Preparation And Properties Of Doping F_e3O₄ Magnetic Shielding Fabrics In Low Frequency

Recently,the preparation,test technology and practical application of electromagnetic shielding fabrics at home and abroad are mainly focused on high frequency protection.The research goal is to achieve the electric conductivity of the materials.However,it is an extremely difficult for shielding low frequency signal because of its low-frequency and low skin effect.Usually it is considered that the high frequency radiation has significant hazards on our human body and the interference of the electronic devices.However,low frequency signal has a weak effect,so it can be ignored directly.By comparison the hazards of high frequency radiation are significant.However,low-frequency radiation also has great potential hazards to us.Therefore this research has both prospective and practical feasibility of electromagnetic shielding technology with important academic value and broad prospect of application.According to the frequency of the magnetic,magnetic shielding is divided into high frequency magnetic??100 KHz?and low frequency magnetic?<100 KHz?.The subject is based on the principle of magnetic shielding in low frequency.The preparation,measurments and properties analysis of the functional fabrics with good magnetic shielding effectiveness is proposed in our study.Fe₃O₄ and its doped magnetic nanocomposites?nanoparticles?were prepared by solvent thermal synthesis method in this paper.The structure,morphology,element composition and magnetic energy of the nanoparticles were analyzed by characterization methods.And the magnetic nanoparticles with excellent soft magnetic properties are selected for the magnetic shielding fabrics with additives by coating technology.The main contents and relevant conclusions are as follows:?1?Preparation of Fe₃O₄ and its doped magnetic nanoparticles and fuzzy analysis on the soft magnetic properties.The Fe₃O₄ and M-Fe₃O₄ nanoparticles in the same mole ratio were successfully prepared by solvent heat synthesis.The results showed that Co,Nd,Ce,La and Ni were successfully doped into Fe₃O₄ crystals.However,the crystal structure was not affected because of the low mole ratio at 10%.The prepared Fe₃O₄ and M-Fe₃O₄ nanoparticles are spherical structure by SEM.The particle size of Co-Fe₃O₄ is obviously larger than other nanoparticles.So it has better hard magnetic property with great Ms and Hc value.However,the soft magnetic property of Nd-Fe₃O₄ is good,because of its lowest Hc and Mr value.The fuzzy mathematics method is used to analyze the soft magnetic performance indexes.According to the comprehensive evaluation,the best soft magnetic property of all is Nd-Fe₃O₄,which is consistent with the magnetic analysis results.?2?Studies on the magnetic properties of Nd-Fe₃O₄ magnetic nanoparticles and the synthesized mechanism.Nd-Fe₃O₄ was selected as research object for the impact analysis on the magnetic properties in different mole ratio and synthesized time.The results showed that Nd-Fe₃O₄nanoparticles had spherical structure.The particle size is gradually decreasing as the mole ratio of Nd in Fe₃O₄ increasing as well as the Ms and Hc.A new lattice plane appears in the crystal when Nd is doped with mole ratio at 20%.So the particle size,the Ms and Hc values of the nanoparticles increased significantly.The analysis of element composition further validates the successful doping of Nd in Fe₃O₄ and the residue of polyethylene glycol in the samples.The formation mechanism of Nd-Fe₃O₄ nanoparticles shows that,ethylene glycol is a strong reducing agent.Some Fe³⁺is reduced to Fe²⁺at a certain temperature in the solvent heat reaction environment.The following REDOX reaction with free EG was carried out.Thus,the loose Nd-Fe₃O₄ nanoparticles were assembled.Then the loose microspheres hold together,and the tight Nd-Fe₃O₄ nanoparticles were obtained by Ostwald ripening.?3?Establishment of low frequency magnetic shielding test mode and setup of the test equipment.The low frequency magnetic shielding efficiency?hollow long circular tube shaft?test model is established based on the shielding principle.According to ASTM d4935-99 and GB/T 30140-2013,the test equipment was setup under weak magnetic field in the low frequency?<100 KHz?.The parameters of the device are as follows.There are two Helmholtz coil.The coil diameter is 300 mm.The coil spacing is 200 mm.The test tube length is 200 mm.The test tube outside diameter is 65 mm.The test tube inside diameter is 55mm.The magnetic field strength betweens 0 Gs and100 Gs.?4?Preparation of magnetic shielding fabrics by coating technology and the study on magnetic shielding effectiveness.The prepared Nd-Fe₃O₄ and Fe₃O₄ nanoparticles were then coated on the polyester fabrics with coating additives.Plasma treatment was taken up for improving the bonding between the coating and the base cloth.There are-COOH,-OH active groups and-COO·,-O·free radicals of polyester macromolecules after plasma treatment.The weight loss rate of coated fabrics was analyzed by orthogonal experiment.The results showed that the best polyester fabrics is the plain weave fabric with warp and weft density of 124/cm and 102/cm,respectively.The best plasma treatment parameters are O₂,300 W and 3 min,respectively.The results also showed that,the coverage of the nanoparticles of the coated fabrics are increasing with the increased weight of the nanoparticles.And the thickness and the permeability are basically increasing.The main elements of C and O are from polyester fabrics.The Fe and Nd elements are from nanoparticles.The addition of Nd has not affected its thermal performance.The particle size is gradually decreasing as the doping of Nd in Fe₃O₄.Ms and Hc are increased.When Nd is doped with mole ratio at 20%,the particle size,Ms and Hc values of the nanoparticles increased significantly.Theoretical analysis and practice test shows Nd?15%?-Fe₃O₄ is the best design scheme of the magnetic shielding effectiveness fabrics.