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Re: Black plastic stuff and Nathan's coil...
>
> I then blasted it with the HV power supply. The arc traveled along it's
> surface which was a bit of a surprise.
This is true of many plastic or semiconductive surfaces... For a real
thrill, try a thin ( 1 cm) layer of distilled water in a metal pan.....
The arcs were definitely drawn to
> the material but it was hard to say if that was just due to the
dielectric
> properties attracting the arc. I didn't have the stuff to test breakdown
> at all handy...
>
Perhaps it was acting like a true artificial dielectric where
> energy goes in but does not come out (like a stealth fighter. Maybe you
> only need to wrap a plan in this stuff ;-))).
That's how they make the stuff for microwave loads and absorbers.. carbon
black in foam or sheet plastic. Sometimes they add ferrite for magnetic
shielding.
> BTW- yesterday at work, some techs came to me asking about a similar
thing
> with black Krylon spray paint (I was afraid to ask the "why" part ;-)).
> They did similar testing and found that it also was made from carbon
black.
Depends on where you buy the paint and which kind... I used to use Krylon
Ultra Flat Black to make high value resistors (Spray it through a mask onto
plastic pipe).. Then, they changed the formulation (probably something to
do with Volatile Organic Content rules for California), and the resistance
went way way up. There were also differences between the various brands of
paint. Same applies to the silver "aluminum" paint. Some is conductive,
some isn't, and I'm not sure why... Perhaps the pigment particles are
oxidized (or anodized) in one and not in the other.