Surfactant is one of the materials in the field of metal surface treatment technology, and it is also one of the indispensable components of most electroplating additives. In the entire process of electroplating, such as chemical degreasing before plating treatment, pickling rust removal, electrolytic degreasing, matrix activation to single metal in electroplating, additives for alloy plating, anti-coating discoloration agent after plating treatment, coating protective film and even electroplating wastewater treatment, almost all use surfactants.
(1) The surfactant reduces the surface tension of the plating solution, makes the hydrogen evolution process of the cathode electrodeposition process easier, prevents the coating from producing dents, pitting and pinholes, and makes the coating and the substrate well combined.
(2) The surfactant is adsorbed on the solid surface stained with oil, and the oil is removed by wetting, permeating, emulsifying, and dispersing.
(3) Surfactants have hydrophilic and hydrophobic groups, and the directional adsorption of hydrophobic groups at the electrode interface forms a double electric layer, which improves the overpotential of the electrode reaction, increases the polarization of the electrodeposition process, makes the coating crystallized, and some can also change the internal stress, hardness, ductility and other mechanical properties of the coating.
(4) The qualitative adsorption of surfactants on the gas-liquid interface forms a dense surface liquid film, and the foaming action of some surfactants forms a foam layer, preventing the escape of acid fog. The solubilization and dispersion characteristics of surfactants help some main brighteners that are insoluble in water to disperse in solution, and the synergistic effect between them can obtain bright and smooth coatings.
Some cationic surfactants make the solid particles in the plating solution positively charged, and form a protective film on the surface of the particles, reduce the surface tension of the solid particles, effectively prevent the solid particles in the solution to aggregate into groups, so that the solid particles in the solution evenly dispersed, and with the metal electrodeposition evenly embedded in the coating, to achieve composite plating. The coating is endowed with special properties.