Chromium is one of the most important alloying agents that allows making high-quality durable and corrosive-resistant materials. Also it is widely used for sputtering decorative and protective metal coatings. This page describes this metal and its physical, chemical properties, applications, grades and types of product.
Main information
Chromium (Cr) is a chemical element. It belongs to the odd subseries of the 6th group of the 4th period of the periodical system. Its atomic number is 24, atomic weight - 51.99. It is a bluish-white metal. Chromium density is 7.19 g/cm3, melting temperature tmelt. = 1856 °С, boiling temperature tboil. = 2671 °С. This metal is very hard.
This chemical element frequently occurs in the earth core. Chromite (FeO·Cr2O3) and crocoite (PbCrO4) are the main chromium-containing minerals..
Discovery
PbCrO4 (crocoite) chromium compound was mentione in M. V. Lomonosov’s work “The Fundamentals of Metallurgy” (1763). In 1797 French chemist L. N. Vauquelin extracted Cr from this mineral (probably not in pure form but with a crabide admixture.
Chromium properties
Physical properties
Property
Value
Atomic number
24
Atomic mass, u
51.99
Atom radius, pm
130
Density, g/cm³
7.19
Molar heat capacity, J/(K·m)
23.3
Thermal conductivity, W/(m·K)
93.9
Melting point, °C
1856
Boiling point, °C
2671
Melting heat, kJ/mole
21.0
Heat of evaporation, kJ/mol
342
Molecular volume, cm³/mole
7.23
Chemical properties
Property
Value
Covalent radius, pm
118
Ionic radius, pm
(+6e) 52 (+3e) 63
Electronegativity (Pauling)
1.66
Electrolytic potential, V
-0.74
Oxidation levels
6, 3, 2, 0
Chromium grades and alloys
Both pure metal with high Cr content and its alloy with iron (ferrochromium) are used for industrial needs. Below the grades of pure Cr are given.
Kh99N1, Kh99N2, Kh99N4, Kh99N5 - at lease 99% of Cr and N admixture; supplied in form of slugs and particles.
ERKh-0, ERKh-1, ERKh-2 - high-purity chromium with at least 99.99%, 99.95% and 99.95% of chrome correspondingly; produced in form of scales or powder.
PKh-1, PKh-2 - powder with 99.12% and 98.8% of Cr correspondingly.
Advantages/drawbacks
Advantages:
has a rather high melting temperature;
has good hardness - one of the hardest among pure metals (trails tungsten, iridium and some other metals);
corrosive-resistant.
Drawbacks:
admixtures deteriorate the properties;
due to high hardness of chromium it requires additional processing for receiving a plastic metal.
Chromium application
Chromium has two main applications: steel alloying and alloy building; sputtering.
Chromium has a high hardness and good corrosive stability. It attains these properties to alloys and steel as it is used as an alloying agent. Even a low Cr content improves the mechanical properties of the material. Nichrome and fecral or stainless (corrosive-resistant) steels serve as examples of chromium-containing precision alloys with a high resistance. Cr that belongs to the group of refractory materials also allows increasing the working temperature of materials containing this metal. This is especially important for fecral and nichrome as these alloys are used as heaters and work under high temperatures.
Chromium is also applied for sputtering decorative and protective metal coatings. It protects the processed surfaces from mechanical damages due to its hardness so as from impact of aggressive environments due to corrosion resistance. Cr also makes them attractive. The process of chromium sputtering is also known as chromium plating.
Chromium products
Contemporary industry offers a wide range of standard products widely used in several spheres. Chromium is not used for making common semi-finished products like wire or pipes. Slugs, scales and powder are main chromium products. So-called targets are produced for sputtering. As a rule, they are usually produced in form of round or rectangular standard blanks (rods, round bars and plates).
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