【作者】 周廷栋；

【导师】 邓龙江；

【作者基本信息】 电子科技大学 ， 材料物理与化学， 2009， 博士

【摘要】 在微波低频段，金属微粉的吸波能力优于铁氧体。棒状、片状、纤维状等形状各向异性的磁性微粉优于球形状微粉。具有大长径比的扁平状微粉，且厚度小于GHz时的趋肤深度，有利于微波吸收。将此微粉和聚合物混炼，制作成类似于交替叠层柱状结构的抗EMI材料，有极大的研究和使用价值。FeSiAl合金微粉便是使用这种工艺的金属合金微粉。本论文通过配制合金，熔炼试棒，快淬薄带，球磨微粉的工艺，得到扁平状微粉。主要研究了微粉的形貌；合金中的Si、Al含量对微粉的结构、电磁参数、吸波性能的影响；同时采用固体与分子经验电子理论对合金的电子结构进行计算，并分析了合金粉的吸波性能。在形貌特征和晶体结构方面，分析了球磨时间对微粉形貌的影响，以及纳米晶结构的形成。球磨70h前，内应力随球磨时间的延长而增大，但90h后降低，退火后更低。快淬薄带中有D0₃超点阵有序相。球磨后D0₃超点阵相消失但出现新的少量的Al原子。有序度随Si含量增大和退火处理温度的升高而增大。微粉在300℃以上无明显的吸放热峰出现。D0₃超点阵结构可通过合金快淬得到，球磨和退火后都消失。首次运用固体与分子经验电子理论，详细计算了FeSiAl系列合金中的理论键距（?）（n）、（111）和（100）方向上的键共价电子对数n_α（α=A、B）、两种键距偏差ΔD／（?）（n_A）％和玻尔磁子数。计算结果表明：微粉球磨引起晶格常数的变化，从而导致（111）方向上的键共价电子对数改变，最终导致微粉的磁特性的改变。Si含量增大，（111）和（100）的键共价电子对数都增大，Fe的杂化台阶也增大，合金的玻尔磁子数减小。微观固态反应导致Fe原子的原子状态改变。计算结果能对合金粉的电磁特性进行解释。在电磁参数方面，发现微粉球磨70h以前，饱和磁化强度随球磨时间的延长而增大，70h达到最大，但球磨时间延长到90h反而减小。在微波低端，Si含量对电磁参数的影响与Al的含量有关。复数磁导率在70h球磨后有较大的值。热处理后的介电常数减小很大。球磨时间越长，介电常数越大。在吸波方面，计算了微粉的反射率和衰减系数，并进行了优化，探讨了合金的吸波机理。球磨时间延长后，反射率向频率低端移动，但峰值减小。Si含量增大，峰值向高端移动。Al含量增大，向低端移动。微粉300℃退火处理后吸收频带变宽但峰值降低。材料厚度增加，峰值移向低端但吸收频带变窄。退火处理后的复数介电常数的模值减小，但其损耗角正切反而增加，介电损耗增加，磁损耗减小。合金粉为磁性损耗。随Si含量的增加，微粉的损耗趋于电损耗为主。本论文得到的主要结论如下：成分为Fe₇₄Si₁₅Al₁₁合金在70h球磨，在3．5GHz时磁导率虚部可4．2。反射率优化后在厚度为2．6mm时有小于-10dB的吸收峰值。Al含量增大到14at％，可使吸收频段移至4～8GHz，并且吸收峰小于-10dB的带宽可达2GHz左右。以磁损耗为主，衰减系数在4GHz时可达到10．25ω／C。300℃退火处理可使吸收频带展宽。球磨引起晶格常数的变化，从而导致（111）方向上的键共价电子对数改变，最终导致微粉的磁特性的改变。更多还原

【Abstract】 In low frequency band of microwave, the ability to absorb electromagnetic wave ofmetal powders excels that of ferrite. The magnetization of magnetic powders, withanisotropic shape, such as stick, flake and fibre, is better than that of sphericity. Flakypowders, with large aspect ratios’ and thicknesses less than shin depth in the frequencyrange of GHz, are beneficial to absorbing electromagnetic wave. Anti-EMI material,with alternate lays structure, prepared by mixing those powders and polymer, is worthinvestigating and using. FeSiAl powders are made by employing this technology. In thisthesis, flaky powders were prepared through designing composition, melting alloyssticks, quenching ribbons and milling powders. This thesis investigated powders’profiles, the effect of the content of Si and Al on the structures, electromagneticparameters and wave absorption ability. Simultaneously it calculated electron structuresemploying the empirical electron theory of solids and molecules, and analyzed thecapability of absorbing microwave.In the part of profiles and crystalline structures, the effect of milling time onprofiles and the formation of nanocrystalline were analyzed. The internal strainincreased with the time lasting before 70h, but it decreased when the time reached 90h,and it became lower after annealing. DO₃ superlattice ordered structure was found inas-quenched ribbons. After milling, it disappeared and a small quantity of novel Alatoms appeared. Ordering degrees increased with the increase of Si content andannealing temperature. There was no obvious exothermic or endothermic peak above300℃. DO₃ superlattice ordered structure can be obtained by melt-quenching, butdisappeared after ball milling and annealing.Firstly, based on the empirical electron theory of solids and molecules, theory bondlength D （n）, pair number of bond covalent electrons in （111） and （100） planes n_α, bondlength differenceΔD/（?）（n_A）% of two planes and Bohr magnetons were particularlycalculated. The results indicate that the lattice constants changed during milling, andthen the pair number of bond covalent electrons in （111） plane changed, andmagnetization changed finally. With the increase of Si content, the pair number of bond covalent electrons in （111） and （100） planes, and hybridization level of Fe bothincreased, but Bohr magnetons decreased. Atom states of Fe atoms were changedbecause of micro solid state reaction. Results can explain electromagneticcharacteristics of powders.In the part of electromagnetic parameters, it was found that saturationmagnetizations increased with the time prolonged before 70h milling, and reachedmaximum at 70h, but decreased at 90h. In low microwave frequency range, the effect ofSi content on EM parameters was related to Al content. The values of complexpermeability were large after 70h milling. After annealing, complex permittivitydecreased greatly. The longer powders were milled, the lager complex permittivity was.In the part of microwave absorption, reflectivities and attenuation coefficients ofpowders were calculated respectively. Reflectivities were optimized, and microwaveabsorbing mechanism was discussed. After long time milling, reflectivities floatedtowards low frequency band, and the peak values decreased. Peak values ofreflectivities floated towards high frequency band with the increase of Si content. But itwas reverse to Al. The bandwidth of absorption was broadened after annealing at 300℃,but the peak value decreased. Thickness increased, peak value floated towards lowfrequency band but bandwidth decreased. Modules of complex permittivity decreasedafter annealing, but dielectric loss tangents increased. So, dielectric loss increased butmagnetic loss decreased. Alloys powders loss was magnetic. Dielectric loss becameprincipal with the increase of Si content.The following main conclusions can be drawn from this thesis: The composition ofalloy is Fe₇₄Si₁₅Al₁₁and milling time is 70h. Imaginary of complex permeability is 4.2 at3.5GHz. After optimizations, peak value of microwave absorption is below -10dB at2.6mm. When Al content reached 14at%, absorbing band floats to the range from 4 to 8GHz frequency. Bandwidth, whose peak value is below -10dB, can reach 2GHz. Theprimary loss is magnetic, and attenuation coefficient reaches 10.25ω/C at 4GHz.Bandwidth of microwave absorption can be broadened after annealing at 300℃. Latticeconstants changed, and then the pair number of bond covalent electrons in （111） planechanged, and magnetization changed finally.更多还原