Growing large silver crystals

[modtheworld44]

Topher

I think you are way over thinking this whole thing with all of the membrane cell, closed loop cell, divided/two chamber cell additives, etc. etc. etc.
....
I do have some ideas - just have not had time to test them out

Kurt

Yes, yes I am. Far too much, on the overthinking.
Its a problem I have.

What might your thoughts be, as far as the "how"?

A gallon cookie jar probably had a pretty good distance between the electrodes, eh?

Topher_osAUrus


My last silver cell gave me some very nice crystals,But I don't run mine like everyone else does.It's been about 2-3 years since I've run it.I start my cell with less than 20 grams a liter,and I limit my cell by using a single hole of about 1/8 1nch in the center bottom of the anode basket.I use a 12v 3amp regulated power supply and a four quart stainless cylindrical soup dish.The type the restaurants use on a buffet line.I'll have to see if I can find the pictures I took.If I were to re design mine for more dense crystals,I would change the size of the cathode to about a dime.I would also move the cathode about a foot away.

I would also use a narrow but tall container,no wider than my anode basket.This is just my opinion and plans for my next cell.Thanks in advance.



modtheworld44

 

[Palladium]

but washing more than a couple pounds of silver cement is a pain in the rear.

What is your process?

 

[Topher_osAUrus]

What is your process?

To wash my cement silver, I usually siphon off all the copper nitrate, then let the silver settle awhile with the vessel tilted, so it compacts in a corner. I slowly turn the bucket, beaker, or whatever Im using and let the copper nitrate continue to ooze out the corner of the compacted cement. Then suction bulb/pipette it up. The removed copper nitrate, goes back to finish cementing whats left (if any).

After satisfied with removing as much as humanly possible (without a filter press), I add enough water to cover the cement, plus just a little more. Heat it up til near boiling, then repeat the siphoning process again. Letting the silver cement compact on one corner, then slowly roll the bottom so it seeps out. These subsequent rinses I save and use as my added water when dissolving sterling or goldfill.

Sometimes it takes awhile for the cement to settle and seep out the rinse waters, but it gets cleaned up in fewer rinses, so I suppose patience is the key. With sterling and inquarts, it has not been a big issue. My problem has come from contact points.

I had recently overshot the nitric because I was fooled by a couple tungston points that had no waffle back pattern. This ended up giving me some cement that likes to float on top. It was difficult to get it to settle, even after breaking up the silver floaters. Lesson learned, the long and hard way. :evil:

 

[peter i]

I’m still alive :wink:

It has been 7 years since I last wrote something in here!

Things have been fine (I even published a book about chemical demonstrations last year), but the refining has been somewhat limited.

I ended up having some pretty nice crystals, but not as big as I would like them to be.


In my summer holiday I dusted off some old parts and started cutting and gluing some perspex to make a cell for slow growth with minimal evaporation. It is chugging along at 0.2 volt at the moment.

Nice to see that this thread had posts for years after I “disappeared”.

 

[anachronism]

That looks fantastic. 8) 8)

 

[FrugalRefiner]

So, other than minimizing evaporation and extremely low voltage, are there any other parameters you can share?

Dave

 

[peter i]

So, other than minimizing evaporation and extremely low voltage, are there any other parameters you can share?

Dave

Minimal evaporation is primarily to avoid having silver nitrate crystals growing all over the place (I wholeheartedly agree with the alchemists for calling it “lapis infernalis”) and to avoid having to top the cell up with distilled water. The lower density made it form a visible layer on top of the silver nitrate solution.

The question is, whether the beneficial effect of very low voltage really is from the low voltage, or if it is Ohm’s law that gives a correspondingly low current. Growing large crystals is all about having the right super saturation to make the crystal lattice grow, but not enough to overcome the energy barrier to nucleate new crystals.

Placing the donor at the bottom of the cell and the receptor at the top could simplify a lot of things, but even at very slow growth, the solution at the top of the cell was depleted.

Another test that gave good results was to cast a 25 mm cylinder from fine silver, cover it with hot melt glue to isolate sides and bottom, then standing it upright in the corner of the cell with the acceptor in the opposite corner. Then it would slowly dissolve, at the available area kept constant (like a “cigarette-burning” rocket motor).
The question is again, what really happened? Was it limiting the current that made it slow?


Stirring did not seem to do anything positive.


The silver nitrate solution was made by saturating a 6 M HNO3 with fine silver crystal.
I later used a donor cast from sterling silver, letting the copper concentration increase, but it did not seem to have any effect.

To sum it up:
High concentration and low voltage/current is good.
Limiting the available area to dissolve seems to be good too.
Copper does not seem to make much of a difference.

I have a theory, that a large cell would be better, because it will even out local fluctuations. When the crystals approach the donor, they tend to nucleate more.
But so far, I will be playing with voltage and area.

 

[peter i]

A couple of pictures of the latest cell:

A vase from IKEA and 5 mm perspex.
The bag is made from non-woven kitchen rag.

 

[Shark]

Thanks for the update.

 

[FrugalRefiner]

Thank you for sharing Peter! One of the many projects on my "to do" list is trying to grow some large crystals.

Dave

 

[Lou]

I have a theory, that a large cell would be better, because it will even out local fluctuations. When the crystals approach the donor, they tend to nucleate more.
But so far, I will be playing with voltage and area.

Peter, could you test it with a ramped cathode that is set further away from the anode? I noticed when I used to run cells that the largest and least tree-and-bud dendrites were always the most distant from the area immediately under the anode. We eventually made anode boxes that moved on tracks to lay down a more even deposit, but when I had to push the cells manually at all hours, I started to notice that. Also, anode-cathode gap of course affected the current density upwards and gave lower voltages. I think the best (edited to add) result might be lower current density with AC superimposed on DC. I have seen that done at very large gold Wohlwill setups to get thicker, better deposits.

What do you think of this design? Lower current density as more cathode area relative to anode but with less flux in concentration of [Ag+] because of phase density differences. I'm surprised stirring did not help but I too have seen DI water sit on top of saturated (1kg Ag/L or more) solutions of silver nitrate.

 

[peter i]

It absolutely makes sense.

I see something along the same lines.
Things will grow at the bottom, but once something gets ahead, that branch tends to accelerate.

What does not make sense is, that sometimes a crystal decides to grow a lot larger than the other for no apparent reason.

This is from today:
(Starting to get some color from using copper-cemented silver and a bit of gunk has made its way through the cloth :evil: )

 

[Lou]

I edited my comment above and dug into some more research. Here's a patent on it:

https://patents.google.com/patent/CA2929515A1/en

that's for copper. Why it's a patent is beyond me as I'm no electrical engineer but it's fairly well known to get smoother deposits and better anode dissolution in a silver and gold cell using that approach.

I think the leading tip of the dendrite tends to grow because the pinpoint/singularity of the growing tip is the closest to the anode and as such will have the least resistance barrier to current/ion mobility-mass transport.

I am not sure, but something about the AC superimposition knocks the leading edges down and fattens the base of the tree. Might be for you to experiment with, I'm already being remiss at work!

Here is a good book on copper refining that talks some about this too (pgs 70-80):
https://books.google.com/books?id=BRVDAAAAIAAJ&lpg=PA75&ots=SGsjaZUz79&dq=what%20causes%20crystal%20formation%20in%20copper%20refining&pg=PA75#v=onepage&q&f=false

 

[peter i]

Interesting!

I have made an arduino controlled relay, that can switch the direction of the current. Letting it deposit, then reversing for a short time, to dissolve a bit again. Small crystals have more relative surface, and should dissolve readily.

(Not tested yet)

 

[Lou]

Yes, forced unnatural selection by surface area to mass.

 

[Lino1406]

It may be interesting for you if you Google for this, and related material

 

[Jodokast]

I would just like to say thank you to this for forum. I've never posted on here before but I felt this being my best Crystal's to date I would share them. Combined weight of 3.22 Oz.

 

[Shark]

Jodokast, those are very impressive! I hope to get mine looking like that some day.

 

[peter i]

Nice!

What conditions were they grown at?

 

[Jodokast]

It's been a lot of trial and error so its hard to say exactly what perimeters made it grow so well (and continuing to do so in one of my cells). This thread has provided a lot of direction, mixed with lots of hours studying and some luck.

• 1000ml beaker.

• Using a cheap variable bench top DC power supply and have found between 300-450mA to be the sweet spot. With amps set, voltage tends to be anywhere from .4-.8v.

• My AgNO3 concentration is difficult to say exactly but after reading Peters post about not having too much to precipitate out as salt because of having to add H2O it clicked in my head. Most crystals are grown in a saturated solution and time to evaporate. So I started with about 7 oz/L then would take the resulting crystals and redissolve them in another beaker and add it until my anode bag began to show AgNO3 crystals on the part above the solution after a day.

• I started with a fine cloth for the bag and after a day switched to cloth which had larger thread to allow the ions to flow. (one thing i noticed is if the anode bag/basket has bubbles collecting under the holes you need to change or go lower thread count.)

• I have silver shot in the basket with a rod the size of a sharpie marker running down the middle of it attached to my power source.

• The cathode is a solid copper wire with a 1cm wide piece of stainless bent over the end and hot glued into place.

• The only thing else I can think of is I added a tiny bit of H2SO4 when dissolving the crystal that I added to the electrolyte.

My thoughts are highest saturation possible is good, temperature seems to play a role its been getting colder here in Denver. Power needed can vary and I make slight adjustments on a daily basis. When I did my change out to pull crystals I used some distilled h20 to rinse and that diluted the solution leading to not as good of growth so I heated my electrolyte to remove some h20 and also added some more AgNo3 and its back to looking good. I also have been knocking down the tall ones and they continue to become more dense with time.