【作者】 解育娟；

【导师】 凤仪；

【作者基本信息】 合肥工业大学 ， 材料学， 2009， 硕士

【摘要】 吸波材料在军用及民用领域有着广泛的应用,已经成为各国军事装备隐身和民用防电磁辐射等技术领域研究的热点。铁氧体由于具有较好的性能和较低的成本,是广泛应用的吸波材料之一。但是传统的铁氧体材料普遍存在粒径大和比重大的特点,限制了其在某些特殊领域的应用。本研究首先采用溶胶凝胶-甘氨酸盐燃烧法成功制备出纳米钡铁氧体粉末,讨论了不同工艺条件对产物的影响。并在此基础上选择轻质漂珠为基核,采用溶胶凝胶-甘氨酸盐燃烧法在其表面包覆一层钡铁氧体涂层:1.利用甘氨酸作为有机络合剂制备纳米钡铁氧体粉末,为了得到磁性能更好的样品,从甘氨酸配比、金属离子配比、加热过程、乙二醇的作用以及煅烧温度五个方面进行了研究:(1)金属离子最佳配比Fe/Ba的范围为11~12,当配比小于11时,样品中出现中间相BaFe2O4。(2)甘氨酸和金属盐最佳配比为3:1。当有机物用量较少时,金属离子在有机链条上形成局域团聚,导致样品无法形成纯相钡铁氧体;当有机物用量较多时,金属离子在有机链条上过于分散,导致样品只有在高温下才能形成纯相。(3)在制备前驱体的过程中加入乙二醇,可以有效的避免颗粒之间的团聚,减少最终产物颗粒晶粒大小。(4)高温煅烧前先将前驱体在500℃预烧,可以避免了中间相α-Fe2O3的生成,降低钡铁氧体的晶化温度。(5)高矫顽力钡铁氧体的最佳煅烧温度为800℃,此时颗粒尺寸约为50~70nm,钡铁氧体在此温度下的磁性能为Hc=4960.3Oe,Ms=45.45emu/g;当温度升高到900℃时,钡铁氧体颗粒长大到200nm以上,颗粒尺寸的增大使磁畴均匀反转变为不均匀反转,导致样品矫顽力的下降。2.采用凝胶溶胶-甘氨酸燃烧法在漂珠表面包覆钡铁氧体的研究。(1)包覆钡铁氧体的关键是前处理工艺,碱洗和粗化处理可以使得漂珠表面的活性点增加,提高漂珠与溶胶结合能力。(2)采用溶胶凝胶-甘氨酸盐燃烧法可以在漂珠表面包裹一层完整的均匀钡铁氧体层,但涂层厚度较薄。在溶胶中预先加入一部分超细铁氧体粉末,能提高涂层的厚度。钡铁氧体溶胶颗粒主要通过化学吸附的方式在漂珠表面形成涂层,其形核机理为非均匀形核。(3)溶胶凝胶-甘氨酸盐燃烧法制备的漂珠钡铁氧体包覆层的复数介电常数实部和虚部都比钡铁氧体超细粉末的复数介电常数的实部和虚部要小。漂珠/钡铁氧体包覆层的反射率曲线中反射率随频率的变化与钡铁氧体粉末有相似之处,它们最大吸收所处的频率均为12.6GHz。更多还原

【Abstract】 Microwave absorbing materials have been widely in stealth technology and in electro-magnetic compatibility (EMC) technology, and they are researching hotspot in these technology field. In most of absorbers, the ferrite is the main component because of good performance and low cost. But the defects of large crystal size and high density are not benefit for the preparation of light absorber. In response to the need for high performance absorber, in this paper, the composite-coating absorbers with hollow cenosphere as nuclear are prepared by sol-gel glycinate combustion technology.This thesis presents a new technology to synthesize barium ferrite based on sol-gel method by using the glycine as the chelator. 1. The barium ferrites have been successfully synthesized by using the glycine as the chelator. Different factors and treatment were selected to obtain better magnetic properties.(1) The optimal stoichiometry of metal ion (Fe/Ba) is 11-12. Antiferromagnetic BaFe2O4 can be found in the sample with less iron, the coercive force of barium ferrite are enhanced, which can be explained by the pinning effect of BaFe2O4.(2) The optimal ratio of glycine matter (glycine:metal ions) is 3:1. When the quantity of organic material becomes less, the metal ions were too agglomerated in the chain of glycine to form the pure barium ferrite; On the contrary, the metal ions can be dispersed in the chain of organic matter when more organic materials were used in the experimental process, thus pure barium ferrite can only be obtained after higher temperature treatment.(3) The aggregation of the particles can be significantly decreased by adding glycol to the precursor solution. And particles with smaller grain size could be finally obtained.(4) By pre-calcining the precurser at 500℃before high-temperature calcination, the formation ofα-Fe2O3 phase can be avoided, and the crystallization temperature can be lowered.(5) The optimal calcined temperature is 800℃. The resultant magnetic parameters of barium ferrite is Hc=4960.3Oe,Ms=45.45emu/g, and the grain size is about 50~70nm; When the calcined temperature is 900℃, the grain size is above 200nm, and the coercive force decrease.2. Thin films of barium hexaferrite are prepared on fly ash cenpsphere particles by sol-gel glycinate combustion method.(1) Pretreatment process is very important in the preparation of the BaFe12O19-coating hollow glass microspheres. The research showed that coupled microspheres had an enhanced of the combination with gel, resulting in more active points on the surface of micro-spheres.(2) Repetitious coatings or adding some ultrafine BaFe12O19 powder to the precursor solution are the two ways to improve the thickness of film. The saturation magnetization and the remanent magnetization of Barium hexaferrite coated cenospheres are smaller than those of ultrafine BaFe12O19 powder. The sol particles of M-BaFe12O19 are absorbed on cenospheres to form films by chemisorption. The formation mechanism is hetergeneous. Adding ultrafine BaFe12O19 powder into the sol can accelerate nucleation, and then thick films can be prepared.(3) The real part and imaginary part in the complex dielectric permittivity of the BaFe12O19-coated cenospheres is smaller than those of BaFe12O19 ultrafine powder. The microwave absorbance curves of BaFe12O19-coated cenospheres and BaFe12O19 ultrafine powder are similar, which both have the largest value at 12.6GHz.更多还原