Preparation Of Fe₃O₄/MWCNT Composites And Study On Their Wave Absorbing Properties

In recent years,with the development of wireless communication technology,the popularity of electronic equipment and the progress of military detection means,electromagnetic wave has been widely used in civil and military fields.However,while we enjoy the convenience brought by electromagnetic wave technology,the harm of electromagnetic wave cannot be ignored.It is of great significance to the study of electromagnetic wave absorbing materials in people's livelihood and military fields.Fe₃O₄is a traditional absorbing material,but its real parts of permittivity and permeability are relatively low.It is difficult for pure Fe₃O₄ to obtain high absorbing performance properties.MWCNT has light weight and adjustable dielectric parameters.Fe₃O₄/MWCNT can obtain materials with good absorbing properties.In this paper,Fe₃O₄/MWCNT composites are prepared by solvothermal method,and their microwave absorbing properties are studied.The growth mechanism and microwave absorbing mechanism of the composites are analyzed.The main research work is as follows:1.Fe₃O₄/MWCNT composites are prepared by solvothermal method.Based on orthogonal design theory,the preparation process of Fe₃O₄/MWCNT composites with the best absorbing properties is explored by taking the absorption bandwidth and the lowest reflection loss as optimization indexes.The optimized process parameters are as follows:the mass of MWCNTs is 120 mg,the concentration of iron ion is 0.030 mol/L,the concentration of acetate is 0.240 mol/L,the reaction temperature is 200 C,and the reaction time is 16 h.The results of range analysis of the orthogonal table experiment show that the order of factors,affecting the microwave absorbing properties of the composites:reaction time>iron ion concentration>reaction temperature>acetate concentration.Then,the Fe₃O₄/MWCNT composites fabricated by the optimum process are characterized by XRD and SEM.The electromagnetic parameters of the samples are measured by vector network analyzer,and the microwave absorbing properties of the composites are analyzed.The results show that the absorption bandwidth is 5.2 GHz and the peak reflection loss is-30 dB.The absorption ability of Fe₃O₄/MWCNT composites to electromagnetic wave mainly comes from the residual loss and the space network formed by MWCNT.At the same time,the growth mechanism of Fe₃O₄/MWCNT composite was explored by time single factor experiment.It is considered that Fe₃O₄ is combined with MWCNT by in situ growth to form Fe₃O₄/MWCNT composite structure.2.Based on the optimized process parameters,the effects of anionic surfactant SDS,cationic surfactant CTAB and non-ionic surfactant PAM on the structure and morphology of Fe₃O₄/MWCNT composites are studied.The mechanism of the effects of different kinds of surfactants and different proportions of surfactants on the structure and morphology of Fe₃O₄/MWCNT composites and the mechanism of their influence on the electromagnetic wave absorption capacity are also studied.Generally speaking,the addition of surfactant provides a large number of active sites for the growth of Fe₃O₄,promotes the growth of Fe₃O₄ and increases the content of Fe₃O₄ in the material.However,the addition of surfactant destroys the role of NO₂^-stabilizer in the solution,which makes Fe₃O₄ grains grow into smooth surface nanospheres by dissolution and recrystallization and makes it impossible to incorporate electromagnetic waveguides into the microspheres.Some surfactant-assisted growth will increase the grain size and reduce the interfacial polarization strength of materials and the reflection between nanospheres.The assisted growth of PAM destroys the space network structure of MWCNT and weaken the conductivity of the material.Therefore,the addition of surfactant will weaken the absorbing properties of Fe₃O₄/MWCNT composites.