eli5: Why is it that glass shatters when it goes from extremely hot to extremely cold temperatures and vice versa? Moreover, what does that say about the glass manufacturing process if anything? Thank you!

Question

I just saw a video of people shattering Pyrex glass by pouring ice cold water within the measuring cup after heating it with a blowtorch, and I am curious as to what causes the shattering!

Here’s a link to the video if anyone is interested:

Thanks in advance to anyone responding!

In: Chemistry

Answer 1

I’ll add something to the others’ good explanations. It usually isn’t an issue when an object expands or contracts due to temperature changes. The issue arises when these deformations are constrained in some way. If you have a very hot glass slab and quickly cool down one of its faces than that face will want to contract, but it will be constrained by the other face which is still hot. At some point within the thickness of the slab the atoms in the cold part will want to move closer but they can’t because they’re still bonded to the “hot” atoms which are fine being as far apart as they are: this generates a stress inside the material. The same happens to the “hot” atoms which are pulled closer together by being bonded to the “cold” ones, however this generates a compressive stress which is usually less dangerous. Long story short, glass being very brittle, the stress might exceed a critical point and a crack will form and propagate leading to fracture by thermal shock. It isn’t actually the temperature itself causing it, but the temperature difference between two regions in the same material. Glasses and ceramics are particularly prone to this, while other materials are more resistant. For example it’s much harder for thermal shock to happen in metals, as they’re ductile (they tend to deform instead of cracking) and also very good heat conductors (so any temperature differences within the material quickly disappear).