共查询到20条相似文献,搜索用时 109 毫秒
1.
由德国德累斯顿金属材料研究所的约根·意科特领导的研究小组采用一种机械合金化工艺制备了具有高临界电流密度的大块MgB2超导体,这种超导体在20K,1T磁场下临界电流密度为10000A/cm2,并具有较高的不可逆场.他们认为,由于在这种材料中含有直径大约为40nm~100nm的球形晶粒,并存在大量的晶界,因此改善了磁通钉扎特性,提高了临界电流密度. 相似文献
2.
以Mg粉和B粉为主要原料,采用两种烧结方法制备出MgB2超导体.利用x射线衍射仪、扫描电子显微镜、阿基米德法和标准的直流四引线法等,分别研究了样品的物相组成、显微结构、密度和临界电流密度等.研究发现,MgB2块材的密度随Mg粉粒度的增加而降低.与常规烧结相比,快速烧结时MgB2块材的密度较低且含有更多的非超导相,如Mg和MgBx(x=4,6或12).快速烧结MgB2线材的临界电流密度低于常规烧结线材的.结果表明,快速烧结不利于获得高性能的MgB2超导体. 相似文献
3.
4.
5.
尽管MgB2超导线材的临界转变温度相对较低,但MgB2没有晶界弱连接,因而具有低的加工成本,相对于BSCCO和YBCO表现出明显的应用优势.目前,粉末装管技术(PIT)广泛用于制备MgB2带材和线材.利用高能球磨工艺的超细粉末制备的MgB2线材临界电流密度达到3.0×105 A/cm2(20 K,自场).为了了解MgB2线材的实际使用条件和提高使用条件下的性能,很有必要对其进行机械性能方面的研究. 相似文献
6.
熔化法制备的超导体具有较高的临界电流密度,为了防止超导体内产生显微裂纹,在制备超导样品时以Ag2O的形式加入微量的Ag. 相似文献
7.
8.
9.
10.
分别制备了8%(质量分数)的TiC和5%(质量分数)的SiC掺杂的MgB2超导块材,并对比分析了这两种掺杂物对MgB2超导块材的性能影响。所有样品均在流动的Ar气保护下在不同退火温度下退火,研究发现TiC掺杂和SiC掺杂的MgB2样品的最优化工艺参数分别是900℃保温1h和720℃保温1h。随后采用XRD和SEM分别对样品进行了相成份和微观结构的分析,并采用PPMS测试了样品的磁滞回线并由Bean模型计算出了样品的临界电流密度。在4.2K,0T下TiC掺杂的五值为1.0×10^5A/cm^2,而10K,0T下SiC掺杂样品的五值为4×100A/cm^2。而且随着外加磁场的增加,SiC掺杂MgB2样品的五值下降得比TiC掺杂的MgB2样品要缓慢很多,这表明了SiC掺杂比TiC掺杂更有利于改善MgB2在高场下的超导电性能。 相似文献
11.
12.
通过调整超导线材的最终附加应变、时效热处理时间和时效热处理温度3个参数来提高NbTiTa超导线材的J_c性能.在法国国家高场实验室通过标准四引线法,在4.2K、0~11T的磁场中测量了线材的临界电流.结果表明,适度升高时效热处理温度、延长时效热处理时间、增加最终附加应变,有益于提高NbTiTa超导线材的临界电流密度.经4次时效热处理385~C×(40~70)h,最终附加应变从2.5增加到3.5,Φ1.25mm超导线材的J_c在4.2K、8T下达到777A/nm~2,与国外文献报道的J_c值相当. 相似文献
13.
Feng Xue Zhaoxia Zhang Jun Zeng Xiaofan Gou 《Journal of Superconductivity and Novel Magnetism》2016,29(8):2023-2029
An analytical investigation is presented to display the distribution of critical current flow and trapped magnetic field around an elliptical nonsuperconducting inclusion within a long cylindrical superconductor. The current streamlines, the critical current density, and the trapped field around the inclusion in the superconductor without deformation are obtained based on the Bean model and the method of conformal mapping. The results show that the critical current density of a superconductor will be decreased dramatically due to a macroscopic nonsuperconducting inclusion. Besides, the maximum trapped magnetic field is limited by the inclusion. 相似文献
14.
This paper presents a numerical (finite element) analysis of superconductor stability and current propagation under random variations of critical superconductor parameters. Instead of using singular (homogeneous) values, random variations potentially are appropriate to take into account any conductor inhomogeneity that can be considered as an obstacle to current propagation. Traditional assumptions like homogeneous current distribution, critical temperature, critical current density and critical magnetic fields are not justified in general; a local disturbance (for example, release of mechanical stress energy), if not immediately distributed by solid conduction, would generate a transient increase of local conductor temperature. Local critical current density and magnetic field then will be reduced, and current distribution will change. Disturbances may arise also from transport currents that locally exceed the critical current of the superconductor. Disturbances of all kinds may increase the conductor temperature above its critical value. A local analysis of all superconductor states thus is mandatory to safely avoid a quench. As an extension of standard stability models, also flux flow resistive states are taken into account. We will try to find a possibly existing correlation between current propagation and superconductor stability. Fault current limiting is discussed as a special case of current propagation. The analysis is applied to a bundle of high-temperature superconductor (HTSC) filaments. As will be shown, temperature profiles in a superconductor do not allow a clear distinction between Ohmic resistive or flux flow resistive fault current limiting. Though frequently made in the literature, this separation is highly questionable, because Ohmic resistive and flux flow resistive states may locally coexist, side by side, but are not very stable in the superconductor volume. 相似文献
15.
Flux-Pinning-Induced Stress and Deformation Analyses of a Long Rectangular Superconducting Bicrystal
Feng Xue Wenqing Zhang Jun Zeng Xiaofan Gou 《Journal of Superconductivity and Novel Magnetism》2016,29(10):2495-2501
The flux-pinning-induced stress and deformation of a long rectangular superconducting bicrystal with an arbitrary aspect ratio are analyzed based on the critical-state model and the finite element numerical method. The flux and current distributions in the superconductor with a low-angle grain boundary (GB) are obtained based on a constant GB critical current density assumption. The distributions of the stresses within the superconductor are obtained for different magnetization stages. The deformation and especially the shape distortion in the irreversible magnetostriction of the superconductor are analyzed. In addition, the relation between the maximum stress on the grain boundary and the ratio of the GB critical current density to the grain critical current density is discussed when the applied magnetic field is reduced to zero. 相似文献
16.
在金属有机盐沉积(MOD)法制备YBCO薄膜的工艺中, 采用无F的α甲基丙烯酸铜取代原来的三氟乙酸铜, 可以降低前驱溶液中大约50%的氟含量. 研究表明, 该方法大大缩短了YBCO前驱薄膜受热分解的时间, 仅为原来的1/7. 通过XRD、SEM分析发现, 该方法可以制备成分单一、具有良好立方织构的YBCO薄膜, 且薄膜表面平整致密, 没有裂纹, 临界温度(Tc)达到了90K左右, 77K、自场下的临街电流密度(Jc)达到了2.84MA/cm2. 通过在制备的YBCO薄膜中引入6mol% 的 Zr元素掺杂, 有效地提高了YBCO薄膜在外加磁场下的超导性能. 相似文献
17.
18.
TSUGIO HAMADA YOSHIHISA OHZONO TADAHIRO AKUNE NOBUYOSHI SAKAMOTO 《Journal of Materials Science》1997,32(13):3469-3473
The critical current density, Jc, in fluorine-doped YBa2Cu3Ox bulk superconductors has been measured at several temperatures. The measured Jc value is 108 A m-2 at 77 K and 0.5 T. A sample with a larger critical current density can be produced by the addition of a small amount of platinum during the sintering process. The added platinum has the effect of evenly distributing Y2BaCuO5 particles and voids in the matrix in comparison with the undoped sample. These distributions of Y2BaCuO5 particles and voids are reflected in an increase in the critical current density. However, these distributions are not directly related to the observed peak effect in the critical current density. If the fluorine-doped YBa2Cu3Ox superconductor consists of the matrix and a phase with a Ginzburg–Landau parameter, that is slightly different from that of the matrix, then the occurrence of the peak effect can be explained. 相似文献
19.
W. Witzeling 《低温学》1976,16(1):29-32
The penetration of screening currents induced in a hollow superconducting cylinder exposed to a transverse magnetic field is calculated two-dimensionally using a numerical model which simulates the superconductor by a system of parallel wires. Assuming the critical state model and taking account of the dependence of critical current density on magnetic field, the penetration depth and local current density is computed. 相似文献
20.
Formation peculiarities of the static thermo-electric modes that may be observed in high temperature superconductors at the DC current are studied taking into consideration the temperature-decreasing dependence of the power exponent (n-value) of the voltage-current characteristic of a superconductor. The used models are based on the steady zero-dimensional models. The study is made for the conduction-cooling and liquid coolant conditions at different operating temperatures. It allows us to investigate the non-isothermal voltage-current characteristic of Bi2223 and YBCO that rooted the development of their stable and unstable thermo-electric regimes. It is shown that the temperature dependence of an n-value may lead, first, to usually observed static voltage-current and temperature-current characteristics having one stable and unstable parts and, second, to unexpected thermo-electric states in the temperature range that is closed to its transition into the normal state. It is a result of the formal temperature variation of the differential resistivity of a superconductor depending on its temperature-decreasing critical current density and n-value. As a result, to describe correctly thermal stability conditions and analyze theoretically the quench processes in high temperature superconductors, the temperature dependences of their critical current density and n-value must be restored before the transition of a superconductor into the normal state as carefully as possible. 相似文献