Control of texture in alumina by colloidal processing in a strong magnetic field

Electrical, mechanical and other properties of ceramic materials can be controlled by designing their microstructures. It had generally been difficult to utilize a magnetic field for tailoring the microstructure in feeble magnetic ceramics, such as Al₂O₃; however, the possibility of controlling the microstructure by a magnetic field occurred with the development of superconducting magnets. In this review paper, we introduce a novel processing for the microstructual design in ceramics by colloidal processing in a strong magnetic field and an electric field. We demonstrate that the textured alumina can be fabricated by slip casting in a strong magnetic field and the production of alumina/alumina laminar composites with different crystalline-oriented layers can be achieved by electrophoretic deposition in a strong magnetic field. In order to control the texture using a magnetic field, a good dispersion of powder in a suspension is necessary because a strong attractive force between the agglomerated particles prevents each particle in a suspension from rotating in the magnetic field. The degree of orientation depends on the processing factors, such as heating temperature, viscosity of suspension, etc. And the grain growth in Al₂O₃ matrix enhances crystallographic texture development. The bending strength of the laminar composite depended on the direction of the multilayered microstructure with alternate crystalline-oriented layers. Crack propagation and fracture mode depend on the direction of microstructure in the laminar composite with controlled crystalline orientation.