Cuprous oxide copper coating

In the case of the production of copper wire, additional complications are present because of the chemical reduction of cupric oxide to a cuprous oxide coating, which cannot be removed by sulfuric acid. This coating has normally been treated by a secondary pickle of chromic acid-sulfuric acid, chromic acid-ammonium bifluoride mixtures, or by nitric acid. All of these techniques produce additional pollutants. Each of the three to four drawing steps required to produce fine copper wire from copper rod requires these pickling and rinse steps. 

When metallic copper is heated in the air it becomes coated with a layer of oxide, which, according to conditions, may be cuprous or cupric oxide, or a mixture of the two. Pure cuprous oxide is most conveniently prepared in the wet way by treating an alkaline cupric salt solution with a reducing agent, whereby the red cuprous oxide is precipitated. 

Copper is not attacked by water at ordinary temperatures, or at 100° C., and only slightly at white heat but very prolonged immersion in sea-water produces a superficial coating of cuprous oxide.4 It is insoluble in dilute sulphuric acid of 5 to 10 per cent, strength,5 but reacts with the concentrated acid in accordance with the equations 6... 

Plates of copper covered by neutral solutions of cupric sulphate always gain weight, becoming coated with a film of cuprous oxide. 

Chromium copper arsenate wood preservative Cuprous oxide in antifouling coatings for ships Pigments, such as copper phthalocyanine... 

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