Some questions for Kephra - I have read many articles here but none of them seemed to satisfy these questions:
A: I've gleaned from reading here that there is a minimum desired potential across the cell. How is that calculated, taking into consideration the Rod-Diameter and Distance between them, etc?
It is calculated from the electrochemical series which gives the voltages needed to oxidize an element or reduce it. This makes the minimum voltage 3.52 volts as explained in the articles if there is 100% conductivity in the solution. But of course, there is not 100% conductivity in the solution and you cannot calculate it. The solution conductivity depends on the amount and kind of electrolyte, the temperature, and the exact electrode geometry. So the practical voltage must be above 3.52 volts. Above 10 volts is a good practical rule.
Electrode geometry is not a factor in determining the minimum voltage of 3.52 volts. Only the two metals involved, namely sodium and silver are determinant.
B: If the answer to A doesn't include WHY, please answer THAT here
C: Would running 3 mA instead of lets say 5 mA produce smaller nanoparticles? How about 15, 20, 60???
No. The size of the nanoparticles is determined by the reduction chemistry factors like the kind of reducing agent, temperature, pH. However, the current does affect affect the rate that silver oxide is produced, and producing it faster than it can escape the boundary layer between the anode and the bulk water allows the silver oxide to precipitate instead of dissolving into the water. Since larger anodes have a higher volume in the boundary layer, larger anodes help prevent the silver oxide to precipitate.
D: Do higher rates affect the solution in ways OTHER than making it faster? I.E. I could make 20ppm in 15 min at 20mA, 6 min at 50 mA (all of course using a electrolyte AND assuming the solution will actually pass the current)
See C.
D: 3 mA seems to be the number thrown around as a minimum.... Why?
Practicality. Very low currents require lower cell voltage. There is no concrete lower limit providing you adjust all the other parameters to fit.
E: Very wide voltage ranges are used in the real world. from 9 to as high as 40. In my mind, It would seem that the smallest particles that one could make would be when the amperage and voltage are JUST above the threshold that allows ionic production. I see it like arms in a pole pushing basketballs off itself. Violent push ( High potential and high current) sloughs off several balls at a time where gentle pushes do only 1 at a time. Am I envisioning this completely wrong?
Yes, its current which is the important factor. However, its the voltage which creates the electric field between the electrodes, and its the electric field which drives ions from one electrode to the other. Since the ideal is to quickly remove the silver ions out of the anode's boundary layer, a higher voltage for the same current is helpful in doing that. If the ions are not removed quickly enough, they precipitate at the anode, and become visible as a brownish cloud. Once precipitated, they are no longer moved by the electric field because the silver oxide particles have a net zero charge.
This is all a big balancing act. Everything you change affects everything else. For example, If you change the electrode spacing, the conductivity between the electrodes change, and the electric field strength also changes. Changing the amount of electrolyte also changes the conductivity, which affects the voltage needed to maintain a given current. Changing the temperature affects everything. Then there are practical considerations like having an electrode spacing that will actually fit in common flasks.
So some things can be exactly calculated like the amount of electrolyte per liter of solution, and some cannot be calculated but must be determined experimentally. I worked out my recommendations based on the pH to produce the best zeta potential, reasonable electrode spacings, workable safe voltages, etc. These recommendations produce excellent nanoparticles in the non-toxic and therapeutic range with no toxic byproducts. Is this the only way to do it? No, but it works easily for the home colloidal silver maker.