Re: Conductive paint?

["Tesla list" <tesla-at-pupman-dot-com>]

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

Hi Marc, All!

>duncan,
>response interspersed below, no argument intended, just something
i've
>thought about


You can argue with me any day!

>yes individually they are slightly thinner and somewhat more active.
>dancing around and seeming to slide across short areas of the toroid.
>the toroid was fairly smooth to start with and after a few coats of
the
>graphite, was almost perfect.


Hmmmm, [Spock mode] fascinating! [Spock mode off].

>right, but is the charge actually flowing through any amount of
>thickness at any given time? the charge being distributed over the
>complete surface of the topload, i was wondering if it really only
>travels through the thickness of a cross section of the material that
it
>is made of. in other words, only the .010" from inside surface to
>outside surface?

Well, yes, it will, um . . . if you think of the electrons popping out
of the top end of the secondary wire and distributing themselves
evenly over the topload surface, they evidently flow through the
coating to get wherever they're going.  Even if the topload is solid
metal, the skin effect will constrain the current to a thin surface
layer.  I think!

>i can see what your saying above that once one streamer
>breaks out, the resistance over the surface may prevent most of the
>charge from traveling to that discharge point, this is interesting. i
>will try it again and see if i notice any streamers actually
connecting
>above the surface, if they do this over a short space then the
>resistance could be why they seem to dance around more.


That's a good thought.  I'm wondering if there's some connection
between what you've seen with graphited toploads/lots of simultaneous
breakouts and what I've seen with very high break rates.  At 1000bps
the streamers are pretty mobile, but at 6000bps the streamers go
absolutely wild, thrashing around like mad.  If I could get the thing
up to 20000bps I think they might take off ;-)  In contrast, 100bps
streamers seem very lethargic.

>> >is the charge of the topc
>> >being held on the conductor or in the dielectric?
>>
>> Gauss' theorem suggests on the conductor, when the conductor is
>> outside the dielectric as in a coated topload.
>
>but the coating is conductive itself, so i would think the air
between
>it and the ground would be the dielectric? it is just my thinking as
i
>have read about lightning only so far.

Ummm, yes, the air is indeed a dielectric, but I've misunderstood
you - I was thinking that you've got e.g. a styrofoam toroid or
whatever which is conductively-coated, that's what I meant by
dielectric here, i.e. the body of the topload is an insulator.
Faraday's ice pail experiments showed that a hollow, charged conductor
has no charge on the inside, i.e. it all sits on the exterior of the
conductive coat.  Now, as regards the role of the surrounding air, it
won't make much odds because the dielectric constant K is only barely
more than 1 (at something like the fifth or sixth decimal place) - if
the topload was immersed in a bath of nitrobenzene, which has a large
value of K, then you'd be right, a large wodge of the charge would be
bound up with the dielectric.  Is this what you meant, or have I got
my brain twisted ;-)?

>so if the charge is distributed
>over the full surface of the toroid, the rate of curvature actually
>gives a more uniform surface contacting the dielectric, allowing more
>charge to build up before at some point a minor imperfection or bump
>starts to develop a corona, and at that instant charge is dumped into
>the streamer, or leader.


Yes.

>if the charge wasn't built up in the surrounding dielectric then
>bringing a grounded object in any vicinity wouldn't force breakout at
>that point, am i correct in this?

The charge resides on the topload, but produces a surrounding field
which may have a sufficiently large gradient at the surface of the
topload (>30kV/cm) to give spontaneous breakouts; if not, distortion
of the field may give rise to breakouts, and this need not be at the
topload.  More below . . .

> the grounded object produces a leader
>that forces a pull from the charge in the dielectric. i've read much
on
>lightning and the leaders are the deciding factor to what is actually
>struck, in the last fifty or sixty feet to ground. i've seen photos
of
>several objects producing leaders at once stretching to intercept one
>bolt.
>though the dynamics of lightning are far different then the discharge
of
>a tc, lightning still travels along stepped leaders to the ground. so
>the charge of the dielectric is being channeled into the main bolt
from
>what we see as forks extending outward to thin air, are actually
charge
>being channeled inward to the main bolt allowing it to jump the next
>step distance.


What is certainly true is that the charge on the topload generates a
local electrostatic field (OK, it's an electrostatic field which
varies at a very high rate, if that isn't a total Irishism, but think
in terms of nanosecond snapshots) which local objects can distort to
the point of dielectric breakdown of the air.  For example, with the
Q&D VTTC, I have blown out the arc on the TC and held a well-insulated
screwdriver near the top of the coil; if I get the distance and angle
just right, the air ionises around the sharp edge of the screwdriver
blade due to the local field distortion being above 30kV/cm, and the
plasma breakout comes off the screwdriver, *not* the Tesla coil!!!!!
I have yet to succeed in getting a photo of this as the angle and
distance are very critical, and each time I try to fix the screwdriver
in a clamp so I can operate the camera, the arc jumps back to the TC
or goes out!  Most frustrating!

>in the tc charge, there are many differences, but the main one that
the
>charge is actually being produced in a somewhat bubble that is
>compressed in the center, top to bottom. this forces the charge to
>travel from the opposite side to a streamer in that short time, i
don't
>think all charge can make it that fast? i'll stop here before i
really
>misunderstand, i'll wait for comments.


Well, if you do misunderstand, you're surely not alone ;-)

>i agree with this, i see what your saying as the cohesion of the
>particles being tight enough to form a sheet. but the charge only
>travels from the center outward, over the conductor? well through it
>somewhat.


It would be nice to be able to produce a blow-by-blow description of
how the charge emerges from the top of the secondary coil and
distributes itself over the topload.  Obviously it does travel from
the centre outward (assuming a centre contact at the base of the
toroid or sphere) and then up and around the surface until -
presumably - you've got an even distribution or breakout occurs.

>> Maybe it carbonises a mini-breakout spike in the poly coating.
>
>i think it is doing this, the pinhole is so small that i have looked
>right at the spot were i know a streamer was stuck, to small for my
>eyes, maybe i will try a magnifying glass and see if it might
increase
>in size?


It could be mere microns across - or less - and very hard to see under
the best of conditions - how wide a hole do you need for electrons to
get in and out?!

>> >just thinking again,

>>Dangerous, that!
>
>yes i have often been told i think to much?

In this miserable world of corporate piffle &c, anyone who thinks at
all independently is definitely an outsider!  Join the club :-)

>the product i use is from:
>superior graphite co., it is called "SLIP PLATE" GRAPHITE DRY FILM
>LUBRICANT. i use it on my hay cutter bar and baler knotting units,
>chutes. i get it at "tractor supply" or "quality farm and fleet"
>if you're interested in trying this i will send you a can.


Thanks for this.  There is an agricultural supply house in town so I
will try there first - if I can't find it locally I'll get back to
you.  I think maybe a fibreglass toroid coated with spray-on graphite
could be an interesting DIY project !

Dunckx