Search

Jet rapid solidification (JRS) is a key process to obtain the ribbon of magnetic materials. Numerical simulation is an effective method to analyze real-time distribution of status parameters during the JRS process and optimize the process. In this paper, the numerical simulation research in two JRS processes, namely, planar flow casting (PFC) and melt spinning (MS), is reviewed. First, based on the principle of rapid solidification, the working principles of PFC and MS processes are summarized and distinguished. The theoretical models, analytical models, and research methods of PFC and MS processes are further introduced and compared in three main research aspects, denoted as melt puddle, cooling roller, and inclusions in the tundish. Regarding the melt puddle, the influence of the melt puddle on the thickness of rapidly solidified ribbons is analyzed. The flow behavior and heat transfer analysis of melt puddle are discussed. In terms of the cooling roller, numerical analyses of the cooling roller structure optimization, parameter optimization, and "fluid–solid-thermal" coupling are summarized. Moreover, the simulation of the movement of inclusions in the PFC tundish is compared. Lastly, the current challenges and future opportunities are also addressed. The development of high-quality JRS ribbons has significant theoretical, social, and economic significance because its quality and stability determine the final characteristics of magnets. Therefore, the application of numerical simulation technology in the JRS process is beneficial for optimizing process routes and system structures, achieving the visual tracking of process, and objectively guiding the development of new JRS equipment. [ABSTRACT FROM AUTHOR]

In order to obtain high magnetic properties in Ce–Pr–Nd–Fe–B spark plasma sintered (SPSed) magnets, the alloys were introduced by the dual-alloy method. The relationship of microstructure, magnetic properties, and thermal stability was investigated. The remanent magnetization, coercivity, and maximum energy product were sharply enhanced from 0.68 T, 653 kA/m, and 75.62 kJ/m3 to 0.80 T, 865 kA/m, and 104 kJ/m3 for the magnets that with 0 and 75 wt.% Pr–Fe–B addition. The Curie temperature also increased from 542 K to 563 K after adding Pr–Fe–B alloys. The scanning electron microscopy (SEM) analysis showed that, during the sintering process, the rare-earth elements migrated into the flake boundary and diffused in 2:14:1 main phases; thus, (Ce, Pr, Nd)2Fe14B hard magnetic phases were formed, which is helpful to optimize the microstructure and magnetic properties. An enhancement of exchange coupling among the grains of SPSed magnets was obtained as a result of grain refinement by adding Pr–Fe–B alloys. [ABSTRACT FROM AUTHOR]

FeSiCr nanoparticles are prepared by plasma arc discharge and ball milling processes. After ball milling, the surface area and sizes of the FeSiCr nanoparticles become larger, and most of the nanoparticles become uneven. The increasing surface area and sizes of nanoparticles contribute to the electrical conductivity, enhance the space charge polarization between metal ions, and increase the shape anisotropy of FeSiCr nanoparticles. The inhomogeneity of nanoparticles reduces the activation energy (ΔE) of the FeSiCr nanoparticles. Therefore, the complex permittivity (εr) is improved, and the impedance matching is optimized. The minimum reflection loss (RLmin) of FeSiCr nanoparticles after ball milling for 6 h reaches −41.5 dB at 6.2 GHz and the effective absorbing bandwidth (RL < −10 dB) improves from 4.5 to 8.1 GHz (d = 2.2 mm). The RLmin of FeSiCr nanoparticles after ball milling for 4 h is −40.1 dB at 6.9 GHz, which is slightly less than that of the sample after ball milling for 6 h, whereas the effective absorption bandwidth (RL < −10 dB) is from 5.8 to 9.0 GHz (d = 2.2 mm). It shows that the absorption performance of FeSiCr nanoparticles can be improved by changing the shape anisotropy. [ABSTRACT FROM AUTHOR]

Development of microwave absorbing materials with tunable thickness and bandwidth is particularly important for practical applications, but its realization remains a great challenge. Here, we report carbon coated core-shell FeSiCr/Fe3C embedded in two-dimensional carbon nanosheets network (FeSiCr/Fe3C@C/C) nanocomposites fabricated by plasma arc-discharging method. FeSiCr/Fe3C@C/C has the best microwave absorption properties in which the minimum calculated reflection loss (RL) can reach − 4 2. 3 dB at 11.5 GHz with a coating thickness of 2.4 mm and the efficient absorption bandwidth (RL < − 1 0 dB) almost covers 4.5–18 GHz range by adjusting the coating thicknesses from 1.3 to 5.0 mm. The improved microwave absorption properties could be ascribed to the optimized impedance matching and enhanced polarization loss, conduction loss and internal reflections of the propagated microwave. Carbon coated core-shell FeSiCr/Fe3C embedded in two-dimensional carbon nanosheets network (FeSiCr/Fe3C@C/C) nanocomposites was fabricated by plasma arc-discharging method. The 2D carbon nanosheets network and core-shell structure can be observed from FeSiCr/Fe3C@C/C, and the average diameter is about 5.4 nm. FeSiCr/Fe3C@C/C is a kind of absorbing material which has excellent microwave absorption performance. [ABSTRACT FROM AUTHOR]

ABSTRACT Perylene diimides (PDIs) and their derivatives are excellent semiconductors, while conjugated polymers based on PDIs have limited applications because of their low electron mobility ( μe) derived from low molecular weight. The reported maximum number-average molecular weight ( Mn) of related polymers is only 21 kDa because PDIs have very poor solubility due to strong π-π stacking of their big planar conjugated cores. Herein, it is found that suitable semi-perfluoroalkyl groups could enhance the solubility of PDIs significantly, and a series of semi-perfluoroalkyl modified conjugated polymers with high molecular weight and electron mobility were synthesized. The maximum Mn reaches 94.8 kDa [P(4CF8CH-PDI-T2)HW]. In their space-charge-limited current (SCLC) devices, all polymers exhibit typical characters of electron transporting semiconductors, and the highest μe is up to 8.40 × 10−3 cm2 V−1 s−1 [P(4CF8CH-PDI-T2)HW], which is similar as that of widely used electron transporting semiconductor PC61BM (6.41 × 10−3 cm2 V−1 s−1). © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018, 56, 116-124 [ABSTRACT FROM AUTHOR]

The grain boundary diffusion process (GBDP) has become an important technique in improving the coercivity and thermal stability of Dy-free sintered Nd-Fe-B magnets. The influence of Dy70Al10Ga20 and (Pr75Dy25)70Al10Ga20 alloys by the GBDP on sintered Nd-Fe-B magnets are investigated in this paper. After diffusing Dy70Al10Ga20 and (Pr75Dy25)70Al10Ga20 alloys, the coercivity (Hcj) of the magnets increased from 13.58 kOe to 20.10 kOe and 18.11 kOe, respectively. Meanwhile, the remanence of the magnets decreased slightly. The thermal stability of the diffused magnets was improved by the GBDP. The microstructure shows continuous Rare-earth-rich (RE-rich) grain boundary phases and (Dy, Pr/Nd)2Fe14B core-shell structures which contribute to improving the coercivity. Moreover, the Dy concentration on the surface of the (Pr75Dy25)70Al10Ga20 diffused magnets decreased with the Pr substitution for the Dy element. The openness of the recoil loops for the (Pr75Dy25)70Al10Ga20 diffused magnets is smaller than that of the original magnets and Dy70Al10Ga20 diffused magnets. The results show that the (Pr75Dy25)70Al10Ga20 alloys can effectively optimize the microstructure and improve the magnetic properties and thermal stability of the sintered Nd-Fe-B magnets. [ABSTRACT FROM AUTHOR]