【作者】 周春华；

【导师】 尹衍升；

【作者基本信息】 山东大学 ， 材料学， 2005， 博士

【摘要】 随着现代科学技术和军事技术的发展,吸波材料(absorbing materials)的研究与应用显得日益的重要。这一发展给吸波材料提出了“薄、轻、宽、强”,耐高温、耐腐蚀和耐候性等方面的要求。显然,传统的吸波材料(e.g:磁性金属粉体、铁氧体等)远远不能满足上述要求。纳米材料作为一种新材料已在航天、电子、化学、生物等领域得到了应用。由于其巨大的比表面积和特殊性能,成为新型的吸波材料,尤其是纳米磁性材料成为现在研究的热点。但是纳米磁性金属粉及其氧化物比重大、易氧化且不适宜低频波段吸收,人们试图以其合金替代。本课题首次选用Fe3Al会属间化合物作为吸收剂进行吸波性能及其机理的研究。Fe3Al金属间化合物具有较高的磁导率和较低的导电性,密度低,而且具有高温抗氧化性、耐腐蚀性等优异性能。这些性能对Fe3Al合金作为微波吸收剂是十分有利的。对于吸波材料,材料的电磁性能对吸波性能的影响是决定性。因此,本文首先制备了纳米Fe3Al合金粉末并对其进行表面处理,研究了Fe3Al粉末的磁性能和电性能,在此基础上,测试了它的电磁参数(ε’、ε"、μ’、μ")和反射率R(dB)～f(GHz)曲线,系统地研究了“Fe3Al+基体环氧树脂”体系在厘米波段(2～18GHz)和毫米波段(26～40GHz)的吸波性能,探讨了纳米Fe3Al吸收剂的吸波机理。为Fe3Al吸收剂的应用打下基础。本论文的主要研究内容如下:首先,采用高能球磨法制备了纳米Fe3Al金属间化合物粉体,并借助XRD、TEM、SEM、DSC、激光粒度分析仪和EDS等测试手段,对球磨过程和低温退火过程的组织结构的演变、Fe3Al粉体的形貌、颗粒尺寸的分布以及纳米粒子的累计百分数进行了表征和测试。研究表明,Fe、Al元素粉末在球磨过程中Al原子逐渐溶于Fe中形成了无序α-Fe过饱和固溶体。球磨过程中晶粒细化和微观应变同时存在,且微观应变随球磨时间增大而增大。分析表明,球磨20h的Fe-28Al粉末在750℃退火过程中,无序α相通过Al原子有序重排和APS畴界移动,转变为有序DO3结构。在相同退火温度下,Fe3Al的形成与球磨时间密切相关。球磨时间越长,球磨过程产生的形变、加工硬化以及晶格畸变越严重,因此将产生更多的畸变能和表面能,原子的扩散速率随之加快,有利于退火过程中Fe3Al的形核和长大,Fe3Al合金结构的有序程度越高。摘要随着球磨时间的延长,粉末颗粒由不规则形状变为球形,平均粒径由微米级下降到纳米级。球磨100h后,体系中纳米粒子累计百分数达80.45%,且大部分颗粒为几十纳米,颗粒尺寸分布呈现正态分布。磁性细颗粒彼此相互吸引聚集而成一种松散的结构。F伪AJ粉体的成功制备为吸波性能的研究奠定了基础。 由于磁性纳米Fe3AI粉末的强烈团聚在聚合物中难以分散,必须对其表面进行处理。采用TG热失重法测定单分子层饱和吸附量作为各种偶联剂的用量。HSt、A一172、铝酸酷和自制的复合偶联剂PHY在超细Fe3AI粉体表面的饱和吸附量分别为1 .24%,1.8%、1.92%和0.05%。IR和SEM分析表明,它们都与超细Fe3川粉体表面发生了化学反应,形成了化学键合。未经表面处理的Fe3AI粉末在聚合物中明显团聚,在单分子层饱和吸附量下超细Fe3川能较好的分散于聚合物基体中,尤其是铝酸酷和PHY偶联作用效果显著。偶联剂对Fe3AI粉末的平均粒径和粒径分布有很大的影响。PHY处理的纳米Fe3川的平均粒径由95Inn下降到79nln,纳米颗粒的含量明显增加;粒径分布变窄,呈现正态分布。说明偶联剂在Fe3AI颗粒表面形成单分子层,可较好地解决超细Fe3AI团聚问题。同时,改善了粉体颗粒与树脂基体的界面粘结性。 利用VSM测试了试样的磁滞回线。用MA法制得Fe3AI合金粉末具有较高的饱和磁化强度和较低的矫顽力,有较好的软磁性能。Fe3AI中灿原子的含量为22%一31 .1%,随着月原子的增加,Fe3AI合金粉体的Ms从1 60.semu.扩降到1 17.oemu.g一,,矫顽力略有升高;当组成和球磨条件相同时,Fe3川合金的有序度随着保温时间的延长而提高,有序度高的Fe3川合金磁性优于较低有序度合金的磁性,D03型的Fe3月磁性远优于BZ型;当组成和退火条件相同时,随着球磨时间的延长(从15h到1 OOh)姚由93 emu.g,增大为161.0 emu.g一’。Fe3AI矫顽力则由600e增至198.ooe,但后期增幅减慢。总之,减小磁性粉体粒子的尺寸,可同时提高Ms和矫顽力Hc,磁滞回线的面积增大,尤其是纳米Fes川的Ms和Hc远大于微米级的样品。 应用价电子理论和原子团簇模型探讨了纳米Fe3AI合金粉末的Ms显著提高的原因。在相同组成和相同退火条件下,由于DO3结构的Fe3甩的Ms远高于BZ结构,球磨时间的延长使得Fe3月的有序化程度提高;纳米粒子的表面未配位的Fe原子增多,Fe原子磁矩增加,形成的原子团簇总磁矩较大;纳米颗粒内部的空泡、杂质量和内应力大大减少有利于磁畴转动和畴壁位移从而使纳米Fe刃的磁性高于微米Fe3AI。矫顽力Hc较大的原因是,通过机械合金化制备的磁粉,矫顽力为钉扎机制,Fe3AI颗粒的晶粒尺寸越小,晶界所占分数越大,因而畴壁位移时所受的钉扎作用也越明显,山东人学博_卜学位论文具有纳米结构的细小晶粒使矫顽力大为增加。较大的Ms和Hc必然导致较高的磁损耗,对吸波材料非常有利。更多还原

【Abstract】 With the development of modern industry and stealth technology, the investigation and application of microwave absorption materials look increasingly important because of reducing radar cross section (RCS) and preventing TV ghosting, and microwave leakage from various electric devices and so on. This means that the microwave absorbing materials should have the characteristics of "thin, light, broad, strong", high temperature resistance, corrosion resistance and the weatherability. So traditional materials (e.g. magnetic metal powders and ferrite) can not satisfied with above demands. Because of the huge surface area and special capability, nanometer materials become new absorbing materials, specially magnetic nanometer absorbers. However, nano-magnetic metals and their oxides have high density and are easily oxided. Then the metal-alloys are very interesting investigation as absorbers. In this paper, Fe3Al intermetallic is used as absorber to study its microwave absorbing characteristics first.Fe3Al intermetallic has high magnetic permeability and definite electric conductivity with low density, high temperature oxidation resistance and excellent corrosion resistance compared with magnetic metal materials. All of these properties make iron aluminum intermetallic ideal candidates for application in microwave absorber. The electro-magnetic property of materials has a crucial effect on its absorbability. Therefore, in this paper at first Fe3Al intermetallic powder is prepared and its surface is modified by coupling agents; Its electric and magnetic properties are studied; The electro-magnetic parameters(ε’、ε"、μ’、μ") of Fe3Al intermetallic powders and R (dB) ~f (GHz) cures are tested, then themicrowave absorbability of "Fe3Al absorber + epoxy resin" coating in both centimeter(2~18Ghz) and millimeter bands (26~40GHz) will been investigated. Finally the absorbing mechanism of nano-Fe3Al powder will be discussed. Above studies provide the firmly theoretical foundation for the practical application of it. The following works have been developed.Nano-Fe3Al powders were prepared by mechanical alloying technology. The structural evolution of Fe-Al elemental during mechanical alloying process under the protection of argon atmosphere and low temperature annealing process, and the Fe3Al particle shape, average particle sizes and the size distribution, and the total amount percent of nano-particle have been investigated by means of XRD、 TEM、 SEM、 DSC、 LSA and EDS. The results show that disordered a-Fe solid solution formed during milling. The reduction of crystal size and the increase of microstrain exist simultaneity, and the microstrain increasedwith the increasing of milling time. The disorder a-Fe solid solution milled for 20h translates to order DO3 structure through Al atom order rearrangement and removing of APS domains during annealing at 750°C for 1h..With increasing of milling time at the same annealing temperature, the deformation, hardening and lattice deformation change more seriously, and then the more rapidly diffusing rates between Fe and Al atom leads to high ordered degree of Fe3Al alloy. After 100h milling time, nonspherical shape of Fe3Al particles becomes spherical-like. The total amount percent of nano-particles reaches 80.45%. Most of them are several ten nanometer particles and average size is 95nm. The particle size distribution shows Gaussian distribution. Ultrafine Fe3Al magnetic particles attract each other to form the aggregates of loose structure in different sizes varying from 400 nm to several micrometer.The kinds and contents of Coupling agents play very important roles on increasing the dispersivity and compatibility between ultrafine Fe3Al powder and polymer matrix. The single molecular layer saturated absorptions of HSt(1.24%,) , A-172( 1.8%) , aluminate (EAX1.92%) and PHY (0.05%)prepared by ourselves on Fe3Al powder surface were determined by TG. By means of IR spectrums and SEM the reaction mechanism is that the chemical reaction between powder surface and coupling agents takes plac更多还原