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Molybdenum
is number 42 on the periodic table. With a melting point of
2610°C, molybdenum has a density of 10.22 gm/cc. It has many
properties that make it an excellent candidate for fabricated parts
that must be made of a refractory metal.
Molybdenum
has been used for many years in the lamp industry for mandrels and
supports, usually in wire form. Today, several unique properties of
molybdenum that satisfy more demanding industry requirements have
increased the use of molybdenum as a material in applications requiring
other mill forms.
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.
Applications:
Mo
spray
wire for the automotive industry
Mo
dipping shields for vehicle lighting
Molybdenum
mandrel and support wires for the lighting industry
Furnace
hot zones
Molybdenum
glass melting electrodes
Mo
sputter
targets for coating
Semiconductor
base plates for power electronics, and many more.
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