Sciencemadness Discussion Board

Cork stopper chemical resistant, and other information

Yttrium2 - 18-11-2015 at 11:24

Are cork stoppers good? Do they hold up well to a variety of chemicals?

Why are corks used as stoppers? Tell me something interesting about corks, and of the material comprising them

Praxichys - 18-11-2015 at 12:54

Cork stoppers are terrible.

They're porous and absorb chemicals, making them hard to clean and lead to contamination if re-used.

Being wood, they're not very resistant to much in the first place, are attacked readily by strong acids and alkalis, and can even be dangerous when used with some oxidizers.

The only good thing about them is that they are cheap. They were used a long time ago before synthetic rubber stoppers came about, since they were good at making seals with glass and could be shaped easily to intorduce electrodes, tubing, etc.. At the time, their shortcomings were often compensated for by soaking them in a sodium silicate solution.

If you want to learn about how they're made, use Google!

Magpie - 18-11-2015 at 13:03

Some solvents will swell rubber stoppers. Cork won't do that.

Sulaiman - 18-11-2015 at 13:39

"Tell me something interesting about corks"

. when suspended by string from the rim of a hat they do not stop flies.
. Australian import of cork for wine bottles peaked around mid 2002, now mostly plastic.
. corks are much easier to bore a hole through than rubber bungs
. corks are not airtight, especially when dry
. corks look more alchemical than rubber bungs


edited ... 2002 was 2012

[Edited on 18-11-2015 by Sulaiman]

aga - 18-11-2015 at 14:39

Please confine this this kind of utter random Garbage to Beginings, Whimsy even.

I thought my threads were bad enough.

Either follow the general Idea of this forum or at least come up with Better random garbage, please, pretty please.

Edit:

If you'd stop wondering what Other people were thinking about you, perhaps you'd have a lot of time to do stuff You want to do.

Depends if you want to actually Do anything i guess.

Further Edit:

Perhaps you'd rather Do Nothing and just Moan endlessly about 'Unfair', 'Not My Fault', 'Nothing I Can Do', 'My Parents Fault' etc etc as most of the wasted lives do.

Deaf ears and No tit to suck on is what happens.

[Edited on 18-11-2015 by aga]

annaandherdad - 18-11-2015 at 19:12

I've been working with NO2 and HNO3. Both of them eat up rubber stoppers, especially HNO3 which is vicious. Webb (the book in the library) recommends coating stoppers with paraffin when working with NO2. I tried it with rubber stoppers, but the paraffin would just fall off. So I bought some corks, and I'm going to try them. The hope is that the paraffin will fill the cavities in the cork and stick to it better than it did with rubber stoppers. Plus I'm thinking that with a heat gun I can melt the paraffin and make a better seal. I'll let you know how it works out.

If this fails, I'll have to buy teflon stoppers. I might have done that already, but I can't figure out if the teflon stoppers I see advertised can be drilled for glass tubing, or what the sizes mean, and they're pretty expensive so I don't want to buy some without figuring all this out. Need to research the topic, but first I'm going to try paraffin on cork.

Magpie - 18-11-2015 at 20:04

Quote: Originally posted by annaandherdad  

If this fails, I'll have to buy teflon stoppers.


Take a look at the Cole-Parmer chemical compatibility chart. Viton might work for you here.

Upsilon - 18-11-2015 at 20:06

I've been down the same road as you.

Trust me, use ground glass joints.

Yttrium2 - 18-11-2015 at 22:05

Quote: Originally posted by Upsilon  
I've been down the same road as you.

Trust me, use ground glass joints.


But then all the ghetto liebig condensers would become impractical. The issue is finding a seal that is resistant. It is always easy to make various liebig condensers for various applications but having a good seal between that and the glass is tricky

Whats wrong with cork??? I'm willing to bet it won't dissolve or cause problems in a variety of solvents. How can I check corks compatability?

Ground glass is expensive, and if you don't need it ya dont need it

[Edited on 11/19/2015 by Yttrium2]

User123 - 19-11-2015 at 02:43

Wrap it in PTFE tape. That will solve the problems of chemical compatibility and porous joints. Same goes for rubber bungs.

Praxichys - 19-11-2015 at 05:38

Nitric acid is not friendly to cork. You will essentially be making nitrocellulose - a disaster waiting to happen. Pure HNO3 is violently reactive and will ignite a ball of tissue paper when pipetted onto it. Think of what will happen if it soaks into a cork! At worst you could experience an explosion. Please do not do this.

The pure acid boils at 83C and the azeotrope at 120C. The highest melting paraffin I can find online commercially melts at 75C... the wax coating on your stoppers will be a liquid at that temperature.

Sometimes there really is no safe substitute for ground glass. Regrettably this hobby is expensive, but using cork for HNO3 is like saying you're going to rebuild an engine with the screwdriver set from the kitchen drawer. You might be able to do a shoddy job once or twice but eventually you're going to get hurt.

It's not too hard to get ground glass. You can get something as simple as this for less than $35 and free shipping. (Although I'd recommend something more like this since its parts can be reconfigured for reflux, and are compatible with other pieces you might purchase in the future.)

Not trying to sound like an elitist douche but with the formal experience now I sometimes wonder how I survived my early years of experimentation.

annaandherdad - 19-11-2015 at 08:23

Magpie, Upsilon, Praxichys, thanks for all your suggestions. All my work with NO2 and HNO3 is cold, so there's no problem with the paraffin melting. I'm experimenting with making HNO3 by combining water with liquid NO2. It's all done about 0 C or lower. I tested some RFNA on a paraffin block and it didn't do anything I could see. On the other hand, it does set nitrile gloves afire, with lots of smoke. I know HNO3 will destroy cork, but I'm hoping the paraffin will protect it. The paraffin covered cork will come into contact with HNO3 vapor, but not liquid. I tried teflon tape on my rubber stoppers, but the HNO3 vapor worked around the tape, especially where the glass tubes came through, and it destroyed the stoppers. As I said, I may be forced to use teflon stoppers, if I can figure out how to get glass tubing through them. I'm also using simple PVC tubing for the NO2. The NO2 does attack it, discoloring it, but slowly. My apparatus is pretty complicated, with lots of valves and things, so I don't think all glass equipment is practical. I can get teflon tubing if I have to, the stoppers seem to be a bigger problem.

annaandherdad - 19-11-2015 at 08:29

By the way, when I bought my teflon tape at the hardware store, I was surprised to find that it wasn't sticky on one side. That's what I expected for something called "tape". So I had to use glue to hold it down to the stoppers. When you guys use teflon tape, how do you hold it down?

annaandherdad - 19-11-2015 at 08:33

Another by the way: I got a small amount of RFNA on my fingers, and although it sets gloves afire, it didn't damage my fingers any worse than ordinary 68% HNO3 will do. That is, it stained my skin yellow. It was just a small amount, washed off rather quickly.

MrHomeScientist - 19-11-2015 at 10:46

It's called tape more because of its shape rather than adhesive properties. It sticks to itself decently (especially when applied with pressure) but that's about it. I just wrap the tape around the part in question and it works fine, never had a problem with it falling off. But I rarely use it, because ground glass is the way to go. I use silicone grease from Home Depot (near the faucet supplies) to grease the joints.

They also sell yellow gas-tight PTFE tape, and I've wondered if that would do better for chemistry applications. When wrapping joints generally you only want one layer, otherwise the joints won't seat properly.

annaandherdad - 19-11-2015 at 17:53

MHS: Thanks for the info. I've enjoyed your videos, wanted to write to you about some of them.

[Edited on 20-11-2015 by annaandherdad]

Texium - 19-11-2015 at 18:01

Quote: Originally posted by aga  
Please confine this this kind of utter random Garbage to Beginings, Whimsy even.

I thought my threads were bad enough.

Either follow the general Idea of this forum or at least come up with Better random garbage, please, pretty please.

Edit:

If you'd stop wondering what Other people were thinking about you, perhaps you'd have a lot of time to do stuff You want to do.

Depends if you want to actually Do anything i guess.

Further Edit:

Perhaps you'd rather Do Nothing and just Moan endlessly about 'Unfair', 'Not My Fault', 'Nothing I Can Do', 'My Parents Fault' etc etc as most of the wasted lives do.

Deaf ears and No tit to suck on is what happens.
Why does it seem like so many of your posts lately have sunken to the level of unsolicited flaming?
Sure, it wasn't the best way to start a thread, but a fine discussion of the pros and cons of corks and other stoppering materials came about from it.

Personally, I try to use ground glass or PTFE whenever possible, but I think corks would probably hold up pretty well to some organic solvents that would dissolve or swell rubber. They may leak over time, but for short term use in a pinch it shouldn't be too bad.

IrC - 19-11-2015 at 22:50

Quote: Originally posted by annaandherdad  
By the way, when I bought my teflon tape at the hardware store, I was surprised to find that it wasn't sticky on one side. That's what I expected for something called "tape". So I had to use glue to hold it down to the stoppers. When you guys use teflon tape, how do you hold it down?


Apply slight steady tension as you wrap it around far enough to have reasonable overlap. What about mechanically holding cork stoppers submerged in molten paraffin for awhile? Would that work better? Possibly using boiling paraffin if you deal with fumes and have no ignition sources the vapor can reach?

careysub - 20-11-2015 at 13:24

Quote: Originally posted by IrC  
What about mechanically holding cork stoppers submerged in molten paraffin for awhile? Would that work better? Possibly using boiling paraffin if you deal with fumes and have no ignition sources the vapor can reach?


That's how I would to it, stick it on the end of sharpened stiff wire (a coathanger perhaps) and submerge it in molten paraffin.

I treat copper and bronze chainmail (therein lies a story) with paraffin to protect from corrosion by immersing it in molten paraffin. It does not need to be very hot, just enough to be good and fluid.

For chainmail I lay it out on cardboard or towels and heat it with a heat gun to get the excess paraffin to run off.

annaandherdad - 20-11-2015 at 20:27

Quote: Originally posted by IrC  


Apply slight steady tension as you wrap it around far enough to have reasonable overlap. What about mechanically holding cork stoppers submerged in molten paraffin for awhile? Would that work better? Possibly using boiling paraffin if you deal with fumes and have no ignition sources the vapor can reach?


I'll try it (tension with the teflon tape), but I found it difficult to work with when I tried it on rubber stoppers. As for the paraffin on the cork stoppers, that's exactly what I plan to do (hold them under molten paraffin). Don't have to heat it too hot. Also, I'm thinking that after I run glass tubing through the stoppers, I can just run a heat gun over the thing to melt the paraffin to create a seal around the tubing.

This project has been going on for a long time, I don't have much time so progress is slow.