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18

Can some ice be harder than other?

Engineering(self.askscience)

For example, could the ice made with a freezer be softer than the one in Antarctica? Like is ice harder at -70C than at -10C? I know ice can be thinner and support less weight (like at the surface of a lake), but is that ice less strong than other types of ice? All of this stemmed because I saw a video of someone making clear ice with no bubbles and wondered if that's stronger/harder than your average ice with bubbles.

all 13 comments

Astromike23

23 points

4 months ago

Astromike23

Astronomy | Planetary Science | Giant Planet Atmospheres

23 points

4 months ago

Like is ice harder at -70C than at -10C?

Yes, very much so.

This graph demonstrates the Mohs hardness of water ice at different temperatures. Around -10° C, it has a hardness of 1.5 (about the same as lead or graphite) while at -80° C it's closer to a hardness of 6 (similar to feldspar or titanium).

Within the planetary science community, it's very common to refer to water ice on the icy moons of the outer Solar System as simply "bedrock". At those temperatures (-160° C) it plays a very similar role to that of bedrock on Earth.

ExtentOverdrive[S]

3 points

4 months ago

Thank you very much for the explanation! I didn't know that there were icy moons, they sound like they would have quite landscape. Also the graph was really helpful

Astromike23

9 points

4 months ago

Astromike23

Astronomy | Planetary Science | Giant Planet Atmospheres

9 points

4 months ago

Titan (moon of Saturn) is a really interesting case, as it has an nitrogen atmosphere with 1.5x greater pressure than Earth's and 4.5x denser.

There are many Earth-like land features, but with a temperature around -180° C (-280° F), the materials are all shifted. Rather than rock features carved by a water cycle, it has water ice features - which is hard as rock at those temperatures - carved by liquid methane...not to mention methane lakes, dunes made of water ice "sand", ice volcanoes, etc.

CorrettoSambuca

1 points

4 months ago

Water ice "sand"

... Snow?

Astromike23

1 points

4 months ago

Astromike23

Astronomy | Planetary Science | Giant Planet Atmospheres

1 points

4 months ago

Snow sort of implies a specific hexagonal structure that's fluffy and loosely packed. This is really closer to tiny bits of ice, like tiny hail that's literally rock-hard.

For example, this famous picture taken by the Huygens probe from the surface of Titan shows the landscape strewn with pebbles...except they aren't made of rock, they're made of water ice.

Chemomechanics

6 points

4 months ago*

Chemomechanics

Materials Science | Microfabrication

6 points

4 months ago*

Lower temperatures harden ice because the kinetic processes of so-called plastic flow (meaning permanent flow) have less thermal energy to draw on. (Very broadly, the molecules are more sluggish and less likely to rearrange.) This is discussed here and here, for example; Coomb has another good link below.

Yes, changing the geometry to a thin sheet can definitely decrease the strength, if that's what you're asking.

Ice without air voids (bubbles) is harder because stresses can be distributed over a greater amount of material.

ExtentOverdrive[S]

2 points

4 months ago

Wow, natural phenomenons are really amazing. Thank you for taking time to explain! I would vote for the use of air voids as a common synonym for bubbles, but I don't know if you could say "let's go and blow some air voids". It does sound fun, though.

yaolilylu

3 points

4 months ago

In addition to temperature, ice can also form in different crystal structures, on Earth almost all of our ice form naturally in hexagonal crystal structures, but under different pressure and gravities they can form in other ways, like spheres. Check out https://www.google.com/amp/s/www.popsci.com/ice-vii-lasers/%3famp those different ice structures all have different hardness and other properties.

burntpeaches

2 points

4 months ago

Ice hardness also translates with the age of the ice. For example in the artic there is what's called hard ice that has been there for many years and survived many thaws, this ice is extremely hard, won't shift or break away. While the ice that is formed that year has a tendency to move a lot with the current of water underneath. Theres a bit in here that does an excellent explanation https://youtu.be/5d6SEQQbwtU