Iron oxide and oxide-hydroxide are widespread in nature, play an important role in many geological and biological processes, and are widely utilized by humans, e.g., as iron ores, pigments and catalysts in thermite. Common rust is a form of iron (III) oxide. Iron oxides are widely used as inexpensive, durable, pigments in paints, coatings and colored concretes. Colours commonly available are in the “earthy” end of the yellow/orange/red/brown/black range.
Iron oxides are produced from ferrous sulfate by heat soaking, removal of water, decomposition, washing, filtration, drying and grinding. Chemical formula: Fe2O3. Appearance: Powder of size around 40 micron.
Iron (III) oxide or ferric oxide is an inorganic compound with the formula Fe2O3. It is one of the three main oxides of iron. As the mineral known as hematite, Fe2O3 is the main source of the iron for the steel industry. Fe2O3 is ferromagnetic, dark red, and readily attacked by acids. Iron (III) oxide is often called rust. To some extent this label is useful, because rust shares several properties and has a similar composition. To chemists, rust is considered an ill-defined material, described as hydrated ferric oxide
The overwhelming application of Iron (III) oxide is as the feedstock of the steel and iron industries, e.g. the production of iron, steel, and many alloys. Black iron oxide has the highest tint strength, generally achieving saturation at 6 percent dosage. Brown has a slightly lower tint strength, levelling -off at approximately 7 percent dosage, followed by 8 percent for red and 9 percent for yellow.
The difference in colour/shade between one pigment and another is due to the surface structure of the particle. Pigments of the same family, such as reds for example, could have different undertone. Upon dilution with a white extender, reds may appear purple or pink. The reason for this is that a red pigment particle, depending on its structure, may reflect the red component of light plus a certain amount of blue (purple undertone) or some yellow (pink undertone).
They are produced in either anhydrous or hydrated forms. Their range of hues includes yellows, reds, browns and blacks. The food-quality iron oxides are primarily distinguished from technical grades by their comparatively low levels of contamination by other metals; this is achieved by the selection and control of the source of the iron or by the extent of chemical purification during the manufacturing process.
Applications
Iron Oxide is a very fine powder of ferric oxide known as “jewellers rouge”, “red rouge”, or simply “rouge”. It is used to put the final polish on metallic jewellery and lenses, and historically as a cosmetic. Rouge is sold as a powder, paste, laced on polishing cloths or solid bar (with a wax or grease binder). Iron(III) oxide is also used as a pigment in cosmetics. Additionally, Iron oxides are used as pigments in dental composites alongside titanium oxides. Iron Oxide pigments are also used in paints and coatings; colour concentrates; and mulch.
Iron oxide dispersant is one of many solutions used to purify water in water treatment facilities. It is considered to be a superior phosphate and zinc stabilizer stressed cooling water systems and an excellent iron and sludge dispersant in boilers.
Compact pigment : Whereas inorganic binders do not disperse to 100% during the usual mixing times allowed, those prepared with organic wetting and deflocculating agents achieve excellent dispersion and hence provide high tinting strength in concrete products.
Bayer developed compacted pigments which also incorporate organic dispersing agents. In making them, a pigment paste is pre-shaped (by the use of perforated rollers or matrices) and the prepared particles are rounded subsequently in granulation drums or on granulation plates.
Comparison of natural iron oxide and synthetic iron oxide pigment
The use of natural iron oxide pigment dates back centuries to prehistoric times and can be seen in cave paintings around the world.
However, natural iron oxide pigments are nearly overshadowed by the synthetic variety, due to its consistency and superior tailor made properties. Synthetically prepared iron oxide pigment has been found to possess better texture, brilliance and staining power compared to natural pigment.
When the colour of the paint is important, synthetic iron oxides are predominantly used because they have greater tinting strength than natural oxides. But in primers or undercoats, which are not so colour dependent as the finishing paints, natural iron oxide pigments may be used. Ceramics may also use natural oxides to provide colour for frits and glazes.
Iron oxide pigment can be either produced in synthetic process or refined from naturally occurring ore deposits.
A number of different processes have been developed for manufacturing synthetic iron oxide pigments. Important actually used production methods are as follows:
· Laux process
· Calcination process
· Penniman process
· Precipitation process
Demand driver
Iron oxide pigments are used in the coatings and colorants, construction, plastics and toner industries. The demand for iron oxide pigment would be mainly driven by the performance and growth of the paint and coating industry and polymer master batch sector.
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