Voltage is virtually irrelevant in making CS
It's current that counts..ie..current density or how much current is
flowing over what surface area of electrode.
You want to keep the current density low enough so that high silver ion
concentration zones don't develop in the microscopic area just off the
surface of the electrode. [Nernst Diffusion Layer]
If the concentration exceeds the solubility limits of silver ions in water,
the ions are forced into making whatever insoluble silver compound it can
out of whatever other elements are around..and once made, these compounds
don't tend to dissolve after they leave the area.
To keep current in check as the conductivity of the water goes up with the
addition of more silver ions...pulling more current [current
run-away]....lower the voltage.
This can be done in several ways...a potentiometer [variable
resistor]...remove a battery...use an automatic current limiter such as a
current limiting diode or transistorized feedback circuit...even reduce the
"apparent" conductivity by moving the electrodes further apart.
Just using a plug in wall power supply, the current will go up and up and
up till it melts down and quits, or catches fire.
9 volt batteries won't deliver enough current to catch fire, but will
deliver plenty enough to make a mess of a batch of CS.
A general consensus ideal current density max has been establish on this
list by experience of 1 Milliamp over 1 active square inch of electrode
surface area.
"Active" has to do with electrode shape where points, corners and edges
[in that order] tend to concentrate ion discharge sending current density
up in those areas and flat expanses of back side and, less so, centers..
having a lower or little current density, thus counting less in the
equation for active surface area.
ie rectangular shapes will erode into a V shape showing that the points of
the corners are the most active..and round shapes with the tips in the
water will sharpen into pins showing that the round edges of the tips are
more active..then, once gone pin sharp into a point, the point is most active.
Bending ends slightly away from each other reduces that activity by
making the ions produced there travel further with less apparent
conductivity pulling less current due to more distance...making the rest of
the electrode work more.
ode
At 07:38 PM 7/24/2010 -0400, you wrote:
I've been making CS/EIS for a couple yrs now & have used the 9 V
batteries & the "plug in the wall " type. I have, --since I
started,-- wondered about the difference between using 3 nine V.
batteries & 4 nine V batteries ( & I know you wise guys it's 9 Vs
) grin---but what would the benefit be of using 3 batteries as opposed
to using 4. ???????
Now for my next "electrically challenged" person question--- Would it
be possible to use a cell phone battery charger - or other "plug in the
wall charger----cut the wire off the end & hook up a multimeter &
alligator clips to the silver wires to brew CS/EIS ????? Lois
{{ I wish I knew more about electricity but ever since lightening hit the
straw stack & 6 of our milk cows were smothered & fired,,,& Mom got
tossed across the kitchen by the electric stove I have been afraid of
it...At least the house wiring kind...}}
--
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