MOLYBDENUM
Molybdenum is used as an alloying addition in steels, and molybdenum and its alloys are used for electrical and electronic
parts, missile and aircraft parts, high-temperature furnace parts, die casting cores, hot-working tools, boring bars, thermocouples,
nuclear energy applications, corrosion-resistant equipment, equipment for glass-melting furnaces and metallizing. Molybdenum also
finds use as a catalyst in chemical reactions. Molybdenum is not suitable for continued service at temperatures above 500 oC in an
oxidizing atmosphere unless protected by an adequate coating.
STRUCTURE
Crystal Structure: Body centered cubic, a= 0.31468 nm at 25 oC
Slip Planes: {112} at 20 oC; {110} at 1000 oC
Slip Direction: [111]
Interatomic Distance: 0.27252 nm min
Metallography: Electrolytic polishing is preferred. Etching: (1) 10 g NaOH + 30 g K3Fe (CN)6 + 600 liters water; (3) Murakami’s
reagent
MASS CHARACTERISTICS
Symbol: Mo
Atomic Number: 42
Atomic Weight: 95.94
Density: At 20 oC: 10.22 g/cm3
Compressibility: At 293 oC: 36 micron 2/N
THERMAL PROPERTIES
Melting Point: 2610 oC
Boiling Point: 5560 oC
Specific Heat: At 20 oC: 0.276 kJ/kg x K
Latent Heat of Fusion: 270 kJ/kg (estimated)
Thermal Conductivity: At 20 oC: 142 W/m x K
Heat of Combustion: 7.58 MJ/kg Mo
Recrystallization Temperature: 900 oC min; commercial products normally require higher temperatures.
ELECTRICAL PROPERTIES
Electrical Conductivity: At 0 oC: 34% IACS
Electrical Resistivity: At 0 oC: 52 n ohm x m
Thermal Electromotive Force: Versus platinum, 0 to 100 oC: 1.45 mV
Electrochemical Equivalent: Valence 6, 0.1658 mg/C
Hydrogen Overpotential: At 100 A/m2: 0.44 V
MAGNETIC PROPERTIES
Magnetic Susceptibility: Mass: 1.17 x 10-8 mks at 25 oC; 1.39 x 10-8 mks at 1825 oC
OPTICAL PROPERTIES
Reflectivity: 46% at 500 nm, 93% at 10,000 nm
Color: Silvery white
MECHANICAL PROPERTIES:
The mechanical properties of molybdenum and molybdenum alloys greatly depend on the amount of working performed
below the recrystallization temperature and on the ductile-to-brittle transition temperature. The minimum recrystallization temperature for molybdenum is 900 oC (1650 oF).
CHEMICAL PROPERTIES:
Molybdenum has particularly good resistance to corrosion by mineral acids, provided oxidizing agents are not present. It is
also resistant to many liquid metals and to most molten glasses. In inert atmospheres, it is unaffected up to 1760 oC by refractory
oxides. Molybdenum is relatively inert in hydrogen, ammonia, and nitrogen up to about 1100 oC, but a superficial nitride case may be
formed in ammonia or nitrogen.
FABRICATION CHARACTERISTICS:
Consolidation: In most instances, molybdenum is consolidated from powder by compacting under pressure followed by sintering in
the range from 1650 to 1900 oC. Some molybdenum is consolidated by a vacuum arc casting method in which a preformed electrode
is melted by arc formation in a water-cooled mold.
Hot-working Temperature: Generally forged between 1180 and 1290 oC down to 930 oC
Annealing Temperature: Normal stress-related temperature is 870 to 980 oC.
Recrystallization Temperature: Depends on prior working and condition; 1180 oC for full recrystallization in one hour of a 16mm
(5/8 in.) bar reduced 97% by rolling.
Suitable Forming Methods: Conventional methods.
Precautions in Forming: Must be heated to the proper temperature relative to its thickness and forming speed.
Heat Treatment: Not hardenable by heat treatment but only by work hardening.
Suitable Joining Methods: Can be brazed or joined mechanically, as well as welded by arc, resistance, percussion, flash, and electron
beam methods. Arc cast molybdenum is preferred to a powder metallurgy product for welding. Absolute cleanliness of surface is
essential. Fusion welding must be carried out in closely controlled inert atmosphere.