Re: hydrogen gaps

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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