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.
Very thin liquid jets can be obtained using electric field, whereas an electrically-driven bending instability occurs that enormously increases the jet path and effectively leads to its thinning by very large ratios, enabling the production of nanometre size fibres. This mechanism, although it was discovered almost one century ago, is not yet fully understood. In the following study, experimental data are collected, with the dual goal of characterizing the electro-spinning of different liquids and evaluating the pertinence of a theoretical model.
Macroporous silica fibers having spherical cavities were fabricated by electrospinning using the spinning solution prepared from the mixed dispersion of tetraethylorthosilicate (TEOS) and polystyrene nanospheres as precursor and sacrificial templates, respectively, by injection through metallic nozzle. By applying electric field, the electro-spun fibers obtained by evaporation-driven self-assembly were collected on flat substrate or rotating drum, followed by the removal of the templates by calcination. The sound absorption coefficient of the porous fibers was measured by impedance tube, and the measured value was larger than 0.9 at high frequency region of incident waves. The surface of the resulting fibers was modified using fluorine-containing silane coupling agent to produce superhydrophobic fibrous materials to prevent the infiltration of humidity.
The technique of electrospinning was employed to fabricate uniform one-dimensional inorganic-organic composite nanofibers at room temperature from a solution containing equal volumes of aluminum 2, 4-pentanedionate in acetone and polyvinylpyrrolidone in ethanol. Upon firing and sintering under carefully pre-selected time-temperature profiles (heating rate, temperature and soak time), high-purity and crystalline alumina nanofibers retaining the original morphological features present in the as-spun composite (cermer) fibers were obtained. Tools such as laser Raman spectroscopy, scanning and transmission electron microscopy together with energy dispersive spectroscopy and selected area electron diffraction were employed to follow the systematic evolution of the ceramic phase and its morphological features in the as-spun and the fired fibers. X-ray diffraction was used to identify the crystalline fate of the final product.