mrjeffy321
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Rainbow Colored Iron Oxide
Lately I have been seeing alot of these Rainbow colored Iron Oxides to be used as pigments and what not. There are only three Iron Oxides I am
familair with, Red (Fe2O3) and Black (Fe3O4) and another black (FeO) Iron Oxide.
Are these other colors true oxide colors that form naturally, or is something special done to it to make it (Yellow, Blue, Green, ...)?
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Lambda
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Temperature and crystal structure and oxides
mrjeffy321, you are discribing quite a complex fenomenon here. Not only are there a limited amount of ironoxides, but they can mix, to form all kinds
of crystaline compositions with each other. Steal for instance, has severall different crystaline modifications it can form whith carbon. Depending on
how high you heat the steal, how fast you cool it, and how low you let it cool down before reheating it. And again how is it then cooled, fast, slow
etc. In this way, not only can the crystaline structure of the steal itself be modified, but the oxide laying above is allso affected by this. When
heating steal in air, carbon in the steal is burnt up, giving it a different apearence than parts where the carbon content is higher. Carbon can just
be disolved in steal, but it can allso form carbides. Carbides can be oxidized to for iron oxides and carbon dioxide. Because these actions largely
depend on temperature, oxygen and carbon interaction, iregular heating and cooling of a steal product will have great effect on surface appearence
from spot to spot. And there you colors come in. The type of iron oxide is thus temperature dependent. By adding additional metals like nickel,
cobalt, chromium, manganese, vanadium, copper, aluminium etc. combined with carbon, sulphur, arsenic, phosphor, nitrogen, oxygen etc. , you will get
the same story as above, only many more visual effects and crystaline modifications.
[Edited on 16-6-2005 by Lambda]
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Ium
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I may be wrong, but I think what mrjeffy321 is talking about is not discolouration of heated iron or its alloys but an actual powdered pigment that is
added to paint to give that rainbow effect.
I could be completely off target here but I think the product you may be thinking of is an invention of BASF the german chemical giant in the last few
years.
Nanometer-scale aluminium discs are coated with a silicon dioxide film which is then subjected to a thin layer of iron oxide. The layer of silicon
dioxide is supposed to act like a complex light wavelength filter to give the varying colours when seen from different angles. Applications such as
cosmetic and automotive paint pigments were considered for the product.
I remember coming across the article in "New Scientist" somehwere. I'll see if I can find some references.
Well here is the article on the New Scientist homepage. However to view the entire article I think you need to pay, unfortunately.
http://www.newscientist.com/article.ns?id=mg16021563.600
From BASF this is the finished product named "Variocrom.
http://www.basf.com/pc_coatings/bcpigmentsvariocrom.html
Is that what you are talking about?
(Hyperlinking button is not working for some reason, however simply typing the address seems to create one? Strange.)
[Edited on 16/6/05 by Ium]
[Edited on 16/6/05 by Ium]
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12AX7
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The metallurgy of steel (not the verb "steal" is simple yet complex; iron
and carbon are just a three-phase system, between iron (in three allotropes: alpha 'ferrite', gamma 'austenite' (which has high
solid-state solubility for carbon) and delta, 'ferrite' again), cementite (iron carbide, Fe3C) and graphite (or diamond under high pressure,
hence GE's original iron-catalyst process). The system has a eutectoid behavior, giving rise to another phase, pearlite, which is a lammelar
combination of ferrite and graphite. Bainite, martensite and others are different forms of quick-quenched carbides which tend to be brittle and
metastable (hence the low temperature tempering process to soften the brittleness).
So uh yeah... that's sort of it in a nutshell, which goes to show you how complex it is, for being so simple.
But anyway, none of that has anything to do with oxidation, which is just Fe + O = FeO. Since this oxide is somewhat transparent, but refractive, it
easily causes a range of interference colors on the surface of oxidized iron. You can see up to two, maybe three modes of interference (i.e., repeats
of color banding) before it gets too thick and looks solid black. This all happens below 1200°F (red heat).
That can color iron itself. It says nothing of the oxide.
I've seen iron as a dark green suspension (produced from electrolytic oxidation with salt solution), Fe(OH)2 I presume; the same oxidation state
produces the green tint in glasses and pottery glazes. Of the more stable Fe(III), you get a range from yellow to orange to red to brown to some sort
of purple - this one I'm guessing is a mixed oxide. I've produced it by calcining FeOOH (aka rust).
Of the bare iron oxides, FeO (actually slightly richer in oxygen, and variable) is unstable below dark red heat (approx. 1000°F), decomposing into
iron and magnetite (Fe3O4). Fe3O4 and Fe2O3 are stable from room temperature to 2600°F (1427°C), where they melt.
Tim
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chloric1
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And this has what to do with iron oxide?
Fellow molecular manipulator
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mrjeffy321
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The stuff I am talking about is advertized as concrete pigment, but I cant seem to find any good pictures of it.
I think the stuff that BASF sells is what I am talking aboutm although they done actually show the colored Iron Oxide.
So if you are right Ium, calling it Iron Oxide isnt really all that accurate, it is really aluminum, coated with silicon coated with iron oxide.
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Feurherz
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I think there's something wrong with this compound: Fe3O4
This metallic oxide may be wrong, Iron can only be: Iron(II) or Iron(III), and Oxigen it's only -2 and in that compound it seemas that its
+/-3...strange, doesn't it?
I think it's requiered some kind of review with that formula
auf wiedersehen
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12AX7
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No, Fe3O4 = FeO.Fe2O3, also known as a spinel. See also MgO.Al2O3 (spinel), FeO.Cr2O3 (chromite), ...... Think ferrous(II) ferrate(III) (otherwise
known as ferrite, hence ferrite ceramic magnets).
Tim
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