[Disclaimer]
Hello everyone!
Today, I'll tell you about the most widespread noble gas in the observable universe,
which can have unique superfluidity properties at extremely low temperatures.
Guys, please meet Helium.
In the periodic table, this element is located in the top right corner.
It is easier to find it by it's atomic number, 2.
I think people acquaint themselves with this inert gas from childhood.
Because of its lightness in relation to air,
Helium is perfect for inflating festival balloons children love so much.
Because of the fact that the molar mass of Helium is almost 7 times smaller than that of air,
it easily floats up above.
Anyways,
Helium isn't as abundant on earth and our atmosphere is only 0.0005% Helium.
Most of Helium that can be used for air balloon comes from natural gas, Helium concentration of which
can reach up to 7% in it.
It's so, because, as a result of radioactive decay of Uranium and Thorium in Earth's crust,
Helium can accumulate in Earth's interior, along with natural gas and not vanish in the atmosphere.
If we extend the scope, however, in terms of abundance,
Helium will be second only to Hydrogen,
among other elements in all of the observable universe.
Just imagine, all atoms that aren't Hydrogen and Helium are only 2% of the overall mass of matter.
It's a great opportunity
to feel how small we are in the universe.
Most of Helium in the universe is in the stars
and in the atmosphere of gas giants, which, like the universe, contained 25% Helium from their whole mass.
According to present-day data,
most Helium that is in the universe formed during the Big Bang about 40 billion years ago.
Let us come down to Earth and consider these gas properties
with the help of more tangible experiments.
I have a small ampule fill with helium,
which is stored at a very low pressure that is roughly one hundredth of atmospheric pressure.
Helium doesn't have a color and it also doesn't have a smell.
You may already know this if you've ever played with Helium
and try to inhale this gas.
However such experiments are really dangerous because our cells don't breathe helium,
they need oxygen instead.
(People breathing Helium) even made Helium cylinder retailers add up to 20% of Oxygen to Helium
in order to make Helium balloons at parties safer.
If high frequency discharge of high voltage is passed through an ampule of Helium,
it will start glowing pale orange. (I will be glowing orange too. And dead.)
Its brightness depends on the voltage and the ampule's diameter.
I use the plasma lamp as a voltage source.
It made it possible for me to hold the ampule right in my hand,
because my body posed as a capacitor,
like everybody else's body, for that matter.
In contrast to Neon or Xenon,
Helium can glow from a distance from the generator wire.
Unfortunately, from the chemical point of view,
Helium doesn't have very interesting properties.
It almost doesn't react with any chemicals.
Also, in the form of plasma, similar to the one you can see in the ampule,
Helium can form extremely unstable compounds
with Hydrogen, Deuterium, and some metals at a high pressure of 100,000 atmospheres.
They even form special substances, clathrate compounds (lattices that contain/trap molecules), of Helium with Nitrogen,
which can be grown as crystals in a diamond anvil cell.
There is no need to display though,
because Helium possesses the most
interesting and unique physical properties among all elements.
The thing is, when the temperature of Helium is reduced to 4.2 K,
Helium becomes the lightest fluid, density of which is almost 10 times smaller than that of water.
It is so cold that some metals even become superconductors,
for instance, like mercury or niobium.
To maintain such a low temperature,
liquid Helium is stored in cryogenic storage dewars,
which are also externally cooled off with Nitrogen.
The same technology of cooling Helium is used
in modern devices for creating nuclear magnetic resonance (NMR).
Superconductors made from Niobium are cooled off with liquid Helium,
which, in turn, is cooled off with the cheaper Nitrogen,
the cost of Helium being too expensive.
Thus, liquid Helium is used in medicine and scientific studies.
The most interesting is still ahead of us.
Until now, we have been talking about the first form of liquid Helium.
If Helium is further cooled off by reducing pressure in the storage dewars,
the liquid will eventually reach
the so-called Lambda point, (Lamb: baaaaaaaaaaa)
or, in other words, will be reduced to the temperature of 2.17 K,
and we've encountered the second form of liquid Helium!
After that, boiling of the liquid stops,
and it starts to exhibit completely different properties.
At such temperatures
thermal conductivity of liquid Helium
increases by millions of times,
and becomes higher than that of copper and silver.
That is why the liquid doesn't boil,
because the heat is spread immediately and evenly through the entire material.
Along with that, upon reaching the Lambda point, Helium becomes a superfluid.
i.e. It loses all viscosity,
which is the resistance of one part of the fluid against the movement of the other part of it.
There is a great experiment that proves that.
If you pour some liquid Helium into small hanging bowl,
the liquid will start creeping out the wall of the bowl. (Whaaaaaa??????)
Besides, it easily passes through a layer of ceramic with one micrometer wide pores.
The lower the temperature is, the easier it is for a superfluid to pass through barriers.
*supercooled* *slides in to DMs* ( ͡º ͜ʖ ͡º)
It's also quite surprising that superfluid Helium is still viscous,
as can be seen from the second experiment:
When the liquid is spun,
the liquid layer actually passes rotation to the upper blades.
What this is, after all,
is when quantum mechanisms,
whose behavior sometimes drastically differs from that of classical mechanics laws,
come into play.
Viscosity is both present and absent. (Like my father.)
That is how it can be characterized.
By the way, superfluidity of liquid Helium was first
discovered by Soviet scientist Pyotr Kapitsa in 1958.
And in 1962, Lev Landau worked out the theory of this effect.
Do you think that's it?
Not at all!
Now let's talk about stars and cosmic travel. (Aw yeah!)
Until now, we have been talking about isotope, Helium-4,
which has two protons and two neutrons.
However, there is yet another isotope, Helium-3,
which has two protons and one neutron.
The thing is,
this isotope is perfect for conducting fusion reactions
with Deuterium and Tritium (isotopes of Hydrogen).
This process can help humanity substitute fossil fuel,
but the problem is that this isotope is very rare on Earth,
because it immediately vanishes in the atmosphere.
Whereas, the isotope remains on the moon,
which does not have an atmosphere.
Hypothetically speaking,
people could extract Helium-3 from lunar dust and use it as a source of energy here on Earth.
As for now though, it seems to be a fantasy.
To sum up,
we can say that such a simple-seeming element as Helium has surprising properties,
and is irreplaceable in medicine
for scanning the human body.
( ͡º ͜ʖ ͡º)
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(Hello Kitty! Meow!)
Translators: These subtitles are given by AlexMeow bleufeline and XingYT,
if there are any errors, you're welcome to correct it, thanks!
(Hi five to you too, cutie pie!)