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Molybdenum a High Temperature Metal: Basic Properties and Applications
There is increasing demand of material which is to be used at ultra high temperature. The material which can be used at elevated temperature should have (a) High melting point (b) good mechanical properties at higher temperature (c) good creep and fatigue resistance (d) better oxidation resistance etc. Refractory metals are the obvious choice for this type of applications because of their very high melting point and their strength. Refractory metals include- W, Mo, Nb, Re, Ta. Here, some of the basic properties, production method and different applications of Molybdenum (Mo) will be discussed in brief.
The General Properties of Molybdenum Includes:
Atomic No. = 42
Atomic Mass = 96 amu
Melting Point = 2,623 °C (4,753 °F)
8382 °F 4639 °C, Boiling Point = 4912K ,
Density (at 20 °C) = 10.28 g/cc
Specific heat capacity = (25 °C) 24.06 J·mol−1·K−1
Atomic radius = 139 pm
Magnetic property = paramagnetic
Crystal structure = bcc
Mo does not occur as the in the free state in nature, instead it is found in the form of minerals principally from molybdenite and Wulfenite. Molybdenum is generally a by-product of copper mining industry. The molybdenite is first heated to a temperature of 700 °C in air which oxidize the sulfide into Mo-Oxide as:
2 MoS2 + 7 O2 → 2 MoO3 + 4 SO2
The oxidized ore is then either heated to 1100 °C to sublimate the oxide, or leached with ammonia which reacts with the molybdenum(VI) oxide to form water-soluble molybdates:
MoO3 + 2 NH4OH → (NH4)2(MoO4) + H2O
Pure molybdenum is produced by the hydrogen reduction of Mo-oxide, while the molybdenum for steel production is reduced by the metallothermy (especially aluminothermic) with addition of iron to produce ferromolybdenum. A common form of ferromolybdenum contains 60% molybdenum. The reduction reaction (aluminothermy ) can be shown as:
MoO3 + Al = Mo + Al2O3
There is a widespread use of Mo in various fields ranging from fertiliser to structural material for spacecrafts. It is material for future. There are many active research is going on worldwide on development of high temperature material based on Molybdenum. In nut shell, the main uses for Molybdenum are:
(1) Alloying element in steel: It is used as alloying element in high-strength steels and stainless steels because it readily forms hard, stable carbides.
(2) High temperature and pressure applications in various industries as Aerospace, Zinc processing industries etc. because of its ability to withstand extreme temperatures and high resistance to corrosion.
(3) Pigments and catalyst.
(4) Aircraft parts and industrial motors.
(5) Mo-99 an isotope of Mo is used in various medical test and cure.
(6) Mo-disulfide as used as lubricant and Mo-dislicide as heating element of high temeparture furnace.
(7) Mo powder is used as fertilizer for cauliflower and some other plants.
(8) As an commercially and technologically important Mo alloy-TZM and TZC