Electrospinning and galvanic displacement reaction are combined to fabricate ultra-long hollow chalcogen and chalcogenide nanofibers in a cost-effective and high throughput manner. This procedure exploits electrospinning to fabricate ultra-long sacrificial nanofibers with controlled dimensions and morphology, thereby imparting control over the composition and shape of the nanostructures evolved during galvanic displacement reaction. It is believed to be a general route to form various ultra-long hollow semiconducting nanofibers.

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Recently, electromagnetic interference (EMI) and electromagnetic compatibility (EMC) have become serious problems due to the growth of electronic device and next generation telecommunication. It is necessary to develop new electromagnetic wave absorbing material to overcome the limitation of electromagnetic wave shielding materials. The EMI attenuation is normally related to magnetic loss and dielectric loss. Therefore, magnetic material coating dielectric materials are required in this reason. In this study, TiO2 coated Fe nanofibers were prepared to improve their properties for electromagnetic wave absorption. Poly(vinylpyrrolidone) (PVP) and Iron (III) nitrate nonahydrate (Fe(NO3)3 x 9H2O) were used as starting materials for the synthesis of Fe oxide nanofibers. Fe oxide nanofibers were prepared by electrospinning in an electric field and heat treatment. TiO2 layer was coated on the surface of Fe oxide nanofibers using sol-gel process. After the reduction of TiO2 coated Fe oxide nanofibers, Fe nanofibers with a TiO2 coating layer of about 10 nm were successfully obtained. The morphology and structure of fibers were characterized by SEM, TEM, and XRD. In addition, the absorption properties of TiO2 coated Fe nanofibers were measured by network analyzer.

In this study, we fabricated Fe nanofibers that had a high aspect ratio and were coated by an oxidation protection layer, because electromagnetic properties are affected by the aspect ratio and oxidized layers. PVP/Fe salt nanofibers were prepared by an electrospinning method using an optimized concentration of PVP solution with Iron(lll) nitrate nonahydrate (Fe (NO3)3.9H2O) solution to apply a high voltage. Subsequently, to prepare the Fe nanofibers, the PVP/Fe salt nanofibers were heated up to 600 degrees C in air and reduced to 450 degrees C in H2. The Fe nanofibers were then coated by PVP to prevent re-oxidation. The S-parameter of the prepared Fe nanofibers was measured by a network analyzer, and the power loss was calculated to estimate the EM absorption ability.

With the recent emphasis on the importance of successfully joining materials, researchers have tried to join metals and ceramics with different coefficients of thermal expansion (CTEs) by using the functionally graded material (FGM) method. This involves inserting interlayers with composition gradients that range from one material to the other, thereby minimizing the stress caused by differences in CTE values. In this study, the FGM that included 10 layers of Ni-Al 2 O 3 with eight inter-layers was studied. Previous studies have focused on controlling the composition of inter-layers and optimizing the dispersion process to prevent cracks. Thermal stress was reduced by varying the weights of the inter-layers and increasing the green-body density by using several powder sizes. The powders were well-dispersed during fabrication by using simultaneous dispersion and dry processes followed by a cold isostatic press (CIP) and pressure-less sintering in an inert atmosphere. As a result, a crack-free Ni-Al 2 O 3 FGM joint was obtained. The residual stress in each layer was calculated to predict cracks using ANSYS simulation and maximum principal stress criterion; experimental values matched simulation results. In addition, an oriented Vickers indentation test was used to assess the quality of the joint. Crack-paths were not deflected across the interface, indicating good bond strength between interfaces. Sample density was measured using the Archimedes method; the sintered joint was less dense than its theoretical density but was denser than the results obtained by using previous methods.