Simona Ovtar

Barium hexaferrite suspensions for electrophoretic deposition

In this investigation we have looked at the preparation of barium hexaferrite suspensions, with the stability of the magnetic barium hexaferrite particles being increased by the addition of a surfactant, dodecylbenzylsulfonic acid (DBSA). The influence of the solubility DBSA in different solvents and its adsorption onto the surfaces of particles with different sizes were determined from zeta-potential measurements. The most suitable and stable suspensions of barium hexaferrite particles, regardless of their sizes, were obtained in 1-butanol, and these were then used for a subsequent electrophoretic deposition. The microstructures of the deposits were examined with electron microscopy. The thickness and density of the deposits as a function of the electric field, the zeta-potential, the particle size, and the separation distance between the electrodes were investigated. The thickness of the deposits was found to increase with the increasing zeta-potential of the suspension and with the increasing separation distance between the electrodes. Denser deposits were obtained from the suspensions of smaller particles that had narrower particle size distributions.

The alignment of barium ferrite nanoparticles from their suspensions in electric and magnetic fields.

The alignment of plate-like barium ferrite nanoparticles, with diameters of 10-350 nm and thicknesses of 3-10 nm, in electric and/or magnetic fields was studied. Stable suspensions were prepared in 1-butanol with dodecylbenzenesulphonic acid as a surfactant. The deposits were produced from the suspensions with classic electrophoretic deposition, electrophoretic deposition in a magnetic field, and with drying in a magnetic field. The experiments, supported by theoretical calculations, show that the alignment of the nanoplates in the deposits was determined by the interplay between the hydrodynamic, electric, and magnetic forces. The preferential alignment of the nanoplates in plane with the substrate coincided with their magnetic orientation, and it increased with the shape anisotropy of the particles. The deposits were sintered at 1150 °C for 5 h to obtain ceramic films, which showed a magnetic orientation up to 90%.

Oriented Barium Hexaferrite Thick Films Prepared by Electrophoretic Deposition in a Magnetic Field

Stable suspensions of nanosized barium hexaferrite particles were prepared with the addition of surfactants. Hydrothermally prepared particles with sizes from 5 to 20 nm and commercial particles with sizes from 10 to 160 nm were used. The films with thicknesses from 1.5 to 9.5 μm were prepared with electrophoretic deposition in an external magnetic field. The orientation of the grains in the films was due to the magneto-crystalline anisotropy of the barium hexaferrite and was determined with X-ray diffraction analysis, scanning electron microscopy and magnetic measurements. The highest degree of orientation in the films with anisotropic magnetic behaviour was 90 %.