[Fresco]

So here I was hydrolyzing some wool in DMSO at 190 degrees celsius for 10 minutes or so.
I then transfer the pyrex beaker to an icebath to cool the solution off quicker, and the beaker cracked. It didnt shatter or anything, it just cracked in a few places.

Is this normal??  What did I do wrong??
Is the sudden transfer from hot to cold not good for pyrex beakers??

Anyone else ever have this happen to them??

[Corribus]

https://en.wikipedia.org/wiki/Thermal_shock

Pyrex is specifically designed to have low thermal expansion, but it still happens. Particularly if it's been cycled many times, it'll crack eventually.

[Fresco]

https://en.wikipedia.org/wiki/Thermal_shock

Pyrex is specifically designed to have low thermal expansion, but it still happens. Particularly if it's been cycled many times, it'll crack eventually.

Is it common for pyrex bottles to crack from just sitting on a heating plate at 190C without moving it to an icebath??

[Corribus]

Any time you heat or cool a material, you apply internal stresses to it. This is because it's virtually impossible to evenly heat the entire volume of the material. Because every material expands or contracts during a temperature change, if the heating rate is uneven, some portions of the material will expand or contract faster than others. If the rate of heating is slow enough, the diffusion of heat will ensure that these forces are minimized... but they will always be there.  Every time you stress the material, it becomes weaker. This is known generally as fatigue. Eventually you will reach a failure point and the material will fracture.

So, yes, simply heating a material could cause it to break, if it has already been subjected to many heating/cooling cycles. Pyrex is more resistant but no material is perfect. Go through enough stress cycles and microscopic fractures will occur at stress concentrators on the surface or at grain boundaries. From there it's only a matter of (usually short) time.

[Fresco]

Any time you heat or cool a material, you apply internal stresses to it. This is because it's virtually impossible to evenly heat the entire volume of the material. Because every material expands or contracts during a temperature change, if the heating rate is uneven, some portions of the material will expand or contract faster than others. If the rate of heating is slow enough, the diffusion of heat will ensure that these forces are minimized... but they will always be there.  Every time you stress the material, it becomes weaker. This is known generally as fatigue. Eventually you will reach a failure point and the material will fracture.

So, yes, simply heating a material could cause it to break, if it has already been subjected to many heating/cooling cycles. Pyrex is more resistant but no material is perfect. Go through enough stress cycles and microscopic fractures will occur at stress concentrators on the surface or at grain boundaries. From there it's only a matter of (usually short) time.

Thanks Corribus.  Good thing I'm doing my experiments outside with a fire extinguisher next to me.
DMSO heated at those temperatures will produce a nice flaming Sambuca if the pyrex cracks and starts leaking

[Corribus]

Generally this kind of thing can be avoided by using good quality laboratory glassware and slow, even heating rates. This is why organic chemists usually use oil/water/sand baths and heating mantles rather than direct heating on a hot plate. Also, it's never a bad idea to inspect your glassware for small cracks before every usage, and certainly plunging a flask/bottle at 190 degrees into an ice bath is tempting the fates.

[Fresco]

Thanks for your help, Cor.

I bought one of these cooking pots that I think is safer than a Pyrex beaker.  It has a .6 cm diameter and can withstand temperatures of 400 Celsius:

http://www.purenature24.com/visions-glaskeramik-kochtopf

[electronpusher96]

Generally this kind of thing can be avoided by using good quality laboratory glassware and slow, even heating rates. This is why organic chemists usually use oil/water/sand baths and heating mantles rather than direct heating on a hot plate. Also, it's never a bad idea to inspect your glassware for small cracks before every usage, and certainly plunging a flask/bottle at 190 degrees into an ice bath is tempting the fates.

I second this.  You should not heat a flammable solvent directly on a hotplate.  If the container were to crack on the hot plate, bad things would happen.   Use a sand or oil bath if you need to exceed 100C, otherwise use a water or steam bath. 

[Ghargkja]

It seems to me the mistake made was putting a hot beaker directly into an ice bath without letting the beaker cool off first. Pyrex is not immune to thermal shock

[Fresco]

So here's my solution to make things safer, you guys.  I bought a very strong Corning glass pot, I then put the Pyrex beaker inside the pot.  That way if the Pyrex cracks again the pot will collect all the flammable DMSO.

See pic: http://oi67.tinypic.com/29o4i10.jpg

I suppose the pot could also crack, but then I at least have the Pyrex beaker to fall back on and I could quickly move both off the hot plate.  If both crack at the same time I guess I'm SOL 

Let me know what you guys think

[electronpusher96]

So here's my solution to make things safer, you guys.  I bought a very strong Corning glass pot, I then put the Pyrex beaker inside the pot.  That way if the Pyrex cracks again the pot will collect all the flammable DMSO.

See pic: http://oi67.tinypic.com/29o4i10.jpg

I suppose the pot could also crack, but then I at least have the Pyrex beaker to fall back on and I could quickly move both off the hot plate.  If both crack at the same time I guess I'm SOL 

Let me know what you guys think

It looks good, but would be great if you took some sand from the nearest sandbox and put it in the glass pot underneath the beaker.   The sand will heat more evenly, meaning a lower chance of cracking the glass, and it's harder to knock over that way.

[Fresco]

So here's my solution to make things safer, you guys.  I bought a very strong Corning glass pot, I then put the Pyrex beaker inside the pot.  That way if the Pyrex cracks again the pot will collect all the flammable DMSO.

See pic: http://oi67.tinypic.com/29o4i10.jpg

I suppose the pot could also crack, but then I at least have the Pyrex beaker to fall back on and I could quickly move both off the hot plate.  If both crack at the same time I guess I'm SOL 

Let me know what you guys think

It looks good, but would be great if you took some sand from the nearest sandbox and put it in the glass pot underneath the beaker.   The sand will heat more evenly, meaning a lower chance of cracking the glass, and it's harder to knock over that way.

Thanks EP96.  I see melting point of sand is very high around 1,600C and I'm only going up to 200C so there's no flammability issues.

How much sand should I use??  A thin layer or 1 cm deep or more??