Making Gas Discharge Tubes.

[jdurg]

I've got a question about manufacturing those gas-discharge tubes which you can use to 'see' gasses. For my element collection, I picked up a set of tubes which were bent into the shapes of the symbols for the element they contain. (I bought them from Max Whitby a few years ago for my Noble Gas samples. They are INSANELY awesome looking). So while I have my noble gases in the form of a discharge tube, I don't have the same for my hydrogen, nitrogen, and oxygen. I asked Max if he'd be able to custom build those tubes for me, and he declined saying that the heat given off by hydrogen, nitrogen, and oxygen was too risky. I do know that those gases give off a lot of heat when excited, but I never have my tubes on for more than a few seconds anyway, so the heat isn't too big of a problem.

 

Therefore, I have decided to make the tubes myself. I decided to start with nitrogen since that's the easiest one to bend. I know that you have to bend it into the proper shape, then seal off one end with an electrode and pull a vaccuum from the other end. You then introduce a small amount of nitrogen gas and seal off the other end with an electrode. My question is, what is the electrode that you use? Could I simply just put a piece of wire in there and seal the glass around the wire, or are there special electrodes to use for these? I think this is something that could easily be done and result in a fantastic display for these three otherwise 'boring' gases. What are your thoughts?

[raivo]

No you can't simply put piece of wire. Main concern is that your electrode must have aproximately the same coeficent of theraml expansion than glass.

 

Usually molybdenium wire is used ( if i remember it right ). Another way is to use strip of very thin metal foil. I have seen it on some xenon tubes that were used for lasers.

 

Edit: If you have time to experiment you can try various available wires. ( for example those you get when you break ordinary tungsten lamp ) If glass will not crack after cooling down and wire sits firmly in place then this is probably ok.

[Gilded]

Smart Elements has brilliant discharge tubes. Deuterium and oxygen, for example. No nitrogen though, and they're awfully expensive. :S

[jdurg]

Smart Elements has brilliant discharge tubes. Deuterium and oxygen, for example. No nitrogen though, and they're awfully expensive. :S

 

Smart Elements is VERY expensive. I think I saw that they were charging about 530 U.S. Dollars for a one-ounce bar of palladium. That's almost 2.5 times the actual cost! The only thing I ever bought off of them was my cesium ampoule because they were offering it really cheap trying to get some business.

 

Also, thank you for the input Raivo. With nitrogen, hydrogen, and oxygen it is very crucial to remember the expansion of the glass/electrode since those gases get really hot when they are 'excited'. I had completely forgotten about that. Thanks for the heads up. I'm pretty sure that there are sites online I can go to in order to get the electrodes I would need.

[YT2095]

I confess to having used plain old solid core copper for my electrodes in the past, with remarkably good results too.

so good infact I`ve not changed from using it since. I agree it`s not the BEST metal, but I`m never intended to use it as Caliubration equip, just something to create interesting light effects with different gasses, and some with NO gas.

 

the no Gas ones I use a "Getter" in, and it has little effect color wise too

 

I think more than the electrode type, attaining the Vacuum with a pure gas sample will be the hard part.

[jdurg]

It won't be all too hard. The first thing you would do is fill the tube with an excess of the gas that you want. Then you try and pull a vacuum on that with your vacuum pump. Unless you have a really good pump, it won't pull a complete vacuum in there which will leave your wanted gas in the tube at a low pressure. It's one of those cases where a cheap vacuum pump may actually be better than a really good one. The only thing you have to deal with is a backflow of gas, but if you have it setup right there won't be one.

[YT2095]

that`s VERY similar to the proc I use anyway, so you`re part way there

 

 

I have the 2 electrodes already sealed and embeded, and then a small bleed tube (a bit larger bore than a capillary tube), I inset a hollow needle in the tube (the sort used for intramuscular injections) then flood the tube with the gas VERY SLOWLY! and for several minutes, while the tube is HOT, then I quickly attatch the vac and suck out all I can still keeping the tube hot.

 

when I can`t remove anymore, I melt the Bleed tube GENTLY!!!!!, it`ll compress it self, then pull the excess off while still heating, then I heat the bleed tube to a ball end and cover it with plastic pipe and fill it with resin so it doesn`t break by accident.

 

it sounds a bit complicated, but if I showed you, you`de not beleive how easy it is to DO, rather than type

[jdurg]

You want to know something scary? I COMPLETELY understood everything you just wrote. lol. That's generally the process I was going to use since having the tube at the high temperature will make sure that the gas is in there at a high pressure. As it cools off, the gas will lower in pressure as well, thus giving the nice low pressure that you want in a discharge tube. (While higher pressure will output more light, it will also shorten the life of the tube. The low pressure gas will still give off a TON of light). The trick for me will be bending the tube into the shape of an N for the nitrogen gas. That will take me quite a bit of time to do, so it may be a few months before it's all set and complete. My goal is to be able to produce glass tubing in the shapes of the elements they contain. Max Whitby over at RGB already has tubes setup for the noble gases, but there are none for hydrogen, oxygen, and nitrogen. I would like to make those tubes for myself, but I'll be practicing with a helluva lot of nitrogen before I attempt oxygen and hydrogen. (I think oxygen and hydrogen may be a bit more dangerous due to their reactivity).

[YT2095]

I wouldn`t use Oxygen with Copper in that case then, it may degrade the O2 trace over time

 

as for Glass bending, it IS an aquired skill

I have 50 half metre lengths here X 6mm. I have broken a few and messed a few up whille practising, but you can always make Pipettes & Stirring rods from the smaller bits. I can make almost anything with them now though

[Gilded]

"(I think oxygen and hydrogen may be a bit more dangerous due to their reactivity)."

 

Yeah, I must admit that I wouldn't like a hydrogen discharge tube lit anywhere near something flammable.

 

"as for Glass bending, it IS an aquired skill :)"

 

I found glass bending to be quite easy. Depends quite a bit on the glass though, but I found it rather easy to bend glass tubes into different forms with a Bunsen burner (I've done it twice).

[YT2095]

it IS easy in principal, but to get it "Perfect" takes alot of practice!

just "bending" glass over a bunsen`s fine, but when you require a specific shape or form, it`s not so easy! you have to "Know" your glass

 

as for Hydrogen, Why???

what`s the big worry?

 

I`de sooner make H2 tube than an O2 one! anyday of the week

[Gilded]

"as for Hydrogen, Why???

what`s the big worry?

 

I`de sooner make H2 tube than an O2 one! anyday of the week :)"

 

Well yeah, probably, but I've been told not to trust in elements that only have one proton. No really, probably if I'd have to choose between O and H, I'd probably take the H. Unless it's a choice of what to breathe.

[YT2095]

well you`de get less than a few mls of Gas if the tube broke anyway, of EITHER gas

 

under High Vac, a mix of H and O with a discharge, I`de be quite surprised if it did anything "dangerous". it would certainly decompose with continued discharge, I strongly doubt it would react as they would at standard RTP tho.

 

not if your vac is good enough!

[jdurg]

With Oxygen I'd have to use a platinum electrode or perhaps a silver one. Whichever element won't react with oxygen at a high temperature. (If it's melting point wasn't so low, I'd use indium since that's very 'unreactive'. I'm not sure if silver reacts with oxygen at any temperature though. I know that silver tarnishes, but that's due to halogens and sulfur oxides in the air). Hydrogen's just fine as long as there's no oxygen in there.

[YT2095]

make a well spaced "Curly" in the wire before it hits the resin sealant

 

I use about 5 turns with a 1mm pitch, also sharpen the electrode tip, for some reason you`ll need less voltage for an "Arc" trigger than with a rounded tip