Transparent iron oxides

Transparent yellow iron oxide has the a-FeO(OH) (goethite) structure on heating it is converted into transparent red iron oxide with the a-Fe203 (hematite) structure. Differential thermogravimetric analysis shows a weight loss at 275 °C. Orange hues develop after brief thermal treatment of yellow iron oxide and can also be obtained by blending directly the yellow and red iron oxide powders. 

Production. Transparent yellow iron oxide [51274-00-1], C.I. Pigment Yellow 42 77492, is obtained by the precipitation of iron(II) hydroxide or carbonate 

Transparent red iron oxide [1309-37-1], C.I. Pigment Red 101 77491, is obtained by heating the yellow pigment (e.g., in a cylindrical rotary kiln) at 400 500 °C (Fig. 82). 

Transparent red iron oxides containing iron oxide hydrate can also be produced directly by precipitation. A hematite content of 85 % can be obtained when iron(II) hydroxide or iron(II) carbonate is precipitated from iron(II) salt solutions at ca. 30 °C and when oxidation is carried out to completion with aeration and seeding additives (e.g., chlorides of magnesium, calcium, or aluminum) [5.271], Transparent iron oxides can also be synthesized by heating finely atomized liquid pentacarbonyl iron in the presence of excess air at 580-800 °C [5.272], [5.273]. The products have a primary particle size of ca. 10 nm, are X-ray amorphous, and have an isometric particle form. Hues ranging from red to orange can be obtained with this procedure, however, it is not suitable for yellow hues. 

Transparent brown iron oxides are produced by precipitating iron(II) salt solutions with dilute alkali (sodium hydroxide or sodium carbonate) and oxidizing with air. Only two-thirds of the precipitated iron hydroxide, oxide hydrate, or carbonate is oxidized. Alternatively, the iron oxides can be produced by complete oxidation of 

These stable pigments are extremely useful in formulating gold and bronze metallic or polychromatic enamels. 

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

Transparent iron oxides are produced by BASE (Germany), Johnson Matthey (U.K.), and Hilton Davis (U.S.). The mid-1990s aimual production is estimated to be around 2000 metric tons. 

Special forms of highly transparent iron oxides are made for use in durable metallized polychromatic finishes. These products are more brown than yellow however, when used in metallized finishes, they impart a golden color. This type of iron oxide tends to be more reactive than the opaque yellows. 

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. 

Thermal decomposition of Fe(CO)s to form transparent iron oxides (see Section 5.4) [3.40]... 

Properties and Uses. As far as resistance to light, weather, and chemicals is concerned, transparent iron oxides behave in a similar manner to the opaque iron oxides (see Section 3.1.1). In addition, they show a high UV absorption, which is exploited in applications such as the coloring of plastic bottles and films used in the packaging of UV-sensitive foods [5.276], [5.277]. 

Worldwide consumption of transparent iron oxides is 2000 t/a. They are mainly used in the production of metallic paint in combination with flaky aluminum pigments and in the coloring of plastics for bottles and fibers. 

Toxicology. Special toxicological studies on transparent iron oxides have not yet been carried out. The results of opaque iron oxides are applicable, see Section 3.1.1.3. 

Trade names and producers include Capelle (Gebroeders Cappelle N.V., Belgium), Fastona Transparent Iron Oxide (Blythe Colours Ltd., UK), Sicotrans (BASF and BASF Lacke + Farben, Germany), and Trans Oxide (Hilton Davis, USA). 

Pigment transparent iron oxide red opaque iron oxide red iron mica... 

The particle sizes of opaque and transparent iron oxides are compared in Figures... 

A comparison of transparent iron oxide pigments formed by the precipitation and the combustion process is shown in Figure 5.41. 

Transparent iron oxides have the same fastness properties as opaque iron oxide pigments, but much higher color strength and significantly higher color purity. Table 5.19 summarizes the properties of selected transparent iron oxide pigments [5.192]. 

Transparent iron oxide pigments are characterized by high UV absorption making them particularly suitable for the coloration of plastic bottles and films for food packaging and the manufacture of wood protection coatings. The precipitated, needle-... 

Transparent iron oxide Yeiiow, needles Red, needles Red, isometric... 

Previously reported work has shown that acid-based anchor groups give the optimum bonding to inorganic surfaces, particularly if no additional treatments are in place. This study looks at a range of dispersants on untreated grades of transparent iron oxides with the formulation shown below... 

Another very important application is the dispersion of pigments that are difficult to disperse (e.g., carbon black, transparent iron oxides, phthalocyanine blue and green, and perylene red). The use of CAB and two-roll milling is the most efficient method of dispersion. 

Sunlight (mainly UV rays) breaks down the wood by depolymerization of the lignin. The UV transparency of the coating therefore has to be low. This is achieved by using UV absorbers in varnishes and transparent iron oxides in stains [11.35]. 

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