Лако-красочные материалы — производство

There are three important methods for manufacturing barium ferrite on an indus­trial scale: the ceramic, hydrothermal, and glass crystallization methods. The main producers were Toshiba and Toda in 1995. Actual data were not disclosed. Ceramic Method Mixtures of barium carbonate and iron oxide react at 1200-1350 °C to produce crys­talline agglomerates, which are ground to […]

Hexagonal ferrites have a wide range of structures distinguished by different stacking arrangements of three basic elements known as M, S, and Y blocks [5.25]. For mag­netic pigments, the M-type structure (barium hexaferrite [12047-11-9] BaFe12O19) is the most important. The magnetic properties of M-ferrite can be controlled over a fairly wide range by partial substitution […]

Barium ferrite pigments have been considered for several years for high-density dig­ital storage media [5.23, 5.24]. They are very suitable for preparing unoriented (e. g., floppy disks), longitudinally oriented (conventional tapes), and perpendicularly ori­ented media. In the latter the magnetization is oriented perpendicular to the coating surface. They are required for perpendicular recording systems, which […]

The largest producers of metallic iron pigments are Dowa Mining and Toda Kogyo (Japan). World consumption in 2002 was ca. 1800 t, of which ca. 65% were used in the manufacture of broadcasting media, 2% for audiotapes, and 33% for data storage applications; this last being expected to increase later. Fig. 5.2 TEM-photographs showing typical […]

The coercive field strength of metallic iron pigments is primarily determined by their particle shape and size, and can be varied between 30 and 210 kA m-1. Pigments for analog music cassettes (Hc ~ 90 kA m-1) usually have a particle length of 0.35 pm (see Section 5.1.1, Table 5.1). The length to width ratio […]

Metallic iron pigments are commercially produced by the reduction ofacicular (needle­shaped) iron compounds [5.21]. As in the production of magnetic iron oxide pig­ments, the starting materials are iron oxide hydroxides (see Section 3.1.1) or iron oxalates, which are reduced to iron in a stream of hydrogen either directly or via oxidic intermediates. Due to their […]

The magnetization of iron is more than three times higher than that of iron oxides. Metallic iron pigments can have a coercive field strength as high as 150 kA m-1, depending on the particle size. These properties are highly suitable for high-density recording media. Oxidation-resistant products based on metallic pigments first be­came available in the […]

Chromium dioxide is used exclusively for magnetic recording media. It may also be used in combination with cobalt-modified iron oxides (see Section 5.1.2) in the pro­duction of magnetic recording media. The world consumption of CrO2 is decreasing continuously as compact disc and digital videodisc are taking over the audio and video market. The sole producer […]

The conversion of an intimate mixture of Cr(III) and Cr(VI) compounds into CrO2 under hydrothermal conditions has been developed into an industrial process in autoclaves at ca. 350 °C and 300 bar [5.18]. Pure CrO2 slowly disproportionates in the presence of water. The CrO2 crystal surface of commercial pigments is therefore topotactically converted to p-CrOOH, […]

Chromium dioxide [12018-01-8], chromium(IV)oxide, CrO2, is a ferromagnetic ma­terial with a specific saturation magnetization Ms/p of 132 A m2 kg-1 at 0 K, corre­sponding to the spin of two unpaired electrons per Cr4+ ion. The Ms/p value of CrO2 at room temperature is ca. 100 A m2 kg-1 [5.17]; CrO2 magnetic pigments reach values of […]