锶铁氧体包覆铁纤维的吸波机理及热动力学研究

The microwave absorbing materials is widely applied in military stealthy technology. The absorbing materials should satisfy broadband, high permeability,light density,good resistance to high temperature and stability in acidity or alkaline.polycrystalline iron fiber has low density and high absorptivity in the broadband, but electromagnetic shielding due to low resistivity will reduce electromagnetic wave absorptive properties. Hexagonal ferrite SrFe12O19 has high resistivity and resonant frequency,It has high permeability due to no skin electric current.so,It has better mincrowave absorbing capability.The SrFe12O19 has low permittivity，it is easy to regulate electromagnetic parameters of radar absorbing coatings use the method of compounding. SrFe12O19 has greater specific gravity,narrow absorption frequency,thick coating,low Curie Temperature,poor high temperature Characteristic.The composite of polycrystalline iron fiber and SrFe12O19 will have better electromagnetic properties and high absorptivity based on their complementary properties.The composite microwave absorbing fiber of polycrystalline iron fiber-SrFe12O19 with core-shell structure were prepared by ol-gel method.The influence of preparation condition on the phases, structure, morphology, exchange-coupling interaction between the phases, electromagnetic properties and microwave absorbing property were studied.Probe the formation of the complex fibrous and The absorbing mechanism of microwave.Establish the thermodynamics condition of colloid dispersion gels and co-precipitation.Found the theoretic model of strongly complex of citric acid with metal ion and the kinetics equation of composite fibre aggregation growth.

微波吸收材料广泛用于军事隐身技术，理想的吸波材料要求频带宽、磁导率高，密度小,有良好的耐温性和环境稳定性。多晶铁纤维比重小,在很宽的频带内吸收率高,但电阻率小，容易对电磁波产生屏蔽降低其吸收效果。六角晶锶铁氧体的电阻率和自然共振频率高，高频时不易产生趋肤电流，可保持较高的磁导率，其介电常数较小，容易通过复合调节吸波涂层的电磁参数,但其比重大、吸波频率较窄、涂层厚、居里温度低、高温特性差。依据多晶金属纤维和六角晶锶铁氧体特性互补的特点,将两者以核壳结构的方式复合,可提高材料的电磁性能和微波吸收强度。本项目用溶胶-凝胶法制备纳米六角晶锶铁氧体包覆亚微米级金属铁纤维的核壳结构复合吸波纤维。研究制备条件对其物相、结构、形貌、两相交换耦合、电磁性能及吸波特性的影响,探索复合纤维的形成及其吸波机理。确定成胶共沉淀的热力学条件，建立柠檬酸与金属离子形成强络合的理论模型与复合纤维凝聚生长的动力学方程。

将软硬磁铁氧体进行核壳结构复合，不仅利用了二者在其电磁性能上的互补性，而且可以有效的利用这种特殊的核壳结构和软硬磁相间的界面极化和界面耦合等交互作用，进一步提高了材料对电磁波的吸收。. La0.7Sr0.3MnO3/ MFe2O4 (M为Ni、Co、Zn)核/壳结构纳米颗粒，随着壳材料所占比例的增加，复合材料的饱和磁化强度(MS)由47.9emu/g减小到25.2emu/g，矫顽力(HC)由25Oe增大到161Oe。. 在磁铅石型结构的SrFe12O19表面包覆一层尖晶石结构的ZnFe2O4，当SrFe12O19与ZnFe2O4摩尔比例为1:2，煅烧温度为850℃时，复合粉末具有明显的核-壳结构，颗粒大多呈椭球形或杆状，粒度分布均匀，包覆层致密，具有良好的硬磁特性，最大反射损耗值可达-35.3dB，具有良好的吸波性能。.当热处理温度为950℃，BaFe12O19:Ni0.6Zn0.4Fe2O4=1:2时，复合颗粒的剩余磁化强度（Mr=30.65emu/g）与饱和磁化强度（Ms=64.84emu/g）都达到最大值。饱和磁化强度(MS=55.61emu/g)比钡铁氧体(MS=53.33emu/g)和镍锌铁氧体（MS=54.13emu/g）的都有提高,并且复合纳米颗粒的最大反射损耗高于两单体，但是其吸收频率发生偏移。. 钡铁氧体/聚苯胺复合材料由于钛离子的掺入吸波性能提高了，其中BaFe11.6Ti0.4O19/PANI具有最佳的吸波性能，当涂层厚度为2mm时，它在14.8GHz处的反射损耗达到了-42.9dB；同时，通过改变吸波涂层的厚度，可以使该材料在比较宽的频带对电磁波有效吸收,证明钛掺杂可以作为提高钡铁氧体聚苯胺复合材料吸波性能的一条有效途径。. SiO2包覆羰基铁粉被证明可以有效提升样品的吸波能力并增强样品的抗氧化能力，是一种有效的改性手段。当APTES与TEOS同时使用时，样品的絮状形貌特征随着TEOS用量的增加而更加显著。用APTES：TEOS：无水乙醇=1:3:2400的化学浴溶液制备的样品具有最佳的电磁波吸波效果，此样品的反射吸收率在频率为10.4GHz处达到-38.8dB。