MANGANESE

Name: Manganese

Symbol: Mn

Group: 7

Period: 4

Block: d

Category: Transition Metals

Atomic Number: 25

Atomic Mass: 54.938 u

Electrons per Shell: 2, 8, 13, 2

Electronegativity: 1.55

Density: 7.47 g/cc

Melting Point: 1246ºC

Boiling Point: 2061ºC

Thermal Conductivity: 7.7 W (m·K)

Electrical Conductivity: 620,000 S/m

Magnetic Order: Paramagnetic

Ordinary State: Solid

Oxidation States: -3, -2, -1, 1, 2, 3, 4, 5, 6, 7

Mohs Hardness: 6

Vickers Hardness: No data

Brinell Hardness: 196 MPa

Most stable isotopes: Mn-55 (100%, monoisotopic element)

Discoverer: Johan Gottlieb Gahn, Swedish (1774)

Manganese (Mn), a transition metal with atomic number 25, was first identified as a new element in the 18th century. Throughout history, its compounds were confused with those of iron (Fe), with which it is often found in nature. The ancient Egyptians and Romans used manganese compounds to color glass black or to lighten its color. However, it wasn't until 1774 that Swedish chemist Johan Gottlieb Gahn isolated pure metallic manganese. Gahn reduced manganese dioxide (MnO2), a mineral known as pyrolusite, with carbon, following the instructions of his colleague and mentor, Carl Wilhelm Scheele. 

This achievement was an important milestone, as it confirmed that pyrolusite was not, as previously believed, a form of iron ore, but contained an entirely new element. The name "manganese" comes from the Latin word magnes, meaning magnet, referring to pyrolusite's magnetic properties. Its use in steel metallurgy began in the late 19th century, when it was discovered that it could remove impurities and improve the metal's properties.

Manganese, a transition metal with atomic number 25, has a steely-gray color and a brittle nature, sharing chemical similarities with iron. Although relatively abundant in nature, its fragility and reactivity limit its use in its pure form, reserving it exclusively as an alloying agent in metallurgy. It is extracted primarily as a byproduct of iron production, as it is often present in the same ores, such as pyrolusite, or during the refining of nickel or aluminum. Its extraction is secondary to metals of greater industrial importance, such as iron, reflecting its complementary but essential role.

Physically, manganese is an opaque metal that quickly loses its luster, taking on a blackened appearance that can be mistaken for corroded iron or slag to the untrained eye. Its rough feel and vitreous fracture when broken, easily under finger pressure, distinguish it from iron. It is a poor thermal conductor and one of the worst electrical conductors among metals, transition or not. Its corrosion resistance is lower than that of iron: although it is passivated in dry air and moderately resistant to fresh water, it is highly vulnerable to acids, both oxidizing and reducing, and to bases. Despite its relatively low melting point, it melts vigorously due to oxidation, so it is usually added in the solid state, either as pure metal or in the form of oxides, to the liquid base metal.

Despite its dull and unattractive appearance, manganese is one of the most versatile and indispensable alloys in modern metallurgy. It is present, in varying proportions, in virtually all aluminum alloys, carbon steels, stainless steels, high-performance bronzes, and nickel and cobalt superalloys. In most cases, its concentration ranges between 0.1% and 2%, although in specific applications, such as manganese bronze or the alloy known as manganin—used in high-precision resistors—it can reach 20% or even exceed this amount.

The most traditional use of manganese in steelmaking is during casting, when it is added as a deoxidizer. No other element, not even silicon or aluminum, can match its ability to combine with undesirable impurities. One of its most valued virtues is its ability to bind the sulfur present in molten iron, forming more stable and less harmful compounds than those produced by the iron itself. These more volatile compounds are eliminated during cooling, thus reducing the detrimental effect of sulfur on the quality of the steel.

In carbon steels, where it is typically incorporated in proportions between 0.1% and 0.8%, manganese provides toughness, refines grain size, and prevents the formation of porosities. It acts as a "sacrificial metal" by combining with oxygen and sulfur, purifying the ferrite grains. The chemical affinity between iron and manganese is excellent, allowing the latter to dissolve easily even when incorporated in a solid state, either as pure metal or as an oxide. As a result of its use in manufacturing processes, all modern steels inherently contain manganese.

In ferritic, martensitic, or duplex stainless steels, manganese's role is essentially the same as in carbon steels: deoxidizing during casting and reducing grain size to improve toughness. In nickel-based austenitic stainless steels, such as AISI 304, 316, or 316L, its presence—around 2%—not only serves as a deoxidizer but also contributes to establishing the austenitic structure, given its "gammagenic" nature. This property increases impact strength and improves ductility, without significantly affecting corrosion resistance.

In austenitic stainless steels predominantly based on manganese, such as AISI 201, this metal can partially replace nickel to stabilize austenite at room temperature. These alloys, developed during the nickel shortage during World War II, are more economical and, according to some studies, even tougher than traditional equivalents, although they have lower corrosion resistance. The 200 series, which includes grades such as 201 and 204, always contains some nickel, since manganese alone cannot completely counteract the destabilizing effects of elements such as chromium or molybdenum on austenite.

In non-stainless alloys, such as Hadfield steel or Mangalloy, the addition of approximately 12% manganese, combined with appropriate heat treatment, produces a non-magnetic, extremely tough, impact-resistant material capable of working under low-temperature conditions. This alloy combines toughness with controlled deformation capacity and is used in components that require high abrasion resistance while simultaneously absorbing mechanical energy, such as high-performance bicycle frames or parts subjected to extreme loads.

Manganese also plays a significant role in alloys with cobalt and nickel. With cobalt, in proportions between 10% and 30%, it significantly increases ductility, contradicting the belief that two brittle metals can only produce brittle alloys. Although these combinations have limited applications, they are useful in cutting tools that require toughness rather than impact resistance. In the case of nickel, its direct combination with manganese is rare, except in alloys such as manganin, where it is complemented with copper.

Because both metals share similar alloying functions and manganese is more economical, there has been ongoing interest in replacing nickel in certain applications. Although they differ significantly in their pure state, their behavior is similar once incorporated into a metallic matrix, whether iron, copper, or cobalt.

In the field of ornamental alloys, manganese can act as an alternative ingredient in the manufacture of nickel silver or "German silver." By combining copper, manganese, and a third metal, usually zinc or nickel, a material with a luster comparable to that of sterling silver is obtained. By adjusting the proportions, ductility or durability can be optimized, reaching up to 20% manganese in compositions designed for greater strength.

In specialty bronzes, such as manganese bronze, this element provides hardness and toughness, although it reduces thermal and electrical conductivity compared to most copper alloys. Manganin, composed of 82% copper, 12% manganese, and 2% nickel, is a representative example, widely used in electrical resistors. These alloys tend to lose their luster easily and exhibit characteristic white hues.

Even in jewelry, manganese has found unique applications. In the manufacture of white gold, it can replace nickel to prevent allergic reactions, producing a hard and tough alloy, albeit with limited malleability. For this reason, zinc or silver are often added to improve workability and allow the artisan to precisely shape the final piece.

Manganese plays a crucial role as a gamma-forming agent, stabilizing the austenite crystal structure in steels when added in proportions close to or greater than 10% by mass. As the second most important transition metal for this purpose after nickel, it allows the production of austenitic steels that, while not matching the chemical resistance of nickel-based steels, offer slightly greater hardness at a more affordable cost. In aluminum bronze, manganese fixes the alpha phase, improving its structural stability. In jewelry and costume jewelry, it acts as a powerful bleach: at 20% by mass, it transforms copper into a silvery hue similar to cupronickel, and is also used to forge white gold, providing an attractive finish.

Manganese's versatility as an alloying agent lies in its excellent solubility with almost all metals, including some p-block metals, such as tin, and especially with transition metals such as iron, copper, cobalt, and nickel. Unlike iron and cobalt, it dissolves easily in molten copper and shows an affinity for silver. A historical example is its use during World War II, when the U.S. Central Bank modified the composition of its five-cent coin, replacing the traditional formula of 75% copper and 25% nickel with a mixture of 56% copper, 35% silver, and 9% manganese, thus imitating the original weight and luster. However, manganese is a poor conductor, being the worst thermal conductor and one of the worst electrical conductors among metals.