Homebrew PCBs

Stefan Trethan wrote:
> Did some experimenting...
> 
> I have now etched away the copper of both welding rods, which nicely
> saturated my etchant too...
> 
> 1 rod is 8mm * 22cm i think which is 55 square cm.
> i connected both rods together to get ~~100 square centimeters.
> 
> 
> for the other electrode i used a copper wire, diameter about 4mm and 
> length 10cm.
> which is 12,5cm square.
> 
> i can only prevent chlorine gas by currents well below 0,5A (you know it 
> is hard to tell when
> there is really no gas).
> 
> - that would be 5mA / square cm at the carbon then.

Excellent work, you now have a starting figure for the current density of 
graphite anodes. In practice you may need less current density to keep long 
life of the anode.

> However i think the area of the copper wire is too big, i can not get 
> hydrogen at all, even
> if there is severe chlorine. so i assumed it is too big and now i use a 
> 1.5mm^2 wire immersed
> only 2 centimeters. now i get hydrogen before i get chlorine.

Can I ask why are you trying to produce hydrogen gas at all ?
Are you saying that no visible signs of copper are plated without also 
producing hydrogen gas at the cathode ? If this is the case then you must 
have very little copper dissolved in the solution, such it would almost 
look very pale clear green.


> The copper plates like a sponge, and it is kind of hard to get it out 
> without
> shaking it all off again (and loosing it in the etchant).

that's correct. When metal and gas co-deposit you get metal sponge.

> 
> I have also another question about chlorine, what are those tablets made 
> of for the swimming pool?

calcium hypochlorite. This may regenerate CuCl2 etchant but I'm not sure 
the effect of byproduct, calcium chloride. It may not make a truly reusable 
etchant. commercially, they sometimes use sodium chlorate, which is similar 
except it is a more powerful oxidant, (more economical), and the byproduct 
is sodium chloride.