calgoldrecyclers
Well-known member
see... science is fun!
Growing large silver crystals
- Thread starter peter i
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calgoldrecyclers said:
You can do the same thing, in bright sunlight and Mozart blaring in the background.
End result? Silver crystals. If you straighten or coil the wire makes no difference. That is the commonly accepted method for recovering silver from a nitrate solution, and is nothing new.
Remember-----we are men of science, not witch doctors.
Harold
calgoldrecyclers said:
Yeah, a classic and the product is crystalline (even made a PXRD just for the fun of it).
But I'm going for huge, mean and nasty crystals in the centimetre range, and I've never seen anything larger than coarse powder from that process (regardless of temperature, concentration and shape/area of the copper plate).
The fun thing is to find the parameters allowing the reproducible growing of large crystals.
#7 Concentrated silver nitrate and 0.1V
Yet another stinker. Lots of small cubic crystal growing in a dense clump.
The positive end was the same old ingot and a pile of silver crystals.
In my mini silver cell, however, nice large crystals are growing. And it seem to prefer growing larger crystals when the dissolving bar is almost gone.
The main differences seem to be:
- Mini cell is operating below 10°C, the micro cell is at low room temperature.
- A large difference in area between growing and dissolving metal. In the mini cell the growing part is the largest, in the micro cell it is the smallest
- Less clean solution in the mini-cell (I'll make a gravimetric test of the actual silver content quite soon)
- larger distance from dissolution to growth in the mini-cell
- pH value will have to be tested too. Acid could prefer eating small crystals, thus favouring the growth of the larger ones.
The fun part will be to find out, what's important.
Yet another stinker. Lots of small cubic crystal growing in a dense clump.
The positive end was the same old ingot and a pile of silver crystals.
In my mini silver cell, however, nice large crystals are growing. And it seem to prefer growing larger crystals when the dissolving bar is almost gone.
The main differences seem to be:
- Mini cell is operating below 10°C, the micro cell is at low room temperature.
- A large difference in area between growing and dissolving metal. In the mini cell the growing part is the largest, in the micro cell it is the smallest
- Less clean solution in the mini-cell (I'll make a gravimetric test of the actual silver content quite soon)
- larger distance from dissolution to growth in the mini-cell
- pH value will have to be tested too. Acid could prefer eating small crystals, thus favouring the growth of the larger ones.
The fun part will be to find out, what's important.
What power source are you using for these experiments?
If it's just a transformer with a rectifier bridge you will get a full wave tension, making crystal growth irregular. Try adding a large electrolytic capacitator to flatten out the voltage produced.
If it's just a transformer with a rectifier bridge you will get a full wave tension, making crystal growth irregular. Try adding a large electrolytic capacitator to flatten out the voltage produced.
A
Anonymous
Guest
Dare I say, try adding some common sugar. I read on line (take that for what its worth) in electrowinning or refining cells often have an organic
material added.
I do not know about the chemistry but electrically, the sugar/organic molecules may interfer with the rapid deposition of atoms allowing time for larger crystals to grow.
I do not t think it could hurt to try, unless there is some problem with silver nitrate and sugar in the same solution. I just suggested sugar because it is common.
Jim
material added.
I do not know about the chemistry but electrically, the sugar/organic molecules may interfer with the rapid deposition of atoms allowing time for larger crystals to grow.
I do not t think it could hurt to try, unless there is some problem with silver nitrate and sugar in the same solution. I just suggested sugar because it is common.
Jim
I agree. Sugar is not the thing to add. Depending on the metal in question, such grain refiners as peptone, iron free molasses, thiourea, or saccharin can be added. For silver, I know of nothing that should be added, except, in rare cases, tartaric acid.
I know thiourea is the thing for decent copper plating. I also use sulfamic acid every now and then.
I've got test number..... darn, I forgot to count!...
Well, I've got a new one running.
This time I try to keep a large area for deposition, and a small area for dissolving, thus hoping to keep the supersaturation lower.
An attempt to keep the vat stirred with a magnetic stirrer, resulted in long wiry chains of crystal, neatly growing in the stirred direction.
Now it's sitting there growing slowly, mostly small crystals, but hopefully, some of them will soon grow larger.
Power supply used: An old lab-supply that should deliver power as smooth as the skin on (self-moderated).
Peter
Well, I've got a new one running.
This time I try to keep a large area for deposition, and a small area for dissolving, thus hoping to keep the supersaturation lower.
An attempt to keep the vat stirred with a magnetic stirrer, resulted in long wiry chains of crystal, neatly growing in the stirred direction.
Now it's sitting there growing slowly, mostly small crystals, but hopefully, some of them will soon grow larger.
Power supply used: An old lab-supply that should deliver power as smooth as the skin on (self-moderated).
Peter
A
Anonymous
Guest
Peter,
What if you took one of the tiny crystals, and used it for a seed. Only that crystal with low current density, so it grows slow and is the only place for the crystal to grow on.
Jim
What if you took one of the tiny crystals, and used it for a seed. Only that crystal with low current density, so it grows slow and is the only place for the crystal to grow on.
Jim
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I believe that was the reason for success that my elderly friend, now deceased, enjoyed. He grew his large crystals, some weighing several troy ounces, off a pin point only. Seems a crystal would develop at the point and grow larger.james122964 said:
Harold
So far, when I've had a small starting point, the nucleation has been far too violent, resulting in a wiry growth of small crystals.
Low current density, and as an effect of that only a light supersaturation is absolutely the classical way to controlled growth of large crystals.
Achieving control of the supersaturation is the problem.
So far, the nucleation seem to have stopped, and the crystals are growing.
(and there is an absolutely beautiful branched cluster of shiny crystals)
Low current density, and as an effect of that only a light supersaturation is absolutely the classical way to controlled growth of large crystals.
Achieving control of the supersaturation is the problem.
So far, the nucleation seem to have stopped, and the crystals are growing.
(and there is an absolutely beautiful branched cluster of shiny crystals)
hello peter i
have you given up on the quest for the abominal silver crystal ?
i really liked reading your updates
i would like to know if you try'd your mini cell under pressure or in a partial vaccume
if not i may give it a try although it may have to wait because of the cold in the garage -0 degrees c last night
hope your well
shyknee
have you given up on the quest for the abominal silver crystal ?
i really liked reading your updates
i would like to know if you try'd your mini cell under pressure or in a partial vaccume
if not i may give it a try although it may have to wait because of the cold in the garage -0 degrees c last night
hope your well
shyknee
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:
I'll let it run until the cylinder has dissolved to see if something happens along the way.
If this indicates that larger crystals are favoured once the area grows larger, I'll try using a piece of silver plate as receiver next time.
(Larger area equals lower current density, again equalling lower supersaturation)
Another option is to increase the silver concentration or use a concentrated copper nitrate solution instead. The last idea comes from the fact, that my refining cell seems to grow larger crystal when the electrolyte becomes contaminated with copper.
Another possibility could be reversing the current for say 10% of the time, in theory preferentially dissolving small crystal.....
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:
I'll let it run until the cylinder has dissolved to see if something happens along the way.
If this indicates that larger crystals are favoured once the area grows larger, I'll try using a piece of silver plate as receiver next time.
(Larger area equals lower current density, again equalling lower supersaturation)
Another option is to increase the silver concentration or use a concentrated copper nitrate solution instead. The last idea comes from the fact, that my refining cell seems to grow larger crystal when the electrolyte becomes contaminated with copper.
Another possibility could be reversing the current for say 10% of the time, in theory preferentially dissolving small crystal.....
I was browsing papers and stumbled upon:
Cryst. Res. Technol. I 32 I 1997 1 5 I 637-642 I
R. RASHKOVA, . DASKALOVCAh, r. N. NANEV
Institute of Physical Chemistry, Bulgarian Academy of Sciences 1113 Sofia, Bulgaria
The influence of tartaric acid on the growth kinetics of silver single crystals
It seems tartaric acid inhibits the nucleation, there might be something there!
( http://www3.interscience.wiley.com/cgi-bin/fulltext/112451421/PDFSTART for those with access to it )
Cryst. Res. Technol. I 32 I 1997 1 5 I 637-642 I
R. RASHKOVA, . DASKALOVCAh, r. N. NANEV
Institute of Physical Chemistry, Bulgarian Academy of Sciences 1113 Sofia, Bulgaria
The influence of tartaric acid on the growth kinetics of silver single crystals
It seems tartaric acid inhibits the nucleation, there might be something there!
( http://www3.interscience.wiley.com/cgi-bin/fulltext/112451421/PDFSTART for those with access to it )
qst42know
Well-known member
Have you experimented with the distance between the anode and cathode to change the shape of the electrical field?
Where I used to work we used a bar magnet to stabilize the arc in a Xenon lamp. The magnet was perpendicular to the arc and as near the bulb as possible. Perhaps you could reshape the field magnetically and get different crystal sizes?
Just thinking out loud.
Where I used to work we used a bar magnet to stabilize the arc in a Xenon lamp. The magnet was perpendicular to the arc and as near the bulb as possible. Perhaps you could reshape the field magnetically and get different crystal sizes?
Just thinking out loud.
