Chromium is a mineral. It is called an “essential trace element” because very small amounts of chromium are necessary for human health. There are two forms of chromium.
Trivalent chromium is found in foods and supplements and is safe for humans. The other form, hexavalent chromium, is a known toxin that can cause skin problems and lung cancer. Only trivalent chromium is discussed here.
Chromium is used for chromium deficiency. It is also used for diabetes, high cholesterol, a hormonal disorder that causes enlarged ovaries with cysts (polycystic ovary syndrome or PCOS), and many other conditions, but there is no good scientific evidence to support most of these uses. But In this article, we discuss chromium as a metal and its properties and uses.
What Is Chromium Metal?
Chromium is a chemical element with the symbol Cr and the atomic number 24. It is the first element of group 6. It is a steel-gray, shiny, hard, and brittle transition metal. Chromium is the main additive in stainless steel, which gives anti-corrosive properties.
Chrome is also valued as a metal that can be polished to a mirror finish while resisting tarnishing. Polished chrome reflects almost 70% of the visible spectrum and almost 90% of the infrared light.
Chrome metal is valued for its high corrosion resistance and hardness. An important development in steel production was the discovery that steel can be made highly resistant to corrosion and discoloration by adding metallic chromium to form stainless steel. Stainless steel and chrome plating together make up 85% of commercial use.
The industrial production of chromium takes place from chromite ore (mostly FeCr2O4) to ferrochrome, an iron-chromium alloy, through aluminothermic or silicothermic reactions.
Ferrochrome is then used to make alloys such as stainless steel. Pure chrome metal is made by a different process: roasting and leaching chromite to separate it from iron, followed by reduction with carbon and then with aluminum.
| Group | 6 | Melting point | 1907°C, 3465°F, 2180 K |
| Period | 4 | Boiling point | 2671°C, 4840°F, 2944 K |
| Block | d | Density (g cm−3) | 7.15 |
| Atomic number | 24 | Relative atomic mass | 51.996 |
| State at 20°C | Solid | Key isotopes | 52Cr |
| Electron configuration | [Ar] 3d54s1 | CAS number | 7440-47-3 |
Who Discovered Chromium?
Chromium was discovered (1797) by the French chemist Nicolas-Louis Vauquelin and isolated as a metal a year later; it was named for its multicolored compounds. He produced chromium oxide (CrO3) by mixing crocoite with hydrochloric acid (HCl).
Although he believed a method for isolating chromium didn’t yet exist, Vauquelin was pleasantly surprised in 1798 to discover that he was able to obtain metallic chromium by simply heating chromium oxide in a charcoal oven.
Today, chromium is primarily obtained by heating the mineral chromite (FeCr2O4) in the presence of aluminum or silicon.
Properties of Chromium
Chromium is a lustrous, brittle, hard metal. Its color is silver-gray and it can be highly polished. It does not tarnish in the air, when heated it borns and forms green chromic oxide.
Chromium is unstable in oxygen, it immediately produces a thin oxide layer that is impermeable to oxygen and protects the metal below.
Chromium has a melting point of 1857+/-20°C, a boiling point of 2672°C, a specific gravity of 7.18 to 7.20 (20°C), with valences usually 2, 3, or 6. The metal is a lustrous steel-gray color that takes a high polish. It is hard and resistant to corrosion.
Chromium has a high melting point, stable crystalline structure, and moderate thermal expansion. All chromium compounds are colored. Chromium compounds are toxic.
Chromium metal is a chemical element by the symbol Cr and atomic number 24. It is the first element in group 6. Chromium is a fairly active metal. It does not react with water but reacts with most acids.
It combines with oxygen at room temperature to form chromium oxide (Cr2O3). Chromium oxide forms a thin layer on the metal surface, protecting it from further corrosion.
Chromium Processing
Chromium (Cr) is a brilliant, hard, refractory metal that melts at 1,857 °C (3,375 °F) and boils at 2,672 °C (4,842 °F). In its pure state, it is resistant to ordinary corrosion, resulting in its application as an electroplated protective coating for other metals. It dissolves in nonoxidizing mineral acids but not in aqua regia or nitric acid, which passivate the metal.
Because chromium and chromium-rich alloys are brittle at room temperature, they have limited application. By far the largest consumption is as an alloying addition to iron.
In amounts varying from 10 to 26 percent, chromium imparts corrosion resistance to steel; it is also used to improve hardenability, wear resistance, and high-temperature strength.
As the mineral chromite, chromium is employed extensively as a refractory material. Other chromium chemicals are used as pigments and tanning agents.
Uses of Chromium
A hard, silvery metal with a blue tinge. Chromium is used to harden steel, manufacture stainless steel (named as it won’t rust), and produce several alloys.
Chromium plating can be used to give a polished mirror finish to steel. Chromium-plated car and lorry parts, such as bumpers, were once very common. It is also possible to chromium plate plastics, which are often used in bathroom fittings.
About 90% of all leather is tanned using chrome. However, the waste effluent is toxic so alternatives are being investigated.
Chromium compounds are used as industrial catalysts and pigments (in bright green, yellow, red, and orange colors). Rubies get their red color from chromium, and glass treated with chromium has an emerald-green color.
Chromium Element and its uses
Chromium elements have many different uses. Some include:
- chromic fluoride (CrF 3): printing, dyeing, and mothproofing woolen cloth
- chromic oxide (Cr 2 O 3): a green pigment (coloring agent) in paint, asphalt roofing, and ceramic materials; refractory bricks; abrasive
- chromic sulfate (Cr 2 (SO 4) 3): a green pigment in paint, ceramics, glazes, varnishes, and inks; chrome plating
- chromium boride (CrB): refractory; a high-temperature electrical conductor
- chromium dioxide (CrO 2): covering for magnetic tapes (“chromium” tapes)
- chromium hexacarbonyl (Cr (CO) 6): catalyst; gasoline additive
FAQs.
What is chromium metal used for?
Chromium is currently used in such widely diversified products as stainless, tool and alloy steels, heat- and corrosion-resistant materials, special purpose alloys, alloy cast iron, pigments, metal plating, leather tanning, chemicals, and refractory materials for metallurgical furnaces.
It is used in the metallurgical industry to enhance such properties as hardenability (response to quenching), creep (unit stress that will produce plastic deformation at a specified rate and temperature), strength and impact strength and resistance to corrosion, oxidation, wear and galling; its major use is in the production of stainless steel.
Chromium pigments represent the largest use of chromium in the chemical industry
Is chromium a safe metal?
Chromium metal (Cr) is a bluish to steel-gray brittle solid, often seen in gray powder form that burns if flame heated.
Chromium is also found in chromic acid (CrO3), chromium compounds, and chromates. It is harmful to the skin, eyes, blood, and respiratory system.
Workers may be harmed from exposure to chromium and its compounds. The level of exposure depends upon the dose, duration, and work being done.
Is chromium poisonous to humans?
Yes, some forms of chromium can be toxic to humans. The respiratory tract in humans is a major target of inhalation exposure to chromium compounds. Chromate sensitive workers acutely exposed to chromium(VI) compounds may develop asthma and other signs of respiratory distress.
How rare is chromium metal?
Chromium is the 21st or 22nd most abundant element in the Earth’s crust. It is present at a concentration of approximately 100 parts per million. Most chromium is obtained by mining the mineral chromite.
Although it is rare, native chromium also exists. It may be found in kimberlite pipe, where the reducing atmosphere favors the formation of diamond in addition to elemental chromium.
Does chromium metal rust?
Chrome metal (the form chromium-0) is the element that makes steel “stainless.” Chromium in this form is hard, stable, and resistant to chemical changes such as oxidation or rust.
Steel alloyed with chromium is harder and less brittle than iron and highly rust-resistant.
This form of chromium is also used to coat or “chrome plate” the surface of other metals to produce a hard, shiny, chemically resistant surface.