We continue to review some of the most important materials in heat treatment and metallurgy.
Manganese (chemical symbol: Mn)
Manganese is a hard metal most commonly found combined with other elements in the form of pyrolusite (Fig. 1) or rhodochrosite. It is also found in combination with iron. Manganese is one of the most common elements and is widely distributed across the surface of the planet.
One of the more interesting occurrences of this element is in manganese nodules (Fig. 2), which are deposits of manganese that form on the ocean floor at the incredibly slow rate of a few millimeters every million years. These nodules are about 24% manganese.
Manganese was discovered in 1774 by Swedish chemist and metallurgist Johan Gottlieb Gahn. He found that manganese dioxide could be reduced to pure metal using carbon and was the first to isolate this element in its metal form by heating the mineral pyrolusite (MnO2) in the presence of charcoal. Most manganese is still obtained from pyrolusite. Gahn was also known for introducing improvements to copper smelting and for establishing several factories, including those for vitriol, sulfur and red paint. Manganese is named after the Latin word for magnet, which is magnes.
Most of the manganese produced today is used in the production of steel. It is added to molten steel to remove oxygen and sulfur and is alloyed with steel to make it easier to form and to increase its strength and resistance to impact. The addition of manganese to steel makes it work-harden when impacted or bent, increasing the hardness of its outer layer by more than double. The interior of the steel remains very tough and ductile, which is highly desirable for strength and durability. Railroad tracks, for example, are made with steel that contains as much as 1.2% manganese. The second most-common use of manganese is in aluminum alloys, where it is added at up to 1.5% to provide increased resistance to corrosion. Manganese is also used to give glass an amethyst color and is responsible for the striking color of amethyst jewels (Fig. 3).
Manganese steel is an austenitic steel, which means it is nonmagnetic. This property makes it widely used in many applications, such as bottom plates for lifting magnets, separator drum shells for magnetic materials and wear shoes on electric brakes.
Here are a few scientific and engineering facts about manganese.
- Atomic number: 25
- Atomic weight: 54.938044
- Melting point: 1519 K (1246°C or 2275°F)
- Boiling point: 2334 K (2061°C or 3742°F)
- Density: 7.3 grams per cubic centimeter
- Phase at room temperature: Solid
- Element classification: Metal
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