Question

In an atmosphere with industrial smog, $Cu$ corrodes to:

• A. basic sulphate $C{u}_2(OH{)}_{2}S{O}_4$
• B. basic carbonate $C{u}_2(OH{)}_{2}S{O}_3$
• C. both $\left(A\right)$ and $\left(B\right)$
• D. none of the above

Answer 1

The correct option is C both $\left(A\right)$ and $\left(B\right)$

Copper is considered a noble metal; it resists attack by oxygen, although some air pollutants, such as $H_{2}S$, change its surface properties, even at ambient temperature, forming a thin layer having completely different properties compared with the pure metal surface. This layer lowers catastrophically the adhesion of the soldering alloy or conductive resins and paste. Compounds such as geerite $\left(C{u}_8{S}_5\right)$ are formed on Cu in the presence of $H_{2}S$ and patinas as $C{u}_{2}O$; posnjakite $\left(C{u}_{4}SO\right(OH{)}_6{H}_{2}O),$ and antlerite $\left(C{u}_{3}S{O}_4\right(OH{)}_4)$ are formed in the presence of humidity. The formation of tarnish films on a copper surface exposed to environments containing atmospheric pollutants and high humidity involves the movement of metallic ions over the surface, away from the metal generating a creep process that increases the contact resistance, leading to electric failures of the electronic devices. Copper sulphidation is a fast process occurring on the metal-gas phase interface impairing the $Cu$ corrosion resistance.