The_Davster
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'Crystals' of tin (with pictures)
In my ongoing project of separating tin and antimony from a solder alloy, I am always getting these beautiful (but annoying) crystals of tin during
the electrolysis. The network of crystals is so looslely held that removing the electrode causes many of the crystals to fall off into solution which
on my current cell design is an annoyance adding more steps to the purification of the antimony. The good news is that I have nearly got a good
method going for the isolation of the metals from solder, when I have completly got it down and reproduceable expect a thread on it.
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BromicAcid
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I have some bars of solder that are 95% Sn 5% Ag that I was dissolving in HCl to make SnCl2 quite some time ago. I took one of the bars (fairly
large, maybe 1.25 kg) and put it into a large jam jar full of HCl. It bubbled vigorously for some time. And I left it outside, letting it dissolve
over the course of a few weeks. One morning I went outide and the bar was covered in a tree of tin (of I guess it could have been silver somehow) and
it was beautiful. Came back later in the day and it was gone. A few days later it was back. Seems it only showed itself during the cooler mornings,
I don't know what caused it exactly but it was pretty. I could try for a repeat.
Although your crystals are very nice Rogue Chemist you have to agree these things look much neater in person, right?
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The_Davster
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Yes definatly, the camera really does not do the fine structure justice.
I would just dissolve my solder in hot acid to get SnCl2 and Sb, but there is the problem of stibine...
EDIT: Forgot to mention that you can actually see these crystals grow as the cell runs, it is almost hypnotic to watch
EDIT2: How do you buy solder by the bar Bromic? I am shelling out around 13$CDN for a pound of the 'wire' type solder...
[Edited on 25-2-2006 by rogue chemist]
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kazaa81
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Can I know what is the electrolyte you used, rogue chemist?
I have some tin alloy (80% Sn, 20% Pb) too and I would like to see the growth of these crystals...Also, what are they made of? SnCl2?
Thanks all
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a_bab
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What are the crystals made of?! Read the topic title again
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Twospoons
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If you don't want crystals, then it looks like you need to add a 'brightener' as used in electroplating baths. This should help reduce the formation
of large crystalline dentrites. What that brightener should be? I don't know - you'll need to do some research !
Helicopter: "helico" -> spiral, "pter" -> with wings
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The_Davster
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Electrolyte used there is made from 300mL 31.45%HCl diluted to 900mL, so ~7.8%HCl, but 90mL being diluted to 550mL has also worked in the past. A
lower concentration of acid should not be used as you will get Sb2O3(another annoyance in this experiment).
Also, only 5V should be used for the electrolysis, more and the Sb2O3 forms..
If any white junk build up on the anode, your tin crystals now contain some Sb, in the second picture you can see what the anode looks like ideally,
Sb flaking off.
EDIT: I have worked with the Sn/Sb solder...lead and tin both dissolve and plate out...just look at electrical potentials, they are much too close for
a nice separation. No 'nice' crystals form, just a spongy sludge of Sn and Sb.
[Edited on 1-3-2006 by rogue chemist]
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kazaa81
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ok...so, could be used as electrodes other tin alloys?
Like brass, bronze or pewter?
Thanks all
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The_Davster
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Brass does not contain tin....
Assuming the bronze is just Sn/Cu, it should work, tin is the most reactive metal there and should be dissolved preferentially. However notice must
be paid to what the remaining copper does, if it adheres to the electrode too well it will block access to the tin in the alloy and the copper will
end up disssolving which will immediatly plate out on the cathode.
Pewter(based on my quick check of wikki) is often of a rather variable composition, some alloys contain lead, which will complicate things as I
elaborated on above. Check pewter for the presence of lead before using if you are wanting nice crystals.
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12AX7
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Meh, "brass" and "bronze" are pretty well the same terms. For historical reasons, "brass" generally refers to zinc-containing alloys, while "bronze"
is all-encompassing, generally with the major component specified ("silicon bronze", "aluminum bronze", "manganese bronze", etc.).
There are alloys with specified composition that overlaps quite well: a "semired brass" might be the familiar 85-5-5-5 (percent copper, zinc, tin and
lead, I think in that order), surely a bronze by all accounts, while a "gunmetal bronze" might be 10% zinc and little of anything else besides copper.
In addition, lead is often added to things to improve machining. The machined brass fittings you get at the hardware store are 37% zinc, 3% lead,
balance copper.
I don't think you'll keep copper in place, it's a big part of the composition. In addition, zinc and tin are typically either held in solid solution
or as an intermetallic phase. Lead is typically a tertiary phase, present as globules around the copper crystals.
If you must go from bronze, you'll have to remove the copper first. This should be easy enough by plating out sponge through a strongly acidic
solution; the tin should remain in solution while the copper plates across.
Tim
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The_Davster
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The tin will go into solution preferentially to the copper, copper will only go into solution when the tin is not exposed at all to the electrolyte or
if an overvoltage is applied. So plating out a copper sponge before tin would not be that easy, it would be heavily contaminated by tin. I have a
feeling this would be something that would be have to be tried to get a feel for.
In any case, pewter would be your best choice as it contains the highest percent of tin.
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12AX7
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What, I've plated copper away from nickel (also an intimate mixture: nickel and copper are continuously soluble metals). U.S. nickels are 75% Cu, 25%
Ni.
Nickel is, by reduction potentials, more reactive (than tin), though.
I don't see any way you could possibly plate a minor constituent out from around the matrix, especially with intimate mixtures like solid solutions
and intermetallics!
Tim
[Edited on 3-5-2006 by 12AX7]
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The_Davster
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I agree that if the tin is a minor constituent it would be annoying to plate out. I was under the impression that bronze had more tin in it than it
actually does, so yeah, it would be difficult to plate out.
I find your results for the plating out of copper from 75% Cu/25% Ni alloy interesting as the nickel should preferentially dissolve as it has the
lower reduction potential. But I figure it can be reasoned as that the Ni does dissolve off the anode first, but as copper is such a high % of the
alloy, contact between the Ni and the electrolyte is broken so the most reactive metal in contact with the electrolyte is now copper. As the copper
dissolves the copper(II) ions in the electrolyte are now the most powerful oxidizing agent present in solution so they are preferentially plated out
to the nickel. I imagine the copper you plated out was slightly contaminated with nickel, especially the very first part of the plating.
Yeah so plating out a minor constituent of an alloy is rather impossible, its best if the alloy's major constituent is the most reactive.
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UnintentionalChaos
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Holy Thread Revival batman!
Anyway, Im doing this with some 95/5 tin/antimony solder through an electrolyte of stannous chloride in HCl using a 4A DC power supply and am running
into some problems (which may be ignorance of electrochemistry, sorry). I find that after running it for a while, the crystals stop looking so nice,
and get ugly and gray and small along the growing edge. Any crystals that break off darken in the solution, but immediately brighten up when I rinse
them in dilute HCl. My anode is a big chunk of the solder (which fizzes slowly as it dissolves slowly in the electrolyte (even when the cell is off,
so it isn't O2 and is wrapped in filter paper to catch the powdery black antimony that flakes off), but I find that the cell eventually becomes
extremely acidic to the point where my crystals start dissolving as they form. Shouldn't more tin be dissolving off the anode? Pieces of crystal that
break off slowly dissolve but leave black "skeletons." Am I to assume antimony is somehow getting into the electrolyte? Thanks for any help you can
give me. Oh and cathode is stainless steel if that helps any.
Department of Redundancy Department - Now with paperwork!
'In organic synthesis, we call decomposition products "crap", however this is not a IUPAC approved nomenclature.' -Nicodem
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The_Davster
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Wow..I did that over 2 years ago...nostalgia 
First off, you said your anode was wrapped in a filter paper to trap the Sb that falls off? This is not a good idea because the antimony that is
precipitated is in constant contact with the anode, and the extensive contact caused the Sb to block all tin/acid interface, so it was forced to
dissolve. As Sb ions are much more easily reduced to the metal than is tin, it instantly plates out at the cathode. I did extensive testing with the
cathode deposits under various conditions and a test often used was dissolving the crystalline tin in HCl again, and if it contained Sb, it left black
flecks in solution.
The best solution was a straight vertical anode of solder (to reduce Sb from sticking too much) and it was elevated off the bottom of the beaker by
about 2cm. Under this was placed a 10mL beaker, that had a cylinder of generic coffee filter taped to it.(Coffee filter superior to lab paper as it
is thinner and more porous). The 10mL beaker is about 1cm tall, leaving 1cm between the bottom of the electrode and the top of the beaker. This is
important because if you look closely while electrolysis progresses, you will see schlieren of higher density tin salts literally running off the
bottom of the electrode. The filter paper allows this to pour out, while retaining the flaking off Sb, I noticed weird effects if the solder
electrode had direct contact with this high density tin salt.
(more later, it is late and I can ramble much on this experiment, I used 2lbs of solder overall  )
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UnintentionalChaos
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Well, thank you for the hasty response...it is coffee filter (I dont have any real filter paper around) and I see very fine antimony powder passing
through occasionally...guess I'll melt down my 10 or 15 grams that passed through (and it looked so shiny too...shame)....cant say I've ever heard the
term schlieren before but I get lots of that when I turn the current on along the growing edge of the crystals...the crystals are growing at 2 inches
a minute along the bottom of a glass dish...deep container you say...I can do that but how did you control the crystal growth? Let gravity keep it low
in the container?
[Edited on 6-24-08 by UnintentionalChaos]
Department of Redundancy Department - Now with paperwork!
'In organic synthesis, we call decomposition products "crap", however this is not a IUPAC approved nomenclature.' -Nicodem
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YT2095
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lol, I did the exact same thing a long time ago also, I love watching tin metal grow.
\"In a world full of wonders mankind has managed to invent boredom\" - Death
Twinkies don\'t have a shelf life. They have a half-life! -Caine (a friend of mine)
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12AX7
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Ah, such ugly deposits... pretty crystals, but you know, kinda dangerous...
I've had that from a lead acetate solution as well. At least when it wasn't shorted out from the growths. I wish I had a levelling agent suitable
for this stuff...
Tim
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Baphomet
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My god I think it's Abhurite! Sn3O3H2Cl2
\"Who ARE you? You\'re like the drummer from REO Speedwagon - nobody knows who you are\" from \'Employee of the Month\'
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YT2095
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no, absolutely not.
it is indeed pure Sn metal crystals, after I had electrolytically extracted all of mine and washed/dried it, I then cast it into an ingot.
it also passed the "Squeek" test, I strongly doubt abhurite would have done the same 
\"In a world full of wonders mankind has managed to invent boredom\" - Death
Twinkies don\'t have a shelf life. They have a half-life! -Caine (a friend of mine)
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DemonsHeadshot
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Hello Dave, quite a while ago you posted on my thread that I should do electrolysis on the Tin Chloride, what I found is that It produces chlorine gas
so It definitely is tin chloride but the crystals are not forming, I used solder wires but no crystals are formed on either side. Can you help me? Do
I need pure tin for this?
[Edited on 24-12-2015 by DemonsHeadshot]
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