Jul 15 2013
Topics Covered
Introduction
Chemical Properties
Physical Properties
Mechanical Properties
Thermal Properties
Applications
Introduction
Chromium is a chemical element with Cr as its symbol. It belongs to group 6, periodic number 4 of the periodic table. Its atomic number is 24.
Chromium is a steely-gray lustrous, brittle, hard metal. It is known to have high corrosion resistance. When polished, it gains a very shiny surface, which is used to plate other metals so as to form a protective and attractive covering.
Chromium is mined as chromite ore. Globally this ore is available in India, South Africa, Finland, Zimbabwe, Kazakihstan and the Philippines. Commercially, chromium is produced from chromite using silicothermic or aluminothermic reactions. Roasting and leaching processes are also used.
Chemical Properties
The chemical properties of chromium are provided in the table below.
|
Chemical Data |
|
CAS number |
7440-47-3 |
|
Thermal neutron cross section |
2.9 barns/atom |
|
Electrode potential |
-0.560 V |
|
Ionic radius |
0.520 Å |
|
Electronegativity |
1.66 |
|
X-ray absorption edge |
2.07 Å |
|
Electrochemical equivalent |
0.971 g/A/h |
Physical Properties
The following table discusses the physical properties of chromium.
|
Properties |
Metric |
Imperial |
|
Density (@20°C/68°F) |
7.19 g/cm3 |
0.259 lb/in3 |
|
Melting point |
1907°C |
3465°F |
|
Boiling point |
2672°C |
4842°F |
Mechanical Properties
The mechanical properties of chromium are tabulated below.
|
Properties |
Metric |
Imperial |
|
Poisson’s ratio |
0.31 |
0.31 |
|
Modulus of elasticity |
248 GPa |
35969 ksi |
|
Hardness, Vickers |
90 |
90 |
|
Hardness, Brinell (converted from Vickers for 500 kg load/10 mm ball) |
80 |
80 |
|
Hardness, Knoop (converted from Vickers) |
102 |
102 |
|
Hardness, Rockwell B (converted from Vickers) |
48 |
48 |
Thermal Properties
The thermal properties of chromium are tabulated below.
|
Properties |
Metric |
Imperial |
|
Thermal expansion co-efficient (@20-100°C/68-212°F) |
6.20 µm/m°C |
3.44 µin/in°F |
|
Thermal conductivity |
69.1 W/mK |
480 BTU in/hr.ft².°F |
Applications
The following are the application areas of chromium:
-
In metal ceramics
-
In chrome plating
-
As dyes and paints
-
To produce synthetic rubies
-
In alloys, e.g., stainless steel
-
To manufacture molds for the firing of bricks
-
As a catalyst in dyeing and tanning of leather
-
In metallurgy to provide corrosion resistance and a shiny finish