Sciencemadness Discussion Board

Beakers cracking

guy - 16-5-2007 at 15:11

I have had my beakers for about a year now. They have been used for heating a lot during that time. Now my beakers are slowing cracking AT ROOM TEMPERATURE. Is this normal?

edit: i got it from UGT

[Edited on 5/16/2007 by guy]

Ozone - 16-5-2007 at 20:31

Are you sure that no one else was fooling with your glass?

I've never had glassware spontaneously self-destruct under ambient conditions...Unless...there was a polymer coating added by me which contracted on cooling straining the glass. I suppose that fluctuations in the ambient temperature could be the "straw that broke the camel's back"?

That one's a bitch. I'd check for "gremlins".

Cheers,

O3

guy - 16-5-2007 at 20:43

Before that I had been heating it on an open flame. But it cracked looong after if it had cooled. I think I heated it yesterday. As I was scraping off the crystals it cracked.

The_Davster - 16-5-2007 at 21:20

Another vote for Gremlins

I prefer open flame, as my heating equipment either stinks(hotplate), or I do not trust that it is not full of asbestos, so I am very friendly with my alcohol burner. Never had an incident with a crack despite using naked flame on aqueous solutions in UGT flasks for hours at a time. Thats gotta be a steep gradient.

[Edited on 16-5-2007 by The_Davster]

UnintentionalChaos - 16-5-2007 at 21:32

Rack up another tally for gremlins. The only glassware I've ever cracked (other than dropping it, which is a sadly common occurence....stir-rods don't have a fighting chance) was several hundred grams of KNO3 and about 200ml of water in a cheapo beaker over a gas stove. The temperature gradient was so steep that there were pockets of molten KNO3 at the bottom shielded from the water by their temperature which was boiling off all the water that tried to seep down. This was a while back and I wasn't paying attention to the beaker until it was too late. A large segment of the beaker slowly cracked out around the largest pocket of molten KNO3, but I was fast enough to save all the contents. I still have the beaker. Except for an oval chunk missing, its structurally sound. I use it for gravity filtration of nontoxic, flushable stuff into the sink. No need to worry about the liquid level hitting the bottom of the funnel since it all flows out and down the drain.

leu - 17-5-2007 at 03:35

Borosilicate glass will crack at ambient temperatures for many reasons, one of which is that using an open flame heats part of the glass to the annealing point thus inducing stresses within the glass which cause fracture upon cooling :( Even if the glass is heated with more gentle methods such as an infra red lamp, a draft of cold air can fracture the glass for similar reasons when it's cooled to room temperature :o One can expect a certain amount of glass breakage during laboratory work, it's to be expected :P

evil_lurker - 17-5-2007 at 07:16

Might be a good time to stick the rest of your glassware in a self cleaning oven and run it thru a cycle and wait till its completely cooled before taking it out.... hopefully that should re-anneal it.

Pyridinium - 17-5-2007 at 11:21

When I stopped heating glassware with a naked flame, I stopped having problems with cracking ;)

A small focus of heat on the glass sets up stresses that can persist after the heat is removed. Of course you could alleviate this problem by having an annealing oven and re-annealing your glass after use :D

Ozone - 17-5-2007 at 13:10

I am curious, guy, what brand of glass are you using?

Cheers,

O3

Bomex

MadHatter - 17-5-2007 at 20:02

That's the only type of glass that's cracked on me for any heat-related reason. I can't
say that about Pyrex/Kimax/Simax/Schott-Duran.

Ozone - 17-5-2007 at 20:24

That's where I was going.

Bomex is the plaything of the gremlins! (I have had the bottom just *fall* out with this stuff)

I have never had this happen with any of the brands you have cited (I don't know about Simax), MadHatter, unless there was an external stress applied--A heavy buchner on a relatively thin-walled vacuum flask (which is a major boo-boo when hot and under vacuum), for example.

Schott-Duran is the "shit",

O3

evil_lurker - 17-5-2007 at 20:26

Hahah, mason jars have more resistance to thermal stress than Bomex!

guy - 17-5-2007 at 20:51

What's the type of glass they sell at UGT?

And what is the "gremlin" joke here?

evil_lurker - 17-5-2007 at 21:49

UGT sells pyrex equivalent glassware (some is actually made from pyrex glass).

Gremlins are small mischevious fictional creatures aviation personel assigned blame for unexplained and/or unexpected mechanical failures of aircraft.

[Edited on 17-5-2007 by evil_lurker]

Magpie - 17-5-2007 at 22:14

I have Kontes RBFs and Pyrex/Kimax beakers and Erlenmeyer flasks. I have only lost one piece to cracking. This was a 1000 mL Pyrex beaker in which I was evaporating a calcium acetate slurry on a stirrer-hotplate. I wasn't watching it closely enough and it got too dry. I blame myself, not the glass.

[Edited on by Magpie]

guy - 17-5-2007 at 22:31

So no heating on open flames?

Pyridinium - 18-5-2007 at 07:34

Quote:
Originally posted by guy
So no heating on open flames?


Correct. It's one of those things you "might" get away with, might not. Why chance it? While others have had good luck with Kimax and Pyrex, I've managed to break these using naked flames.

I use Bomex all the time. Just use wire gauze or some other way to diffuse the flame. Better yet heat with a water bath or heating mantle.

undead_alchemist - 19-5-2007 at 06:33

For those of you who don't know, Bomex is owned by Kimble. So at the same time, you don't know if your Kimax brand glass is coming from Kimble's US plants, or from the Kimble-Bomex plant in China.

http://gerresheimer.com/index.php?id=194&L=1
http://gerresheimer.com/index.php?id=193&L=1

[Edited on 19-5-2007 by undead_alchemist]

DerAlte - 22-5-2007 at 11:25

Have never had such a problem, but I always use a sandbath for temps >100 C and a water bath for those below. A water bath even works with commercial glass jars provided there is no temp shock. I also use Corelle by Corning for evaporations, although I have a nice porcelain dish. It is basically a glass, I beleive. Great stuff. Even looks professional if undecorated.

All glasses have internal strain. If you scratch it you provide a stress relief line and it cracks there preferentially as all glaziers and glass blowers know. Perhaps you had a scratch.

I have destroyed many flint glass test tubes but only one borosilicate (Kimex, Pyrex) and that was due to drying a powder with liquid on top. A red hot tube can't stand being suddenly cooled!

chemkid - 22-5-2007 at 17:43

I just recently cracked a 400mL bomex beaker on the stove heating sodium bicarbonate. I use my glassware a ton and sometimes i am working on rough surfaces etc. so my glassware is taking a lot of wear and tear. Which would be more recomendable for a replacement - pyrex (another buck more expensive) or bomex again?

UnintentionalChaos - 22-5-2007 at 18:00

Its all about luck. I'd splurge on the pyrex. They are generally much better made, have thicker walls, and fewer occurences of bubbles (if any). I've trashed a few bomex items, but all of the pyrex and chemglass has given me no issues.

guy - 22-5-2007 at 18:45

So if I want to fuse something like sodium bisulfate, what should I use?

Ozone - 22-5-2007 at 19:12

It seems to me that crystallization or heating to dryness is key. Perhaps the crystallization leads to a contraction whilst intimately adhered to the glass (which strains and can crack it, with least provocation)?

Either way, I have crystallized in Pyrex with no ill effects.

Cheers,

O3

chemkid - 29-5-2007 at 14:27

Ok I will go with the pyrex

Heating non-Pyrex glass

prole - 11-10-2008 at 07:43

I purchased some 4L amber glass bottles for solvent storage, and they arrived smelling like an essential oil wharehouse, which is fitting because that is where they came from. Soap and water, and acetone do not remove this smell. 10% ammonia does so very effectively. It takes several days for the smell of ammonia to dissipate after an ammonia rinse, and of course I need it clean and dry before then. The reference from which I got the ammonia idea says to bake in an oven after rinsing, and they are for sure talking about Pyrex and other heat tolerant glasses. My bottle is not Pyrex. So my question is this: can I drive off the smell of ammonia in an oven at 150F without cracking my bottle? I am guessing it will crack ( I see a few bubbles in the glass), but if slowly heated and slowly cooled, would it possibly remain intact?

12AX7 - 11-10-2008 at 08:34

It'll be fine in the oven. If you want to be even more cautious you can even put a towel between the beaker and the metal grate. Both oven, towel and beaker will be safe up to 300F (cotton or wool towel).

Tim

prole - 11-10-2008 at 09:26

Thanks, Tim. If it does crack, I won't blame you:D. I like your towel idea. I have some welder's cloth that won't even blink in the oven at these temps. I'll give it a whirl and post back with my results.

It worked like a charm. No cracks or nuttin'. Smells are gone. It took about 5 hours at 150 F to drive off the smell of ammonia. I didn't have the stones to run it hotter. Maybe next time, I've got several more bottles to de-aromatize. And thanks again for the towel idea, I'm gonna use that from now on.

[Edited on 10/11/2008 by prole]

jarynth - 11-10-2008 at 20:41

Temperature itself is not the problem. Glass is still glass up to 1000K and more. You only have to pay attention to the temperature change rate. Pyrex expands little, quartz even less, that's why it's more resistant to rapid heating. Insulating your bottle from the metal parts by means of a bad heat conductor (cloth, fiber wool etc) ensures slower, smoother heating.

prole - 12-10-2008 at 12:22

That clears it up, jarynth. You can soften glass without cracking it if it's heated slowly and evenly, and as long as you don't quench it in water or otherwise rapidly cool it, it won't crack. In the past, I've dried pyrex glass in the oven directly on the metal grates or a cookie sheet. Nothing happened to the glass, but now that I am less ignorant on the subject, I'll be using the welder's towel for those purposes. The towel wasn't even warm after I heated the above bottle for 5 hours at 150F. Next time, the oven will be a bit hotter, because five hours is too long.

On a distantly related note, I once attempted to heat a solid mixture in a porcelain crucible, which is made for heating (right?) and as soon as I put the flame to it, it popped into several pieces. I replaced that piece of crap with a stainless steel one, which had damn well better not 'pop' when I put flame to it!

Thanks for your replies, guys.

12AX7 - 12-10-2008 at 12:51

Porcelain has a high glass content, you have to be careful with it as well. More porous, refractory ceramics tend to perform better.

Tim