Effects of high magnetic field on thermodynamic properties of pure Fe and Cu

By the use of PPMS (Physics Property Measurement System), specific heat values of pure Cu at 2–300 K were determined under the magnetic field of 0, 3, 6 and 9 T, respectively. Magnetization curves of pure Fe under the magnetic field of 0–9 T were obtained at different temperature ranging from 5 to 300 K. Analyses of the experimental results indicate that below 300 K, magnetic fields have no effects on the specific heat values of diamagnetic Cu and very little effects on those of ferromagnetic Fe.     

Experimental studies of the magneto-mechanical memory (MMM) technique using permanently installed magnetic sensor arrays

The magneto-mechanical memory (MMM) method, that is often referred to as the metal magnetic memory method, has been reported to be a non-destructive testing technique capable of quantifying stress concentrations and detecting defects in ferromagnetic materials. The underlying mechanism behind MMM has been explained in the literature, but the sensitivity to stress concentration has not been satisfactorily investigated. In this paper, both the normal and tangential components of the stress-induced MMM signal were measured by permanently installed magnetic sensor arrays on specimens made from three grades of L80 alloy steel and 20 other structural steels; tests were also carried out on a pipe made from the 4140-L80 steel. As expected, the stress history affects the MMM signal, but the experimental results show that significant irreversible change of magnetization always occurs only in the first cycle of loading regardless whether the deformation is purely elastic or partially plastic. If the peak stress level is increased at a given point during cycling, the immediately following next cycle acts as a new “first” cycle at that peak stress level and causes additional significant irreversible change of magnetization, but there is no evidence that plastic deformation might build up a cumulative magnetization. The MMM effect is very small in the steel samples tested, indicating that it will not be useful in field applications. In un-notched specimens the irreversible change in magnetization caused a proportional change in the measured external magnetic field on the order of only 5–10 A/m, while in the case of notched specimens the leakage field was on the order of 30–60 A/m.     

Comparative Study of the Magnetic Properties and Glass-Forming Ability of Fe-Based Bulk Metallic Glass with Minor Mn,Co, Ni,and Cu Additions

Fe_(43)M_5Cr_(15)Mo_(14)C_(15)B_6Y_2 (M=Mn,Co,Ni,and Cu in at.%)bulk metallic glasses(BMGs)are synthesized using the suction casting technique,and the glass-forming ability(GFA),microstructure,and thermal and magnetic properties of these glasses are extensively examined using X-ray diffraction,differential scanning calorimeter,and vibrating sample magnetometer techniques.Among the four BMG alloys,Fe_(43)Ni_5Cr_(15)Mo_(14)C_(15)B_6Y_2 exhibits the lowest coercivity and the highest saturation magnetization,Curie temperature,effective magnetic moment,and GFA.By contrast,Fe_(43)Mn_5Cr_(15)Mo_(14)C_(15)B_6Y_2 presents the poorest magnetic properties,such as the highest coercivity and the lowest saturation magnetization,Curie temperature,and effective magnetic moment.Fe_(43)Cu_5Cr_(15)Mo_(14)C_(15)B_6Y_2 demonstrates the lowest thermal stability and GFA.The observed thermal,structural,and magnetic properties of these BMG alloys are discussed in terms of the kinetics of BMG synthesization and the formation of different ferromagnetic,ferrimagnetic,and antiferromagnetic phases.     

纳米复合永磁材料中软硬磁性相间交换耦合作用的表征

软硬磁性相间的交换耦合作用对纳米复合永磁材料的性能有重要的影响。介绍了目前几种常用的表征软硬磁性相间交换耦合作用强弱的方法,并相应地给出了一些典型的测量结果。     

磁化浮选铜冶炼废渣中铜及其它有价金属的研究

根据某有色金属公司铜冶炼废渣的特点,开展了利用浮选方法进一步回收其中的铜、金和银等有价金属的研究工作.探索了不同捕收剂对废渣中铜及金、银网收的影响,进行了中矿再磨再选、载体浮选、磁场强化浮选等工艺方案的试验研究.结果表明,在磁场条件下采用高效铜组合捕收剂(丁黄药+Z-200)和组合抑制剂(石灰+Na2S)及合理的工艺流程能获得含铜16%以上的铜精矿,可进一步回收其中的有价金属.铜冶炼废渣的进一步利用不但能为矿山提供新的资源,减少环境污染,而且对矿山盘活固定资产和闲置设备及寻找新的经济增长点都具有十分重要的意义.     

Size dependence of the magnetic properties of electrochemically self-assembled Fe quantum dots

A quasi-periodic array of Fe quantum dots of cylindrical shape has been synthesized by electrodeposition of Fe in porous alumina. By controlling the fabrication parameters, we have controlled the length, diameter, and spacing of the dots. The magnetic properties are shown to depend on these parameters. It has been found that at room temperature, there exists a critical diameter of the dots for which the coercivity is a maximum. The largest value of coercivity obtained at room temperature is 2640 Oe which rises to 2900 Oe on annealing. At a low temperature of 5K, an increase in coercivity is observed for most of the samples. The largest value is 3800 Oe which rises to a value of 4100 Oe in the corresponding annealed counterpart. At 5K, no maximum is seen in the coercivity as a function of diameter. Instead, the coercivity is found to decrease with increasing diameter. This dependence of the coercivity on diameter is discussed in terms of localized reversal effects.     

漏磁检测技术研究进展

漏磁检测技术具有原理简单、工程实现容易和对被检测工件表面要求不高等特点,一直是管道无损检测领域的研究热点之一,尤其在长距离管道检测中被广泛使用.本文就漏磁场泄露理论、漏磁场影响因素、检测技术与设备、漏磁信号处理等方面对漏磁检测技术的发展进行了论述,总结了亟待解决的问题以及该技术未来的发展趋势,旨在为漏磁检测技术的研究和系统研制提供参考与借鉴.     

磁化曲线的连续可导拟合方法

为了满足磁场储能迭代计算的需要,提出了磁化曲线的连续可导拟合方法。磁化曲线具有高度非线性,难以用一个函数来逼近,根据其特点,提出了线性插值和二次插值相结合的方法,分为三段来拟合。根据曲线连接点处的约束关系,通过求解约束方程获得拟合函数的待定系数,保证了整条曲线的连续可导。由拟合结果给出了磁导率随磁通密度的函数关系及其导函数关系。最后给出了一个具体的拟合算法实例,验证了拟合精度。     

一种改善贮氢电极合金电化学性能的新方法

提出一种用以改善AB5型贮氢电极合金的综合电化学性能的新方法,即采用一定强度的外加磁场对电极进行磁化处理,以期提高电极合金的综合电化学性能,结果表明,外加磁场化处理可以不同程度地改善磁体贮氢电极合金La0.9Sm0.1Ni5.0-yCoy(y=2.0,2.5,3.0)的电化学容量,循环寿命以及大电流放电能力等电化学性能,磁化处理对电极合金电化学性能的影响还与合金中的Co含量有关,合金中的Co含量增加,磁化处理后电极中存在的剩剩磁强度瑚之增强,磁化处理对电极合金电化学性能的影响也更为显著。     

漏磁法无损检测中铁磁材料内部磁场分布的研究

铁磁材料内部磁场分布的计算是漏磁法无损检测的基本问题之一,首先利用磁荷理论计算漏磁通无损检测中常用的U形永磁体的磁场分布,利用尝试函数的方法建立了非均匀磁化条件下磁导率μ-H关系的数学模型,并与实验结果进行了比较,理论与实验结果符合得非常好,最后给出 材料内部的磁场分布的数学表达式。