掺杂SiO_2对FeCo纳米晶磁粉电磁性能的影响

用高能球磨法制备了掺杂SiO_2的FeCo纳米晶磁粉,用SEM、XRD等分析手段对纳米晶磁粉进行结构分析,研究了掺杂SiO_2对FeCo纳米晶磁粉/石蜡复合物复介电常数和复磁导率的影响.结果表明,杂质SiO_2主要以非晶态的形式存在于FeCo纳米晶颗粒中;与未掺杂SiO_2的FeCo纳米晶磁粉相比,在复磁导率变化很小的情况下,掺杂适量的SiO_2可显著降低纳米晶磁粉/石蜡复合物的复介电常数,可较好的解决吸波涂层设计中的阻抗匹配问题.     

Ni_(1-x)Co_xFe_2O_4铁氧体纳米粉末的磁性能和微波吸收特性

利用柠檬酸溶胶-凝胶自蔓延燃烧法合成了Ni1-xCoxFe2O4(x=0,0.1,0.3,0.5)铁氧体纳米粉末。利用XRD、VSM和矢量网络分析仪测定了粉末样品的晶体结构、磁性能和电磁参数。定性分析了样品的饱和磁化强度、矫顽力、复磁导率和复介电常数随频率和Co含量的变化关系。结果表明,自蔓延的所有粉末样品经过600℃,2h高温退火后均为尖晶石相纳米晶颗粒。随着Co替代量x的增加,样品的自然共振频率先增大后减小,并对微波吸收特性有一定的改善。     

BST掺杂对Co2Z六角铁氧体相结构及动态电磁参数的影响

采用陶瓷工艺制备Co2Z(Ba3(Co0.4Zn0.6)2Fe23.4O41)六角铁氧体,通过二次球磨掺杂少量BST(BaSrTiO3)铁电材料。研究BST掺杂对Z型铁氧体的烧结温度、相结构、晶粒生长及其在频率1MHz～1GHz的动态相对复介电常数(ε′=ε″r—iε″r)和相对复磁导率(μ=μ′r—iμ″)的影响。结果表明：在BST掺杂量为Co2Z一次预烧料重量比的0～1.5％内．随BST含量增加,形成在Z型六角结构相生长同时,伴生M相六角结构和钙钛矿结构的多相结构;六角结构晶粒明显长大,材料密度增加;μr和εr增大;铁磁共振和铁电共振频率点移向低频。当BST掺杂量为1.5％、频率1MHz时．μ′=28,ε′=100,相对于纯相Co2Z材料μ′r和ε′,明显提高。     

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。      

BaPbZnCo-Y型铁氧体的柠檬酸溶胶-凝胶合成及其微波性能研究

采用柠檬酸sol-gel工艺合成了Ba2-ZpBZzN1.2Co0.8Fe12O22(z=0.0、0．5、1．0、1．5）Y型铁氧体。采用XRD、SEM对其相成分、显微结构进行研究。并对其复介电常数和复磁导率在1MHz-6GHz下的变化规律进行了研究。结果表明，铁氧体的复介电常数基本不随测试频率的变化而变化，其μ″谱上显示出非常明显的由自然共振引起的共振峰，该共振峰随铁氧体粉末热处理温度的升高移向低频。     

BST掺杂对M/Z型六角铁氧体复磁导率(1MHz～1GHz)的影响

摘　要: 　采用陶瓷工艺制备 Co2Z ( Ba3 ( Co0.4Zn0.6)2Fe23.4O41)和BaM(BaFi1.4Co1.4Fe9.2O19)六角铁氧体,二次球磨时掺杂少量 BST(BaSrTiO3 )铁电材料,对比研究了 BST 掺杂对 Z 型和 M 型铁氧体在1MHz~ 1GHz 频率范围内相对复磁导率(μr =μr′ iμr″)的影响。BST的掺杂使Z型铁氧体μr 增大,共振频率点移向低频;使M型铁氧体的μr 减小,共振频率点移向高频。通过对其微观结构和磁参数的测试分析,讨论了 BST掺杂对 Z型和 M型铁氧体复磁导率不同影响的作用机理。     

颗粒形貌对Fe-35%Co合金吸收剂磁性能的影响

采用高能球磨的方法处理水雾化Fe-35%(质量分数)Co软磁合金粉末,运用SEM、VSM和矢量网络分析仪分析测试不同球磨时间下合金粉末的微观形貌和静磁参数及其1~18 GHz频率范围的复磁导率(μ=μ'-jμ″)。结果表明,球磨处理可以使合金粉末颗粒扁平化,使得其复磁导率实部和虚部均明显提高;随着球磨时间增加,合金粉末的饱和磁化强度逐渐减小、矫顽力逐渐增大、扁平率以及复磁导率实部和虚部均先增大后减小,过度球磨会使合金粉末软磁性能恶化,不利于其微波磁导率的提高。     

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。     

传输/反射法测量固体复介质材料介电常数

介绍/传输反射法测量固体介质材料复介电常数等关键技术难点,通过建立固体介质材料的介电谱和磁谱测量装置,开展复介电常数、复磁导率、复损耗角正切测量技术研究,在30 MHz～18 GHz采用空气线同轴传输的方法、在18～50 GHz采用三段波导传输的方法,实现了30 MHz～50 GHz全频段固体介质材料电磁参数的测试能力,提出了复介电常数、复磁导率、复损耗角正切测量的数学模型,编制了材料测试软件,实现了同轴和波导的全频段测量。     

三维连通网络陶瓷电磁参数的改性

以水玻璃为溶胶、以SiO2气溶胶粉末和磁性γ-Fe2O3粉末为填料，通过浸渍挂浆、凝胶、无机化等步骤，对三维连通网络陶瓷的介电常数和磁导率进行了改性．结果表明，填加SiO2气溶胶粉末可以有效降低网络陶瓷的介电常数，控制SiO2气溶胶的填加量可以实现网络陶瓷介电常数的连续可调．填加磁性材料亦可以在一定范围内改变网络陶瓷的磁导率．在水玻璃溶胶浆料中加入不高于10％(质量分数)的SiO2气溶胶粉末，可使网络陶瓷的抗压性能显著提高；SiO2气溶胶粉末的填加量大于10％后，溶胶在网络陶瓷骨架表面及Si02颗粒之间难以形成连续结合而使网络陶瓷的抗压强度下降．     

活性炭载体对TiO2/活性炭中二氧化钛晶粒生长及相变的影响

以活性炭为载体,采用溶胶-凝胶法制备了TiO2/活性炭(TiO2/AC)复合体,并利用SEM和XRD手段对复合体进行表征,通过Dt2=ktnexp(-E/RT)方程的计算,分析,研究活性炭对复合体中TiO2晶粒生长及其相变的影响.结果表明TiO2/AC复合体晶粒粒径增长的时间比TiO2本体短;TiO2/AC复合体纳米粒子平均尺寸为50nm比TiO2本体小;锐钛矿向金红石转变的相变温度和晶粒生长最快温度TiO2/AC复合体比TiO2本体高.锐钛矿和金红石晶粒生长的表观活化能TiO2/AC复合体分别为6.21±1.27和46.54±1.56kJ/mol,TiO2本体分别为5.764±1.02和36.4±1.14kJ/mol.在锐钛矿阶段和金红石阶段TiO2/AC复合体反应指数分别为0.19和0.35,而TiO2本体分别为0.13和0.26.原因是活性炭的强吸附力和非晶相层对TiO2晶粒生长的阻遏作用.     

Preparation and microwave properties of Y-type magnetoplumbite microcrystalline glass ceramic with the composition 0.5(Ba2ZnZCo2-ZFe12O22)·0.5SiO2

The citrate sol-gel synthesis technique was used to prepared Ba₂Zn_ZCo_2-ZFe₁₂O₂₂/SiO₂ microcrystalline glass ceramic with Z=2.0, 1.6, 1.2, and 0.8. Several methods such as X-ray diffractometry, scanning electron microscopy and HP vector network analyzer were used to obtain detailed information on the crystallography and magnetic properties of Ba₂Zn_ZCo_2-ZFe₁₂O₂₂/SiO₂ microcrystalline glass ceramic. The correlation of the formation of Ba₂Zn_ZCo_2-ZFe₁₂O₂₂/SiO₂ microcrystalline glass ceramic with thermal treatment was studied. The complex dielectric constant and complex permeability of microcrystalline glass ceramic-paraffin wax composites were measured by the transmission/reflection coaxial line method in the range from 100MHz to 6 GHz. The effects of composition, annealing temperature and measuring frequency on complex permittivity and permeability of Ba₂Zn_ZCo_2-ZFe₁₂O₂₂/SiO₂ microcrystalline glass ceramic were also investigated. Received 23 July 2001 / Accepted: 24 July 2001     

Synthesis of single-phase Sr3Co2Fe24O41 Z-type ferrite by polymerizable complex method

Synthesis of single-phase Sr₃Co₂Fe₂₄O₄₁ Z-type (Sr₃Co₂Z) ferrite was realized by adopting the polymerizable complex method. Crystal structure of samples has been investigated by powder X-ray diffraction (XRD). Single-phase Sr₃Co₂Z ferrite was obtained by heating at 1473 K for 5 h in air. Magnetic properties were discussed by measurements of M-H curves with vibrating sample magnetometer (VSM). Sr₃Co₂Z ferrite prepared by polymerizable complex method showed typical M-H curve of soft ferrite, with a saturation magnetization of 21.5μ_B/formula unit (50.5 emu/g) and a coercive force of 0.014 T at room temperature.     

铁氧体-微晶玻璃纳米复合材料的结构与性能

采用溶胶-凝胶工艺首先合成了NICuZn铁氧体纳米粉末和MgO－Al₂O₃-SiO₂(MAS)凝胶玻璃粉末,将两种粉末按一定比例均匀混合,烧结后得到了由NiCuZn铁氧体和堇青石微晶体两相共存的铁氧体一微晶玻璃纳米复合材料。该材料具有可调控的电磁性能,其起始磁导率高于3、介电常数低于6、截止频率高于2GHz,可望用作持高频多层片式电感介质材料．     

SPS原位反应制备TiC/Ti2AlC/TixAly系复合材料的微观结构及其导电性能

以Al₄C₃、Ti和石墨混合粉体为原料, 采用放电等离子技术原位反应制备了TiC/Ti₂AlC两相复合材料和TiC/Ti₂AlC/Ti_xAl_y三相复合材料. 利用XRD、SEM、TEM研究了复合材料的相组成和微观结构, HRTEM的观察结果显示复合材料的相界面清洁干净, 无非晶相存在. 同时研究了TiC/Ti₂AlC/Ti_xAl_y三相复合材料的原位反应烧结过程, 并对复合材料的导电行为进行了表征. 在室温时TiC/Ti₂AlC材料的电导率大于TiC/Ti₂AlC/Ti_xAl_y三相复合材料,其中TiC/40vol%Ti₂AlC的电导率最高达到8.83×105S/m. TiC/Ti2AlC两相复合材料和TiC/Ti₂AlC/Ti_xAl_y三相复合材料的电导率均随温度的升高而下降, 呈现电导的金属性特征, 同时电导率随温度变化关系符合Arrhenius理论.     

FeSiCrB amorphous soft magnetic composites filled with Co2Z hexaferrites for enhanced effective permeability

Z-type Sr₃Co₂Fe₂₄O₄₁ hexaferrites (Co₂Z hexaferrites) were synthesized with sol–gel method and were mechanically mixed with spherical Fe₈₈Si₇Cr_2.5B_2.5 (FeSiCrB) amorphous powders, and then compacted to form toroidal Co₂Z hexaferrites/FeSiCrB amorphous soft magnetic composites (Co₂Z/FeSiCrB SMCs). The compositions, morphology and soft magnetic performance were characterized through SEM, XRD, VSM, EDS, B-H analyzer and impedance analyzer. All results reveal that Co₂Z hexaferrites in Co₂Z/FeSiCrB SMCs should mainly exist in air gaps between spherical FeSiCrB amorphous powders, leading to the increasing density. Saturation magnetization decreases a little for magnetic dilution and coercivity increases for the stronger magnetic interaction of Co₂Z/FeSiCrB SMCs. The introduction of Co₂Z hexaferrites in air gaps increases the conduction area of magnetic circuits and decreases the demagnetization effect, leading to the higher effective permeability of 27.4 for Co₂Z/FeSiCrB SMCs, much higher than 25.0 for FeSiCrB SMCs. Furthermore, Co₂Z/FeSiCrB SMCs present the smaller core loss and more stable DC bias characteristics owing to the insulating Co₂Z hexaferrites.     

Influence of SiO2 fillers on microwave absorption properties of carbonyl iron/carbon black double-layer coatings

Epoxy resin (ER) based double-layer composite coatings were prepared with the thickness of 1.2 mm, employing carbonyl iron (CI) and carbon black (CB) as absorbents in the matching layer and absorption layer respectively. Especially, SiO₂ was introduced into the matching layer as wave-transmission material to improve the matching impendence. The complex permittivity, complex permeability and absorption properties were investigated in 2–18 GHz. With increasing SiO₂ content in the matching layer, the reflection loss (RL) was enhanced in the range 2–18 GHz. When the coating with the optimized SiO₂ and CI weight concentration (SiO₂:CI:ER) of 2:5:1, the optimal RL got to −17.3 dB and the effective absorption band (RL better than −4 dB) reached 5.7 GHz. In comparison, the minimum RL value was only −5.9 dB and the bandwidth (RL better than −4 dB) was just 4.1 GHz for the SiO₂-free composite coating.     

烧蚀产物ZrO2对ZrC改性C/C复合材料烧蚀的影响

采用ZrOCl₂溶液浸渍法把含锆组元引入碳纤维预制体, 结合热梯度化学气相渗透、高温石墨化工艺制备了ZrC改性C/C复合材料. 用氧乙炔烧蚀测试材料的烧蚀性能, XRD测试材料烧蚀前后的物相组成, 采用SEM观察材料的微观形貌. 烧蚀结果表明：随着烧蚀次数的增加, 若每次烧蚀后不去除ZrO₂, 材料的线、质量烧蚀率呈先增加后减小的趋势, 最后趋于稳定; 若每次烧蚀后去除ZrO₂, 材料的线、质量烧蚀率均呈增大的趋势. 产物ZrO₂的蒸发吸收了材料烧蚀表面的热量, 减缓了火焰对烧蚀表面的冲蚀, 材料的线烧蚀率减小, 然而, ZrO₂的蒸发会增加材料的质量损失速度, 导致材料的质量烧蚀率增大.     

Low-temperature sintering of Z-type hexagonal ferrite by addition of fluorine containing glass powder

In order to reduce the sintering temperature of Ba₃Co₂Fe₂₄O₄₁ (Co₂Z), fluorine containing glass powder was added as a sintering aid to ferrite powder with a Co₂Z stoichiometric composition prepared by a solid-state reaction, and dense sintered specimens could be obtained at 1000°C in air. The densification was achieved by liquid-phase sintering which was induced by the melting of the additive glass at 800°C. The main crystalline phase was Co₂Z, and spinel ferrite appeared as the impurity phase. By sintering in a sealed container, the densification was accelerated still more, and in addition to spinel ferrite, Ba-M also appeared as the impurity phase. The Ba-M contained some Co instead of Fe, and grew to discontinuously large hexagonal plate-like grains. In a fluorine and/or fluorides rich atmosphere, Co₂Z was discomposed to Ba-M and spinel ferrite, and large hexagonal plate-like grains appeared. These results suggest that fluorine and/or fluorides evaporated from the additive glass decomposed Co₂Z to Ba-M and spinel ferrite, and induced the discontinuously grain growth of Ba-M. The initial permeability was lower than that of the specimen with no additive glass but remained almost constant in the frequency regions up to 1 GHz.     

BaFe12O19/SiO2微晶玻璃陶瓷的柠檬酸盐Sol-Gel合成及其微波性能的研究

采用柠檬酸sol-gel工艺合成了BaFe12O19/SiO2微晶玻璃陶瓷,并对其介电常数及其磁导率在100MHz-6GHz下的变化规律进行了研究。结果表明,BaFe12O19/SiO2微晶玻璃陶瓷的合成与体系中Fe/Ba,烧结温度密切相关;其介电常数、磁导率基本都随测试频率的增加而下降,介电损耗值最大达到0．40,磁损耗值较小。