Non-Diffusion Control Mechanism of Vacuum Chrome Plating

Non-Diffusion Control Mechanism of Vacuum Chrome Plating

According to the dominant non-diffusion factor in electroplating, the non-diffusion control mechanism of additives can be divided into electro-adsorption mechanism, complex formation mechanism (including ion bridge mechanism), ion pair mechanism, changing Helmholtz potential mechanism, changing Electrode surface tension mechanism, etc.

​Diffusion Control Mechanism of Vacuum Chromium Plating

In most cases, the diffusion of additives to the cathode (rather than the diffusion of metal ions) determines the metal electrodeposition rate. This is because the concentration of metal ions is generally 100 to 105 times that of additives, and for metal ions, the current density of the electrode reaction is much lower than its limiting current density.

In the case of additive diffusion control, most of the additive particles diffuse and adsorb on the protrusions, active sites and special crystal planes with large surface tension of the electrode, causing the adatoms on the electrode surface to migrate to the depressions on the electrode surface and enter the crystal lattice. So as to play the role of leveling light.

How Vacuum Chrome Plating Additives Work

The electrodeposition process of metals is carried out in steps: first, the electroactive species particles migrate to the outer Helmholtz layer near the cathode for electrosorption, and then, the cathode charge is transferred to the partially desolvated ions or simply adsorbed on the electrode. ions, form adatoms, and finally the adatoms migrate on the electrode surface until they are incorporated into the crystal lattice.

The first process mentioned above all generate a certain overpotential (respectively, migration overpotential, activation overpotential and electrocrystallization overpotential).

Only under a certain overpotential can the metal electrodeposition process have a sufficiently high grain nucleation rate, a moderate charge transfer rate and a sufficiently high crystallization overpotential, so as to ensure that the coating is flat, dense and glossy, and is firmly bonded to the matrix material.

Appropriate electroplating additives can improve the overpotential of metal electrodeposition and provide a strong guarantee for the quality of the coating.

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