Sciencemadness Discussion Board

impurities in tin

ldanielrosa - 17-10-2010 at 00:17

I purchased some tin ingots from someone who I discovered sold some crappy manganese dioxide to someone else.

Is there a good method of determining first that I wasn't sold junk metal, then a means of testing the purity of the tin?

DDTea - 17-10-2010 at 01:38

If you're doing analysis for a wide range of potential contaminants, especially without spectroscopic techniques (i.e.: Atomic Emission Spectroscopy or Mass Spectrometry), you're going to have to rely on a few hunches. First of all we need to limit the question: how pure do you expect/need the tin to be? >90%, 99% or what? Did your tin come with a certificate of analysis that listed the results of the company's in-house quality testing? You may want to research what kinds of contaminants are common in tin before you even start; that way you can have some idea of what you are looking for.

EDIT: of course, you could start with the easy stuff like measuring its density and melting point. I feel like some simple flame test should help too. Transition metals have brightly-colored flames; however, your impurities might be too dilute to be seen above Tin's blue flame color.

[Edited on 10-17-10 by DDTea]

ldanielrosa - 17-10-2010 at 02:22

Okay, back story. His previous infraction involved cutting MnO2 with sand (Nurdrage). I didn't ask, but there's a fair chance he included a false CoA with the sale. That being said, yes a certificate (or copy thereof) did come with my metal.

I'll start with the density measurements- I think I can manage that with the equipment at home. I can also try the melting point- I have an electric furnace of sorts that should do the job and a pyrometer in my tool box at school (welding class). Those two should give me an idea.

Aside from that, I'm not as worried about 3n vs. 6n as I'm concerned that the guy melted some pewter plates or zinc or something.

I may have trouble telling the difference between tin's blue and lead's blue, copper (I) blue, arsenic blue- but maybe zinc bluish green or antimony pale green I could pick out. I don't have any experience with flame tests.

I guess I'm in a ticklish spot here. I originally purchased it to alloy with indium and bismuth, and one of those isn't cheap (you know which one). I suppose this leads down a path illuminated by paranoia- how can I tell if my indium is legit?

blogfast25 - 17-10-2010 at 05:49

Quote: Originally posted by ldanielrosa  
Okay, back story. His previous infraction involved cutting MnO2 with sand (Nurdrage). I didn't ask, but there's a fair chance he included a false CoA with the sale. That being said, yes a certificate (or copy thereof) did come with my metal.

I suppose this leads down a path illuminated by paranoia- how can I tell if my indium is legit?


The MnO2 may simply have been a pottery grade: many of these pottery grade oxides are cut with acid-insolubles, usually silica or siliceous matter.

Re. Indium, what DDTea said... But to identify impurities spectrally without at least a primitive spectroscope will be difficult unless they're in abundance: flame tests are usually carried out using simple compounds of one main element...

And simple spectroscopy can even be misleading to those who have little experience with it: with a spectroscope you may well find the prominent Na D line ('sodium yellow') in your tin and conclude that your tin is 'cut with Na'. In reality you find sodium in a lot of things because its spectral D doublet is so intense! Even sample contamination with human sweat can cause it to show up...

Similarly accurate density determinations aren't easy to carry out and not very sensitive to small amounts of impurities. Ideally you need a decent picnometer and 0.01 g (at least) scales to get a reliable reading... Not to mention that your ingot has to be cavity free...


[Edited on 17-10-2010 by blogfast25]

watson.fawkes - 17-10-2010 at 06:42

Quote: Originally posted by ldanielrosa  
I'll start with the density measurements- I think I can manage that with the equipment at home.
Even there, start with specific gravity, as it doesn't require an absolutely calibrated balance, just one that doesn't drift within a few minutes.

Eclectic - 17-10-2010 at 07:04

Melting points would be good indicator of reasonable purity. Tin you can dissolve in boiling hydrochloric acid...copper, antimony,lead will remain undissolved. You can get 97-3 tin-copper solder for making bronze.

[Edited on 10-17-2010 by Eclectic]

Ozone - 17-10-2010 at 07:49

If it "whines" and you can feel it "crackling" when you bend it, and it work hardens (you can no longer bend it by hand) quickly after multiple bends, then it is most likely high purity tin.

smuv - 17-10-2010 at 15:58

The common, impurities in tin are lead and silver.

Rogeryermaw - 17-10-2010 at 16:35

the seller was gumby96 and as far as the bad transaction, i saw the video result. it was pretty crappy to sell such a diluted product but one must consider that he is just a re-seller and may have recieved it that way. that does not excuse it nor does it excuse his inaction in fixing the bad transaction. that's only an observation of one possibility. on the other hand, i purchased aluminum powder from the same seller for my phosphorus experiments and it seems to be working well. i can't attest to the purity of the Al but there is certainly no sand in it.

i can say i hated to see nurdrage get taken like that. i have enjoyed his experiments and it sucks when you're in the middle of one that fails due to garbage reagents. oh well...it's e-gay. buyer beware!

Panache - 18-10-2010 at 03:31

throw it on the floor from a decent height, the louder and purer the ring the higher proportion tin it is (the stuff is used in church bells for a reason), no ring no tin. I got taught this old trick from a metal scrapper, has worked for me always in the past. The ring is unmistakable even if you've never heard it, sounds like a bell, and continues to reverberate.

spirocycle - 18-10-2010 at 10:15

^thats awesome
makes me want to buy some tin

blogfast25 - 22-10-2010 at 09:44

I carried out my own tests:

0.87 g of tin/lead solder (15 y old 60 Sn / 40 Pb - admittedly this is more than just a lead 'contamination') alloy and 0.91 g of lead (roadkill: from a car wheel balancing weight) where treated with about 10 ml of 38 w% HNO3. With the solder reaction started immediately but the lead was more sluggish. After briefly heating the solder it dissolved in about 15mins, forming a precipitate of SnO2. The lead by contrast had to be steam bathed for about an hour.

At the start:



The solder solution/precipitate was then filtered and slightly diluted and divided into three portions. The third was repeatedly (2 x) boiled to almost nothing to get rid of excess HNO3. The filtrate is slightly yellow because the solder contains a fluxing resin core.

Solder filtrate:



NaCl (left), K2Cr2O7 (middle) and KI (right) were then respectively added to tube 1, 2 and 3:



It's always a joy to see the typically delayed precipitation of PbCl2: in this case it was like snowing inside the tube, with crystals as long as 4 mm needles formed. With KI, no I2 was formed.

The lead nitrate solution had developed a white precipitate but clearly crystalline in nature. The clear liquid was decanted off and some 10 ml cold water added to the precipitate which dissolved quickly and completely upon shaking. That liquid was then added to the rest and divided over three test tubes.

NaCl (left), K2Cr2O7 (middle) and KI (right) were then respectively added to tube 1, 2 and 3:



Here the higher concentration of Pb caused the PbCl2 to drop out more quickly in a 'cheese-like' precipitate. Notice also how the iodide tube did develop some iodine: here the tube hadn't been boiled to expel HNO3.

Some interesting additional observations were also made. Turns out that the SnO2.n H2O precipitate was soluble in hot 22 w% HCl, from which with 5 M NaOH fresh Sn(OH)4 can be precipitated which redissolves effortlessly to Na2Sn(OH)6 with more 5 M NaOH.

That would explain why inldanielrosa's experiments the tin did dissolve into 'aqua regia' and a mixture of HNO3 and HCl may indeed be the best solvent for tin. Sn (IV), at least according to the potential series, can be reduced to Sn (II) by H2 (but H2 cannot further reduce Sn (II) to Sn (0), at least not in watery solution). So adding Zn and HCl should make the hydrogen in statu nascendi reduce the Sn (IV) to Sn 2+. Precipitating with ammonia should cause Sn(OH)2.n H2O to form, while the Zn ammonia complexes (Sn(OH) is also amphoteric - see stannites - but I doubt if NH4OH is alkaline enough). This may be a faster route to Sn (II) salts than direct dissolution in HCl which is reported to be very slow...


Some more results with HNO3/HCl mixtures with surprising results to be posted shortly...

[Edited on 22-10-2010 by blogfast25]

Eclectic - 22-10-2010 at 12:09

Directly dissolving 95-5 or 97-3 solder in simmering hydrochloric acid is slow, but only required topping up the HCl and adding more solder occasionally to create a hot saturated solution of almost pure SnCl2.

The alloying components remain undissolved unless H2O2 is added.

A really cheap electric crock pot works well for this.

ldanielrosa - 22-10-2010 at 23:26

Careful there blogfast25, I think you're mistaking me for smuv. I haven't done any experiments with tin yet, but I plan to.

Anyway, I'm getting hammered at work with some "emergency" overtime and lots of people in my area are designated for a 66 hour work week. I get a partial exemption for being in school, but not much.

I have some crucibles on order and a pyrometer in my tool box at school and a small electric furnace, so I should be able to determine the freezing point. Between that and a density test I should be able to sort out tin bearing from pure zinc. I'll get back to y'all when I'm that far. Thanks.

blogfast25 - 23-10-2010 at 08:35

Quote: Originally posted by ldanielrosa  
Careful there blogfast25, I think you're mistaking me for smuv. I haven't done any experiments with tin yet, but I plan to.



Oooops! ldanielrosa is right and I managed to post this comment in the wrong thread! Mea culpa...

bquirky - 23-10-2010 at 09:40

ive not tryed but why dont you consider electrorefining it. ?

http://en.wikipedia.org/wiki/Electrorefining


setup a electrolitic cell with some h2s04 make your ignot (or a slice of it) your annode. use a small peice of known good tin as the cathode. and electroplate away.

if your ignot has a bit of lead in it then it will just become sludge and wont plate over.

if there is a lot of lead or annimoty in it then the anode will pasivate and nothing will happen

if it has copper in it your electrolyte will go blue, iron & nickle green

if it has a lot of zinc in it you should see your cathode fizz away when the power is turned off.


Anyway just an idea..