Synthesis
Zinc-copper couple has been prepared by numerous methods, which vary mainly with respect to the source of copper, but also by the ratio of copper to zinc, the physical state of the zinc (e.g. powder or granules), the use of protic acids and other additives, and temperature of the preparation. Most often the couple is generated and isolated prior to use, but routes have been described to storable forms of the alloy. Most methods involve reduction of an oxidized copper species with zinc, which is used in excess.
An early method for the synthesis of zinc-copper couple entailed treatment of a mixture of zinc dust and copper(II) oxide with hydrogen gas at 500 °C. A more convenient and cheaper method proceeds by treatment of zinc powder with hydrochloric acid and copper(II) sulfate. Treatment of zinc powder with copper(II) acetate monohydrate in hot acetic acid is reportedly highly reproducible. The couple may also be generated in situ by reaction of one equivalent of zinc dust with one equivalent of copper(I) chloride (or copper powder) in refluxing ether.
The choice of method is dictated primarily by the application. The development of newer methods was motivated by the need for zinc-copper couple with reproducible behavior.
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