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Abstract

In this research, we investigated the effects of reduction atmospheres on the creation of the Mo-Si-B intermetallic compounds (IMC) during the heat treatments. For outstanding anti-oxidation and elevated mechanical strength at the ultrahigh temperature, we fabricated the uniformly dispersed IMC powders such as Mo5SiB2 (T2) and Mo3Si (A15) phases using the two steps of chemical reactions. Especially, in the second procedure, we studied the influence of the atmospheres (e.g. vacuum, argon, and hydrogen) on the synthesis of IMCs during the reduction. Furthermore, the newly produced IMCs were observed by SEM, XRD, and EDS to identify the phase of the compounds. We also calculated an amount of IMCs in the reduced powders depending on the atmosphere using the Reitveld refinement method. Consequently, it is found that hydrogen atmosphere was suitable for fabrication of IMC without other IMC phases.
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Abstract

Neodymium-Iron-Boron (Nd-Fe-B) magnets are considered to have the highest energy density, and their applications include electric motors, generators, hard disc drives, and MRI. It is well known that a fiber structure with a high aspect ratio and the large specific surface area has the potential to overcome the limitations, such as inhomogeneous structures and the difficulty in alignment of easy axis, associated with such magnets obtained by conventional methods. In this work, a suitable heat-treatment procedure based on single-step and multistep treatments to synthesize sound electrospun Nd-Fe-B-O nanofibers of Φ572 nm was investigated. The single-step heat-treated (directly heat-treated at 800°C for 2 h in air) samples disintegrated along with the residual organic compounds, whereas the multistep heat-treated (sequential three-step heat-treated including three steps;: dehydration (250°C for 30 min in an inert atmosphere), debinding (650°C for 30 min in air), and calcination (800°C for 1 h in air)) fibers maintained sound fibrous morphology without any organic impurities. They could maintain such fibrous morphologies during the dehydration and debinding steps because of the relatively low internal pressures of water vapor and polymer, respectively. In addition, the NdFeO3 alloying phase was dominant in the multistep heat-treated fibers due to the removal of barriers to mass transfer in the interparticles.
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