Molybdenum (Mo) - Properties, Applications

Topics Covered

Introduction
Chemical Properties
Physical Properties
Mechanical Properties
Thermal Properties
Applications

Introduction

Molybdenum is a chemical element with Mo as its symbol. It belongs to group 6 and periodic 5 of the periodic table. Its atomic number is 42, and has a Mohs hardness of 5.5.

Molybdenum can be obtained from the minerals molybdenite, wulfenite and powellite. It is also obtained as a byproduct during tungsten and copper mining and processing. It has one of the highest melting points of all pure elements; however it is not resistant to acids.

The main molybdenum mining areas are USA, Canada, Chile, and Russia.

Chemical Properties

The chemical properties of molybdenum are provided in the table below.

Chemical Data

CAS number 7439-98-7
Thermal neutron cross section 2.5 barns/atom
Electrode potential -0.200 V
Ionic radius 0.620 Å
Electronegativity 2.16
X-ray absorption edge 0.61977 Å
Electrochemical equivalent 1.79 g/A/h

Physical Properties

The following table discusses the physical properties of molybdenum.

Properties Metric Imperial
Density 10.22 g/cm3 0.3692 lb/in3
Melting point 2610 °C 4730°F
Boiling point 4825 °C 8717°F

Mechanical Properties

The mechanical properties of molybdenum are tabulated below.

Properties Metric Imperial
Tensile strength 324 MPa 47000 psi
Poisson’s ratio 0.38 0.38
Modulus of elasticity 330 GPa 47900 ksi
Shear modulus 120 GPa 17400 ksi
Hardness, Brinell 225 225
Hardness, Vickers 230 230
Hardness, Rockwell A 60 60
Hardness, Rockwell B 98 98
Hardness, Rockwell C 19 19

Thermal Properties

The thermal properties of molybdenum are tabulated below.

Properties Metric Imperial
Thermal expansion co-efficient (@20°C/68°F) 5.35 µm/m°C 2.97 µin/in°F
Thermal conductivity 138 W/mK 958 BTU in/hr.ft².°F

Applications

The following are the application areas of molybdenum:

  • As an alloying agent to provide hardness and toughness to quenched/tempered steels, and to improve the strength of steels at high temperatures
  • As electrodes for electrically heated glass furnaces and forehearths
  • In nuclear energy applications
  • As missile and aircraft parts requiring high temperature resistance
  • As a catalyst in petroleum refining
  • As a filament material in electronic/electrical applications
  • Flame- and corrosion-resistant coatings for other metals
  • As a support member in radio and light bulbs
  • In arc resistant electric contacts
  • In thermocouple sheaths

Molybdenum can be formed into many useful compounds. Some are listed below with their specific application areas:

  • Molybdenum sulfide and selenites - as a high temperature lubricant in favor to petroleum based oils, due to its superior high temperature resistance.
  • Sodium molybdate (anhydrous form) - as a dry powdered fertilizer

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