Heterogeneous Preparation,Structure And Properties Of Magnetic Metal/ZnO Composite Nanoparticles

Magnetic-loss and dielectric-loss microwave absorbing materials are the main directions for the study of microwave absorbing materials.However,with the continuous development of the electromagnetic technology,the single magnetic-loss or dielectric-loss absorbing material have various disadvantages,so that they cannot meet the requirements.The conventional magnetic-loss absorbing materials include ferrite,magnetic metals and alloys.In the high-frequency magnetic field,there will be skin effect to reduce the microwave absorbing properties of magnetic metals and alloys by the high conductivity,and they also have the poor ability of anti-oxidation and acid-alkali corrosion.The disadvantages of ferrites are poor high-temperature properties,low magnetic permeability,and difficult electromagnetic matching.The difference between the dielectric constant and the magnetic permeability of dielectric-loss absorbing material is very large,and it is difficult to achieve the impedance matching which greatly affects the electromagnetic wave entering the interior of the material.In summary,we need to develop a composite material combining magnetic-loss and dielectric-loss to improve the microwave absorption performance.The magnetic metal/ZnO core-shell composite particles are an effective combination of magnetic loss-and dielectric-loss.In this work,firstly,Ni,Co,and FeNi magnetic metals and alloy nanoparticles with different morphology or different structures were prepared by liquid-phase reduction method.Then magnetic metal and alloy particles were used as cores,and low-temperature liquid heterogeneity coating technology was used.The zinc oxide coating on the surface of the particles was realized,and core-shell ZnO@Ni,Zn O@Co and ZnO@Fe Ni composite nanoparticles were prepared.Through XRD,we determined that the prepared Ni nanoparticles and FeNi alloy particles were FCC structures.Co particles prepared with different reducing agents had the crystal structure of HCP crystal structure and HCP and FCC coexistence,respectively;The prepared Ni nanoparticles and FeNi alloy particles have two different morphologies,respectively,and the two structures of Co nanoparticles are flaky morphologies;through the VSM,when the prepared magnetic metal and alloy particles are aggregated into micron-scale The coercive force of the composite particles is almost constant,and the coercive force of the composite particles increases when the nanoparticles are prepared with good dispersibility.It is speculated that the increase in coercivitymay be due to zinc oxide and metals or alloys.The exchange of particles occurs at the interface,but the specific surface area of the particles decreases when they are aggregated into micron-sized particles,which results in the exchange effect on the effective anisotropy field being inferior to other anisotropies,resulting in little change in the coercivity.Finally,Ni and FeNi alloy particles were mixed with paraffin wax to prepare a composite.The microwave magnetic properties and microwave absorption characteristics were studied.It was found that the composite particles had a wider effective absorption width than the metal and alloy particles and the absorption peak moved to a low frequency direction.