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WAYNEL
science forum beginner
Joined: 20 Aug 2005
Posts: 26
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 Posted: Sat May 20, 2006 7:37 pm Post subject:
Other spcies migrating from Cu/Pt electrodes
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I have two electrodes bias (15VDC) in a water solution (in water Pt is
inert), with the assumption there are no contaminates in the water, and
the Cu is the anode and Pt the cathode.
Then Cu2+ will migrate from the anode to the cathode and OH- will
transfer to the anode.
Q: is there any other species (or complexes) that may also migrate?
If, with the same experiment, we change the polarity such that we get
the Cu at the cathode and the Pt at the anode, then H3O+ would transfer
from the anode to the cathode and OH- would transfer from the cathode.
Q: is there any other species (or complexes) that may also migrate,
under these conditions?
Also, is there any papers with copper and inert electrodes that discuss
this further?
Cheers
WayneL |
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nagy@anl.gov
science forum beginner
Joined: 18 Jul 2005
Posts: 16
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| Posted: Mon May 22, 2006 3:19 pm Post subject:
Re: Other spcies migrating from Cu/Pt electrodes
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The H3O+ will be migrating in both of the cases you describe.
As a matter of fact, you probably will not have any Cu2+ in any case.
If you have no other anions present, the copper will precipitae as
either oxide or hydroxide, these are not very soluble in water.
Good luck: Z.N.
WAYNEL wrote:
| Quote: | I have two electrodes bias (15VDC) in a water solution (in water Pt is
inert), with the assumption there are no contaminates in the water, and
the Cu is the anode and Pt the cathode.
Then Cu2+ will migrate from the anode to the cathode and OH- will
transfer to the anode.
Q: is there any other species (or complexes) that may also migrate?
If, with the same experiment, we change the polarity such that we get
the Cu at the cathode and the Pt at the anode, then H3O+ would transfer
from the anode to the cathode and OH- would transfer from the cathode.
Q: is there any other species (or complexes) that may also migrate,
under these conditions?
Also, is there any papers with copper and inert electrodes that discuss
this further?
Cheers
WayneL |
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Mike Monett
science forum beginner
Joined: 21 Jun 2005
Posts: 11
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| Posted: Mon May 22, 2006 9:09 pm Post subject:
Re: Other spcies migrating from Cu/Pt electrodes
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"WAYNEL" <home@wlawson.co.uk> wrote:
| Quote: | I have two electrodes bias (15VDC) in a water solution (in water
Pt is inert), with the assumption there are no contaminates in the
water, and the Cu is the anode and Pt the cathode. Then Cu2+ will
migrate from the anode to the cathode and OH- will transfer to the
anode. Q: is there any other species (or complexes) that may also
migrate?
If, with the same experiment, we change the polarity such that we
get the Cu at the cathode and the Pt at the anode, then H3O+ would
transfer from the anode to the cathode and OH- would transfer from
the cathode. Q: is there any other species (or complexes) that may
also migrate, under these conditions?
Also, is there any papers with copper and inert electrodes that
discuss this further?
Cheers
WayneL
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This method is used with distilled water to obtain copper ions in
solution. My experience is you can obtain a bit over 3 ppm of copper
ions in solution before it begins to plate out at the cathode.
Others have confirmed this value.
When the plateout starts, small branches begin growing from the
cathode to the anode. If you disconnect power, the branches drop,
but they spring back horizontal when you reapply power. This
indicates the ions are plating out as copper, which is conductive,
and not copper oxide.
A similar process occurs with silver and zinc as the anode. Silver
reaches about 20 ppm before it starts plating out. I believe zinc
plates out almost immediately and leaves few ions in solution. Zinc
and silver do not grow branches.
In all these cases, it is necessary to use a constant current supply
instead of a fix voltage, like your 15V. The reason is adding ions
to the solution increases the conductivity. With a fixed voltage,
the increased conductivity increases the current. This happens
exponentially, so you quickly reach a point where the current is
much too high. This causes undesired side reactions at the
electrodes which ruins the batch.
For best results, set the current to about 100 microamps per square
inch. This allows a fairly low supply voltage to drive the constant
current source - perhaps 30 Volts or less. You can use the Faraday
electrolysis equation to monitor how much copper was released into
solution.
Regards,
Mike Monett |
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WAYNEL
science forum beginner
Joined: 20 Aug 2005
Posts: 26
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