Additive For Metal Plating Mechanism of action
Electroplating additives in the adsorption process in the cathode surface to form a layer of resistance film, thereby enhancing the polarization. (1) why does the addition of organic additives increase the cathodic polarization? A: The organic additives adsorbed on the surface of the cathode by physical adsorption and chemical adsorption, and the metal ions or metal coordination ions in the plating solution are reduced and precipitated on the cathode surface, so that the superposition potential of the cathode is increased to achieve the purpose of increasing the cathodic polarization The (2) the increase in cathodic polarization, why is conducive to the formation of metal nickel nuclei? A: The increase in cathodic polarization will inhibit the growth of nuclei, and promote the formation of new nuclei, grain refinement, in order to get bright nickel coating. (3) How does the organic additive reduce the precipitation of cathodic hydrogen? A: increase the cathodic polarization. (4) What are the effects of organic additives on the resistance of the cathode coating? (3) to reduce the electrode reaction temperature; (4) to make the coating bright and smooth; (5) to make the coating grain fine; (3) to reduce the surface temperature of the solution; (2) to improve the solution of the electrode wetting effect; (6) to change the mechanical properties such as internal stress, hardness, ductility and so on of the coating; (7) to prevent the formation of pinholes and pits in the plating; (8) to promote the dispersant to the plating solution; (9 ) To eliminate the solution of the foam and prevent the generation of fog. Plating this thing is a three-dimensional existence of high current and low current area, the current size of the two are not the same to restore the number of substances out of the same, high-current area to restore the coating more low area, so It is not uniform. Adding electroplating additives can add their resistance, so that the high area with the low area of the current size close to similar, so the high area, low area of the coating can be uniform, in the microscopic, to fill the bright part of the plating will say " Smoothing fine crystal principle ", the greater the resistance, the smaller the current through the reduction of things smaller and slower, if it is nickel, nickel ions reduced to nickel, the formation of the so-called" crystal nucleus ", the greater the resistance, The slower the reduction, the slower the nickel reduction, the "nuclei" generated after the reduction, the slower the growth.
"In fact, the nickel is stacked on top," so the nuclei are small and at the same time produce a new "nucleus" The same nuclei do not grow up, continue to generate by the nucleus gap and the production of new rugged. So fill well, the naked eye can not see it is smooth, while the crystal nucleus is small, that is, fine crystal so bright, the two are together to see, can not be said alone. Electroplating additives include inorganic additives (such as copper salt for copper plating) and organic additives (such as nickel coated coumarin, etc.) two categories. Most of the early use of electroplating additives for the inorganic salts, followed by organic materials in the ranks of electroplating additives gradually made a dominant position. By function classification, plating additives can be divided into brightener, leveling agent, stress relief agent and wetting agent. Different functional additives generally have different structural characteristics and mechanism of action, but the versatile additives are also more common, such as saccharin can be used as a nickel plating brightener, but also commonly used stress relief agent; and different functional additives may also follow the same Mechanism of action. The electrodeposition process of the metal is carried out step by step: first, the electroactive material particles migrate to the outer Helmholtz layer near the cathode and are electroabsorbed, and then the cathode charge is transferred to the adsorbed portion of the electrode Solvated ions or simple ions to form adsorbed atoms, and finally, the adsorbed atoms migrate on the electrode surface until the lattice is incorporated. The first of these processes produces a certain overpotential (for migration over potential,
Activated overpotential and electrochemical overpotential).
Only at a certain overpotential, the metal electrodeposition process has a sufficiently high grain nucleation rate, a medium charge transfer rate and a sufficiently high crystalline overpotential to ensure that the coating is smooth and glossy and solid with the matrix material. And the appropriate plating additives can improve the metal electrodeposition over-potential, for the coating quality to provide a strong guarantee.