Dendrites from the Anode?

[WAYNEL]

Hi


I have been conducting some test on dendrite growth on gold plated
copper (with nickel barrier) printed circuit board pads.
After applying a small quantity of water and biasing with 15v I
observed a dendrite emanating from the cathode. From the literature I
have read the dendrite grows from the cathode.
Placing 15 volts directly on the pads with no current limiting caused
large quantities of gas bubbles that damage the dendrites.


So, I placed a resistor in series 500K ohms.


However, this produced a dendrite from the anode. I have measure the
polarity and it is correct.
A search on the internet reviled a site that said batteries can produce

anode to cathode dendrites if overcharged.
http://www.nasatech.com/Briefs/Nov98/NPO19966.html


Is this correct and if so how can dendrites for from on the anode
surely metal ions (M+) migrate from the anode to the cathode.

In addition if the circuit is connected with the resistor (1M ohms) in
series with
the earth then dendrites grow from the anode.


15v+ -
---
gold plated Cu pads
---
Ś
1M ohm
Ś
GND


However, if the resistor is in series with the +V supply then dendrites

grow from the Cathode??


15v+ -
Ś
1M ohm
Ś
---
gold plated Cu pads
---
Ś
GND


Cheers


WayneL


Reply

 

[John Woodgate]

I read in sci.electronics.design that WAYNEL <home@wlawson.co.uk> wrote
(in <1124785391.806873.138400@f14g2000cwb.googlegroups.com&gt about
'Dendrites from the Anode?', on Tue, 23 Aug 2005:

Is this correct and if so how can dendrites for from on the anode
surely metal ions (M+) migrate from the anode to the cathode.

You have three metals present. Under those conditions, the most
electropositive migrates to the cathode, while the most electronegative
migrates to the anode. This is a bit simplified, but it explains the
basic mechanism.

In addition if the circuit is connected with the resistor (1M ohms) in
series with
the earth then dendrites grow from the anode.


15v+ -
---
gold plated Cu pads
---
Ś
1M ohm
Ś
GND


However, if the resistor is in series with the +V supply then dendrites

grow from the Cathode??

If that really happens, and you can explain it, you stand to get a Nobel
Prize. But I suspect that your experiment or report contains an
inadvertent error.
--
Regards, John Woodgate, OOO - Own Opinions Only.
If everything has been designed, a god designed evolution by natural selection.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk

 

[John Popelish]

WAYNEL wrote:

Hi


I have been conducting some test on dendrite growth on gold plated
copper (with nickel barrier) printed circuit board pads.
After applying a small quantity of water and biasing with 15v I
observed a dendrite emanating from the cathode. From the literature I
have read the dendrite grows from the cathode.
Placing 15 volts directly on the pads with no current limiting caused
large quantities of gas bubbles that damage the dendrites.


So, I placed a resistor in series 500K ohms.


However, this produced a dendrite from the anode. I have measure the
polarity and it is correct.
A search on the internet reviled a site that said batteries can produce

anode to cathode dendrites if overcharged.
http://www.nasatech.com/Briefs/Nov98/NPO19966.html


Is this correct and if so how can dendrites for from on the anode
surely metal ions (M+) migrate from the anode to the cathode.

In addition if the circuit is connected with the resistor (1M ohms) in
series with
the earth then dendrites grow from the anode.


15v+ -
---
gold plated Cu pads
---
Ś
1M ohm
Ś
GND


However, if the resistor is in series with the +V supply then dendrites

grow from the Cathode??


15v+ -
Ś
1M ohm
Ś
---
gold plated Cu pads
---
Ś
GND


Cheers


WayneL


Reply

If the location of the resistor changes the effect, then I expect you
have a supply that is not completely isolated from ground and an
experiment that is not completely isolated from ground (or other
inadvertent conduction paths). Try it with a 9 volt battery and the
whole experiment in a glass dish sitting on an inverted glass dish and
see if it doesn't change the result.