Studies On The Preparation And Properties Of Fe₃S₄ And Its Wave Absorption Composites

The rapid development of electronic technology has brought many conveniences to modern life,but at the same time it has also brought huge challenges to human beings.In the civil field,electromagnetic wave pollution has intensified,causing great harm to human body.In the military field,the continuous advancement of radar detection technology has put forward higher ground performance requirements for the electromagnetic wave absorbing materials of radar stealth technology.In response to the above problems,composite electromagnetic wave absorbing materials with the characteristics of"thin thickness,light weight,wide absorption frequency band,and strong absorption capacity"have become the research focus of scholars.Pyrite-type Fe₃S₄ has the advantages of environmental protection,low cost,convenient synthesis,etc.,and at the same time has semi-metallic and ferromagnetic properties.Theoretically,it can attenuate electromagnetic waves through the mechanism of both dielectric loss and magnetic loss.In this subject,Fe₃S₄ is used as the matrix,compounded with conductive polymers and carbon materials to avoid the performance shortcomings of single component and exert the synergistic effect of each component,and improve the electromagnetic wave absorption capacity.The specific research contents are as follows:（1）First,using C₃H₇NO₂S as the sulfur source and FeSO₄·7H₂O as the iron source,Fe₃S₄micron particles were synthesized by hydrothermal method,and the effects of reaction time,reaction temperature and molar ratio of raw materials on the crystallinity and purity of Fe₃S₄were investigated.The micro morphology and ferromagnetic properties of Fe₃S₄ were analyzed by SEM and VSM.The electromagnetic parameters of Fe₃S₄ were tested with a vector network analyzer,and the reflection loss（RL）value was calculated.The test results show that the filling ratio of Fe₃S₄ in the paraffin matrix has an important effect on the electromagnetic parameters and RL value.When the filling ratio is 80wt%,Fe₃S₄ shows a certain electromagnetic wave absorption performance.in the low frequency range（2-8.5 GHz）,electromagnetic wave attenuation mainly depends on magnetic loss,while in the higher frequency range（8.5-18 GHz）,it mainly relies on dielectric loss.The optimal RL value of Fe₃S₄is-55.0 d B when the matching thickness is 1.2 mm,and the effective absorption bandwidth（EAB）is 2.0 GHz when the matching thickness is 1.3 mm.（2）On the basis of the Fe₃S₄ micron particles prepared by the hydrothermal method,the Fe₃S₄@polypyrrole（Fe₃S₄@PPY）composites were synthesized by the in-situ Chemical oxidation polymerization method.The influence of the types and dosage of initiators and dopants on the conductivity of the composites was investigated.The composition and micro morphology of the composites were analyzed by XRD,FT-IR,and SEM,and the influence of the charging ratio on the microwave absorption performance was explored.The test results show that the filling ratio of Fe₃S₄@PPY composite decreases to 25wt%and the maximum EAB increases to 5.84 GHz,reflecting the advantages of light weight and broadband.（3）Using HCl as dopant and K₂S₂O₈ as initiator,aniline monomer was oxidized and polymerized in situ on the surface of Fe₃S₄ micron particles to prepare Fe₃S₄@polyaniline（Fe₃S₄@PANI）composite.By changing the addition ratio of Fe₃S₄ and aniline monomer,the electrical conductivity and electromagnetic parameters were studied.The results showed that the electrical conductivity and complex permittivity of the composites increase with the increase of the relative content of aniline monomer.When the filling ratio is 40wt%,the sample F@A-2 shows the best electromagnetic wave absorption performance,with the minimum RL value reaching-63.8 d B and the maximum EAB up to 5.04 GHz.And when the matching thickness is in the range of 2.0-5.5 mm,the minimum RL values of sample F@A-2 are all less than-20 d B.The excellent performance is due to the synergy of good impedance matching and excellent attenuation ability.（4）Reduced graphene oxide（RGO）has the advantages of large specific surface area,high dielectric properties and low density,and is often used in the field of electromagnetic wave absorption.In this paper,Fe₃S₄/RGO composites with Fe₃S₄ particles modified with two-dimensional RGO were prepared by the improved Hummers method combined with a solvothermal method.The Fe₃S₄/RGO composites make up for the large quality of Fe₃S₄ and avoid the shortcomings of poor impedance matching of RGO.Meanwhile,The Fe₃S₄/RGO composites exert the synergistic effect of the two components,which significantly improves the electromagnetic wave absorption capacity.At a filling ratio of 30wt%,the maximum EAB of sample F-R-3 reaches 4.08 GHz at a matching thickness of 1.37 mm,and the minimum RL reaches-62.3 d B when the matching thickness is 1.29 mm.