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Re: Zinc based spark gap
Tesla List wrote:
>
> Original Poster: MJoeyB-at-aol-dot-com
>
> Would a zinc based spark gap hold up to the electric given shock? Also, how
> would it perform with pre-ionization. Should I just use them for a safety on
> the capacitors, or should I use them at all?
> If you can help, it would be much appreciated. Thanks in advance.
Hi!
This is an excellent question!
In the days of spark radio earlier in this century, zinc and
magnesium(!) electrodes were often used in low power static and rotary
spark-gap transmitters. This was because because zinc sparkgaps are
"non-arcing", they quenched rapidly, and they low arc-voltage drop.
Zinc electrodes offered improved performance in low power systems versus
say, copper, which is an "arcing metal". Arcing metals, which include
copper and tungsten, can be locally heated to a point where thermionic
electron emission accounts for most of the arc's conduction mechanism.
Arcing metals, sometimes called hot cathode or refractory metals, tend
to have boiling temperatures significantly above 3000 degrees Celsius.
Copper is often classified as an arcing metal for copper-air arcs even
though its boiling point is only 2300 degrees. This is because an oxide
surface quickly forms which effectively enhances its thermionic
behavior, making it behave as though it had a higher boiling point...
that ugly looking "black stuff" that builds up on your static copper
gaps is really cupric oxide.
Because of its relatively low melting temperature and comparatively poor
thermal conductivity, zinc is not as robust as copper or tungsten at the
typical power levels and longer run-times encountered in modern Tesla
Coils. Zinc electrodes can certainly be used in safety gaps, and should
work in your main-gap(s) as long as you keep the electrodes cool by
using thermally-massive electrodes, you use forced-air cooling, and
you're willing to put up with more rapid erosion of your gap electrodes.
So the bottom line appears to be that zinc electrodes may permit you to
quench more quickly, they may have lower arc-voltage losses, but they
will also erode more rapidly than copper or tungsten electrodes. As in
many other areas of coiling, there are seldom perfect solutions, only
trade-offs. If you DO decide to try using zinc electrodes, please share
the results with the group.
P.S., I'd stay away from using magnesium electrodes.... :^)
Safe gappin' to you!
-- Bert --