Homebrew PCBs

Stefan Trethan wrote:
>>A constant current source is not essential. Often the voltage can
>>be set and the cell ohmic resistance is enough to get reasonable
>>consistent current. When experimenting use a electronic power
>>supply so you know for sure that your power source is stable. If
>>you get into full scale then you should worry about power supply
>>requirments.
>>
>>......
> 
> 
> Thanks a lot, that gave some numbers.
> I will see if i can find carbon electrodes.
> I was very afraid using them seeing the carbon brush from the motor
> coloring the etchant around it dark, but then i had loads of gas and
> the brush may have been dusty with carbon dust.
> I think i understand the issues you said may happen with titanium.
> 
> ST
> 
> I have a 1.2 to 1.4 specific gravity hydrometer floating in the etchant,
> do you think i can use this to monitor the process?
> 
> 

I cannot remember the exact numbers but I think 1.2 to 1.3 was 
the range. The problem is your test cell may need to be 
relatively large >500ml in order to fit hydrometer. Brushes are 
made from a copper/graphite composite. The dark color could of 
been the copper forming copper(1+), which as you know is dark.
The graphite rods I've used normally just disintegrate into 
course powder and settle to the bottom of the container. If no 
gas is formed then the rods should in theory last forever.

Adam