Fast hard chromium additive: the action principle of electroplating additive

2021-09-01 1083

Electroplating additives include inorganic additives (such as cadmium salt for copper plating) and organic additives (such as coumarin for nickel plating). Most of the electroplating additives used in the early stage were inorganic salts, and then organic substances gradually took the leading position in the team of electroplating additives. According to function classification, electroplating additives can be divided into brighteners, leveling agents, stress relief agents and wetting agents. Additives with different functions generally have different structural characteristics and effect mechanisms, but multi-functional additives are also common. For example, saccharin can be used as both a brightener for nickel plating and a commonly used stress relief agent; Moreover, additives with different functions may follow the same mechanism.

Effect mechanism of electroplating additives

The electrodeposition process of metal is carried out step by step: first, the electroactive material particles are moved to the outer Helmholtz layer adjacent to the cathode for Electrosorption, and then the cathode charge is transferred to the desolvated ions or simple ions adsorbed on the electrode to form adsorbed atoms. The adsorbed atoms are moved on the surface of the electrode until they are incorporated into the lattice. In the first process mentioned above, overpotential occurs (respectively, relocation overpotential

Activation overpotential and electrocrystallization overpotential). As long as it is under the overpotential, the electrodeposition process of metal can have sufficiently high grain nucleation rate, medium charge transfer rate and sufficiently high crystallization overpotential, and then ensure that the coating is flat, compact and glossy, and firmly combined with the base material. Proper electroplating additives can improve the over potential of metal electrodeposition and provide a strong guarantee for the quality of the coating.


1. Decentralized control mechanism

In most cases, the dispersion of the additive to the cathode (rather than the dispersion of the metal ions) determines the electrodeposition rate of the metal. This is because the concentration of metal ions is generally 100-105 times of the concentration of additives. For metal ions, the current density of electrode reaction is far lower than its current density.

In the case of additive dispersion control, most of the additive particles are dispersed and adsorbed on the protrusions, active sites and special crystal surfaces with large external tension of the electrode, causing the adsorbed atoms on the electrode surface to move to the depressions on the electrode surface and enter the lattice, and then play the role of leveling the bright light.

2. Non decentralized control mechanism

According to the dominant non dispersive factors in electroplating, the non dispersive control mechanism of additives can be divided into electro adsorption mechanism, complex formation mechanism (including ion bridge mechanism), ion pair mechanism, modified Helmholtz potential mechanism, modified electrode surface tension mechanism and so on.

Source: fast hard chromium additive