On 11/12/07 7:00 PM, in article
1194922802.829179.171940@[EMAIL PROTECTED]
"Wener"
<lvwener@[EMAIL PROTECTED]
> wrote:
> I encountered an strange electrochemical problem in my recent
> experiments, which really drove me crazy.
>
> Since I do not know how to attach a image with my post, the following
> URL will links to the figure of my problem.
> http://web.mit.edu/lvwener/www/Rig.jpg
>
>
> As shown in left part of the attached figure, I am using an cubic
> acrylic tank of 10cm by 10cm by 10cm, containing a saline solution of
> conductivity 1mS/cm.
>
> 1 pair of surface platinum electrodes (A1-A2) is mounted through the
> wall of the tank, at midpoints of two opposite walls.
>
> By using a voltage-controlled current source shown by the right part
> of the attached figure, a 10 kHz sinusoidal signal was converted into
> a sinusoidal current of fixed peak amplitude 0.25 mA.
>
> No air bubble was observed.
>
> Then, another platinum eletrode pair (B1-B2) was added into this
> system, i.e., I applied sinusoidal current signals through both A1-A2
> and B1-B2 simultaneously. As shown by left figure, B1-B2 is fixed at
> midpoints of other two opposite walls.
>
> Shown by the right figure, the current signal between B1-B2 was
> generated by the same function generation and similar conversion
> circuit.
>
> HOWEVER, now things became totally different, since tons of air
> bubbles can always be observed at A1 and B1.
>
> After I read some references on 'water electrolysis', I become even
> more confused:
> (1) Since B1-B2 is at the symmetric positions with A1-A2, which means
> the equivalent resistance between A1-A2 is identical to that between
> B1-B2, no large voltage difference between A1 and B1 should be
> expected.
> (2) Even though there is such a voltage difference, since the
> frequency is as high as 10KHz, the eletrolysis phenomenon should not
> be so rapid.
> (3) If a 10KHz current signal is enough to induce such a terrible
> electrolysis, Why did not it arise when I had only A1-A2? The
> frequency is always 10KHz, and the voltage difference between A1-A2
> should be much larger than between A1-B1.
>
> Can anybode help me explain this phenomenon, and give me some
> suggestion about how to avoid the bubble generation during my multi-
> electrodepair experiment????
>
> Millions of thanks!!!
>
> P.S. (1), after a calucation with conductivity value, the equivalent
> resistance of the saline between A1-A2 (or B1-B2) is approximately
> given by 6.4 Kohm.
> P.S. (2), when I measured the potentials at each electrodes, I found
> DC voltage difference between A1 and A2, between B1 and B2, between A1-
> B1. And the DC voltage difference ranges from 0.x Volts to x Volts. I
> still cannot figure the source of this DC component:
> (i) the DC offset of my function generator is as low as uV
> level;
> (ii) this DC difference was also observed when there was
> only a single electrode pair A1-A2. Why did not it cause any
> electrolysis at that time?
> (iii) I am not sure if there does exist such a DC
> difference, or it is just becuase the ru****ng air bubbles disturbed my
> voltage measurement.
>
I am having difficulty understanding your description. Maybe more
diagrams,
a table of conditions with results, and better description would help.
Is this a homework assignment? I ordinarily try to avoid helping out with
such requests.
Whatever else may be going on, A1 and B1 together will act as one
electrode,
while A2 and B2 will act like another.
Bill
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