' Pit - Free Nickel Electroplating

he wide use of nickel coatings is T due to their valuable properties.l-2 Nickel coatings are used primarily for decorative and industrial purposes. The uses of nickel in the decorative field are. numerous including automobile parts, fumiture, general hardware and fasteners, bicycles, as undercoats in low-cost jewelry, sporting equipment, toys, cutlery, lamps and plumbing fixtures. Most of the decorative applications involve products that are used almost daily by the average consumer-the highly decorative, smooth, bright, pit-free and corrosion-resistant nickel-chromium deposits. Iass familiar is the industrial use of electrodeposited nickel for electroforming and other engineering applications where it is expected to provide resistance to corrosion, oxidation and wear. Decorative nickel coatings are obtained by plating from solutions containing organic additives. Nickel coatings for engineering purposes are, on the other hand, produced from solutions that deposit pure nickel. In general, deposit properties such as corrosion resistance, strength and ductility are influenced by composition of the solution. In decorative nickel plating, the most common defects are. darkening of recessed areas, surface roughness and pitting? Among these defects, pitting is very common, resulting in heavy rejections. Pitting in nickel deposits may be due to substrate surface defects, firm attachment of air or gas bubbles on the surface, presence of organic or inorganic contaminants in solution or the presence of oily globules formed over the solution due to incomplete dissolution of additives. Pitting is normally reduced either by motion of the cathode during plating, by cathode-rod or by solution-agitation. Pitting can also be brought down by reducing the surface tension of the solution with a suitable wetting agent. The use of compressed air for agitating the electrolyte may introduce finely divided oil droplets. In this paper, the authors report on the usefulness of potassium chloride versus nickel chloride as a bath constituent for substantial minimization of pitting of deposits. The effects of sodium chloride or ammonium chloride instead of nickel chloride in the nickel bath is also reported.& Other deposit characteristics studied are the effects of operating parameters on bath characteristics such as surface tension and throwing power, and deposit properties such as stress, microhardness and structure.