Barium ferrite pigments

Production. There are three important methods for manufacturing barium ferrite on an industrial scale the ceramic, hydrothermal, and glass crystallization methods. The main producers are Toshiba and Toda. 

Ceramic Method. Mixtures of barium carbonate and iron oxide are reacted at 1200-1350 °C to produce crystalline agglomerates which are ground to a particle size of ca. 1 pm. This method is only suitable for the high-coercivity pigments required for magnetic strips [5.35], 

Hydrothermal Method. Iron [Fe(III)], barium, and the dopants are precipitated as their hydroxides and reacted with an excess of sodium hydroxide solution (up to 6 mol/L) at 250-350 °C in an autoclave. This is generally followed by an annealing treatment at 750-800°C to obtain products with the desired magnetic properties. Many variations of the process have been described [5.36]-[5.40], the earliest report being from 1969 [5.41], In later processes, hydrothermal synthesis is followed by coating with cubic ferrites, a process resembling the cobalt modification of iron oxides (see Section 5.1.2). The object is to increase the saturation magnetization of the material [5.42]-[5.44], 

Magnetic Recording Properties. Typical values of physical properties of barium ferrite pigments used in magnetic recording are given in Table 38. 

Application Specific surface area, m2/g Platelet diameter, nm Platelet thickness, nm Hc, kA/m MJq, A m2/kg 

This process was developed by Toshiba [5.36]. The starting materials for barium ferrite production are dissolved in a borate glass melt. The molten material at ca. 

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Table 38. Typical properties of barium ferrite pigments...

Barium carbonate Barium carbonate (1 1) Barium monocarbonate BE 1 (salt) BW-C3 BW-P C.i. 77099 C.l. Pigment White 10 Carbonic acid, barium salt Carbonic acid, barium salt (1 1) Caswell No, 069 Cl 77099 Cl Pigment White 10 Durex White EINECS 208-167-3 EPA Pesticide Chemical Code 007501 HSDB 950 NSC 83508 Pigment White 10. Used in the treatment of brines in chlorine-alkali cells to remove sulfates, as a rodentlcide, in production of barium salts, ceramic flux, optical glass, case-hardening baths, ferrites, in radiation-resistant glass for color television tubes. White powder mp 811 bp = 1450 d = 4.430 ... 

The toxicity of lead, chromium, cadmium, and barium has made the continued use of paints containing these elements highly undesirable. The health and environmental problems associated with these heavy metals are serious, and new problems are discovered all the time. To address this issue, pigment manufacturers have developed many alternative pigments, such as zinc phosphates, calcium ferrites, and aluminum triphosphates, to name a few. The number of proposed alternatives is not lacking in fact, the number and types available are nearly overwhelming. 

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