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Re: Polyethylene in Aus.
From: Wes A Brzozowski[SMTP:wesb-at-blue.spectra-dot-net]
Sent: Tuesday, June 24, 1997 9:50 AM
To: Tesla List
Subject: RE: Polyethylene in Aus.
On Sun, 22 Jun 1997, Tesla List wrote:
>
> From: Alfred A. Skrocki[SMTP:alfred.skrocki-at-cybernetworking-dot-com]
> Sent: Wednesday, June 18, 1997 7:29 PM
> To: Tesla List
> Subject: Re: FW: Polyethylene in Aus.
>
> > I have actually used black concreters plastic for my cap only because
> > its so much cheaper than the clear poly, and I still believe many layers
> > work better than one thick one.
>
> Ah ha! Again we hear the much malined black polyethylene not living
> up to it's bad ( and aparently false) reputation! This indeed seems
> to be one of those situations where a lie repeated long enough
> becomes accepted as truth! This must be about the fifth time I've
> heard that someone was using black polyethylene in their capacitor,
> with no problems!
This is mostly a problem we run into because as coilers, we often use
materials for purposes never intended my their manufacturers. Because of
this, there are parameters that the manufacturers don't have any desire
to control, but which may be very important to us. As a result, one batch
of a product may work perfectly adequately for coil construction, while
another batch may work abysmally.
I wouldn't be surprised if someone had terrible luck with black plastic in
a cap somewhere, any more than I'm not surprised that some have used it
sucessfully. A bad result by someone would lead some to jump to the
conclusion that black = carbon = somewhat conductive, and this may be
true, at least part of the time. It's also likely that a plastic that's
going to be given a black filler may have started out discolored,
recycled, or otherwise contaminated, and this may give unpredictable
variations from lot to lot.
The black material often used as a filler for plastics and pigment for
paints is lampblack, a complex organic that contains a large percentage of
carbon. Unlike graphite, whose atoms are arranged in a repeating hexagonal
structure reminiscent of chicken wire, and which is quite electrically
conductive, lampblack contains a very twisted, broken-up structure, with
some of those graphite-like hexagons, and its conductivity may vary all
over the place, depending on the conditions in which it was manufactured.
Lampblack is actually soot, collected from incomplete combustion of
hydrocarbons. The flame licks against a long metal plate, on which the
stuff collects. The stuff that settles on the cooler portions of the plate
is pretty much amorphous and non-conductive. On the hotter portions of the
plate though, the broken graphite structure has time to slowly "heal" and
become more graphite-like, and hence more conductive.
I have some lampblack that shows little in the way of conductivity, as
well as other stuff, sold specifically as conductive lampblack, which I've
used with graphite to produce moderately conductive paints for plating
overotherwise non-conductive surfaces. The conductive lampblack is quite
electrically conductive stuff, and produces a satisfying synergy when
mixed with graphite powder, due to their very different particle sizes
(the very-tiny lampblack particles fill in the gaps between the larger
graphite particles, meaning that the resulting paint will be composed of
a much larger percentage of conductive material, and less of the plastic
or varnish that binds them together). But enough about my pet projects...
The point of all this is that depending on where the lampblack was
collected from the plate, the black plastic may have the potential for a
good capacitor or not. The maker of the plastic is not likely to be
concerned over variations in the conductivity of stuff that's just going
to be thrown over the wood pile to keep the snow off. In the end, it may
lust be a matter of luck as to wether an individual batch will work or
not.
Wes B.
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