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Molybdenum

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Molybdenum
Molybdenum
General Info
Atomic Symbol Atomic symbol::Mo
Atomic Number Atomic number::42
Atomic Weight Atomic weight::95.94 g/mol
Chemical series Transition metal
Appearance gray metallic
Sample of Molybdenum.jpg
Group, Period, Block 6, 5, d
Electron configuration [Kr] 5s1 4d5
Electrons per shell 2, 8, 18, 13, 1
Electron shell molybdenum.png
CAS number CAS number::7439-98-7
Physical properties
Phase solid
Density Density::10.28 g/ml
Melting point Melting point::2896K
Boiling point Boiling point::4912K
Isotopes of Molybdenum
iso NA half-life DT DE (MeV) DP
92Mo 14.84% 92Mo is stable with 50 neutrons.
93Mo syn 4x103y ε - 93Nb
94Mo 9.25% 94Mo is stable with 52 neutrons.
95Mo 15.92% 95Mo is stable with 53 neutrons.
96Mo 16.68% 96Mo is stable with 54 neutrons.
97Mo 9.55% 97Mo is stable with 55 neutrons.
98Mo 24.13% 98Mo is stable with 56 neutrons.
99Mo syn 65.94 h β⁻
Y
0.436, 1.214
0.74, 0.36, 0.14
99Tc
-
100Mo 9.63% 7.8x1018y β⁻β⁻ 3.04 100Ru
All properties are for STP unless otherwise stated.

Molybdenum is a chemical element, which is part of the series of elements known as transition metals. With an atomic number of 42, it remains in group 6, period 5, between elements niobium and technetium. Although this metal can not be found pure in nature, its specific properties make it an important asset in certain compounds, especially steel production. With an extremely high heat tolerance and strong durability the addition of this element to steels, in particular, gives it the qualifications it needs to be as useful as it is today.

Properties

Being among the transition metals, molybdenum is very hard, but it is still softer and more ductile than other elements such as tungsten. This silvery-white colored metal can be easily made into a thin wire. It has a very high heat capacity [1]and a melting point of 2623 degrees celsius.[2] The only way it can be hardened is by working it, not by heat. Its heat conductivity is double that of iron. Molybdenum shows a high elastic modulus and a low thermal expansion. When it gets to temperatures above 760 degrees celsius, it forms an oxide that evaporates as it forms. This rapid oxidation occurs because while the oxide layer sublimes the base metal is under attack. This all adds up to a high resistance to corrosion. It is one of only a few metals that retains some kind of resistance to hydrofluoric acid. [3]

It is among the refractory metals, meaning it has a high resistance to heat and wear. It has good thermal conductivity as well as electrical. Because of its high melting point, molybdenum is mostly used in high temperature applications. Its great strength at high and room temperature is more than that of steel. This element operates well at temperatures over 1100 degrees celsius, which is higher than both steel and nickel-based alloys. This element has a low co-efficient of thermal expansion and performs the best when it is in inert of vacuum environments.[4]

Occurrences

Wulfenite mineral

Molybdenum can never be found pure in nature; it will always be a part of a compound. The most common compounds that molybdenum is found in are molybdenite, powellite (Ca(MoW)O4), and wulfenite minerals (PbMoO4). As a by-product, it may also be discovered in copper and tungsten. [5]Molybdenite is made up of both molybdenum and sulfur to form molybdenum disulfide (MoS2). Molybdenum disulfide is a soft, black powder that takes the appearance of graphite. Although graphite and molybdenum disulfide are completely different elements, early chemists had believed them to be one in the same. One difference is that molybdenum disulfide can't be ground up because of its soft and squishy texture.[6]

Leading the molybdenum production is the United States of America, second is Chile, third is Canada. Although the majority comes from the Western Hemisphere, there are some other countries that bring in a modicum amount of molybdenum, such as China. [7] In the United States alone, it can be found in states such as, Alaska, Colorado, Idaho, Nevada, New Mexico, and Utah. Molybdenum also accounts for 1 to 1.5 parts per million of the earth's crust.[8]

Uses

Stainless steel used in the building façade of the 7 World Trade Center is molybdenum-containing Type 316, which provides improved resistance to corrosion.

Molybdenum is an important building agent. This alloying agent's primary use is to makes steels hard and durable. It also gives better strength to steels when under high temperatures, this application is called red-hardness. [9] When added to steel, concentrations of .25%-8% will enable it to endure pressures up to 300,000 pounds per square inch.[10] In both nickel-based alloys and stainless steels, it gives them the ability of heat resistance and corrosion resistance to chemical solutions. It also provides flame and corrosion resistant coating for other metals. Molybdenum's electrodes are used for electrically heated glass furnaces and forehearths. Because of its high heat tolerance, it is used in certain nuclear energy applications such as missile and aircraft parts. This element is used in filament materials for electronic and electrical applications. It will support members in radio and light bulbs and create arc resistant electric contacts.[11]

Molybdenum compounds also have several applications. For example, molybdenum sulphide and selenites may take the place of petroleum based oils in a high temperature lubricant when it is needed to endure increased temperatures. As an anhydrous form, sodium molybdate (NaMoO4) is used as a powder type of fertilizer. Molybdenum compounds found in steels are calcium molybdate (CaMoO4), molyte, molybdic oxide, and molybdenum-chromium.[12]

History

The 1938 Phantom Corsair's lower frame was made of chrome molybdenum steel

Molybdenum was not discovered until the late 18th century because the metal doesn't form in nature. Molybdenite is the predominate mineral and was the source of discovering molybdenum. Although molybdenum wasn't discovered until late, it is assumed that molybdenite was used in ancient times. For the longest time molybdenum was thought to be lead or graphite ore. Back then a person wouldn't have been able to distinguish this element from others such as: lead, galena, and graphite because they all have similar properties. These four elements were simply known as molybdos, meaning "lead-like". Later, a Japanese sword created in the 14th century was found to be composed of molybdenum.[13]

It wasn't until 1778, that Carl Wellhelm Scheele, a Swedish chemist, positively identified molybdenum. He was able to accomplish this by decomposing molybdenite. In this process he heated it with nitric acid in air which therefore produced a white oxide powder. Four years later, in 1782, Peter Jacob Hjelm reduced the oxide with carbon which brought forth a dark metallic powder which he named molybdenum.[14]

Molybdenum was first used in mass production in 1891, when a French company, Schneider & Co. used it as an alloying element in their armour plates. This is when it was realized that molybdenum was a good replacement for tungsten in steel alloying applications. During World War I, tungsten was in too high a demand creating a supply shortage. Because of this molybdenum replaced it in hard and impact resistant steels. This change made the search for molybdenum sources sky rocket. After both World War I and World War II there was an increase in civilian applications for this metal. Soon after World War I, it was being used in automotive steels. Currently the rise in demand have been equally proportionate to the sources recovered. Since 1945, the applications of its alloys and compounds have been ever expanding.[15]

Field emission microscope image of Mo

References