So, today I will tell you about the top refractory metal on Earth – tungsten. Tungsten is one of the transition metals, and is located in group 6 of the periodic table of chemical elements.
It got it’s name from the mineral wolframite, from which this mineral is obtained. Also, a tiny fun fact, wolfram is a Swedish word.
Now if we look at the appearance, tungsten looks like a shiny metal with gray tint, though if you hold a rod of tungsten in the hand you may experience one special characteristic. The density of tungsten is almost 20 grams per cubic centimeter, which is very close to the density of gold.
That is the reason why tungsten was used for faking gold bars. A couple of years ago there was news that some gold bars had a filling of tungsten inside, which of course is significantly cheaper than gold.
Though the forgery causes skepticism among some scientists.
To clearly demonstrate to you how much is 20 gram per cubic centimeter, I will compare the mass of a rod of tungsten and a rod of magnesium.
As you can see, the tungsten rod is not only several times smaller than the magnesium one, but is also even heavier than the latter.
Also, tungsten is a fairly brittle metal, it is plastic only when it has a very high purity. In addition, tungsten has the highest tensile strength.
However, this is not the main feature of this metal. To melt a piece of tungsten, you need to reach an extremely high temperature of 3422 degrees Celsius.
That is why this metal was at first used as the filament in incandescent bulbs.
However, if you pass a current through the thin tungsten filament, it can overheat and then break, thereby ceasing any production of light .
All is due to the fact that in air tungsten oxidizes at a high temperature, forming on its surface oxides of tungsten.
Also, the tungsten rod after calcination with a gas burner obtains beautiful colored stains, caused by the different thickness of the oxide film on the metal surface.
However, in light bulbs it’s not really about the beauty, more about the ability to actually produce light, hence all the oxygen from the bulb is pumped out and is replaced with a mixture of nitrogen and argon under reduced pressure.
In these circumstances, the filament can shine for quite a long time. Also another fun fact, when taking pictures of the the filament in macro I’ve noticed the difference of the more powerful old light bulbs and the less powerful modern ones.
In the old light bulbs the filament is made simply in the form of a spiral, but it turns out the modern ones have a double helix, making the filament thinner, which creates more sections of uneven thickness in the yarn, which then leads to the more rapid failure of the bulb. From a chemical point of view, tungsten is fairly stable, it is not soluble in hydrochloric or sulphuric acids. And the most stable compounds of hexavalent tungsten, such as, for example, the sodium tungstate are used as a catalyst of epoxidation in the organic synthesis, andin manufacturing of pigments. Sodium tungstate is soluble in water, but instead of water I will use the 30% acetic acid to obtain the so-called tungsten blue pigment that has a very intense color.
To do this, we’ll add a piece of magnesium to the test-tube. Magnesium reacts with acetic acid, releasing hydrogen, which in turn recovers tungsten from the hexavalent state to tungsten oxide 3 with an admixture of other oxides.
The formed particles of oxides are of a small size, allowing them to form colloidal solution of a bright blue or blue-green color.
The shade depends mainly on the acidity of the environment.
The obtained tungsten blue can be used as a good dye for fabric, paper or other items that have the ability to adsorb particles of tungsten blue.
The metal tungsten has a very high hardness and is hardly turned on the grinding wheel. Today tungsten finds many applications.
First and foremost, this metal is used in filaments for the halogen lamps, refractory electrodes for argon-arc welding, as well as in hard projectile cores in some military shells. The most common substance of the tungsten compounds is tungsten carbide, which also goes by the name Pobedit but mainly in Russia (which if you translate that to English means “will win”). It is mostly used as a cutter when machining metals or stones because of its high hardness. Quality high hardness steel would almost always be composed of tungsten. So that’s what this metal tungsten is like, which is found in practically every house and has the most interesting and unique properties.