# Balbach-Thum cell current dependancy



## Mojeho (Apr 18, 2012)

Hello,

I've encountered interesting problem - got a balbach-thum cell, cathode stainless rod 2cm diameter, 40cm length(approx. 190cm2 submerged surface, @50mA/cm2 current density should allow up to 9 amps), using a 5,5V voltage. Electrode spacing is approx 30cm(cathode - anode distance). Silver content in electrolyte should be more than 100g/litre, with some copper added(light sky blue color) to form better crystals.
I use Polypropylene small bucket(15cm diameter, 20cm depth) with stacked bars of crude silver, perforated on bottom with filterpaper and protective mesh, and perforations on sides for better electrolyte flow.

However, as hard as i try, i am not able to get higher cell currents than 3 amps(dc source is up to 11 [email protected],5V). Even when silver crystals grow as close as 5cm away from anode, still holds at 3amps.

Anyone knows what affects maximum current in cell? Any ideas what i've got wrong?

Thanks for any help
Have a nice day
Moje


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## goldsilverpro (Apr 18, 2012)

Mojeho said:


> Hello,
> 
> I've encountered interesting problem - got a balbach-thum cell, cathode stainless rod 2cm diameter, 40cm length(approx. 190cm2 submerged surface, @50mA/cm2 current density should allow up to 9 amps), using a 5,5V voltage. Electrode spacing is approx 30cm(cathode - anode distance). Silver content in electrolyte should be more than 100g/litre, with some copper added(light sky blue color) to form better crystals.
> I use Polypropylene small bucket(15cm diameter, 20cm depth) with stacked bars of crude silver, perforated on bottom with filterpaper and protective mesh, and perforations on sides for better electrolyte flow.
> ...



I'm having trouble visualizing your setup. Photos? Sounds like, by your setup, you have added resistance in the system. Stainless is a poor electrical conductor. If I remember right, it's only about 1/35 of copper, but that surely depends on the type. Maybe the filter paper, etc., is too fine and it's blocking the current flow. The very wide anode/cathode spacing of 30cm (about 12") would increase the resistance. When calculating the surface area of the SS rod, you can only figure the side facing the anode. That would cut it in half. Are the connecting wires and clips large enough to carry the current? Are your connections sound?

In a traditional Thum cell, the cathode surface area is almost twice the anode surface area. Therefore, when using a typical anode current density of 50A/ft2 (.053A/cm2), the cathode current density would only only be half of that.

Were it me, I would first focus on increasing the surface area of the cathode considerably by using fairly heavy SS sheet (1/8" would be good). Also, I would reduce the electrode spacing to about half.


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## element47 (Apr 18, 2012)

Didn't Lou or another poster state somewhere that the voltage should not be this high? (5.5 volts) I don't especially think this would affect current density, though it might, over time. It would affect deposition rates and perhaps induce undesirable chemistry within the cell. 

Indeed, if the electrolyte bath is viewed a pure resistor of fixed value, then higher voltage should produce higher current, and lower voltage should produce lower current. E = IR. But this description of an electrolyte is probably quite inadequate.


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## goldsilverpro (Apr 18, 2012)

My take on it was that his power supply only applies 5.5V.


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## Mojeho (Apr 20, 2012)

@GSP: 
Thanks a lot for reply - i'll try increasing cathode surface.
Cathode anode distance should not be a problem, as i said, even when crystals grow as close as 5 cm to anode, current is not increased.
I'll post photos later today.

@element47:
Deposition at 5.5 volts is ok, got only small copper contamination in cell, so so far so good - only silver is deposited. I'm planning when there will be higher contamination of electrolyte to reduce voltage to 4,5V(that's minimum my DC source can give)

Thank you both for suggestions.
Have a nice day
Moje


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## Lou (Apr 20, 2012)

Less is more with voltage, but as long as the silver is the great majority in the electrolyte you can run high.


Lou


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## Mojeho (Apr 21, 2012)

@Lou: Thanks for confirming my suspicion  Do you have any numbers on concentrations/voltage/deposition dependencies? Or links? Any help would be very welcome, as i could not find any detailed descriptions of balbach cell operation parameters. And because i've processed only relatively small quantities, i'm still new to this.

@GSP: Increasing cathode surface had no effect, decreasing electrode spacing also had no effect. Guess that my anode bucket is not ion-permeable enough. Will try to construct new one.

Thanks
Have a nice day
Moje


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