【作者】 赵海涛；

【导师】 孙旭东；

【作者基本信息】 东北大学 ， 无机材料工程， 2009， 博士

【摘要】 微波吸收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(?)电磁辐射等技术领域研究的热点。在众多的吸波材料中,铁氧体吸收剂由于具有较好的吸波性能和较低的成本,往往是其中的主要吸波成分。但是铁氧体有一个致命的缺点就是密度太大,不利于制备出质量轻的吸波材料。为解决这一难题,本论文以丙烯酰胺为聚合单体,N,N’-亚甲基双丙烯酰胺为网络剂,采用高分子凝胶法制备了尖晶石型纳米镍铁氧体,并把纳米镍铁氧体与空心微珠、多孔陶瓷、导电聚苯胺和聚苯乙烯等轻质材料复合,通过控制工艺过程能得到具有良好电磁性能、质轻、宽频带、强吸收的新型吸波材料。采用高分子凝胶法制备了纳米镍铁氧体(NiFe204).考察了单体与网络剂的配比、反应温度、反应时间对凝胶形成的影响,优化了工艺条件。结果表明,干凝胶为无定型状态,煅烧至500℃时,形成纯相的尖晶石型纳米NiFe204；煅烧温度为500、600、700、800和900℃时,粉体平均粒径分别约为8、20、45、80和120 nm；红外光谱显示金属-氧离子(M-O)键的特征吸收峰红移了23 cm-1；纳米镍铁氧体在8.2～12.4 GHz的测试频率范围内具有介电损耗与磁损耗,随着热处理温度的升高,纳米镍铁氧体的介电损耗、磁损耗和反射率增加。以空心微珠为基核,用高分子凝胶法在空心微珠表面制备了一层完整的镍铁氧体包覆层。复合粉是由镍铁氧体、石英和莫来石相组成。当空心微珠含量为25 wt%时,在空心微珠表面上可获得完整的镍铁氧体包覆层。与其它样品相比,空心微珠含量为25 wt%的复合材料在X波段具有更高的介电损耗和磁损耗,其介电损耗角正切值tanδε,和磁损耗角正切值tanδm分别可达0.30和0.10。空心微珠含量为25wt%的复合材料的电磁波反射率小于-10 dB的带宽可达2.1 GHz,其最小反射率为-13.7dB。空心玻璃微珠的加入大大降低了复合粉的密度,因此空心微珠表面镍铁氧体包覆层材料有望应用于轻质电磁波吸收领域。采用高分子凝胶法在多孔碳化硅陶瓷表面制备了镍铁氧体包覆层。当煅烧温度为600℃时,在多孔碳化硅陶瓷表面有立方晶系尖晶石结构的镍铁氧体晶相生成。随着包覆层数的增加,多孔陶瓷表面的镍铁氧体涂层的致密性和均匀性逐渐增强,涂层附载量缓慢增加。800℃时制备的涂层牢固度较高。与多孔陶瓷基体相比,包覆镍铁氧体涂层的多孔陶瓷的介电损耗角正切值taδε减小,而磁损耗角正切值tanδm增大,表现出较好的磁损耗特性,tanδm值最大可达0.55。包覆镍铁氧体涂层的多孔陶瓷在X波段的tanδm值随频率的升高呈现减小的趋势。以苯胺为单体、十二烷基苯磺酸为掺杂剂、过硫酸铵为氧化剂,采用超声乳液聚合法制备了导电率较高的聚苯胺。在超声场下采用原位聚合法制备了镍铁氧体/聚苯胺复合材料。聚苯胺与镍铁氧体按照不同质量比进行复合时,当镍铁氧体的含量为15 wt%时,复合材料的电导率具有最大值0.8455 S/cm。与聚苯胺相比,镍铁氧体/聚苯胺复合材料的介电损耗角正切tanδε值与磁损耗角正切tanδm值都增大。镍铁氧体的含量为5wt%和15 wt%的复合材料分别具有最大的tanδε值和最大的tanδm值。镍铁氧体的含量为15 wt%的试样在8～18 GHz范围内综合吸波性能最好,具有最大衰减-23.4 dB,-8 dB带宽为5.73 GHz。采用热压法制备了镍铁氧体/聚苯乙烯和羰基铁/聚苯乙烯复合材料。随着镍铁氧体含量的增加,镍铁氧体/聚苯乙烯复合材料的复数介电常数和复数磁导率增大。随着羰基铁含量的增加,羰基铁/聚苯乙烯复合材料复数介电常数和复数磁导率增大。145 MPa压力下制备的羰基铁/聚苯乙烯复合材料具有较好的微波吸收性能。通过采用镍铁氧体/聚苯乙烯与羰基铁/聚苯乙烯双层复合的结构形式达到阻抗匹配、展宽频带和提高吸收峰值的效果,从而改善单一一种吸波材料在雷达波段的吸波性能。更多还原

【Abstract】 Microwave absorbing materials have been widely used in military and civilian applications. They are the hotspot in the field of stealth technology and electromagnetic compatibility technology. In most of the absorbers, ferrite is one of the main components because of its good performance and low cost. Its main disadvantage is high density which limits its application in light absorbers. In response to the requirement for high performance absorbers, the spinel type nanocrystalline nickel ferrite was prepared by the polyacrylamide gel method with acrylamide as the monomer and N,N’-methylenediacrylamide as the lattice agent. Then the composites of nanocrystalline nickel ferrite with hollow microspheres, porous ceramics, polyaniline and polystyrene were fabricated. These new microwave absorbing materials are light weight and have good electromagnetic, wide band and high absorbing properties.Nanocrystalline NiFe2O4 ferrite was prepared using the polyacrylamide gel method. The effects of ratio of acrylamide/N,N’-methylenediacrylamide, reaction temperature and reaction time on characteristics of the polycrylamide-gel were studied. XRD results show that the dry gel is amorphous, and after calcining at 500℃or a higher temperature, it transforms into spinel nickel ferrite. TEM observation shows that particle sizes of the spinel nickel ferrite obtained by calcination at 500℃,600℃,700℃,800℃and 900℃, are 8 nm,20 nm,45 nm,80 nm and 120 nm, respectively. FT-IR analysis illustrates that the characteristic absorption peak of the M-O shifts from 590 cm-1 to 613 cm-1. The nanocrystallne spinel nickel ferrite has both dielectric loss and magnetic loss in the range of 8.2-12.4 GHz, and its dielectric loss, magnetic loss and reflection loss increase with increasing heat treatment temperature.Hollow glass microspheres were coated with nickel ferrite using the polyacrylamide gel method. The obtained composite powder is composed of nickel ferrite, quartz and mullite. A continuous NiFe2O4 coating was obtained at a microsphere content of 25 wt%. The composite with 25 wt% microspheres exhibits better dielectric loss and magnetic loss properties in the X band. Its dielectric loss tangent and magnetic loss tangent are 0.30 and 0.10, respectively. The composite shows a minimum reflection loss of-13.7 dB with a bandwidth of-10 dB over the extended frequency range of 2.1 GHz. It is also low in density, implying its potential application as a good and light electromagnetic wave absorbing material.SiC porous ceramics were coated with nickel ferrite using the polyacrylamide gel method. Spinel structured NiFe2O4 forms on the porous ceramics at 600℃. With the increase of coating layers, the coating becomes more uniform and homogenous, and the loading of nickel ferrite coatings increases slowly. The nickel ferrite coating prepared at 800℃adheres well to the surface of SiC. The porous ceramics coated with nickel ferrite exhibit lower dielectric loss and higher magnetic loss compared with the porous ceramics matrix. Its maximum tanδm is 0.55, indicating a better magnetic loss property. The tanδm of the porous ceramics coated with nickel ferrite decreases with increasing frequency in the X band.Polyaniline with good electric conductivity was prepared by an ultrasoonic and emulsion polymerization process using aniline as monomer, dodecylbenzene sulfonic acid as dopant and ammonium peroxydisulfate as oxidant. The nickel ferrite/ polyaniline composites were prepared by the in situ polymerization method under ultrasonic field. The composite with a content of 15 wt% nickel ferrite has a maximum conductivity of 0.8455 S/cm. Dielectric loss tangent and magnetic loss tangent of the nickel ferrite/ polyaniline composites are higher than those of the polyaniline. The composites with a ferrite content of 5 wt% and 15 wt% have the maximum tanδεvalue and tanδm value, respectively. The composite with 15 wt% ferrite content shows better electromagnetic wave absorbing property, with a minimum reflection loss of-23.4 dB and a bandwidth of-8 dB over the extended frequency range of 5.73 GHz.A nickel ferrite/polystyrene composite and a carbonyl-iron/polystyrene composite were made by hot pressing. The complex permittivity values and complex permeability values of the nickel ferrite/polystyrene composite show an increasing trend with the increase of nickel ferrite content. The complex permittivity values and complex permeability values of the carbonyl-iron/polystyrene composite show an increasing trend with the increase of the carbonyl-iron. The material pressed at 145 MPa has the minimum reflection loss and the best microwave absorption. The double layer structure composed of the nickel ferrite/polystyrene and the carbonyl- iron/polystyrene has an effect impedance coupling, widening the band and improving minimum reflection loss, so that the electromagnetic wave absorbing properties can be improved compared to those of the single materials.更多还原