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

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Original poster: "Terry Fritz" <twftesla-at-uswest-dot-net>

Hi All,

They sell the glass plates used in welding masks for a pretty cheap price.
I have one here in the desk and it looks like it can be cut with a glass
cutter and all that.  Guaranteed to be good for UV!

Cheers,

	Terry

At 11:26 PM 2/20/2001 +0000, you wrote:
>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
>