Re: hydrogen gaps

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Jim Lux by way of Terry Fritz <twftesla-at-uswest-dot-net>" <jimlux-at-earthlink-dot-net>

H2 has very fast quenching and not a huge breakdown voltage.  SF6 is good
for preventing arcs, but I don't know about it's quenching ability.  As
previously mentioned, the standard way to get hydrogen into a gap is to put
something like alcohol in the container, heat it up a little so that the
alcohol starts to vaporize, filling the container, then sealing the
container. The spark dissociates the alcohol into H2 (and stuff)..

As long as there is some liquid in the container (absorbed in a wick,
perhaps), then as it heats, it will be at a positive pressure relative to
the outside, so it will tend not to allow air in, even if there is a small
leak. 

As a practical matter, sealing something with H2 in it at low pressures
isn't all that big a deal.  The problems with H2 diffusing through valves
and metals are at high pressures. Think of the problem this way, if making
a gas tight seal were all that hard, making vacuum tubes last for decades
would be quite a challenge (of course they DO have getters in them, but you
get the idea).

Tesla list wrote:
> 
> Original poster: "Eric Davidson by way of Terry Fritz
<twftesla-at-uswest-dot-net>" <edavidson-at-icva.gov>
> 
> Hi All,
> 
> Been following the hydrogen gap thing.  Time for my $0.02.  First of all the
> term "volatile" doesn't really mean much when describing an element or
> compound that is a gas at room temp and pressure.  Volatile means readily
> vaporizable at a low temp, and while this is certainly true of hydrogen, it
> doesnt mean much at room temperature since hydrogen has been in its gaseous
> state for 200 degrees, or so. As an example, diethyl ether is more volatile
> than water which is more volatile than motor oil, these compounds are all
> LIQUIDS at room temp, the temperature at which "volatile" is being used to
> describe them.  Hydrogen will readily diffuse through many substances which
> are usually considered to be "air tight" due to its small size.  Hydrogen
> gas is diatomic (so its "last orbit" is indeed full) and about the same size
> as helium.  Even thin mylar balloons will easily contain helium (or
> hydrogen) they eventually leak out at the string attachment, not by
> diffusion thru the mylar.  On the other hand, a standard latex rubber
> balloon will leak helium mainly by diffusion, rubber is quite porous.  If
> you had a spark gap contained in a plexiglas enclosure (1/8th inch thick or
> so) you would not get any diffusion of hydrogen thru the plastic itself.  As
> far as other leaks go, at the seams etc. its highly unlikely you would be
> able to create a leak large enough to allow hyrdogen to escape but not
> oxygen or nitrogen.  As far as the reactivity of hydrogen goes, its about in
> the middle of the scale, so to speak.  Its certainly more reactive than the
> inert gasses (which can be coaxed to form compounds with fluorine, chlorine
> and even oxygen) and nitrogen, a bit less reactive than oxygen and much less
> reactive than fluorine and chlorine.  My guess is that a spark gap operating
> in a PURE hydrogen atmosphere would be rather uneventful from a chemical
> standpoint. Yes, maybe tiny amounts of metal hydrides would form, but thats
> about it.  Obviously any oxygen or other reactive gas in the mixture would
> change the forcast drastically, but I'm assuming the idea is to quench the
> arc, not create an explosion.  I guess my question is: Why hydrogen? Because
> it was used in old thyratron tubes? If you want a more insulating gas try
> sulfur hexafluoride, it would be a much better choice in my opinion. Its
> relatively nontoxic, non flammable, non reactive and fairly inexpensive in
> lecture bottle quantities. Hope this helps. Coil safe.
> 
> Eric Davidson
> edavidson-at-icva.gov