Electrolytic Silver Cell

Here is a photo of a 2 liter (two, one liter cells wired in series) electrolytic silver cell that I have operating.

I had to replace the wire lead going to the graphite cathode at the bottom of the cell on the right.

The electrolyte had breached the seal and dissolved away the copper wire lead where it connected to the graphite cathode.

I drilled the hole a little bigger and replaced the lead with a larger diameter copper wire.

This decreased resistance and voltage and caused the silver crystals to form abnormally (very thin needle like) instead of thick chunky crystals like the ones produced by the cell on the left.

The electrolyte is silver nitrate made by dissolving 110 grams of fine silver in 1 liter of liquid in each cell. The anode bars are cement silver from 925 and sterling jewelry items - dissolved with dilute nitric acid and cemented on clean copper.

The anode basket is a tupperware style plastic food container with dacron material for filter bags. The material came from vacuum cleaner bag filters at Lowes.

Uses a converted PC power supply running off the 3.3 volt rail of the power supply.

As pictured, the cells contain about 25 or so troy ounces of pure silver metal. The blue color of the electrolyte is from copper that came along from the cementation process when I made the silver anode bars.

The anode bars are about 99% pure silver (after cementing on copper) with copper as the main contaminant.

After running through the cells, the silver is a little over 99.9% pure.

After all the anode bars have dissolved I will harvest the pure silver from the cells and send it all back through the cells one more time to try and get the silver to 99.99% purity.

I harvested the silver crystals from the cells and installed new cathodes - each one identical in size with identical diameter lead wires.

This seems to have solved the problem I was having as both cells are now operating properly and crystal growth is uniform in both cells.

kadriver

Here is a shot of the beaker containing nice fat chunky pure silver crystals. They have bright reflective facets.

Crytals out of the container, washed and dried in my hand as you requested.

The picture does not do them justice - they sparkle like gems - absolutely beautiful.

If anyone is interested, I can set some of these aside and sell them individually.

I have not had them assayed, but I am fairly certain that they are pretty close to 99.99% pure elemental silver.

kadriver

Silver refining

HCl does not produce silver and would serve limited refining utility. As there are plenty of other insoluble materials that can get in the cell (like PbCl2, slag).

Also, avoid ammonia or ammonium and silver combinations. As a good rule, keep ammonia away from gold and silver, at the risk of forming fulminating compounds that are indeed most unpleasant.


While kadriver's crystals are beautiful and over 99.99% pure in his well-managed cell, they are not what is preferred for production.

As copper content increases in solution, silver sand and fine needles are produced rather than large dendrites. This finer grain material is more easily rinsed and does not entangle so that it may be filtered and pack better into crucibles.

Here is a Balbach-Thum cell.

To grow large crystals, a Thum cell is better as there is less stress on the crystals than if they were clinging to an anode. It is also best to use a high concentration of pure silver in the electrolyte and less current density. A production cell runs at 40-50 A/ft^2, a fifth of this is more than enough to grow large crystals. Voltage should be on the lower side (max silver should ever be plated at is 3.8 V).

I'm trying to replicate what I guess would be the "failure" of the original poster. In other words I'm trying to grow the long slender crystals and not the compact, easily filterable form. I'm not trying to do a purification, I'm just trying to grow large crystals.

I attempted to duplicate the above cell (although not two of them). I'm using a computer power supply, 3.3 V rail as above.

The cathode is a block of graphite 2 x 3 x 0.375". Total surface area 16.6 in.². It was fitted with a very heavy gauge copper wire that is threaded into the heart of the block. The hole is thoroughly sealed with hot melt adhesive (by warming the graphite).

The electrolyte was prepared by placing 150 g of small silver chunks into 115 mL of concentrated nitric acid. The solution was heated until several things were observed. Bubbling at the surface of the silver stopped. No further brown fumes were being evolved and the solution have lightened to a pale green. The undissolved silver was recovered and it was found that 112.5 g had dissolved. This solution was clarified by filtration after first being diluted to a volume of 950 mL. The concentration is thus 118.4 g/L of Ag.

The electrical parameters of my cell were quite different. The voltage across the cell when operating, was 3.35 V. Interposing an in-line ammeter only gave it a current of 1.80 A, suggesting a cell resistance of 1.86 ohms. Curiously, when I simply measured the resistance of the cell with no current passing, I could only get values in the 7 - 8 ohm range. I have no idea why this occurs, but I trust the calculated value of 1.86 ohms (because it sounds better to me?).

The silver crystals that grow change from the original slender columnar structures seen at the bottom of the picture, to a more broccoli type structure. Still I am not seeing any substantial crystals.

I'm at a loss to explain the difference in the electrical parameters of the cell. I'm also unsure of what direction I want to go in to modify the crystals that grow.

The apparent bubbles that you see in the solution are not rising from the electrode. They are simply stuck to the glass wall. As with the original poster, the pale green color is caused by a tiny copper impurity from cementation.

Can anybody suggest where to go from here?

Edit: Is all graphite created equal (more or less)?. This graphite from a Monofrax factory, where it serves as a mold material. Does this, perhaps, explain the low current?






[Edited on 7/20/2017 by Dan Vizine]

Second time through (same electrolyte)

Current = 1.43 A Electrode = 0.115 square foot Current density = 12.4 A/sq. ft.

Entirely different crystals, much cleaner looking.





[Edited on 7/21/2017 by Dan Vizine]

Seems that I was just reinventing the wheel. Fleaker's site (naturally) has all the information needed to optimize parameters for this task. The above run gave a few fair crystals (picture). The largest is only 5/8" inch long, though.

The present run (substituting a wall wart for the PC power supply) and having only a small surface area anode (solid) is currently growing much nicer crystals. Parameters: 2.1 VDC measured across cell, current = 0.71 A (higher than I'd like).

Fleaker's forum also taught me that you only count the cathode surface area that faces the anode (and the sides). My recalculated cathode area is 10.6 sq. in., which is 0.074 sq. ft. The current density is 9.6 A/sq. ft.


As all of this is old news, I won't be updating this thread any further.





[Edited on 7/23/2017 by Dan Vizine]

Many moons ago I found a circuit that was for charging dry cell batteries (Zinc carbon). These batteries cannot be charged according to the book but I belived you can charge them and make them last longer. There was an actual law passed in Japan way back to stop people stating that this type battery could not be recharged ( I believe).

See:
https://electronicsproject.org/dry-cell-charger/

Anyhow I remember experimenting with a circuit similar to attached using copper sulphate solution and growing some very elaborate looking copper trees. The small current reversal seems to give much better dendrites than plain old dc.
Should give a similar effect with silver I would imagine.

Yob

Quote: Originally posted by yobbo II

See: https://electronicsproject.org/dry-cell-charger/ Anyhow I remember experimenting with a circuit similar to attached using copper sulphate solution and growing some very elaborate looking copper trees. The small current reversal seems to give much better dendrites than plain old dc. Should give a similar effect with silver I would imagine. Yob

Ahh yes....this contraption seems to utilize the same principle as a method called "reverse pulsed plating" where a portion of the current is passed through the plating cell in the reverse direction. The objective being the prevention of dendrite formation for purpose of plating very thick layers on geometrically complicated substrates. As dendrite formation is predominantly favored on edges and protruding parts of the cathode where the field density is highest, so is their dissolution during the reversed current pulse. By selecting the correct ratio of cathodic and anodic pulse periods and current densities one can effectively stunt the dendrite growth or grow a more sturdy wellformed dendrite stucture that may look very spectacular:

http://www.physic.ut.ee/materjalimaailm/Pildid/th_102_0232_R...

This copper "crown" was grown in a reverse pulse plating mode and turned out quite impressive

Thanks for that suggestion, it seems very worthwhile to try.

Meanwhile, I've gotten crystals as long as 1.5 inches. The picture is processed to maximize the contrast of the faces. The crystal is bright silver in color.



And without jacking up the contrast they look like the second image.

[Edited on 8/1/2017 by Dan Vizine]

I decided to go ahead and build the circuit today. R1 is a 16 ohm wire-wound potentiometer. R2 is 500 ohms. The resistors are generic rectifiers from an old power supply. I incorporated a couple switches so that I could easily adjust the ratio of the currents between the 2 legs. My power supply is a 12 VAC 1 A wall wart plugged into a Variac to control the output voltage.

I had been running another electrodeposition at 1 V and was getting dense crystals, but nothing large. I hooked the new circuit up and adjusted the Variac until the output across the normal polarity leg (hooked to the cell) was reading 1.44 V and and the current flowing through the cell was 0.38 A. I switched that leg of the circuitry out, and switched the reverse polarity leg in. As expected voltage was the same within the limits of reading errors, and then the potentiometer was adjusted so that the reverse polarity current would be 0.03 A. I switched both legs on and interrupted the earlier deposition and switched the new supply in. I had to run an errand for a couple hours and when I returned I found that the nature of the crystals that were growing were different . Instead of forming endless fields of uniform dense crystals, straight arms had begun to grow. Now comes the hard part, waiting.

I want to thank you both for the suggestion (for the reverse polarity). Early results seem to suggest it's going to be very useful.



[Edited on 8/1/2017 by Dan Vizine]