掺杂铁氧体复合吸波材料的研究进展

叙述了铁氧体吸波材料吸收电磁波原理,总结了铁氧体吸波材料的研究现状。将硝酸铁、硝酸铝与柠檬酸混合,用自蔓延法制备氧化铁氧化铝复合铁氧体吸波剂,研究其复介电常数变化,发现随着氧化铝含量的增加,介电常数实部逐渐下降,虚部损耗峰则逐渐移向高频。通过控制氧化铝含量,可以调节吸波剂的损耗峰。     

Al2O3/Ni金属陶瓷力学性能和介电性能的研究

以热压烧结的方法制备了Al2O3/Ni金属陶瓷,探讨了Al2O3/Ni金属陶瓷显微结构、力学性能及微波介电性能随Ni粒子含量变化的规律.结果表明,在垂直于压力方向上,Ni粒子有明显的受压拉伸现象;当Ni粒子含量从5%(体积分数)增加至20%(体积分数)时,金属陶瓷中Ni粒子的分布由孤立向部分桥连方式转变.随Ni粒子含量的增加,金属陶瓷致密度略有下降,抗弯强度明显降低.与纯氧化铝陶瓷相比,含20%(体积分数)Ni粒子Al2O3/Ni金属陶瓷的断裂韧性提高了50%左右,达到6.4MPa·m1/2.复介电常数测试结果表明,在8.2～12.4GHz频率范围内,金属陶瓷复介电常数的实部和损耗随Ni粒子含量的增加逐渐上升.当Ni粒子含量达到20%(体积分数)时,由于Ni粒子之间的部分桥连现象而使介电常数虚部在一定频段出现负值.     

环氧树脂含量对Ni-Zn铁氧体复合材料电磁特性的影响

本文研究了环氧树脂含量对粘结软磁Ｎｉ－Ｚｎ铁氧体在１～１０００ＭＨｚ频率范围电磁特性的影响。结果表明，随环氧树脂含量增加，磁导率实部及虚部逐渐降低，且在此频段内降低幅度基本一致；其介电常数实部及虚部也随环氧树脂含量的增加而降低，但在此频段内下降幅度不同，＜３０ＭＨｚ频段，其下降幅度较大，＞３０ＭＨｚ其下降幅度较小，这是由于环氧树脂与Ｎｉ－Ｚｎ铁氧体之间的界面极化产生变化所致     

Ni0.5Zn0.5Nd0.02Fe1.98O4-聚苯胺纳米复合材料的制备及电磁性能（英文）

在Ni0.5Zn0.5Nd0.02Fe1.98O4纳米粒子表面原位聚合苯胺制备了Ni0.5Zn0.5Nd0.02Fe1.98O4-聚苯胺(PANI)纳米复合材料.铁氧体含量为0%、15%和30%样品的结构、形貌和电磁性能分别采用X射线衍射仪(XRD)、透射电子显微镜(TEM)和HB8510B网络分析仪进行了研究.结果表明,聚苯胺包覆层对Ni0.5Zn0.5Nd0.02Fe1.98O4的结晶度有一定影响.在X波段(8.2～12.4 GHz),复介电常数的实部随铁氧体含量的增加而减小,虚部随铁氧体含量的增加而增大.复磁导率的实部和虚部都随铁氧体含量的增加而增大.     

轴向送粉等离子喷涂Ni/Al2O3涂层的力学及微波介电性能

以轴向送粉等离子喷涂法制备了Ni/Al2O3陶瓷涂层,分析了Ni含量变化对涂层材料的显微结构、力学性能及微波介电性能的影响.结果表明,随着Ni含量增加,涂层中Ni粒子的分布逐渐由孤立向部分桥连方式转变;陶瓷涂层的相对密度、抗弯强度呈下降趋势,这主要是由于在陶瓷涂层中Ni与Al2O3不润湿,Ni与Al2O3热膨胀系数不匹配从而形成空隙引起的.涂层断裂韧性随Ni含量的增加而升高,则是由于材料中Ni粒子发生了延展变形和引起裂纹转向.复介电常数性能测试结果表明,在8.2～12.4GHz微波频率范围内,陶瓷涂层复介电常数的实部值随Ni粒子含量的增加先逐渐上升后逐渐下降,复介电常数的虚部上升.这与Ni粒子形成的桥连结构有关.     

Cu含量对BaTiO3/Cu复相陶瓷材料介电性能的影响

用传统固相法制备了(1-x)BaTiO3/xCu(x=5 wt%,10 wt%,15 wt%,20 wt%,25 wt%,30 wt%)复相陶瓷,研究了Cu含量对复相陶瓷材料的显微结构、渗流阈值及介电性能的影响.研究结果表明:BaTiO3/Cu复相陶瓷材料的电阻率随着铜含量的增加而下降,且在渗流阈值(x=25wt%)附近呈现非线性的下降趋势,复合材料从绝缘体逐渐变为导体.室温下1 kHz当Cu含量达到x=30wt%时复相陶瓷的介电常数为~9000,这是由于在导体和绝缘体的相界面处积累大量的空间电荷,并由此产生界面极化,导致介电常数的显著增大,且随着导体含量的增加,这种界面效应更加明显.复相陶瓷的介电损耗随着铜含量的增加而增大,但随着频率的升高,由于空间电荷的减少又会使损耗呈现下降的趋势.在25~115℃的温度范围内,复相陶瓷温度系数小于5%,具有很高的介电常数温度稳定性.     

碳/氧化铝/二氧化硅涂层的介电和吸波性能研究

研究了炭黑或碳纤维填充氧化铝/二氧化硅吸波涂层在X波段范围的介电和吸波性能. 结果表明: 吸波涂层的复介电常数随着炭黑或碳纤维含量的增加而增大. 当吸收剂含量相同时, 填充碳纤维的吸波涂层比填充炭黑的吸波涂层具有更大的复介电常数. 当吸收剂含量大于5wt%时, 吸波涂层的介电常数在低频急剧增加, 且随频率增大而减少, 出现频散效应. 反射率测试结果表明: 吸波涂层的最大吸收峰随涂层厚度的增大向低频移动, 当涂层中炭黑含量为2wt%、厚度为1.8 mm时, 吸波涂层在9.2~12.4 GHz范围内反射率小于-10 dB, 具有较好的吸波效果.     

BaM、BaCoTiM、BaZnTiM的柠檬酸溶胶-凝胶合成及其微波介电性能、磁性能研究

采用柠檬酸sol—gel工艺，以柠檬酸铁、碳酸钡、硝酸钴、硝酸锌、钛酸四丁酯以及柠檬酸等为原料合成了BaFe12O19，、Ba(CoTi)xFe12—2xO19、Ba(ZnTi)sFe12—2xO19(x＝0．2、0．6、1．0)铁氧体。采用XRD、SEM对其相成分和显微结构进行研究。并对其复介电常数、复磁导率在1MHz-6GHz下的变化规律进行了研究。结果表明3种铁氧体的复介电常数随微波测试频率的增加而变小，其磁导率虚部随测试频率的变化曲线上显示出非常明显的由畴壁共振引起的共振峰，该共振峰随铁氧体粉末热处理温度的升高移向低频。     

纳米Si/C/N复相粉体-硅溶胶涂层的介电和吸波性能研究

以硅溶胶为粘结剂,氧化铝为主要填料,纳米Si/C/N复相粉体为吸收剂,制备了一系列不同吸收剂含量的耐高温吸波涂层.结果表明,当氧化铝和硅溶胶的质量分数分别为64.7%和32.3%时,涂层具有很好的耐高温性能.随着纳米Si/C/N复相粉体含量的增加,试样的复介电常数显著提高,尤其是复介电常数的虚部;且随着频率的增大,复介电常数的实部有明显的减小趋势,呈频散效应.当纳米Si/C/N复相粉体的含量为2.92%(质量分数,下同),涂层厚度为1.6mm、1.7mm、1.8mm时,最高吸收峰随着厚度的增加向低频移动,反射率均小于-4dB.     

BaMnZnCoTi—W型铁氧体微波吸收特性的研究

对用Co2 + 、Ti4 + 置换Fe3 + 的BaMnZn -W型铁氧体的制备和微波吸收性能进行了分析研究 ,发现涂层厚为 1.0 6mm在 7.0～ 12 .0GHz频率范围内有 3个损耗吸收峰 ,峰值最高达 3 4dB以上 ;同时测量了复数磁导率 μ～( =μ′ -jμ″) ,复介电常数ε～( =ε′ -jε″) ,求出了磁损耗角正切tgδm 和介电损耗角正切tgδe,初步分析了 3个损耗吸收峰可能产生的机制。比较了在相同工艺条件下 ,随Co2 + 、Ti4 + 含量增加 ,铁氧体的吸收频率特性和涂层厚度的关系。     

Plasma spraying of Al2O3 and Al2O3Y2O3

A microstructural study has been carried out of plasma-sprayed Al₂O₃ and mixed and sintered Al₂O₃Y₂O₃. In order to ascertain the degree of metastability achieved by plasma spraying, these results are compared with a similar experiment utilizing a CO₂ laser for melting and the hammer-and-anvil technique for quenching of the same materials. X-ray diffraction methods were used to determine the obtained phases and crystal structures. In addition, transmission electron microscopy was used to confirm the phases present and to study their morpology. The porosity was studied with both mercury intrusion porosimetry and small angle neutron scattering. The addition of Y₂O₃ is shown to decrease the porosity from 15% to 7.5%. Adhesion is likewise related to the addition of Y₂O₃ and it is seen that adhesion of the mixture is measurably improved over that of pure Al₂O₃. The implication of these results is discussed.     

Al2O3/Al2O3 Joint Brazed with Al2O3-particulate-contained Composite Ag-Cu-Ti Filler Material

1.IntroductionTo improve the mechanical properties and relieve mis-matches between the filler metals and base materials,the particulates of superalloys,ceramic or carbon fiberswere added into the conventional brazing filler metal toform composite filler material.The method has beenused in aero-engine component repairing[1,2],fine castcomponent joining[3],wide clearance butt jointing[4],ce-ramic brazing[5,6]and electronic package[7].However,the method was used mostly in metal brazing.The mi-cro…     

Al2O3—Coated Nano—SiC Particles Reinforced Al2O3 Matrix Composites

Properties of Al2O3-coated nano-SiC have been compared with those of as-received SiC.The isoelectric point(IEP) of SiC changed from pH3.4 to pH7.3 after coating with the alumina precursor,which is close to that of alumina.Because both surfaces of coated SiC and Al2O3 possess higher positive charge at pH=4.5-5.0 ,they are uniformly dispersed in the two-phase aqueous suspensions.Then a mixed powder containing nano-SiC dispersed homogeneously into the Al2O3 matrix was achieved from flocculating the two-phase suspension.Finally,Al2O3/SiC nanocomposited were obtained by coating nano-SiC with Al2O3 ,in which the majority of SiC particles were located within the Al2O3 grains.The observation by transmission electron microscopy(TEM) and the analysis by the X-ray photoelectron spectroscopy(XPS) showed that cracks propagated towards the intragranular SiC rather than along prain boundaries.     

Slip casting of Al2O3 and Al2O3/ZrO2 composites

Al₂O₃ and Al₂O₃/ZrO₂ composites have been fabricated by slip casting from aqueous suspensions. The physical and structural characteristics of the starting powders, composition of the suspensions, casting behaviour, microstructure of the green and fired bodies and the mechanical properties of the products were investigated. The addition of ZrO₂ to Al₂O₃ leads to a significant increase in fracture toughness when ZrO₂ particles are retained in the tetragonal form (transformation-toughening mechanism) but when microcracking (due to the spontaneous transformation of ZrO₂ from the tetragonal phase to the monoclinic one) is dominant, an excellent toughness value is accompanied by a drastic drop in strength and hardness.     

Microstructure and Strength of Al2O3/Al2O3 Joints Bonded with ZnO-Al2O3-B2O3-SiO2 Glass-Ceramic

ZnO-Al2O3-B2O3-SiO2 （ZABS） glass powder was used as interlayer to join alumina ceramics. The effect of joining temperature on the microstructure and strength of joints was investigated. The results showed that the ZABS glass can react with alumina substrate to form a layer of ZnAl2O4 at Al2O3/glass interface. Bending test exhibited that low joining temperature （1150℃） led to low joint strength due to the formation of pores in the interlayer, originated by high viscosity of the glass. High joining temperature （1250 ℃） also resulted in low joint strength, because of large CTE （coefficient of thermal expansion） mismatch between amorphous interlayer and alumina substrate. Therefore, only when the joining temperature was appropriate （1200℃）, defect-free interface and high joint strength can be obtained. The optimum joint strength reached 285 MPa, which was the same as the base material strength.     

Surface,grain-boundary and interfacial energies in Al2O3 and Al2O3-Sn,Al2O3-Co systems

Using the multiphase equilibrium method for the measurement of contact angles, the surface and grain-boundary energies of polycrystalline Al₂O₃ in the temperature range of 1473 to 1923 K were determined. Linear temperature functions were obtained by extrapolation for both quantities between absolute zero and the melting point of Al₂O₃. The temperature dependence of the surface and grain boundary energies can be expressed as $$\gamma _{{\rm A}l_2 O_3 } = 2.559 - 0.784 \times 10^{ - 3} T(J m^{ - 2} )$$ and $$\gamma _{{\rm A}l_2 O_3 - Al_2 O_3 = } 1.913 - 0.611 \times 10^{ - 3} T(J m^{ - 2} )$$ respectively. The interfacial energies of Al₂O₃ in contact with the molten metals tin and cobalt revealed a linear dependence on temperature.