On Thursday, 12 February 2015 14:20:39 UTC, johnk wrote: > > > Maybe I am missing something when it comes to the way this works, but, > when it is not a vacuum as is required for a valve/tube then what about the > idea of pump a bit, add some of the eventual gas, pump again etc. The > original impurities would distribute 'evenly' through the added gas and > when it was pumped out a percentage of that older pollutant would be > removed again. Thus it seems to me that a quite 'feeble' pump can do the > job when the eventual fill is a gas [even if at a lowish pressure] >
There are many issues involved in making tubes, and getting the right pressure and gas mix is just a small part. The glass, and all the other mechanical components, contain impurities that have to be removed during manufacture else they will taint the behaviour and life-span of the finished tube. Impurities are found in all components, - moisture and other organic and non-organic contaminants will even embed in the glass walls and survive the initial chemical cleaning phases - these contaminants have to be baked out under a decent vacuum, typically around 1 micron (10-3 Torr) which is about 1/750,000 of an atmosphere. Whilst this sounds like a high vacuum, its actually pretty easy to obtain with straight-forward kit. A TM pump is distinctly over-kill (several orders of magnitude better), but, hey, if you have one, then flaunt it baby! (slight paraphrase there from Zero Mostel!). Even small levels of contaminants will cause quality problems.To avoid this, the tube is baked (various techniques exist for this) to release the contaminants whilst being pumped to about 10-3 Torr - the pumps remove almost all the cr*p. Then the pumps are sealed off and an amount of the highly pure nobel gas being used is let back in - in the case of nixies, this will be about 99% neon and 1% argon at a pressure of about 30 Torr - about 1/25th of atmospheric pressure - and the tubulation is sealed. The above is a very simple explanation - it does not explain about induction heating or "Bombardment" or how mercury is introduced etc. but the principles are the same. Nick -- You received this message because you are subscribed to the Google Groups "neonixie-l" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send an email to [email protected]. To view this discussion on the web, visit https://groups.google.com/d/msgid/neonixie-l/2ca373d4-057b-4fe8-a743-986d7af21c6e%40googlegroups.com. For more options, visit https://groups.google.com/d/optout.
