Re: Golka's Wendover "secret" gap

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: Jim Lux <jimlux@xxxxxxxxxxxxx>

At 07:03 AM 9/27/2005, Tesla list wrote:
> Original poster: Russell L Thornton <Russell.L.Thornton@xxxxxxxx>
>
>
> Greetings All,
> As a temporary lurker here I usually refrain from comments and leave 
> it to the experts.  However in the case of SF6 I do have some experience.
> I have 17 years of radar experience with the Air Force and we use it 
> in the waveguides of high powered radars.  The purpose is to provide 
> additional insulation above normal compressed air or 
> nitrogen.  Typically our pressures are lower than the 45 PSI 
> mentioned in Jim's website.  I don't have a copy of the curves with 
> me but I believe that increasing the pressure asymptotically 
> approaches a limiting insulation effect.

It should increase without limit in direct proportion to the density 
(until the SF6 is liquefied).. SF6 follows the Paschen law, just like 
most other gases.  There are practical problems, and if you have 
mixtures of gases, it gets more complex.


>  My main point is that the idea is to NOT have an arc in our 
> systems.  If an arc does occur it converts the SF6 into a white 
> power that must be removed by maintenance before resuming operation.

Those would be the fluorides resulting from the SF6 decomposing into 
S and F and the F reacting with other stuff in the chamber.


>   I cannot imagine designing a system that continuous exposed SF6 
> to arcing.  Maybe that is why it was a secret!
> An alternative that I noticed in the Reference Data For Radio 
> Engineers is Freon 12 ( I know, It's an old copy).  However, R134a 
> is still real similar to its predecessor and may exhibit similar 
> insulating characteristics.  It might be worth some 
> experimentation.  Then that could be a secret!

The various halogenated hydrocarbons (R-12, R134, etc.) all work 
moderately well.  I think the reason that SF6 is preferred are:
1) It's traditional.. it's been around longer and people know that it works
2) It used to be cheaper than R-whatever
3) It doesn't produce phosgene gas on contact with hot metal, like 
most chlorinated hydrocarbons do
4) It doesn't produce HCl on decomposition, either.
5) because it uses Fluorine, rather than Chlorine, it recombines 
faster, providing a higher breakdown strength for a given density.
6) It's really dense, and to a first order, breakdown strength is 
proportional to density.

That said, there are a lot of other substances that might work as 
well:I think they use hexafluoro cyclopropane (C3F6), for 
instance.  I think there is a real incentive to avoid compounds that 
don't have ALL the bonds taken up by halogens though. R22 being 
better than R12, for instance.



> Cheers,
> Russ
>
>
> Aerospace Corporation