Copper-zinc alloys coatings

Attractive metallic effects can be obtained by incorporating very thin, small flakes of aluminium, copper or copper/zinc alloys in otherwise transparent surface coatings. The metal flakes act as tiny mirrors within these paints, which are particularly effective on the curved surfaces of cars since the colour changes with the angle from which the surface is viewed. The orientation of the flakes within the paint film also changes the colour seen by the eye, so that careful dispersion of the metal components of the paint is essential. 

Copper-zinc alloys with a higher zinc content (brass) cannot be ground or formed into flake pigments on account of their brittleness. Controlled oxidation of natural bronze powders converts them into fired bronze powders. These shades (e.g., English green, lemon, ducat gold, fire red) are produced as a result of interference effects that depend on the thickness of the oxide coating. 

Metal Effect Pigments Some metals, when prepared as small flakes, impart a special metallic appearance to the coatings and plastics in which they aie dispersed. Metals most often used in these applications are aluminum (aluminum bronzes), copper and copper-zinc alloys (gold bronzes), and in smaller amounts zinc, tin, nickel, gold, silver, and stainless steel. 

Many alloys may be electrodeposited, including copper-zinc, copper-tin, lead-tin, cobalt-tin, nickel-cobalt, nickel-iron, and nickel-tin. The copper-zinc alloys are used to coat steel wire used in tire-cord. Lead-tin alloys are known as terneplate and have many corrosion resistant applications. 

The development of new alloys as a means of modifying existing electrodeposits for example the production of hard gold by alloy codeposition of copper, cadmium etc. to yield 23 or 18 carat alloys, or the use of zinc alloys for improved electrogalvanised coatings. 

Post-Treatments. Although many post-treatments have been used over plated metals, chromate conversion coatings remain as the most popular. Chromates are used to improve corrosion resistance, provide good paint and adhesive base properties, or to produce brighter or colored finishes. Formulations are usually proprietary, and variations are marketed for use on zinc, zinc alloys, cadmium, copper and copper alloys, and silver (157). Chromates are also used on aluminum and magnesium alloys (158,159). More recently, chromate passivation has been used to extend salt spray resistance of autocatalytic nickel plated parts. 

Politecnico di Milano and Ineos Vinyls UK developed a tubular fixed bed reactor comprising a metallic monolith 67,130). The walls were coated with catalytically achve material, and the monolith pieces were loaded lengthwise. Coming, the world leader in ceramic structured supports, developed metallic supports with straight channels, zigzag channels, and wall-flow channels. These metallic supports were produced by extrusion of metal powders, for example, copper, tin, zinc, aluminum, iron, silver, nickel, and mixtures and alloys (131). An alternative method is extmsion of softened bulk metal feed, for example, aluminum, copper, and alloys thereof. The metal surface can be covered with coating such as carbon, carbides, and alumina, for example, by application of a CVD technique (132). 

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