【作者】 张鑫；

【导师】 顾家琳；

【作者基本信息】 清华大学 ， 材料科学与工程， 2009， 硕士

【摘要】 铁氧体是常用的磁损耗吸波剂,但用其制成的吸波材料密度比较大。碳管比较轻,但只具有电损耗,吸波频段比较高,吸波频带比较窄。因此本论文拟利用溶胶-凝胶法和共沉淀法制备纳米铁氧体与碳管复合吸波剂,以获得同时具有磁损耗和电损耗的新型吸波材料。首先利用溶胶-凝胶法制备了纳米晶的尖晶石型铁氧体Ni_0.5Zn_0.5-xCo_xFe₂O₄颗粒,发现提高热处理温度、延长热处理时间可以改善尖晶石型铁氧体的静磁性能。当Co²⁺含量x为0.05,800℃热处理8h,颗粒粒径在100nm左右时材料具有比较好的静磁性能,并且吸波频段在2⁶GHz之间。同时发现,磁场下热处理可以改善Ni_0.5Zn_0.45Co_0.05Fe₂O₄的静磁性能。利用溶胶-凝胶法制备了尖晶石型铁氧体Ni_0.5Zn_0.45Co_0.05Fe₂O₄/铁填充碳管复合吸波剂,随着复合吸波剂中铁填充碳管添加量的提高,吸收峰向高频移动。当铁填充碳管的添加量为3wt%时,复合粉末的工作频段主要在较低频2⁶GHz之间,吸收峰峰值达到5dB。复合粉末在石蜡中添加量的增加提高了材料的吸波性能,添加量为70wt%时,吸收峰峰值在6GHz处,达到8dB,在4.2⁷.3GHz之间大于5dB。利用共沉淀法制备了尖晶石型铁氧体Ni_0.5Zn_0.45Co_0.05Fe₂O₄/碳管复合吸波剂,但铁氧体颗粒和碳纳米管团聚严重,并有杂质相α-Fe₂O₃产生,造成复合吸波剂的电磁参数比较低,吸波性能比较差。利用溶胶-凝胶法制备了在微波高频段具有较好吸波性能的Y型六角铁氧体BaCo_0.6Zn_1.4Fe₁₂O₂₂,然后采用机械复合工艺,将Ba铁氧体与铁钴填充碳管混合制备复合吸波剂,与环氧树脂混合后制成反射率测量板,但测量板的吸波性能比较差,推测原因是Ba铁氧体在树脂基体中没有均匀分散。更多还原

【Abstract】 Ferrite,which is a kind of magnetic loss materials,is widely used in the microwave absorption field, but its density is high. In contrast, the density of carbon nanotubes（CNTs） is low and it has excellent dielectric loss, which results in its microwave absorption at high frequency range and with narrow bandwidth. Therefore, in this thesis carbon nanotubes and nano-power ferrite will be combined effectively in order to produce a kind of absorber possessing both dielectric and magnetic loss.Firstly, nano-power spinel ferrite Ni_0.5Zn_0.5-xCo_xFe₂O₄ was prepared by using sol-gel method. It is found that with the increasing of heat treatment temperature and time, the static magnetic properties are improved. When x=0.05 and heat treated at 800℃for 8h, the spinel ferrite Ni_0.5Zn_0.5-xCo_xFe₂O₄ power size is about 100nm and the nano-power possesses high static magnetism properties, and the microwave absorption peak keeps in low frequency from 2GHz to 6GHz. The effect of magnetic heat treatment on static magnetism properties was also studied. The magnetic heated treatment for Ni_0.5Zn_0.45Co_0.05Fe₂O₄ ferrite could improve its static magnetism properties.Using the sol-gel method, the composite, the Fe-filled CNTs coated with nano-power spinel ferrite Ni_0.5Zn_0.5-xCo_xFe₂O₄, were prepared. When the addition of Fe-filled CNTs increases, the microwave absorption ability of Ni_0.5Zn_0.5-xCo_xFe₂O₄/Fe-filled CNTs is improved and the microwave absorption peak moves to higher frequency. When the content of Fe-filled CNTs is 3wt%, the absorption range keeps in low frequency from 2GHz to 6GHz, and the maximum reflection loss（RL） reaches 5dB. As the addition of Ni_0.5Zn_0.5-xCo_xFe₂O₄/Fe-filled CNTs to wax matrix increases, the microwave absorption ability is also improved. The sample with 70wt% nano-composite powers reaches a maximum reflection loss of 8dB at about 6GHz, and the frequency bandwidth for RL>5dB reaches 2.8GHz,from 4.2GHz to 7.3GHz. The composite, CNTs coated with nano-power spinel ferrite Ni_0.5Zn_0.5-xCo_xFe₂O₄, was also prepared by using coprecipitation method. The nano-power spinel ferrite Ni_0.5Zn_0.5-xCo_xFe₂O₄ and CNTs are easily to form agglomerates, which results in low electromagnetic parameters and microwave absorption ability.Nano-power Y-BaCo_0.6Zn_1.4Fe₁₂O₂₂ was prepared by using gel-sol method in order to expand the working bandwidth. To prepare microwave absorption composite, the mechanically mixed Y-Ba-ferrite and Fe-filled CNTs were added to the epoxy resin. However, it is found the Y-Ba-ferrite is not dispersed homogeneously in the epoxy resin matrix, which may be the main reason resulting in the low microwave absorption ability.更多还原