一种使用新型润滑剂压制高密度磁体的方法

文章涉及一种磁体的制作方法,尤其是使用新型润滑剂模压制作高密度磁体的方法。包括造粒、模压固化等六个步骤。文章的方法生产制作高密度磁体,在压制过程中新型润滑剂能从固体变成粘性液体,并在文章方法作用下流动到阴模壁,既能润滑模壁,又能润滑磁粉颗粒,从而使磁粉颗粒间的空隙被压缩,使其运动并达到磁粉颗粒的最佳排列,有效地提高磁件毛坯密度以及保证磁件的密度均匀。不但成型压力大大减小,节约了能源,而且有效地保护了模具,使生产磁体的成本大大降低。

粘结剂含量对粘结NdFeB磁体磁性能和抗压强度的影响

用环氧树脂粘结剂制备了NdFeB粘结磁体,探讨了粘结剂含量对粘结磁体磁性能和抗压强度的影响规律及机理。当粘结剂含量为1%(质量分数,下同)时,磁粉不能完全被包覆、粘结,磁体密度、磁性能和抗压强度低;当粘结剂含量为5%时,粘结剂体积分数大,稀释了磁体的磁性能,多余的粘结剂也使磁体抗压强度降低。粘结剂含量为2.5%时磁体具有较佳的性能:剩磁Br=0.616T;内禀矫顽力Hcj=784kA/m;最大磁能积(BH)m=58kJ/m3;抗压强度为236MPa。

新技术、新设备在NdFeB稀土磁体生产中的应用之四——烧结工艺

针对NdFeB磁体的特点,根据相关技术需求,中国已开发出一整套有自已特色的生产设备,能有效生产高档磁体。前文分别介绍了NdFeB磁性合金的制备新工艺——速凝铸片(SC)制备工艺和设备、氢爆碎及气流磨(HD+JM)制粉以及磁场取向成形工艺与设备,本文是系列文章的第四篇,侧重介绍烧结工艺的理论基础。

抑制永磁体局部温升最高点的不均匀轴向分段技术

针对永磁体局部温升过高易导致永磁体局部过热退磁的问题,提出一种抑制永磁体局部温升最高点的永磁体不均匀轴向分段技术。在考虑了永磁体涡流损耗分布特性的基础上,使用迭代热计算方法,研究了未分段情况下的永磁体温升分布情况,并通过在线温升测量验证了其计算的准确性。根据永磁体涡流损耗密度计算公式和温升计算结果,给出了永磁体不均匀轴向分段技术流程图,并使用该技术来抑制永磁体局部温升最高点,使永磁体的最高温度降低了12.63℃,温差降低了2.26 K,温升分布更加均匀、合理。

不同添加剂对钕铁硼磁体结构及其性能的影响

为制备更高性能和结构更稳定的钕铁硼磁体材料,在对传统钕铁硼磁体材料制备工序研究的基础上,分析了不同工序环节的主要功能;重点研究了添加氧化镝和钬元素对最终制备所得钕铁硼磁体材料的结构及相关性能的影响;为后续钕铁硼磁体材料的实际生产制备提供借鉴意义。

Electronic Structure and Magnetic Properties of Cu[C(CN)_3]_2 and Mn[C(CN)_3]_2 Based on First Principles

The electronic structure and the magnetic properties of the molecule-based ferromagnets Cu[C（CN）3]2 and Mn[C（CN）3]2 are studied according to first principles within density-functional theory （DFT） and the full potential linearized augmented plane wave （FP-LAPW） method. The total energy, atomic spin magnetic moments, and density of states （DOS） of Cu[C（CN）3]2 and Mn[C（CN）3]2 are all calculated. The calculations reveal that the compounds have a stable ferromagnetic ground state and half-metallic properties. The total spin magnetic moment is 1.0μB for Cu[C（CN）3]2 and 5.0#B for Mn[C（CN）3]e per molecule, the magnetic moment mainly comes from metal atoms, although there is a slight contribution from N and C atoms.

Dust Acoustic Solitary Waves in Saturn F-ring's Region

Effect of hot and cold dust charge on the propagation of dust-acoustic waves （DAWs） in unmagnetized plasma having electrons, singly charged ions, hot and cold dust grains has been investigated. The reductive perturbation method is employed to reduce the basic set of fluid equations to the Kortewege-de Vries （KdV） equation. At the critical hot dusty plasma density Nho, the KdV equation is not appropriate for describing the system. Hence, a set of stretched coordinates is considered to derive the modified KdV equation. It is found that the presence of hot and cold dust charge grains not only significantly modifies the basic properties of solitary structure, but also changes the polarity of the solitary profiles. In the vicinity of the critical hot dusty plasma density Nho, neither KdV nor mKdV equation is appropriate for describing the DAWs. Therefore, a further modified KdV （fmKdV） equation is derived, which admits both soliton and double layer solutions.

Magnetism and Sound Velocities of Iron Carbide （Fe3C） under Pressure

The elastic property and sound velocity of FeaC under high pressure are investigated by using the spin-polarized generalized gradient approximation within density-functional theory. It is found that the magnetic phase transition from the ground ferromagnetic （FM） state to the nonmagnetic （NM） state occurs at ～73 GPa. Based on the predicted Hugoniot of Fe3C, we calculate the sound velocities of FM-Fe3C and NM-Fe3C from elastic constants. Compared with pure iron, NM-FeaC provides a better match of compressional and shear sound velocities with the seismic data of the inner core, supporting carbon as one of the light elements in the inner core.

The Effect of the Under-dense Magnetized Plasma on Electron Density Distribution and Field Profile

Propagation of a high frequency electromagnetic wave in under-dence plasma in presence of an external magnetic field is investigated. When a constant magnetic field perpendicular to the motion of electrons is applied, then the electrons rotate around the magnetic field lines and generate electromagnetic part in the wake with a nonzero group velocity. Using of the Maxwell equations and nonlinear differential equation for the electric field a direct one dimensional （ID） procedure for calculating wake equations are developed and the electric and magnetic field profile in the plasma are investigated.

粘结钕铁硼永磁材料模压成型的压力研究

利用力学性能测试、磁性能测试和宏观形貌检测等方法,研究了压制压力对常温模压成型制备粘结钕铁硼磁体抗压性能和磁性能的影响。结果表明:采用快淬钕铁硼磁粉加环氧树脂制备粘结磁体,在压制压力为600 MPa时,粘结磁体能获得较好的抗压性能和磁性能。

Measurements on Different Ferrite Materials

The resonant frequency of the ferrite-loaded cavities used in the future China Spallation Neutron Source (CSNS)sweeps from 1.02MHz to 2.42MHz.The ferrite property is very important to the accelerator structure in the CSNS ring.A primary experiment was set up to measure theμrQf value and the power density of different ferrite materials.According to the comparison results,4M2 ferrite rings were chosen to meet the requirement of CSNS.

Statistical study of the properties of the magnetic field and plasma in the earth's magnetotail near lunar orbit

Based on the magnetic field and plasma data obtained by GEOTAIL in 1992-1995 and WIND in1994-2009, the magnetic field and plasma properties in the magnetotail near lunar orbit were studied statistically using the superposed epoch analysis. The results showed that near the 0° sector the plasma density was negatively correlated with Dst index while the temperature was positively correlated with Dst index. The plasma velocity and magnetic field strength had little correlation with Dst index. Around the current sheet near the lunar orbit, the Bx varied between -15-15 nT, the plasma density was less than 0.4 cm^-3, the median of plasma density for all events was less than 0.1 cm^-3, the temperature varied from 0.016 to 8.98 keV, the median of the plasma temperature for all the events was -3 keV, the median of speed was about 200 km/s and the maximum speed was up to 1500 km/s. The tailward and earthward flows could be observed accompanied with the current sheet. For the current sheet cases with tailward flow, the Bx varied from -15 to 15 nT, the upper quartile of plasma velocity was more than 400 krn/s, the maximum speed was up to 1500 km/s. For the current sheet cases with tailward flow, the Bx varied from -10 to 10 nT, the upper quartile of plasma velocity was less than 400 km/s, the maximum speed was up to 1200 km/s. The median of plasma density, temperature and velocity were similar for the two categories. This paper discussed the relationship between above results and magnetic reconnection at magnetic tail, compared the above results with the observation in the far magnetotail. We fitted the statistical results according to the Harris current sheet model, and the observation was consistent with Harris current sheet model. The above results can provide useful information for the design and protection of lunar-orbiting spacecraft and can be used as the background magnetic field and plasma parameters in the numerical simulation of mid-magnetotail reconnection.

Radio spectral index of BL Lac objects

In this paper, the preliminary data from University of Michigan Radio Astronomy Observatory database （UMRAO） are used to discuss the radio spectral index properties of 8 BL Lacs. To do so, we calculated the radio spectral index, a （F oc va）, which was obtained by fitting the averaged flux densities in the bands （4.8 GHZ, 8 GHz, and 14.5 GHz） by binning the original for 7 d. We also calculated the time delay between the averaged lightcurves and the spectral variance. Our calculations and analysis give the following results. 1） The averaged logarithmic flux density at 8 GHz （logF） and the corresponding spectral index （or） have strong correlation for all the BL Lacs; 2） the lightcurves and the spectral variability have the similar profile for all the BL Lacs; 3） the lightcurves delay spectral variability for all sources but PKS 0735＋178, with the delay time ranging from 31 d to 125 d.

Numerical and experimental study of magnetic fluid seal with large sealing gap and multiple magnetic sources

To improve the pressure capability of magnetic fluid seal with more than a 0.25 mm single edge gap,a magnetic fluid sealing structure with multiple magnetic sources which has five permanent magnets was designed.Magnetic field distributions under the pole pieces of the magnetic fluid seal with single and multiple magnetic sources were simulated by finite element method and its sealing pressure difference could be calculated according to the theoretical formula of the magnetic fluid seal.The effects of sealing gap height and magnetic source amount on the sealing capability were investigated experimentally.The theoretical and experimental results were compared,analyzed and discussed.The results demonstrated that the magnetic fluid seal with multiple magnetic sources was an effective method to improve the sealing capability for the rotary shaft with large gaps.The theoretical results agreed well with the experimental results when the height of the single edge gap was equal to 0.4 mm.However,it was found that when the height of the single edge gap was larger than 0.4 mm,the difference between the theoretical values and experimental values increased with the gap height because part of magnetic source had less or even no effect on magnetic fluid sealing capability.

Electron dynamics and wave activities associated with mirror mode structures in the near-Earth magnetotail

We report the observation of mirror mode structures by Cluster spacecraft at around X^-16 RE in the Earth’s magnetotail.The wavelength of the mirror structure is larger than 7000 km,corresponding to tens of ion gyroradii.Features of the mirror structures are similar to those detected in the magnetosheath:the anti-correlation between the magnetic field strength and plasma density,zero phase velocity in the plasma rest frame and linear polarization.The structures were observed in a region bounded by two dipolarizations during a substorm intensification.Thus,the dipolarization process may provide a plasma condition facilitating the growth of the mirror mode structures.Another interesting feature is the electron dynamics within the mirror structures.Thermal electron energy flux has an enhancement at 0°and 180°pitch angles inside the magnetic dips of the first three mirror structures and an enhancement at 90°pitch angle inside the magnetic dip of the last structure.The different electron distribution inside the mirror structures might be a result of different evolution stages of the mirror wave.The last structure may be in the nonlinear stage of the mirror instability,whereas the three others with quasi-sinusoidal waveforms may be in the linear stage.In addition,we found that intense whistler waves were confined within the magnetic dips.We conjecture that whistler waves observed in the first three dips were generated in a remote region,then they were trapped in the mirror mode troughs and transported toward the spacecraft;while the whistler wave detected in the last dip was excited locally by the electron anisotropy instability.

The first principles investigation of ferrite magnetic response with mismatch stress

The quasi-ferrite model is proposed and an appropriate PBE exchange functional with the spin density functional theory （SDFT） is selected for the calculation of the relation between magnetic moment and residual stress in ferrite using a quantum mechanics code. The relationship between ferrite magnetism and the carbon content is determined, and then a ferrite interstitial solid solution （ISS） model in a low carbon concentration state is replaced with an a-Fe model in the case of majority magnetic calculation. The band structure of the loaded α-Fe is compared with that of the unloaded a-Fe. The comparison shows that the energy of Fe atomic 3d orbital changes a little, while the energy of electron orbital of iron core below 3d almost keeps un- changed. The relationship between the magnetic moment and the stress appears intermittent due to the Bragg total reflection. The change in the magnetic moment due to lattice mismatch is much larger than that caused by mechanical loading.