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.     

前驱粉末对（Bi，Pb）-2223／Ag超导带材临界电流密度的影响

采用双相粉工艺即分别制备出2212粉末和（Ca2CuO3＋CuO）粉末，将它们分别热处理后，按照2223比例混合均匀，分别在四个不同温度下（800℃，815℃，830℃，845℃）进行了10h的烧结，并采用PIT技术制备出37芯超导带材．通过X射线衍射、SEM观察和临界电流的测试，分析了粉末不同烧结温度对（Bi，Pb）-2223／Ag超导带材临界电流密度的影响．结果表明：采用不同的前驱粉末制备的带材具有不同的临界电流密度，最佳的前驱粉末最终烧结温度是830℃左右．     

前驱粉末对(Bi,Pb)-2223/Ag超导带材临界电流密度的影响

采用双相粉工艺即分别制备出2212粉末和(Ca2CuO3 CuO)粉末,将它们分别热处理后,按照2223比例混合均匀,分别在四个不同温度下(800℃,815℃,830℃,845℃)进行了10h的烧结,并采用PIT技术制备出37芯超导带材.通过X射线衍射、SEM观察和临界电流的测试,分析了粉末不同烧结温度对(Bi,Pb)-2223/Ag超导带材临界电流密度的影响.结果表明:采用不同的前驱粉末制备的带材具有不同的临界电流密度,最佳的前驱粉末最终烧结温度是830℃左右.     

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.     

Pr离子缺陷对Bi-2223／Ag带材磁通涡旋运动的影响

Pr部分替代Ca可以在Bi-2223的超导层中引起局域缺陷（简称Pr离子缺陷），本文分析了不同含Pr量的Bi-2223／Ag带材在垂直于带面的外场下电阻转变特性，研究了其磁通钉扎势垒的变化规律．结果表明：Pr离子缺陷显著提高了Bi-2223带材的磁通钉扎势垒（U）．不同含Pr量样品的磁通钉扎势垒（U）均满足U／（1-Tirr／Tco）（1／H^α的规律．其不同α值反映了样品中不同的磁通蠕动方式．在不含Pr离子缺陷的样品中．磁通主要以双弯结的方式进行蠕动，含Pr离子缺陷的样品中磁通蠕动主要以直接剪切的方式进行．     

纳米银掺杂对Bi(2223)超导体的影响

研究了不同含量纳米银掺杂的（Ｂｉ,Ｐｂ）２Ｓｒ２Ｃａ２Ｃｕ３Ｏｘ块材。ＤＴＡ分析表明纳米银掺杂使材料熔点降低,加速了高Ｔｃ相的形成。磁场下Ｒ－Ｔ展宽测试表明,纳米银掺杂大大提高了磁通蠕动激活能,其中最佳掺杂１５ｗｔ％Ａｇ时激活能提高５～６倍;掺杂样品的钉扎能Ｕ（Ｈ）随磁场降低比非掺杂样品要慢,改善了磁场下的传输性能。交流磁化率测量表明纳米银掺杂使晶间损耗峰向高温移动２０Ｋ,说明纳米银掺杂改善了晶界     

Pr离子缺陷对Bi-2223/Ag带材磁通涡旋运动的影响

Pr部分替代Ca可以在Bi-2223的超导层中引起局域缺陷(简称Pr离子缺陷),本文分析了不同含Pr量的Bi-2223/Ag带材在垂直于带面的外场下电阻转变特性,研究了其磁通钉扎势垒的变化规律.结果表明:Pr离子缺陷显著提高了Bi-2223带材的磁通钉扎势垒(U).不同含Pr量样品的磁通钉扎势垒(U)均满足U/(1-T irr/Tc0)(1/Hα的规律,其不同α值反映了样品中不同的磁通蠕动方式.在不含Pr离子缺陷的样品中,磁通主要以双弯结的方式进行蠕动, 含Pr离子缺陷的样品中磁通蠕动主要以直接剪切的方式进行.     

热处理条件对Bi系2223相超导体的相结构和Tc的影响

采用两次烧结的固相反应法,制备了高质量的名义组分为Bi_(1.92)Pb_(0.37)Sr_2Ca_2Cu_(3.03)O_y的2223单相多晶样品,其零电阻温度为107K。研究了烧成温度和冷却速率对样品的单相性和T_c的影响。结果表明,烧成温度对样品的单相性起决定作用,冷却速率对其影响不大。但是烧成后冷却速率的变化可以使2223相的T_c至少在10K的范围内移动。缓慢冷却使其T_c向高温移动,这与通常在2212相中见到的移动相反。T_c的变化主要归因于超导体中氧含量的变化,而氧含量、载流子浓度、T_(co)以及正常态的电阻行为等因素之间存在密切相关。当样品充分吸氧过程基本完成后,冷却速率的变化,对样品的颗粒T_c影响很小,但对体T_c仍有一定影响。     

先驱粉对(Bi,Pb)-2223/银超导带材的显微结构及临界电流密度的影响

本文通过控制粉末的烧结温度,得到三种由不同相含量组成的前驱粉末,并采用这些前驱粉末制备出超导带材.通过对带材的显微结构的观察和临界电流密度的测量表明,前驱粉末的相组成对(Bi,Pb)-2223/银超导带材的显微结构和临界电流密度有很大影响.采用不同的前驱粉末所制备的带材具有不同的临界电流密度,带材的临界电流密度取决于所形成的微观组织.通过SEM观察三种带材的微观组织发现,样品中的杂相(第二相)主要是残留的2212相,(Sr,Ca)2CuO3相和CuO相,这些残留相的生成与前驱粉末中各相比例的失衡有关.杂相的尺寸,含量及其形状是影响带材临界电流密度的主要因素.因此,获得合理的前驱粉末相组成是改善带材超导性能的关键之一.     

拉伸应变对Bi2223/Ag带材Ic不均匀性的影响

研究了Bi2223/Ag带材的Ic和n值沿带长方向的不均匀性在拉伸应变下的变化。结果表明,Ic和n值的大小并不是逐点一一对应的;当应变小于不可逆拉伸应变时,Ic随应变增加缓慢下降,n值随应变增加缓慢下降并有小幅震荡;Ic的均匀度随应变增加基本上没有变化,n值的均匀度随应变增加变好并有小幅振荡,而且变化范围很小。     

Heat treatment on phase evolution of Bi-2223 precursor powder prepared by spray pyrolysis method

The phase evolution of Bi-2223 precursor powder prepared by spray pyrolysis method is studied with different heat treatment parameters. The results show that the reaction temperature and phase composition of precursor powder depend on heat treatment atmosphere. Phase assemblage of(Bi,Pb)-2212, AEC, CuO, and small Bi-2201 can be obtained by heat-treated in N2-0.1%O_2 atmosphere. For precursor powder, there is sufficient reaction process at 770℃, and the dimension of Bi-2212 phase increases rapidly with the increase of heat treatment temperature and time. The dimension of AEC phase also increases by extending heat treatment time. As a balance among phase assemblage, dimension of particle and adequate reaction, a reasonable precursor powder can be obtained by heat-treated at 770℃ for 12 h–16 h in N2-0.1%O_2 atmosphere. Critical current of 37-filament Bi-2223 tape is about 120 A, which confirms that these heat treatment parameters are reasonable.     

制备参数对改进共沉淀法制备Bi-2212粉末的影响

实验采用改进共沉淀法制备了Bi-2212粉末,选用乙醇作为主要溶剂,通过对共沉淀过程金属离子溶液滴加速度、氨水滴加速度、溶液p H值、陈化温度以及时间的控制,最终获得成分均匀、颗粒细小、粒度均匀、符合原始配比的前驱粉末,采用该方法制备的前驱粉末制备的Bi-2212线材的超导电性达到了较高水平,在4.2K,自场条件下,同牛津公司制备线材性能接近。     

Role of vanadium in Bi-2223 ceramics

The effect of substitution of vanadium in Bi_1.6Pb_0.4Sr₂Ca₂Cu₃ O_δ ceramic at Bi and Cu sites has been investigated for the resistivity, a.c. susceptibility, XRD and a.c. magnetization studies. Enhancement in T _c for the smaller concentrations of V at either of the two sites was observed which followed an expected lattice distortion and decrease in T _c for higher V concentrations. V plays a role of substituting element more than just a sintering agent as reflected in the more rapid decrease in T _c at Cu-site and further in the magnetization values that are higher compared to the values at the Bi-site. It indicates higher magnetization scattering at the Cu site. The results were explained keeping in mind the liquid phase mechanism behind the formation of the 2223 phase and the possibility of magnetic scattering.     

Fabrication of joint Bi-2223/Ag superconducting tapes with BSCCO superconducting powders by diffusion bonding

61-Filaments Bi-2223/Ag superconducting tapes have been successfully joined with BSCCO superconducting powder interlayer by diffusion bonding. The electrical properties of the diffusion bonding joints were tested by standard four probe method and the microstructures of the joints were also examined by SEM. Additionally, the phase constituents of the superconducting powders between the tapes before and after bonding process were evaluated by XRD analysis. The result shows that the diffusion bonding joints are superconductive. The microstructures of the joint display a good bonding with no cracks and discontinuities. The joining zones are mainly composed of Bi-2223 phase, Bi-2212 phase and a small amount of CuO, Ca₂PbO₄. At last, the phase transformations of the superconducting powders in the bonding process are discussed.     

AC susceptibility study in the single-phase Bi-2223 system

We have found that the composition, Bi_1.2Pb_0.33Sr_1.54Ca_2.06Cu₃O_y which is comparatively poorer in Bi and Sr with respect to 2:2:2:3, a single-phase 110 K superconductor can be obtained. Such polycrystalline samples have been synthesized by two different methods. The synthesized samples have been characterized by their X-ray diffraction patterns and temperature dependence of DC electrical resistivity and AC susceptibility down to 20 K have been carried out. The samples have been identified as having single phase with a sharp transition. The results of their AC susceptibility have been analysed using Clems critical state model. The effective volume fraction of the grains and the temperature dependence of the intergranular current density have been estimated.     

高温超导带材Bi-2223/Ag的焊接接头电阻研究

针对高温超导带材Bi-2223/Ag的焊接问题进行了研究.利用ANSYS建立焊接接头电阻特性的有限元计算模型,仿真和计算分析了焊料材料、搭接长度和焊锡层厚度对接头电阻值的影响,并进行了实验验证.实验表明:可通过减少焊料厚度,增加焊接搭接长度来减少接头电阻,当焊接长度在2～5cm,焊料厚度为0.5mm时,Bi-2223/...     

Effect of alkali metal on the properties of Bi-based glass powders prepared by spray pyrolysis

Bismuth-based glass powders with different quantities of Li₂O were directly prepared by high-temperature spray pyrolysis. The bismuth-based glass powders were completely spherical and submicron in size irrespective of the quantities of the Li₂O additive. The high optical transmittances of the dielectric layers formed from the glass powders obtained by spray pyrolysis were due to the decrease in the glass-transition temperatures of the glass powders with the addition of Li₂O. The ‘yellowing phenomenon’ was not observed in the dielectric layers formed from the glass powders obtained by spray pyrolysis, whereas it occurred in the dielectric layers formed from the glass powders obtained through the conventional melting process. PACS 42.70.Ce; 85.60.Pg; 71.55.Jv     

Effect of Gd addition on the activation energies of Bi-2223 superconductor

We have investigated the effect of addition of Gd in Bi_1.8Pb_0.35Sr_1.9Ca_2.1Cu₃Gd_xO_y superconductor with x=0, 0.1, 0.2, 0.3, 0.4 and 0.5. The samples were prepared using the standard solid-state reaction method. The activation energies, irreversibility fields (H_irr), upper critical fields (H_c2) and coherence lengths at 0 K (ξ(0)) were calculated from the resistivity versus temperature (R-T) curves under DC magnetic fields up to 7 T. The superconducting transition temperature, T_c, and activation energy, U₀, were found to decrease with increase in Gd concentration and with increase in applied magnetic field. The offset transition temperature of the pure (Gd00) sample without applied magnetic field is 108 K, whereas for Gd05 sample, the offset transition temperature drops to 5 K with 7 T applied magnetic field. The activation energy of the Gd00 sample without applied magnetic field is 34,980 K, and for Gd05 sample with 7 T applied field it is 98 K. H_irr and H_c2 values also decrease with increase in Gd addition. The possible reasons for the observed degradation in microstructural and superconducting properties due to Gd addition were discussed.     

Decrease of magnetic AC loss in twisted-filament Bi-2223 tapes

In AC power-engineering applications, a large part of the AC loss in the superconductor is due to magnetization by the external field. This magnetic AC loss has been well described for the low-T_c conductors. In Bi-2223 tapes the picture is different due to strong anisotropy, granularity and flux creep. Magnetic AC loss in various twisted and non-twisted Bi-2223 tapes has been measured at power frequencies by a pickup method. The results are compared to theoretical models of magnetization loss. When the field is parallel to the tape plane, the filaments in twisted tapes can be decoupled and the AC loss is decreased even when the matrix is pure silver. The extra effect of higher-resistance matrix materials is studied. In perpendicular field it is more difficult to decouple the filaments, due to the particular tape geometry. Contrary to a wire, there are essential differences between the AC loss mechanisms in a long twisted tape and those in a short piece of non-twisted tape. Finally, the dynamic resistance caused by the AC magnetic field is examined.