jhonn - 19-11-2012 at 15:58
I bought this MMO anode at ebay:
http://www.ebay.com/itm/5-x-1-Expanded-Titanium-with-MMO-Coa...
I would like to know the maximum current density that these anodes can handle without being damaged. Also, any other care must be taken to avoid
damage? I don't know its surface area because it is a mesh electrode (it would be 10 square inches, if it was a sheet),does anyone has an idea on how
to calculate the area?
Swede - 28-11-2012 at 06:49
The mesh ends up being about equivalent in surface area to a solid sheet. If you sandwich the anode between two cathodes, the surface area will be
approximately 2 X the area of one side, so a 3" X 5" mesh anode would have a 30 square inch area. One cathode, and the bulk of the current is coming
from one side, so call it 15 square inches.
As far as current density... the recommended CD is around 250 mA per square centimeter, but I am convinced it can be higher, perhaps much higher.
I've gone over 500 mA with no problems. MMO is tough stuff chemically. Realize that pH control does two important things... it dramatically
increases overall efficiency, and importantly, it helps inhibit oxidation of Ru. Voltage should not be much higher than 5 or 6 VDC... 3 to 4 is more
typical.
Most of the work in MMO is done by the electrocatalytic action of RuO2. At high pH, which is going to happen naturally with no pH control, some of
the RuO2 (insoluble) can convert to RuO4 (soluble) and you can have losses.
I've personally not seen this, but again, I don't have the sort of milligram balance that can detect this, and I have since gone to pH control.
Overall: again, MMO is tough. You can soak it in concentrated mineral acids with little effect. In fact, I use HCl to clean them. Go ahead and use
it with little fear of degradation.