Study On Ferrites Wave-absorbing Materials Prepared With Magnetism Cenosphere

With the development of radio-technology, electromagnetic wave plays an important role in facilitating people’s life. However, a serious electromagnetic pollution ensues which is a threat to human’s living space. Thus the research on the electromagnetic-shield materials has attracted intense concern recently. Wave-absorbing materials have advanced with exceptional speed, ferrites wave-absorbing materials as the most widely researched and used possess efficient absorbency and low cost of preparation. In this dissertation, a ferrite wave-absorbing material was explored using low-cost magnetic cenospheres which was separated from industrial solid waste fly-ash. This kind of materials can be used for civil electromagnetic-shield to provide a new economical engineering material for buildings that need special protection. Furthermore, the recycle of magnetic cenospheres which is the primary raw-material of the research can relieve the problem of fly-ash depositing which is significant for protecting environment and saving resource.In light of the basic theory of ferrites and wave-absorbing materials, Ni-Zn series ferrites were selected to be our objective. The Ni-Zn ferrite with pure phase was prepared using magnetic cenospheres, and the preparation process and composition were optimized. Moreover, CuO and TiO₂ doping were carried out to improve the apparent performance, microstructure and electromagnetic properties.Firstly, the Ni-Zn ferrites with a series of designed compositions were prepared using starting materials of NiO, ZnO and magnetic cenospheres as well as analytically pure Fe₂O₃ for comparison. The results show that single crystal phase was obtained for all the samples and the electromagnetic properties of the samples synthesized by magnetic cenospheres were similar to those from pure Fe₂O₃ in the range of operating frequency. The samples with composition of Ni_0.3Zn_0.7Fe₂O₄ turn out to be the one with greatest imaginary part of complex permeability.To improve the densification and hence the electromagnetic properties of samples, the fluxing agent CuO was introduced into the matrix compound. The density measurement and SEM images of sintered samples reveals that the doping of CuO remarkably improved the densityand the microstructure became more symmetrical and compact. The amplification of densification reached about 40%. x（CuO）=5%-doped sample was verified to be densest one. In addition, the electric conductivity of materials was increased for the densification of samples, which results in the distinct increase of the imaginary part of complex permeability and complex permittivity, magnetic loss factor and dielectric dissipation factor were also improved and consequently the improvement of the electromagnetic energy dissipation capability.TiO₂ was also introduced into the samples as an additive to further improve the electromagnetic energy dissipation capability. The TiO₂-doped samples exhibit no appreciable improvement in other performances but show a complex permittivity with 4 fold increasing imaginary part which effectually enhances the dielectric loss. The microcosmic morphology of samples which added 0.3wt% TiO₂ was more symmetrical than others.For the sake of potential application as engineering materials, the wave-absorbing efficiency of the samples was calculated by the emulation software. The results indicate that the materials investigated in this dissertation possess a good capability in absorbing the incident electromagnetic wave within the frequency range of 750MHz¹GHz.