Electrochemistry Power Supplies & Cell Size

[kurt]

PM sent to me -----

Kurt, when I was speaking of current density, I was meaning at the cathode. I have since found several articles mentioning .35A/sq inch current density for the anode.

My anode bars have been 2.5" long x 1" wide x 0.375" thick so that would give me about 8 sq in. I have been running 2 bars at once for a total anode area of about 16 sq in. That calculates out to about 5.6 amps I could run and not exceed that limit. With 2 bars for the anode I was getting around 6 amps at 1.5V. I had also added a little KOH to increase the current flow.

With a 75 sq inch cathode I could run almost 15 amps and not exceed the capacity for the cathode.

So, the smaller current limit prevails! I guess if I had more surface area for the anodes I could run higher current.

I notice that Lazersteve has said in old posts that the cathode should be only 2 or 3 times the area of the anode. Why?

My reply --------

That’s just it - there is so much different info out there & its spread out in bits & pieces here & there that its hard to piece it together in order to calculate the anode size &/or the cell size you can run given the amp out put of the power supply

I was hoping posting a thread on the subject would bring the info to calculate this all together in one place

I don't think it is the cathode that matters in figuring the current density because you can use SS for your cell & the cell its self becomes the cathode - so I believe its the anode that figures in (I could be wrong)

So - as I understand - the volt setting you run the cell at determines the current density delivered to the anode - amps avalible determines anode size (surface area) - to small an anode & you wont utilize the full amp potential - to large an anode you don't get optimum current density (current density drops off if you go over size on anode - or you would have to change volt setting to deliver desired current density)

So (if I am right) amps avalible determines anode size - anode size determines cell size

All based on standard numbers for running a cell (electrolyte consentration - anode/cathode spacing - volt setting - amps avalible)

I just don't know if I have the numbers right &/or other things that factor in ???

 

[kurt]

PM sent to me ---------

I agree with you. No where on this forum have I been able to find an 'optimum' current density for either the anode or the cathode. It seems like there should be a scientific publication on that very subject somewhere. Nor, have I been able to find an optimum ratio of anode size to cathode size, if any such thing makes a difference. I have seen some statements that it does matter without any real value or reasons given.

I have come to think lately that the amount of current is not the issue. Rather it is the current density. What I'm saying is that you could run 100 amps if you kept the voltage in the proper range and had the anode and cathode sizes to fit. Oh, then there is the temperture thing.

What about Ph. Some say it matters and some say it doesn't.

I'd like to get a little deeper into the subject.


My reply ------

Yes – so would I


I would like to post your PMs to the thread I started (on the forum) along with my replies & see if what we have discussed here in PMs will spark more in put on the subject

 

[kurt]

PM sent to me ---------

Current density at the cathode -

Seems to me like slow growing crystals would get fat (not skinny and long). Also, smaller current at the site of a particular crystal should allow it to grow slower and get fatter. So, how would you get a smaller current at the site of a crystal? Either decrease the total current (taking longer to dissolve a particular anode), or spread the current out over a bigger area.

I think size does matter (!). If you used a cathode to large then you would have to run a lot more anode silver before the crystals got to the size desired. A cathode to small would encourage long skinny crystals.

So, we need to find a happy medium for the cathode size. Does that make sense?

Next, we can't push the electrons off the anode to fast (why not?). Than means we need to find a maximum rate we can push them off without causing other undesirable factors.

Then there is the electrolyte. What factors are there in the electrolyte itself that encourage or discourage a fast production rate and desirable crystals?

Basically I'm trying to figure out what questions to ask.

My reply --------

All good questions - I just don’t have all the answers


I believe (or at least hope) that what we have discussed here in private once posted to the forum will spark in put from some of the real pro's