Inert test tubes & teflon (or glass) cap liners.

I have been hunting on ebay for small cheap vials in the 8 to 16mL range to use in lieu of traditional test tubes with rubber bungs. The rubber bungs pop out under low pressure and aren't chemically inert, anyway. I've found vial with phenolic caps that it can take heat up to 220C before breaking down. This allows me to melt urea and other substances in a tube that is sealed off from air and do non-aqeuous chemistry. However, I haven't been able to find low cost phenolic capped vials with teflon sealing liners (or teflon plugs like a stopper in addition to a screw on cap). Phenolic resin isn't chemically inert. The manufacturer of the vials was also inconsistent, some of them have a plastic foam liner ... some of them don't. (see picture). But it's not PTFE... so I might as well assume it's not chemically inert and remove the liners anyway.

I searched sciencemadness and ebay for suggestions on how to get low cost teflon cap liners that would seal a dram vial, but it's a no go. I found that lots of users had problems with using teflon tape or commercial caps with pre-made liners since the teflon was not always pore-free. (porous teflon leaks gasses.)

White teflon tape for plumbing from the hardware store is porous, and several people noted that caustic chemicals or gasses can get through the tape if it's used as a liner. ( Goretex is a form of PTFE too ... it passes gas, but not liquids.)

I've seen several thicker teflon tapes, such as a natural gas sealant tape which is supposed to be impermeable. However, these are colored yellow and I have no idea if the coloring is chemically inert.

I've seen some tapered ground joint liners for $40 / set of three, but that kind of price is riduculous for a piece of teflon paper.

This seems like such a common problem that there has to be someone who sells just plain teflon cap liners; or someone can tell me what colors of extra thick teflon tape are the most chemically inert ... or explain a way to get a cheap punch and a thick white teflon sheet for a reasonable price.

Does anyone have good pointers on where to buy/make/find a low cost circular disk liner or plug that can handle heat to 220*C, and caustic chemicals?

I'm looking for solutions under $20 for 25 vials.

I bought 24 vials for experimenting from ebay seller homeluxe-grandparfums . I'm not entirely sure vial dimensions/threads are standard and the glass is quality. I just bought them and measured them with a precision dial caliper. The cap insides have about a 13.45mm (~0.525 U.S.A. inch) diameter to the threads; so that's the max size circular disc that will fit. The vial's glass neck (minimum O.D. not including threads) is 12.55mm. That's the minimum size disk I would want so that it compresses properly. (1/2 inch.). The inner neck diameter for a plug is 9.40mm ( 0.370 inch).

The vials are only worth half a dollar each. I want low cost vials, so that when I do experiments that are really hard to clean up ... I can just throw away a vial and not feel bad about it. But if there are teflon sealers for a different vial at low cost, I would consider switching vials (especially if they are borosilicate).

The only other thing I can imagine might work, is if there was someone who sold borosilicate glass disks that were thick enough to take the stress of being compressed in a cap without cracking. In that case, I could put a little silicone in the phenolic cap to glue them in, and put a little glass etchant on the lip of the vial. Then after screwing the cap on, the etchant it would naturally frost only the sealing contact points making it like ground glass.

Anyone have other ideas?




[Edited on 17-12-2017 by semiconductive]

Quote: Originally posted by semiconductive

The rubber bungs pop out under low pressure [Edited on 17-12-2017 by semiconductive]

Quote: Originally posted by unionised

Quote: Originally posted by semiconductive   The rubber bungs pop out under low pressure [Edited on 17-12-2017 by semiconductive] That's a whole lot better than the glass shattering.

The vials sold to me show between del = 0.0005 and 0.0008 inch expansion, on 3.7445 inch length from 21.5*C to 80*C.
del / 3.7445 / (80-21.5) = 2.28 to 3.65 ppm.

Soda lime glass has 8.5-9.5 ppm expansion and borosilicate has 3.3 ppm.
So, I believe that ebay seller: homeluxe-grandparfums is presently (Dec 2017) selling cheap borosilicate vials. YAY!

I am looking for punches to make 0.5 inch AKA 12.7 mm cuts from teflon tape. If no one has any leads on pre-made teflon liners, I'll make my own and test them for chemical resistance.

I was thinking a drop or two of hydrogen peroxide (3%) mixed in with fuming sulfuric acid might be a good test of oxidizibility. Can anyone think of a more corrosive substance that can be made from hardware store chemicals to test the quality of teflon that various tapes are made of?

Quote: Originally posted by JJay

Qorpak sells PTFE liners. Oh and I'd use something more concentrated than 3% hydrogen peroxide... I typically use 3 parts by volume concentrated sulfuric acid (fuming sulfuric acid is slightly stronger but not by much) and 1 part 30% hydrogen peroxide. [Edited on 25-12-2017 by JJay]

I just looked the MSDS up, and ROOTO is supposed to be 92.3%. So your typical analysis is closer to what it's supposed to be.

The MSDS doesn't mention any inhibitors; do you have any idea what kind of chemicals are used for inhibitors and why? ( I plan on using ROOTO to clean vials after organic chem, to get rid of trace amount of oils. )

Note: The yellow gas tape turned a fairly uniform brown after 24 hours. No further leaching occurred after the first half hour or submerging in sulfuric acid.

I added 1 drop of H2O2, 3%, which of course got very warm !
It didn't fizz, though. The tape started to turn back to yellow toward the top of the vial where the drop of H2O2 was added.

Then I added 1 drop of ~43% HCl. The tape turned more yellow at the top.
Then I added a few crystals of KNO3, hoping to relase nitrate ions and make a weak aquia regia type mixture. It outgassed very rapidly, and there's a good chance that all the NO3 was converted to oxygen + nitorgen by heat. I don't know. But, there was no noticable change on the tape. It's still yellow near the top of the vial, and uniformly brown all the way to the bottom. Even after 12 hours, the situation has not changed. ( Edit: I spoke too soon, the tape is suddenly starting to turn white, 20 hours after adding the K2NO3. )

So, the yellow dye can be leached. eg: It can probably be "pickeled" to be less chemically active. ( I plan on trying sodium Hydroxide later, as well. )


Regardless of the outcome, using tape to make liners isn't a very practical idea. I bought a paper punch with 1/2 inch diameter. It very crisply cuts paper discs. However PTFE tapes (The normal white kind) are extremely thin, and tend to tear into strings that align with lengthwise with the tape. OTOH; The yellow gas tape is thicker, and does punch cleanly most of the way around. But since the tape itself is only 1/2 inch wide, it's impossible to align it and a very ragged cut always happens near the sides of the tape which gets pulled into the cutter.

So, basically, to be able to punch PTFE would require full density teflon sheeting that is on the thicker side (say 0.003 of an inch thick, ~0.08mm ) and significantly over half inch wide (>> 12.7mm) in order to punch cleanly. That's not available locally in my hardware stores, so it's an ebay or mail order item; buying qorpak caps is likely the best solution.

Doh!!! Qorpack caps also use the yellow colored PTFE. !!! , So, I'd still have to pickle them before using them on strong acids.

Thanks for the help.


[Edited on 30-12-2017 by semiconductive]

Quote:

Quote: Originally posted by JJay   I.. but I have seen for myself that Rooto definitely contains unwanted impurities: https://www.sciencemadness.org/whisper/viewthread.php?tid=75...

I bought rooto because several people on Sciencemadness mentioned it as good quality.
Mine happens to be a very clear solution, which really looks like distilled 98% solution. But you're right, it likely needs distilation to be used analytically. I do have a 300mm Vigerux column, and 300mm Allihn condenser, but the distillation temperature is daunting ... 218 to 260 Celsius. ( 500 Farenheit.) I've only got an alinco V stir rod ... and I think it might demagnetize at a temperature somewhere near that point.

I'm wondering about your thread; wouldn't 90%+ of H2SO4, distilling to an acid with only 8% or so more density?

What do you mean in that thread by "distilled to 1/3rd it's volume?" do you simply mean that ~2/3rds of the solution is distilled into a separate container, while ~1/3 remains in the boiler flask? eg: is the sludge in the boiler?

The color change of the precipitate reminds me of zinc oxide; ZnO turns yellow as it gets hot but is white when allowed to cool off. At the temperatures required to distill sulfuric, I imagine a yellow tinge would be noticable on zinc oxide and probably zinc sulfides.

I'm not sure if the color I saw on the tape could be related to impurities or not.
The yellow Teflon tape I tested turned dark streaky brown when hit with Rooto, and then after other acids are added the brown leaves the tape and drifts into solution (see picture). Most of the brown leachate precipitates to the bottom of the vial, but enough is still in solution to make the rooto turn slightly brown. But the tape is nearly white compared to the yellow it started out with.



This makes me wonder what the dye could be. I tend to think that organics would generally be oxidized by high concentration sulfuric acid with hydrogen peroxide added. I would expect them to turn to carbon, or hydrocarbon gasses. When you say you've seen techniques to purify sulfuric on youtube, did they try adding hydrogen peroxide before and after condensing the sulfuric to precipitate and destroy orgnaics?

I'm mostly interested in strong sulfuric for cleaning purposes; like getting rid of traces of oil on glassware, etc.

Although I could distill the Rooto, in the end, I would still also have to put it into another container ... because who knows if the impurities are actually part of the bottle or filler in the plastic Rooto uses. I'm not good enough with chemistry to be able to test it yet.


I have NAPA auto store battery acid ( 25 - 30% H2SO4) in another container. I'm guessing that would have to be quite pure because car batteries are ruined by side reactions caused by impurity ions like sodium, etc. The NAPA auto battery acid bag has held sulfuric for a long time but with a lot of water in it. I'm not sure how much the properties of H2SO4 change when it hits that 98% borderline fuming range. I've had the bag for over seven years ... which shows how slowly I've been using it; but I'd hate to distill the stuff just to have it ruin the bag; Watering it back down after going through distilling it seems like a waste too.

[Edited on 3-1-2018 by semiconductive]

Quote: Originally posted by semiconductive

I've seen several thicker teflon tapes, I've seen some tapered ground joint liners for $40 / set of three, but that kind of price is riduculous for a piece of teflon paper.

Quote: Originally posted by weilawei

Quote: Originally posted by semiconductive   I've seen several thicker teflon tapes, I've seen some tapered ground joint liners for $40 / set of three, but that kind of price is riduculous for a piece of teflon paper. Those tapered ground glass joint liners: I bought a set of 10 for about $35, years ago, and I virtually never use them. They don't seal particularly well, and they tend to be arduous to remove afterward (crinkling up, etc.). I don't recommend them unless you have an absolute need to avoid grease in your setup--and even then, it'd be worth the extra expense to buy the super pricey fluorinated grease just to avoid the hassle that is working with them.

Quote: Originally posted by JJay

I mean when 2/3 of the volume is distilled off, a precipitate forms. It is likely largely ammonium bisulfate from the destruction of the inhibitor. It is widely believed among hobbyists that Rooto is high quality sulfuric acid, but this is a myth. The specific gravity of high strength sulfuric acid is not really a good indicator of its concentration either; if you want to verify that it is 98%, you will have to do a titration. Check some density tables and check the precision of your equipment, and you will see what I mean.

Quote: Originally posted by JJay

The specific gravity of high strength sulfuric acid is not really a good indicator of its concentration either; if you want to verify that it is 98%, you will have to do a titration. Check some density tables and check the precision of your equipment, and you will see what I mean.

OK. The virgin teflon sheets came in the mail, finally .... only about a month later.
The sheets were obviously cut from a roll, because even though it was put into a cardboard press in the mail to keep it flat ... it still curled when removed. The mail package wasn't damaged, but there are also signs of dents on the surface. Ironing uncurled the teflon, but did not remove the shallow crease marks. SInce none of marks are deep, they don't appear to affect sealing of the flasks any. The glass vial lips will crush the teflon and replace the crease marks with lip dents ... so I don't think the wrinkles matter.

It turns out that either thicknesses of virgin teflon punches perfectly. I have extra teflon left-over even after making 24 liners for my bottles. If anyone wants them ... contact me privately. I'm happy to punch and get rid of the rest of the teflon for a worthy amateur just to recover my costs. I will do transactions on e-bay, so you are protected. It's going to be about 10 cents each (US) for the 0.3mm thick punched liners, and 25 cents each for the 0.5mm thick punched liners. They are presently punched at 1/2 inch (12.7mm) diameter which is typical for vial necks. If you want a different diameter, it will cost more because I'd have to get a different punch.

I can also coat one side of them with silicone to act as as a rubber spring to aid in sealing if anyone cares for the extra; just add $1.00 to cover the silicone cost.




[Edited on 23-1-2018 by semiconductive]

Quote: Originally posted by JJay

I mean when 2/3 of the volume is distilled off, a precipitate forms. It is likely largely ammonium bisulfate from the destruction of the inhibitor. It is widely believed among hobbyists that Rooto is high quality sulfuric acid, but this is a myth. The specific gravity of high strength sulfuric acid is not really a good indicator of its concentration either; if you want to verify that it is 98%, you will have to do a titration. Check some density tables and check the precision of your equipment, and you will see what I mean.

I've been trying to distill rooto at 150Celsius after adding hydrogen peroxide, and then later I tried adding some distilled water; I just wanted to to see if a bad distillation setup would work at lower temperature with moisture added. It does work (barely), and if I use a fish tank pump to move air across the surface of the hot sulfuric acid ... much more of the acid gets carried up the still and condenses in a standard allihn condensor. The water/peroxide doesn't even appear to be critical.

Unfortunately, without a piece of glass to force the acid to go through a "wet" spot during condensation, about half the acid stays in the air and gets out of the still and into the room where the still is causing a choking gas to appear. When I put a silicon carbide ball bearing on the vacuum take-off, almost all of the acid is forced to go through the acid pool where the bearing touches the cold glass. That seems to be enough to get almost all the acid out of the air. It can still be smelled ... faintly ... but it's at a very low level and not choking... the air exchanger is only six feet away for the whole house and it seems to be doing its job. No smell when more than 10 feet away from the still, even after running for a week.

I learned the hard way that concentrated sulfuric acid attacks silicon carbide and some of it dissolves into the collection jar. Once the surface of the marble became clear with silica only ... the dissolution appears to have drastically slowed down or stopped. The concentrated sulfuric in the condenser is perfectly clear ... but there is a slight brown from the silicon carbide in the collection jar.

I refluxed old 3% hydrogen peroxide solution at 120Celsius for a day to concentrate it before adding any to the acid. H2O2 bottles were over a year old, but about two quarts of solution concentrated down to just under 200ml after cooking for a day at 140Celsius with a vigereux column above it. I figure its > 15% now because even wiping off the surface moisture from a glass rod turned my skin instantly white.

After letting the H2SO4 cook with H2O2 (just a few drops) for a day or two I could see small impurities floating around in the solution, crystallized. So, I'm backing you up on your find that there is something in Rooto in spite of it being very clear. It's not pure sulfuric, whatever they added. I can't get a picture of the floaters as they don't show up in the camera easily.

I'm thinking of making a water-glass frit and silicone exit plug to allow air out ... but preventing strongly polar chemicals from getting out in the air. (Silicone has non-polar bonds, so strongly polar acid gasses like sulfuric ought not want to go through.)

Lower temperature distillation seems possible, if the still is properly constructed and air is used analogous to steam distillation.

Unfortunately, the European 24/40 joints I have are not truly ground but stamped on a machine. I can see air bubbles in the joint where there are small gaps in the tapered surface. A tiny bit of sulfuric can work its way out the joints through those concave areas .. say a drop every four hours or so. It ruined the washcloth that I was using as an insulator to keep the boiling flask temperature up. Sigh.

I've got some valve grinding silicon carbide for a car engine from NAPA ... perhaps after crushing it fine with a hammer I can use that to regrind the glass joints against each other to get rid of the slight concave points that are leaking acid. The only other thing I can do is use my welding torch to heat the inner tube of the allihn condenser, and widen the tube at the mouth so liquid isn't trapped there against the glass joint in the first place. It seems that allihn condensers aren't very carefully designed to avoid trapping fluid....

Quote: Originally posted by semiconductive

I've got some valve grinding silicon carbide for a car engine from NAPA ... perhaps after crushing it fine with a hammer I can use that to regrind the glass joints against each other to get rid of the slight concave points that are leaking acid. The only other thing I can do is use my welding torch to heat the inner tube of the allihn condenser, and widen the tube at the mouth so liquid isn't trapped there against the glass joint in the first place. It seems that allihn condensers aren't very carefully designed to avoid trapping fluid....

Quote: Originally posted by semiconductive

It seems that allihn condensers aren't very carefully designed to avoid trapping fluid....

Quote: Originally posted by Deathunter88

I don't think allihn condensers are used for simple distillations, rather refluxing in the vertical orientation.

Quote: Originally posted by JJay

I wouldn't bother grinding those joints any more; they are only airtight if they are sealed with grease or something. Pretty much the only oil or grease that would seal effectively at those temperatures is sulfuric acid, and even it would be boiled off pretty quickly.

Quote: Originally posted by Ozone

I've had good results with these at up to about 160°C. A small stir bar will fit just fine. I will also tell you that if your reaction takes off, it will strip the threaded plug out of the glass--which remained intact (not so much objects hit by the projectile or the oil bath it was in). You may also need to clean out your pants. https://www.ebay.com/itm/Chemglass-15mL-HW-Cylindrical-Press... O3

Those are basically what I want to put the little glass vials inside of to do reacctions. Right now, I can only put them in a steel container that can withstand explosions with silicone oil over the top to keep the glass vial from taking the pressure by itself .. but with a good pressure reaction vessel, I'd be able to see the reaction going on inside the disposable glass vial; That way I can see the reaction going on, and if the vial is still surrounded by silicone oil; even if it's ruined by a burnt chemical or even if it breaks ... the more expensive pressure reaction vessel should still have a layer of protection.

Thanks, that idea is definitely a step up from what I have.