二氧化硅/片状金属磁粉壳核粒子制备及电磁特性

以正硅酸乙酯为前驱体, 采用溶胶-凝胶工艺对厚度1 μ m、 直径5 μ m左右的片状金属磁性微粉进行表面改性, 获得SiO₂ /金属壳-核结构复合粒子。用SEM、 TEM、 RA-IR等方法对磁粉表面SiO₂纳米粒子膜的形貌、 结构进行表征, 并对改性前后磁粉/石蜡复合材料的复磁导率和复介电常数等微波电磁参数进行测试。结果表明: SiO₂纳米粒子吸附在磁粉表面, 形成高电阻率的包覆膜; 将该微粉按质量比(5 ∶ 1)与石蜡复合, 在2~18GHz频率范围内测量介电常数, 与未改性样品比较, 其介电常数实部平均下降约20, 虚部平均下降约7, 而对应的复磁导率变化较小。用金属磁粉制备1mm厚的吸波涂层, 涂层在8dB的吸收带宽由改性前的3.2GHz (7.0~10.2GHz)增加到改性后的7GHz (7.6~14.6GHz), 改善了吸收剂的吸波性能。      

粉末挤出成型法制备FeCuNbSiB纳米晶磁粉芯

采用粉末挤出成型法制备了FeCuNbSiB纳米晶磁粉芯,并讨论了纳米晶粉体粒度对磁粉芯磁性能的影响。结果表明,粘结剂配方为硬脂酸1%、聚丙烯40%、石蜡59%采用粉末挤出成型法可以制备粉体与粘结剂比例为5∶1的FeCuNbSiB纳米晶磁粉芯;粉级搭配可提高磁粉芯密度,300、200与100目质量比为6∶3∶2的磁粉芯密度相对于300目FeCuNbSiB纳米晶磁粉芯提高了5%,达到了3.76g/cm2;200目FeCuNbSiB纳米晶粉为33%,180℃、1h热处理,磁粉芯有效磁导率μe为10.44、中心频率为600kHz、中心频率品质因数Q值为44。     

微观结构对FeCo/TiO_2纳米复合材料微波共振的影响

采用机械化学法合成了FeCo/TiO_2纳米复合材料,该材料与石蜡的复合物在13.5GHz处复介电常数的实部ε′值具有较大的波动,复介电常数的虚部ε″产生强烈的介电共振峰,ε′-ε″的复平面上Cole-Cole图呈现一个全圆。制备态样品经500℃退火后,退火样品中FeCo纳米粒子的衍射峰明显变窄,表明晶粒尺寸增加,晶格缺陷减少,微观应力得到释放;同时,退火导致饱和磁化强度增加,矫顽力减小,介电共振行为消失。制备态样品的厚度为8.15mm时,反射损耗在12.6GHz处取得最大值-38.3dB,且当厚度为7.5mm时,超过-10dB的频宽为12~16.5GHz,几乎覆盖了整个Ku波段(12~18GHz)。该体系良好的电磁波吸收性能归功于FeCo/TiO_2纳米复合物特殊的微结构带来的非线性介电共振、强烈的自然共振和良好的电磁匹配。     

片状Fe-Cr-Si-Al 磁粉/Co2Z铁氧体粉末混合组分的电磁特性

采用机械球磨的方法扁平化处理气雾化Fe-Cr-Si-Al软磁合金（SMSS）粉末，并以柠檬酸溶胶-凝胶法合成六角铁氧体Ba3Co2Fe24O41（C02Z）粉末．运用SEM、XRD表征粉末的表面形貌和晶体结构，并测试不同质量比的片状SMSS磁粉与Co2Z粉末混合组分在2．0-8．2GHz范围的复介电常数和复磁导率．结果表明，随着Co2Z粉末质量分数的增加，样品的复介电常数和复磁导率减小；同时计算得到的反射系数曲线显示样品的匹配频率移向高频，当SMSS磁粉与Co2Z粉末的质量比为4／1时，样品具有最小的反射系数峰值．     

粉末挤出成型法制备FeSiAl/FeCuNbSiB磁粉芯

采用粉末挤出成型法制备了FeSiAl/Fe-CuNbSiB纳米晶磁粉芯,并讨论了FeSiAl粉复合量、粉胶质量比对磁粉芯磁性能的影响。结果表明粘结剂配方为硬脂酸1%、聚丙烯20%、石蜡79%,挤出成型粉胶质量比10∶1的FeSiAl/FeCuNbSiB纳米晶磁粉芯,磁粉芯密度达到4.69g/cm3。200目FeSiAl粉与300目FeCuNbSiB纳米晶粉复合,当磁粉芯磁粉质量配比为"200目FeSiAl粉30%+300目FeCuNbSiB纳米晶粉70%"、粉胶质量比为10∶1、44℃×0.5h石油醚脱脂、热处理温度160℃×1h时,磁粉芯取得最佳的软磁性能,磁粉芯中心频率f为600kHz,有效磁导率μe达到16.48,品质因数Q值为57.5;频率及温度的变化对磁粉芯的有效磁导率的影响小。     

纳米Fe/石蜡复合材料的微波介电谱拟合及极化机制

采用直流电弧等离子体蒸发法合成Fe纳米粒子,并与石蜡混合制备出Fe/石蜡纳米复合材料,测定在2—18 GHz频率范围内的复介电谱。结合普适介电理论、德拜弛豫理论及Cole-Cole方程对该类材料的复介电谱进行拟合并与实测谱进行比较。结果表明:普适介电理论能拟合介电常数的基本变化趋势,而Cole-Cole方程能更准确地拟合介电常数的变化规律。这表明Fe/石蜡纳米复合材料在微波段的多重极化机制可等效为取向极化机制。     

二氧化硅包覆片状金属磁性微粉电磁特性分析

以Na2SiO3溶液为前驱体,稀H2SO4为催化剂在乙二醇溶剂中对片状金属磁性微粉进行表面包覆.用SEM、XRD、RA-IR,VSM等分析手段对包覆前后的金属磁性微粉进行分析表征,并对包覆前后SiO2/金属磁性微粉复合材料的复介电常数和复磁导率等微波(2～18GHz)电磁参数进行了测试.结果表明Na2SiO3溶液在以稀H2SO4为催化剂的条件下在磁性微粉表面以非晶态的形式生长了一层致密、均匀的高电阻率SiO2薄膜,该薄膜使磁性微粉在复磁导率变化不大的情况下,有效降低了磁性微粉的复介电常数.     

铁、镍及其合金纳米粒子的制备及电磁性能研究

利用直流电弧等离子法在105Pa H2 Ar混合气氛下制备了Fe,Ni及FeNi合金纳米粒子,通过XRD,TEM,XPS,VSM及TC-436(LECO LTD.)N/O分析仪等对纳米粒子结构、形貌、成分、表面状态及静态磁性能进行了表征,并通过矢量网络分析仪,利用同轴波导的方法对金属纳米粒子进行了电磁参数的测定.结果发现:在2～8GHz频率范围内,Fe,Ni,FeNi合金纳米粒子/固体石蜡复合材料的复介电常数虚部ε″在3～4,7～10,14～16GHz频段均出现三个峰值,随着Fe元素含量的增加,FeNi合金纳米粒子的复介电常数ε″损耗值成规律性的增加;复磁导率实部μ′也逐渐增大,且在2～4GHz范围出现极大值,复磁导率虚部μ″吸收峰值向高频段移动,而且当成分(质量分数/%)为Fe49.00Ni和Fe28.35Ni时,材料的吸收频带展宽.     

微带法测试薄膜0.5～5G磁导率

提出了可以在0.5～5GHz频带扫频测量磁性薄膜复磁导率μr的微带线法,推导出了由倒置短路微带线单端口网络的反射系数R(S11)表示μr的理论公式.对微带线夹具进行了设计,并结合虚拟仪器技术,以LabVIEW为软件平台建立了一套测量薄膜微波复磁导率的自动测量系统.给出了FeCo基磁性纳米颗粒膜的磁导率测试曲线,表明微带法具有准确性较高、既适宜于面内各向异性薄膜又适合于各向同性薄膜的测量和容易操作等优点.     

纯化处理对碳纳米管2～18GHz复介电常数与复磁导率的影响

研究了纯化处理对多壁碳纳米管2～18GHz复介电常数与复磁导率的影响。纯化处理在部分频段降低了复介电常数的实部与虚部,增强了复磁导率的实部,而对复磁导率的虚部几乎没有影响。通过拉曼光谱对不同纯化处理的样品进行了表征,研究发现碳纳米管的晶化程度越好,介电常数降低和磁导率实部增强的幅度越大。     

组分对FeCoB纳米晶微波电磁参数及吸波性能的影响

利用两步机械球磨法制备了薄片状的Fe-CoB纳米晶材料,并研究了B含量对材料物相结构、静态磁性能、微波电磁参数和吸波性能的影响。结果表明,适当地加入非晶B会加强晶相与非晶相的交换耦合作用,从而使FeCoB的磁导率随着B含量的增加先增大后减小,复介电常数则随着B含量的增加单调降低,显著地改善了吸波材料的阻抗匹配特性。通过计算机模拟表明,与未添加非晶B的样品相比,FeCoB纳米晶材料在低频端有优异的吸波性能。当B含量从3%变化到15%时,在1.8～6.7GHz范围内的吸收强度均-6dB,可应用于拓展吸波材料吸收带宽的设计中。     

Microstructure and Magnetic Properties of Bulk FeCo Alloys Fabricated from Mechanically Alloying and Chemically Synthesized Powders

Three different methods of fabrication of FeCo soft magnetic material using ferromagnetic powders are compared: (i) simple sintering of elemental powders of Fe and Co, (ii) sintering of mechanically alloying FeCo powder, and (iii) sintering of chemically synthesized FeCo powder. The microstructure of ferromagnetic powders and bulk sintered alloys is characterized using scanning electron microscopy and energy-dispersive X-ray spectroscopy analysis. The best magnetic properties with high saturation magnetization, M _s = 211.3 emu/g, are obtained for bulk FeCo alloy sintered from chemically synthesized powder. It consists of nearly spherical FeCo particles with diameters from 5 to 15 μ m. The mean particle size of chemically synthesized FeCo powder can be controlled by changing the melt composition, temperature, and process duration. The relatively large size of FeCo particles reduces the influence of surface oxidation on the particle magnetic properties. The low-cost chemical technology developed is promising for a large-scale production of small FeCo magnetic components of arbitrary shapes with high-dimensional precision.     

Hyperfine interactions and structural features of Fe–44Co–6Mo (wt.%) nanostructured powders

Nanocrystalline Fe–44Co–6Mo (wt.%) powders have been prepared by high-energy ball milling from elemental Fe, Co and Mo pure powders in a P7 planetary ball mill. The obtained powders were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and Mössbauer spectrometry techniques. The influence of milling process and Mo substitution for Co in equiatomic FeCo have been examined in order to study structural evolution and formation mechanism of nanostructured Fe(CoMo) solid solution. XRD results show the formation of a BCC Fe(CoMo) solid solution (a = 0.2874 nm) where unmixed nanocrystalline Mo with a BCC structure is embedded. Disordered Fe(CoMo) solid solution is characterized by a broad hyperfine magnetic field distribution with two regions centered at B₁ = 35.0 T and B₂ = 30.7 T, respectively, attributed to disordered Fe(Co) solid solution and CoMo enriched environments. Prolonged milling and Mo addition cause the decrease of average hyperfine magnetic field while the average isomer shift remains nearly constant.     

纳米铁钴合金/石墨复合材料的微波吸收性能研究

利用氧化石墨的吸附性能将Fe³⁺和Co²⁺吸附到氧化石墨层间制备出Fe³⁺Co²⁺/氧化石墨复合物, 再通过氢气还原制备出纳米铁钴合金/石墨复合材料, 采用XRD和SEM以及磁滞回线测试等手段对其晶体结构、微观形貌以及磁学性能进行表征, 探讨了FeCo合金含量对其微波吸收性能的影响。结果表明: 所制备的产物为石墨和纳米FeCo合金颗粒组成的二元复合材料, FeCo合金分散在石墨表面和层间, 粒径为30~150 nm。纳米铁钴合金/石墨复合材料是典型的软磁性材料, 饱和磁化强度随FeCo合金含量的减小而降低。随着FeCo合金含量的减少, 纳米FeCo/石墨复合材料的介电损耗逐渐增加, 磁损耗逐渐减小。FeCo合金含量适当时, 介电损耗和磁损耗的协同作用使复合材料具有较好的微波吸收性能。     

SiO2在FGH96高温合金中的遗传特征

研究了SiO2颗粒在FGH96高温合金各不同工艺状态中的行为特征,结果表明:经热等静压处理后,SiO2尖角分明的特征消失,在界面处有反应过渡区生成,变成了一种"复合"非金属夹杂物.反应的驱动力为粉末和SiO2颗粒的表面能及在热等静压过程中球形粉末变形产生的应变能.在随后的各工艺状态中,SiO2在形貌、尺寸和元素分布等方面表现出了一定的行为特征.     

Synthesis and properties of graphene and graphene/carbon nanotube-reinforced soft magnetic FeCo alloy composites by spark plasma sintering

The effect of the addition of graphene nanoplatelets (GNP) and graphene nanoplatelet/carbon nanotube (GNT) mixtures on the mechanical and magnetic properties of spark plasma sintered soft magnetic FeCo alloys was studied. Three different volume fractions (0.5, 1 and 2 vol%) of GNPs and GNTs were investigated. Ball milling was used to disperse the GNPs in monolithic FeCo powder, while magnetic stirring and ultrasonic agitation were used to prepare hybrid GNT prior to ball milling. The highest saturation induction (B _sat) of 2.39 T was observed in the 1 vol% GNP composite. An increase in the volume fraction of the ordered nanocrystalline structure was found to reduce the coercivity (H _c) of the composites. The addition of CNTs to the GNP composite prevented grain growth, leading to grain refinement. An 18 % increase in hardness was observed in the 1 vol% GNP composite as compared to the as-received FeCo alloy. A reduction in tensile strength was observed in all of the composite materials, except for the 0.5 vol% GNT composite, for which a value of 643 MPa was observed. Raman spectroscopy indicated a reduction in the defect density of the GNPs after adding CNTs.     

镀Al空心玻璃微球FeCo合金/环氧树脂复合材料的吸波性能

利用磁控溅射法对空心玻璃微球表面镀Al。研究了由镀Al空心玻璃微球FeCo合金/环氧树脂制成的复合材料在2~18GHz频段范围内的电磁特性, 利用模型计算了所制备样品的微波反射率。结果表明, 在镀Al空心玻璃微球和FeCo合金粉末总体积分数一定的条件下, 随着镀Al空心玻璃微球与FeCo 合金体积比的增加, 复合材料介电常数实部ε′减小, 虚部ε″ 变化不明显; 磁导率的实部μ′ 和虚部μ″ 均减小; 反射率峰值向高频方向移动。 当 镀Al空心玻璃微球与FeCo合金体积比2∶1时, 涂层厚度为2mm, 吸收峰值达到-29.69dB, 其面密度仅为3.71kg/m2, 吸收率小于-10dB的带宽达到2.4GHz。由此可见, 通过改变镀Al空心玻璃微球与FeCo合金的体积比, 可以调节电磁参数, 提高材料的吸波性能。      

Spark plasma sintered Sm(2)Co(17)-FeCo nanocomposite permanent magnets synthesized by high energy ball milling

Nanocomposite Sm(2)Co(17)-5?wt% FeCo magnets were synthesized by high energy ball milling followed by consolidation into bulk shape by the spark plasma sintering technique. The evolution of magnetic properties was systematically investigated in milled powders as well as in spark plasma sintered samples. A high energy product of 10.2?MGOe and the other magnetic properties of M(s) = 107?emu?g(-1), M(r) = 59?emu?g(-1), M(r)/M(s) = 0.55 and H(c) = 6.4?kOe were achieved in a 5?h milled and spark plasma sintered Sm(2)Co(17)-5?wt% FeCo nanocomposite magnet. The spark plasma sintering was carried out at 700?°C for 5?min with a pressure of 70?MPa. The nanocomposite showed a higher Curie temperature of 955?°C for the Sm(2)Co(17) phase in comparison to its bulk Curie temperature for the Sm(2)Co(17) phase (920?°C). This higher Curie temperature can improve the performance of the magnet at higher temperatures.     

交流电化学沉积FeCo合金纳米线阵列及其磁性能研究

采用二步阳极氧化法制备孔结构高度有序的多孔氧化铝(AAO)模板。在不同Fe2+/Co2+摩尔比的电解液中,利用交流电化学沉积,在模板孔内成功制备了FeCo合金纳米线阵列。分别采用透射电子显微镜(TEM),场发射扫描电子显微镜(FE-SEM),X射线衍射仪(XRD)和震动样品磁强计(VSM)对样品的形貌,结构及磁学性能进行了表征。结果表明,制备的FeCo合金纳米线排列有序,粗细均匀;其直径与模板孔径一致,填充率较高,且具有明显的[110]择优取向。VSM测试结果表明,不同溶液浓度下制备的FeCo合金纳米线阵列均具有良好的垂直磁各向异性,易磁化轴沿着纳米线轴线方向。随着电解液Fe2+/Co2+摩尔比的不同,可在一定范围内对FeCo合金纳米线阵列的磁性进行调控,并对其原因进行了讨论。     

纳米BaF2粉体的热稳定性

采用醇/水混合溶剂方法制备了不同粒径的纳米BaF2粉体,研究了粉体的热稳定性.结果表明,纳米BaF2粉体的粒径随着混合溶剂中乙醇含量的提高而减小,粉体的形貌和分散性也都随之改变.根据在不同升温速率下测量的每种粒径纳米BaF2粉体的DSC曲线,由Kissinger方程求出了各晶粒长大激活能.BaF2晶粒长大激活能随着粉体粒径的减小而线性地减小,纳米晶BaF2的热稳定性随着粒径的减小而降低.