旋转超导铌球在磁场中的力矩分析

由金属铌制成的超导球体,利用超导体的迈斯纳效应悬浮在球腔中,在外磁场的影响下会有少量俘获磁通存在,本文引入球谐函数计算磁场,分析了俘获磁通和外磁场相互作用后对超导转子产生的干扰力矩。在磁场中旋转的超导球体也会产生一个与转速成比例的伦敦磁场,与外部磁场相互作用从而产生干扰力矩作用于超导球。本文从旋转超导球体的电磁特性和磁场分布入手,计算和分析了伦敦磁矩对旋转超导球体的干扰力矩及对超导球体运动的影响。     

超导磁悬浮涡旋电流元模型磁场分布特征

通过详细分析超导磁悬浮特征,论述了各理论模型与实际应用情况存在的偏离,其原因在于理论上为超导体设置边界,从而严重限制了超导体对外磁场的动态响应。为了避免这种缺陷,文中取自然边界,并将涡旋电流(VC)作为独立的微磁场源与外磁场相互作用,运用基本电磁场理论描述超导磁悬浮特征。经过严格推导,给出了超导磁悬浮系统的磁场分布表达式。对测量结果进行反演,有望为超导透析技术奠定理论依据。     

GL-I方程在超导磁悬浮涡旋电流元模型中的应用

由于现有超导磁悬浮理论为超导体设置边界,严重限制了对其超导态内部特征的认识,一些参数设置与实际应用情况也有相当距离。为了避免其局限性,根据超导磁悬浮特征,将涡旋电流(VC)作为独立的微磁场源与外磁场相互作用,并取自然边界,经过严格推导,建立了超导磁悬浮力表达式,理论计算与实验观测比较效果良好。用GL-I方程求解超导电子密度可进而提高理论计算精度,结合高分辨率超导磁悬浮力和磁场观测,以期能够建立超导透析技术。     

超导环的磁化性质研究

计算了双结超导π环、零环及规则超导环阵列的自由能随外加磁场及温度的变化,给出了超导转变温度附近的系统相图。针对高温超导体及低温超导体中出现的顺磁迈斯纳效应,用π结、零结概念,给出了一种简单的理论解释。     

用热等静压在MgB2线中引入的晶体学缺陷的结构

最近,美国洛斯阿拉莫斯实验室的X.Z.Liao等用TEM详细研究了用热等静压方法在MgB2线中引入的缺陷的结构。因为新发现的MgB2超导体具有39K的超导转变温度,具有大的相干长度,较小的各向异性,低的制作成本等很多优点,使得它有可能在4K～30K温度范围,0T～12T磁场下的一些应用中替代低温超导体或Bi系高温超导材料。为了实际应用MgB2超导体,必须使制备的MgB2超导体在高磁场下具有高的临界电流密度,为此必须增加MgB2超导体中的钉扎中心。多种晶体学缺陷,如位错网、堆垛层错、晶界、非超导相等都可作为超导体中有效的磁通钉扎中心。在高Tc…     

超导材料实用化50年的回顾

1911年发现的超导现象是20世纪独特的新发现之一，20世纪50年代中期发现了金属系高磁场超导体，以后又加工成超细多芯线，随着相关技术的发展，其应用向当初未料想的领域拓展。超导MRI已广泛普及，高磁场核磁共振(NMR)已活跃在基因组科学最前沿，大型超导发电机连续运转成功，核聚变装置用的大型超导磁体也投入运行。1987年发现的铜氧化物系超导制得的线材已在100m长的输电电缆上进行实用试验。这样，超导作为关键技术在21世纪的能源、医疗、交通、信息等领域的研究开发正在不断进展。日本东海大学太刀川教授撰文回顾了20世纪50年代金属…     

直流超导量子干涉器的无损检测研究

利用高温直流超导量子干涉器（DC SQUID）建立一套无损检测装置，对无磁不锈钢材料受到外力冲击后产生的剩余磁场进行了探测，利用电磁激励的方法，对有内部缺陷的铝板进行了试验研究，并对激励频率的选择进行了初步的讨论。     

高温超导氧化物YBCO的掺杂效应研究进展

综述了近10年来高温超导氧化物YBCO掺杂效应研究的进展。通过化学掺杂不但能提高YBCO的临界电流密度和临界转变温度等超导性能，而且能改善超导体的力学性能和影响晶体生长的热力学行为等。掺杂效应的研究使YBCO的应用性能得到了提高，同时为研究超导机制提供了更多的理论信息。     

可以维持强电流的铁基超导体

<正>日本成蹊大学三浦正志教授等人对一种铁基超导体进行改良,就是在超导材料中分布不属于超导体的一般导电微粒子,这种粒子可以抑制破坏超导状态的磁场效应。超导电流由于外加磁场而逐渐减弱,然而导电微粒子抑制磁场作用的力量却增强,维持强电流的时间就延长了。本研究采用Fe、Ba、As、P化合物,在-260℃温度下外加1T外磁场,则在1cm2超导体内可流入500kA电流,24h电流减弱约12%。这种铁基     

超导材料

Fullerene纳米晶须超导材料 Fullerene是一种碳素材料，它有可能成为一种重量很轻的超导体。日本筑波市茨城县的国家材料科学研究所的研究人员实验证明了fullerene纳米晶须的超导性。这种具有细纤维状的轻质纳米级碳素材料，可以通过热处理技术来合成。Fullerene超导材料可以是丝状物也可以是布状物，其超导转变温度大约为17K。临界电流密度即使在磁场中也非常之高（105A／cm2），其临界电流密度随着磁场强度的增高而稍有减低，有可能成为性能优良的超导材料。     

Thin-skin AC field in anisotropic rectangular bar and ACPD stress measurement

This paper presents some theoretical and experimental studies on the magnetostrictive anisotropy (stress-induced anisotropy) in a long rectangular steel bar that were recently conducted at the University College London. In order to obtain the thin-skin field in the anisotropic bar, the validity of the general boundary conditions at the interface between the conductor and the exterior (air), which were established in earlier studies for isotropic media, were firstly examined. The thin-skin field solution of Zhou and Lewis [Zhou J, Lewis AM. Thin-skin electromagnetic fields around a rectangular conductor bar, Journal of Physics D: Applied Physics, 1994;27:419–425] for the isotropic bar was then extended to include magnetic anisotropy. Using the extended thin-skin field solution, an electromagnetic stress model has been presented by relating the stress level to a quantity that can be used as a measure of the amount of magnetic anisotropy in the material. For the application of this model, experimental stress measurements on mild steel rectangular bars with different dimensions were conducted based on the Alternating Current Potential Difference (ACPD) technique. The ACPD stress measurement results showed that the theoretical stress model could predict the stress values with the calibration of a magnetic anisotropic parameter.     

Probing into the effects of a magnetic field on the electrode processes of iron in sulphuric acid solutions with dichromate based on the fundamental electrochemistry kinetics

The effects of an applied magnetic field on the electrode processes of iron in sulphuric acid solutions with dichromate have been investigated by electrochemical measurements. Open circuit potentials, cathodic and anodic polarisation curves, values of polarisation resistance were measured in the presence or absence of a 0.4 T horizontal magnetic field (HMF). A potentiostatic polarisation plus magnetic field perturbation technique was used to study the effect of the magnetic field on open circuit corrosion. Cathodic reaction rates at open circuit potentials for iron in sulphuric acid solutions containing dichromate ions are controlled by both the electron-transfer process and the diffusion process. A magnetic field made the open circuit potential move in the positive direction, and changes of the open circuit potentials due to the magnetic field increase with increasing dichromate concentration. When iron was potentiostatically polarised at open circuit potentials in the absence of a magnetic field, a cathodic current was observed after a magnetic field was imposed. Such cathodic currents induced by the magnetic field increases with increasing dichromate concentration. The positive shifts of open circuit potential, the decrease of polarisation resistance, and the occurrence of cathodic currents induced by the magnetic field are caused by the accelerating effect of magnetic field on the cathodic diffusion process. Measured current densities showed lower, equal, or higher values in the presence of the magnetic field than those in the absence of a magnetic field at certain anodic potentials. This effect of the magnetic field is related to the contribution of the cathodic and anodic reactions to the measured current and the types of rate-determining steps for each reaction at certain potentials. The applied magnetic field significantly decreased the polarisation resistance. The experimental results in this paper are formulated based on the fundamental electrochemistry kinetics after introducing a coefficient term of the magnetic field effect on the mass transfer process of reactive ions.     

螺旋磁场对Pb-Sn合金成分偏析的影响

测试分析新型电磁搅拌器内螺旋磁场和旋转磁场的磁感应强度、分布和作用规律,研究螺旋磁场对Pb-80%Sn过共晶合金凝固组织影响的作用机理,并与无磁场和旋转磁场条件下合金凝固组织的形貌特征及成分分布进行对比分析。结果表明:螺旋磁场相比于旋转磁场可以在铸锭内部更大区域内形成均匀搅拌,更易于破碎和细化枝晶组织,既能促进椭球或球状晶的生成,又能更好地改善宏观偏析;在频率一定的情况下,初生相晶粒尺寸随着励磁电流的增大而减小;当励磁电流为125A时,旋转磁场和螺旋磁场细化晶粒的效果最好;继续增大电流,晶粒产生粗化;螺旋磁场可基本消除成分偏析,并在较小励磁电流(100A)下达到采用旋转磁场(125A)时的最佳搅拌效果。     

磁场形态对等离子弧堆焊层组织性能的影响

在低碳钢表面进行Fe5自熔合金等离子弧堆焊时外加纵向磁场,并改变磁场形态,对不同磁场参数下堆焊试样进行硬度和磨损试验.采用显微电镜和扫描电镜对堆焊层显微组织进行分析,研究磁场形态和参数对堆焊层组织性能的影响规律和作用机理.结果表明,交、直流纵向磁场均可以改善堆焊层的组织性能,由于交流纵向磁场中频率可调,增加了磁场的可控性,对堆焊层组织性能的作用效果比直流纵向磁场更明显.在焊接电流为160A,磁场电流为3A,磁场频率为10Hz时,堆焊层金属性能达到最佳值,此时硬度为68HRC,磨损量为0.0318g.     

地磁场中铁磁构件应力集中区的力磁耦合模型

为了更有效地表征铁磁材料中应力集中区与其在空间中的磁场关系,基于力与磁畴非线性关系,从宏观热力学关系出发,结合应力影响磁致伸缩应变饱和值的微观物理机制及其变化规律,建立了磁场强度与应力的唯象关系。并将应力集中区等效为磁耦极子,结合电磁场理论与上述唯象关系,建立了反映应力-磁场的耦合模型。在该模型基础上,建立了石油管道缺陷磁记忆检测试验系统。在50m长的石油管道上制作了焊缝裂纹等缺陷。采用磁检测仪对焊缝缺陷的磁特征信号进行了检测。结果发现,随着测试路径的不同,磁信号发生规律性变化,与所建模型预测吻合,证明了模型的可靠性。所建模型可以用于分析缺陷在空间产生的磁场分布、缺陷大小、缺陷深度以及缺陷的分布,为磁检测仪的研制以及定量分析缺陷磁信号打下了基础。     

直流横向磁场作用下钴基合金的组织及性能

为了提高堆焊层的性能,研究直流横向磁场对等离子弧堆焊层的组织和性能的影响.在低碳钢表面进行钴基合金粉末等离子弧堆焊时施加直流横向磁场,焊后对堆焊层进行硬度、磨损、显微组织以及X射线衍射分析,并系统地分析直流横向磁场对等离子堆焊层硬度和耐磨性的影响规律.结果表明,施加磁场时堆焊层性能比无磁场时堆焊层性能好.当堆焊电流为1...     

Effect of excitation current intensity on mechanical properties of ZL205A castings solidified under a traveling magnetic field

The effect of excitation current intensity on the mechanical properties of ZL205 A castings solidified under a traveling magnetic field was studied. The results of the experiment indicate that the excitation current intensity of the traveling magnetic field has a great influence on the mechanical properties of the ZL205 A castings. When the excitation current intensity is 15 A, the tensile strength and elongation of ZL205 A alloy castings increase 27.2% and 67.7%, respectively, compared with those of the same alloy solidified under gravity. The improvement of mechanical properties is attributed to the decrease of micro-porosity in the alloy. Under the traveling magnetic field, the feeding pressure in the alloy melt before solidification can be enhanced due to the electromagnetic force. Moreover, the melt flow induced by the traveling magnetic field can decrease the temperature gradient. The feeding resistance will be increased because the temperature gradient decrease. So traveling magnetic field has an optimum effect on feeding.     

Adsorption of formaldehyde at mineral nanoporous sorbents exposed to a pulse magnetic field

The influence of the preexposure of various nanoporous aluminosilicate sorbents to a pulse magnetic field on the adsorption of the formaldehyde vapor was considered. The effect of the pulse magnetic field on the surface morphology of the sorbents and intensifying the sorption activity was estimated. A magnetic field with B = 0.011 T intensified the adsorption by a montmorillonite sample, while an increase in the magnetic induction from 0.011 to 0.12 T enhanced the adsorption by clinoptilolite-containing samples. A combination of the pulse magnetic field (B = 0.011 T) and thermal treatment intensified the adsorption of formaldehyde at all the sorbents studied. The sorbents exposed to the pulse magnetic field were most active 48 h after the exposure. The relaxation time was 72 h for all the systems studied at different B values.     

金属基陶瓷复合等离子弧堆焊层组织与耐磨性能

等离子弧堆焊镍基钴基合金粉末时外加纵向磁场,对两种合金陶瓷复合堆 焊层进行硬度和磨损试验及显微组织分析.结果表明,施加磁场时的堆焊层性能比无 磁场作用的堆焊层性能高.钴基合金的最佳焊接电流和磁场电流分别为160 A和3 A. 此时堆焊层组织晶粒细化效果最明显;而镍基合金为140 A和1 A,此时堆焊层Cr7G3截 面的六角形陶瓷硬质相数量最多且均匀分布,说明Cr7G3硬质相的轴向平行方向一致, 因而硬度和耐磨性最好.随着磁场电流的继续增大,由于电磁阻尼占主导地位,这两种 合金的性能均下降.