Preparation of magnetic ceramics

Ferrites can be prepared by almost all the existing techniques of solid state chemistry, leading to a very wide variety of forms polycrystalline aggregates, thin and thick films, single crystals. Some of these methods have been developed to prepare ferrites with specific microstructures. The oldest one, the ceramic method, involves the same operations as the classical techniques for fabrication of conventional ceramics. This explains the origin of the term magnetic ceramics. Many of the techniques recently developed consist of improvements in one or several of the basic operations of ceramic fabrication. 

The four basic operations in the ceramic method are shown schematically in Fig. 3.1. Raw materials are usually iron oxide (a-Fe203) and the oxide or the carbonate of the other cations in the desired ferrite. These combine according to the overall reactions  

Since ferrites possess a very high melting temperature, both reaction and densification usually take place in the solid state. Initial formation of the product occurs at the contact surface between particles of the two reactants. As reaction proceeds, the product layer becomes thicker, increasing the length of the diffusion paths of the reactants and thus 

Coprecipitation Precursor routes Sol-gel methods Spray-drying Freeze-drying Combustion synthesis Glass crystallisation 

Hot isoslalic pressing Liquid phase sintering Microwave sintering 

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Preparation of magnetic ceramics 3.4.1 Solid-state reactions... 

Preparation of magnetic ceramics Table 3.4. Sintering stages. 

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