Applied Mechanics and Materials Vols. 423-426

Abstract: This paper presents an analysis for electromagnetic energy in dispersive composite media based on classical electrodynamics. An investigation of the relation between reactance rate and electromagnetic energy derived from the Fosters theorem is conducted. The material energy of this kind is discussed in the frequency band of the left handed property. It is illustrated that the time average electromagnetic energy density is still positive even after an effect of dissipation is cancelled in the left handed band, which is reasonable in physics.

Abstract: This paper presents a fundamental study of processing, morphologies, properties, and applications of a novel non-woven nanopaper based on carbon nanofibers (CNFs). Unique material formulations were developed to tailor the non-woven nanopaper to specific engineering applications. The non-woven nanopaper was made from a variety of nanomaterials (e.g. carbon nanotubes, carbon nanofibers, graphene, nanoclay, nickel nanostrands, POSS, etc.) with tailored nanostructures by precisely controlling composition, dispersion, functionalization, orientation, porosity, and thickness during the vacuum infiltration, pressure infiltration, or spray/infiltration process. The polymer matrix was impregnated into the stacked nanopapers to form multi-layered laminated composites. Such non-woven nanopaper based composites were designed and fabricated to achieve high energy dissipation capability for vibrational damping, high thermal conductivity and thermal stability for fire retardancy, ultra-high electrical conductivity and current-carrying capacity for lightning strike protection, and electro-actuation of shape memory polymer composites.

Abstract: Nanofiber yarn, since it might be used in weaving and knitting, has been of great interest recently due to the potential application in many fields. A modified method to produce continuous nanofiber yarn using two oppositely spinnerets system with an auxiliary rotating circular plate is suggested in this work. The influence of process parameters, such as applied voltage, spinneret-plate distance and the angle between the two spinnerets, on the morphologies and properties of nanofiber yarn were investigated in detail. The optimum process parameters obtained include that the applied voltage was 15kv, the spinneret-plate distance was 7cm and the angle between the two spinnerets was 130o. The mechanical properties of these yarns have been evaluated, including twist and tensile strength. This work can provide a novel and general approach to design and produce nanofiber yarns for textiles, biomedical and industrial applications.

Abstract: The relationship between the etching current density and the macropore diameter was studied in the macroporous silicon (MPS) photo-electrochemical (PEC) etching. By measuring the depth of the channel with different etching time, the variation of critical current density with time was calculated. The importance to real-time adjust the etching current was discussed in the etching process. Based on the PSoC chip, an automatic control system for etching current was designed. The MPS growth was realized with the pore diameter constant using the automatic control system for etching current with a pre-set curve of etching current versus time.

Abstract: With addition of surfactants, a nanocrystalline HZSM-5 zeolite was prepared by hydrothermal synthesis method. X-ray diffraction (XRD) characterization results showed that surfactants can constraint the crystallization of HZSM-5. Scanning electronic microscopy (SEM) characterization revealed that nanocrystalline HZSM-5 with more regular morphology and smaller particle size can be prepared with suitable surfactants as additives. The HZSM-5 particles were 200-800 nm in size and constructed by primary HZSM-5 nanocrystals of 3050 nm. The average particle size will grow up to 800 nm with a cationic surfactant, and decrease to 200 nm with a anionic surfactant.

Abstract: The template method combined with sol-dipping deposition or sol-electrophoresis was used to prepare titania (TiO₂) nanowires with shape of rod or string of beads. When irradiated under ultraviolet (UV) light for 1 hour, the degradation rate of methyl orange (MO) using nanowire arrays reached 98.5% which was 1.84 times as much as that of the thin film on glass plate, and when irradiated under visible light for 6 hours, the degradation rate reached 96.7% which was 4.17 times as much as that of the thin film.

Abstract: Undoped and B-doped silicon-based nanowires (SiNWs) were synthesized by vapor-liquid-solid growth, and SiNW devices using Au electrodes were prototyped using focused ion beam (FIB) processing. Needle-shaped thin SiNWs were formed at a substrate temperature between 1170 and 1313 °C. The average and minimum diameters of the B-doped SiNWs were 72 nm and 52 nm, respectively. According to the current-voltage characteristics, SiNW devices have ohmic properties, and the estimated resistivity of the undoped and B-doped SiNWs are about 3.8 × 10³ Ωcm and 1.7 × 10³ Ωcm, respectively.

Abstract: This work presents a facile approach to grow carbon nanotubes (CNTs) on the surface of carbon foams (CFs) for the fabrication of hierarchical CNTs/CF composites, which exhibit enhanced oil adsorption capability. The preparation of CFs is carried out by using commercially available polyurethane (PU) foams as hard template and resol as carbon precursor. Fe/Mg/Al layered double hydroxide (LDHs) is used as catalyst precursor for the efficient growth of CNTs on CFs via chemical vapor deposition (CVD), in which CNTs are controllably grown onto the strut of CFs. The presence of CNTs in the CFs can significantly improve the hydrophobicity of the composites and enable the selective separation of oil from water with the combination of hydrophobicity and capillary action. Such well-designed hierarchical nanostructures are benefit for maximum utilization of cell structure and surface property of the composites and display good oil adsorption performance. The synthesis procedure paves the way for the exploitation of the CFs as adsorbent for the removal of spill oil and environmental protection.

Abstract: A monodisperse nanocrystalline HZSM-5 zeolite was prepared by varying-temperature synthesis method with aluminum nitrate (Al (NO₃)₃), tetraethyl orthosilicate (TEOS), and tetrapropyl ammonium hydroxide (TPAOH) as raw materials. X-ray diffraction (XRD) characterization results showed that the crystallinity of HZSM-5 prepared by varying-temperature synthesis method was higher than constant-temperature synthesis . The influence of crystallization temperature and time on morphology and particle size of HZSM-5 is represented by scanning electronic microscopy (SEM) characterization: nanocrystalline HZSM-5 with more regular morphology and smaller particle size can be prepared by varying-temperature synthesis method. The minimum average particle size is 0.3μm. The particle size will grow up to 3.0μm with the crystallization time prolonged.

Abstract: Pores are common defects in the coating formed via plasma spraying. In order to investigate the formed mechanism of pores in plasma sprayed nanostructured Al₂O₃-TiO₂ coatings, the microstructure of the feed stock, splat and coating were characterized by means of scanning electron microscopy (SEM). The coating shows a typical lamellar morphology, which contains fully melted (FM) zone and partly melted (PM) zone.The pores in different places of the coating were generated from different sources. The shapes and the size of the pores are also different. Keywords: plasma spray, coating, pores, formed mechanism