Ultrafine Sub-micron Research Articles

High frequency application of ultrafine submicron FeBP amorphous soft magnetic composites

A novel amorphous soft magnetic composites (ASMCs) for hundreds MHz frequency applications have been prepared under the hot-pressing molding by ultrafine submicron FeBP amorphous powders. These ultrafine submicron FeBP amorphous particles were synthesized with the NaBH4 chemical reduction method and the particles size was regulated by the drop rate of the reducing agent. The morphology, microstructure, elemental composition and high-frequency magnetic properties of the amorphous soft magnetic composites was systematically investigated. The particle sizes of FeBP amorphous powders are distributed in 600–900 nm which gradually increase with the decrease of the drop rate of the NaBH4 aqueous solution. Meanwhile, the Fe element content and saturation magnetization strength of the amorphous powder increase and the coercivity gradually decreases. The corresponded ASMCs also appear a commensurate permeability in the range of 6–9 responding to the GHz high frequency range with the lowest loss tangent only 0.20 and 0.44 at 500 MHZ and 1 GHz, respectively. Such ultrafine amorphous soft magnetic composites have enormous potential for high frequency applications in wide band gap semiconductor switching power supplies, RF inductors and chips.

Are ultrafine submicron sized gliadin fibrous materials suitable as bio-absorbents? Processing and post-treatment derived structures and functional properties

Gliadins were electrospun into ultrafine fibrous membrane-like materials to evaluate their processability and suitability as bio-absorbents. From a wide range of tested protein concentrations and processing conditions, 15 and 20% protein solutions were optimal to produce uniform fibers with sizes <1 μm. The results showed that the 20% gliadin solution produced uniform round fibers, while 15% gliadin solution resulted in formation of diverse morphologies such as round and flat-ribbon shaped fibers. Importantly, post-heat treatment of fibrous materials at 130 °C for 2 h increased crosslinking of gliadin protein and improved functionality of fibers. Heat-treatment induced formation of higher amounts of α-helices and random coils, though no change in β-sheets were observed. With post heat-treatment, the fibrous gliadin materials indicated crosslinking of proteins by inter and intramolecular disulphide, hydrogen bonding and other weaker protein interactions. The newly fabricated gliadin fibrous material demonstrated certain stability and ability to absorb and “lock” defibrinated sheep blood, suggesting a support from submicron sized structural morphology of the material. For further development steps of gliadin-based fibrous materials, new efforts are needed in modification of gliadins to maintain the ultrafine structures and improve their strength in order to explore them as bio-absorbents or even scaffolds.

Multipass Friction Stir Processing of Steel/SiC Nanocomposite: Assessment of Microstructure and Tribological Properties

A surface layer of steel/SiC nanocomposite was fabricated by multiple passes of friction stir processing (FSP) on a low-carbon steel. The characterization methods such as optical microscopy, field emission scanning electron microscopy, microhardness, and wear test were performed to obtain the microstructure and mechanical properties of the produced layers. The results revealed that the dispersion of nano-SiC particles is directly related to the FSP passes and that the superior scattering of the nanosized SiC particles is achieved at higher FSP passes. Nano-composite surface layers demonstrated an average microhardness value of ~ 424 HV, which is ~ 3.4 times higher than that of the as-received substrate. Moreover, ultra-fine submicron grains were formed by FSP due to the role of SiC particles as obstacles to grain growth. The produced surface-layer nanocomposite exhibited an outstanding enhancement in wear resistance in comparison with the FSPed sample without reinforcing particles.

Synthesis and characterization of ultrafine sub-micron Na-LTA zeolite particles prepared via hydrothermal template-free method

Ultrafine sub-micron Na-LTA zeolite crystals ranging from 150 to 350nm were synthesized without template via hydrothermal method. Aluminum iso-propoxide and colloidal silica were used as Al and Si sources, respectively, to synthesize the small and uniform zeolite crystals. Zeolite Na-LTA was synthesized hydrothermally from a gel formula of 1.0 Al2O3: 2.7 SiO2: 5.85 Na2O: 150H2O in molar basis. The crystallization conditions including synthesis time, and synthesis temperature were optimized to reduce the zeolite particle size. The final crystals were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results confirmed that synthesis temperature should be lowered for better control of the crystal growth. On the other hand, at low synthesis temperatures, synthesis time should be extended to acquire the high crystallinity. Ultrafine sub-micron Na-LTA zeolite crystals were synthesized at synthesis temperature of 60°C and synthesis time of 11h.

Avoiding fusion of electrospun 3,3′,4,4′-biphenyltetracarboxylic dianhydride-4,4′-oxydianiline copolymer nanofibers during conversion to polyimide

Man-made high-performance fibers produced a revolution in structural materials in the twentieth century. Fiber properties are known to increase with the decrease of their diameters. Ultrafine sub-micron and nanometer-sized fibers attract rapidly growing interest due to their unique advantages for diverse applications. Electrospinning is a straightforward low-cost top-down nanomanufacturing technique producing continuous nanofibers. Electrospinning allows direct fabrication of macroscopic nanofilamentary assemblies for structural and functional applications. Recently, high-performance polyimide nanofibers have been produced by electrospinning of polyamic acid precursors followed by thermal curing. However, curing resulted in fusion of nanofilaments at contacts. While fusion might be beneficial for some applications, it usually results in deterioration of the ordered molecular structure and mechanical properties of fibers in bundles and tows. In this report, we investigated the effect of residual solvent dimethylacetamide (DMAc) on the fusion of nanofibers in electrospun nanofiber bundles during thermal curing of polyimide. Feasibility of removal of the residual DMAc by aging in vacuum and by washing with other solvents was explored. The effect of an additive, dodecylethyldimethylammonium chloride (DEDAC) on fusion was investigated. It was found that the removal of residual DMAc by aging in vacuum reduced the nanofilament fusion during imidization. The presence of DEDAC in the absence of DMAc was shown to further reduce the fusion. DEDAC may represent a new class of additives with a potential to preserve nanostructure of polyamic acid precursors during thermal conversion to polyimides. The results of this report can be used in the development of ultrahigh-performance nanofilamentary fibers.

Electrospinning and Characterisation of Poly(vinyl alcohol) Blend Submicron Fibres in Aqueous Solutions

Poly(vinyl alcohol) (number-average degree of polymerisation 1700 (PVA-17) and 4000 (PVA-40)) blend submicron fibres were fabricated by the electrospinning method in an aqueous solution of 5–10% polymer concentration. Scanning electron microscopy (SEM), differential scanning calorimetry (DSC), X-ray diffraction (XRD), and thermal gravimetric analysis (TGA) were utilised to characterise the morphology and physical properties of the PVA fibres. The role of PVA blend mass ratio and concentration and of processing parameters such as applied voltage and capillary-to-collector distance in the production of ultrafine submicron PVA blend fibres was investigated. Uniform PVA fibres with an average submicron-scale diameter (250–600 nm) could be prepared from a 7.5% PVA-17/PVA-40 blend solution with various mass ratios. With a lower PVA blend concentration (5%), using different PVA-17/PVA-40 mass ratios, beads appeared in the fibre morphology, and homogeneity was also absent. At a higher PVA blend concentration (10%), larger-diameter (&lt;700 nm) ribbon-like fibres were produced. Moreover, with a higher percentage of PVA-40 in the PVA blend fibres, superior crystallinity, thermal stability, and mechanical properties could be obtained by comparison with PVA-17.

Fe-Nd-B magnets via the hot extrusion of amorphous powders

A rapid solidification melt spinning technique has been developed to produce amorphous powders of Fe-Nd-B alloys modified with hafnium diboride. The amorphous powders are consolidated by the hot extrusion technique into bulk magnets of various cross sections. Consolidated magnets show ultrafine grain structure stabilized by ultrafine submicron hafnium diboride particles. The extruded magnets develop strong texture-induced magnetic anisotropy which leads to attractive energy product values of up to 16MGOe. Significant improvement in coercivity is also achieved due to ultrafine grain structure of the extruded magnets.