【作者】 高瑞；

【导师】 王成国；

【作者基本信息】 山东大学 ， 材料学， 2014， 硕士

【摘要】 在电子科技日新月异的信息时代,吸波材料在军事隐身与民用防护等方面的应用越来越广泛,而传统的吸波材料渐渐不能满足当今社会的需求,所以制备高性能的新型吸波材料成为了目前的研究热点。本课题依托于山东大学碳纤维工程技术研究中心成熟的碳纤维制备技术,采用聚丙烯腈(PAN)、微米羰基铁粉和纳米铁粉为原材料,从丙烯腈的聚合、成形、预氧化、碳化工艺入手,将微米羰基铁粉和纳米铁粉以物理混合的方式加入聚丙烯腈(PAN)聚合液中,控制预氧化、碳化各工艺参数,制备碳/铁系化合物复合吸波材料,研究不同工艺对复合材料结构及性能的影响；利用气体渗氮法制备铁氮化合物,通过调节氮势制备不同铁氮物相的材料,测其电磁性能；借鉴气体渗氮工艺,将碳化后的碳/纳米铁系化合物复合材料进行渗氮处理,以期得到更为优异的物相组合,从而制备出“薄、轻、宽、强”的高性能吸波材料。将微米羰基铁粉或者聚乙烯吡咯烷酮(PVP)处理后的纳米铁粉以物理混合的方式加入PAN聚合液中,压制成膜制得聚丙烯腈(PAN)/铁粉复合膜,对复合膜进行预氧化、碳化处理制得碳/铁系化合物复合吸波材料。在原膜阶段,加入的铁粉会与聚丙烯腈(PAN)的部分官能团结合,生成络合物,从而影响聚丙烯腈(PAN)的化学结构,但是此过程没有化学反应发生,铁粉还是以单一Fe的物相存在；预氧化后铁粉仍旧不会发生化学反应,直到碳化阶段铁粉会与聚丙烯腈(PAN)裂解释放的小分子物质发生反应,生成铁氮化合物,即在碳化过程中碳和铁系化合物同步生成。微米铁粉和纳米铁粉因其粒径尺寸不同,在相同碳化工艺下,生成的化合物比例会不同。对比掺杂两种不同尺寸铁粉的复合材料的形貌,可以看出,铁系粒子在基体中的分布比较均匀,与基体的结合也比较牢固,但是掺杂纳米铁粉的复合材料,由于纳米材料的小尺寸效应和表面效应,其均匀分散性和与基体结合性都优于掺杂微米羰基铁粉的复合材料。在高纯氮气气氛保护下,对预氧化后的复合材料分别在700℃、750℃和800℃的温度下进行碳化处理,制得碳/铁系化合物复合材料,利用矢量网络分析仪,在2～18GHz的频率范围内测其电磁参数,并模拟计算其反射损耗率,分析吸波性能,可知制得的碳/铁系化合物复合吸波材料是一种兼具介电损耗和磁损耗的吸波材料。对于碳/微米铁系化合物复合吸波材料,随着碳化温度的升高,复合材料的介电性能提高,吸波强度和低频吸波效果也越来越好,800℃碳化处理的复合材料,当匹配厚度为2.0mm时,在11.5GHz附近的吸收峰值为-15.5dB,RL<-10dB的频宽为5GHz。对于碳/纳米铁系化合物复合吸波材料,由于纳米铁粉本身具有较好的介电性能,750℃碳化处理的复合材料的吸波性能最为优异,当匹配厚度为2.0mm时,在10GHz附近的吸收峰值为-13dB,RL<-10dB的频宽为3GHz。分析碳/铁系化合物复合吸波材料的物相组成与吸波性能,得知物相中Fe4N含量较多时,复合材料的吸波性能较好。故我们利用气体渗氮的方法,在520℃下,氨气气氛中,保温5h对微米羰基铁粉进行气体渗氮,通过调节氮势得到了物相组成不同的吸波材料。当氮势为0.8786时,生成Fe4N和Fe物相组成的材料；氮势为2.9540时,生成Fe4N和Fe3N物相组成的材料；在氮势为1.6985时,可生成纯Fe4N物相的材料。在此工艺条件下,微米羰基铁粉只发生了物相的改变,其表面形貌不发生变化。对制备的三种物相组成的铁氮化合物材料进行电磁测试及吸波性能模拟计算得知,对于Fe4N和Fe3N物相组成的材料,其电磁波吸收强度比较大,但是其低频吸波效果较差；而Fe4N和Fe物相组成的材料,其吸波强度相对较弱；纯Fe4N物相组成的材料,具有优异的磁导率实部和虚部,在吸波强度和低频吸波性能方面均具有较好的效果。当其匹配厚度分别为2.0mm和2.5mm时,其在8GHz和6GHz附近的吸收峰值分别为-16dB和-21dB,RL<-10dB的频宽分别为4GHz和3GHz。借鉴铁氮化合物吸波材料的制备与性能研究,将750℃碳化处理后的碳/纳米铁系化合物复合吸波材料进行渗氮处理,可使材料中的Fe4N含量增多,Fe3N和Fe的含量减少,测其吸波性能,当匹配厚度为2mm时,在11GHz附近,其吸收峰值为.-21dB, RL<-10dB的频宽为5GHz。对比未经渗氮处理的复合材料的电磁波反射损耗曲线,可明显看出,渗氮处理后,复合材料的吸波性能无论是从吸收强度还是频宽方面,都有了很大的提高。更多还原

【Abstract】 With the rapid development of electronic science and technology, microwave absorbing material has been widely applied in fields of military stealth and civil protection. However, the traditional absorbing materials can’t keep pace with the needs of society, so the preparation of new absorbing materials with high performance has become a current research hotspot. Based on the mature preparation technology of carbon fiber in our laboratory, carbon/iron compounds composites are prepared using polyacrylonitrile (PAN), carbonyl iron powder and nano-iron powder. At first, carbonyl iron powder or nano-iron powder is added in PAN solution respectively using the method of physical mixture. Then the mixed solution is pressed into thin film. The following process is preoxidation in the air atmosphere and carbonization. As we control the process parameters of the pre-oxidation and carbonization, different carbon/iron compounds composites are obtained. Another part of this paper is the research about electromagnetic property of the iron nitride. The iron nitride is prepared by gas nitriding method. The materials of different phase based on Fe and N are obtained by controlling the concentration of nitrogen, resulting in different electromagnetic property. Finally, in order to obtain high-performance absorbing material with thin thickness, light weight, wide frequency and high absorption property, the carbonized carbon/nano-scale iron compounds are nitrided further in our work.When the original film of composite is prepared, the added iron power will react with the functional group of PAN. The generated complex compound will change the chemical structure of PAN. In this process, chemical changes don’t take place and the iron still keeps the original phase. The preoxidation can’t change the phase of iron as well until the carbonization treatment. In the carbonization process, the iron power can react with these small molecules released by decomposing of PAN to get iron nitride. So amorphous carbon and iron compound are created synchronously. Because of the different size of micron-scale iron powder and nano-scale iron power, the generated compounds will have different proportion under the same carbonization treatment, but the type of products remains the same. In the prepared composites, iron particles could disperse uniformly in the matrix. Compared with micron-scale iron powder, nano-scale iron power disperses more uniformly and combines more easily with matrix because of small-size effect and surface effect.Carbon/iron compounds composites are prepared by carbonizing the composites at700℃,750℃and800℃with pure nitrogen as protective atmosphere. Vector network analyzer is used to measure the electromagnetic parameters of the composites in the frequency range of2-18GHz. Reflection attrition rate is also simulated. The results show that carbon/iron compounds composite is a kind of light absorbing material combining electrical loss with magnetic loss. As for carbon/micron-scale iron compounds composites,dielectric property, absorbing property and absorbing effect of low frequency arise as the rise of carbonization temperature. Effective reflection loss (RL<-10dB) was observed in a frequency range of5.0GHz and the minimum absorption peak around-15.5dB appeared at approximately11.5GHz with the absorber thickness of2.0mm for the composites carbonized at800℃. Because of the dielectric property of nano-scale iron power, carbon/nano-scale iron compounds composites carbonized at750℃show high microwave absorbing property. Effective reflection loss (RL<-10dB) was observed in a frequency range of3.0GHz and the minimum absorption peak around-13dB appeared at approximately10GHz with the absorber thickness of2.0mm for this kind of composites.In this study, it is found that there is a positive correlation between absorbing property of carbon/iron compounds composites and the content of Fe4N.So the carbonyl iron powder is nitrided in ammonia atmosphere at520℃for5h. Different compounds are obtained by controlling the concentration of nitrogen. When the concentration of nitrogen is low, iron nitride composed of Fe4N and Fe are created.on the contrary, iron nitride composed of Fe4N and Fe3N are created. Here we can control the concentration of nitrogen at a specific value to create pure Fe4N.In the nitridation process, we can only change the phase of iron power, but not its surface morphology. We do electromagnetic analysis for the three kinds of iron nitride. Pure Fe4N shows high real and imaginary part of permeability, resulting in good electromagnetic wave absorbing ability and good absorbing effect for low frequency wave. Iron nitride composed of Fe4N and Fe3N shows good electromagnetic wave absorbing ability, but poor absorbing effect for low frequency wave. Iron nitride composed of Fe4N and Fe shows poor electromagnetic wave absorbing ability. Effective reflection loss (RL<-10dB) was observed in a frequency range of4.0GHz or3.0GHz, the minimum absorption peak around-16dB or-21dB appeared at approximately8GHz or6GHz with the absorber thickness of2.0mm or2.5mm for this kind of iron nitride.Based on the process of preparing iron nitride, we design new composites by nitriding carbon/nano-scale iron compounds composite carbonized at750℃. As a result, Fe4N increases, Fe3N and Fe decline. Then microwave absorbing property test shows that the effective reflection loss (RL<-10dB) was observed in a frequency range of5.0GHz and the minimum absorption peak around-21dB appeared at approximately11GHz with the absorber thickness of2.0mm for this kind of new composite. Compared with the composites without the nitriding treatment, nitrided composites show better electromagnetic wave absorbing property both in absorbing ability and bandwidth.更多还原