Yuichi Satsu

Increase of Coercivity and Composition Distribution in Fluoride-Diffused NdFeB Sintered Magnets Treated by Fluoride Solutions

Rare-earth and fluorine were diffused along grain boundaries in NdFeB sintered magnets during heat treatment after rare-earth fluoride liquid coating. In the case of Dy fluoride coating, the coercivity for NdFeB sintered magnets with a thickness of 1 mm after the diffusion was increased from 0.80 MA/m to 1.13 MA/m (41%) with remanence reduction of 0.6%. Segregations for Dy atoms near the grain boundaries and fluorine atoms at the grain boundary were found by TEM observations. The increase of coercivity per the weight of the rare-earth fluorides has a correlation with the anisotropy field of the RE2Fe14B (RE is rare-earth elements). Furthermore, the Dy quantity required for the observed increase of coercivity can be reduced to 1/3 compared to the previous NdFeB sintered magnets using the fluoride coating and diffusion process.

Magnetic properties of a Nd–Fe–B sintered magnet with Dy segregation

The magnetic properties and microstructures of a Nd–Fe–B sintered magnet with Dy segregation obtained by applying a fluoride-solution technique were studied using transmission electron microscopy and micromagnetic analysis. By applying 0.1–0.2 wt % fluorides in comparison with weight of the magnet and heating the magnet, coercivity increased by about 1.3 times from 1.1 to 1.4 T at 298 K while retaining remanence. Dy segregated within about 250 nm from the grain surfaces and coercivity was controlled by the area near the grain boundaries. Furthermore, we estimated that the range for reducing the magnetic anisotropy field near the grain boundaries was one or two unit cells by applying micromagnetic analysis to the magnet, which may indicate larger coercivity with less Dy.

High electrical resistance hot-pressed NdFeB magnet for low loss motors

Fluoride-coated hot-pressed NdFeB magnets with electrical resistivity of 1.4mΩcm, which is ten times larger than that of a noncoated sintered NdFeB magnet, were prepared using fluoride coating powders. The high resistive NdFeB magnets consist of coated powders and are sintered with a neodymium fluoride layer, which was grown using a fluoride solution. No degradation of coercivity was observed in the fluoride coated NdFeB powders. The increase in magnet temperature caused by an alternating magnetic field (Eddy currents) was eightfold with the use of a fluoride-treated magnet. Furthermore, the increase in temperature at the magnet’s rotor was reduced by 50% when the high resistive hot-pressed magnet was substituted for the conventional commercial magnet.

Fabrication of thin-film multilayer substrate using copper clad polyimide sheets

A novel fabrication process is proposed for thin film multilayer substrates. The feature of the process involves the lamination of polyimide sheets with previously inspected wiring patterns. Several technical points were investigated during development of the process. Fairly large dimensional changes occur in the polyimide sheets in the copper etching and lamination steps. However, these changes can be restrained by fixing the sheets to rigid frames. Excimer laser ablation is a useful method to form blind via holes with a high aspect ratio. These holes can be metallized successfully by electroless copper plating. >

Heat-resistant epoxy-silicon hybrid materials for printed wiring boards

An epoxy-silicon hybrid resin based on a new concept has been developed. This resin has a structure in which epoxy-silicon oligomers by sol-gel reaction are incorporated into the epoxy resin matrix at the nanometer level. The nanostructure was confirmed by /sup 29/Si NMR spectrum and a time-resolved energy filtering-transmission electron microscopy technique. This epoxy-silicon hybrid resin shows excellent mechanical properties at high temperatures. The elastic modulus at 260/spl deg/C was 0.6 GPa, much higher than the 0.08 GPa of conventional epoxy resins; and the thermal expansion coefficient above the glass transition temperature was two-thirds of the conventional one. It was confirmed that conventional fabrication process for FR-5 was applicable to copper clad laminates for the epoxy-silicon hybrid resin.

Structure and magnetic properties of NdFeB powder surrounded with layer of rare-earth fluorides

The effect of a layer of rare-earth fluorides on the structure and magnetic properties of NdFeB powders was studied. Rare-earth fluorides such as REFx (RE: rare-earth element, x=2 or 3) were grown using fluoride liquid solutions in order to cover the surface of the NdFeB powders. For NdFx-coated NdFeB powder, NdF3 with a hexagonal structure was grown below 400°C. A structure change from NdF3 to cubic NdF2 was observed after annealing at the temperature of 400°C or more. Coercivity (iHc) for 3vol% NdFx-coated NdFeB powder decreased to 14.0 from 15.0kOe for noncoated NdFeB powder after annealing at 800°C. The rare-earth fluoride layers of LaFx-, TbFx-, and DyFx-coated NdFeB powders showed a iHc of 16.8, 16.6, and 16.4kOe, respectively, all of which were higher than that for noncoated NdFeB powder, indicating a diffusion of rare-earth atoms in the fluoride layer.

Magnetization reversal mechanism of a sintered Nd-Fe-B magnet with Dy segregation

The magnetization reversal mechanism of a sintered Nd-Fe-B magnet with Dy segregation near grain boundaries (GB) was studied using spin polarized scanning electron spectroscopy and magnetization measurements. More fine magnetic domains near GB were found in the magnet with Dy segregation than in the magnet without treatment. Magnetic modifications near the GB had no effect on the magnetization development. The domain wall motion of a quasihard magnetic component in the magnet with Dy segregation was suppressed in comparison with those in the magnet without treatment; this could also be confirmed in the different behaviors of asymmetry components toward a magnetic field direction between both magnets. From analyzing the probability of rotating magnetization near the GB, the magnetization reversal of the magnet with Dy segregation was more difficult to produce than those of the magnet without treatment.

Microstructure and Magnetic Properties of NdFeB Magnets Using Fluorides Nano-Coated Process

Nd2Fe14B magnets could be sintered using terbium fluoride coated Nd2Fe14B powders. Fluorine atoms were segregated at the triple junctions and grain boundary after sintering and aging process. NdOF with fcc structure was grown at the triple junction. Terbium atoms were also distributed near grain boundaries by interdiffusion between the fluoride and Nd2Fe14B. No fluorine atoms were detected in Nd2Fe14B phase. The coercivity for 0.5wt% terbium fluoride coated magnet showed 1.23 MA/m which was 1.2 times higher than that for non-coated magnet with 1.04MA/m. The distribution of terbium and fluorine atoms increases the coercivity without reduction of remanence.

Curie temperature rising by fluorination for Sm2Fe17

Fluorine atoms can be introduced to Sm2Fe17 using XeF2 below 423 K. The resulting fluorinated Sm2Fe17 powders have ferromagnetic phases containing Sm2Fe17FY1(0<Y1<1), Sm2Fe17FY2 (1<Y2<4), Sm2Fe17, and α-Fe. The unit cell for Sm2Fe17 is elongated by the fluorination. The largest unit cell volume among the rhombohedral Sm2Fe17 compounds is 83.8 nm3, which is 5.8% larger than Sm2Fe17. The rhombohedral Sm2Fe17 with the largest unit cell volume is dissociated above 873 K, and fluorination increases Curie temperature from 403 K for Sm2Fe17 to 675 K. This increase can be explained by the magneto-volume effect.