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

Re: Unusual capacitor dielectrics

You are right about water being a great dielectric but of course as
always there is a catch, the water that is being tested for a
dielectric constant test is unbelievably pure and assuming you get
some really great de-ionized H2O you have to put electrodes in your
water to make a cap and almost any contamination due to say (metal
electrodes) will very quickly contaminate your water and make it
worthless as a capacitor. I once had the idea of using ice as the
dielectric in a capacitor but I was told that ice is not that good a
dielectric although the professor I was talking to about the subject
might have told me that just to get rid of me. I can sometimes be a
pest with all sorts of oddball questions. Anyhow I figured that ice
would slow down or stop the ionic migration that ruins water as a
dielectric. Does anyone know the dielectric strength and or constant
for ice? I have heard of the military building extremely large, multi
mega Joule, sized caps using de-ionized water. The electrodes had and
ion free plating, maybe plastic, gold or?. Apparently they discharged
these building sized capacitors to generate a simulated EMP like from
a nuclear explosion. I don't have any real details
but it sure sounds like fun.
   
Steve Ivy
adder_black_the-at-yahoo-dot-com
Dallas Texas



---Tesla List <tesla-at-pupman-dot-com> wrote:
>
> Original Poster: Jacob Roberto <jroberto-at-ieway-dot-com> 
> 
> I've noticed that pure water has a dielectric constant of 80 (about
40 times
> higher than that of polyethylene). Would it be practical to build
capacitors
> that use water as the dielectric? Such a capacitor could probably be
built by
> taking pieces of sheet metal, drilling holes in their corners, and
then
> bolting
> them together, using nylon washers or other flat insulators to
separate the
> plates.
> 
> Guessing that water has a breakdown voltage of 250 volts/mil, A
0.0864 uF
> 7.5 kV
> capacitor could be built by simply taking two 12x12 inch pieces of
sheet metal
> and using 30 mil seperators. Stacking 9 such plates (making 8
capacitors in
> series) would yield 0.0108 uF at 60 kVDC, suitable for
small-to-medium Tesla
> coils. Several of these would then be wired in parallel and placed
> vertically in
> a rectangular container, with ceramic blocks to prevent the plates
from
> touching
> the edges of the container, and with very pure water, very slowly so
air
> bubbles
> don't get trapped.
> 
> If two plates very large (8 by 8 foot) plates are used with a
separation of
> 0.5", then the capacitor would be 0.332 uF -at- 125 kV -- that's 2600
joules!
> Increasing the spacing to 1.5 inch would make it 0.111 uF -at- 375 kV
-- that's
> 7750 joules! Increasing the spacing still farther to 4 inches would
make the
> capacitor 0.0415 uF -at- an amazing 1 MV -- that's 20,750 joules!
> 
> Of course, for this to work, the water would have to be very pure. I
doubt
> that
> the distilled water available at the grocery store would work.
Aldrich has
> some
> water marked "Water, A.C.S. reagent" for 17.55 for 2L or 55.00 for
8L. I might
> also be possible to build a distillation system and then
triple-distill the
> standard grocery-store water.
> 
> I don't have any idea what the RF loses of water are; they might
prohibit its
> use in Tesla coils. However, it might still be useful for pulse
discharge
> applications.
> 
> 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.
> 
> Does anyone know the puncture voltage and RF losses of pure water
and barium
> titanate???
> 
> -- 
> 	-- Jacob Roberto
> "Some people dream about being famous and having fancy cars. I dream
about
> 1000KVA transformers and 1000KJ pulse caps!"
> 
> 
> 

_________________________________________________________
DO YOU YAHOO!?
Get your free -at-yahoo-dot-com address at http://mail.yahoo-dot-com