angelhair
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Vacuum grease substitute?
Can you use the silicon grease found in auto stores as a good enough substitute for high vacuum grease?
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vulture
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If it's pure silicon grease it could certainly serve well. Test if it contains compounds that'll dissolve in common solvents or whatever you're going
to distill first.
One shouldn't accept or resort to the mutilation of science to appease the mentally impaired.
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bio2
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Some of it is a good substitute.
Not the thin stuff as it melts too low. It needs to be thick, not runny and colorless.
Do a melting point test or just try it.
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ShadowWarrior4444
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There is a 'Teflon' based grease designed for plumbing and thread seal applications, it claims to be resistant to +/- everything, will not dry out,
wipes clean, operates in temperatures from -200F to +550F, pressures up to 10,000 psi, and will withstand expansion, contraction, and vibration. It
will also not drip or run from joints, and is completely non-toxic. It indicates that it is not for use on oxygen gas carrying lines.
The brand is Hercules, Product: real-tuff Teflon Paste Thread Sealant
This may work, though I haven’t used it for vacuum applications, I normally use it to coat the various parts of electrodes or other things that I
don’t want exposed to a corrosive environment.
I have also heard that Gas-Line PTFE (Teflon) thread seal tape will work for making a vacuum distillation apparatus. (This is the yellow tape in the
plumbing section of nearly any hardware store.) The Teflon paste may be found there as well.
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bio2
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The thin white PTFE tape is better for ground glass joints.
The yellow is for gas lines and is much thicker causing the joint to not fully seat.
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MagicJigPipe
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Every time I use the white stuff I get a lot of permeation and sometimes leaks. It sucks. Even EtOAc went through a little bit when boiled at
atmospheric pressure.
"There must be no barriers to freedom of inquiry ... There is no place for dogma in science. The scientist is free, and must be free to ask any
question, to doubt any assertion, to seek for any evidence, to correct any errors. ... We know that the only way to avoid error is to detect it and
that the only way to detect it is to be free to inquire. And we know that as long as men are free to ask what they must, free to say what they think,
free to think what they will, freedom can never be lost, and science can never regress." -J. Robert Oppenheimer
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chemrox
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by the white stuff did you mean the tape or the white grease? I just ordered some teflon sleeves from Scientific Machine and Supply in Middlesex NJ.
The are extruded Teflon and nothing else. I got them in 24/40 plus a few in other st sizes. They are a little dear but should last forever. I have
one that is over 20 years old. They are more likely to get lost than wear out. I would like to know if the Hercules paste is a reasonable backup.
"When you let the dumbasses vote you end up with populism followed by autocracy and getting back is a bitch." Plato (sort of)
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grind
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A good vacuum grease is "kapsenberg schmiere" (ks) made from glycerine and soluble starch. It is water soluble, so cleaning of the glassware is very
easy, no need for organic solvents. I´ve made a comparison between baysilon(R) and ks, there is (I couldn´t find) no difference concerning
suitability for high vacuum.
I solely use this water soluble grease for almost all applications with success and great satisfaction.
A further convenience is that you can alter freely the consistence of the ks by adding more glycerine or soluble starch to the heated ks.
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bio2
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The thin white PTFE tape comes in many qualities and some will
not stretch evenly and is not soft like virgin PTFE.
Get the high quality expensive brand as there is a big difference.
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ShadowWarrior4444
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| Quote: | Originally posted by chemrox
by the white stuff did you mean the tape or the white grease? I just ordered some teflon sleeves from Scientific Machine and Supply in Middlesex NJ.
The are extruded Teflon and nothing else. I got them in 24/40 plus a few in other st sizes. They are a little dear but should last forever. I have
one that is over 20 years old. They are more likely to get lost than wear out. I would like to know if the Hercules paste is a reasonable backup.
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I have noticed organic and hydrocarbon vapors passing through, and in some cases discoloring the white tape, as such if I require a chemically
resistant seal, I will usually combine it with another sealant--such as the Hercules paste. A combination of Teflon tape and Teflon grease may be a
very OTC solution. White Teflon tape alone I would not recommend, as it appears to be quite porous and will stretch easily to translucence. In
contrast, yellow Teflon tape is specifically designed to be impermeable to gas, which is the general idea in vacuum systems.
I have also heard of specialty "full density" Teflon tapes designed for laboratory use, though I doubt they would be much of an improvement over a
combination of Teflon tape and Teflon grease.
A site with various grades of tape: http://www.mercotape.com/html/body_threadmaster_teflon_and_p...
The Hercules site (they may even be giving out free samples): http://www.herchem.com/products/thread_sealants.html
Teflon Paste specifications: http://www.herchem.com/specs/realtuff.pdf
Teflon Paste MSDS: http://www.herchem.com/msds/MSDS11_realtuff.pdf
[Edited on 5-8-2008 by ShadowWarrior4444]
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MagicJigPipe
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I use the good white Teflon tape. Whenever I use it with an organic solvent it turns translucent (almost transparent) and starts leaking. It only
leaks slightly but it's enough for me to smell it from about .5 feet away.
I'll try the yellow stuff and then I'll try the combination with the paste. I'll report back here with the results.
"There must be no barriers to freedom of inquiry ... There is no place for dogma in science. The scientist is free, and must be free to ask any
question, to doubt any assertion, to seek for any evidence, to correct any errors. ... We know that the only way to avoid error is to detect it and
that the only way to detect it is to be free to inquire. And we know that as long as men are free to ask what they must, free to say what they think,
free to think what they will, freedom can never be lost, and science can never regress." -J. Robert Oppenheimer
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-jeffB
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| Quote: | Originally posted by grind
A good vacuum grease is "kapsenberg schmiere" (ks) made from glycerine and soluble starch. It is water soluble, so cleaning of the glassware is very
easy, no need for organic solvents. I´ve made a comparison between baysilon(R) and ks, there is (I couldn´t find) no difference concerning
suitability for high vacuum. |
Is this a commercial product, or is it something you make yourself? Do you have preparation instructions?
This sounds like just the thing for sealing a bell-jar to a plate for simple vacuum demonstrations. I probably won't use it when it's time to distill
nitric acid, though. 
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not_important
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| Quote: | Originally posted by grind
A good vacuum grease is "kapsenberg schmiere" (ks) made from glycerine and soluble starch. ... |
This is one type of stopcock/ggg lubricant that are useful around organic solvents, and relatively easy to clean up. Glycerol plus starch or
bentonite type clays, or syrupy phosphoric acid plus bentonite. Both of those liquids are not soluble in many organic solvents, especially
hydrocarbons and halogenated hydrocarbons. The starch or bentonite form a gummy yet slipper film with water if it comes into contact with the lube
and washes out some of the glycerol/H3PO4, retaining the lubrication and seal. And all of these clean up with water.
Bentonite+H3PO4 is safe around nitric acid and NOx, as well as SO2Cl2 and other acid halides, although there will be a slight amount of reaction.
None of these is meant for high temperatures, say above 150 - 200 C. Glycerol and starch break down, H3PO4 will react with glass. But they do have
low vapour pressure at more ordinary temperatures, and are of low toxicity and cost.
Older lab technique books often mention one or another of these, although you can just about mix them up by the feel of the result, adding the liquid
or solid if too pasty or runny.
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-jeffB
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| Quote: | Originally posted by not_important
Older lab technique books often mention one or another of these, although you can just about mix them up by the feel of the result, adding the liquid
or solid if too pasty or runny. |
Do you simply stir the ingredients together at RT? Is ordinary grocery-store cornstarch appropriate?
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grind
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Heat glycerine to 160°C, add soluble (!) starch while stirring with a glass rod. Test a little portion after cooling to RT for consistence. If too
pasty, add more glycerine, if too runny, add more starch (of course at 160°C).
As far as I know, ordinary grocery store starch cannot be used, cause it´s not a soluble form. I always used starch called Zulkowsky soluble starch.
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12AX7
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Do you know any difference between soluble starch and, say, corn starch? Could the difference be merely that it's been cooked?
I can give you this (some (important!) kitchen chemistry): add starch to cold water and shake to disperse. Then add it to the hot liquid, e.g. gravy
in the works. Starch breaks up with heat, swells and thickens / gels the dish. Tasty! I have no idea if hot glycerin would have the same effect as
hot water (i.e., non-cold-water-dispersed starch swells on the outside, making stupid balls of starch that never break up no matter how much you stir
that gravy).
Tim
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grind
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Here is a german wiki artikel about the conversion of normal starch into soluble starch with the aid of glycerine:
http://de.wikipedia.org/wiki/L%C3%B6sliche_St%C3%A4rke_nach_...
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unionised
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Rubber bands dissolved in boiling vaseline works, and (just to show I'm not making it up)
http://www.physics.utoronto.ca/overview/history/microsco/mic...
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Mumbles
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It seems that mixing the starch and the glycerol at elevated temperature is designed to covert starch into the soluble form required. I suppose the
heat could be used to create a super saturated paste of sorts. Given the information given by grind in the initial post, and a rough translation of
the wikipedia article, it seems that it would be possible to create the grease from ordinary starch. The article mentions that potato starch for some
reason gathers a great increase in strength from the workup. I wonder if stock soluble starch simply mixed with the glycerol would be adequate, or if
the heat is necessary for production.
I have some soluble glutinous rice starch at home. Perhaps I will give it a try next time I am distilling something. It seems this would be a bad
choice for nitric specifically. Nitroglycerin is toward the bottom of the list of things I want in my ground glass joints.
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angelhair
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I found a product by ROCOL called saphire silicon grease. It comes in a 250g tube, 500g and 2.5kg can. The one in the can is thicker than the tube.
Thew data sheet say's that the base fluid is silicon oil and the thickner is silica. The MSDS say's the ingriedant is Silicone Bonded Integrated Mica
>60% and performance addatives <10%
I used it down to 5 torr for about 6 hours and it seems to work although it's not as thick as the Dow Corning which from memory is about 60%
polymethylsiloxane. So it works but It's borderline because if you apply it on too thin, you will see tiny spider viens start to appear.
I wonder if I can thicken it myself by simply adding some silica flour from the pottery suppliers. Will the particles be small enough?
[Edited on 1-6-2008 by angelhair]
[Edited on 1-6-2008 by angelhair]
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angelhair
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What about getting some silica fume, cleaning it up and adding that to the grease? I believe I can get a product thats >88% silica the rest is Iron
Oxide and dolomite. The particle size is around 0.2 microns. The only silica flour I can get is about 350 mesh. That sounds to big.
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angelhair
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I made some of that water soluble grease using suppermarket starch, turning that into soluble starch then heating with glycerol. So far I'm very happy
with it.
I also stiffened up the silicon grease with boric acid, ( same way they make silly puttty) heating up to 170 - 180 deg C using from 2% up to 7% acid.
It has made a difference to the viscosity and seems to work well up to 40 mbar, but I have yet to try it under deeper vacuum.
I must say though, that when applying the grease and fitting two pieces together, you get a disturbing sensation of siezure and broken glass or sand
being ground, but that disappears after you turn the joint. No dammage.
Adding SiO2 didn't do anything to help. I also want to try using calcium soap.
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nannah
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Do teflon spray work as a substitute?
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Mailinmypocket
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I use this stuff for vac and for greasing joints, works surprisingly well and is quite inert. Most car places have it.
http://www.permatex.com/products-2/product-categories/specia...
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