Barium ferrite micro-/nanofibers with special morphology,nanowires with diameters of 100 nm,nanoribbons with diameters of 1μm,and nanotubes with outer diameter of about 300 nm while inner diameter of 100 nm were successfully prepared via electrospinning using different solvents(dimethyl formamide(DMF),solutions of deionized water and ethyl alcohol,and solutions of deionized water and acetic acid,respectively).The barium ferrite micro-/nanofibers were characterized by scanning electron microscope(SEM),X-ray diffraction analysis(XRD),and vibration sample magnetometer(VSM).The results demonstrate that the pure BaFe_(12)O_(19) ferrite phase is successfully formed.And the SEM results show excellent morphologies.The magnetic hysteresis loops demonstrate that their magnetic properties are quite different with different morphologies.The specific saturation magnetization is approximately the same(46.12-49.17 A·m^2·kg^(-1)),but the coercivity of the BaFe_(12)O_(19) increases from wires(190.08 kA·m^(-1)),ribbons(224.16 kA·m^(-1)) to tubes(258.88 kA·m^(-1)).
Gui-Fang LiuRun-Hua FanZi-Dong ZhangJing LiMin ChenQian-Qian LiLu LuPei-Tao Xie
Cermets are widely applied as attenuating materials due to high electromagnetic loss and better mechanical properties. In this paper, multiphase cermets composed of iron, iron oxide and alumina were successfully prepared by a two-step in situ synthesis process,which includes pressureless sintering and a selective reduction in hydrogen atmosphere. The phase composition and microstructure of cermets were analyzed by X-ray diffraction(XRD) and scanning electron microscopy(SEM), respectively. It is shown that nanosized cuboid Fe particles and octahedral Fe_3O_4 particles are distributed in alumina matrix. The permittivity and permeability of composites were tested with radio frequency impedance analyzer(0.01–1.00 GHz). The results show that permittivity presents obvious frequency dispersion. Furthermore,dielectric constants of multiphase cermets get enlarged due to the enhancement of interfacial polarization. On the other hand, there is a magnetic loss peak in permeability spectra,which indicates typical relaxation behavior. It is possible to achieve better electromagnetic attenuation property by adjusting process parameters.
Kai SunRun-Hua FanZi-Dong ZhangKe-Lan YanXi-Hua ZhangChuan-Bing ChengMin ChenPei-Tao Xie
The nano-graphite sheet/alumina composites were prepared in situ by a facile impregnation-reduction process.The microstructure of the composites was analyzed by X-ray diffraction(XRD),and the final phase composition after reduction is Al_2O_3,metal Fe and graphite crystal.Scanning electron microscopy(SEM) images show that the particle size of Fe is about 20 nm,and the lamellae thickness of the graphite is about 30 nm.Then,the dielectric properties and conductive mechanism of the composites were investigated experimentally in the frequency range of 0.01-1.00 GHz by impedance analyzer.The results show that the real part of permittivity of composites increases with Fe^(3+) concentration,which is due to the increase in interfacial polarization between Fe and Al_2O_3 and the three-dimensional network of lamellar graphite formation.Therefore,tunable microtopography and electrical parameters of nano-graphite sheet/alumina composites can be realized by changing Fe^(3+) concentration.
