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Author: Subject: Iron Oxide color
Metallus
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[*] posted on 12-9-2013 at 08:22
Iron Oxide color


Hi there

I've searched the forum to see if I could find a topic dealing with the multitude of colors you can find Fe2O3, but couldn't find none so made a new topic.

So far I was able to see blue, red, yellow and "natural" (brownish) color.

Now, the Fe2O3 obtained from the reaction between Fe3(SO4)2 and NaOH, filtered and dryed was blackish/brownish but the one my father bought somewhere for some unknown reason was blue.

The thing is, the reactivity of the two was well different: the one I synthetized reacted according to what I learnt from theory: it readily dissolved in HCl, yelding a strong yellow solution of FeCl3. Also tried oxidizing it (to see if there were traces of reducing agents) with a diluite solution of H2SO4 and K2Cr2O7, but nothing happened.

However, when I tried to dissolve the blue Iron oxide in HCl, it didn't dissolve; a part of it lost its former blue color and a smelly gas was emitted. A blue/gray powder remained in the bottom of the beaker. I tried with H2SO4 but nothing again.

I'm 100% positive it wasn't prussian blue. The blue powder looks like this


Any idea of what kind of silly pigment was put in there? Are all the colored iron oxides sold basically everywhere so unreactive like this? In that case, what kind of Iron Oxide would be appropriate for thermite? Yellow, red, blue, black... what does change?

Thanks for your attention
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Antiswat
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[*] posted on 12-9-2013 at 08:49


i know that Fe3O4 is magnetic, cover a magnet in plastic and run it over the powder, spikes should be observed if there is Fe3O4 in it, also Fe3O4 + HCl seemingly gives off 2FeCl3 and FeCl2, in which i recall as differing from Fe2O3, which doesnt produce (AS I REMEMBER!!) any FeCl3

so already with the HCl you could have found a hint towards what it is..
but why dont you just go ahead and see if it will react as thermite oxidizer?

i could be wrong, i could be very wrong.. but it could potentially be an organic substance that gives the blue colour, and most organics decompose at a relatively low temperature (dont wanna say ALL, as that might be wrong at some point in history of chemistry)

oh another thing, Fe3O4 should if heated in the presence of oxygen turn into Fe2O3, this happens just around 200*C IIRC

btw could you try to put some in a bottle, then shake it alot, with water, and then see if some of it settles before some of the other, and then perhaps try to have it fractionally decanted?




~25 drops = 1mL @dH2O viscocity - STP
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https://en.wikipedia.org/wiki/Solubility_table
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[*] posted on 12-9-2013 at 08:50


I don't believe that's iron oxide. A smelly gas with HCl? It might be something in a high oxidation state that's giving off chlorine, or it might be a sulphide.



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[*] posted on 12-9-2013 at 09:17


Quote: Originally posted by DraconicAcid  
I don't believe that's iron oxide. A smelly gas with HCl? It might be something in a high oxidation state that's giving off chlorine, or it might be a sulphide.


I've worked with HCl and chlorine so much that I can detect their smell from distance and that wasn't any of those. It was closer to sulphide...

Also, when I put this blue oxide in water, it precipitates but the water is no longer limpid. When adding HCl, the powder loses some of its blue color, turning a bit on the gray side and releasing this smelly gas. It looks like a bit of it dissolves but I can't really understand what's exactly going on since the solution is too torbid. Most of it stays in the bottom anyways.

@ Antiswat:
Shouldn't Fe2O3 react with HCl according to the following?
Fe2O3 + 6HCl --> 2FeCl3 + 3H2O

By the way, as I currently don't have powdered Al, I tried using some "home-grinded" Al, but miserably failed to ignite it (Tried using black powder or KNO3 + sugar. I don't have a blowtorch).

Putting a lighter near the powder doesn't lead to any noticeable change.
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[*] posted on 12-9-2013 at 09:26


If it reacts with acid to give crap, try reacting it with aqueous ammonia instead. That colour doesn't look like any iron compound I can think of, but it might be a cobalt compound (isn't that the colour of cobalt(II) thiocyanate?).



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[*] posted on 12-9-2013 at 11:13


Quote: Originally posted by DraconicAcid  
If it reacts with acid to give crap, try reacting it with aqueous ammonia instead. That colour doesn't look like any iron compound I can think of, but it might be a cobalt compound (isn't that the colour of cobalt(II) thiocyanate?).


Nothing happens; it's just like it was clear water. By the way, I did some more research and found what the blue pigment could be http://en.wikipedia.org/wiki/Ultramarine

If it's indeed this compound, then that would explain the smelly gas: the sulphide would react with HCl to give out H2S.
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[*] posted on 12-9-2013 at 15:33


yes: ultramarine.
(Na<sub>8-10</sub> Al<sub>6</sub> Si<sub>6</sub> O<sub>24</sub> S<sub>2-4</sub>;)
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[*] posted on 12-9-2013 at 22:46


When I read the OP this also was the first thing I was thinking about. Ultramarine gives off H2S when added to acid and it looses its blue color.



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[*] posted on 13-9-2013 at 03:41


how did they manage to sell ultramarine as iron oxide anyways? ohwell it has been seen theyre stating their product contains no chemicals

seemingly i was very wrong about Fe2O3 with HCl, it should give pure FeCl3




~25 drops = 1mL @dH2O viscocity - STP
Truth is ever growing - but without context theres barely any such.

https://en.wikipedia.org/wiki/Solubility_table
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