Monday, May 18, 2009

Copper Plating From Cyanide Solutions

Copper plating is most commonly achieved using a double cyanide solution, because the acid sulfate solution can not e utilize on steel or on zinc base articles.

Copper plating is wisdom used alone are alone as a protective or decorative plating since it readily mature. It strongly accelerates the corrosion of steel and most other basis metals, when they are exposed at pores or sites of mechanical damage. Electroplated copper coatings are, however, often used as the initial or undercoat on difficult basis irregular and highly recessed articles because of their excellent covering and throwing power.

In such cases copper deposits of one to two ten thousands of an inch of an inch are applied, and then the articles are thoroughly rinsed and transferred immediately to a nickel plating bath. The simple double cyanide bath is slow and is too alkaline for zinc base dies casting. For these purposes a solution containing Rochelle salt sodium potassium tartarate is used at a higher temperature and current density. It may be pointed out that the copper in copper cyanide is monovalent, i.e. only one electron is needed to deposit each atom, compared with two electrons per atom from the copper sulfate bath.

Thus at the same current density the rate of deposition is twice as great in the cyanide copper bath as in the copper sulfate bath. Copper cyanide baths give a very smooth but matt deposit; addition can be made to provide a lustrous deposit but this is less necessary since copper is usually only in undercoat.

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