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Because of its corrosion resistance, zinc is often plated to other metals in a process called galvanization; galvanized roofing shown here. |
Zinc
| Atomic Number: | 30 | Atomic Radius: | 139 pm (Van der Waals) |
| Atomic Symbol: | Zn | Melting Point: | 419.5 °C |
| Atomic Weight: | 65.39 | Boiling Point: | 907 °C |
| Electron Configuration: | [Ar]4s23d10 | Oxidation States: | -2, 0, +1, +2 (an amphoteric oxide) |
History
From the German word Zink, of obscure origin. Centuries before zinc was recognized as a distinct element, zinc ores were used for making brass. An alloy containing 87 percent zinc has been found in prehistoric ruins in Transylvania.
Metallic zinc was produced in the 13th century A.D. India by reducing calamine with organic substances such as wool. The metal was rediscovered in Europe by Marggraf in 1746. He demonstrated that zinc could be obtained by reducing calamine with charcoal.
Sources
The principal ores of zinc are sphalerite (sulfide), smithsonite (carbonate), calamine (silicate), and franklinite (zinc, manganese, iron oxide). One method of zinc extraction involves roasting its ores to form the oxide and reducing the oxide with coal or carbon, with subsequent distillation of the metal.
Isotopes
Naturally occurring zinc contains five stable isotopes. Sixteen other unstable isotopes are recognized.
Properties
Zinc is a bluish-white, lustrous metal. It is brittle at ordinary temperatures but malleable at 100 to 150°C. It is a fair conductor of electricity, and burns in air at high red heat with evolution of white clouds of the oxide.
It exhibits superplasticity. Neither zinc nor zirconium is ferromagnetic; but ZrZn2 exhibits ferromagnetism at temperatures below 35°K. It has unusual electrical, thermal, optical, and solid-state properties that have not been fully investigated.
Uses
The metal is employed to form numerous alloys with other metals. Brass, nickel silver, typewriter metal, commercial bronze, spring bronze, German silver, soft solder, and aluminum solder are some of the more important alloys.
Large quantities of zinc are used to produce die castings, which are used extensively by the automotive, electrical, and hardware industries. An alloy called Prestal(R), consisting of 78 percent zinc and 22 percent aluminum, is reported to be almost as strong as steel and as easy to mold as plastic. The alloy said to be so moldable that it can be molded into form using inexpensive ceramics or cement die casts.
Zinc is also used extensively to galvanize other metals such as iron to prevent corrosion. Zinc oxide is a unique and very useful material for modern civilization. It is widely used in the manufacture of paints, rubber products, cosmetics, pharmaceuticals, floor coverings, plastics, printing inks, soap, storage batteries, textiles, electrical equipment, and other products. Lithopone, a mixture of zinc sulfide and barium sulfate, is an important pigment.
Zinc sulfide is used in making luminous dials, X-ray and TV screens, and fluorescent lights.
The chloride and chromate are also important compounds. Zinc is an essential element in the growth of human beings and animals. Tests show that zinc-deficient animals require 50 percent more food to gain the same weight as an animal supplied with sufficient zinc.
Handling
Zinc is not considered to be toxic, but when freshly formed ZnO is inhaled a disorder known as oxide shakes or zinc chills sometimes occurs. Where zinc oxide is encountered, recommendations include providing good ventilation to avoid concentration exceeding 5 mg/m3, (time-weighted over an 8-hour exposure, 40-hour work week).