[Prev][Next][Index][Thread]

Re: Unusual capacitor dielectrics

Tesla List wrote:

> Original Poster: Gavin Hubbard <ghub005-at-xtra.co.nz>
>
> >Also, what about barium titanate capacitors? Barium tatanate has a *huge*
> 1200
> >dielectric constant. It isn't exactly easy to find, but "barium titanate,
> >powder, < 3 micron, 99%" can be purchased from Aldrich for 22.80 for
500g or
> >66.90 for 2kg. I might be possible to make it into a sheet by building a
open
> >box out of high-temperature steel, sprinkling a uniform coating of barium
> >titanate power inside it, melting the barium titanate with a hot torch
> >until it
> >forms a uniform sheet, and finding some way to remove the sheet without
> >breaking
> >it. I have no idea what barium titanate is like, but I'll bet it's brittle.
>
> A big problem with Barium titanite is that it anisotropic. Crystalline
> solids commonly have different dielectric properties in different crystal
> directions because the charges that constitute the atoms of the crystal are
> able to move more easily in some directions than in others. The
> polarisation ~P is then parallel to ~E only when ~E is along certain
> preferred directions.
>
> However, most ceramic capacitors still use various compounds of titanium as
> dielectrics.
>
> The other problem with Barium titanite is that e_r has a non-linear
> response to temperature, applied voltage, and operating frequency. This
> makes them of little use in Tesla Coil tank circuits. I recommend that you
> use conventional low density polyethylene capacitors in your coils (but
> don't let this stop you from experimenting!).

    I have been using barium titanate doorknob caps in my 4" TC, and they out
perform Maxwell pulse caps. Using 7.4nF of barium titanate caps, I was
getting 24"
arcs, when I put maxwells in instead, I had to increse the value to 20nF in
order
to restore the same level of performance.

--
**********************************************************************
*Stephen Rodway             Legion-at-Bigfoot-dot-com *  Support your local *
*Tel. 01761 300615                             *     coroner....     *
*For Email use PGP where possible.             *    Die strangely!   *
*http://www.legion-elec.demon.co.uk/index.htm  *                     *
**********************************************************************