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Iron oxide red is the inorganic compound with the formula Fe2O3.
Iron oxide red is one of the three main oxides of iron, the other two being iron(II) oxide (FeO), which is rare; and iron(II,III) oxide (Fe3O4), which also occurs naturally as the mineral magnetite.
As the mineral known as hematite, Iron oxide red is the main source of iron for the steel industry.
CAS: 1309-37-1
MF: Fe2O3
MW: 159.69
EINECS: 215-168-2
Iron oxide red is readily attacked by acids.
Iron oxide red is often called rust, and to some extent this label is useful, because rust shares several properties and has a similar composition; however, in chemistry, rust is considered an ill-defined material, described as Hydrous ferric oxide.
Iron oxide red Powder E127.
Iron oxide red is suitable for cosmetics and is stable in CP soap, however colours may fade and can differ depending on your recipe, it also works well in M&P soap.
Offering natural earthy tones, test with just a small amount until you achieve the shade that you are happy with.
Iron oxide red is a fine powdered pigment.
Iron oxide red is an insoluble pigment so it will need to be mixed with a small amount of light oil before adding to cold/hot process soap.
Mixing with isopropyl alcohol or liquid glycerine is recommended for opaque melt and pour soap.
Synthetic Iron oxide red is the most common colorant in ceramics and has the highest amount of iron.
Iron oxide red is available commercially as a soft and very fine powder made by grinding ore material or heat processing ferrous/ferric sulphate or ferric hydroxide.
During firing all irons normally decompose and produce similar colors in glazes and clay bodies (although they have differing amounts of Fe metal per gram of powder).
Iron oxide red is available in many different shades from a bright light red to a deep red maroon, these are normally designated by a scale from about 120-180 (this number designation should be on the bags from the manufacturer, darker colors are higher numbers), however, in ceramics these different grades should all fire to a similar temperature since they have the same amount iron.
The different raw colors are a product of the degree of grinding.
In oxidation firing iron is very refractory, so much so that Iron oxide red is impossible, even in a highly melted frit, to produce a metallic glaze.
Iron oxide red is an important source for tan, red-brown, and brown colors in glazes and bodies.
Iron oxide red, for example, are dependent on the crystallization of iron in a fluid glaze matrix and require large amounts of iron being present (eg. 25%).
The red color of terra cotta bodies comes from iron, typically around 5% or more, and depends of the body being porous.
As these bodies are fired to higher temperatures the color shifts to a deeper red and finally brown.
In reduction firing iron changes Iron oxide red's personality to become a very active flux.
Iron glazes that are stable at cone 6-10 in oxidation will run off the ware in reduction.
The iron in reduction fired glazes is known for producing very attractive earthy brown tones. Greens, greys and reds can also be achieved depending on the chemistry of the glaze and the amount of iron.
Ancient Chinese celadons, for example, contained around 2-3% iron.
Iron oxide red is available in spheroidal, rhombohedral, and irregular particle shapes.
Some high purity grades are specially controlled for heavy metals and are used in drugs, cosmetics, pet foods, and soft ferrites.
Highly refined grades can have 98% Fe2O3 but typically Iron oxide red is about 95% pure and very fine (less than 1% 325 mesh).
Some grades of Iron oxide red do have coarser specks in them and this can result in unwanted specking in glaze and bodies (see picture).
High iron raw materials or alternate names: burnt sienna, crocus martis, Indian red, red ochre, red oxide, Spanish red.
Iron oxide red is the principal contaminant in most clay materials.
A low iron content, for example, is very important in kaolins used for porcelain.
Structure
Iron oxide red can be obtained in various polymorphs.
In the main one, α, iron adopts octahedral coordination geometry.
Iron oxide red, each Fe center is bound to six oxygen ligands.
In the γ polymorph, some of the Fe sit on tetrahedral sites, with four oxygen ligands.
Alpha phase
α-Fe2O3 has the rhombohedral, corundum (α-Al2O3) structure and is the most common form.
Iron oxide red occurs naturally as the mineral hematite which is mined as the main ore of iron.
Iron oxide red is antiferromagnetic below ~260 K (Morin transition temperature), and exhibits weak ferromagnetism between 260 K and the Néel temperature, 950 K.
Iron oxide red is easy to prepare using both thermal decomposition and precipitation in the liquid phase.
Iron oxide red's magnetic properties are dependent on many factors, e.g. pressure, particle size, and magnetic field intensity.
Gamma phase
γ-Fe2O3 has a cubic structure.
Iron oxide red is metastable and converted from the alpha phase at high temperatures.
Iron oxide red occurs naturally as the mineral maghemite.
Iron oxide red is ferromagnetic and finds application in recording tapes, although ultrafine particles smaller than 10 nanometers are superparamagnetic.
Iron oxide red can be prepared by thermal dehydratation of gamma iron(III) oxide-hydroxide.
Another method involves the careful oxidation of iron(II,III) oxide (Fe3O4).
The ultrafine particles can be prepared by thermal decomposition of iron(III) oxalate.
Other solid phases
Several other phases have been identified or claimed.
The β-phase is cubic body-centered (space group Ia3), metastable, and at temperatures above 500 °C (930 °F) converts to alpha phase.
Iron oxide red can be prepared by reduction of hematite by carbon, pyrolysis of iron(III) chloride solution, or thermal decomposition of iron(III) sulfate.
The epsilon (ε) phase is rhombic, and shows properties intermediate between alpha and gamma, and may have useful magnetic properties applicable for purposes such as high density recording media for big data storage.
Preparation of the pure epsilon phase has proven very challenging.
Material with a high proportion of epsilon phase can be prepared by thermal transformation of the gamma phase.
The epsilon phase is also metastable, transforming to the alpha phase at between 500 and 750 °C (930 and 1,380 °F).
Iron oxide red can also be prepared by oxidation of iron in an electric arc or by sol-gel precipitation from iron(III) nitrate.
Research has revealed epsilon Iron oxide red in ancient Chinese Jian ceramic glazes, which may provide insight into ways to produce that form in the lab.
Additionally, at high pressure an amorphous form is claimed.
Liquid phase
Molten Fe2O3 is expected to have a coordination number of close to 5 oxygen atoms about each iron atom, based on measurements of slightly oxygen deficient supercooled liquid iron oxide droplets, where supercooling circumvents the need for the high oxygen pressures required above the melting point to maintain stoichiometry.
Reactions
The most important reaction is Iron oxide red's carbothermal reduction, which gives iron used in steel-making:
Fe2O3 + 3 CO → 2 Fe + 3 CO2
Another redox reaction is the extremely exothermic thermite reaction with aluminium.
2 Al + Fe2O3 → 2 Fe + Al2O3
This process is used to weld thick metals such as rails of train tracks by using a ceramic container to funnel the molten iron in between two sections of rail.
Thermite is also used in weapons and making small-scale cast-iron sculptures and tools.
Partial reduction with hydrogen at about 400 °C produces magnetite, a black magnetic material that contains both Fe(III) and Fe(II):
3 Fe2O3 + H2 → 2 Fe3O4 + H2O
Iron oxide red is insoluble in water but dissolves readily in strong acid, e.g. hydrochloric and sulfuric acids.
Iron oxide red also dissolves well in solutions of chelating agents such as EDTA and oxalic acid.
Heating iron(III) oxides with other metal oxides or carbonates yields materials known as ferrates (ferrate (III)):
ZnO + Fe2O3 → Zn(FeO2)2
Preparation
Iron oxide red is a product of the oxidation of iron.
Iron oxide red can be prepared in the laboratory by electrolyzing a solution of sodium bicarbonate, an inert electrolyte, with an iron anode:
4 Fe + 3 O2 + 2 H2O → 4 FeO(OH)
The resulting hydrated iron(III) oxide, written here as FeO(OH), dehydrates around 200 °C.
2 FeO(OH) → Fe2O3 + H2O
Uses
Iron industry
The overwhelming application of Iron oxide red is as the feedstock of the steel and iron industries, e.g. the production of iron, steel, and many alloys.
Polishing
A very fine powder of ferric oxide is known as "jeweler's rouge", "red rouge", or simply rouge. Iron oxide red is used to put the final polish on metallic jewelry and lenses, and historically as a cosmetic.
Rouge cuts more slowly than some modern polishes, such as cerium(IV) oxide, but is still used in optics fabrication and by jewelers for the superior finish Iron oxide red can produce.
When polishing gold, the rouge slightly stains the gold, which contributes to the appearance of the finished piece.
Rouge is sold as a powder, paste, laced on polishing cloths, or solid bar (with a wax or grease binder). Other polishing compounds are also often called "rouge", even when they do not contain Iron oxide red.
Jewelers remove the residual rouge on jewelry by use of ultrasonic cleaning.
Products sold as "stropping compound" are often applied to a leather strop to assist in getting a razor edge on knives, straight razors, or any other edged tool.
Synonyms:
Ferric oxide(II,III), magnetic nanoparticles solution;
Ferric(III) oxide;
Iron(III) oxide, 99% trace metals basis;
Iron(III) oxide, 99.9% trace metals basis;
Iron(III) oxide, 98% trace metals basis;
Iron(III) oxide, 99.95% trace metals basis;
Iron(III) oxide, 99.99% trace metals basis;
Iron(lll) oxide
