Chromium (Cr) - Properties, Applications

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

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