Re: Mississippi Mud Caps: Was, Barium Titanate Caps.

["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 Al, All!

<snip>
Thanks for the details!

>Now, our next
>objective is to weld/sil-fos the leads somehow to the thin copper
plates

Commercially, I'm pretty certain these are simply soft soldered in the
usual manner.  Any particular reason you want to go for welding?  I
can well believe that doing this on very thin plates is difficult.

<snip>


>But a lot of
>these glazes contain some lead, not sure of the content or how
>detrimentally conductive it would be, we will have to fire these
>compounds and see what the conductibility is of the coating.

Lead-based glass is a pretty good insulator, but as you say, try it
and see is the only way to be sure . . .

>Also, we
>will try a mostly 'white clay' base for the next capacitor, hoping
that
>it will produce a higher plate 'Q' than the first mostly red mud
>capacitor did.

That'll be interesting.

>We are also
>wondering about introducing a teflon 'micro sphere' compound into the
>clay as a binder/insulator, does anyone think that may help?  Wonder
what
>the melting point of teflon is?

Eek!  No!  Teflon gives off very nasty fumes when it gets hot.  Toxic
and very highly corrosive - avoid like the plague.

>The auto body compound we used on the
>first cap was really not a good binder/additive, since it seemed to
coke
>up a lot on the finished fired clay capacitor(I should have known
>better!).

I imagine that if the kiln gets hot enough, the carbon will burn away,
especially in an oxidising kiln.  Unfortunately my limited knowledge
of ceramics technology does not extend to binders so I can't suggest
any improvements.

>The puzzle now is proper support from the wire leads only so
>that we can get a good glazed cover all around the capacitor body.
Copper
>wire leads will probably tend to sag upon high temperature heating in
the
>kiln and may pull apart from the copper plates. We are thinking of
>brazing, or silver brazing a brass bolt to the copper plates, problem
is,

Ah, is this why you're thinking of welding rather than soft soldering,
to give support to the cap in firing?  You know those three legged
ceramic thingies like the centre of a Mercedes emblem you use to prop
things up in a kiln?  (Probably called "props" ;-)  Could you rest the
cap on one of those, as it would only contact the prop at three small
points?

>the copper plates are not really plates, they are very thin shim
stock
>and we have not had any luck brazing a terminal stud to the thin
sheet.
>Perhaps a thicker copper plate would be in order?  But it may change
the
>whole balance of the capacitor internals as we now have them and may
not
>be at all beneficial.

I'm wondering since the copper is thin if you could simply fold the
plate to give an external flange for later attachment?  Like ____|____

>Anyhoo, these caps take a lot of effort to make,
>and I would not wish the process upon anyone! The best thing that I
can
>say at this point is:  It was a expensive, tedious, time consuming
>project, but we did it just to see if it could be done, even on a
small
>scale. If we did not already have the clay tools and kiln, arc
welder,
>stainless steel sieves, hydraulic jacks, etc. there is no way we
would
>have done this.  The clay is 'dirt' cheap!  The apparatus is not.
>However, the final product made it all worthwhile when it actually
worked
>for a short time in the OBIT fired small Tesla coil.   Al.


I'll bet!  Well done again!

Dunckx
Geek#1113 (G-1)