Preparation And Characterization Of Magnetic Iron-based Oxide Foam By Autocombustion Method

As an important branch of functional materials,magnetic materials have been widely used in machinery,electronics,medical treatment,biology,environment and military industry.With the development of nanotechnology,magnetic nanomaterials have attracted great interest from materials scientists because of their unique nano effects and special magnetic properties.Compared with the rare earth permanent magnetic materials,ferrite have better magnetic properties,chemical corrosion resistance,and their preparation is simple,convenient and low-cost.Porous foam-like materials have the advantages of low mass density,large specific surface area and good adsorption performance,which extend the application fields of the materials.The proper pore strcture in the micromorphology can cause the pinning force which is beneficial to the improvement of coercivity.Iron-based oxide foam has the advantages of both magnetic materials and foam materials,is consided as an important multifunctional magnetic nanomaterial.This research adopted the sol-gel self-propagating combustion method to synthesize iron oxide,cobalt ferrite and barium ferrite magnetic foams.The structure,morphology and magnetic peroperties were characterized and analysized by the XRD,SEM and VSM,respectively.The experimental conditions were optimized aimed at getting the low density and excellent magnetic performance of the magnetic iron-based oxide foam nanomaterials.We prepared ?-Fe₂O₃,Fe₃O₄ and Co_xFe_2-xO₃ foams by the sol-gel autocombustion method,and the effects of glycine to nitrate ratio?G/N?,annealing temperature on the structure,morphology and magnetic properties of foam-like products were studied.The porous film-like ?-Fe₂O₃ and Fe₃O₄ composite were obtained directly at the G/N was 0.6,and the Fe₃O₄ content increased with the increasing of G/N.The large porosity 3D net structure of pure ?-Fe₂O₃ foam was obtained after annealing at 700? in the air atmosphere,and the highest coercivity was obtained after annealing at 550 ?.The hightest saturation magnetization of Fe₃O₄ foam reached 58 emu/g at the G/N of 0.6 and has a large porosity with the specific surface area of 199.2 m²/g.Cobalt ferrite magnetic foam was prepared by autocombustion method and the effects of the ratio of glycine to nitrate?G/N?,heat treatment temperature and cobalt content on the structure,morphology and magnetic properties of spinel CoFe₂O₄ foam were studied.The optimum prepare conditions are G/N of 0.8,heat treatment temperature of 450 ? and Co content x of 0.8.The Co_0.8Fe_2.2O₄ foam has the largest coercivity of 3 k Oe and the maximum saturation magnetization of 42 emu/g.The mass density of Co_0.8Fe_2.2O₄ foam is 45 mg/cm³,which is far below the crystal density of CoFe₂O₄ of 5.2 g/cm³.Barium ferrite magnetic foam was prepared by autocombustion method and the effect of annealing temperature,Al³⁺ substitution amount,and the soft magnetic phase composition on the structure,morphology and magnetic properties were studied.We found that the particle size increases with the annealing temperature.The product Ba Fe₁₂O₁₉ has the largest coercivity at the annealing temperature of 1000 ?,with different Al³⁺ substitution amount,the highest coercivity of 13.7 k Oe was obtained at Ba Fe₈Al₄O₁₉.The effect of the soft magnetic phase content in the Ba Fe₈Al₄O_19-xWt.% Co_0.6Zn_0.4Fe₂O₄ composite foam was studied.The hard-soft phase of Ba Fe₈Al₄O₁₉ and Co_0.6Zn_0.4Fe₂O₄ exchange coupling well at the soft phase content below 30%,and the residual magnetization is improved effectively in this case.The smooth hysteresis loop shows the well exchange coupling between the hard magnetic phase and the soft magnetic phase.