【作者】 龚春红；

【导师】 张治军；

【作者基本信息】 河南大学 ， 高分子化学与物理， 2008， 博士

【摘要】 作为一种重要的多功能磁性金属材料,具有特种形貌的超细镍晶材料在多个领域具有广阔的应用前景,其在电磁屏蔽和吸波研究领域的重要性更是不言而喻。正因为如此,条件温和、操作简单、成本低廉、环境友好且易于实现形貌和结构调控的超细镍晶材料制备方法具有重要的理论和应用价值。为此,本论文开展了以下几个方面的研究工作:(1)以蒸馏水为溶剂,利用快捷、温和的液相还原法制备了较大量的超细镍粉,将得到的超细镍粉作为填料制备了复合材料,考察了复合材料的电磁屏蔽和吸波性能。结果表明,所制备的超细镍粉在电磁屏蔽和吸波领域具有很好的应用前景。超细镍粉含量为33.3wt%的树脂基复合材料在130 MHz～1.5 GHz测试频段内的电磁屏蔽性能均高于22 dB;而厚度为2 mm的超细镍粉/石蜡复合材料在7GHz附近的反射率绝对值高达27 dB。与此同时,在具体应用中,作为填料的超细镍粉在复合材料中的分散状态对电磁屏蔽性能具有至关重要的作用。(2)在上述工作基础上,研究了搅拌条件下外加磁场对超细镍粉形貌和磁性能的影响;并将在蒸馏水体系中得到的超细镍粉作为填料制备复合材料,评价了复合材料的电磁屏蔽性能和吸波性能。结果表明,同无外加磁场条件下得到的超细镍粉复合材料相比,在外加磁场条件下得到的超细镍粉复合材料的电磁屏蔽性能较优,而吸波性能变差。(3)利用金属镍的塑性性质,利用湿法研磨法由微米镍粉得到了片状镍粉,研究了相关研磨参数对片状镍粉形貌和微结构的影响。将得到的片状镍粉作为填料用于制备复合材料,测定了复合材料的电磁参数,并评价了其电磁屏蔽性能。结果表明,片状镍粉复合材料的电磁屏蔽性能不如微米镍粉复合材料,而其吸波性能优于微米镍粉复合材料;厚度为5 mm的片状镍粉/石蜡复合材料的最小反射率小于-27 dB。(4)在常压下,采用水合肼还原镍盐的方法成功地制备了长度约为5μm,直径约为250 nm的超细镍链状结构;利用透射电子显微镜(TEM)首次观察了超细镍链状结构的反应过程,并进而分析了一维链状结构在自生磁场诱导作用下的形成机理。所建立的制备方法可望拓展用于其它种类的磁性纳米金属材料的形貌可控制备,具有较为广阔的应用前景。(5)在常压下,利用磁场诱导作用,在不同的磁场强度条件下制备了长度从几个微米到几百微米,直径约250 nm的超细镍纳米晶纤维。系统研究了反应条件对产物形貌及磁性能的影响,分别测定了超细镍纳米晶纤维复合材料的电磁参数和电磁屏蔽性能。结果表明,所制备的超细镍纳米晶纤维是一种很有潜力的电磁屏蔽导电填料。更多还原

【Abstract】 As a kind of important multi-functional magnetic metallic materials,ultrafine nickel nanocrystallites with special morphologies have huge potentials in many fields.In particular,they are of extraordinary significance in the theoretical and experimental investigations of electromagnetic shielding and electromagnetic wave absorption. Needless to say,the study of the controllable synthesis of ultrafine nickel nanocrystallites with special morphologies and the establishment of simple,facile, cost-effective,and environment-friendly synthetic routes are of significant theoretical and practical values.Therefore,the following researches have been conducted and the main conclusions are drawn as below:(1)Ultrafine Ni particles were synthesized via a facile and mild chemical route in distilled water.The resulting ultrafine Ni particles were used as a kind of conductive fillers to fabricate conductive composites.The shielding of electromagnetic interference (EMI)and electromagnetic wave absorption behaviors of the composites were evaluated. The results indicated that the ultrafine Ni particles might be potential fillers for shielding of electromagnetic interference and electromagnetic wave absorption as well. The resin-based conductive composite containing 33.3wt%of the ultrafine Ni particles recorded a shielding effectiveness(SE)value as much as above 22 dB within a frequency range of 130 MHz to 1.5 GHz,while the ultrafine Ni particles/wax composite with a thickness of 2 mm had a reflection loss R(dB)of 27 dB at about 7 GHz. Moreover,the distribution state of the ultrafine Ni particles in the composites was found to play a key role in determining the properties in terms of the practical application of the ultrafine nickel particles as fillers for shielding of electromagnetic waves.(2)Based on the above-mentioned work,the effect of an external magnetic field on the morphologies and magnetic properties of the targeted ultrafine Ni particles was investigated under stirring condition.At the same time,the electromagnetic shielding effectiveness and the electromagnetic characteristics of the composites filled with ultrafine nickel particles obtained from distilled water were measured.The results showed that the composites filled with nickel particles obtained in the presence of an external magnetic field showed better EMI shielding effectiveness than the composites filled with nickel particles obtained in the absence of an external magnetic field,while the former had poorer electromagnetic wave absorption effectiveness than the letter.(3)Flake-like Ni powders were fabricated by wet sand-milling of micro-sized nickel powders and the effect of related milling factors on the morphology and microstructure of the Ni powders was studied.The resulting flake Ni powders were used as a kind of conductive fillers to fabricate conductive composites.It was found that the composites filled with flake-like Ni powders had a lower EMI shielding effectiveness than the composites filled with micro-sized nickel powders.Moreover,the composites filled with flake-like Ni powders had better electromagnetic wave absorption effectiveness than the composites filled with micro-sized nickel powders, and the flake-like Ni powders/wax composites with a thickness of 5 mm registered a reflection loss R(dB)of-27 dB at about 2 GHz.(4)Ultrafine chain-like Ni assemblies with a length of about 5μm and an average diameter of about 250 nm were successfully prepared by the reduction of Ni salts with hydrazine hydrate under normal pressure.Moreover,the growth process of the Ni chains was investigated for the first time.Based on the experimental results,the self-assembly mechanisms of the Ni nanocrystallites induced by self-generated magnetic field were investigated for the first time,which could be used as a new general method for the preparation of other magnetic metal nanostructures with a controllable morphologies,so as to fully exploit their peculiar properties and unique applications.(5)Under normal pressure,untrafine nanocrystallite Ni fibers with lengths from several microns up to several hundreds of microns and an average diameter of about 250 nm were fabricated in the presence of external magnetic fields with different intensities. The effects of the reaction conditions on the microstructures and magnetic properties of the Ni fibers target products were systematically investigated.Moreover,the electromagnetic shielding effectiveness and electromagnetic characteristics of the Ni fiber reinforced composites were measured.The results showed that the Ni fibers might be potential conductive fillers for shielding of electromagnetic interference(EMI).更多还原