Dear John C. Polasek:
On Jun 19, 6:48=A0am, John C. Polasek <jpola...@[EMAIL PROTECTED]
> wrote:
=2E..
> >> Timo, if the electrode is thinly insulated, wouldn't
> >> all the ions get attracted very close to their
> >> respective electrodes thus leaving the water
> >> "relatively" pure?
>
> >Yes. =A0"Electrodeionization".
>
> >> In this case, wouldn't the dielectric
> >> constant of the water is retained?
>
> >Yes, as I gave you numbers before:
> >pure water, k =3D 80
> >salt water, k =3D 81
>
> The water might break down under fairly weak
> fields because K =3D 80 is a very high number for
> a simple natural substance.
They are two different measures. Water is polar, so without breaking
down it can rotate to where most of the oxygen atoms are
preferentially oriented towards the anode.
> What this means is that the bound electrons
> are on very weak "springs" and have large
> deflections (K =3D 80) so that a moderate field might
> break the springs and free the electron for
> conduction.
No. You are conflating conduction or conductivity with permittivity.
In conduction (your "breakdown"), electrons / ions are free to migrate
through the material the electric field is applied to. In
permittivity, the material undergos a "physical" change NOT requiring
the motion of loose charges.
Roughly, imagine a bunch of frozen chickens hanging from "pegs" inside
an enclosure in empty space. The chickens will be randomly oriented.
Now move it into a gravity field, and the chickens will hang "down".
In this (silly) analog, the center of mass is slightly lower in the
graivtational field... because the average chicken is closer to the
"bottom". This is how energy is liberated from "charging" a
dielectric.
> If the battery remains connected, the E field is still
> there, exacerbated by local ionizations, and able
> to do more ionization rather than herding ions where
> they can't do any harm.
Mobile ions / electrons serve to reduce the field in the dielectric,
since they tend to hover very near the plate.
> What is "thinly insulated"?
For a capacitive cell, with a dielectric thickness t_d, and "thin
insulator" thickness t_i:
2 * t_i << t_d
David A. Smith
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