The Anodic Behaviour of Nickel in Nickel Sulphamate Electroplating Solutions

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Abstract
This paper describes some aspects of the anodic behaviour of non-activated and sulphur-activated nickel in nickel sulphamate solutions and relates these to the performance of these materials in commercial electroplating and electroforming processes. The results show that non-activated nickel is more easily passivated and more resistant to dissolution in sulphamate-based solutions than it is in sulphate-based ones. Sulphuractivated nickel, on the other hand, dissolves just as readily in both types of electrolyte. This means that the difference in dissolution potential between the two materials is much greater in sulphamate-based solutions, leading to greater savings in cell voltage when using the sulphur-activated material. The results also shed further light on the anodic reactions of sulphamate ions to produce compounds which are capable of reducing the stress in the deposit produced at the cathode. There appear to be three distinct types of behaviour possible, depending upon the anode material used. Sulphur-activated nickel dissolves at such low potentials that no oxidation of the sulphamate ion takes place. Non-activated nickel, however, dissolves at higher potentials. A stress reducing substance is produced by anodic oxidation of the sulphamate ion but this is only produced in very small amounts. When using inert anodes, such as platinum, the anodic potential is very high and stress reducing species such as azodisulphonate ions are produced in comparatively large amounts.