I'll say this stuff works pretty darn good for lubing and sealing ground joints...
But, I have a tendency to overdo things a bit (better safe than frozen joint I say), and the grease enevitably leaks out around joint, especially when
distilling organic solvents.
Then I'm left with some slightly contaminated product and this nasty cloudy film on the glassware that absolutely nothing will completly remove.
Any suggestions for removing this stuff?The_Davster - 26-9-2006 at 04:54
In my inorganic lab we use the same grease, and we are told to remove it with pentane, so probably standard camp fuel should remove it.The_deadly_dustbin - 26-9-2006 at 05:04
If you are talking the silicone stuff, the last resort is a soak with KOH-alcohol. It will slightly etch the glass, it's not to be used on volumetric
calibrated stuff. It also slowly messes up stopcock joints.
Before that you can try refluxing kerosene or similar high boiling hydrocarbon in the equipment, poured off hot but not boiling. Repeat several times.
watch out for ignition sources! When I did this I feed some CO2 in as I turned off the heat, and emptied in a metal bucket that had a chunk of dry ice
in the bottom. Some silicones become soluble enough in the hot solvent that they will be cleaned out, others won't.
In the old days a mixture of bentonite and glycerol or syrupy phosphoric acid would be used for joints exposed to organic solvents; glycerol couldn't
be used when acid or oxidising vapours were being formed, while phosporic was a no-no for acid sensitive compounds. When usd with sep funnels, if
exposed to water the bentonite would swell slightly and form a somewhat slippery film that still sealed. The glycerol or phosphoric acid have too many
hydroxy to dissolve well in many organics. But it is still a hack, teflon sleeves work better in most cases.neutrino - 26-9-2006 at 16:49
This thread may help. Look toward the second half.evil_lurker - 26-9-2006 at 18:58
That is probably what I'm going to have to do... is get some teflon sleeves.
But dayum those things are freaking expensive at $12USD EACH.
How well do these thing seal under vacuum?
This company seems to offer a pretty good deal on them and has several to choose from... which one would you recommend?
[Edited on 27-9-2006 by evil_lurker]not_important - 26-9-2006 at 21:39
A little note for homebrew sourcing. Before vacuum greases were common, or at least in the days when chemists still made their own reagents and
apparatus, high vacuum grease would be made by heating petroleum jelly (vasoline) to a fairly high temperature under a good vacuum ti distill off the
more volatile components; the stuff left behind was used as vacuum grease. This will dissolve in hydrocarbon solvents - pentane, petroleum ether,
ligroin, and so on.12AX7 - 26-9-2006 at 22:27
Would wax work? Solvents or melt it in place?
Timnot_important - 26-9-2006 at 22:51
Quote:
Originally posted by 12AX7
Would wax work? Solvents or melt it in place?
Tim
As a seal/lube? Some waxes were and still are used for vacuum seals, but they are not candle wax or kitchen paraffine. The melting point of the common
waxes can be a problem, some of the vacuum waxes had fairly high melting points.
They do dissolve in common organic solvents, so they aren't very useful in reaction or distilling apparatus.neutrino - 27-9-2006 at 06:11
Teflon sleeves for $12 EACH? You need to comparison shop, my friend. Froogle is your friend.
For starters, take a look at ScienceGear. They have the cheapest PTFE sleeves I've seen (10 x 24/40 for $15), but my links database is old and there may be a cheaper supplier
out there.
Keep in mind also that sleeves can be cut up into multiple sealing rings. This way you can seal multiple joints for the price of one!Mr_Benito_Mussolini - 27-9-2006 at 15:55
Silicone is a dog to remove. Can't you get by with soft teflon plumbing tape? Cheap and easy to apply.
**************
Ralph,
Dow Corning silicone grease is the most difficult of all greases to get off. Acetone will not do
it.
Trichloroethylene or a produce call Opti-Clear (a trichlor alternative) should do the trick.
Good Luck!
Brent
Ralph Hinkley wrote:
> Dear MEMS colleagues,
>
> I'm having difficulties removing the high vacuum grease.
> High vacuum grease is used in attaching small samples to a dummy wafer for Si deep etch process.
> After the deep etch process, I managed to detach the samples in acetone,
> but totally removing the grease with acetone seems impossible.
> Can anyone shed some light on?
> I'm using Dow corning high vacuum grease.
>
> Regards.
>
> Ji.
***************
There is a silicone solvent you can buy that takes the stuff right off. It's not cheap, but it strips the layer of silicone completely off. It
becomes very evident on ground joints because they turn very white again, and water will once again sheet after rinsing.
It's made of a low molecular weight silicone (also made by Dow), and they used to call it "OS-2" which was for "Ozone Safe 2" (it also evaporates
fairly quickly). The can I have says it contains:
hexamethyldisiloxane and,
octamethyltrisiloxane
As an alternative you can use silicone gasket maker (it's just high temp sil. caulk), which cures to form a nice rubbery seal. It can be peeled off
when you are done. I have never used it on ground joints though, so I can't say how hard it would be to remove.12AX7 - 4-10-2006 at 13:38
Hmm, I wonder just how different those are from the methylated analogs of ethane and propane (or perhaps ethers, considering the -oxane linkage). For
instance, di-tert-butyl ether and bis-di(tert-butoxy)-propane (I think those are right ).
).