Plating bath protective coatings

Uses. The most important commercial use for benzonitrile is the synthesis of benzoguanamine, which is a derivative of melamine and is used in protective coatings and molding resins (see Amino RESINS Cyanamides). Other uses for benzonitrile are as an additive in nickel-plating baths, for separating naphthalene and alkylnaphthalenes from nonaromatics by azeotropic distillation (qv), as a jet-fuel additive, in cotton bleaching baths, as a drying additive for acrylic fibers, and in the removal of titanium tetrachloride and vanadium oxychloride from silicon tetrachloride. 

Electroplating is the process involving electrolysis to plate, or coat, one metal with another or a plastic with a metal. Often the purpose of electroplating is to give a protective coating to the metal beneath. For example, bath taps are chromium plated to prevent corrosion, and at the same time are given a shiny, more attractive finish (Figure 5.19). 

Electrolytic plating of metals is performed for both protective and decorative reasons. The arrangement and chemistry of the plating bath must be such that a coat of even thickness, non-porous, adherent metal is produced. The "throwing power is a measure of the ability of the metal ions to reach remote sections of the article to be plated. Accurate control of current, potential, plating bath chemistry, and temperature is essential in order to obtain high-quality results. 

Corrosion Protection by Metallic Coatings 577 Tab. 4 Composition and working conditions of different copper plating baths... 

Uses Anticorrosion pigment for paints metal protective coatings colorant in PVC resins pyrotechnics chrome plating reagent sulfate ion control in electroplating baths... 

Such agents are of importance in the plating baths used for the deposition of decorative as well as corrosion-protective coatings, e.g. bright nickel plate which confers protection to nickel-chromium coatings. The addition agents in this instance are more specific, more stable and more controllable in their effects than the colloidal type of agent they are characterised by the presence of unsaturated bonds, e.g. dimethyl fumarate. 

The next phase will address eliminating lead from board finishes—the protective coatings applied to termination pads on printed wiring boards to protect metal conductors from degradation (e.g., oxidation, corrosion) and remain solder-wettable. Finishes are applied in a number of ways, including dipping into a molten metal bath (e.g., tin, solder), electroless plating, etc. Alternative finishes must, of course, be compatible with the lead-free alloy selected in Step 1. 

The electroless nickel/electroless palladium/immersion gold (ENEPIG) finish is simply an ENIG finish into which an intermediate layer of palladium (0.1 to 0.5 pm thick) is deposited between the electroless nickel and immersion gold coatings. Palladium is deposited from an autocatalytic plating bath. Palladium is a noble metal applied to protect oxidizable Ni. Palladium (m.p. 1552°C) is not fusible but rather dissolves in the molten solder in a manner similar to gold, and... 

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