Neon - Argon mixture

[ErikPaul]

So I've been working on making my own nixies, main dream is to produce a tube using uranium glass tubing in place of your regular boro or soda lime glass. In sourcing fill gases(not a huge quantity of suppliers who sell in small quantities to non-commercial) i keep coming across a mix called "K4" which is 75% neon 25% argon. My question is would the much higher percentage of argon make the breakdown voltage too high? I found a couple of Ne-Ar voltage to concentration graphs but the highest Ar % that they show is 5%, but it looks as though the curve trends upwards with higher %.

My main draw to the K4 is it would remove the need for separate Ne and Ar valves and inlets. My gut tells me that it won't work well but I figured I'd chuck the question to the experts(you guys).

Erik

Here is a link to the graph I mentioned

http://www.lamptech.co.uk/Documents/SO%20Gas.htm

[gregebert]

The well-known Penning mixture is 0.5 to 2.0% Argon, and that seems to fit with your graphs. Mixing this on your own into the tube itself could be challenging due to the small fraction of Ar; You might be able to find it pre-mixed, or otherwise try to mix K4 with neon on your own in a separate gas cylinder. I dont know how you would measure the gas concentration after mixing. Maybe spectral analysis after-the-fact ?

I wanted to do my own neon art years ago, but was put-off by the dangers of bombarding and the cost of the vacuum equipment. From what I've read, you need a diffusion pump to get down to a few microns if you want good quality tubes. An alternative to the high vacuum might be to pump-down as far as your vane pump will go, then "flush" the impurities with neon and re-evacuate.

I'd really like to know what you had to go thru to get your first glowing tube, so please keep us updated.

[Nick Andrews]

Okay, so I can confirm I'm not the only psycho with crazy aspirations...  Using U glass seems like a very cool idea.  Watching Dalibor's videos is mesmerizing and I can't imagine the frustration and hours of trial and error he went through.  But that's half the fun, right?

A diff pump or turbopump setup and I think a way to bake out the tube to get that last little stubborn fraction of molecules sticking to the inside to release.  Keep looking on ebay and you can find pumps and such.  I recently sent a deal to a friend I saw at $250 for a small turbopump with controller.  Thought about buying it myself as a secondary, but my junk stash is already quite large.  I am buying parts to build a functional system for all sorts of experiments and would love to get some glowing tubes at some point.  Lasers, nixies, discharge, etc.  Just learning machining processes on my 11" Sheldon lathe and South Bend vertical mill, both 1950s vintage.  Logan 8" shaper is pretty antique as well.

As for mixing your own gas, like setting up an aquarium the larger the vessel and amounts of gas, the easier it will be to control the proportions and get it right or close enough.  Maybe a manifold with gases going in at same pressure/flow rates, through same orifice sizes, and solenoid valves controlled by a uprocessor to get the ratio you want?  Flow gauges for argon used in welding are easy to come by with a little ball that shows flow rate.  These might be calibrated for specific gases.

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[ErikPaul]

Greg

I actually contact every supplier of small neon cylinders about getting the gas premixed, and most of them discussed the difficulties you mentioned about getting the proper mix in small quantities. The cheapest I could find for a pre-mix was ~$350, which is quite a bit more than I am looking to spend on my mad science project. 

Nick

I found a used diffusion pump on ebay for less than $100.

The best idea I have come up with is to try to outlet a small shot of argon and then fill the remaining with neon up to the desired pressure. I am using swagelok metering valves which have a rated flow coefficient, which one might be able might be able to calculate the time/position of the valve opening. In watching Dalibor's video(his website is the best resource I've found, but there are two YouTube videos of others who created their own nixied. One is a Darth Vader including a light saber!) you can see him using the swagelok metering valves that have micrometer knows for precise control.

My main concern is what the extra argon in the k4 mix would do to the striking voltage. I could simply use pure neon but that would lead to shorter life, but as my goal isn't commercial production that may not be a big problem. 

One idea that did occur to me was to possibly harvesr/transfer the gas from another tube, as I just purchased a large lot of malfunctioning tubes on ebay. No idea how to accomplish the transfer without needing a pump but I may try to look into that option. 

[gregebert]

If you are looking for longer life, I dont think the gas mixture will make a big difference. The quality of the glass seal is the most important thing, and I suggest using kovar wire for your leads as it was formulated to seal with glass. Second, you will need a good vacuum and need to bake-out the impurities by running at high temperature. For neon signs, this is done during the bombarding process and electrodes get red-hot while the glass gets to several hundred degrees; one trick is to see if the glass is hot enough to burn newspaper. Lastly, electrode degradation from sputtering will literally cause electrodes to "dissolve" over time, so choosing the right material and adding a small amount of mercury has been done by many manufacturers. If you look thru this forum, you should be able to find a link to a scanned copy of the Weston book (Cold Cathode Discharge Tubes); it's pretty heavy reading but will give you more knowledge than you  can imagine.

[artg...@gmail.com]

There are some ideas for creating gas mixtures here : https://www.youtube.com/watch?v=Ax7xlcFS2QY&t=567s