substance responsible for the progressive corrosion of the surface nickel layer.
To address this issue, we have developed two-layer nickel plating (electrochemically protecting the underlying plating or material from corrosion by slowly oxidizing the upper plating layer) and three-layer nickel plating with bright nickel containing 0.1-0.2% sulfur in between the two-layer plating. In addition, the aforementioned nickel-chromium plating, etc. has also been developed. Nickel-chromium plating, as mentioned above, is also useful.