Papers by Keyword: Rare-Earth Magnets

Abstract: Fe-Nd-B Rare earth magnets are widely used in high performance applications but suffer from poor corrosion resistance due to their multiphase microstructure and the preferential dissolution of rare earth rich intergranular phases. In this study, the corrosion behaviour of Fe-Nd-B magnets was investigated and the effectiveness of electroless nickel coatings as a protective solution was evaluated. Microstructural and compositional analyses were combined with potentiodynamic polarisation tests, comparing bare and coated magnets with low alloy steel. Coating adhesion was assessed by pull off testing according to ASTM D4541. The results show that Fe-Nd-B magnets are significantly more susceptible to corrosion than steel, while nickel exhibits a passive behaviour in the investigated environment. Electroless nickel coatings provide effective protection and display adhesion comparable to that measured on steel substrates, demonstrating their suitability for corrosion protection of Fe-Nd-B magnets.

Abstract: Nanoparticles of Nd(Fe_1-xCo_x)B with Co concentrations ranging from x = 0 to 0.5 were prepared using a modified Pechini-type sol-gel method. We have shown the influence of Co on the morphology and size of nanoparticles, as well as on elements distribution in nanostructures. It was found that nanoparticles with increased content of Fe and Co were formed during the synthesis process. There was an interdiffusion of Nd and Fe, both after oxidation and after reduction. This study helped to define promising “bottom-up” approaches for the fabrication of nanomaterials for the advanced Nd(_Fe1-xCo_x)B permanent magnets by chemical synthesis.

Abstract: Magnetic force microscopy (MFM) and magnetometry, scanning electron microscopy (SEM) and atomic force microscopy (AFM) are used to study the magnetic and structural properties of the (Nd,Pr)-Fe–B and (Nd,Ho)-(Fe,Co)-B alloys. The alloys are synthesized using an arc or induction furnaces. The nanocrystalline state of the (Nd,Ho)-(Fe,Co)-B alloys is reached by two techniques, namely, melt spinning (MS) and severe plastic deformation (SPD). Hydrogenation and multistage treatment of (Nd,Ho)-(Fe,Co)-B alloys, which includes severe plastic deformation of melt-quenched ribbons and subsequent heat treatment, is also used. The surface morphology and domain structure of samples are studied. These pictures are used to interpret the observed magnetic hysteresis loops of the samples. It was found that multistage treatment allows one to obtain samples with higher values of coercivity due to the formation of a special microstructure with oval grain (the aspect ratio equal to ∼ 3).

Abstract: This paper presents material properties of a micromachined mesoscopic acoustic speaker for hearing aid applications. The microspeaker has a single turn copper coil on a polyimide membrane, and an NdFeB permanent magnet beneath the membrane. The fields due to the permanent magnet were computed using FEMM. Then, forces based on the fields and on the coil driving current were computed. Finally, IntelliSuite was employed to simulate membrane displacements and stresses. The device, with a polyimide membrane diameter of 2.5 mm and thickness of 2 µm, consumes 3.4 mW to generate a sound pressure level of 108 dB in the human ear.

Abstract: The objectives of this study are to investigate the influence of class III orthopedic forces generated by repelling rare earth magnets of class III magnetic orthopedic appliance (MOA-III) on the zygmaticomaxillary suture of Rhesus monkeys. Six male Rhesus monkeys in the stage of mixed dentition were used in this study. Fluorescent dyes were injected intravenously in each animal before and during the experimental period. Distinct changes from physiologic growth remodeling were observed in some sutures but not in the control groups. No inflammation was noted in both experimental and control monkeys. The results show that MOA-III is a small intraoral appliance to treat class III malocclusion, and the 300gm per side heavy orthopedic forces are safe and effective for Rhesus monkey.