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deltaH
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shocked.gif posted on 11-10-2013 at 12:00
Burning iron wool


A really simple question with all kinds of answers according to the net, WTF?

When you burn iron wool, you make iron oxide... simple, but which iron oxide...

I thought the answer was quite straight forward, Fe3O4, but then made the mistake of checking this online and found all kinds of (bfesser would love this) unreferenced answers, including FeO and Fe2O3, both of which I feel are wrong.

Can someone please confirm this for me?!




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elementcollector1
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[*] posted on 11-10-2013 at 12:01


Can't be FeO, probably is Fe2O3. Fe3O4 requires high temperatures, which burning steel wool may or may not provide.



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deltaH
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[*] posted on 11-10-2013 at 12:06


Agreed, surely not FeO, but Fe2O3 is red and burning steel wool makes a black product from what I remember... granted that was 20 years ago for me lol

Is there no referenced answer to this?




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[*] posted on 11-10-2013 at 12:14


I've always assumed that it's a mixed product, possibly even containing chromium, manganese, etc. from the steel. I'll see if I can find any references.



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deltaH
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[*] posted on 11-10-2013 at 12:31


Indeed, thanks bfesser, in this case I actually want the thoroughness for a change lol



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[*] posted on 11-10-2013 at 12:41


The "iron oxide" samples that I have are coloured/labeled: red (Fe2O3), black (Fe3O4 / FeO.Fe2O3) and yellow (Fe2O3.H2O / FeOOH). I'm not sure if that helps!
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deltaH
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[*] posted on 11-10-2013 at 12:53


Thanks Sonogashira, so this also seems to confirm Fe3O4 (magnetite), granted maybe some contaminants in there, but mostly Fe3O4. Look I don't care so much if it's amorphous or highly crystalline just need a formula for mass calculations and stoichiometry.

Do we have consensus that there's no chance for it to be FeO, because that is the only other black iron oxide as far as I know.




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[*] posted on 11-10-2013 at 14:12


Could be an impurity of chromium oxide - is it stainless steel?
All things aside, in that case it likely is Fe3O4.




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[*] posted on 11-10-2013 at 15:49


you can determine FeO and Fe2O3 contents by colour.

"In the colorimetric determination of FeO, a sample is
dissolved by a mixture of HF and H2SO4 in the presence
of o-phenanthroline. This organic reagent serves two purposes:
(1) it prevents oxidation of the sample's ferrous iron
during dissolution by selectively complexing with the released
ferrous iron during acid attack; and (2) it forms an
orange-colored complex with Fe2+ whose intensity is directly
proportional to the ferrous content of the digested
sample" -- http://www.minsocam.org/ammin/AM70/AM70_961.pdf

with that said, however, i dont have any o-phenanthroline and dont know who does.
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deltaH
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[*] posted on 12-10-2013 at 00:05


Hi Elementcollector1,

Our 'steel' wool looks to be very much plain iron, it's dull and soft.

One can buy stainless steel scourers, they are very shiny and hard. I've never see the stainless steel variety available in a really fine grade like iron wool is.

I would hazard a guess that apart from minor impurities, ordinary fine iron wool is indeed mostly just iron.

Wiki article on 'steel wool' also suggests low carbon steel is used, which they say is essentially just iron with minor impurities.

***********************
Look I know I could dissolved the steel wool in HCl, convert part of it into Fe3+ and then precipitate magnetite by neutralising a mixed solution of Fe2+ and Fe3+ in the appropriate amounts, then filter and wash the resulting slimes (anybody who has worked with such iron oxide precipitations know what a pain they are to filter), but this is one heck of a long winded approach compared to just setting the stuff a light and ta-da, you're done.





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[*] posted on 13-10-2013 at 08:41


<iframe sandbox width="560" height="315" src="//www.youtube-nocookie.com/embed/_2HHuUMkg58?rel=0&start=268&end=546" frameborder="0" allowfullscreen></iframe>



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[*] posted on 13-10-2013 at 09:32


The results are going to depend on the composition of the original wool. Most of this stuff is pretty much iron and carbon. Unless you specifically get stainless which is much coarser and harder to light. If there is a lot of carbon you may get some FeO (very little) and unreacted Fe (more common). Otherwise it is probably going to be mostly Fe3O4. You will also get some Fe2O3 which can be eliminated by heating in a neutral to slightly reducing atmosphere. Too much reduction produces Fe again. With heating Fe3O4 in an oxidizing atmosphere producing Fe2O3. Obviously temperature and the amount of oxygen available will also effect the outcome. Fe2O3 is red while Fe3O4 is black with varying shades between the two indicating some mixture. Color is probably the the easiest indicator without non-OTC chemicals.
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[*] posted on 13-10-2013 at 12:19


Thanks all for your points, I think we can safely assume you make mostly Fe3O4.

Bfesser, I have to wait for off peak to watch the clip you uploaded :(




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