The Hunt for the Highest Melting Point
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The Hunt for the Highest Melting Point

December 15, 2019


If you follow our sister channel SciShow Space,
you might remember something that we pointed out recently: Even the coolest places on the Sun’s surface
are hot enough to melt every compound that humans have ever found, created, or even predicted. And it turns out that there’s a whole field
of scientific research devoted to finding the compounds with the highest melting and
boiling points — meaning they’ll stay solid or liquid even if it’s super hot. Scientists are also pretty sure that they’ve
already found the substance with both the lowest possible melting and boiling points,
plain old helium, which really likes to be a gas. But before we get into why that is, let’s
talk about why things melt and boil in the first place. A things’ melting point, where it goes from
a solid to a liquid, is mostly determined by how much its particles, the atoms or molecules
that make up the substance, attract one another. That’s because solids are made up of particles
that are held together very rigidly, but in liquids they’re much more loosely attached. And at higher temperatures, particles have
the energy to move around more. So, our mystery substance will have a higher
melting point when the attraction between its particles is stronger; they need the extra
energy of a higher temperature to move around enough to turn into a flowy liquid. And when the attraction’s weaker, the melting
point is lower. The same thing is true for boiling points,
when something goes from a liquid to a gas. If you keep heating the atoms or molecules
until they have enough energy to totally escape each other’s attraction, they start rocketing
around as a gas. But pressure’s important too, because it forces
the particles closer together — to the point that they bond and form a liquid or solid
again. That’s why we generally compare melting and
boiling points at a constant pressure — usually standard atmospheric pressure, or about a
hundred thousand pascals. And helium has the lowest ones because its
atoms attract each other extremely weakly, so it doesn’t take much energy to separate
them. In fact, helium doesn’t even /have/ a melting
point at standard pressure. It can never be a solid — not even as you
approach absolute zero temperature, where the atoms wouldn’t moving around at all. You have to put helium under 25 atmospheres
worth of pressure in order to get it to be solid, and even then you have to cool it down
to just 1 Kelvin: 1 degree Celsius above absolute zero. But it does have a boiling point at standard
pressure. Helium’s boiling point is about 4 Kelvin, the lowest of anything that we’ve
ever found. And there’s no reason to think that record
will be broken any time soon. Helium is one of the only elements that we’ve
never seen bonded to anything else, both because of how weakly it attracts other atoms and
because it’s what’s known as a noble gas, it has just the right number of electrons
that none of them are available for bonding. It has the lowest boiling point of any element,
which is easy to test. And any full-fledged molecule, because it’s a group of atoms
already attracted to each other, is going to attract other molecules more than helium
does, giving it a higher boiling point. So helium’s records seem to be safe — and
are also incredibly useful. See, things that tend to stay liquid when
are really good at … keeping things cold. Some of the world’s fastest trains, for example,
float over the tracks, but they need to be really cold — supercooled, in fact — for
that to work. Engineers do that by flowing a ridiculously
cold liquid like helium around the tracks. And lots of complicated equipment, like particle
accelerators, needs to be kept very cold to work. But hot liquids and solids can be just as
useful, which is why researchers are hunting for the compounds with the highest melting
and boiling points ever. We already know that tungsten has the highest
melting point of any pure element, melting at just under 3700 Kelvin at atmospheric pressure. But we’ve found compounds that stay solid
/way/ above that. In 1930, chemists discovered that an alloy
called tantalum hafnium carbide has a melting point of about 4200 Kelvin. That’s over 500 Kelvin hotter than tungsten,
the hottest we know of — at least, when it comes to compounds we’ve actually /made/. Because in July 2015, a team of researchers
published a paper in the journal Physical Review B predicting an even /higher/ melting
point for a compound made of nitrogen, hafnium, and carbon, 4400 Kelvin. The authors found it by simulating how molecules
attract one another and just trying a bunch of different compounds until they found the
one that would melt at the highest temperature. It’s much easier to do that sort of thing
in the computer than in the real world, where you have to, you know, make the actual compounds. They haven’t actually tested their prediction
by making the compound yet, though. As for boiling point, a compound called tungsten
carbide holds the current record. It boils at 6273 Kelvin, which IS actually
higher than the temperature of the surface of the Sun! That’s why we can’t say that the Sun’s surface
is hot enough to boil everything we know of. Not only do these compounds tend to stay solid
at super high temperatures — they’re also very hard to break. So compounds with high melting and boiling
points are often used in places that need to be solid and unbreakable even when it’s
hot — like inside engines and as heat shields for spacecraft. These kinds of compounds with really high
melting points were just right for the job. And unlike helium’s record, compounds with
higher melting or boiling points might still be waiting to be discovered. We just need to keep looking. And burning stuff, just making it real hot! Thanks for watching this episode of SciShow,
which was brought to you by Audible. Rightnow Audible’s offering SciShow viewers a
free 30-day trial membership. Where you can choose from 180,000 titles. So, go to audible.com/SciShow for a free 30-day
trial and download a free title today.

Only registered users can comment.

  1. title of video – highest melting point. spends more than half the video talking about the lowest melting and boiling point

  2. Helium was briefly bonded with hydrogen by replacing one of the electrons with a heavier particle, using a particle accelerator.

  3. I could just see the US military sponsoring this. “This episode is brought to you by the US military, they were not joking about fire and fury”

  4. Your jet engine has the thrust reverser deployed, but it doesn’t seem to be reversing any thrust. You should probably get that checked out.

  5. I found a factual error. We have had helium bonded to something else, in a labratory, at extreme pressure between two diamonds. Na2He has been created as a stable bonded molecule at 1.1 million atm, about the pressure at outer skin of the earth's mantle.

  6. Believe it or not, helium DOES form some chemical compounds, very weakly.

    https://en.m.wikipedia.org/wiki/Helium_compounds

  7. Tungsten IS NOT the highest melting element. Carbon is (at 3550C versus tungsten's 3422C). But tungsten's boiling point is higher than that of carbon, which is why tungsten is better for incandescent lamps. Either filament loses mass by sublimation well before it melts, so it is the sublimation of the filament that sets the highest practical filament operating temperature (about 3500K or 3200C) in order to get a practical life.

  8. Water can be compressed. Anything can.
    Fact: when our sun collapses to a white dwarf the pressure will create degenerate matter which is a million times more dense than water. (~200,000 times more dense than granite)
    In core collapse supernovae matter is condensed to it's schwarzschild radius. That is as small as it gets.

  9. The surface of the sun has 2 temperatures. The main one is ~ 10,000° Fahrenheit. The other is the temperature of sunspot umbra which is ~ 5,200° Fahrenheit. That happens to be below the boiling point of iron (Fe) which explains the luminosity discrepancy.
    The surface is about double the temperature of an umbra so according to the stefan-boltzmann law it should be 4 times brighter.
    It is not anywhere close.
    The surface is 10,000 times brighter because sunspots are a different element (iron) and a different state of matter (liquid).

  10. I was hoping to hear: "This episode is brought to you by hot chocolate that is so hot that it burns your tongue and lips instantly and turns what should be an excellent experience into a rather unsatisfactory one."

    Instead… Audible

  11. For the record, Tungsten is also known as Wolfram. I always used the name Wolfram and never heard of Tungsten before. (Symbol W and atomic number of 74)

  12. Just for fun:

    “They found that if you put sodium and helium together and compress it to pressures like at the center of the Earth, sodium can actually react with helium and form stable compounds.”

    https://www.scientificamerican.com/article/a-noble-gas-surprise-helium-can-form-weird-compounds/

  13. What about starlite?
    https://en.m.wikipedia.org/wiki/Starlite
    Its either wrong info on wiki or there is a substance that can withstand suns surface temperature.

  14. 2:25 gold is like helium, unreactive. Point me out is for some magical reason, I am wrong. Or reply, and give me a credible source.

  15. It's a shame they glossed over all the we weird helium "molecules" done by messing with its energy level, ionization and pressure. I'm most curious about He13H+

  16. "Hunt For The Highest Melting Point" spends majority of the video talking about the physical and chemical properties of helium

  17. Anyone want to fund my kickstarter to drop loads of tungsten carbide out of solar orbit and build a river on the sun?

  18. The number one use for Tungsten Carbide is inserts for machine tools. Basically the cutting edge used to cut steel, aluminum, inconel, etc.

  19. I have a question.

    If liquid molecules are still connected, if only loosely, when I jump into a pool am I breaking those bonds or just moving through them?

  20. There is a ghast in the thumbnail. Therefore, the Nether is the hottest place, which would hold the hottest melting point.

  21. Why you talk with kelvins?
    Man i want to learn but you come at me with all that wikipedia stuff i cant understand it
    Speak in Celsius or Farhenhait bro…

  22. Before video tip
    im not that smart but i think it should be like uranium or radium i dunno

    … i dont have anything to say here

  23. before ayone goes and gets excited and tries to melt some tungsten carbide, just remember that the majority of it is a sintered product bound together with cobalt or nickel (foodgrade).

    ie, you can make a carbide insert melt if you blast it with an oxy torch, but you find the carbide itself just laughs and stays as a crystalline mass. it really looks cool actually, under intense heat.

    there is cast tungsten carbide but its very, very unusual. as its so damn hard to make!

    the carbide in most drill bits etc is already a fine powder as its converted from an ore, and precipitated out of solution… as superfine particles. from there its just glued together.

  24. If ashes are made from burning wood.
    Are you saying that those ashes can then get heated to a point where they melt?, and hotter and they will boil?

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