聚偏氟乙烯/碳纳米管复合材料的形态结构及性能

通过超声分散方法制备了聚偏氟乙烯/多壁碳纳米管复合材料,研究了复合材料的形态结构、导电性和热膨胀性质。扫描电镜观察表明碳纳米管被均匀地分散在聚偏氟乙烯基体中。虽然碳纳米管和聚偏氟乙烯之间存在相互作用,但超声并没有引起聚偏氟乙烯的化学交联。同时还研究了复合材料的导电性和正温度系数效应,发现这些复合材料具有较低的逾渗阈值,掺入少量碳纳米管就可使聚偏氟乙烯/碳纳米管复合材料的导电性获得明显改善。此外,碳纳米管的添加能够明显降低聚偏氟乙烯/碳纳米管复合材料的热膨胀系数。     

MWNTs/PVDF复合材料导电和介电性能的研究

用熔融共混和热压工艺制备了多壁碳纳米管(MWNTs)和羧基化多壁碳纳米管(MWNTs-COOH)填充聚偏氟乙烯(PVDF)复合材料.研究了多壁碳纳米管体积含量、测试频率和温度对复合体系的电性能的影响.实验发现,MWNTs-COOH/PVDF复合体系的渗流阈值和渗流阈值附近的介电常数明显大于MWNTs/PVDF体系.利用渗流理论、Maxwell-Wagner界面极化效应和微电容模型解释了实验现象.     

MWNTs/PVDF复合材料导电和介电性能的研究EI

用熔融共混和热压工艺制备了多壁碳纳米管(MWNTs)和羧基化多壁碳纳米管(MWNTs-COOH)填充聚偏氟乙烯(PVDF)复合材料.研究了多壁碳纳米管体积含量、测试频率和温度对复合体系的电性能的影响.实验发现,MWNTs-COOH/PVDF复合体系的渗流阈值和渗流阈值附近的介电常数明显大于MWNTs/PVDF体系.利用渗流理论、Maxwell-Wagner界面极化效应和微电容模型解释了实验现象.     

碳纳米管/石英复合材料的电磁波吸收性能

采用溶胶-凝胶法合成了碳纳米管/石英复合粉体, 复合粉体经热压烧结获得致密的复合材料. 在8.2～2.4GHz波段测试了该复合材料的复介电常数, 发现复介电常数随着碳纳米管含量的增加而大幅度提高, 大的介电常数虚部说明该复合材料具有很大的介电损耗. 采用传输线理论计算了该复合材料对电磁波的反射损耗, 发现复合材料在此波段对电磁波具有吸收效果, 并且反射损耗 与复合材料的厚度、碳纳米管体积含量具有密切的关系. 本文还采用了层状设计的方法提高了复合材料的吸波性能.     

聚苯胺-钴铬锌铁氧体复合材料的微波吸收性能和磁性能

用聚丙烯酰胺凝胶法和原位聚合法分别制备了钴铬锌铁氧体(Co0.7Cr0.1Zn0.2Fe2O4)和聚苯胺-钴铬锌铁氧体复合材料(PANI-Co0.7Cr0.1Zn0.2Fe2O4),用XRD和FT-IR对材料的结构进行了表征。结果表明,制备的Co0.7Cr0.1Zn0.2Fe2O4铁氧体为尖晶石结构,少量Cr3+离子替代了铁氧体八面体位置上的Co2+离子,导致铁氧体的晶格常数从0.8409 nm减小到0.8377 nm。用振动样品磁强计(VSM)测量了材料的磁性能,结果表明,PANI-Co0.7Cr0.1Zn0.2Fe2O4复合材料的饱和磁化强度(Ms)、剩余磁化强度(Mr)和矫顽力(Hc)分别为8.80 emu/g、14 emu/g和37.22 k A/m,小于铁氧体的相应数值;用波导法研究了PANICo0.7Cr0.1Zn0.2Fe2O4复合材料的微波吸收性能,在5-20 GHz频率范围内14.1 GHz和17.9 GHz处出现两个极大反射损耗,分别为-13.17 d B和-15.36 d B,大于铁氧体的反射损耗。     

层状碳纳米管/石英复合材料的制备及其微波衰减性能

采用溶胶-凝胶法合成了3种不同体积分数的碳纳米管/石英复合粉体,将其中的2种复合粉体先后装入同一石墨模腔中,经热压烧结获得致密的层状碳纳米管/石英复合材料.测试了层状复合材料在8.2～12.4GHz波段的微波衰减性能,研究发现,层状碳纳米管/石英复合材料具有优良的微波衰减性能,并且微波从不同的材料面入射对微波产生的反射差别很大.对于10%(体积分数)碳纳米管/石英-纯石英层状复合材料,微波从10%(体积分数)碳纳米管/石英面入射造成的微波反射量是从纯石英面入射造成的微波反射量的5倍以上.采用层状设计制备了一种对微波反射少、吸收量大的碳纳米管/石英复合材料.     

镍铁氧体/聚苯乙烯复合材料的制备与性能

采用高分子凝胶法制备了纳米镍铁氧体,然后用热压法制备了镍铁氧体/聚苯乙烯复合材料.镍铁氧体的结构、形貌和复合材料的电磁性能分别采用X射线衍射仪(XRD)、透射电镜(TEM)和HP8510网络分析仪进行了研究.结果表明,当煅烧温度为600℃时,镍铁氧体晶相生成.随着煅烧温度的升高,镍铁氧体晶体晶型趋向完整.在X波段,复合材料的复介电常数和复磁导率值随着镍铁氧体煅烧温度的升高而增大.1000℃煅烧的镍铁氧体所制备的镍铁氧体/苯乙烯复合材料在11.47GHz处的最小反射率为-12.67dB.     

MWNTs/PVDF复合材料的介电性能

基于熔融法制备多壁碳纳米管(MWNTs)/聚偏氟乙烯(PVDF)基复合材料,研究不同含量的MWNTs对MWNTs/PVDF复合材料介电性能的影响规律,并探讨其对复合材料介电常数的影响机制。结果表明,随着MWNTs含量的增加,复合材料中α-PVDF相转换成γ-PVDF相;通过宽频介电阻抗谱仪测试,发现介电常数随着温度的增加而增加,并向高温方向移动;在电场的作用下,添加MWNTs能加剧PVDF材料分子键的热运动以及极化现象。另外,研究发现,由于介电损耗降低,表明复合材料的介电性能得到了改善。     

导电聚偏氟乙烯/碳纳米管复合膜的制备与性能研究

通过浸没沉淀相转化法制备了聚偏氟乙烯/多壁碳纳米管导电复合膜,研究了复合膜的亲水性、导电性、通量、表面形态以及机械性能。研究表明,碳纳米管的加入可以使复合膜中的β相增多,α相减少。扫描电镜表明通过超声分散处理可以使碳纳米管均匀地分散在聚偏氟乙烯基质中,同时由于碳纳米管的加入,复合膜的亲水性、通量、导电性、介电常数以及机械性能都得到了改善。     

高介电常数PVDF/PZT/Terfenol-D复合材料的介电性能研究

以聚偏氟乙烯(PVDF)为聚合物基体,PZT为陶瓷相,稀土铁合金粒子Tedenol-D为添加组分,运用聚合物熔融压片法制备了聚合物体积含量为30%的0.3PVDF/(0.7-f)PZT/fTerfenol-D三相复合材料.研究了Tedenob-D的体积含量、频率对复合材料介电性能的影响.结果显示:Tedenol-D粒子的加入,可以提高0.3PVDF/0.7PZT复合材料的介电常数,PVDF/PZT/Terfenol-D复合材料具有介电常数高、介电损耗小的特点.     

Structural and optical properties of AlxOy/Pt/AlxOy multilayer absorber

We report on the microstructure and optical properties of Al_xO_y–Pt–Al_xO_y interference-type multilayer films, deposited by electron beam (e-beam) deposition onto corning 1737 glass, silicon (1 1 1) and copper substrates. The structural properties were investigated by Rutherford backscattering spectrometry, X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy and atomic force microscopy. The optical properties were extracted from specular reflection/transmission, diffuse reflectance and emissometer measurements. The stratification of the coatings consists of a semi-transparent middle Pt layer sandwiched between two layers of Al_xO_y. The top and bottom Al_xO_y layers were non-stoichiometric with no crystalline phases present. The Pt layer is in the fcc crystalline phase with a broad size distribution and spheroidal shape in and between the rims of Al_xO_y. The surface roughness of the stack was found to be comparable to the inter-particle distance. The optical calculations confirm a high solar absorptance of ∼0.94 and a low thermal emittance of ∼0.06 for the multilayer stack, which is attributed not only to the optimized nature of the multilayer interference stacks, but also to the specific surface morphology and texture of the coatings. These optical characteristics validate the spectral selectivity of the Al_xO_y–Pt–Al_xO_y interference-type multilayer stack for use in high temperature solar-thermal applications.     

Synthesis of a new perovskite Pb(Li14Nb34)O3

A high-pressure technique was adopted to obtain perovskite-type $\text{Pb(Li}{}_{\mathrm{<mtext>1</mtext><mtext>4</mtext>}}\text{Nb}{}_{\mathrm{<mtext>3</mtext><mtext>4</mtext>}}\text{)}\text{O}{}_3$. A new perovskite $\text{Pb(Li}{}_{\mathrm{<mtext>1</mtext><mtext>4</mtext>}}\text{Nb}{}_{\mathrm{<mtext>3</mtext><mtext>4</mtext>}}\text{)}\text{O}{}_3$ was characterized to have a cubic symmetry with $\text{a}{}_{\mathrm{<mtext>o</mtext>}}\text{= 4.069}\text{A}\text{?}$; Li and Nb ions in the B-site of perovskite lattice may be in a random arrangement.     

Bulk crystalline BaPb34Bi14O3: A ceramic superconductor

The preparation conditions of the high T_C ceramic superconductor Ba(Pb,Bi)O₃ is correlated with the superconducting transition. Transition onsets of all materials are similar, but transition widths and transition completeness is strongly dependent on firing temperature. Only materials prepared over a narrow temperature range, resulting in a nearly ideal weight loss, have a complete and narrow transition.     

Optimization of AlxOy/Pt/AlxOy multilayer spectrally selective coatings for solar-thermal applications

Spectrally selective Al_xO_y/Pt/Al_xO_y multilayer absorber coatings were deposited onto corning 1737 glass, Si (111) and copper substrates using electron beam (e-beam) vacuum evaporator at room temperature. The employment of ellipsometric measurements and optical simulation was proposed as an effective method to optimize and deposit multilayer solar absorber coatings. The optical constants (n and k) measured using spectroscopic ellipsometry, showed that both Al_xO_y layers, which used in the coatings, were dielectric in nature and the Pt layer was semi-transparent. The optimized multilayer coatings exhibited high solar absorptance α ∼ 0.94 ± 0.01 and low thermal emittance ? ∼ 0.06 ± 0.01 at 82 °C. The Rutherford backscattering spectroscopy (RBS) data of Al_xO_y/Pt/Al_xO_y multilayer absorber indicated the Al_xO_y layers present in the coating were nearly stoichiometry. The scanning electron microscope analysis (SEM) result indicated that the average diameter and inter-particles distance of Pt grains were statistically about 146 ± 0.17 nm and 6-10 ± 0.2 nm respectively.     

Electrostriction in Pb (Zn13Nb23)O3

The electrostriction in $\text{Pb (Zn}{}_{\mathrm{<mtext>1</mtext><mtext>3</mtext>}}\text{Nb}{}_{\mathrm{<mtext>2</mtext><mtext>3</mtext>}}\text{)}\text{O}{}_3$ crystals has been investigated using a strain gauge method. In the ferroelectric phase below 140 C, the strain vs the electric field shows a hysteresis, which is ascribed to the effect of ferroelectric domains. A quadratic relation holds between the strain x and the electric polarization P as x = QP² above about 170 C in the paraelectric phase. Values of the electrostrictive Q coefficients are determined from the measurements near 190 C, as Q₁₁ = 1.6·10^?2m⁴/C², Q₁₂ = ?0.86·10^?2m⁴/C², and Q₄₄ = 0.85·10^?2m⁴/C².     

Magnetic,electrical and thermal studies on the V1−xMox02

The monoclinic-to-tetragonal structure transition of oxides V_1?xMo_x0₂ with $\text{0≤}\text{x}\text{≤0.20}$ has been studied by means of DTA, X-ray diffraction, magnetic susceptibility (powder samples) and electrical conductivity (single crystals) measurements within the temperature region 80 K to 400 K. A linear decrease of the transition temperature of 11 K per atom % Mo was observed. The magnetic susceptibility of the low temperature phase was found to be temperature independent paramagnetic for all preparations. Electrical conductivity measurements on the same phase showed crystals with $\text{x}\text{? 0.04}$ to be semiconducting, while a metallic behavior was observed in the region $\text{0.10 ?}\text{x}\text{? 0.14}$.     

n-PbTep+−Pb1−xSnxTe heterojunctions prepared by a modified hot wall technique

$\text{n-PbTe}\text{p}{}^{\mathrm{+}}\text{?}\text{Pb}{}_{\mathrm{1?x}}\text{Sn}{}_{\mathrm{x}}\text{Te}$ heterojunctions with a long wavelength spectral cutoff (λ_c ≈ 6 μm) were prepared using the double-channel hot wall technique. The electrical and photoelectrical properties of the heterojunctions at 77, 197 and 300 K were investigated. Detectors with R_oA equal to 170 Ω cm² and a quantum efficiency of 25–40% were obtained. Reasons for the shift of the long wavelength spectral cutoff of the heterojunctions towards shorter wavelengths are given.     

Reactive plasma deposited SixCyHz films

Si_xC_yH_z films have been prepared at 200°C by reactive plasma deposition from SiH₄ and CH₄ diluted in helium in a tubular reactor. These films have a ratio s (equal to $\text{Si}\text{(}\text{Si+C}\text{))}$ ranging from 0.2 to 0.8, a refractive index ranging from 1.96 to 2.6 and an optical energy band gap in the range 2.7-2.2 eV. The total quantity of hydrogen in the film is 40% when s=0.5. Infrared analysis shows that these films have large fractions of homonuclear bonds and that this material is best described as a polymer. Mass spectrometric measurements of the gaseous products formed in the SiH₄-CH₄-He plasma have been performed and the results are related to the composition of the deposited layers.     

Core-current-enhanced domain-wall pinning in nanocrystalline Fe/sub 73.5/Cu/sub 1/Nb/sub 3/Si/sub 15.5/B/sub 7/ ribbon

We have studied the influence of surface fields H/sub p/ (generated by either direct or alternating core current) on soft magnetic properties of amorphous and nanocrystalline Fe/sub 73.5/Cu/sub 1/Nb/sub 3/Si/sub 15.5/B/sub 7/ ribbon. While in an amorphous ribbon the coercive field H/sub c/ decreases with H/sub p/, in the same optimally annealed ribbon (H/sub c/=1.3 A/m, M/sub m//spl ap/M/sub s/) H/sub c/ increases with H/sub p/ for all the explored types of H/sub p/ (static and dynamic with different phases with respect to that of the magnetizing field H). The unexpected increase of H/sub c/ in nanocrystalline ribbon is associated with the influence of H/sub p/ on the surface and main (inner) domain structure. Here, we develop a model that takes into account this influence and explains the experimental results.