Growing large silver crystals

[peter i]

Yes, I've tried changing shapes, and the crystals would grow as the liked anyway (changing the shapes radically).

I've also tried using a magnetic stirrer, which made the crystals grow in a slight bend along the direction of stirring, nothing else.

 

[qst42know]

This is from the reference book GSP posted in the other thread. Found down a couple pages.

"Parting of Bullion.—The electrolytic parting of bullion rich in gold is effected by the same methods. At the Philadelphia mintl a modified Moebius process is used. The anodes (30 per cent. Au, 60 per cent. Ag, 10 per cent. Cu, Pb, Bi, Zn) are encased in cloth bags and hung alternately with rolled fine silver cathodes in an earthenware trough. The electrolyte contains 3-4 per cent. AgN03 and 1-5 per cent. HN03, with certain quantities of dissolved anodic impurities. The current density used is only 0-75 amp./dm.2, and the voltage is low—one volt. A trace of gelatine (1 : 8,000-10,000) is added to the electrolyte. This causes the silver (or nearly all of it) to deposit in a coherent crystalline form, a behaviour rendered easier by the low current density. The metal is exceedingly pure, and the current efficiency approaches 100 per cent. The anodes, after parting, retain their original form owing to the high content of gold. Owing to the large percentage of base metal dissolving, the electrolyte needs frequent renewal."

Could gelatine be the missing piece?

 

[peter i]

Could gelatine be the missing piece?

It could yery well be the case. I found a paper describing the effect of tartaric acid in the growth of silver crystals, and it seemed to have a similar effect of inhibiting the nucleation.
Normally I would expect a thin solution of gelatine to be "alive" with bacteria/fungi rather quickly.....but with lots of silver in it, I think that should be taken care of.

My present experiment will be terminated this weekend, it has grown a nice and shiny cluster (or rather a bush) of small crystals.

0.6 M AgNO3
0.7 Volt
Cast ingot with limited surface access
low temperature

I'll recover the crystals and let it continue with addition of a bit of tartaric acid.

 

[peter i]

I've started a new run.

Cast a 140g cylinder from cupper cemented silver powder, covered bottom and sides with hot-melt glue to limit available area to approx 4 square cm
Stood the cylinder on bottom of beaker
Covered with electrolyte (silver nitrate, approx silver content 60g/litre ~0.6 M)
Voltage 0.7 V
"Receiver": 10cm of fine silver wire coiled to a flat spiral
Temperature: ~5°C

The general idea is to limit nucleation to allow continued growth of crystal. Nucleation increases with supersaturation and temperature, and I attempt to counter this with low temperature and low current. So far it has resulted in a lot of small crystals...
:shock: .....

And this is the result of a month of growth:
A bush of very dendritic crystals.
Total weight: 50 grams, meaning there is still 90 grams in the original lump for further experiments.

 

[Anonymous]

Hi Peter,
Its been a while since I checked on this thread. Got a couple questions, have you tried voltage even lower than .7v? or haveing a reversing period of the polarity to redissolve the tiny crystals? do you have a method of stirring the solution? I am very interested as the pictures Harold posted of the large crystals are awesome and I think would be nice to be able to make and maybe even get a premium on the silver content.

thanks
jim

 

[Anonymous]

Flash of inserpation, what if your anode was half a hemispere so that no point of your seed crystal was actually pointed at the anode making the electrical field more uniform and allowing the one seed to grow in all dimensions with a more uniform solution at the same time.

Jim

 

[lazersteve]

Peter,

Beautiful silver you have grown there!

Steve

 

[peter i]

Peter,
Beautiful silver you have grown there!
Steve

Thanks, not the crystals I wanted, but certainly pretty.


Regarding stirring:
Yes, I've tried that, and it only gave the same dendritic growth. The crystals were however showing a tendency to "grow with the flow" rather than forming a symmetric hemisphere.

Reversing the current for short periods of time (say 10% of the total time) is a strategy that I seriously consider. It is however in the department of electronics, and I prefer to test all the possibilities in chemistry before opening a new field of parameters.
In theory it could dissolve newly formed crystals preferentially to the larger well established. "pulse-reverse plating" is quite common in electroplating to ensure uniform layers of metal as far as I know.

(Using tartaric acid has moved a little down the list. According to the papers I've found, quite a bit of tartaric acid is incorporated in the deposited silver, not something I'd like to happen )

I've tried to change the shapes, but the crystals just seem to grow as they please :|

An alternative to stirring would be to rotate the negative lead slowly (another technique common in growing large crystals) but this raises a lot of other technical problems. I have some possible solutions, but will prefer not having to use them if simpler solutions are available.


For the next run. I'll simply raise the concentration of silver ions in the cell as much as possible (aka saturated solution)

 

[peter i]

and a picture of the crystal cluster and the silver wire:

 

[peter i]

I've started a new run.

Same set-up as before, but a higher concentration of silver ions (I will have to test to give the exact concentration) and only 10 mm of exposed silver wire for growing the crystals.

I can see them growing, but let's see in a month or so....

 

[peter i]

basically the same parameters, but a much higher (analysis pending) concentration of silver nitrate.

Faster growth, larger crystals!
(Largest 8 by 12 mm)

47 grams total, grown in 18 days.

 

[pinman]

Simply Beautiful, and inspiring.

 

[butcher]

jewlry is worth much more than metal, and those crystals are artwork. 8)

 

[peter i]

Thanks, and yes, they are fascinating.

Reflecting almost all of the light falling on then, they glitter like a cluster of diamonds (I really tried to photograph it, but failed miserably). Thousands of little mirrors pointing in all directions.....

The value as jewellery is unfortunately limited.
- the crystals will tarnish with time
- Very pure silver is pretty soft, and they will easily become scratched, or the rather weak bonds between the crystallites will fail
- soldering them onto something is likely to tarnish them, and it will be hard to regain that "pure crystal plane"-shine

(On the other hand, I have a tendency to make my jewellery in a way that makes it usable as a knuckle duster without deforming.... maybe I should reduce the workmanship and emphasize the "art" using these anyway)

 

[Irons]

Thanks, and yes, they are fascinating.

Reflecting almost all of the light falling on then, they glitter like a cluster of diamonds (I really tried to photograph it, but failed miserably). Thousands of little mirrors pointing in all directions.....

The value as jewellery is unfortunately limited.
- the crystals will tarnish with time
- Very pure silver is pretty soft, and they will easily become scratched, or the rather weak bonds between the crystallites will fail
- soldering them onto something is likely to tarnish them, and it will be hard to regain that "pure crystal plane"-shine

(On the other hand, I have a tendency to make my jewellery in a way that makes it usable as a knuckle duster without deforming.... maybe I should reduce the workmanship and emphasize the "art" using these anyway)

You have to watch out for people with diamond rings on every finger. The police are wise to that trick. :twisted:

 

[jimdoc]

The value as jewellery is unfortunately limited.
- the crystals will tarnish with time
- Very pure silver is pretty soft, and they will easily become scratched, or the rather weak bonds between the crystallites will fail
- soldering them onto something is likely to tarnish them, and it will be hard to regain that "pure crystal plane"-shine

Couldn't you seal the crystals in resin and make paperweights or other items that will last forever. I see people selling element samples sealed in resin blocks. Sealing in the crystals to preserve them and their beauty and also to protect the fragility. I know I would buy a paperweight made with your crystals.
Jim

 

[peter i]

That's a nice point!
(hmmm, I've long wanted to cast other object in resin, must find some now!)

 

[Toobigfortx]

First A Little Background Info:

I'm 23 I've Been Interested In Chemistry Ever Since I First Learned What It Was. However I Have Not Completed My Studies. Presently I Have A Makeshift Lab Set Up I Have Nearly All The Equipment For This Project Of Mine I Just Need Some Helpful Advice/Instruction.

Project(Keep In Mind I'm Still A Beginner)

Purifying Silver To The .9999 Level.

I Have Roughly 5 Pounds Of Silver At .900 Or Better. I Want To Raise It's Level To .9999.
Methods I Know Of are: Nitric Acid + Silver -> Copper (II) nitrate*. And Precipitating .96-.98 Silver

From There I Know I Can Use Electro-chemical Refining From There On, But I Think There May Be Other Ways Of Doing This That Dont Involve Me Having To Buy Or Make Nitric Acid. Seeing As How The Price Of Nitric Acid Is High, As well As Silver Nitrate I Would Prefer Some Information On Alternative Means To Refine The Metal.

Also As A Side Note I Have a Question About The Electrochemical Refining. Can I Just Melt Down The .900 Silver And Still End Up With .9999 After The EC Process Is Finished, Or Will I Have To Use The Nitric Method First? Sorry I Know Its Not In Line With Crystal Growing But I Would Still Like to Learn Both If Possible


**Corrected from 'sulfate' to nitrate by Lou. PS--Hereafter, please do not capitalize every single word in Every Single Sentence You Write. It is very irksome.

 

[qst42know]

Running .900 silver in your electrolytic refining cell will quickly contaminate your electrolyte as I understand the process.

 

[Toobigfortx]

Running .900 silver in your electrolytic refining cell will quickly contaminate your electrolyte as I understand the process.

Thats what I was afraid of. Well then I'll have to go the nitric acid route and use the electrochem to purify. further