Hello everyone! What do you think?
Why do we need this unprepossessing piece of ceramics, costing $150?
Soon you will get to know that.
But first I will tell you what ceramic is, and why we need it in the modern world.
Humans began using ceramics around 20,000 years ago.
It was the first material ancient humans produced by firing clay.
Later on, as technologies advanced, people began to mix clay with other natural minerals -
- for instance with quartz and feldspar.
As a result of such experiments humans would get porcelain that was harder than fired clay.
Porcelain or faience were much more convenient materials to use.
They could be used not only as household items, but also as adornments.
Just take a look at these gorgeous porcelain figurines.
The only disadvantage of porcelain is that it's quite fragile and relatively soft.
It also doesn’t conduct very high temperatures well.
As chemical industries advanced, humans began to need harder ceramic materials with higher melting point.
I have a few samples of modern ceramics.
The first is aluminium oxide ceramic, which is in fact
pressed aluminium oxide powder, which is later baked at high temperatures.
A distinctive feature that sets this ceramic apart from, say, porcelain
is that it can withstand enormously high temperatures of up to 1700℃.
and can also be molten alkali or acid resistant.
That is the reason why furnace crucibles are often made of aluminium oxide ceramics.
Besides, such ceramic is very durable and is a great dielectric material.
For this reason it is also used to make spark plug insulators
and also to make some high-temperature resistant printed circuit boards.
The only disadvantage of this material is its pretty high thermal expansion coefficient.
In other words, if a crucible made of such material is rapidly heated up or cooled down
it may easily crack due to the thermal stress.
It was the case with me -
- when I was melting bismuth metal in such a crucible
- although I tried to heat it up carefully.
Aluminium oxide ceramics is very hard.
It easily scratches glass but still it isn’t as durable as some other ceramics.
It is also noteworthy that aluminium oxide ceramics glows red in ultraviolet light.
Besides aluminium oxide, zirconium dioxide is also used to make ceramic materials.
Zirconium dioxide ceramics have lots of advantages over aluminium oxide ceramics.
The first difference can easily be seen if I take two crucibles of different materials
Zirconium dioxide ceramic is almost two times denser than that made of aluminium oxide.
Besides, when baked zirconium dioxide is harder and more durable.
That is why ceramic knives that don’t need to be sharpened
and dental implants are also made from it too.
These ceramics can be made even harder
if about five percent of yttrium oxide, a rare-earth metal compound, is added to it
Yttrium oxide smooths out the structure of ceramics
thus making it even harder and suitable for hardening.
Quite often special bearing ceramic balls are made from such ceramic too
They are used for grinding or polishing metals or other materials
Such balls can also be used in the high speed bearings
of everybody's favorite fidget spinners, for instance.
But don't think it's an ideal material
Zirconium dioxide ceramics has also got its disadvantages
For instance, it's three times more expansive than aluminium oxide
and is also very sensitive to temperature changes.
That is why it cannot be heated up or cooled down too rapidly.
However, progress does not stand still
and humans have invented a material that almost doesn't undergo thermal expansion -
- and can withstand rapid changes of temperature.
Please meet one more material: Boron nitride.
It's a compound made of boron and nitrogen.
Pure tetrahedral boron nitride -
- looks like white powder, that can be baked and pressed at 2,000 degrees.
Having done that you will get a light ceramic, which is only two times heavier than water.
Such material can be rapidly heated up and it wouldn't crack.
That is why it's frequently used as shielding for tungsten welding electrodes -
- in plasma arc welding,
because this material is also a great dielectric.
Besides, boron nitride is a great lubricant;
liquid glass and molten metals don't stick to it.
Although oxidized Bismuth managed to stick to this crucible -
- and I had a hard time making it come off.
Because of the high heat transfer, metals in this crucible will melt down quickly.
This ceramic's disadvantage is that it's very soft and scratchable.
Its structure resembles that of graphite
and it is easy to draw with it, just like with a pencil.
Besides compounds with nitrogen, boron can also form stable compounds with carbon
forming boron carbide, one more type of boron ceramic.
Unlike nitride, boron carbide is one of the hardest substances, being very light at the same time.
Boron carbide also easily scratches glass
and its powder is mainly used to grind and polish different wares.
Finally, let us consider that old square of quite expensive ceramic.
This piece cost roughly $150.
How come it costs so much, you might be wondering?
This ceramic is composed of Boron and a quite expensive rare-earth metal, Lanthanum,
- forming lanthanum hexaboride.
Unlike the previously considered ceramics, this one conducts electricity well
- and its melting point is 2,200°C.
Today this ceramic's unusual properties are used in thermionic cathodes of many devices
for instance, in electron beam welding
or as a source of cathode beams in electron microscopes.
It is so because this material has one of the lowest electron work-functions
or to put it simply, a piece of this ceramic will be losing its electrons more easily
at significant differences in electric potential.
In the future, this material may substitute such refractory metals as Molybdenum or Tungsten in fusion reactors.
But it's not that easy.
Lanthanum hexaboride's unique properties come at a high price
it is expensive to extract and difficult to break and shape, making it a quite expensive material.
Lanthanum hexaboride is extracted by electrolysis of lanthanum trioxide with borax
and by collecting the extracted hexaboride with graphite cathodes.
Of course, there is one more type of exotic and expensive ceramic materials.
So-called "high temperature super-conductors"
that are made of oxides of different metals.
Some of such most widespread materials
are yttrium-barium-copper oxides
in the proportions you can see on the screen __
The unique thing about this ceramic is that it becomes a super-conductor, or loses all its electrical resistance
to be precise, at pretty high temperatures from the physics point of view, -184°C
If a piece of such ceramics is frozen and placed next to a Neodymium magnet
it causes quantum locking effect, or in other words quantum levitation.
To get to know more about such ceramic, make sure to watch my previous video.
I put a link in the description.
Those ones who like this video about unusual materials,
make sure to give this video a thumbs up!
For the provided ceramic materials, I will thank the company Stanford Advanced Materials.
I put a link to their site in the video description.
In the future when you cut something with a ceramic knife, or look at spark plugs
you will know what these white ceramic materials are made from.