Metallic zinc was produced in the 13th century A.D. in India by reducing calamine with organic substances such as wool. It was not until 1746, that it was rediscovered by Marggraf who showed that it could be obtained by reducing calamine with charcoal.
The principal ores of zinc are sphalerite or blende (ZnS), smithsonite (ZnCO3), calamine (silicate) and franklinite (zinc, manganese, iron oxide). Zinc can be obtained by roasting its ores to form the oxide and by reduction of the oxide with coal or carbon, with subsequent distillation of the metal. Zinc has five (5) naturally occurring stable isotopes, there are sixteen (16) other unstable isotopes recognised, half of which are zinc 64. The stable isotope zinc 67 occurs to the extent of 4% in natural zinc.
Zinc is a blue-white, lustrous metal. It is brittle at ordinary temperatures but is malleable at 100°C to 150°C. It conducts electricity moderately, and burns in air at high red heat with the evolution of white clouds of the oxide.
On exposure to air, zinc becomes coated with film of carbonate and is then very corrosion-resistant.
Zinc is used for:
- Galvanising and plating
- Making brass, bronze and nickel silver
- Electric batteries
- Die castings
- Alloyed sheets for flashings, gutters and stamped and formed parts.
Cathodic zinc is 99.99% pure and is used on hulls of ships/ocean-going vessels or attached to underground pipelines to reduce electrolytic corrosion.
Zinc powder is used in pyrotechnics, in paints, as a reducing agent and catalysts, in rubbers as a secondary dispersing agent and to increase flexing and to produce Sherardised steel.
Zinc alloys find applications in areas such as die castings for decorative parts, auto and appliance parts, hardware, locks, toys and novelties.