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Iron Oxide Yellow

Alternate Names: Iron(III) oxide, hydrated iron oxide, iron(III) hydroxide, yellow iron oxide

Description: FeO(OH).H2O, Fe(OH)3, Goethite

Notes

This is one of the many raw colors of iron oxide powder. It is an iron hydroxide. Yellow ochre clay contains yellow iron oxide. In ceramics, red iron oxide is most commonly used in glazes and clay bodies, but black is also used. Yellow is the least color-stable form. Yellow iron oxide is a synthetic material of very fine particle size (but not as fine as black or red). All forms of iron normally produce red coloration when fired in clay bodies in oxidation.

Actual yellow iron oxides are around 85% Fe2O3 and about 12% LOI with some impurities (e.g. SiO2, CaO).

Theoretically, any form of iron could be used to source Fe in the fired ceramic product (of course they lose different amounts of volatiles on firing so they cannot be substituted gram-for-gram). However, in practice, this is not the case. Yellow iron, in our tests, for example, does not stain a glaze but it does stain a clay body. The reason is not apparent.

Yellow iron is not as fluffy and light as black, but more than red. It does not agglomerate as badly as red, but more than black. It is coarser in particle size and can leave some lighter colored residue on a 325 mesh screen (up to 8% in one specimen we tested whereas the others left zero).

Like other forms of iron, this is never used pure, it is always part of a recipe (a glaze, engobe or body).

Yellow iron is also used in paints, enamels, concrete colorants, plastics, rubber, and paper where permanent yellow is required. It has excellent hiding power, absorbs ultraviolet light, is compatible with a broad range of vehicles, disperses well in aqueous and solvent systems, and does not contain heavy metals.

One process of manufacture involves precipitation of ferric oxyhydroxide followed by purification through washing, drying and milling.

Related Information

Yellow Iron Oxide original container

If you want to learn more, please visit our website Iron Oxide Colors for Roofing.

Iron oxide powder is available in many colors. Here are three.

How can there be so many colors? Because iron and oxygen can combine in many ways. In ceramics we know Fe2O3 as red iron and Fe3O4 as black iron (the latter being the more concentrated form). But would you believe there are 6 others (one is Fe13O19!). And four phases of Fe2O3. Plus more iron hydroxides (yellow iron is Fe(OH)3).

Yellow, black and red Iron oxide in a buff burning body at cone 6 oxidation

Plainsman M340 buff cone 6 stoneware. 3% iron was added has been added to each of these. The yellow iron (left) is clearly not as concentrated (and not mixed in as well). The black (center) gives a maroon color.

Yellow iron oxide vs. Yellow Ochre - fired at cone 6

The rear two samples are just dried. The fired iron oxide (front left) is clearly exhibiting a metallic sheen and has shrunk and become much more dense. And heavy. In the raw state, both exhibit a measure of plasticity when water is added. The yellow iron really holds on to the water, drying out much more slowly. The iron oxide densifies and shrinks even more by cone 8, taking on the characteristics of the metal.

Matching the color of a natural clay using and iron oxide mix

The freshly thrown piece on the left front is a medium-temperature plastic stoneware body. Its color comes from a natural iron-bearing clay in the recipe. However, that red clay is becoming much more expensive and difficult to obtain because of trucking availability and cross-border issues. We are investigating the addition of iron oxide to a blend of buff burning materials (which can be tuned to match the working and firing properties of the original body). A 3% iron oxide addition is producing the same fired color. But raw color also needs to be matched. The answer is a blend of red:yellow:black iron oxides. The 3% iron addition in the rear centre piece is a 50:50 mix of red and yellow iron oxides, clearly it is too red. The right front piece is a 40:50:10 mix of red:yellow:black iron oxides. This is getting closer, for the next trial we will try more black and less red.

Links

Author: Subject: Rainbow Colored Iron Oxide 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, ...)? 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]

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]

The metallurgy of steel (not the verb "steal&quot 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




Electronic Design, from Concept to Layout.
Need engineering assistance? Drop me a message!

Seven Transistor Labs LLC http://seventransistorlabs.com/ Electronic Design, from Concept to Layout.Need engineering assistance? Drop me a message!

And this has what to do with iron oxide?

Fellow molecular manipulator

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.

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

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




Electronic Design, from Concept to Layout.
Need engineering assistance? Drop me a message!

Seven Transistor Labs LLC http://seventransistorlabs.com/ Electronic Design, from Concept to Layout.Need engineering assistance? Drop me a message!

For more information, please visit oxide pigments.