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Author: Subject: Inert test tubes & teflon (or glass) cap liners.
semiconductive
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[*] posted on 16-12-2017 at 21:44
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?

2dram.png - 5kB IMG_20171216_150125_121.jpg - 517kB


[Edited on 17-12-2017 by semiconductive]
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[*] posted on 17-12-2017 at 02:38


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.
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[*] posted on 17-12-2017 at 10:46


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.


I have Erlenmeyer flasks with keck-clips to hold ground glass. Even at full boil of water, they don't shatter. There's pressure release. So, not all glass shatters at high temperature or even pressure if set up correctly. Urea does not generate much pressure, and never shatters glass: note: That's one of the chemicals I mentioned in the O.P.

However: There are techniques I have developed to handle vials as well under pressure even with cheap and thin walls.

Vials can be put in a sealed thermal chamber with silicone oil over the top of them and no air space. Since silicone oil is incompressible, the vials are not able to shatter ... they are only able to be contaminated by silicone oil if there is any leakage. And if the chemicals are corrosive or damaging to phenolic caps ... it's a matter of time before they weaken the cap due to chemical attack.

Borosilicate glass is far better than normal glass when it comes to handling shock resistance and leaching of alkali into solutions. That's the only reason I mentioned that I would rather have definite borosilicate than regular glass.

From the data I have seen on glass corosion, there are other glasses that are even more resistant to alkali attack than borosilicate. Kimble glass )Tm) , for example, etches much slower than than Pyrex (Tm) according to data easily found on the web.
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[*] posted on 24-12-2017 at 13:40


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?
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[*] posted on 24-12-2017 at 16:09


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]




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[*] posted on 26-12-2017 at 15:24


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]


Thanks! I found quorpack, and they do indeed sell green thermoset caps with PTFE liners for a quarter dollar each. I'm not sure what threads the vials I have are .. but even if the caps don't fit the vials I got, the liners will work ... so it's worth buying a set to test.

I don't see H2O2 in concentrated form, locally. I'd have to evaporate some 3% down or mail order it. Mail carriers seem to get antsy over 30% peroxides and charge more, so I'll test a few drops of the 3% stuff first to see if there's any obvious effect.

I put the yellow teflon "full density" gas tape into 97% sulfuric acid (Rooto from ACE hardware), and am letting it set to see how much dissolves.

Before I put the tape in, I could see it was white near the edges and yellow in the middle; so I think the yellow color may be mostly a surface dye.

Once in the acid, the tape immediately turned from yellow to dark orange in some places near the middle of the tape. I think something is also diffusing into the acid by the look of it ... If the color is just a surface coating, maybe most of it will dissolve off.
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[*] posted on 26-12-2017 at 17:57


If your Rooto is 97%, you got a good batch. I find that it is typically around 90% when analyzed using the best methods I have available around the lab. It contains inhibitors.

I think you can ship small quantities of hydrogen peroxide ORM-D. I get mine from a hydroponics store.





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[*] posted on 29-12-2017 at 11:24


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. :D

Thanks for the help.


[Edited on 30-12-2017 by semiconductive]
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[*] posted on 30-12-2017 at 00:20


I saw the name of the inhibitor stated at one point but the source was a bit dubious, and I have not been able to find it again... but I have seen for myself that Rooto definitely contains unwanted impurities: https://www.sciencemadness.org/whisper/viewthread.php?tid=75...

If you want really clean sulfuric acid and all you have is drain cleaner, you will have to distill it. Everyone wants to avoid doing that, and there are 20 different YouTube videos claiming that the channel owners can obtain pure sulfuric acid OTC by some cheap and easy method that doesn't involve distillation, but they are all wrong.




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[*] posted on 2-1-2018 at 15:22


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.

bleachtape.jpg - 39kB

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]
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[*] posted on 2-1-2018 at 15:37


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.
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[*] posted on 2-1-2018 at 15:48


semiconductive, you seem to be doing pretty good at chemistry so far.

B.P. of sulfuric acid is a good bit higher than you specify, though. Sorry to burst a bursted bubble further.

When a binary solution is boiled, the more volatile component leaves at a higher rate. The lower boiling compound usually leaves a bit, too. The distillate will have more of the more volatile compound, and the boiling flask or "bottoms" will have more of the less volatile component. "Distilled to 1/3 volume" probably means that it may or will take distilling off 2/3 of your total liquid before your bottoms will reach a concentration of 98% H2SO4, the azeoptrope (I dunno because I didn't check the thread). You can also concentrate it on a beaker on a hotplate, outdoors or in a hood, although I have never done it I am sure it is pretty straightforward: drive off water until you reach a room temperature specific gravity of 1.84, I think.

Edit: Though I have never done the beaker method, I would probably use heavy boiling chips (porous ceramic chunks, broken coffee mug) because H2SO4 bumps like something I've never seen. Regular boiling chips float on the surface of the acid.

[Edited on 1-3-2018 by happyfooddance]
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[*] posted on 2-1-2018 at 19:23


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.




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[*] posted on 2-1-2018 at 20:17


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.


That doesn't surprise me. I am hoping to figure out a way to slightly regrind glass joints using fine silicon carbide grit to improve glass joint seals, and after connecting the joints -- wrapping the outside of the pipe with teflon tape a lot of times (I've got two rolls of Teflon with nothing to do...and it's wasted money anyhow.);

I don't have the hands on experience with all the lab equipment yet; but for most of the stuff I am planning to do, I think plain silicone oil may work OK as a grease; as long as I can clean it off afterward.

For the little glass vials, I just ordered two virgin white PTFE sheets at 0.3x100x100mm and 0.5x150x150mm respectively from China. Since I only need to make half inch disks to seal the vials, even 100mmx100mm sheets should easily make 24 to 36 cap liners by punching. (I only need 24 total. )

The thicker PTFE sheet is just in case I don't get perfect punches from the thinner sheet. I'll let everyone know which works best ... and I suppose I could sell off any good extras to recoup some of my costs for the punch and wasted tape. (P.M. me as customelectronic on ebay if you care). I think vials have pretty standard neck sizes, so 1/2 inch (12.7mm) necks should be fairly common.

I also have a way to make a silicone backing to imitate the foam backing that my vials were sold with, but with better chemical resistance. With that for a spring loading and a Teflon liner, I don't think I should have any serious risk of chemical contamination problems or cap failures.

Even if the PTFE material isn't "full density" its extremely thick compared to teflon tape and no porosity issues or chemicals from seeping into the phenolic caps. I'll let everyone know how it comes out after I test them.


[Edited on 3-1-2018 by semiconductive]
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[*] posted on 2-1-2018 at 21:21


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 see. Again, sorry, I didn't check the thread he was talking about, I made an assumption about what I thought he was talking about.

You are correct, I always rely on a titration, even when a thermometer says 335 for 12 hours. Carefully neutralizing and weighing the residue works well, I usually do these and a few other analytical things, just so I can sleep well at night. I mean, spending all day and risking life and limb to distill this stuff, it isn't really going much farther to check its purity.
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[*] posted on 2-1-2018 at 21:57


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.


Right now, I'm having trouble being sure of the density measurements for plain water. See the end of my other thread on volumetric flasks.

https://www.sciencemadness.org/whisper/viewthread.php?tid=78...

I've figured out that air dissolution really messes up density measurements of most liquids.
I'm not finished with that thread, so answering your post is a bit of a chicken and egg problem as there will be more posts. I've been testing Henry's law at boiling, and comparing data sets with those made by other people like engineering toolbox, but I managed to delete my gnuplot graphs so it's going to be a few days before I can get it all back and re-enter data.

The problem is that gas dissolution charts expect "equilibrium" conditions, and steam flowing away from a flask is not equilibrium ... So the meaning of the charts showing de-gassification by boiling is very tricky to compute; it requires the partial pressure of steam to be corrected for how much gas is actually trapped over the liquid at equilibrium.

On the other hand, liquid is *SURPRISINGLY* susceptible to volumetric distortion by dissolved gas, and potentially allows very sensitive and cheap tests to be developed based on volume rather than full titration. But, I'm not there yet. Even water is very non-linear in it's expansion with temperature, and reviewing thermodynamics after 25 years is a bit slow for me. I'm used to doing statistical mechanics at the quantum level, and the crude thermodynamics used for water and chemicals is just painful.
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