Design Of FeSiAl Flake Composites And Study On Electromagnetic Absorption Mechanism

With the development of electronic information technology,the continuous demand for miniaturization,high efficiency and high frequency of electronic equipment has led to serious electromagnetic pollution and interference.The development of"thin,light,wide and strong"effective electromagnetic absorption materials has become one of the key issues in the progress of the times.As a traditional soft magnetic material,iron silicon aluminum alloy is widely used as an absorbing material due to its high magnetic permeability,high saturation magnetic flux density,and good mechanical processing performance.Due to the low dielectric loss capacity of metal alloys and the Snoek limit of microscale powders,the application of iron silicon aluminum microscale materials in the microwave field is severely limited.Obtaining micro iron silicon aluminum powders with excellent electromagnetic absorption performance has become a challenge.Reducing the large dielectric constant and breaking through the Snoke limit are the key to achieving good microwave absorption performance in the GHz range for iron based micron scale materials.This article introduces flake iron silicon aluminum powder.Due to its strong anisotropy in shape,the resonance frequency in the gigahertz frequency range may exceed the Snoek limit.However,due to the large aspect ratio of flake iron silicon aluminum metal powder,it is easy to form a conductive network,resulting in a higher dielectric constant,which is not conducive to impedance matching and exhibits poor microwave absorption performance.Based on the research and conclusions on reducing the dielectric constant of iron silicon aluminum metal powder,the commonly used methods mainly include coating,surface modification,and micro oxidation of the powder using inorganic insulation materials.The traditional planetary ball milling technology needs a lot of time to obtain FeSiAl flaky powder and the output of a single experiment is low.Therefore,this paper uses a vertical ball mill to prepare FeSiAl flaky powder by high-energy ball milling,study the powder microstructure and performance,and conduct subsequent surface treatment on the powder.The main research contents are summarized as follows:（1）Preparation of FeSiAl flaky powder.Constantly adjust and optimize the ball milling parameters and powder ratio of the vertical ball mill to obtain FeSiAl flaky powder with thickness less than 1μm.The diameter thickness ratio of the powder after 6 h ball milling reaches 74.93.By observing and analyzing the micro morphology of the powder,we found that with the increase of milling time,the interface experienced the following in-situ evolution:nano oxide layer and particle interface,some interfaces between nano oxide layer and iron nanoparticles,complete iron nanoparticles and oxide layer interface,nano oxide layer and particle interface.The evolution of the interface and the ratio of height to diameter can effectively adjust the permittivity and permeability,thereby optimizing the electromagnetic absorption performance.The effective absorption bandwidth of the ball milled 5 h sample at 3.2 mm is 3.12 GHz,and the minimum reflection loss at7.44 GHz and 3.3 mm is-44.47 d B.（2）On the basis of the research in（1）,phosphate coating with high resistivity was obtained by phosphoric acid passivation of the powder.Due to the large planar anisotropy,the magnetic loss ability of FeSiAl thin films is enhanced,and the high resistivity phosphate（Fe PO₄,Al PO₄ and Fe₃（PO₄）₂）layers can effectively reduce the dielectric constant.In order to obtain good microwave absorption performance,changing the phosphoric acid content optimizes impedance matching,attenuation constant and electromagnetic loss capability.The experiment shows that the minimum reflection loss of the composite is-48.47 d B and the effective bandwidth is 2.56 GHz when only5wt%phosphoric acid is added to the 5h flake FeSiAl powder.（3）On the basis of the research in（2）,select 5wt%phosphate coated samples for 3 h ball milling,and the Ti O₂ coating with different proportions was continued to analyze and study the effect of Ti O₂ coating on the properties of powder samples.Ti O₂ layer is prepared on the surface of flake FeSiAl/phosphate composite through hydrolysis reaction to construct a double-shell structure Ti O₂@phosphate@FeSiAl sheet composite.The synergistic effect of the Ti O₂-phosphate interface and the phosphate-FeSiAl interface results in a wide peak of dielectric loss,microwave absorption ratio and attenuation constant,and an effective absorption bandwidth of 3.2 GHz is obtained,which is wider than that of the original FeSiAl/phosphate composite（2.4 GHz）.