Nickel Coating Essay

Nickel coating is used extensively for decorative, engineering and electroforming purposes because the appearance and properties of electrodeposited nickel can be varied over wide ranges by controlling the composition and the operating parameters of the electrolyte. Decorative applications account for about 80% of the nickel consumed in plating and 20% is consumed for engineering and electroforming purposes [1].

Compared to plain coatings, composite coatings have improved physical and electrochemical properties. Based on the properties of different particles used in the bath, their applications are decided. Their applications can be divided into three main categories: dispersion hardening, wear resistance and electrochemical activity [2].

In general, a metallic solution of the metal to be deposited is electrolyzed to have a uniform coating of the metal on the cathode. The anode is normally the pure metal with some exceptions, e.g., in the chromium plating, chromium is not used as anode. During the electrolysis, the anode dissolves into the electrolytic bath and metal ions from the bath solution get deposited over the cathode as pure metal. The following reactions show the electrodeposition process:

The electrolyte MA ionizes in the bath as:
MA (aq)Mn+(aq)+ An-(aq)…………………………..(1)

At the anode, the reactions can be carried out in two ways depending in the anode. Soluble anodes dissolve anodically into the electrolyte, whereas the reaction on insoluble anodes is generally the oxidation of water. Soluble anodes are usually used in chloride baths, and insoluble anodes are used in sulphate baths. Insoluble anodes are used to complete the electrical circuit to the solution; hence it is necessary for it to be a good conductor and to be unattacked by the bath with or without current flowing.

For soluble anodes the reaction is:
M(S) Mn++ ne-