Application of surfactants in metal electroplating

In the process of electroplating, in order to improve the performance of electrolyte and the quality of coating, it is often necessary to add some additives. Among them, surfactant is one of the main varieties. It has the functions of leveling, brightening, diffusing, changing the physical properties of coating and inhibiting the escape of acid mist.

The surfactants commonly used in electroplating include Pingjia, OP emulsifier, sodium dodecyl sulfate, sodium methylene naphthalene sulfonate, fluorine surfactant, fatty acid polyethylene oxide ester, polyethylene oxide castor oil, etc

1. Cleaning solution before plating

Before electroplating, the metal workpiece must be degreased and cleaned to make its surface clean. Otherwise, the deposition layer is not well bonded on the surface, and even can not get the deposition layer in serious cases

There are animal, vegetable oils and mineral oils on the surface of workpieces. Animal and vegetable oils can be saponified in alkaline solution to form water-soluble soap and glycerin; However, mineral oil or other unsaponifiable oil cannot be chemically decomposed by alkali, and can only be removed from the metal surface with the help of surfactant. In the process of oil removal, surfactant molecules are first adsorbed on the interface between oil and solution. Under the action of lipophilic and hydrophilic groups of surfactant, plus the convection and agitation of solution, the oil gradually separates from the metal surface When it enters the solution, it is a very small spherical emulsion

Typical oil removal formula for carbon steel parts:

Sodium hydroxide 20 ~ 30g / L, trisodium phosphate 30 ~ 40g / L, sodium carbonate 30 ~ 40g / L, OP emulsifier 1 ~ 2G / L, 30 ~ 50 ℃

When the surface of the parts is removed from the oxide scale for strong corrosion, all kinds of harmful gases are generated during the corrosion process. When the gas escapes, acid fog is produced, which has a great impact on the environment and equipment. If a small amount of OP emulsifier is added to the pickling tank, the surface of the pickling solution can produce a layer of foam to prevent the acid mist from escaping.

2. Electroplating solution

In chromium plating, the current efficiency is very low (10% ～ 15%), and the use of insoluble lead anode will produce a lot of hydrogen and oxygen after being electrified, which is easy to produce harmful chromic acid smoke, pollute the environment, endanger the health of operators, and cause corrosion of equipment. In order to inhibit the production of chromium mist, a small amount of perfluoroalkane ether sulfonate surfactant can be added into the chromium plating solution The formation of a foam on the surface inhibits the escape of chromium mist, which ensures the health of the operator and reduces the consumption of chromic acid.

The surfactants used in electroplating play a direct and indirect role in the electrodeposition process. The essence of these effects is the surface activity of organic compounds at the interface between electrode and solution. With the progress of science and technology, the application of surfactants in electrodeposition will be further valued and developed.

3. Application in corrosion prevention and other aspects

For most metals, due to the influence of the surrounding media, the metal surface will suffer from corrosion due to chemical or electrochemical changes. According to statistics, the metal consumed due to corrosion and scrapped metal equipment and materials are about 30% of the annual output of metal. In order to reduce metal corrosion, it is necessary to coat a protective layer on the metal surface or change the nature of the corrosive medium to isolate In addition to the phosphating and electroplating methods mentioned above, there are also methods of coating antirust oil on the metal body in direct contact with the surrounding environment.