Re: REAL CAPACITOR (where can i buy one?)

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

Hi Al, All!

>Hi Ed, All.  What kind of plate or conducting/insulating surface
>arrangement did you find when you went inside the faulty barium cap?
>What the heck is in these things anyway?  I mean, the barium is just
an
>exotic clay is it not?  So what makes it work?  What kind of
manufactured
>plates are hidding inside that hard clay matrix?  Or is it just the
>different mixtures of clay at center point that give out with the
effect
>of capacitance.   Reason I ask, is I am into ceramics and glass
fusion
>and I would like to try to make and bake them on an experimenter
scale if
>in any way feasible.  Do you think it possible for a home brewer to
do
>this with standard compaction and a kiln or hi powered glass fusion
>microwave oven? I would like to fabricate my own ceramic caps, even
if
>they are not up to the standard of the industry, it would be a neat
>experiment to try by using the good old red clay from my own
backyard!
>Is it possible?   Ideas anyone?   Al.


This is a great idea (it must be, I thought of doing it myself but
don't have a kiln and never got that round tuit ;-) and if you have
the equipment I'd say go for it!  More than that, please let the list
know how it goes :-)

The active dielectric is barium titanate, which has a very high
dielectric constant K, anything from 1000 to 10000 depending on what
"impurities" have been introduced.

You'll need some titanium dioxide (this is sold under the names rutile
or anatase, two different crystal forms of the same stuff) enamel
grade (low impurities, particularly iron) and some barium carbonate,
as fine particle size as you can get.  I know some pottery suppliers
in the UK stock both of these and I assume that those in the USA do
too, but beware, some pottery suppliers use the name "rutile" to refer
to the crude mineral rutile, which has a lot of iron in it - do be
sure you get highly pure TiO2.  Mix them in the proportions BaCO3 197g
: TiO2 80g and fire the mixture.  Alternatively, you might want to buy
a commercial premix, though I have no idea how much it will cost you.
Try a websearch on "barium titanate".  A site which sells a premix for
K=4400 barium titanate is at

http://www.ceramics-dot-com/mra/K4400.html
(that might be a lower case k if I wrote it down incorrectly)

If you go this route, they will supply precise firing instructions.
Otherwise, if you make your own mix, you might want to use some kind
of binder to form it into a solid mass (no idea what you ceramics
enthusiasts use, I expect it's an organic material which burns away
when the kiln gets hot) and I anticipate there will be much CO2
evolved between 600-900C, so a slow ramp on the kiln temperature and
good ventilation of the kiln would be advisable around this point.
The first firing probably only needs to go to 1100C.  Next, the barium
titanate is ground to a fine powder (a ball mill will be useful here)
and you make a liquid slip with it, just like when casting clay in
plaster of paris moulds.  You cast the finished shape you want, let it
dry, and fire that at maximum temperature to sinter the ceramic, the
higher the better, if you can get 1300C+, good.  Then paint on a
copper salt and fire again at around 1050-1100C in a reducing
atmosphere.  This will leave a film of metallic copper on the surface.
Bingo!  Home-made capacitor!  I believe the commercial manufacturers
then cycle the cap between room temp and say 300C several times to
stabilise the temperature characteristics.

Good luck!

Dunckx