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Re: Water As Dielectric




From: 	Bert Hickman[SMTP:bert.hickman-at-aquila-dot-com]
Reply To: 	bert.hickman-at-aquila-dot-com
Sent: 	Saturday, November 08, 1997 9:56 PM
To: 	Tesla List
Subject: 	Re: Water As Dielectric

Tesla List wrote:
> 
> From:   Alfred C. Erpel[SMTP:aerpel-at-op-dot-net]
> Sent:   Friday, November 07, 1997 6:07 PM
> To:     tesla-at-pupman-dot-com
> Subject:        Water As Dielectric
> 
>      Is distilled water considered to be a viable dielectric material for a
> plate capacitor? High voltage vs. low voltage? DC vs. RF?  Since it's k=80+
> it would seem to be a good choice.  As a toolmaker, I would have no problem
> making a sealed, watertight plexiglas cube, void of air, with evenly spaced
> copper plates inside, and I would like to do this if someone doesn't tell me
> it is a dumb idea.
>      What is water's dielectic strength? I did a search on the internet for
> this value and the only thing I kept finding was it's dielectric constant.

Alfred,

Pure water is an excellent dielectric. The problem is that pure water
just doesn't _stay_ that way. Water is an excellent solvent - a
universal solvent. Over time, metallic ions (cations) transfer into the
water from the metal surfaces of the capacitor plates. Anions (typically
chlorides and sulfates) also leach out of virtually any plastic or glass
container. These cause the water dielectric's leakage current to rise
(reducing breakdown voltage and reducing the time between voltage
application and dielectric breakdown) unless the ions are continually
removed by actively reprocessing the water through a deionizer. 

Pure, deionized, water's dielectric strength and high dielectric
constant are used to create high power, very low impedance, transmission
lines for high power pulse work and temporary energy storage. However,
because of the difficulty in keeping water deionized, it doesn't make
for a practical TC capacitor dielectric. Hope this helps!

Safe coilin' to you!

-- Bert --