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Presentations
Nickel Anode Materials (PDF, 2.29MB)
Nickel Electroplating Trends (PDF, 1.34MB)
Frequently Asked Questions
Q. What is an activated nickel anode material?
A. S-ROUNDS® Electrolytic Nickel and S®-Nickel Pellets are activated by small amounts of sulfur retained during refining. Current density-voltage curves measured in nickel plating solutions show that for any specified current density, the anode dissolution potential is almost 0.5 volt lower for sulfur-containing materials than for sulfur-free products. The lowering of the anode potential is called activation. The effect is sometimes called depolarization, because resistance to current flow (polarization) is lowered. Because the activating effect of sulfur prevents oxide films from forming on the surface, S-ROUNDS® Electrolytic Nickel and S®-Nickel Pellets dissolve smoothly.
Q. Why does the nickel concentration in the plating solution increase faster with the activated forms?
A. It doesn't! But to answer this fully, anode and cathode efficiencies were determined in our laboratory for different anode materials in eleven different commercially available bright nickel plating solutions. Anode efficiency measures the percentage of current that is available to dissolve nickel. Cathode efficiency measures the percentage of current available to deposit nickel. The activated and non-activated nickel anode materials dissolved at 100 per cent anode efficiency in eleven bright nickel plating solutions. The cathode efficiency, however, varied from 92 to 96 per cent depending on the exact composition of the proprietary bright nickel plating solution.
Because all of the available current, 100 per cent, dissolves nickel, but only 92 to 96 per cent of that current goes towards the deposition of nickel, slightly more current is available to dissolve nickel than to deposit it at the cathode. As a result, the nickel concentration slowly increases as the bath is operated.
The rate of increase of the nickel concentration depends on the difference between anode and cathode efficiencies. It does not depend on the type or activity of the anode material. The concentration of the nickel in solution will increase irrespective of the type of anode material used.
Q. How Fast Do Different Anode Materials Dissolve?
A. Anode dissolution rates are determined by the anode current density, which is calculated by dividing the total current by the total anode area. For example:
If 1000 amperes are flowing through a plating tank with ten titanium baskets and the area of each face of the basket is 5 dm2, then each basket will receive 100 amperes of current, and the anode current density is 20 amperes/dm2.
If the same current flows through a tank with 20 similar titanium baskets, each basket will receive about 50 amperes of current and the current density is 10 amperes/dm2. The nickel will dissolve twice as fast in the basket operating at 20 A/dm2 than in the one operating at 10 amperes/dm2.
If a plater converts from a non-activated nickel anode material like electrolytic nickel squares or strip to an activated material like S-ROUNDS® electrolytic nickel, the activated material will dissolve faster if the tank voltage is not lowered. Failure to adjust the voltage is why some platers believe that sulfur-containing anode materials dissolve faster than non-activated ones. To control the rate of dissolution of the anode material, the plater must control the current density.
Q. Which are the best anode materials?
A. Vale S-ROUNDS® Electrolytic Nickel and Vale S®-Nickel Pellets are the best anode materials to use because of the following advantages that derive from sulfur activation:
- 100 per cent anode efficiency in all plating solutions, even those without chloride ions;
- lower dissolution potentials even at high current densities;
- two to twenty per cent power cost savings depending on anode current density;
- uniform dissolution and settling of the load in baskets; and
- absence of metallic residues.
The lower dissolution potential minimizes side-reactions at the anode such as the evolution of chlorine, oxidation of sulfamate anions, and breakdown of some organics. The spherical form of S®-Nickel pellets lends itself to automatic loading of anode baskets.
Vale's non-activated products, however, are excellent and extremely popular. The key to the effective use of non-activated products like R-ROUNDS® Electrolytic Nickel, Nickel Pellets and Vale Nickel FLATS is chloride ions. As long as the chloride level in solution is high enough, these products will dissolve at 100 per cent efficiency and satisfy the most important function of an anode material…to replace the nickel deposited at the cathode.
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© Vale 2010
Last Updated: Friday, March 30, 2012
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