Chromium itself is not particularly practical, but due to its characteristic properties it is valuable when used together with other metals. It is one of the most important alloying elements that makes it possible to obtain high-quality durable and corrosion-resistant materials. In addition, chrome is often used for decorative and protective metal coatings.
In nature, large amounts of chromium are found in two minerals. The more common one, chromite, was discovered in 1798 and is a dark, dull stone that is completely unremarkable from the outside.
The second mineral, crocoite, or lead chromate, is unusual in appearance but is extremely rare. It was discovered in 1763 at the Berezovsky gold deposit and at the same time it was first mentioned in the work of M. C. Lomonosov's “The first foundations of metallurgy” as red lead ore.
The bright orange mineral was valued by stone collectors for its tetrahedral crystals. Artists loved the crocoite fragments for their beautiful reddish-orange color. However, this ore is too rare for commercial use.
A year before chromite was discovered, in 1797, French chemist Louis Nicolas Vauquelin isolated a new refractory metal (chromium) mixed with carbides. He calcined green chromium oxide with coal, and the oxide itself was obtained by decomposing crocoite. The modern method of producing pure chromium was invented in 1894; it differs from Vauquelin's method only in the type of reducing agent.
Chrome is a bluish-white metal. It is quite widespread in the earth's crust. The chemical element of the side subgroup of group 6 of the 4th period of the periodic table of chemical elements D. AND. Mendeleev.
The atomic number is 24 and the atomic mass is 51.99. Symbol — Cr (lat. Chromium). The boiling point is 2671°C, the melting point is 1856 °C, the density is 7.19 g/cm³.
Starting in the mid-1800s, cast iron producers found that adding chromium to steel made it harder and more resistant to corrosion.
The thing is steely It is an alloy of iron with a small amount of carbon — about 1%. In its purest form iron it can be heated and then bent, forged and shaped into many shapes. Iron objects made in this way have a moderate hardness and can bend when used. When iron is melted and poured into molds, “cast iron” products are obtained, which, after cooling, become brittle. But adding carbon to iron changes its microstructure and properties. When this mixture is heated, it reaches an extremely ductile stage and can be easily formed. As steel cools, it gains strength and stiffness, becoming stronger than iron. This process is called tempering. Different amounts of carbon and cooling rates determine the final properties of steel.
The addition of chromium to this mixture results in harder steel by slowing down the conversion that occurs during cooling. Since 1865, steels with a chromium content of 3-5% have been produced.
Today, the use of chromium in the production of stainless steel accounts for 60% of the consumption of this metal. Most stainless steel contains about 18% chromium; the “18-8" stamp on items such as cutlery shows that the alloy contains 18% chromium (for strength) and 8% nickel (for shine).
Since this steel does not rust and is easily sterilized, it is part of many items that we use in everyday life: kitchen appliances, food processing equipment, as well as medical and dental instruments.
Chrome in superalloys (high-performance alloys) allows jet engines to operate in a high-temperature, high-load environment. Chromite is used in blast furnaces and brick kilns because it retains its strength at high temperatures.
Moreover, chromium as a chemical element is vital for good health. Its insufficient content in the body leads to glucose intolerance. By-products, mushrooms, wheat germ, and broccoli are all good dietary sources of chromium.
