To clarify:
An electrolyte does not conduct. Chemical reactions occur at the electrodes
that accept and give up electrons. Current flows through the metal conductors
between the anode and cathode.
When I say that the voltage drop occurs withing around 1nm of the electrode
(the debye length), that is only the case for low voltage experiments on the
order of the red-ox potentials for a given electrochemical reaction. At 6kV
this would not necessarily be true. Because the ions in the electrolyte of
much much lower mobility than electrons in a metal conductor they may not be
able to effectively screen the high applied fields, especially if the solution
is being mixed (a quick search of the literature did not yield a relevant
example at high field) . If the fields were oscillating, the E field would
definitely be felt within the electrolyte (this is what I would have done).
When you say:
The situation has nothing to do with "free charges that can migrate to the
surface" of anything. The mode of conduction is irrelevant.
I fail to understand what you mean. The only reason that the field inside the
electrolyte can be zero is if charge carriers migrate to the surface of the
cell to screen the bulk of the electrolyte from the externally applied field.
I don't believe your example of probing the electrolyte with two probes and a
bridge is relevant to this experiment, since the external electrodes are not in
contact with the electrolyte, no chemical reaction can take place, and so no
current can flow, the field can only be screened by the build up of charged
ions at the cell walls.
Maybe you can explain it in a way i can understand.
What would happen if you had two metal plates separated by an air gap, then you
applied a 6kv bias between them, and then put your two probes into the air gap?
> Date: Tue, 3 Jul 2012 19:13:40 -0500
> To: vortex-l@eskimo.com; vortex-l@eskimo.com
> From: a...@lomaxdesign.com
> Subject: RE: [Vo]:SPAWAR has yet to respond re simple error in claims of
> effects of external high voltage dc fields inside a conducting electrolyte:
> Rich Murray 2012.03.01 2012.07.02
>
> At 03:44 PM 7/3/2012, Finlay MacNab wrote:
> >It should be noted that in an electrolyte the current results from a
> >chemical reaction at the anode and cathode (in this case the
> >generation of hydrogen and oxygen) there are no free charge carriers
> >in the solution itself. The cations and anions are bound together
> >by electrostatic attraction and exist inside cloud quasi organized
> >solvent molecules. Electrolyte ions do organize on the surface of
> >electrodes to screen the electric field at low potentials (most of
> >the voltage drop in an electrochemistry experiment happens within
> >the first nanometer of the electrode surface). At the high fields
> >quoted in the linked paper, I cannot imagine how the electrolyte
> >could screen the applied field. It seems reasonable to me that an
> >electric field could exist inside the cell, since electrolytes do
> >not have free charges that can migrate to the surface of the dielectric.
> >
> >Electrolytes do not conduct electrons, they accept electrons and
> >donate electrons. There are no charges flowing through the
> >solution, just reactions at the electrode surface.
> >
> >Now I must get back to my electrodeposition experiment.
>
> An ounce of experiment is worth a pound of theory. Or even a ton.
>
> Now, I'd love to be wrong here. However, I remain unconvinced, and
> obviously so does Rich. The objection is an obvious one, so one might
> think there would be a definitive answer somewhere. I see, however,
> that Mr. MacNab may have confused himself with his own knowledge. The
> situation has nothing to do with "free charges that can migrate to
> the surface" of anything. The mode of conduction is irrelevant.
>
> An electric field *does* exist in the cell. It is complex, and varies
> from location to location. If the statement about the "first
> nanometer" is true, we could be looking at a field strength there of
> more than 10^7 V/cm. Much higher than the field from the "high
> voltage" supply. But just for a nanometer.
>
> Here is the problem. Electric fields are measured relative to some
> potential. There is only one electric field at any given location.
>
> How do we know what the electric field is at a location? Well, we can
> use a voltage probe. That won't tell us the field, we will need to
> use two probes for that, which will give us the potential difference
> between the two locations.
>
> We can use a bridge to measure potential difference without any need
> for current to flow through the probe, complicating things.
>
> So if we stick two probes into the electrolyte, on either side of the
> cell, when we have this 6 KV sitting across the cell, what voltage
> will we need to place across the probes, so that the current through
> them is zero?
>
> In the electrochemical cell, I'll predict this. The voltage will be
> very low, probably less even than the voltage between the anode and
> cathode, if Mr. MacNab's statement about the voltage drop is true
> (and I have no reason to doubt it).
>
> Imagine, though, that it would instead be thousands of volts. This is
> at zero current. But thousands of volts across two probes --
> electrodes -- in a conductive electrolyte? If you had the available
> current, the thing would blow up!
>
> (In fact, here, the high voltage power supply is from a TV set, there
> is only low available current.)
>
> So the voltage across the probes would be very low, perhaps
> millivolts. If the probes were in contact with the cathode and anode,
> respectively, it might be a few volts, whatever the electrolysis voltage is.
>
> There is no "screening" of the field. There is just the shorting of a
> portion of the field, by the electrolyte. The current from the HV
> supply is very low, it might be picoamps. [I estimate it below]
>
> If we plot the field with a series of measurements, we'd find that
> there is about 3 KV across a cell wall, about 1/16 inch thick.
> Acrylic plastic, probably. Then there is a very low voltage across
> the electrolyte. then there would be another 3 KV across the opposite
> wall, giving us a total drop across the cell of 6 KV.
>
> The cell wall is about 1.6 mm thick, and with 3 KV across it -- which
> could easily be measured -- that's 19 KV/cm. Looking for the
> electrical properties of acrylic, I found that it has a bulk
> resistance of 1.6 X 10^16 ohm-cm . We might be looking at about 16
> cm^2 for each plate. I get on the order of 1.6 x 10^14 ohms per piece
> of acryclic. Current for 3 KV would be about 5 x 10^10 amps, or 500
> pA. That is the leakage current through the acrylic.
>
> Breakdown voltage for acrylic is 17 KV/mm. That's probably a minimum
> guarantee. 170 KV/cm. Actual breakdown would not normally occur until
> substantially higher voltage. (I've tested actual breakdown voltage,
> it was, under the situations I was testing, over double the
> specification or more.) If the acrylic does break down, all bets are
> off. The current though the acrylic would go way up, but the supply,
> though, won't supply much current. The current from the electrolysis
> supply will probably still be greater. I.e., the "high voltage"
> supply wouldn't be high voltage any more.
>
> Other than with breakdown, the field is completely undetectable in
> the electrolyte, given that the actual DC current in the electrolyte
> is in the range of 1 - 500 mA, perhaps. The electric field from the
> electrolysis voltage will be much higher.
>
> This is a DC field, remember. Things would get quite dicey if the
> voltage is varying.
>
> Ah, but what if there was breakdown? Could that explain the effect?
> Well, the problem is that the voltage wouldn't be 6 KV any more. Did
> they measure the voltage? And all this would do would be to add a bit
> of current between two new "electrodes." And you could get the same
> effect with just putting two electrodes in the cell. Might work. What
> would that do? Who knows?
>
> There cannot be a high voltage DC field across an electrolyte without
> a corresponding current, and put a few hundred volts across an
> electrolyte -- there are some youtube videos showing this -- you get
> some spectacular effects. Not just a little shift in plating morphology!
>
