The Properties and Uses of Zinc Metal
Zinc (Zn) is an abundant metal, found in the Earth’s crust, with a myriad of industrial and biological uses. At room temperature, zinc is brittle and blue-white in color, but it can be polished to a bright finish.
A base metal, zinc is primarily used to galvanize steel, a process that protects the metal against unwanted corrosion. The alloys of zinc, including brass, are vital to a wide range of applications, from corrosion-resistant marine components to musical instruments.
Strength: Zinc is a weak metal with less than half the tensile strength of mild carbon steel. It is generally not used in load-bearing applications, although inexpensive mechanical parts can be die cast from zinc.
Toughness: Pure zinc has low toughness and is generally brittle, but zinc alloys generally have high impact strength compared to other die casting alloys.
Ductility: Between 212 and 302 degrees Fahrenheit, zinc becomes ductile and malleable, but at elevated temperatures, it reverts to a brittle state. Zinc alloys greatly improve on this property over the pure metal, allowing more complex fabrication methods to be used.
Conductivity: Zinc’s conductivity is moderate for a metal. Its strong electrochemical properties, however, serve well in alkaline batteries and during the galvanizing process.
The History of Zinc
Man-made zinc alloy products have been reliably dated as far back as 500 BC, and zinc was first intentionally added to copper to form brass around 200-300 BC. Brass supplemented bronze during the Roman Empire in the manufacture of coins, weapons, and art. Brass remained the chief use of zinc until 1746 when Andreas Sigismund Marggraf carefully documented the process of isolating the pure element. While zinc had been previously isolated in other parts of the world, his detailed description helped zinc become commercially available throughout Europe.
Alessandro Volta created the first battery in 1800 using copper and zinc plates, ushering in a new era of electrical knowledge. By 1837, Stanislas Sorel had named his new process of zinc-plating “galvanization” after Luigi Galvani, who had discovered the animating effect of electricity while autopsying frogs. Galvanization, a form of cathodic protection, can protect a wide variety of metals. It’s now the primary industrial application of pure zinc.
Zinc in the Marketplace
Zinc is primarily extracted from ore containing zinc sulfide, zinc blende, or sphalerite.
The countries mining and producing the most refined zinc, in descending order, are China, Peru, Australia, the United States, and Canada. According to the U.S. Geological Survey, about 13.4 million metric tons of zinc in concentrate was mined in 2014, with China accounting for about 36% of the total.
According to the International Lead and Zinc Study Group, about 13 million metric tons of zinc were consumed industrially in 2013—through galvanizing, brass and bronze alloys, zinc alloys, chemical production, and die casting.
Zinc is traded on the London Metal Exchange (LME) as “Special High Grade” contracts at 99.995% minimum purity in 25-ton ingots.
Brass: 3-45% Zn by weight, it’s used in musical instruments, valves, and hardware.
Nickel silver: 20% Zn by weight, it’s used for its shiny silver appearance in jewelry, silverware, model train tracks, and musical instruments.
Zinc die casting alloys: >78% Zn by weight, it usually contains small amounts (less than a few percentage points) of Pb, Sn, Cu, Al, and Mg to improve die casting characteristics and mechanical properties. It’s used to make small intricate shapes and suitable for moving parts in machines. The cheapest of these alloys are referred to as pot metal, and they serve as inexpensive replacements for steel.
Interesting Zinc Facts
Zinc is critical for all life on Earth, and it’s used in more than 300 enzymes. Zinc deficiency was recognized as a clinical health problem in 1961. The International Zinc Association explains that zinc is critical to proper cellular growth and mitosis, fertility, immune system function, taste, smell, healthy skin, and vision.
United States pennies are constructed with a zinc core that makes up 98% of their total weight. The remaining 2% is an electrolytically plated copper coating. The amount of copper used in pennies is subject to change if the U.S. Treasury deems them too expensive to produce. As many as 2 billion zinc-core pennies are circulating in the U.S. economy.