Ferromagnetic Inclusions in Geomaterials: Implications

Various laboratory and field techniques used to study geomaterials utilize the principles of electromagnetism. Applications in geotechnical engineering such as resistivity profiling, induced polarization, ground-penetrating radar, and time-domain reflectometry, focus on the electrical properties of the materials and neglect the magnetic component. Yet the a priori assumption that the medium is nonferromagnetic may lead to significant errors in data interpretation because the presence of ferromagnetic materials affects the propagation of electromagnetic waves. An experimental study is conducted using kaolinite with ferromagnetic inclusions. Results show that magnetic permeability is a function of the volume fraction and spatial distribution of ferromagnetic inclusions; the interaction among inclusions increases with increasing volume fraction and proximity. These results and published data show that a relaxation due to “wall bowing” occurs at kilohertz frequencies, and a relaxation due to “wall displacement” occurs at megahertz frequencies. It is shown that the relative permittivity (real and imaginary components) inferred from wave-propagation measurements is larger than the actual value by a factor approximately equal to the real relative magnetic permeability. Corrections for ferromagnetic effects must be computed using parameters measured at the same frequency.     

滚动轴承拟静力学分析与应用研究

针对某冶金设备传动装置严重轴承失效现象,就其改进方案进行拟静力学分析,通过对改进前后滚动轴承滚动体负载计算以及滚动体接触应力应变分析,比较结构改进前后滚动轴承受载变形状况,从而证明改进方案的正确性和可靠性。     

Ferromagnetic bulk amorphous alloys

This article reviews our recent results on the development of ferromagnetic bulk amorphous alloys prepared by casting processes. The multicomponent Fe-(Al,Ga)-(P,C,B,Si) alloys are amorphized in the bulk form with diameters up to 2 mm, and the temperature interval of the supercooled liquid region before crystallization is in the range of 50 to 67 K. These bulk amorphous alloys exhibit good soft magnetic properties, i.e., high B _s of 1.1 to 1.2 T, low H _o of 2 to 6 A/m, and high μ _e of about 7000 at 1 kHz. The Nd-Fe-Al and Pr-Fe-Al bulk amorphous alloys are also produced in the diameter range of up to 12 mm by the copper mold casting process and exhibit rather good hard magnetic properties, i.e., B _r of about 0.1 T, high H _o of 300 to 400 kA/m, and rather high (JH)_max of 13 to 20 kJ/m³. The crystallization causes the disappearance of the hard magnetic properties. Furthermore, the melt-spun Nd-Fe-Al and Pr-Fe-Al alloy ribbons exhibit soft-type magnetic properties. Consequently, the hard magnetic properties are concluded to be obtained only for the bulk amorphous alloys. The bulk Nd- and Pr-Fe-Al amorphous alloys have an extremely high T _x/T_m of about 0.90 and a small ΔT _m(=T _m−T _x) of less than 100 K and, hence, their large glass-forming ability is due to the steep increase in viscosity in the supercooled liquid state. The high T _x/T_m enables the development of a fully relaxed, clustered amorphous structure including Nd-Nd and Nd-Fe atomic pairs. It is, therefore, presumed that the hard magnetic properties are due to the development of Nd-Nd and Nd-Fe atomic pairs with large random magnetic anisotropy. The Nd- and Pr-based bulk amorphous alloys can be regarded as a new type of clustered amorphous material, and the control of the clustered amorphous structure is expected to enable the appearance of novel functional properties which cannot be obtained for an ordinary amorphous structure. This article is based on a presentation made in the “Structure and Properties of Bulk Amorphous Alloys” Symposium as part of the 1997 Annual Meeting of TMS at Orlando, Florida, February 10–11, 1997, under the auspices of the TMS-EMPMD/SMD Alloy Phases and MDMD Solidification Committees, the ASM-MSD Thermodynamics and Phase Equilibria, and Atomic Transport Committees, and sponsorship by the Lawrence Livermore National Laboratory and the Los Alamos National Laboratory.