- I just wanna talk about ice.
The weird properties of water,
thanks to our favorite hydrogen bonds
that cause ice to be less dense than liquid water,
are key to life on Earth.
But ice itself is pretty boring.
It's got some ordered hexagons.
The solid configuration is less dense
than the liquid form,
makes our ice tea nice and cold
and it forms some pretty snowflakes,
but that's kinda it, right?
No, wrong. Ice is fascinating.
I'm gonna prove it to you.
Ice is amazing.
(upbeat music)
We're talking about ice.
Is this delivery too weird or is it not weird enough?
Nobody knows.
Not only is ice fascinating,
but all that stuff I just mentioned is right here.
It is ice I,
but there's also all these other kinds of ice
plus more that can't even be represented here.
We don't even know how many kinds of ice there are.
We have found about 20 so far,
but there could be as many as 74,963.
So it's somewhere between 20 and 74,963.
Each kind has its own structure and properties
and some of them are found in diamonds or on Galilean moons.
And we are going to talk about all of them
or like the 20-ish we know about, I mean not all, 74,963.
Let's start with the ice
that we're all pretty familiar with, ice I.
If you take liquid water at normal atmospheric pressures
and cool it to zero degrees Celsius,
it'll align itself into hexagonal crystal in structures.
Ice is actually considered to be a mineral
because it is a naturally occurring solid
with an ordered structure.
Pretty much all ice in the biosphere,
which is the part of the Earth
where all the living stuff is,
is this kind of hexagonal ice one also called ice Ih.
That hexagonal molecular structure is what helps seed
the hexagonal structure of snowflakes.
But there's also a little bit of cubic ice I or ice IC
which as the name applies, has a cubic structure.
And this exists at temperatures between 130 and 220 Kelvin
and might actually occur way up high in our atmosphere.
There's also probably a little bit
of stacking disordered ice one up there too,
which is like a metastable ice
that exists somewhere between cubic and hexagonal ice.
And that also helps give snowflakes
their threefold symmetry.
But what happens if you subject ice
to all kinds of temperatures and pressures
to force it into other configurations?
That is what this diagram is all about.
This is key to everything we're gonna talk about.
So let's take a closer look.
What we've got here are phases of ice
at different temperatures and pressures.
The X axis is pressure from low to high
and the Y axis is temperature.
Here in orange, we have ice Ih
at pretty normal ambient temperatures and pressures.
Now you can change the phases of most materials
by changing the temperature or pressure that they're under.
And we are super familiar with this, right?
So changing the temperature of water can change the phase
it's in from a solid to a liquid or a gas.
And changing the pressure can have some effect too,
but with ice, it doesn't just stop at solid.
Imagine the hexagonal crystal structure of ice Ih.
If you subject that to much, much colder temperatures
or much, much higher pressures
you can deform and change that molecular structure
into all of these other shapes.
So what if we go this way on our chart
and we look at ice at higher pressures.
And I should mention
that these pressures are really, really higher.
We are looking at mega and gigapascals.
A gigapascal is 1 billion pascals.
Your bike tire might be around 500 pascals.
So this is 2 million times more pressure than that.
It's a lot of pressure.
And if we apply that pressure, we start to move into things
like ice III where the hydrogen bonds start
to bend and compress,
and then we get to ice V,
which has rings with both more
and fewer water molecules than our hexagonal ice.
And then if we keep adding pressure,
we get to ice VI and we get to ice VII.
Now look, the numbers just indicate the order
that they were discovered in,
not anything about their actual structure.
But this first batch of ices I, III, V, VI,
and VII are likely found on icy moons in our solar system.
Places like Jupiter's moon, Ganymede.
On these moons,
the layers of ice could be up to a thousand kilometers thick
causing huge amounts of pressure on the bottom layers,
forming these other phases of ice.
When ice is compressed like this to give different phases,
it is called a density-driven transition.
And amazingly, that can also happen here on Earth.
Ice VI and VII have been found
in diamond inclusions deep in the Earth's crust.
So you can pull up a diamond
and find ice VI and VII trapped inside.
Because of this, they have also been designated as minerals.
They can be indicators of water deep in Earth's mantle
and it's possible that they can contribute to friction
between slabs of earth that could lead to ice quakes,
ice quakes.
Now if we zoom in on the structure of ice VI,
I think this one is really, really cool.
It's actually composed of two sublattices
that fit inside one another,
but aren't connected.
There are no hydrogen bonds between the two
so they just kind of nestle together.
They're not connected, they're just hanging out.
Now what if we go the other way on the graph
and turn the pressure to negative,
essentially stretching ice.
Well, what we can actually get are forms of ice
that are less dense than ice I,
things like ice XVI and XVII,
these are empty clathrate hydrates.
Clathrates are molecular cage structures
that often enclose another molecule.
So these are basically big empty cage structures.
Typically, these are made in the lab by forming
the cage structure around another molecule,
something like neon and then vacuum pumping
all of those cage molecules out.
Now if you let the pressure come back to ambient pressure
the structures will typically collapse back to ice I
unless you keep the temperature really, really low.
What is this?
This is zero Kelvin, it's real low.
Now there's something I haven't mentioned yet
about all of the ices we have talked about so far.
They are hydrogen-disordered ices.
This means that if we zoom in
to the tetrahedral bonds surrounding a water molecule
in the ice crystal,
the center water molecule could be oriented in any direction
and that's confusing so I made a model, hold on.
(balls screeching)
Hello, this is my art project.
And if we think way back to gen chem
or our video on water weirdness,
what we're talking about here is actually changing
the hydrogen dipole
or the separation and orientation
of the charges on the water molecule.
So remember, all we care about is the orientation
of this center water molecule.
If you were to zoom into an ice crystal,
it could be oriented like this
or if the water molecules around it were in say,
this position, we still have these four bonds,
but now the dipole is pointing in a different direction.
So before it was going this way
and now it is going this way,
but there are some phases of ice
that are hydrogen-ordered ices.
This means that there are favored configurations
for the hydrogen dipole rather than just random ones.
And often the disordered
and ordered ices can be found in pairs.
So if you cool many of the ices that we talked about down,
you can go through an entropy-driven transition
where moving, again, down this figure,
so lowering the temperature
you can find that their ordered match.
For example, ICE XV is an ordered form
of ice VI right there, one's right below the other.
There is six pairs that we know about right now.
For each of these pairs, you're lowering the temperature
and therefore you're lowering the entropy
so you're getting more order.
I love when things like that make sense
like that made sense in my brain when I read it.
One of the newest addition to the lineup is ice XIX.
Ice XIX was first described as an ordered form
of ice VI that used to be called ice beta XV.
So goes right there.
But newer work has shown that it may be better described
as a distorted version of ice VI
and it might just form at higher pressure.
So it might actually go a little closer to over here.
There is ice controversy around
where some of these boundaries lie
and I love that controversy means that science is happening.
But you can even look for structures
that don't fit on this graph.
We are talking about some really weird conditions.
So for example, if you take ice VII
and you compress it to 50 to 300 gigapascals,
you can get to ice X.
And ice X is strange
because the water molecules aren't even
water molecules anymore
because the hydrogen bonds become symmetrical
between the oxygen that you cannot assign a hydrogen
to a single oxygen anymore.
(Alex inhales deeply)
And if you heat it to over 2,500 Kelvin, it doesn't melt.
Instead it turns into ice XVIII,
which undergoes super ionicity
where the oxygen stay in a lot of structure
and the hydrogens just kind of move around them.
Now this hydrogen mobility means
that ice XVIII may be as conductive as some metals
and it is possible that ice XVIII is hanging out
in the center of really dense and hot planets
like Uranus and Neptune.
And there's also another super ionic form of ice described
in October 2021 that is angling for the title of ice XX.
And look, we've been looking at most of these as like ball
and stick models so far,
but we can also look at them as 3D structures like this.
Here you can see that ice Ih and ice II
both have what's called these open channel structures.
That's really obvious there.
While in ice XVI, you can much better see
those expanded clathrate cages that I talked about before.
Here, it is easier to see how pressure can really deform
the structures to create things
like ice V and VI and VII.
They are clearly much more dense than ice I.
Additionally, this diagram only shows
these stable forms of ice
while there are also metastable phases
like ice IV and ice XII.
Disordered forms of ice that only exist
in small intermediate conditions,
which is why they just don't have a stable position
here on our graph.
But there's also amorphous ice.
Amorphous ice doesn't have a long range order
to its structure often because it has been cooled so quickly
that there just wasn't time for a lot of structure to form.
There's no nice order
like any of these that goes on forever.
It's just like water molecules randomly arranged
kind of like liquid water,
which is why it's called amorphous ice.
It's actually the dominant form of water in the universe,
as far as we know.
No one's out here measuring every single chunk of ice.
But amorphous ice occurs on things
like interstellar dust and in places like Saturn's rings,
there is a lot of it out there.
So much in fact that
it might just deserve a video of its own.
Let us know.
Do you wanna know about amorphous ice?
I do.
So is that it?
Do we just stop at 20-ish phases of ice and call it a day?
Absolutely not.
In fact, a recent computational study found
the potential structures for 74,963 types of ice.
So no, science is not done with ice structures,
but to name a structure to add to that Roman numeral list,
you have to experimentally show the crystal structure.
And so for now, we're still waiting on ice XXI.
But here, I think, our scientists disagree
so I'm also gonna do a take with ice XX.
And so for now, we're still waiting on ice XX.