Oxide pigments

The continually increasing importance of iron oxide pigments is based on their nontoxicity chemical stability wide variety of colors ranging from yellow, orange, red, brown, to black and low price. Natural and synthetic iron oxide pigments consist of well-defined compounds with known crystal structures [3.1]  

1) a-FeOOH, goethite [1310-14-1], diaspore structure, color changes with increasing particle size from green-yellow to brown-yellow 

4) y-Fe203, maghemite [12134-66-6], spinel super structure, ferrimagnetic, color brown 

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Titanium dioxide is extensively used for both house paint and artist s paint, because it is permanent and has good covering power. Titanium oxide pigment accounts for the largest use of the element. Titanium paint is an excellent reflector of infrared, and is extensively used in solar observatories where heat causes poor seeing conditions. 

Iron oxide is also used for nonpigmentary applications, eg, ferrites (qv) and foundry sands making total world demand for iron oxide close to 1 X 10 t. The principal worldwide producers of iron oxide pigments are Bayer AG (ca 300,000 t/yr worldwide), and Harcros Pigments Inc., a subsidiary of Harrisons Crosfield PLC. In the United States, Bayer produces the Bayferrox line of iron oxide pigments in New Martinsville (see Iron compounds). 

About 100,000 t of titanium dioxide aimuaHy are used as formulation components in the production of glass (qv), ceramics, electroceramics, catalysts, and in the production of mixed-metal oxide pigments. 

About 60% of the natural iron oxide pigments is used to color cement and other building materials (qv). About 30% is consumed in the production of paints. For coloring plastics and mbber, synthetic iron oxide pigments are preferred. The main advantage of the natural iron oxide pigments, as compared to the synthetic ones, is cost. However, the quaHty is inferior, and in most cases, they are consumed in close proximity to the mines. As colorants, the natural iron oxides are about 50% weaker than synthetically produced iron oxides. 

Synthetic Iron Oxides. Iron oxide pigments have been prepared synthetically since the end of the seventeenth century. The first synthetic red iron oxide was obtained as a by-product of the production of sulfuric acid from iron sulfate containing slate. Later, iron oxide pigments were produced direcdy by the thermal decomposition of iron sulfates. In the 1990s, about 70% of all iron oxide pigments consumed are prepared synthetically. 

Iron Blocks. Chemically, iron blacks are based on the binary iron oxide, FeOFe2 O3. Although the majority is produced in the cubical form, these can also be produced in acicular form. Most of the black iron oxide pigments contain iron(III) oxide impurities, giving a higher ratio of iron(III) than would be expected from the theoretical formula. 

Mixed-Metal Oxide Pig ments. Mixed-metal oxide pigments can be considered a subcategory of complex inorganic color pigments. The name, mixed-metal oxides, does not, however, represent the reaUty as these pigments are not mixtures but rather soHd solutions or compounds consisting... 

Transparent iron oxide pigments have exceUent weatherabiHty, Hghtfastness, and chemical resistance, comparable to opaque iron oxides. 

In the Bnchamp process, nitro compounds are reduced to amines in the presence of iron and an acid. This is the oldest commercial process for preparing amines, but in more recent years it has been largely replaced by catalytic hydrogenation. Nevertheless, the Bnchamp reduction is still used in the dyestuff industry for the production of small volume amines and for the manufacture of iron oxide pigments aniline is produced as a by-product. The Bnchamp reduction is generally mn as a batch process however, it can also be mn as a continuous (48) or semicontinuous process (49). 

Some of the important parameters in the Bnchamp process are the physical state of the iron, the amount of water used, the amount and type of acid used, agitation efficiency, reaction temperature, and the use of various catalysts or additives. When these variables are properly controlled, the amine can be obtained in high yields while controlling the color and physical characteristics of the iron oxide pigment which is produced. 

Report of the British Intelligence Objectives Subcommittee on (1) The Manufacture of Nitration Products ofBenyene, Toluene, and Chlorobenyene at Griesheim and Eeverkusen, (2) The Manufacture of Aniline andiron Oxide Pigments at Uerdigen, PB 77729 (also issued as BIOS Report No. 1144) and BIOS Trip Report No. 2526, Sept.-Oct. 1946, pp. 25-32. 

The exceUent adhesion to primed films of polyester combined with good dielectric properties and good surface properties makes the vinyhdene chloride copolymers very suitable as binders for iron oxide pigmented coatings for magnetic tapes (168—170). They perform very weU in audio, video, and computer tapes. 

Bayer Agricultural Products Group, See Bayer CropScience, Subsidiary of Bayer AG (Gemiany), 161 Bayer Basic and Fine Chemicals Business Group, 161 Bayer Corporation, 161,219 Bayer CropScience, 161 BAYFERROX , hon oxide pigments, 22 BAYFIT , poljoirethane foam, 22 BAYGON , propoxur, 22 Baymag, 148... 

Most pigments can be used in any type of binder therefore, paints cannot be identified by pigment type alone. For example, micaceous iron oxide pigment is traditionally in an oil-based binder but is being increasingly used in epoxies, etc. In the paint coating film, the pigment content may vary from 15 to 60 per cent. In the special case of zinc rich primers, it is over 90 per cent. 

Poly butadiene with zinc oxide pigment 495... 

Titanium dioxide (E171, Cl white 6) is a white, opaque mineral occurring naturally in three main forms rutile, anatase, and brookite. More than 4 million tons of titanium dioxide are produced per year and it is widely used for industrial applications (paints, inks, plastics, textiles) and in small amounts as a food colorant. ° "° Production and properties — Titanium oxide is mainly produced from ilmenite, a titaniferous ore (FeTiOj). Rutile and anatase are relatively pure titanium dioxide (Ti02) forms. Titanium oxide pigment is produced via chloride or sulfate processes via the treatment of the titanium oxide ore with chlorine gas or sulfuric acid, followed by a series of purification steps. High-purity anatase is preferred for utilization in the food industry. It may be coated with small amounts of alumina or silica to improve technological properties. 

The most important synthetic routes to iron oxide pigments involve either thermal decomposition or aqueous precipitation processes. A method of major importance for the manufacture of a-Fe203, for example, involves the thermal decomposition in air of FeS04-7H20 (copperas) at temperatures between 500 °C and 750 °C. The principal method of manufacture of the yellow a-FeO(OH) involves the oxidative hydrolysis of Fe(n) solutions, for example in the process represented by reaction (1). 

Mixed-phase oxide pigments are manufactured by high temperature (800-1000 °C) solid state reactions of the individual oxide components in the appropriate quantities. The preparation of nickel antimony titanium yellow, for example, involves reaction of Ti02, NiO and Sb203 carried out in the presence of oxygen or other suitable oxidising agent to effect the necessary oxidation of Sb(m) to Sb(v) in the lattice. 

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