I noticed after running my silver cell for 2 days gray/soft non-shiny crystal are depositing on top part of the cathode(about 3/4 of a inch under the surface of the electrolyte). I have no idea what's going on, the deeper part of the cathode still grow hard shining crystal. The color of the liquid is still very clear with only a light green color so I guess it's not overloaded by copper. Are those crystal less pure or does it has something to do with oxidation since it is close to the surface? Anyone got a idea?
Silver cell growing gray/darker crystal
- Thread starter elfixx
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Any change in amperage? Voltage? Check to see if you have bridged somewhere, and you're depositing something that isn't silver. If there's any stainless in your anode basket, for example---if it becomes part of the circuit, it will co-deposit things you don't wish to include in your pure silver. Look for signs of conductivity that's created by silver nitrate crystallizing on surfaces above the electrolyte that can be a pathway.
Something isn't right-----your anode bag may be too tight and your silver level in your electrolyte has dropped. Been there, done that.
Harold
Something isn't right-----your anode bag may be too tight and your silver level in your electrolyte has dropped. Been there, done that.
Harold
Everything look fine... the voltage and amperage still the same, there is no non-silver part touching the electrolyte and I used the same filter material as I usualy use, I can't find anything wrong. I know the silver from the anode contain a few unusual contaminant since it is from litho, could it has anything to do with this?
That could make sense, the cell is a 4l glass beaker just in front of a window.And I just melted a very small sample of these gray crystal and I saw no sign of oxide or impurity. And I also noticed that these crystal grow only when directly on the cathode, what I mean is when they start to grow bigger and therefore growing on top of existing crystal and not directly on the cathode, they look silvery and shinny just like regular silver crystal.
Another thing, I just lerned that I can set the voltage when the cell is running and not only before hooking the power, so I raised the volatage to 3v giving about 9 amp and those famour gray crystal on the top of the cathode turned out black but as soon as I shut the power off the black color disapear and they became gray again. Does that provide any clue to what's going on? Would that have anything to do with the fact that the cathode is made of titanium and it is forming some kind of oxide?
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I'm at a loss. So far as I know, titanium is inert. Do let us know what you determine, however.
One thing that makes me wonder is electrolyte depletion. I had that experience when I processed silver that had an excess of platinum metals included. They formed a hard coating around the anode, so hard it was difficult to scrape off. As the silver content declines, the cell started co-depositing palladium. I'm not suggesting that that is your situation, but if your electrolyte is lacking in silver, the electrons will deposit what ever is at their disposal, or so I think.
You may gain some insight by dissolving a small amount of the darkened crystals. That's how I used to determine if my silver was pure. The slightest trace of copper would be exposed by testing with ammonium hydroxide. Should you elect to follow up, use more silver than you expect to dissolve, so you can consume all of the nitric. I found that the solution would clarify by taking to a light boil, keeping it covered with a watch glass. Solution color would generally shift from a pale green to a pale yellow color as the gasses were liberated. If the color remains slightly green, that's a fair indicator that you have been co-depositing copper. That's what I expect may be happening.
Any sulfur included?
Harold
One thing that makes me wonder is electrolyte depletion. I had that experience when I processed silver that had an excess of platinum metals included. They formed a hard coating around the anode, so hard it was difficult to scrape off. As the silver content declines, the cell started co-depositing palladium. I'm not suggesting that that is your situation, but if your electrolyte is lacking in silver, the electrons will deposit what ever is at their disposal, or so I think.
You may gain some insight by dissolving a small amount of the darkened crystals. That's how I used to determine if my silver was pure. The slightest trace of copper would be exposed by testing with ammonium hydroxide. Should you elect to follow up, use more silver than you expect to dissolve, so you can consume all of the nitric. I found that the solution would clarify by taking to a light boil, keeping it covered with a watch glass. Solution color would generally shift from a pale green to a pale yellow color as the gasses were liberated. If the color remains slightly green, that's a fair indicator that you have been co-depositing copper. That's what I expect may be happening.
Any sulfur included?
Harold
I have no Idea how sulfur could have been introduced to the cell so I would doubt that's the issue. However I melted a very small sample of those soft crystal and there was no sign of impurity on the button, perhaps disolving some of them would give a better idea. I took note that you said it could be related to the lack of silver in the electrolite, so I disolved some more silver in nitric to add to the cell and raise the concentration. I did started with a concentration of 80g per litre which should have been enought and my filter bag is quite porous, I guess the electrolyte depletion is related to the size of electrode or volt/amp versus the sise of the cell. It look like it solved the problem however that doesn't explain why those strange crystal where only forming on the part of the cathode that was closer to the surface.
Perhaps your cathode is contaminated with a base metal that is cementing some of the silver from the solution giving the darker crystals?
Steve
Steve
