Re: RQ gaps was -JF efficiency theory (again) - A possible work around.

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Original poster: "Dr. Duncan Cadd by way of Terry Fritz <twftesla-at-uswest-dot-net>" <dunckx-at-freeuk-dot-com>

Hi Garry, All!



>Original poster: "Garry Freemyer by way of Terry Fritz
<twftesla-at-uswest-dot-net>" <garry-at-ndfc-dot-com>
>
>I remember reading that glass tends to block ultraviolet and for that
>reason, they make black lights with a special glass that lets the uv
>through. I also remember that certain plastics that are used in
sunglasses
>also block UV.
>
>I was wondering if maybe the degradation could be reduced by slipping
thin
>strips of glass or this plastic between the gaps would help. Or maybe
if
>certain varnishes might block UV and maybe the interior of the pvc
could be
>coated with this?
>


Well, short of smearing it with sun cream . . . Seriously, you make
some good points, any of which would be worth a try, and your
remembered transmission data on glass is generally correct.  Perhaps
even a thin layer of "polyfilla" or similar decorating, hole-filling
type goop, or a bit of silicone inside the tube would do.

If you have a glass drill (and I recall there was a good thread on
drilling glass some time ago, December last year maybe) you can always
use a length of clay drainpipe or chimney pot or even flower pot
instead of plastic.  Low-tech clay has a lot in its favour.  Perhaps
you could set the tubes in fireclay, let it dry, remove the tubes and
bake it, then reinstall the tubes.  If you have access to a kiln,
pottery class or whatever, all manner of things become possible.

I think ultimately the problem is the PVC itself.  Almost anything
would be preferable to PVC.  The problem with PVC is that it was one
of the first plastics discovered and it was pressed into service
despite many serious technical problems which, if it was discovered in
a lab today would result in it being declared worthless.  The entire
plastics additives industry grew up around PVC in an effort to render
it usable ;-)

>I also wonder if the ozone or nitrous oxide in the gap might also be
>contributing to the degradation. Since the gap is constantly
producing NO
>and 03, it would always be present to some degree.


No doubt these things don't help any.  Almost anything will induce
decomposition in PVC.  It readily loses HCl gas to form a
semiconducting poly(acetylene) intermediate which easily undergoes
electrical tracking, oxidisation and hence to the fully carbonised
state.  Once PVC begins to decompose, its decomposition products tend
to catalyse the further breakdown of the good bits nearby.

Bleugh!  PVC is fine for coil forms, but where there's heat, UV,
aggressive gases, you name it, you're better off with something
(anything!) else.  But _all_ plastics you are likely to come across in
local stores will be UV-sensitive to some extent, though probably
nothing as bad as PVC.  Those polymers which are very UV-resistant
[poly(aramids) i.e. Nomex, Kevlar (TMs) etc - bullet proof spark gaps
anyone ?] tend to be quite pricey and not easily obtainable via local
suppliers.

OK.  Polymer chemistry lesson over.  I hope you were all taking notes
as I may set a test at the end of the Spring term ;-)

Dunckx