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Author: Subject: Suggestions for glass joint-grease that won't get stuck after vacuum distillations?
Sidmadra
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[*] posted on 12-11-2019 at 10:39
Suggestions for glass joint-grease that won't get stuck after vacuum distillations?


I've tried a handful of grease products, silicone grease, petroleum jelly, and a few others I don't recall, and often I end up needing to break out my blow torch to heat the joint to loosen it in order to separate the joint, which I strongly dislike doing doing after distilling something highly flammable. I searched and saw 1 user here claiming that Lithium Grease has never gotten stuck on them, but I figured I'd make an open post before spending any money.


In the past I had used PTFE joint-sleeves, but they are kind of expensive and a little bit fragile, being easily ripped if snagged by joint clips for instance. Also, for them to work effectively they the joints need to be very clean, but the upside to them is that they offer no risk of contamination.

What is the best grease that you've managed to find to solve this issue of joints being stuck?
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monolithic
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[*] posted on 12-11-2019 at 11:17


Dow high vacuum grease works well and has never frozen my joints, but it's expensive. Check eBay for some old stock.
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[*] posted on 12-11-2019 at 11:34


Joint quality can be a big issue too with stuck joints.

Some joints stick a lot more.
I think it has to do with quality control problems on dressing the joints, but I've had much less trouble using glass from major American makers than I have from Chinese glass. The exception to this in my experience would be Laboy, which seems to have some pretty good workmanship.

If a joint seems grabbier than usual I'll often grind it lightly with toothpaste to get the joint surfaces a little smoother.
It seems to help.

I use Dow silicone grease, but I don't bother unless things are going to be getting pretty hot. I usually just wet the joints with whatever solvent the reaction is running in.






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Dr.Bob
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[*] posted on 12-11-2019 at 17:54


They make some very thin Teflon sleeves that work well for vacuum work, but not cheap. I agree that Dow's is the best there is, I use it for most stopcocks and vacuum joints, if I use anything. I also know that not using any grease works in most cases, if you don't have basic solutions. Those are really bad for seizing joints. Good luck.
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Sulaiman
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[*] posted on 12-11-2019 at 18:44


I have wrapped a few turns of ptfe plumbers tape around the male joint in a single tape-width winding,
it seems to seal well and be removeable.
I do not know how high a temperature would be usable as I've only used water:ethanol for this seal so far.
I would expect ptfe to be ok for anything up to oil bath tempertures.




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draculic acid69
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[*] posted on 12-11-2019 at 21:14


PTFE tape is a common method of sealing joints around here.works for most reactions.havent come across anything that ruins it yet.
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Herr Haber
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[*] posted on 13-11-2019 at 04:48


I use Teflon sleeves and like them a lot more than grease.
True, I never used brand or expensive grease like the ones suggested above.




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Dr.Bob
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[*] posted on 13-11-2019 at 20:00


Teflon tape is fine for most cases, but will not hold a high vacuum as it is both slightly gas permeable, as well as not nearly as tightly sealing as grease, which fills the tiniest gaps and scratches to get a much better vacuum than with teflon tape. But that only matters if you are below 1 mm of Hg.
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Sidmadra
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[*] posted on 20-11-2019 at 13:26


Teflon joint sleeves are useful but I've found that if the joint isn't totally clean and free of particulates/dust/dirt then a strong vacuum can be hard to achieve. In such cases, a good grease is more user friendly because it can easily compensate for any kind of particulates. Joint sleeves would be more preferable if I could find a reasonably cheap source of them. The last time I purchased them I had to pay $100 for 5 of them, and I had some rip in the first couple days, just getting snagged on clips, or ripped when trying to pull them out of the flask-joint head. I see there are some cheaper ones online now, but if anyone can suggest the cheapest place to get them, that'd be awesome.

I believe I tried PTFE plumbers tape before, different grades, including the non-gas permeable ones, but I don't think I've ever been able to get any sufficient seal with them; maybe I'll try again sometime soon.
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Herr Haber
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[*] posted on 21-11-2019 at 04:22


True, you have to make sure the joints are clean but from what I have seen my sleeves actually make up for small imperfections in my Chinese glassware.
On my Duran Rodaviss glassware I get the opposite effect: the joints are already perfect and adding a sleeve is counterproductive.

My biggest surprise comes from the prices and quality you all seem to get. It's not the first time I've seen reports like Sidmarta's.
I pay mine 1.34 Euros and most seem to last between half a dozen to a dozen uses even when used to distill acid.




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[*] posted on 21-11-2019 at 05:58


i think there are silicone bands that can use as a sealant for vacuum work .maybe you can make them by your self. it just act as a separator. atmospheric pressure do the rest by pushing two joints together so no air can get in, like in Magdeburg hemispheres .
https://en.wikipedia.org/wiki/Magdeburg_hemispheres




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[*] posted on 21-11-2019 at 16:38


Even you do shell out the money for the Dow grease, a tube will last for a LONG time. Less is more with Vac grease- I have seen a lot of people use it like caulking. Also, just be aware, Dow HVG is super insidious and tends to travel and contaminate things around the lab. Its something to be aware of if you are doing mid-to high end spectroscopy work. There was a joke in my old lab that "one day, years from now, the entire planet will be coated in a monolayer of Dow High-Vac grease. It is funny because, at least around the lab, it is sort of true. :]



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S.C. Wack
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[*] posted on 21-11-2019 at 19:00


Dow is not expensive at all compared to Krytox and Apiezon greases, but it has an officially short shelf life, IDK why. It seems fine.



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[*] posted on 22-11-2019 at 03:40


Somebody on another website did some MSDS searching & found vacuum grease is the same as car battery terminal grease.
My local car place sells sachets of it & red/green fibre washers to protect car battery terminals. Its red grease.
The Hershell ( H-500 ?) version is Silicon grease & clear. $8 for 100gms.

[Edited on 22-11-2019 by eesakiwi]
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[*] posted on 22-11-2019 at 04:56


I changed to ptfe tape from automotive silicone grease because
my cheap (Chinese) glassware joints needed a lot of grease to fill the joints,
and at higher temperatures the grease would dribble out of the joints,
into the glassware, contaminating my experiments.




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