热处理升温速率对钡铁氧体空心微珠形貌与吸波性能的影响

Morphology and Microwave Absorption Properties of Barium Ferrite Hollow Microspheres with Heat-Treatment of Different Heating Rates

采用将火焰热喷涂技术、自蔓延高温合成技术及快速冷却凝固技术结合在一起的自反应淬熄法,制备了以尖晶石型钡铁氧体为主的空心微珠,然后分别以3,7和15℃·min-13种升温速率将其加热到1100℃、保温4 h后再冷却至室温,通过扫描电镜(SEM),X射线衍射(XRD)和矢量网络分析仪等手段,研究了3种升温速率下空心微珠形貌和吸波性能的变化。结果表明:未热处理时,空心微珠主要由Al2O3,Fe2O3,Fe3O4,BaFe2O4组成,表面无明显晶粒出现,最低反射率为-2 dB;3℃·min-1慢速升温条件下,空心微珠物相主要由Fe2O3,BaFe12O19,BaAl12O19和Al2O3组成,表面出现了典型的六角晶型,反射率有3个极值,最低反射率为-16.5 dB,低于-10 dB的吸收带宽为2.2GHz;7℃·min-1中速升温条件下,物相组成为Fe2O3,BaFe12O19,BaAl12O19,Al2O3和Fe3O4,微珠表面以片状晶为主,最低反射率为-6.5dB;15℃·min-1快速升温条件下,由于晶体生长和受扩散控制的固相反应不充分,物相组成中出现了Ba0.83Fe11O17.33和BaFe13.2O20.8中间相,空心微珠表面主要为等轴晶,最低反射率为-3.9 dB。慢速升温时钡铁氧体空心微珠吸波性能优于中速和快速升温条件。

Hollow ceramic microspheres containing barium ferrites with spinel structure were synthesized by self-reactive quenching technol- ogy based on flame hot spraying technology, self-propagating high-temperature synthesis （SHS） technology and rapid solidification technolo- gy. The samples were calcined to 1100 ℃ with different heating rates of 3, 7 and 15 ℃.min-1, and were kept at 1100℃ for 4 h, and then cooled to room temperature. Effects of there heating rates on the morphology and microwave absorption properties were tested by scanning e- lectron microscopy （SEM）, X-ray diffraction （XRD） and vector network analyzer. The results showed that, when hollow microsphers were not heated, the phases were mainly made up of Al2O3, Fe2O3, Fe3O4 and BaFe2O4. There was no obvious crystal on the surface, and the minimum value of reflection loss was -2 dB. When heated with 3 ℃.min -J slow heating rate, the phase components of hollow microspheres were Fe2O3, BaFe12O19, Ba^12019, A12O3, and the surface took on classical hexagonal crystals. The reflection loss had three extremas, with the minimum value of - 16. 5 dB, and the frequency bandwidth for lower than - l0 dB was 2.2 GHz. When heated with 7 ℃-min -j medium heating rate, the phase components were Fe2O3 , BaFe12O19, BaAl12O19, Al2O3 and Fe3O4. The surfaces were mainly made up of plate crys- tals, and the minimum value of reflection loss was -6.5 dB. When heated with 15 ℃.min-1 fast heating rate, intermediate phases of Ba0.83 Fe11 O17.33 and BaFe13.2O20.8 were obtained, because the crystal growth was insufficient and solid phase reaction controlled by diffusion was in- sufficient, too. The crystals on the surface of hollow microspheres were mostly isometric crystals, and the mimimum value of reflection loss was -3.9 dB. The microwave absorption properties with slow heating rate were better than those with medium and fast heating rates.