Why do ice cubes crack in certain temperatures?

Submitted by opbananas t3_11ksrgh in askscience

So I’ve been sick with covid and making a lot of tea not being able to leave my dorm. I had a bunch of ice cubes and ran out of milk to cool down my tea.

When my ice cubes get put into room temp or slightly colder then room temp water they violently crack and come apart when touched.

When I put it into tea water fresh from the kettle it doesn’t crack and maintains solid form while slowly getting smaller

Why does this happen? It makes me very uncomfortable and I don’t know why

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Liberty-Justice-4all t1_jbbdq3c wrote

I know why they crack at all, but I'm actually surprised that almost boiling water doesn't cracked them best.

The cracking is due to the fact that almost everything expands as it gets warmer, and if one part expands (or shrinks) more than other parts the stress forces can cause the connecting areas to snap and disconnect.

You get the same effect and can shatter glasses and mugs by very rapidly cooling or heating them (think hot tea in a cold glass, or ice cold drinks in a glass from a hot dishwasher).

My best guess on it NOT cracking in super hot water would be that it melts the surface quicker than the layer of warmed (but still frozen) ice can get thick enough to have enough stress built up to shatter free.

It's also possible the latent heat absorbed by melting off that surface is acting to cool the transition a bit, so the faster it melts the (effectively) better the cube is insulated, as sort of an ablative thermal stress guard, but I would expect that effect to be swallowed up by the vastly greater thermal difference without much notice.

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