Zinc has been used, if not recognized, since ancient times. Brass was made directly from copper and calamine (a kind of zinc ore) in the early Roman Empire. In an imprecise process, calamine was heated in a furnace such that it would give off zinc vapors that soaked into the accompanying copper. Actual zinc metal was the peculiar condensation at the bottom of the furnace.
Better efforts to isolate zinc and control the manufacture of alloys are seen around the year 1000 in China and India, and later imported to Europe. Not until the 18th century is brass regularly made directly from local zinc in Europe. There is no specific date for the recognition of zinc as a distinct metal. This makes zinc unusual, standing between the ancient elements (carbon, iron, and so on) and the discoveries of modern chemistry.
Mining and Production
Zinc is mined world-wide, led by China (38%), Australia (11%), and Peru (10%). At thirteen million tonnes extracted per year, it is the fourth major metal behind iron, aluminum, and copper.
Zinc-bearing minerals are normally extracted, isolated, and oxidized to zinc oxide. The traditional next step is to burn the zinc oxide with carbon and distill the resulting zinc vapor. This is much like the original Roman process. Another more recent method uses electrolysis of a precise voltage to deposit zinc on an electrode from a solution of zinc sulfate.
Purified zinc oxide itself is also a commercial product as an ointment and whitener. Calamine lotion is zinc oxide tinted with ferric oxide (rust).
Properties and Uses
Zinc is a blue-gray metal that is moderately reactive with many substances. It has a relatively low boiling point (907°C) that makes preparation somewhat problematic. It burns when heated to form zinc oxide.
Most zinc is used in metal alloys, especially brass. Brass is decorative, malleable, and corrosion-resistant. Zinc as a plating forms galvanized steel. Zinc is the primary metal in the U.S. penny, being less expensive than copper. Zinc-aluminum is a class of alloys that resist wear well and are suitable for bearings.