Superconducting joint of Bi-2223/Ag superconducting tapes by diffusion bonding

61-Filaments Bi-2223/Ag superconducting tapes have been joined by diffusion bonding. The critical currents (I_Cs) of the joints are obtained by using standard four probe method under no magnetic field in the liquid nitrogen. The microstructures of the joints are evaluated by the electron microscope in electron backscatter diffraction mode and the phase compositions of the superconducting cores of the joint and the original tape are determined by X-ray diffraction (XRD). The results show diffusion bonding is effective bonding technique for HTS tapes, and the bonding time is reduced greatly from hundreds of hours to a few hours, and the bonding pressure also changes from 140–4000 MPa to 3 MPa. Furthermore, the diffusion bonding joints sustain superconducting properties, and the critical current ratios (CCR_O) of the joints are in the range of 35%–80%. Microstructures of the typical joint display a good bonding and some defects existed in traditional method are avoided. XRD results show that the phase compositions of the superconducting cores have no obvious changes before and after diffusion bonding, which offers physical and material bases for high superconducting property of the joints.     

Study of air heat treatment on Bi-2223/Ag superconducting tapes

Heat treatment has been carried out on commercially available Bi-2223/Ag superconducting tape under various temperature conditions in air. The critical currents (I_C) of tape after heat treatment at different annealing temperatures were tested at the liquid-nitrogen temperature. The microstructures and phase constituents of the tapes were investigated by SEM and XRD, respectively. The results indicate that annealing temperature has a very important influence on the superconducting properties of the tapes. When the temperature is above 840 °C, I_C value drops dramatically. Furthermore, when the temperature reaches up to 860 °C, the tape loses most of its superconducting property because of the decomposition of the superconducting phase Bi-2223.     

添加超导中间层扩散连接BSCCO带材

采用超导粉末作中间层对BSCCO带材进行连接是比较有效的方法.超导粉末中间层中Bi-2223超导相的含量影响着连接的效果,超导相含量为88.5%的中间层连接所得到的接头的连接效率比含量为55%的中间层连接的接头的连接效率高18个百分点.另外在超导粉末中间层中添加适量的金属Ag可以有效的降低中间层的熔点,增加中间层的粘性,减少连接的缺陷,提高连接的质量.     

Bi-2223喷雾热分解粉末热处理工艺优化

Bi-2223带材目前在电流引线、超导电机、超导电缆、超导限流器等领域实现了许多示范性应用,载流性能是表征其性能的重要指标,而高质量的前驱体粉末是最终带材性能的关键保障.本文选用具有工艺简单、粉末效率高、批次稳定性好等优点的喷雾热分解法制备的Bi-2223前驱体粉末,利用TG-DSC、XRD、SEM等测试手段对低氧条件下不同保温时间烧结的粉末进行分析,并结合最终带材的载流性能测试结果,获得了最优粉末烧结参数,为后续喷雾热分解粉末的进一步生成Bi-2223相以及高性能粉末的制备提供了依据.     

Reactivity and oxygen diffusion property of resistive barriers for Bi-2223/Ag tapes

Reactivity of several oxide materials (OM) with BSCCO powder and oxygen diffusion through OM layer has been tested at temperature ≈840 °C in air. The OM (e.g.: BaZrO₃, SrCO₃, MgO and ZrO₂) showing the low or no reactivity with BSCCO have been mixed (10 wt.%) with precursor powder and used for single-core tapes. Bi-2223/Ag/OM/Ag single-core tapes with oxide barriers made of BaZrO₃, SrCO₃, ZrO₂ and Al₂O₃ have been also prepared by a standard powder-in-tube technique. The used OM in the direct contact with BSCCO influences the electrical properties of Bi-2223 phase differently. These is because the oxides react with BSCCO during the heat treatment and simultaneously affect the 2212→2223 phase transformation, the Bi-2223 grain growth and so also grain connectivity. SrCO₃ powder has been evaluated as the best material from the point of no destructive effect on 2223 phase transport current property. The oxide barrier controls the oxygen diffusion during the tape heat treatment and simultaneously the HTS phase formation kinetics, its purity and content within the superconducting core. For single-core Bi-2223/Ag/OM/Ag tapes, the highest current density was measured for Al₂O₃ due to only slightly reduced oxygen diffusion through the barrier.     

收集方式对喷雾热分解Bi-2223 前驱粉末的影响

采用国产喷雾热分解设备制备了Bi-2223 前驱粉末, 分别选用一步收集和分级收集热分解后的粉末, 对不同方式收集的粉末进行了XRD 分析、SEM 观察以及ICP-AES 分析, 对比了粉末在相成份以及含量、 外观形貌、 粒径大小和元素原子配比等方面的差别, 最终发现采用一步收集方式采集的粉末在相组成、 成分均匀度以及原子配比方面均优于分级收集粉末, 一步收集方式更适合于收集Bi-2223 喷雾热分解粉末.     

Addition of nanometer SiC in the silver-sheathed Bi2223 superconducting tapes

Nanometer SiC particles were added to (Bi,Pb)₂Sr₂Ca₂Cu₃O_x (Bi2223) precursor powders and the powders were transformed into silver-sheathed superconducting tapes by the standard powder-in-tube (PIT) technique. The influence of SiC on the melting temperature, high-T_c (Bi2223) phase formation, microstructure and transport property of the tapes was studied by means of DTA, XRD, SEM/EDX, electrical and magnetic measurements. The results showed that SiC addition lowered the melting temperature of the superconductor powders and consequently, decreased the optimum sintering temperature of the tapes. However, the addition did not affect the Bi2223 phase formation and critical temperature (T_c) of the tapes up to 1.00 wt.% of SiC. Most importantly, the addition of a small amount of SiC (0.15 wt.%) improved the critical current (I_c) and I_c behavior in magnetic field as a result of the enhancement in density, grain alignment, grain connectivity and flux pinning of the tapes.     

Influence of Precursor Powder Fabrication Methods on the Superconducting Properties of Bi-2223 Tapes

Bi-2223 precursor powders are prepared by both oxalate co-precipitation(CP) and spray pyrolysis(SP) methods.The influence of fabrication methods on the superconducting properties of Bi-2223 tapes are systematically studied. Compared to the CP method, SP powder exhibits spherical particle before calcination and smaller particle size after calcinations with more uniform chemical composition, which leads to a lower reaction temperature during calcination process for Bi-2223 tapes. Meanwhile, the non-superconducting phases in SP powder are more uniformly distributed with smaller particle sizes. These features result in finer homogeneity of critical current in large-length of Bi-2223 tape, higher density of filaments and better texture after heat treatment. Therefore,the SP method could be considered as a better route to prepare precursor powder for large-length Bi-2223 tape fabrication.     

Bi-2223/Ag超导带材的失超传播速度研究

文中对超导带材的失超产生机理进行了详细分析,建立了其失超传播的计算模型。在此基础上,对Bi-2223/Ag高温超导带材失超传播进行了实验研究,用四引线法测得不同条件下其失超传播的U-t曲线,由此计算出Bi-2223/Ag超导带材的失超传播速度为0.4cm/s～1.98cm/s。实验结果表明:带材的失超传播速度与载流大小有关,与触发失超的能量无关,带材载流越大,失超传播得越快。     

Investigation of Bi-2223 high temperature superconducting tape as the material for gradient coil in MRI

The use of Bi-2223 high temperature superconducting (HTS) tape as a material for gradient coils in MRI is evaluated in this paper. Bi-2223 tapes have a very high critical current and a very low power loss. A HTS tape gradient coil is expected to provide much higher gradient strength and generate much lower heating than a copper coil. Measurements of the AC power loss of Bi-2223 tapes at typical operating frequencies for gradient coils are presented. The degradation of the critical current and its effect on the increase of AC power loss is analyzed. Practical technical issues such as resistance, gradient strength and mechanical performance are also discussed. A prototype Bi-2223 HTS tape gradient coil is evaluated to verify the concept.     

The frequency dependence of AC transport losses in stacked Bi—2223／Ag superconducting tapes

AC transport losses in a single superconducting tape, double-and triple-stacked Bi-2223/Ag superconducting tapes were measured by use of electrical method. The measurements were carried out at 77K with the frequency of AC transport currents ranging from 50 to 100Hz. The dependence of AC losses on frequency and the number of tapes in the stack were presented and analysed.     

Bi-2223/AgAu 带材及应用进展

Bi-2223/AgAu 高温超导带材因为较低的热导率和较高的载流性能, 被认为是制备高温超导电流引线的最佳材料之一. 这篇文章简单介绍了高温超导电流引线的工作特点和不同包套 Bi-2223 带材的热导率, 在此基础上详细介绍了目前 Bi-2223/AgAu 带材和高温超导电流引线国内外研究进展, 最后展望了 Bi-2223 带材的发展趋势.     

Soldering of Bi-2223/Ag high temperature superconducting tapes with Sn–Pb–Bi–Ag alloy paste

Soldered joints of Bi-2223/Ag-sheathed high temperature superconducting multifilamentary tapes were fabricated using 63 wt.%Sn–34 wt.%Pb–1 wt.%Bi–2 wt.%Ag paste. The soldered joints were observed by scanning electron microscope (SEM) and X-ray diffraction (XRD). Moreover, the electrical properties of joints were evaluated by current–voltage curves, and the tensile strengths of the joints were also tested. The results show that the soldered joint consists of Ag sheath – Ag₃Sn compound layer – PbSn₂ and Ag₃Sn solder layer – Ag₃Sn compound layer – Ag sheath. The joints are obeyed with Ohms Law and the magnitude of the joint resistance, which deceases with the increase of the overlap length, can reach the order of 10^?8 Ω. The tensile strength of the joints with a brittle fracture mode is a little lower than that of the original tapes.     

一维热传播模型下高温超导带的失超特性研究

对Bi-2223/Ag高温超导带材的失超传播特性进行了研究。测量了Bi-2223/Ag带材在有绝缘材料包裹和液氮浸泡环境下的电压变化曲线,同时利用一维热流方程模型,模拟出超导体失超传播过程中由超导态过渡到正常态的温度变化行为,同时还对传输电流和触发能量对失超传播速度的影响进行了实验研究。这些工作对高温超导磁体及电力系统的应用有着重要的参考价值。     

Effect of secondary phases evolution in the first sintering process on the critical current density of Bi-2223/Ag tapes

Effect of the evolution of the secondary phases in the first sintering process on the microstructure and critical current density of Bi-2223/Ag tapes has been studied. The amount and grain size of secondary phases were characterized by XRD and SEM/EDS. It has been found that both the microstructure and critical current of the fully reacted tapes depended strongly on the secondary phases formed in the first sintering process. The (Ca,Sr)₂CuO₃ and (Ca,Sr)₁₄Cu₂₄O₄₁ phases were easily formed and to be stable at higher temperature, however, at lower temperature, the CuO particles appeared easily and keeping stable with dwelling time. The best conversion to Bi-2223, together with the lowest amount of the total secondary phases was achieved when samples treated at 830 °C in 8.5% O₂. Samples with the lowest amount and minimum size of secondary phase produced in the first sintering process will obtain the best performance of the fully reacted tapes. The optimum sintering parameters are obtained by controlling the evolution of the secondary phases during the first sintering process.     

35kJ高温超导储能磁体的优化设计

介绍了35kJ高温超导储能磁体的设计步骤。为了减少常规寻优方法的计算量,将加权粒子群优化算法(WPSO)引入到高温超导储能磁体的优化设计中,给出了用B i-2223超导线材进行35kJ储能磁体设计的优化结果,分析了高温超导线材的各向异性对磁体临界电流的影响,并比较了两种不同的单螺线管磁体结构在不同优化目标的情况下,超导线材用量和杂散磁场的分布的变化。     

Influence of tape-specific properties on local stress and strain in Bi-2223/Ag tapes

Superconductors are typically fragile, and their superconducting properties are reduced under strain. Moreover, superconductor wires operate under large mechanical loads in most applications. Thus, a careful mechanical analysis is essential when designing superconducting applications. So far, plenty of experimental and computational studies concerning stress and strain in, e.g. Bi-2223/Ag tapes have been carried out. However, Bi-2223 tapes contain several properties that vary between different tapes and are often unknown when designing a specific application. The largest uncertainties are related to the creep at high temperatures, stiffness and anisotropy of filaments and the yield strength of silver. In this paper, the influence of uncertainties on the local stress and strain in Bi-2223/Ag tapes is studied computationally to determine efficient strategies to reduce inaccuracy of the results. The results suggest that the filaments can be described as an isotropic material and the filament stiffness is the most important input parameter to estimate the total stiffness of the tape.     

Mechanism of Bi2Sr2CaCu2Ox crystallization and superconducting properties for Bi2Sr2CaCu2Ox/Ag tapes prepared using isothermal partial melting method

The mechanism of Bi₂Sr₂CaCu₂O_x (Bi-2212) crystallization from a partially molten state has been studied by means of thermal analysis, X-ray diffraction (XRD) measurement, and microstructural observation in Bi-2212/Ag tapes. Tapes have been prepared using the isothermal partial melting (IPM) method, under which partial melting and solidification are carried out at the same temperature in an nitrogen atmosphere and 20% oxygen partial pressure (p(O₂)), respectively. The Bi-2212 phase crystallizes by peritectic reaction between (Sr, Ca)CuO₂ (1:1 phase) and the liquid phase at processing temperatures (T_p)≥855°C. At the beginning of Bi-2212 crystallization, only the 1:1 and the liquid phases are present in tapes. The Bi-2212 nucleation occurs in the vicinity of 1:1 grains (homogeneous nucleation). This peritectic reaction progresses by recovery of oxygen in the liquid phase. In contrast, the nucleation of the Bi-2212 phase occurs heterogeneously at T_p≤850°C. The Bi-2212 phase co-exists with four Bi-free phases ((Sr, Ca)₁₄Cu₂₄O₄₁ (14:24 phase), (Sr, Ca)₂CuO₃ (2:1 phase), (Sr, Ca)O (1:0 phase), and the 1:1 phase) and the liquid phase in the early stage of the Bi-2212 crystallization step. Since the precipitation temperature of the Bi-2212 phase is higher than 850°C, the Bi-2212 crystallization progresses by direct precipitation. The crystallization paths affect microstructure and transport critical current density (J_c) of Bi-2212 tapes.     

Gel stabilization in chelate sol–gel preparation of Bi-2223 superconductors

A chelating sol–gel method was used for the preparation of the superconducting Bi-2223 phase. We compared pH range of both solution and gel stability in samples with EDTA, TEA and their equimolar mixture addition. A pH range of stability (for precipitation) was extended in EDTA solutions with addition of TEA. IR spectroscopy was used to identify the type of bonding between EDTA and TEA in a stabilized solution. IR bands belonging to polyester bonding were found in the IR spectra of gels prepared at 130 °C. We describe the influence of both gel decomposition and calcinations regime on the evolution of Bi-2223 phase. The optimized temperature treatment was used for the comparison of superconducting transport and of magnetic properties of the prepared samples. Moreover, an extra 800 °C calcination step was tested to enhance the decomposition of unfavorably formed carbonates.     

Bi-2223复合导体直流磁场下自场损耗热稳定性分析

对于一种Bi-2223的复合导体,利用ANSYS软件,我们分析了在直流磁场下励磁过程中,自场损耗对复合导体热稳定性的影响;然后假定Bi-2223超导带内不同的损耗值,通过计算,确定了达到超导带分流温度的最小损耗值。