Researches on Preparation and Electromagnetic Response Property of Nano-composite Magnetic Particles

Author:Li Shi Chuan

Supervisor:zhang tong lai zhou zun ning


Degree Year:2017





With the development of optoelectronic and computer technology,the traditional smoke screen,decoy and other passive photoelectric countermeasure technologies,of which only work in single-band and have high demands on meteorological environment,are limited in the application on the battlefield.Therefore,it is necessary to study the new multi-functional and smart passive interference material with large-scale information suppression capability.It is also an important opportunities and challenges for researchers in the field of passive electro-optical countermeasure.In this paper,based on comprehensive analysises of development needs of passive countermeasure equipment,the nano-superparamagnetic materials,extinction materials,conductive metals and energetic materials are combined using the cutting-edge nano-composite technology.The brand-new multi-function interference particles show excellent application potentials on electromagnetic target directed moving,interference band magnetic controlling,optical signal suppressing and electrical power system disabling,which has laid a theoretical and technical foundation for the sustainable development of passive interference photoelectric countermeasure technology and has significant military significance.The main works and achivements as followings:(1)Combined with rules of nano-materials composite preparation and extinction,the two different core-shell structure composites with magnetic core and magnetic shell are designed.The IR extinction characteristics of both core-shell structure composites and their chain structures are simulation studied by FDTD method.The structure and size of multi-function layers are optimized according to the simulation.It is found that the shell thickness of the core-shell particles only need 30 nm to completely inherit the extinction characteristics of the material.The extinction coefficient of the magnetic assembly chains is about five times of single particles.Data shows that by controlling the length of chains,the extinction peak band of the particles can be precisely tunned.At last,the nano-core-shell composite particles with the superparamagnetic cluster as the core,SiO2 as the protective medium,extinction and conductive matel as the shell are designed to combine the properties of magnetic response,electrical conductive and optical signal interference.The core-shell composites with potassium picrate microcrystalline ignition as the nuclear,superparamagnetic nano-crystal as surface decoration are designed to combine the properties of magnetic response and ignition based on the application characteristics,nano material growth theory and compatibility.(2)By improved solvothermal reduction method,the superparamagnetic Fe3O4nanoclusters with size range of 100700 nm and Fe3O4 nanocrystalline with as high as 87.63emu/g magnetization and superparamagnetic critical size were prepared.The functions of different surfactants and their effects on the particle structure and magnetic properties were discussed.The ratio of different polyalcohols are discovered that is the mean reason for tuning the sizes of both superparamagnetic nanocrystallines and clusters..The structure,magnetic properties and composition characteristics of the prepared particles were tested by XRD,TEM,SEM,VSM,FTIR and XPS.(3)The magnetic core-shell composite particle,Fe3O4@SiO2@Ag,Fe3O4@SiO2@C and KPA@Fe3O4 were prepared by the method of seeded growth,in-situ homogeneous polymerization method,high temperature pyrolysis method and microcrystalline coprecipitation method,respectively.The magnetic properties and composition characteristics,the conductivity and microwave loss characteristic of the first two compisite particles were analyzed by four-probe resistivity tester and network vector meter.The influence of the thickness of the shell materials on the properties of magnetic,conductivity and microwave loss characteristic were discussed.The resistivity of the Ag shell composite particles is as low as 8.06×10-5Ω·cm,and the microwave shielding band below-10 dB of C shell composite particles can cover the wide band of 1216 GHz.The energy releasing property of the KPA@Fe3O4 composite particles were analyzed by DSC.The last optimized mass ratio of the energetic and magnetic components was 1:2 by considering the stability and efficiency of magnetic response of energy release.(4)The finite element multi-physics simulation model of magnetic particle transmission under the magnet induced magnetic field and air flow field is established by combining the particle magnetization equation,the Navier-Stokes equation and concentration diffusion equation.The distribution of concentration and velocity for the composite particles are studied.The effects of magnetic field strength and particle magnetic response intensity on the magnetic induced directed transport of magnetic composite particles are discussed.The calculation data shows that the concentration of the composite particles increasing when nearing the magnetic source.The 40 mT magnetic source can induce the eddy current in the near area flow field,which also cause the nearby particle concentration is more than 14 times to the initial concentration.And the ability for convergencing the magnetic particles of magnetic sourse are found that it is increasing according to the formula:(?)(5)The experimental test system for the magnetic induced directed transport performance of magnetic composite particles is designed.The composite particles’magnetic induced directed transport performance are studied experimentally.The experimental data shows that the particle concentration near the 10 mT magnetic sourse is nearly 20 times of the case without magnetic sourse.It is proved that the magnetic composite particles have obvious convergence effect on the weak magnetic target.(6)The magnetic assembly of magnetic composite particles was simulation studied by Monte Carlo method.The assembly structure of magnetic composite particles under different parameters such as size,concentration,external magnetic field strength and field direction were simulated.The results show that the composite particles tend to form chain structure along the direction of external magnetic field.The length of the magnetic assembly chain is positively correlated with the size and concentration of the magnetic particles.Under the volume concentration of the composite magnetic particles less than 1%,the particles with the size in range of 400800 nm tend to form stabilized chain structures in which always contains 812 particles.It is an important candidate for the far-infrared interference material due to the extinction peak value of the chain structure matchs with longwave infrared window.