Effect of particle size on the preparation and microwave absorption properties of FeSiAl magnetically soft alloy hollow microspheres

FeSiAl magnetically soft alloy hollow microspheres(MSAHMs) were prepared by self-reactive quenching technology based on Fe + Si + AI + KNO_3 reactive systems, in order to obtain absorbents with light weight, low frequency and high efficiency. Firstly, twice-balling adhesive precursor method was used to obtain FeSiAl magnetically soft alloy agglomerate powders. Then agglomerate powders with the mesh number of 150-240, 240-325 and 325-400 were sprayed through the flame field into the quenching water. At last, FeSiAl MSAHMs with coarse(average at 86.97 μm), medium(average at 52.16 μm) and fine particles(average at 31.80 μm) were got. Effect of particle size on the phases and microwave absorption properties in low frequency band was studied by XRD and vector network analyzer. The results show that,Fe_3 Si_(0.7)Al_(0.3) and Fe_3 Si_(0.5)Al_(0.5) appear in the phase components of FeSiAl MSAHMs,which is important to improve the microwave absorption properties in low frequency. In addition, the real part(ε′) and imaginary part(ε″) of complex permittivity, the real part(μ′) and imaginary part(μ″) of complex permeability of FeSiAl MSAHMs all present the trend of fine particles > medium particles > coarse particles. The microwave absorption properties in low frequency are improved with the increasing of particle size, and the absorption peak moves to lower frequency range. The properties of fine particles are the best. Their matching thickness of samples is at 5 mm, and the minimum reflectivity is-43 dB at this thickness. The absorption frequency band lower than-10 dB is 4.6-7.6 GHz with a bandwidth of 3 GHz.

Preparation of micro-nano hollow multiphase ceramic microspheres containing MnFe_2O_4 absorbent by self-reactive quenching method

Fe–Fe2O3–MnO2–sucrose–epoxy resin and O2 as reaction system and feed gas,separately,were used to prepare micro-nano hollow multiphase ceramic microspheres containing MnFe2O4absorbent by self-reactive quenching method which is integrated with flame jet,selfpropagating high-temperature synthesis(SHS),and rapidly solidification.The morphologies and phase compositions of hollow microspheres were studied by scanning electron microscope(SEM),transmission electron microscope(TEM),X-ray diffraction(XRD),and energy dispersive spectroscopy.The results show that the quenching products are regular spherical substantially with hollow structure,particle size is between few hundreds nanometers and 5 lm.Phase compositions are diphase of Fe3O4,Mn3O4,and MnFe2O4,and the spinel soft magnetic ferrite MnFe2O4 with microwave magnetic properties is in majority.Collisions with each other,burst as well as‘‘refinement’’of agglomerate powders in flame field may be the main reasons for the formation of micro-nano hollow multiphase ceramic microspheres containing MnFeOabsorbent.

热处理对自反应淬熄法制备低频LiZn铁氧体空心微珠的影响（英文）

目的:自反应淬熄法制备的LiZn铁氧体空心微珠密度小,低频吸波性能良好,但微珠表面晶型生长不充分。对其采用特定热处理工艺不仅可以使晶体充分发育,获得特定晶型,还可以实现对低频吸波性能的有效调控。本文旨在研究热处理工艺对LiZn铁氧体空心微珠表面形貌、相结构和低频吸波性能的影响。创新点:1.通过热处理工艺,实现对LiZn铁氧体空心微珠表面形貌、相结构和低频吸波性能的有效调控;2.深入分析热处理工艺对LiZn铁氧体空心微珠低频吸波性能的改善机理。方法:1.通过工艺探索,确定热处理的详细工艺参数。2.通过扫描电子显微镜检测和X射线衍射分析,获得热处理前后LiZn铁氧体空心微珠的微观形貌(图2)和物相组成(图3)。3.通过矢量网络分析仪,获得热处理前后材料的电磁参数(图4);在此基础上对比其吸波性能(图5),并研究吸波影响机理。结论:1.采用240°C/min升温至1200°C并保温4 h的热处理后,LiZn铁氧体空心微珠表面晶粒明显长大;2.热处理后,微珠四个电磁参数均有所增大,低频吸波性能明显提高,吸收峰值向低频移动;3.表面多种形状微纳米晶粒的形成和长大可能是LiZn铁氧体空心微珠低频吸波性能得以提高的主要原因。

Preparation of hollow ceramic microspheres absorbent based on self-reactive quenching technology

A1 ＋ BaO2 ＋ Fe2O3 ＋ sucrose and O2 as reaction system and feeding gas, respectively, are used to prepare hollow multiphase ceramic microspheres （HMCMs） absorbent based on self-reactive quenching technology. The morphologies, particle size distribution, hollow structure and phase compositions were characterized by scanning electron microscope （SEM）, X-ray diffraction （XRD） and size analysis. The results show that the quenching products possess high sphere-forming rate, and most of them are hollow structures. Owing to the self-burst, the particle size is between 40 and 70 μm. The phase compositions contain Al2O3, Fe3O4, Fe2O3, Ba2Fe14O22, BaO2 and BaFe4O7. The microwave absorbing tests show that the lowest reflectivity of HMCMs is -19 dB. The frequency bands less than -10 dB are from 13.0 to 15.8 GHz. The reasons for HMCMs possessing good microwave absorbing properties may be their magnetic and electrical properties as well as special hollow structure.