Preparation Of CoO/MWCNTs Composites Material And Its Microwave Absorbing Properties

The rapid development and popularization of communication technology and large electronic equipment have played an important role in economic growth and the improvement of people’s living standards.However,the electromagnetic radiation and pollution not only lead to the abnormal operation of precision electronic instruments and equipment,but also threaten human health.Therefore,the development of high performance electromagnetic wave absorbing materials has very important practical significance.Co-based materials have attracted wide attention in the field of electromagnetic wave absorption.However,the high density,impedance mismatch and narrow frequency band of single cobalt-based electromagnetic wave absorber hinder its practical application in the field of absorption.Therefore,combining materials with strong dielectric loss to construct composite absorbers with high impedance matching and strong attenuation ability has become a hot topic in the field of absorbing.In this thesis,hollow CoO nanomaterials with special structure were firstly prepared,and then the hollow CoO was combined with multi-walled carbon nanotubes（MWCNTs）by physical assembly and hydrothermal process respectively to construct high performance electromagnetic wave absorber.The growth mechanism of hollow CoO nanomaterials and the absorption mechanism of CoO/MWCNTs composites were explored,and the effects of filling ratio and MWCNTs content on the absorption properties of the composites were systematically studied.The main results are as follows:（1）To explore the preparation technology and growth mechanism of hollow CoO nanomaterial.Using Co（OH）₂ hexagonal nanosheets prepared by hydrothermal method as precursors,the growth conditions of doughnut-shaped hollow CoO nanomaterials were investigated by adjusting annealing temperature,annealing time and heating rate.The structure and morphology of the prepared samples were characterized by XRD and SEM.The results show that annealing temperature and heating rate are the main factors affecting the formation of hollow CoO.When annealing temperature e was 450℃,heating rate was7℃/min and holding time was 2 h,the uniform hollow CoO nanostructure was formed.The formation of hollow CoO nanostructure is mainly attributed to Ostwald curing.The lowest reflection loss（RLmin）of the sample prepared was only-4.10 d B when the filling ratio was30 wt%and the sample thickness was 5.0 mm,which failed to show good absorbing performance.（2）Hollow CoO/MWCNTs nanocomposites were prepared by hydrothermal method,and the effects of different filling ratios and MWCNTs content on the absorption properties of the composites were systematically studied.The results showed that when the filling ratio was 30 wt%and the MWCNTs content was 7%,the sample showed excellent absorption performance.The lowest reflection loss of the composite is-72.57d B,the matching thickness is 2.0mm,and the EAB reaches 4.10 GHz.At an ultra-thin thickness of 1.5 mm,the sample also has a reflection loss of-42.10 d B and an effective absorption bandwidth of 3.30 GHz.（3）It is found that the absorption performance of CoO/MWCNTs composites prepared by hydrothermal method is significantly better than that of CoO-MWCNTs composites prepared by physical mixing.This is because CoO/MWCNTs nanocomposites have more heterogeneous interfaces,which is beneficial to promote the interface polarization effect and improve the dielectric loss performance.The large specific surface area of the hollow CoO nanostructure makes the composite sample have multiple reflection and scattering characteristics and can attenuate more electromagnetic waves.When MWCNTs were interwoven around the hollow CoO,it was easier to form a spatial conductive network,leading to rapid electron transfer and transition in the composites,thus promoting the conductivity loss.In addition,the excellent impedance matching of the composites makes the CoO/MWCNTs nanocomposites exhibit excellent porter absorption properties.