KNO3对FeSiAl软磁合金空心微珠制备及低频吸波性能的影响

Effect of KNO3 on the preparation and microwave absorption properties in low frequency of FeSiAl magnetically soft alloy hollow microspheres

摘要:

为了获得轻质、低频、高效吸波剂，本文采用自反应淬熄法，分别以Fe+Si+Al、Fe+Si+Al+KNO3为反应体系制备了FeSiAl软磁合金空心微珠，通过SEM、XRD、矢网分析仪等手段研究了KNO3对其密度、形貌、相组成和低频吸波性能的影响。结果表明，未加KNO3时，反应难以进行，淬熄产物由球形颗粒、类球形颗粒、不规则颗粒和片状颗粒组成，物相主要为Fe、Si、Al及部分Fe0.9Si0.1，未生成FeSiAl合金，基本无吸波性能；添加KNO3后，反应体系的淬熄产物主要为空心微珠，粒径分布均匀，物相由Fe3Si0.5Al0.5、Fe3Si0.7Al0.3、Fe0.9Si0.1和Fe组成，获得了FeSiAl合金，在5 mm厚度条件下，吸波试样最低反射率达-22.1 dB，吸收峰值对应频率为7.0 GHz，低于-10 dB的有效吸收频带为5.3-8.5 GHz，带宽达3.2 GHz。KNO3分解反应所产生的高放热量和大量气体是促使反应温度升高、反应产物熔融、目标产物形成、成球率和空心率提高及低频吸波性能显著改善的根本原因。和机械合金化法制备的片状FeSiAl软磁合金相比，自反应淬熄法制备的FeSiAl空心微珠的低频吸波频带有效拓宽，同时材料的密度降低了38 %，有效实现了新型低频吸波料“薄、宽、轻、强”的特点。

Abstract:

FeSiAl magnetically soft alloy hollow microspheres were prepared by self-reactive quenching technology based on Fe+Si+Al and Fe+Si+Al+KNO3 reactive systems, respectively, in order to obtain absorbents with light weight, low frequency and high efficiency. Effect of reaction heat-releasing on their density, morphology, phase and microwave absorption properties in low frequency band was studied by SEM, XRD and vector network analyzer. The results show that, chemical reactions can not happen without KNO3. In addition, the quenching products consist of spherical particles, near-spherical particles, irregular particles and lamellar particles. The phase components are Fe, Si, Al and Fe0.9Si0.1. FeSiAl alloys are not formed and their microwave absorption properties do not exist basically. After adding KNO3, the quenching products mainly consist of hollow microspheres with uniform particle size distribution. The phases are made up of Fe3Si0.5Al0.5, Fe3Si0.7Al0.3, Fe0.9Si0.1 and Fe. FeSiAl alloys are obtained. The minimum reflectivity of the absorbent sample at 5 mm is -22.1 dB, and the corresponding frequency is 7.0 GHz. The effective absorption frequency band lower than -10 dB is 5.3-8.5 GHz, with the bandwidth of 3.2 GHz. The high heat-releasing and large amount of gas from the decomposition of KNO3 makes the reaction temperature be higher. In addition, the target products are obtained and then melt. Moreover, the spherical rate and hollow rate are both improved. These are the reasons for obvious improvement of microwave absorption properties in low frequency. Compared with flake FeSiAl magnetically soft alloy prepared by mechanical alloying method, FeSiAl hollow microspheres prepared by self-reactive quenching technology have a broader absorption frequency band in low frequency. In addition, the density of the material has decreased by 38 %. So the characteristics of new absorbents in low frequency including “thin, broad, light and strong”are effectively realized.