Barium ferrites

Pillai etal. [301] reported synthesis of barium hexaferrite (BaFei20i9) via a two-microemulsion process. The surfactant used was CTAB with 1-butanol as a co-surfactant, and n-octane as the continuous oil phase. The aqueous phases in the two microemulsions were (i) a solution of 0.0IM Ba(N03)2 and 0.12M Fe(N03)3 and (ii) a 0.19M solution of (NH4)2C03. The microemulsions were mixed under constant stirring, leading to the precipitation of barium iron carbonate. The precipitate was washed with 1 1 methanol and chloroform, followed by only methanol and dried at 100°C. The dried carbonate thus obtained was calcined at 950°C/12h for obtaining a phase-pure barium hexaferrite. However, the Fe Ba ratio was found to be slightly more than the stoichiometric, because of preferential dissolution of barium carbonate in water. As a result, the samples also contained some amorphous iron oxide impurities. The precursor particles had a size range 

The large difference in solubility of Ba and Fe sources and the consequent problems in the wet chemical synthesis of Ba-Fe compounds prompted Chhabra et al. [215] to use a new and modified method of synthesis through microemulsions. In this method, the dispersed phase was anhydrous ethanol while the continuous phase was isooctane. 

Functionalized surfactants (see Section 5.2) Ba(AOT 2 and Fe(AOT 3 were dissolved in the ratio 1 12 in the continuous phase. Dry ethanol was added to form the reverse (alcohol-in-oil) microemulsion. Ba and Fe oxalates were co-precipitated by the addition of an ethanolic solution of oxalic acid. The precipitate was recovered by centrifugation (10,000 rpm) and washed with dry acetone. Practically phase-pure BaFei20i9 was obtained by calcination of the dried precipitate (barium carbonate + ferric oxide) at 950 C/12h. The precursor particles were 10-20 nm in size, while the calcined ferrite particles, almost spherical in shape, had a mean diameter of 60 nm. 

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In 1989, 30% of the barium carbonate produced was used in glass manufacturing, 30% in brick and clay products, 20% in the manufacture of barium chemicals, 5% in the manufacture of barium ferrites, 5% in the production of photograpliic papers, and 10% in miscellaneous uses. 

Barium carbonate of finely controlled particle size reacts in the soHd state when heated with iron oxide to form barium ferrites. Magnetically aligned barium ferrite [11138-11-7] powder can be pressed and sintered into a hard-core permanent magnet which is used in many types of small motors. Alternatively, ground up magnetic powder can be compounded into plastic strips which are used in a variety of appHances as part of the closure mechanism. 

The barium ferrite was found to have an increase in magnetic anisotropy, as in the nickel ferrite, but its overall effect on magnetization was less because of greater magnetocrystalline anisotropy. The shock modification caused reduced crystallite size and local damage that resulted in increased microwave absorption. 

The product crystals find industrial application as a component raw material for optical glass, fibreglass, Braun tubes, electric condensers, barium ferrite, etc. Needles shaped crystals are obtained at high pH, while pillar-shaped crystals are formed at neutral pH. The formation of carboxyl ions is via hydroxy ions at high pH, but at neutral pH it may accompany the production of hydrogen sulphide, as... 

Magnetic properties Barium ferrite, iron oxide Ba, Fe... 

Barium Ferrite Uses small bits of magnetized barium ferrite, placed inside a plastic card. The polarity and location of the "spots" determine the coding. Moderate Low susceptibility to damage durable since spots are embedded in the material Moderate-high... 

Which would be stronger (a) a chair made from PP or (b) one of equal weight made from cellular PP What advantage would a barium ferrite-filled PVC strip have over an iron magnet ... 

Flexible Magnets. Flexible magnets are made by embedding ferrimagnetic ceramics in a polymer matrix, such as barium ferrite or strontium ferrite in nylon or... 

Figure 5.22 Lattice image of MYMYg intergrowth in the barium ferrite system. (From Anderson Hutchison, 1975.)...

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