Molybdenum

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History of Molybdenum

Characteristics of Molybdenum

Typical Analysis

Typical Properties

Plasma Spray

Molybdenum in Biology

Molybdenum Metal Properties

 

 

 
Molybdenum: Molybdenum facts

History of Molybdenum:

Molybdenum was first discovered in 1778 by a Swedish chemist named Carl William Scheele who thought that he was observing lead while studying a sample of molybdenite. Named from the Greek word "molybdos, which actually means lead, Scheele notice an apparent visual similarity, which upon further analysis, proved to be incorrect. His studies led him to conclude that the ore sample did not contain lead, but a new element, which he named molybdenum after the mineral molybdenite.

Though Scheele is credited with the discovery of molybdenum in its elemental (oxide) form, it was Peter Hjelm who in 1782 first reduced the oxide with carbon to produced the gray metallic powder which he also named molybdenum.

After the initial isolation of molybdenum in 1782, a commercial application for molybdenum was not identified until the early 1900's. Industrial and Military applications required stronger steels with greater resistance to corrosion and damage. The First World War saw the demand for molybdenum rise dramatically as alloyed steels used for transportation and armor plating increased with the war effort. It was found that molybdenum could impart an impact resistance similar to tungsten when alloyed with steel, with less weight. Demand for molybdenum initiated an intensive search for new sources to insure a reliable supply. This led to the discovery of the enormous Climax deposit in Colorado, which began production in 1918. In addition to primary molybdenum mines, molybdenum is also recovered as a byproduct of copper and tungsten mining operations. The metal is produced from purified ammonium molybdate or molybdic trioxide powder through hydrogen reduction at high temperatures.

In its elemental form, Molybdenum is a silvery-white metallic element. Its symbol in the periodic table is Mo and its atomic number is 42. Though molybdenum is chemically stable, it will react with acids.

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Molybdenum Ore

Molybdenum Ore

Molybdenite sample

Molybdenite Sample

Characteristics of Molybdenum


Molybdenum is a transition metal (refers to the "D" block of the periodic table), or more strictly, "a transition metal as "an element whose atom has an incomplete d sub-shell, or which can give rise to cations with an incomplete d sub-shell". (source Wikipedia). In its pure form, molybdenum metal is a soft, silvery white metal which has one of the highest melting points of all elements. The melting point of molybdenum is 2,623 C (4,753 F), which is 2,000F higher than the melting point of steel. It is also 1,000F higher than the melting point of most rocks. Though it has the fifth highest melting point of all of the elements, it has the lowest coefficient of thermal expansion, making it a highly sought after component in high temperature applications.

Though molybdenum has a very high melting point, it oxidizes readily at temperatures in excess of 760C. When exposed to air at this temperature, an oxide layer sublimes as the base metal reacts with oxygen, resulting in an oxidation process that resembles smoke. When properly controlled, the oxide can be recovered and reduced again to reclaim its molybdenum content. To avoid oxidation loss however, molybdenum is often utilized in inert or vacuum environments.

The largest use of molybdenum is as an alloy in the production of steel and stainless steel where it improves the strength and hardness of the alloyed metals. Ultra high strength steels with up to 8% contained molybdenum can withstand pressures up to 300,000 pounds per square inch. It also improves the strength of steel at elevated temperatures. In the United States, steel production consumes approximately 60% of manufactured molybdenum. In alloy applications, molybdenum content varies from 0.5% to 8%, dependent upon desired characteristics. Overall, iron and steel account for more that 78% of the worlds molybdenum consumption.

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Typical Chemical Analysis of Molybdenum Powder:

Element 

Wt%

Al 0.002
C 0.007
Cr 0.0025
Cu 0.002
Fe 0.01
Ni  0.004
W 0.03
Co 0.002
Mg 0.001
Mn 0.001 
  Medium Coarse
O2 0.15 0.08
Mo 99.95 Minimum excluding gases

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Typical Physical Properties of Molybdenum powder

  Medium* Coarse*

Average Particle Size by Fisher Sub-Sieve Sizer  

FSSS as Supplied 2.0 3.5 3.5 6.0
Porosity as Supplied >0.60 >0.60
     
Scott Density g/In3 12 25 15 30
Tap Density g/cc 1.9 3.5 2.0 4.0
     
Mesh Analysis >150 02% >150 02%
<150 98% Min <150 98% Min

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Plasma Spray of Molybdenum Powder:

Molybdenum powder can be applied to hard metallic surfaced through the application of a thermal spray or plasma spray process. The plasma spray process involves the spraying of a heat softened or molten material onto a surface to provide a coating. Molybdenum powder is injected into a very high temperature plasma flame where it is quickly heated and accelerated at high velocity. The heated material then impacts the substrate surface and quickly cools, forming a coating. Molybdenum powder is often used in plasma spray applications to improve the heat and wear resistance of the substrate material.

 

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Molybdenum in Biology:

Molybdenum is an essential trace mineral in human and animal nutrition. Molybdenum can be found in several tissues in the human body and is required by some enzymes in the catabolism of sulfur amino acids and purines. The average adult body contains about 9 mg of molybdenum with the highest concentrations being in the liver, kidneys, skin and bone. Molybdenum is reasonably scarce in the Earths crust, being only three times more abundant than gold.

Estimated Crustal Abundance: 1.2 milligrams per kilogram

Estimated Oceanic Abundance: 110-2 milligrams per liter

Molybdenum toxicity in grazing animals (ruminants) can occur when grazing on soil abundant in molybdenum but nutritionally deficient in copper. The excess molybdenum causes the excretion of copper reserves, eventually leading to copper deficiency and early death.

 Molybdenum deficiency in humans is extremely rare.

Though the molybdenum content of plants can vary dependent upon the soil in which they are grown, good sources of dietary molybdenum include:

  • Lima beans 100g 870 mcg
  • Small white beans 100g 450 mcg
  • Yellow split peas 100g 250 mcg
  • Oats 100g 180 mcg
  • Green peas 100g 130 mcg
  • Chili beans 100g 110 mcg
  • Raisin bran 100g 76 mcg
  • String beans 100g 60 mcg
  • Spaghetti 100g 41 mcg
  • Macaroni 100g 38 mcg
  • Rice 100g 29 mcg
  • Bakery sweets 100g 27 mcg
  • Bread 100g 21 mcg
  • Cheese 100g 11 mcg
  • Pineapple 100g 9 mcg
  • Eggs 100g 9 mcg
  • Banana 100g 8 mcg
  • Corn 100g 8 mcg
  • Spinach 100g 7 mcg
  • Potatoes 100g 7 mcg
  • Cabbage 100g 6 mcg
  • Chicken 100g 5 mcg
  • Milk 100g 5 mcg
  • Bean sprouts 100g 5 mcg
There is no RDA for molybdenum. The estimated safe and adequate intake is 75 to 250 mcg per day.

 

Recommended Dietary Allowance (RDA) for Molybdenum
Life Stage  Age  Males (mcg/day)  Females (mcg/day) 
Infants  0-6 months 2 (AI) 2 (AI)
Infants  7-12 months   3 (AI)  3 (AI)
Children  1-3 years  17 17
Children  4-8 years  22 22
Children  9-13 years  34 34
Adolescents  14-18 years  43 43
Adults  19 years and older 45 45 
Pregnancy  all ages  50
Breastfeeding  all ages  50

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Molybdenum Metal Properties - Condensed:

PROPERTY
Atomic Number 42
Atomic Weight 95.94
Density (20C) 10.22 g/CC
Melting Point 2896 K, 2610C, 4753Fm
Boiling Point 4912 K, 5560C, 8382F
Coefficient of Thermal Expansion (20C) 4.9 x 10-6/C
Electrical Resistivity (20C) 5.7 microhms-cm
Electrical Conductivity 30% IACS
Specific Heat .061 cal/g/C
Thermal Conductivity .35 cal/cm2/cmC/sec
Modulus of Elasticity (20C) 46 x 106 psi

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Molybdenum Metal Properties - Extended

General
Name, Symbol, Number molybdenum, Mo, 42
Chemical series transition metals
Group, Period, Block 6, 5, d
Atomic mass 95.94(2) g/mol
Electron configuration [Kr] 4d5 5s1
Electrons per shell 2, 8, 18, 13, 1
Physical properties
Phase solid
Density (near r.t.) 10.28 gcm−3
Liquid density at m.p. 9.33 gcm−3
Melting point 2896 K
(2623 C, 4753 F)
Boiling point 4912 K
(4639 C, 8382 F)
Heat of fusion 37.48 kJmol−1
Heat of vaporization 617 kJmol−1
Heat capacity (25 C) 24.06 Jmol−1K−1
Vapor pressure
P/Pa 1 10 100 1 k 10 k 100 k
at T/K 2742 2994 3312 3707 4212 4879
 
Atomic properties
Crystal structure cubic body centered
Oxidation states 2, 3, 4, 5, 6
(strongly acidic oxide)
Electronegativity 2.16 (Pauling scale)
Ionization energies 1st: 684.3 kJmol−1
(more) 2nd: 1560 kJmol−1
  3rd: 2618 kJmol−1
Atomic radius 145 pm
Atomic radius (calc.) 190 pm
Covalent radius 145 pm
Miscellaneous
Magnetic ordering no data
Electrical resistivity (20 C) 53.4 nΩm
Thermal conductivity (300 K) 138 Wm−1K−1
Thermal expansion (25 C) 4.8 mm−1K−1
Speed of sound (thin rod) (r.t.) 5400  ms−1
Young's modulus 329 GPa
Shear modulus 20 GPa
Bulk modulus 230 GPa
Poisson ratio 0.31
Mohs hardness 5.5
Vickers hardness 1530 MPa
Brinell hardness 1500 MPa
CAS registry number 7439-98-7
Notable isotopes
Main article: Isotopes of molybdenum  
iso NA half-life DM DE (MeV) DP  
92Mo 14.84% Mo is stable with 50 neutrons  
93Mo syn 4103 y ε - 93Nb  
94Mo 9.25% Mo is stable with 52 neutrons  
95Mo 15.92% Mo is stable with 53 neutrons  
96Mo 16.68% Mo is stable with 54 neutrons  
97Mo 9.55% Mo is stable with 55 neutrons  
98Mo 24.13% Mo is stable with 56 neutrons  
99Mo syn 65.94 h β- 0.436, 1.214 99Tc  
γ 0.74, 0.36, -  
0.14  
100Mo 9.63% 7.81018 y β-β-  ? 100Ru  
Source: Wikipedia http://en.wikipedia.org/wiki/Molybdenum

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ASTM Standard Specification for Molybdenum and Molybdenum Alloy Bar, Rod, and Wire

Molybdenum 360Unalloyed vacuum arc-cast molybdenum.

Molybdenum 361Unalloyed powder metallurgy molybdenum.

Molybdenum Alloy 363Vacuum arc-cast molybdenum-0.5% titanium-0.1% zirconium (TZM) alloy.

Molybdenum Alloy 364Powder metallurgy molybdenum-0.5% titanium-0.1% zirconium (TZM) alloy.

Molybdenum 365Unalloyed vacuum arc-cast molybdenum, low carbon.

Molybdenum Alloy 366Vacuum arc-cast molybdenum, 30% tungsten alloy.

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