Study On Preparation And Properties Of CoFe₂O₄ Ferrite And Its Composites

With the rapid development of microwave communication technology, electromagnetic pollution has become more and more serious, therefore the study of anti-electromagnetic interference coatings and microwave absorbing materials have been increased widespread concern. Due to their unique micro-structure and magnetic-electronic properties, magnetic micro-nano structured material has been expected to a new type materials with high-performance microwave absorbance and has become a hot topic in the materials science. CoFe₂O₄ ferrite has a great saturation magnetization and high Snoek restriction, which can generate high complex permeability in its broadband extension and make it as thin broadband absorbers in a highly application values. Recently, although there are a variety of preparation techniques reported and adopted, however, the morphology, performance and other aspects control under magnetic-field annealing still need to further study. CoFe₂O₄ ferrite and its composites have been prepared with chemical precipitation route etc in this thesis. The structures, morphologies, magnetic and microwave absorbing properties changes with the magnetic field annealing have been systematically studied. This paper includes the following components.1. CoFe₂O₄ particles have been fabricated using chemical precipitation route with zero magnetic-field and magnetic field of 0.5T, annealing temperature of 800℃, respectively. Their phase structure, morphology, magnetic properties were characterized by XRD, SEM and SQUID, respectively. sample annealed under the magnetic field became well-crystaled, while CoFe₂O₄ particles induced by the magnetic-field annealing became regular spheral particles. The saturation magnetization (Ms) and complex permeability have a great enhancement with the magnetic field strength increasing which was easier to achieve impedance matching to improve the absorbing property.2. The hollow low-density magnetic balls have been synthesized through chemical precipitation method by the hollow glass sphere (cenosphere) coated with a layer CoFe₂O₄. Their phase structure, morphology, magnetic properties were characterized by XRD, SEM and SQUID, respectively. The complex permittivity and permeability of mixture of samples and paraffin in the 2-18GHz have been analyzed with microwave vector network analyzer. The response of reflection loss absorbing curve has been simulated with computer simulation program. The experiment results showed that hollow spheres coated CoFe₂O₄ was some good and light-weight microwave absorbing materials.3. ZnO/ CoFe₂O₄ composites have been successfully fabricated in two steps through hydrothermal and chemical precipitation route. The experimental data on SQUID and microwave vector network analyzer shows that microwave absorbing of ZnO/ CoFe₂O₄ composites was better than pure CoFe₂O₄. It was a feasible way to acquire light-weigh and strong microwave absorbing materials with the combination on magnetic loss and dielectric loss of CoFe₂O₄ and ZnO.