Preparation, Structure And Properties Of Micro/nano Ferrite Composite Fibers

Electromagnetic pollution becomes more serious with the development of the electronic industry, which will not only interfere with the normal operation of electrical equipments, but also threaten our health. Owing to their excellent ability of reducing or eliminating electromagnetic pollution, microwave absorbing materials have attracted lots of attention.Ferrite magnetic materials have high resistivity and permeability, in addition, they can be easily combined with other materials to improve absorption performance, lead to their wide application in the field of microwave absorption.Compared with powder and thin film materials, ferrite fibers have an great advantage in weight. Besides, ferrite fibers could restrain the aggregation of particles due to their shape characteristics and enhance the exchange-coupled interaction effectively especially for ferrite composite fibers, which will be helpful to reduce the weight and broad the microwave absorption bandwidth. In this paper, a series of ferrite fibers was successfully prepared by electrospinning and sol-gel spinning methods; TG-DSC, FTIR,XRD, SEM and TEM analysis were used to character ferrite fibers’ components, grain size, microstructure and surface morphology. Their magnetic and microwave absorbing properties were also investigated via VSM and vector network analyzer. Brief results are summarized as follows:Single phase Ni_0.5Zn_0.5Fe₂O₄ and Sr Fe₁₂O₁₉ fibers were prepared by electrospinning,respectively. Smooth surface become rough after calcination, both of the grain sizes increased with calcined temperature increasing. The magnetic property is mainly affected by calcined temperature, at the calcined temperature of 900 °C for 2 h,Ni_0.5Zn_0.5Fe₂O₄ fiber had a saturation magnetization（Ms） of 68.3 emu/g and coercivity（Hc） of 13.2 kA/m, while SrFe₁₂O₁₉ fiber had a saturation magnetization（Ms） of 51.4emu/g and coercivity（Hc） of 358 kA/m, showed typical soft and hard magnetic characteristic, respectively.Ni_0.5Zn_0.5Fe₂O₄/Sr Fe₁₂O₁₉ composite fibers have been successfully prepared by electrospinning, cubic grains of Ni_0.5Zn_0.5Fe₂O₄ and hexagonal plate-like grains of SrFe₁₂O₁₉ constructed the structure of these fibers. With the content of hard phase, morehexagonal plate-like SrFe₁₂O₁₉ grains are observed, while the soft grains adhere on the surface of SrFe₁₂O₁₉ grains, the saturation magnetization（Ms） of ferrite composite fibers decreased by degrees, coercivity（Hc） showed a continuous increase. The microwave absorption properties of ferrite composite fibers were strongly depended on soft/hard mass ratios and speciman thickness. When the soft/hard mass ratio was 1:3,the sample with 3.5 mm coating thickness exhibited the best microwave absorption, the minimum RL value reached-31.9 dB at 10.6 GHz, and the effective bandwidth with RL<-10 dB reached 10.5 GHz covering the whole X-band and Ku-band.Ni_0.8Zn_0.2Fe2O4/Sr Fe₁₂O₁₉ composite fibers were successfully fabricated using the sol-gel spinning method. Ferrite composite fibers exhibited an obvious shrinkage after calcination at different temperatures, while the continuous 1D structure was still remained, the average diameter of fibers is 1.0±0.25 μm. Pure phase ferrite composite fibers, consisting of magnetically soft phase Ni_0.8Zn_0.2Fe2O4 and hard phase Sr Fe₁₂O₁₉,were obtained at 900 °C for 2 h. Calcined temperatures had an great influence on the magnetic properties of Ni_0.8Zn_0.2Fe2O4/SrFe₁₂O₁₉ composite fibers. At the calcined temperature of 900 ℃, the VSM results appeared remanence enhancement and showed a smooth hysteresis loop, implying existence of effective exchange coupling between the Ni_0.8Zn_0.2Fe2O4 phase and the SrFe₁₂O₁₉ phase. The saturation magnetization（Ms）,coercivity（Hc） and remanence（Mr） revealed an increase at first and then decreases with calcined temperature increasing, and reached their maximum values at 1000 ℃,respectively.