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Immersion zinc plating is an electroless (non-electrolytic) coating process that deposits a thin layer of zinc on a less electronegative metal, by immersion in a solution containing a zinc or zincate ions, Zn(OH) 2− 4. A typical use is plating aluminum with zinc prior to electrolytic or electroless nickel plating.
The chromate coating acts as paint does, protecting the zinc from white corrosion, thus making the part considerably more durable, depending on the chromate layer's thickness. [8] [9] [10] The protective effect of chromate coatings on zinc is indicated by color, progressing from clear/blue to yellow, gold, olive drab and black.
A phosphate coating is usually obtained by applying to the steel part a dilute solution of phosphoric acid, possibly with soluble iron, zinc, and/or manganese salts. The solution may be applied by sponging, spraying, or immersion. [6] Phosphate conversion coatings can also be used on aluminium, zinc, cadmium, silver and tin. [7] [8]
Solutions prepared from dissolving zinc hydroxide or zinc oxide in a strong alkali like sodium hydroxide, which contains various zincate anions, are used in the metal plating industry, in processes such as immersion zinc plating and electroplating (electrogalvanization). Any of these techniques may be called zincate process. [3]
It can be used on copper and its alloys, silver, nickel, iron, gold. The color depends on the duration of immersion, the sequence of colors on brass: Golden yellow-copper-purple-dark, blue-light, blue-chrome-nickel-red-grey, blue, and gray-black to iron or carbon steel. [32]
A conversion coating is a chemical or electro-chemical treatment applied to manufactured parts that superficially converts the material into a thin adhering coating of an insoluble compound.
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