Containing Iron Oxide Pigments

Production. The iron oxide pigments described in Section 5.1.1 are either doped or coated with cobalt  

Field of application Pigment type Approximate particle length, pm Specific surface area, m2/g Coercive field strength 7/c, kA/m Saturation magnetization, Ms, pT m3/kg MJMS 

1) Body-doped pigments contain 1-5% cobalt that is uniformly distributed throughout the bulk of the pigment particles. It is either incorporated during production of the FeOOH precursor or precipitated as the hydroxide onto one of the intermediate products [5.11] using cobalt(II) salts as the cobalt source. 

Properties. Pigments with a coercive field strength of 50-56 kA/m are used in video cassettes, high-bias audio cassettes (chromium dioxide operating point IEC II), and high-density floppy disks. Depending on the quality of the tape, the particle size varies between 0.2 and 0.4 pm (see Section 5.1.1, Table 36). 

Pigments with a higher coercive field strength (ca. 70 kA/m) and smaller particle size (particle length ca. 0.15-0.2 pm) are used for super VHS cassettes. 

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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. 

The natural iron oxide pigments are termed the ochres which are yellow and contain goethite (10-50%) as the Fe oxide constituent, the reds, with a high content of hematite, the medium to dark yellow siennas, the umbers and the blacks, which consist of magnetite (Benbow, 1989 Buxbaum Printzen, 1993). 

Mixed metal oxide pigments containing iron oxide are also used (see Section 3.1.3). Magnetic iron oxide pigments are discussed in Sections 5.1.1 and 5.1.2. Transparent iron oxide pigments are described in Section 5.4.1. Methods of analysis and specifications of iron oxide pigments are listed in the standards given in Table 1. 

The Penniman process is probably the most widely used production method for yellow iron oxide pigments [3.26], [3.27], This method considerably reduces the quantity of neutral salts formed as byproducts. The raw materials are iron(II) sulfate, sodium hydroxide solution, and scrap iron. If the sulfate contains appreciable quantities of salt impurities, these must be removed by partial precipitation. The iron must be free of alloying components. The process usually consists of two stages (Fig. 23, Route B). 

Iron oxide pigments produced from pure starting materials may be used as colorants for food and pharmaceutical products [3.42], Synthetic iron oxides do not contain crystalline silica and therefore are not considered to be toxic, even under strict Californian regulations. 

Natural Iron Oxides. The earth s crust contains about 7 wt % iroii oxides, but only a few deposits are rich enough in iron to be suitable for mining pigmentary-quality iron oxides. Deposits that are a suitable source of natural iron oxide pigments are usually hydrated aluminum silicates that contain various amounts and forms of iron oxide. 

The most prominent pigments that were used prehistorically are the iron-oxide pigments, often referred to as ochre . While the term is used widely, it is also very problematic. In the strictest sense, it only denotes the color it produces, even though it is often used interchangeably with hematite (Fe ). In fact, the term ochre does not describe any elemental or mineralogical composition, which can vary greatly and in some cases, the ochre-colored material that is described does not contain measurable amounts of iron. 

PMMA and CPVC from neutral solvents (30). The results obtained with four pigments containing iron oxide are shown in Table 3. 

Use Levei 10-20% (transparent iron oxide pigment) 5-15% (inorg. pigments) 10-30% (oig. pigments) borage Redose containers immediately after use Disperbyk -107 [BYK-Chemie GmbH BYK-Chemie USA]... 

It has recently been shown that the flaming disaster of the Hindenburg Zeppelin in 1937, in which 36 lives were lost, may have been caused by static electricity igniting the outer fabric. This was shown to contain an iron oxide pigment and reflecting powdered aluminum. Such a combination, known as a thermite mixture, results in the highly exothermic Gouldshmidt reaction (first reported in 1898) ... 

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