Sciencemadness Discussion Board

glassware fused

cavgdad - 14-9-2004 at 09:20

after a lengthy distill of a high bp oil (220C under reduced pressure), my glassware won't come apart. its all lab grade boroscillate glassware. i used vasoline on ground glass joints, but it all burned off at the high temps. i had to wrap the top of flask and 3 way distilling adaptor in glass wool to get it to come over at all, so the joints were subjected to at least 220C temp. i have soaked them for to days in different solvents to no avail! any help tips, or suggestions would be welcome.

vulture - 14-9-2004 at 09:42

Have you tried DCM or commercialy available strong degreaser?

Furthermore, try heating the outer part of the joint with a hairdryer. It might take a while, but usually it will loosen because of expansion. Several heating/cooling (SLOWLY!) cycles can help too.

Whatever you do, don't resort to a burner! That is only for highly experienced glassblowers.

Next time use teflon tape.

Which oil were you distilling?

svm - 14-9-2004 at 10:07

sometimes rocking the joint back and forth is more effective than trying to twist the joint loose. at any rate, be careful because it's easy to break a joint like this. a combination of one of these methods with the heating trick above might be good too.

another trick that sometimes works is to soak in a base bath for a couple of days. I use a solution of 500 g KOH in 4L of 95% ethanol as a base bath. that mixture is really corrosive, but as long as you don't leave your glassware in there for more than a week it should be fine. make sure you wear heavy gloves and use tongs to get your glassware out of there too.

fused glassware

cavgdad - 14-9-2004 at 12:18

yes i tried dcm and degreaser... did not work, but the hair dryer trick, that worked incredibly. thanks!! and thanks for such fast replies. i usually post at the hive and replies are much slower, and my account keeps not working. oh btw the oil was mdp2p (not really oil but high enough bp to give me problems)

BromicAcid - 30-10-2004 at 18:07

I had some fused glass joints today too.

A 500 ml glass bottle with a 24/40 ground glass joint and stopper froze up on me. I bought the container used and made the mistake of not cleaning it out first. I don't know what was in it previously but this time it was H2SO4 (35%) that was within. The edges of the stopper came down and covered the edges of the container. I tried soaking in acetonitrile and some other organic solvents to try and losen it, no sucess. Then I tried prying it up with a metal rod, it bent the rod, tried it in several places (of course I tried twisting it too and such). The hot water, then a lighter, then a blow torch, the last one made water vapor boil out of the H2SO4 and I could watch it bubble up through areas of the joint. So I twisted it and tried to get it off while hot, no luck. Then I heated more and more, white smoke started to come off. I tried to pry it off with the metal rod again and the lip of the stopper broke off and hit me in my closed eye. Got an acid burn on my eye lid and on my cheek. Tried to heat again and pull off, no luck, more solvents, no luck, then I twisted and the rest of the stopper broke off in my hand.

Well, that's as waste of $3 in acid and $3 for a reagent bottle. Oh well.

Another good tip

vulture - 31-10-2004 at 08:18

Glassware has moods too.

Seriously. There are days you'll break it by just looking at it and other days where you can drop it from eye height and catch it when it bounces back unscatched.

I guess it has something to do with Zen or something, but Philou can probably tell you more about that.