Chromium

Chromium is a metal, essential in metallurgy and many other applications.

CHEMICAL ELEMENT

Chromium is a chemical element of the group 6 of the period 4 of the periodic table of chemical elements by D. I. Mendeleev, and with atomic number 24. It is indicated by the symbol Cr (lat. Chromium).

PROPERTIES

• Solid metal of bluish-white color.
• It has all the properties characteristic for metals – conducts heat and electric current well, has metallic luster inherent in most metals. It is an antiferromagnet and a paramagnet.
• One of the most robust pure metals in nature.
• In its pure form, it lends itself well to mechanical processing.
• Stability in the air due to passivation. Does not react with sulfuric and nitric acids.
• At 2000 °C it burns with the formation of green Chromium (III) Oxide Cr2O3.
• When heated, it reacts with many non-metals, forming carbides, borides, silicides, nitrides, etc.
• It forms numerous compounds with various degrees of oxidation, mainly +2, +3, +6.

HISTORY

The birthplace of Chromium is considered to be the Central Urals, where the ore containing Chromium, called "Siberian red lead", was first discovered at the Berezovsky gold ore field in the first half of the 18th century. In the scientific literature, red lead ore (chemical formula - PbCrO4) was first described in 1763 by the great Russian scientist M.V. Lomonosov. And soon, in 1797, another chemist, the French scientist Vauquelin produced a new refractory metal from the ore.

The modern method of producing pure Chromium metal was invented in 1894. It should be noted that it does not differ much from the method proposed by Vauquelin.

Vauquelin not only obtained a new metal in the course of his research, he also produced various Chromium derivatives – multicolored Salts and Oxides. That is why he called the new metal "Chrome" from (Greek) χρῶμα - meaning color.

NATURAL CHROMIUM ORE FIELDS

Chromium is a fairly common element in the Earth's crust. The main natural Chromium compound is Chromic ironstone (Chromite) FeO·Cr2O3.

The identified global reserves of Chromium ores in 47 countries of the world amount to about 15 billion tons.

The largest Chromium ore fields are located in South Africa, Kazakhstan, Russia, Zimbabwe, Madagascar, as well as Turkey and India. Russian Chromium ore fields are located in the Urals, Karelia, and the Murmansk region. Chromium ore reserves have also been discovered in the Yamal-Nenets Autonomous Area.

MINING AND PRODUCING

Chromium (better to say Chromium ore), like the most of minerals, is mined in an open, underground or combined way. At the same time, due to the availability of reserves, open mining method is the most common in the world.

The extracted raw materials – Chromium ore (usually in the form of Chromic ironstone or otherwise Chromite) is mainly used to produce an alloy of Ferrum and Chromium, Ferrochromium. For this purpose, Chromite is reduced with coke (Carbon) in electric furnaces. Ferrochromium plays an important role in modern metallurgy and is used for the production of stainless steel.

The various physicochemical methods of extracted ores processing are used to produce the pure Chromium as well as other derivatives of Chromium ore. The most widely used in modern metallurgy is the alumothermal method. This method was invented in 1859 by the Russian academician N. N. Beketov and put into commercial operation at the turn of the XIX-XX centuries.

Alumothermy is a method of producing metals, nonmetals, and alloys by reducing their Oxides with metallic Aluminum. A large amount of heat is released in such reactions, and the temperature of the mixture may reach 3000 ° C.

The aluminothermic method of producing Chromium involves several stages. First, iron Chromite is fused with soda ash. As a result, Sodium Monochromate is produced. Monochromate converts to Dichromate by acidification with Sulfuric Acid. The next step is to reduce Sodium Dichromate with coal and produce Chromium (III) Oxide. At the final stage, Chromium Oxide is converted into metallic Chromium by means of alumothermy.

It should be noted that it is also possible to produce pure electrolytic Chromium by electrolysis method from a solution of Chromic Anhydride (Chromium (VI) Oxide).

CHROMIUM ALLOYS AND THEIR APPLICATION

Due to its properties, Chromium is widely used in steel production. This alloying element allows to protect iron from corrosion, increase its hardness and reduce the critical cooling rate during hardening.

Chromium is an important component in many alloy steels (in particular, stainless steels), as well as in a number of other alloys. The additive of Chromium significantly improves the quality and consumer properties of alloys, such as hardness and corrosion resistance. The use of Chromium is also due to its heat resistance and hardness.

There are two types of Chromium alloys: low-alloyed with a Chromium content up to 1.6%, in such alloys strength and hardness are increased, as well as high-alloyed, with a Chromium content of more than 12%. These are stainless alloys with high corrosion resistance. The composition of alloys often includes other metals that give additional consumer properties to metallurgical products, for example: Manganese, Aluminum, Silicon, Tungsten, Cobalt.

Chromium steels are used for the manufacture of weapons, armor plates, fireproof safes and ovens, as well as the hulls of ships and submarines. Chromium is used for the production of alloys, irreplaceable in the aerospace industry. Submarine hulls, gun barrels, metal-cutting tools, medical safes and chemical equipment, and even parts of plasmatron are produced from Chromium steels.

CHROMIUM DERIVATIVES AND THEIR APPLICATION

Refractory production

A significant part of Chromium is used for the production of refractories — Chromite and Magnesitochromite bricks that withstand high temperatures and sudden temperature changes for a long time. Such bricks are used in the manufacture of metallurgical furnaces and exceed quartz products in terms of service life.

Chromium plating

Powdered chromium is widely used for the production of decorative corrosion-resistant coatings, metal-ceramic products and materials for welding electrodes.

Chromic anhydride (Chromium (VI) Oxide) is also used for chromium plating of various products. The thinnest film, about 0.005 mm thick, is applied to the surface of the finished product or part by electrolytic method, which makes it possible to form a chrome-plated surface. Such a protective layer – chromium coating or chromium plating not only makes the product elegant and beautiful, but also protects it from moisture and air for a long time.

Wood preservation and leather treatment

Not only metals need protection, but also wood. Wood treated with Chromium derivatives, such as Chromic Anhydride, becomes inaccessible for destruction by microorganisms, insects and, moreover, has a lower probability of mechanical damage.

Fabrics are treated by Chromium compounds during dyeing. Chrome Sulfates are used as tanning solutions in the leather industry. Chrome tanning agent is still the most effective material for leather treatment and its consumption continues to grow, despite the appearance of alternative chromium-free chemicals on the market.

Production of paints

Due to the rich palette of colors, Chromium compounds are part of a variety of dyes and pigmenting substances. Chromium (III) Oxide is the basis of the green pigment, and Sodium Dichromate is the basis of the orange-red pigment. Pigments based on Chromium compounds are used not only for the production of decorative and artistic paints, but also as a dye in the glass industry, in the production of plastics, for painting various artificial surfaces. For example, the green or yellow color characteristic for some decorative glass products is based on Chromium compounds.

Chemical industry

Hexavalent Chromium compounds (for example, Chromic Anhydride) are the strongest oxidizer and are used in various industrial chemical syntheses, as well as in the production of catalysts.

Important to know

Chromium is a microelement necessary for the normal development and functioning of the human body. Its most important biological role is to regulate carbohydrate metabolism and blood glucose levels.

You can learn more about the application of chromium and its derivatives on our website in the PRODUCTS section.