火焰法制备非晶态“实心”炭纳米纤维的结构模型及其电输运行为

火焰法制备的非晶态"实心"炭纳米纤维内部原子排列无序紊乱,依靠常规的表征手段,难以得到其三维原子构型分布。根据非晶态"实心"炭纳米纤维的XRD图谱提供的衍射强度数据,采用逆向蒙特卡罗法,重构了非晶态"实心"炭纳米纤维的微观原子构型,并对获得的模型进行充分的误差分析。计算得到了非晶态炭纳米纤维的费米能级及其导电机制,认为其具有半导体特征;实验测量单根非晶态"实心"炭纳米纤维的电输运行为发现,其I-V曲线呈现对称和非线性特征,且电阻随着温度的升高而下降,进一步证明非晶态"实心"炭纳米纤维的原子构型具有一定的真实性。     

Ba-Y-Cu-O系陶瓷厚膜材料

本文报导采用典型的微电子学厚膜工艺即丝网印刷法,制备Ba-Y-Cu-O系的陶瓷厚膜超导材料,研究了不同热处理温度及时间对厚膜材料性能的影响。实验证明,陶瓷超导材料的厚膜工艺设备简单,适合于大规模生产。用这种方法制备的厚膜超导材料已具有较高的临界超导转变温度:T_c(mid)=80K,T_c(ρ=0)=72.1K,而且工艺稳定,重复性好。     

Fe25 Co25 Ni25 Cr5 P10 B10高熵块体非晶态合金磁热效应的研究

利用Fluxing提纯处理和J-Quenching技术相结合的方法成功制备了最大尺寸为1.2 mm的Fe_(25)Co_(25)-Ni_(25)Cr_5P_(10)B_(10)高熵块体非晶态合金,并对它的磁热性能进行的表征和研究,以探讨高熵效应对非晶态合金磁热性能的影响。目前的高熵块体非晶态合金的居里温度为572 K。在外加磁场为1.5和5 T时,它的最大等温磁熵变和制冷能力的值分别为0.66 J/(kg·K),42.9 J/kg和1.88 J/kg,136.1 J/(kg·K)。与其它非晶态合金磁热性能的对比显示,高熵效应对非晶态合金磁熵变似乎并没有明显影响,但高熵非晶态合金磁熵变随温度变化曲线显示了较大的半高宽温度区间。     

Y-Ba-Cu-O厚膜超导材料

本文报导了采用丝网印刷法制备 Y-Ba-Cu-O 系厚膜超导材料的工艺以及热处理对厚膜超导体微结构、超导电性的影响。在 ZrO_2基片上烧出的厚膜,其临界温度 T_(c(p-o))>77K。     

高炉渣中非晶态物质含量的定量分析

首先通过化学分析法和X射线衍射法,准确确定高炉渣中的物相组分,然后通过加入标准物质CaF_2,对高炉渣的物相组分进行定量分析,并使用K值法计算出非晶态物质的含量。结果表明:采用X射线衍射法和K值法相结合的方法可以快速准确地测得高炉渣中非晶态物质含量;且标准物质CaF_2的加入质量分数控制在20%时,测定结果更加准确。     

国际热核聚变(ITER)用低温超导线研究进展

国际热核聚变实验反应堆(ITER)是目前伞球最大的国际合作研究项目.该计划将首次建造可实现大规模聚变反应的聚变实验室.研究解决核聚变关键技术难题,是人类实现受控热核聚变研究走向实用化关键的步骤.由低温超导线材绕制的磁体系统是ITER装置的核心部件.我们通过开展Nb3Sn及NbTi超导线批量化制备技术的研究,掌握了纵向场(TF)磁体及极向场(PF)磁体用高性能Nb3Sn及NbTi超导线制备的关键技术.生产出性能达到ITER项目的设计要求的青铜法Nb3Sn超导线和内锡法Nb3Sn超导线,单根长度大于5 000 m,临界电流Ic(4.2 K,12 T)均大于190 A,磁滞损耗小于500 mJ/cm3(4.2 K,±3 T),n值大于25;制备出满足ITER项目要求芯数为2 600根的NbTi超导线,单根长度大于10 000 m,临界电流Ic值达到360 A(4.2 K,5 T),n,值大于30,磁滞损耗值小于45 mJ/cm3.(4.2 K,±3 T)的技术指标.     

锆钒合金非晶膜的制备及性能研究

采用磁控溅射法制备出V/Zr比为2:1的非晶态锆钒合金膜,系统研究了合金膜的物相、表面成分、生长形貌和动态力学性能。研究结果表明,在533～773K的沉积温度区间内,合金膜呈现非晶态,表面存在约26nm厚的氧化层,其组成与膜基体显著不同;合金膜在钼基片上以球形岛状模式生长;膜的动态硬度DHT115和弹性模量Eit/(1-υ2)随沉积温度的升高在583K处出现极大值,分别达到436.8GPa和1.13E+5N/mm2。     

组成对Bi系微晶玻璃超导纤维性能的影响

用熔体快速淬冷法制备了数种Ｂｉ（Ｐｂ）ＳｒＣａＣｕＯ玻璃，进而用动态加热荷重法将这些玻璃拉成纤维。用Ｘ射线衍射、差热分析、电子探针和能谱及电流测量、拉丝试验等手段研究了玻璃成分变化对成丝能力和晶化后超导性能的影响。结果表明，Ｓｒ、Ｃａ含量的变化不仅对超导性能，而且对玻璃成丝能力有很大影响。获得的超导纤维的最大长度为５３ｃｍ，在７７Ｋ和零磁场下超导短纤维的最高电流密度Ｊｃ＝１５Ａ／ｃｍ＾２。     

二硼化镁超导线带材及磁体应用研究进展

由于具有超导转变温度（39K）较高,晶体结构简单,原材料成本低廉以及长线制备容易等一系列特点,金属间化合物二硼化镁（ MgB2）超导体自2001年被日本科学家发现以来,引起人们广泛的关注,被认为是目前最有可能首先实现大规模工业应用的超导材料。尤其在制冷机工作温度（15～20 K）、较低磁场（1～2 T）条件下的医疗核磁共振成像仪（ MRI）超导磁体应用上有着广泛的前景。本文主要围绕实用化 MgB2超导长线（带）制备研究而展开,重点回顾了近年来粉末套管法、连续粉末装管成型法及中心镁扩散法等MgB2超导线（带）材制备及加工方面的最新研究进展;同时综述了在 MgB2超导线带材工程临界电流密度性能改进方面的最新研究工作;最后,对近几年来 MgB2超导磁体及线圈等应用研究进展进行了回顾。     

超导线圈的等效热膨胀系数的理论与实验研究

给出了计算超导线圈等效热膨胀率的理论模型和计算方法,对比了各种测量材料线膨胀系数的实验方法,并且给出了低温应变片测量热膨胀系数的技术原理.采用低温应变片法测量了矩形截面导线缠绕成型的超导线圈由77 K到300 K的线膨胀系数,并将实验测试结果与理论计算结果进行了对比分析.     

High-temperature superconducting dual-mode resonator on (100) MgO substrate

We report, for the first time to our knowledge, a clear resonant peak split in the range of 7.7–9.7 GHz in a perturbed dual-mode disk-type resonator (DMDR) made of YBa₂Cu₃O_7–x (YBCO) superconducting thin film on MgO substrate. Epitaxial YBCO superconducting thin films were grown on (100) MgO substrates by pulsed laser deposition technique. The critical temperature of superconducting thin film on MgO substrate was 85 K. Superconducting dualmode disk resonators were designed by microwave design software, EEsof, and patterned by photolithography and a wet-etch process. The unloaded quality factor (Q_UL) of the superconducting DMDR was found to be 1,312 at 77 K. We believe this type of DMDR can be utilized for dual-mode resonator-based filters for satellite communications.     

Superconductivity above 90 K in the Bi-Mg-Sr-Ca-Cu-O system

Investigations on the influence exerted by magnesium on the superconducting properties and phase composition of samples from the Bi-Mg-Sr-Ca-Cu-O system are reported. The synthesized materials are analyzed by X-ray diffraction, emission spectral analysis, scanning electron microscopy, and electrical resistance measurements as a function of temperature. It is found that the addition of magnesium results in changes in the phase composition of the materials. The critical temperature is in the range of 93–95 K. The addition of Mg in certain optimum concentrations can have a positive effect on the superconductivity of the Bi-Sr-Ca-Cu-O system.     

Structural and electrical properties of the Y-Ba-Cu-O superconducting films prepared by spray pyrolysis

High-T _c , superconducting YBa₂Cu₃O_7– thin films have been grown on (100) MgO substrates by a chemical spray pyrolysis method. The crystal structure and surface morphology have been studied by X-ray diffraction and scanning electron microscopy, respectively. The assprayed films were amorphous and insulating, but upon annealing the films became superconducting and show a textured surface morphology with an average grain size of the order of 5–15m. The films were highly oriented with thec-axis being perpendicular to the substrate surface. Three different microstructures were recorded: long rod-shaped grains, platelet or rounded-shape grains, and a melting-like growth. Electrical measurements were carried out in a low-temperature cryostat using a standard d.c. four-probe technique. The onset transition temperature was around 83–86 K, and the completion of the transition to zero resistance was in the range 73–78 K. The magnitude of the measured critical current density was in the range 750–3750 A/cm² at 30 K. A correlation between the resistance of the tunnelling junctions and the critical current density was found from the theoretical models.     

连续致密 Bi 系/Ag 基超导复合带的制备

用电流加热熔化涂层法制备出结构致密、涂层均匀的 Bi 系/Ag 基超导复合带。条带可连续制备,且有较强的抗弯曲性能,在3mm 弯曲半径下不出现裂纹。热外理后样品的扫描电镜(SEM)形貌分析、EDAX 成分分析及表面 X 射线衍射结果表明,复合带界面结合紧密,超导层结构致密,成分均匀,而且组织有明显的织构特性。经860℃,50h 处理的样品,在零磁场、77K 下,临界电流密度为2.2×10~2A/cm~2。     

基于液氮冷源超导磁体氦气循环预冷系统设计

为了提高超导磁体300-80 K预冷过程中的降温效率和安全性,开发了一种新的预冷方法.设计了一台以液氮为冷源、氦气为循环介质的可控温预冷装置,对其内部结构进行了优化设计,包括低温风机、板式换热器、气动调节阀、翅片换热器等主要组成部分,整个装置与磁体构成一个闭合循环系统.在预冷装置的作用下,该超导磁体从300 K到80 ...     

DC-sputtered Bi(Pb)SrCaCuO films on single (MgO) and polycrystalline (MgO,CuO) substrates

Bi(Pb)SrCaCuO films have been deposited on single (MgO) and polycrystalline (poly MgO, CuO) substrates by DC sputtering. All the films became superconducting after post-annealing them in air. The films on single crystal MgO showedT _c onset at 120 K andT _c at 92 K. However, the extrapolated zero resistivity is obtained at 106 K. The ac susceptibility showed an onset at 106 K and a sharp transition at 85 K. The films on poly MgO and poly CuO had aT _c=72 K. The preparation, X-ray diffraction and morphology of these samples are presented.     

Chemical fabrication of superconducting Y-Ba-Cu oxide films

High-T _c superconducting films of Y-Ba-Cu oxide were prepared on (100) MgO substrates by a chemical sol gel method. A procedure is described for preparing a superconducting film using acetate compounds dissolved in salicylic or lactic acids in the presence of ethylene glycol. This solution has superior qualities in terms of homogeneity, viscosity, and stability against atmospheric hydration. The results indicate that the nature of the solvent influences the microstructure and superconducting properties of Y-Ba-Cu-O films. X-ray diffraction analysis reveals that the annealed films are textured and had orthorhombic orientation. Transport measurements indicated that the onset temperatures of the superconductivity transition occurred between 82 and 95 K. The zero-resistance transition temperature was above the boiling point of the liquid nitrogen. The highest critical current density was 2700 A/cm² at 20 K. It is also demonstrated experimentally that the results obtained from the X-ray diffraction analysis alone cannot provide a good criterion for evaluating the quality of a superconductor. A correlation between the crystal structure and the superconducting properties of the Y-Ba-Cu-O films is presented.     

Field enhancement in superconducting solenoids by holmium flux concentrators

The magnetic field strength in the bore of a 13 T superconducting solenoid was enhanced to 16 T in the 5.5 mm gap between two cylindrical holmium flux concentrators. This method is an economic way of extending the field region for measuring critical data of superconducting materials. The measured dependence of the gap field on coil current was reproduced in computer calculations by fitting the magnetization curve of holmium at 4.2 K. This curve may be used for optimizing the geometry of holmium flux concentrators at 4.2 K.     

Superconducting properties of the Bi-Ca-Sr-Cu-O system

The electrical properties of unquenched and rapidly quenched bulk samples of granular Bi₂-Ca₁-Sr₂-Cu₂-O _x system have been studied. Electrical resistivity measurements show superconductivity transition temperature (R=0) at 72 K, 80 K and 90·5 K. X-ray crystallographic studies show that most samples were of single-phase.     

Formation and characterization of Y : 247 film through spray pyrolysis technique

The synthesis of high temperature superconducting films of Y : 247 (T _c ～ 73 K) have been successfully achieved. The difficulty in synthesis owing to narrow range of stability of Y : 247 has been taken care of through several quenching modes, e.g. quenching of the films synthesized at ～850°C, in air or in liquid nitrogen. The energy dispersive analysis of X-rays (EDAX) and transmission electron microscopy (TEM) studies of the as processed film, Y₂Ba₄Cu₇O_14+x, exhibit nearly correct cationic stoichiometry of 2 :4 :7; also narrow regions (< 50 Å) of minority Y : 124 phase and stacking faults capable of working as flux pinning sites have been invariably found to be present. In addition to Y : 247, Ag admixed films have also been investigated. TheT _c here is ～ 70–75 K which is similar to that of the film without silver. Representative estimates of transport critical current density (J _c) for Y : 247 films is ～10³ A/cm², and with silver corresponding to Y₂Ba₄Cu₇O_14+x (Ag_0.1) is found to be ～ 10⁴ A/cm².