【作者】 刘立东；

【导师】 刘顺华；

【作者基本信息】 大连理工大学 ， 材料加工工程， 2011， 博士

【摘要】 目前FeSiAl合金粉吸收剂的形貌较为单一,并且制备方法有限,本文通过对传统的离心制粉方法进行改进,制备了球形FeSi和纺锤形FeSiAl合金粉。同时,由于电子和通讯设备越来越趋于微型化、高度集成化,设备内部元器件之间的电磁干扰以及对人体的辐射危害越来越突出,为了解决这一问题,本文制备了以铁磁性材料为吸收剂、氯化聚乙烯为基体的吸波贴片。此外,针对单一吸收剂吸波涂层吸收频带窄的缺点,制备了由铁磁性材料和炭黑组成的复合吸收剂的单层环氧树脂基吸波涂层,并且引入Si02粉作为透波剂制备了双层结构的吸波涂层。本文借助SEM、XRD、振动样品磁强计、电磁参数测试设备和吸波性能测试装置等材料检测方法对吸收剂、吸波贴片和涂层进行了测试和分析。结果表明通过对传统离心设备的改进,能够在低转速(<8000r/min)下制备出粒度较小的球形FeSi和纺锤形FeSiAl合金粉吸收剂。粉体在成形的过程中先后经过了液滴的一次破裂、一次球化、二次破裂和二次球化。较高的转速和过热度有利于合金粉的细化,但会降低实验装置的使用寿命。Al元素的加入导致FeSi和FeSiAl合金粉在形貌上有较大的差异。在球形FeSi合金粉中,当Si的含量较低时,合金粉以α-Fe(Si)固溶体为主,电磁特性较好,尤其是磁损耗性能；当Si含量过高时,合金粉中出现化合物Fe1.34Si0.66或FeSi相,电磁性能显著降低。此外,降低FeSi合金粉的粒度有利于提高其电磁吸波性能。纺锤形FeSiAl合金粉具有优良的电磁特性,尤其磁损耗能力突出,其成分须控制在Sendust合金(Fe85Si9.6Al5.4)附近,A1或Si含量过高均会大大降低粉体的电磁特性,纺锤形FeSiAl合金粉与球形相比在电磁特性上更具优势,通过理论分析和实验对比都证明了这一点。羰基铁粉和FeSiAl合金粉作为铁磁性吸收剂均具有优良的电磁特性,尤其磁损耗性能更为优异。分别以这两种材料为吸收剂,所制备的氯化聚乙烯基吸波贴片在2-18GHz和130MHz-1.8GHz两个频段显现出良好的吸波性能,尤其是在厚度较薄的情况下表现出良好的低频吸收效果,具有较强的应用价值。当贴片厚度较薄时,吸收峰随着吸收剂含量的增加向低频区域移动；当厚度较大时,材料阻抗匹配特性被破坏,匹配频率随吸收剂含量的变化不再遵循上述规律。随着贴片厚度的增加,吸收峰向低频段移动。在阻抗匹配特性良好的情况下,贴片的最小反射率随着厚度的增加而减小,吸波性能提高。对于以羰基铁粉为吸收剂的贴片材料,当吸收剂与基体质量比为16：1、厚度为1.5mm时,贴片在2-3.7GHz范围的吸收性能优于-8dB,当厚度为2.0mm时,贴片在650MHz-1.8GHz范围的吸收性能优于-4dB；对于以FeSiAl合金粉为吸收剂的贴片,当吸收剂与基体的质量比为16：1、厚度为1.1mm时,贴片在590MHz-1.8GHz范围的吸收性能均优于-4dB。分别以单一的铁磁性合金粉和炭黑为吸收剂的单层环氧树脂基涂层吸波性能较差,吸收带宽较窄,而由铁磁性合金粉与炭黑组成的复合吸收剂能够大大提高涂层的吸波性能,同时降低涂层的面密度和成本。对于FeSi粉/炭黑复合涂层,当FeSi粉、炭黑与基体的质量比为1.8：0.2：1时,反射率小于-4dB的频宽达到15.1GHz,涂层厚度为1.2mm；而羰基铁粉/炭黑复合涂层在高频段具有较好的吸波特性,当羰基铁粉：炭黑：环氧树脂为0.7：0.6：1、涂层厚度为1.5mm时,涂层在7.9-18GHz频率范围的吸波性能均优于-4dB。分析认为,当两种不同类型的吸收剂复合时除了发挥各自对电磁波的衰减作用外,同时彼此互相间隔,当含量较高时形成电阻较大的复合导电网络,这能够在一定程度上抑制涡流效应的影响。此外,首次将Si02粉作为透波剂引入到吸波涂层中,根据阻抗匹配原理设计了双层结构的吸波涂层,Si02粉的加入改善了涂层的阻抗匹配特性,提高了涂层的吸波性能,尤其是在低频段。更多还原

【Abstract】 Now, for the sigle morphology and limited preparation method of FeSiAl alloy powders, the improved centrifugal atomization method was used in this paper to prepare spherical FeSi and spindly FeSiAl alloy powders. Meanwhile, electromagnetic interference and radiation damage on the human body have become more serious with the rapid development of electronics and communications equipment. To solve the above problem, an absorbing sheet employing ferromagnetic alloy powders as absorbent and chlorinated polyethylene as matrix was prepared. Besides, to broaden the absorption frequency band of the absorbing coatings filled with sigle absorbent, a single-layer coating employing composite absorbents and epoxy resin as matrix was introduced in this paper. We also prepared a double-laye absorbing coating introducing the SiO2 powders as wave-transmitting materials. The absorbent, absorbing patch and coatings were measured by SEM, XRD, vibrating specimen magnetometer, electromagnetic parameters and absorption properties testing device, respectively.The results showed spherical FeSi and spindly FeSiAl alloy powders were prepared at lower rotate-speed (<8000r/min) by the improved centrifugal atomization method. The forming process included the first droplet rupture, the first spheroidizing, the second droplet rupture and the second spheroidizing. The higher rotate-speed and degree of superheat were beneficial to obtain the finer powder, but the working life of equipment was reduced. The difference in morphology between FeSi and FeSiAl alloy powders resulted from the addition of Al element. For the FeSi alloy powders, when the content of Si was lower, the phase structure wasα-Fe(Si), and the alloy powders showed excellent electromagnetic properties, especially permeability; when the content of Si was higher, the phase changed into Fe1.34Si0.66 or FeSi compound, microwave absorption properties decreased dramatically. In addition, the decrease of particle size could improve microwave absorption properties of alloy powders. Spindly FeSiAl alloy powders with the near composition of Sendust alloy (Fe85Si9.6Al5.4) showed excellent electromagnetic properties, especially permeability. The higher Al or Si content would decrease obviously the electromagnetic properties. Spindly shape FeSiAl alloy powders showed more excellent electromagnetic properties than the spherical powders which was confirmed by theoretical analysis and contrast test. Carbonyl-iron powder and FeSiAl alloy powders as ferromagnetic absorbent both exhibited excellent electromagnetic properties especially permeability. The absorbing sheet with the smaller thickness showed good microwave absorption properties in lower frequency range. When the thickness was small, the absorption peaks moved towards the lower frequency range with the increase of absorbent content, but the rule was unsuitable to the thicker samples due to the broken impedance matching characteristics. The absorption peaks shifted to the lower frequency range with the increase of thickness, and the microwave absorption properties could be improved as the increasing thick while the impedance matching characteristics was good. For the sheets employing carbonyl-iron powder, when the ratio of absorbent to matrix was 16:1, the reflection loss of absorbing sheet with 1.5mm thickness was below -8dB in 2-3.7GHz, and the reflection loss was below -4dB in 650MHz-1.8GHz for the samples with 2mm thickness. For the sheets based on FeSiAl powders, the reflection loss was below -4dB in 590MHz-1.8GHz for the samples with 1.1mm thickness and the ratio of absorbent to matrix was 16:1.The microwave absorption properties was bad for the epoxy resin matrix absorbing coating employing single absorbent, such as ferromagnetic alloy powders and carbon black, but the properties could be improved by the application of composite absorbents consisting of ferromagnetic alloy powders/carbon black, and the density and cost of the coating could be reduced. For the FeSi powders/carbon black coating, when the ratio of FeSi powders:carbon black:epoxy resin is 1.8:0.2:1, the absorption bandwidth (reflection loss below -4dB) achieved 15.1 GHz for the samples with 1.2mm thickness. For the carbonyl-iron powder /carbon black coating, when the ratio of carbonyl-iron powder: carbon black: epoxy resin is 0.7:0.6:1, the reflection loss of the samples with 1.5mm thickness was below -4dB in 7.9-18GHz. For the absorbing coatings employing composite absorbents, the different types of absorbent could play their own role respectively in attenuating electromagnetic wave. Moreover, when the content of composite absorbents was higher, the conductive network with larger resistivity was formed in the coating, which was beneficial to suppress the unfavorable eddy-current effect. Besides, according to impedance matching principle, a double-laye absorbing coating with the introduction of the SiO2 powders firstly as wave-transmitting materials was designed. The addition of SiO2 powders improved the impedance matching characteristics of the coating, and the absorption properties increased, especially in low frequency range.更多还原