Re: hydrogen? spark gap

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

Original poster: "Michael H Nolley by way of Terry Fritz <twftesla-at-qwest-dot-net>" <nolleym-at-willamette.edu>

>         Main problem with hydrogen, other than explosive air-fuel mixes, is
> that it burns with a colorless flame and it's easy to get burned if
> there's a hydrogen burner running.  As for passing through steel, that's
> just plain incorrect.

    Hydrogen is useful as a quenching medium in spark gaps.
    It's been discussed before that hydrogen is less of a hazard
than other flammable gases since it doesn't have the energy density which
carbon atoms confer
to hydrocarbons.  The chief obstacle seems to be the difficulty in making
completely sealed
gaps.  Additionally, once a gap is sealed, it cannot be adjusted without
de-gassing it, unless
the gap lengths can be adjusted remotely.
    There doesn't seem to be enough benefit from running hydrogen gaps
that it is worth passing up on the fly adjustability air flow control--etc.
etc.
    That said, there is really no reason not to experiment with it--if one
is careful.
    There are a variety of designs one could consider, using off the shelf
components.
    For example, those aluminum project boxes with the rubber seals would
probably
be suitable for low power gaps.  For feed-throughs, one could utilize spark
plugs with the
ground electrode removed.  This is about the cheapest
source for a ceramic feed through one is likely to find... Some spark plugs
will be
more appropriate than others--can't remember which though.
    The cheapest way to do this would be to find a relatively long, sealed
aluminum
box--install spark plugs at either end, and to fill the space with a number
of closely
spaced copper pipe elements.  If you can't find a long enough box, use
small diameter copper
pipe, as airflow will not be an issue anyway.  You could conceivably use
soft copper pipe found
in rolls, but straightening it would be a hassle.  The classiest option
would be something like
1 cm silver tubing found on
jewellers websites--extremely high thermal and electrical conductivity :))
By my calculations
this wouldn't cost more than $30 for a 10 gap system.
    You could mount the tubing on PCB with silicone or epoxy.  Let the
silicone cure first, of
course...  Silicone has the advantage of being both hv and temperature
resistant.  Still, a
hydrogen sealed gap is not likely to get very hot, considering the heat
removal capacities of
hydrogen.
    I'm not exactly sure how you'd go about acquiring some hydrogen, or
introducing hydrogen
into the chamber.  Hydrogen is difficult to get ahold of except in large
tanks, or by
electrolysis.  The gas ports and various equipment would also be a bit of
trouble.  Another
option would be to use alchohol vapor, (denatured ethanol) which
dissociates into mostly
hydrogen.  Most Poulsen gaps used alchohol vapor in the sealed chamber.
Once the vapor was
ignited by the first spark, a small release valve let off the excess
pressure.  This would
probably be too complex for our design, but there would be a variety of
ways of removing most
of the air from the chamber. The trick would be to create an alchohol
resevoir in the bottom of
the chamber, below the PCB (mounted on insulating studs or more
silicone--perhaps 1cm).
    Then you could ignite it (alchohol burns at a low enough temperature
that one can pass a
hand over it without burning oneself) and slap the lid on.  I've done this
before--it's not
particularly dangerous.  The heat is concentrated in the upper part of the
flame, and once the
lid is on, it extinguishes immediately.
    If you wanted to go the non-flammable route, liquid nitrogen might be
serviceable.
    However, the benefits of using nitrogen over air are negligible, except
in the matter of
gap corrosion.  Argon and noble gases don't work.  Terry tried it :)
    Hope some of this was some help.  If you haven't worked with flammable
gases
and liquids before, this might not be a first project ; )
            --Mike