Hello everyone.
Today I would like to dedicate this video to such a refractory metal as molybdenum.
In the period table of chemical elements
molybdenum belongs to the 6th group
and is located above tungsten.
Because of having a smaller atomic radius
molybdenum is a bit more reactive than tungsten
and has a lower electrochemical potential.
Molybdenum does not occur naturally as free metal
but it can be obtained through a chemical synthesis from minerals.
This metal's name is derived from the Greek word molybdos, meaning Lead
since its ores were frequently confused with lead ores.
This metal is produced
by reduction of molybdenum trioxide with hydrogen.
Pure molybdenum metal looks like a grey shiny metal
which is extremely similar to tungsten.
If two identical pieces of these metals are put together
the difference between them will become clear
as molybdenum looks smoother than tungsten.
Besides appearance, the density of molybdenum is two times smaller
than that of tungsten.
Speaking of the physical properties of this metal
molybdenum is a quite solid, yet fragile metal.
This property can be tested with a firearm.
*bang*
*slow-motion bang*
When a 9mm bullet is shot on a 3mm thick molybdenum plate
it easily pierces a hole.
Along with that, it can clearly be seen how the bullet tears out bits of molybdenum.
That is why this metal is not likely to be used for producing tank armor.
Speaking of the chemical properties of molybdenum
in air this metal is quite resistant to being oxidized at room temperature.
But, when heated up, it quickly starts oxidizing
covering in molybdenum dioxide and trioxide layer.
Uneven thickness of the oxide layer makes an oxidized molybdenum rod multicolored.
Moreover, when electric current is passed through molybdenum wire
because of this metal's high internal impedance
molybdenum wire starts heating up and glowing bright
at the same time melting down.
This metal's melting temperature is more than 2500 Celsius degrees.
Also, when pressed against a rotating grinding wheel
molybdenum starts self-igniting
producing molybdenum oxide
which is used as glue for spraying vitreous enamel on metal.
One of the most widespread of molybdenum's chemical compounds
is ammonium orthomolybdate
which is used for producing pure molybdenum metal
as well as corrosion inhibitor of some metals.
When alkali is added, it forms sodium heptamolybdate
which dissolves well in water.
If such a solution is made more acidic with hydrochloric acid
and if you add a piece of magnesium to it
the hydrogen produced as a result of the reaction
will reduce molybdenum in the solution
producing so-called molybdenum blue.
This compound is molybdenum oxide fine particles
with different oxidation states.
The color of molybdenum blue can differ, depending on the acidity.
For instance, when PH value of greenish solution is increased to 4
the color changes to blueish.
Whereas, when a very acidic molybdate solution is reduced, its color changes to reddish orange.
I think that in very acidic solutions
this reaction produces molybdenum tetrachloride.
As a matter of fact
molybdenum blue composition can be very unpredictable and very complex.
Upon further reduction of sodium molybdate in acidic environment
a black solution is produced
and to determine the exact content of this
poses a challenge
because of being very complex.
Probably it contains molybdenum compounds with different oxidation states.
Adding of alkali to such a solution produces sediment
which I believe consists of black molybdenum hydroxide
and molybdenum tetrachloride
along with lots of other chemicals.
If anyone of you is a specialist in molybdenum compounds
please share your suggestions about what you think happens in the test-tube.
Nowadays, more than 80% of metallic molybdenum is used in metallurgy
as a steel alloying addition
which makes steel harder
and more corrosion resistant.
Molybdenum disulphide is used as an excellent lubricant for machine elements.
Because of having a high melting temperature
this metal is also used in the production of incandescent light-bulbs
to make support wires for tungsten filaments.
Moreover, molybdenum is a very essential mineral in living organisms.
It serves as a metal heteroatom
in the active site of many enzymes.
For instance, in such an enzyme as xanthine oxidase
which catalyses oxidation of hypoxanthine into xanthine
which is a very important process in the metabolism of nitrogen-containing purines in human cells.
To sum up, we can say that molybdenum is a very important metal
which also plays an essential role in our organism.
For the provided molybdenum plates for the experiments, I will thank the company
Stanford Advanced Materials.
I will put a link to their site in the video description.
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