Design of High-Remanence Nd-Fe-B Hot-Pressed Magnets by Manipulating Coercivity of Hydrogenation-Disproportionation-Desorption-Recombination Treated Anisotropic Precursors.

We propose a method of manipulating the coercivity of anisotropic hydrogenation-disproportionation-desorption-recombination (HDDR) powders to fabricate high-remanence and fine-grained Nd-Fe-B magnets using only hot-pressing without a subsequent hot-deformation process. By reducing the Nd content of anisotropic HDDR precursors such that their coercivity (Hcj) is lowered, the c-axis of each HDDR particle is well-aligned parallel to the direction of the applied magnetic field during the magnetic alignment step. This is because the magnetic repulsive force between adjacent particles, determined by their remanent magnetization, decreases as a result of the low coercivity of each particle. Therefore, after hot-pressing the low-Hcj HDDR powders, a significantly higher remanence (11.2 kG) is achieved in the bulk than that achieved by hot-pressing the high-Hcj HDDR powders (8.2 kG). It is clearly confirmed by the large-scale electron backscatter diffraction (EBSD) analysis that the alignment of the c-axis of each anisotropic HDDR particle in the bulk is improved when low-Hcj HDDR powders are used to fabricate hot-pressed magnets. This coercivity manipulation of HDDR powders can be a helpful method to expand the use of HDDR powders in fabricating anisotropic Nd-Fe-B bulk magnets.

Effect of Cathode Microstructure on Electrochemical Properties of Sodium Nickel-Iron Chloride Batteries.

Sodium metal chloride batteries have become a substantial focus area in the research on prospective alternatives for battery energy storage systems (BESSs) since they are more stable than lithium ion batteries. This study demonstrates the effects of the cathode microstructure on the electrochemical properties of sodium metal chloride cells. The cathode powder is manufactured in the form of granules composed of a metal active material and NaCl, and the ionic conductivity is attained by filling the interiors of the granules with a second electrolyte (NaAlCl4). Thus, the microstructure of the cathode powder had to be optimized to ensure that the second electrolyte effectively penetrated the cathode granules. The microstructure was modified by selecting the NaCl size and density of the cathode granules, and the resulting Na/(Ni,Fe)Cl2 cell showed a high capacity of 224 mAh g-1 at the 100th cycle owing to microstructural improvements. These findings demonstrate that control of the cathode microstructure is essential when cathode powders are used to manufacture sodium metal chloride batteries.

Enhanced Crystallinity and Luminescence Characteristics of Hexagonal Boron Nitride Doped with Cerium Ions According to Tempering Temperatures.

Hexagonal boron nitride was synthesized by pyrolysis using boric acid and melamine. At this time, to impart luminescence, rare earth cerium ions were added to synthesize hexagonal boron nitride nanophosphor particles exhibiting deep blue emission. To investigate the changes in crystallinity and luminescence according to the re-heating temperature, samples which had been subjected to pyrolysis at 900 °C were subjected to re-heating from 1100 °C to 1400 °C. Crystallinity and luminescence were enhanced according to changes in the reheating temperature. The synthesized cerium ion-doped hexagonal boron nitride nanoparticle phosphor was applied to the anti-counterfeiting field to prepare an ink that can only be identified under UV light.

A chemically bonded supercapacitor using a highly stretchable and adhesive gel polymer electrolyte based on an ionic liquid and epoxy-triblock diamine network.

Despite significant advances in the development of flexible gel polymer electrolytes (GPEs), there are still problems to be addressed to apply them to flexible electric double layer capacitors (EDLCs), including interfacial interactions between the electrolyte and electrode under deformation. Previously reported EDLCs using GPEs have laminated structures with weak interfacial interactions between the electrode and electrolyte, leading to fragility upon elongation and low power density due to lower utilization of the surface area of the carbon material in the electrode. To overcome these problems, we present a new strategy for constructing an epoxy-based GPE that can provide strong adhesion between electrode and electrolyte. The GPE is synthesized by polymerization of epoxy and an ionic liquid. This GPE shows high flexibility up to 509% and excellent adhesive properties that enable strong chemical bonding between the electrode and electrolyte. Moreover, the GPE is stable at high voltage and high temperature with high ionic conductivity of ∼10-3 S cm-1. EDLCs based on the developed GPE exhibit good compatibility between the electrode and electrolyte and work properly when deformed. The EDLCs also show a high specific capacitance of 99 F g-1, energy density of 113 W h kg-1, and power density of 4.5 kW g-1. The excellent performance of the GPE gives it tremendous potential for use in next generation electronic devices such as wearable devices.

Surface characteristic of chemically converted graphene coated low carbon steel by electro spray coating method for polymer electrolyte membrane fuel cell bipolar plate.

Graphene was coated on low carbon steel (SS400) by electro spray coating method to improve its properties of corrosion resistance and contact resistance. Exfoliated graphite was made of the graphite by chemical treatment (Chemically Converted Graphene, CCG). CCG is distributed using dispersing agent, and low carbon steel was coated with diffuse graphene solution by electro spray coating method. The structure of the CCG was analyzed using XRD and the coating layer of surface was analyzed using SEM. Analysis showed that multi-layered graphite structure was destroyed and it was transformed in to fine layers graphene structure. And the result of SEM analysis on the surface and the cross section, graphene layer was uniformly formed with 3-5 microm thickness on the surface of substrate. Corrosion resistance test was applied in the corrosive solution which is similar to the polymer electrolyte membrane fuel cell (PEMFC) stack inside. And interfacial contact resistance (ICR) test was measured to simulate the internal operating conditions of PEMFC stack. As a result of measuring corrosion resistance and contact resistance, it could be confirmed that low carbon steel coated with CCG was revealed to be more effective in terms of its applicability as PEMFC bipolar plate.

Advantages of using Ti-mesh type electrodes for flexible dye-sensitized solar cells.

We used Ti meshes for both the photoanodes and counter electrodes of dye-sensitized solar cells (DSSCs) to improve the flexibility and conductivity of the electrodes. These mesh type electrodes showed good transparency and high bendability when subjected to an external force. We demonstrated the advantages of cells using such electrodes compared to traditional transparent conducting oxide based electrodes and back side illuminated DSSCs, such as low sheet resistance, elevated photo-induced current and enhanced sunlight utilization. Nanotube layers of different thicknesses were investigated to determine their effect on the photovoltaic parameters of the cell. The overall efficiency of the best cells was approximately 5.3% under standard air mass 1.5 global (AM 1.5 G) solar conditions. Furthermore, the DSSCs showed an efficiency of approximately 3.15% due to the all Ti-mesh type electrodes even after illumination from the back side.

Pure SF6 and SF6-N2 mixture gas hydrates equilibrium and kinetic characteristics.

Sulfur hexafluoride (SF6), whether pure or mixed with inexpensive inert gas, has been widely used in a variety of industrial processes, but it is one of the most potent greenhouse gases. For this reason, it is necessary to separate and/or collect it from waste gas streams. In this study, we investigated the pure SF6 and SF6-N2 mixture gas hydrates formation equilibrium aswell asthe gas separation efficiency in the hydrate process. The equilibrium pressure of SF6-N2 mixture gas was higher than that of pure SF6 gas. Phase equilibrium data of SF6-N2 mixture gas was similar to SF6 rather than N2. The kinetics of SF6-N2 mixture gas was controlled by the amount of SF6 at the initial gas composition as well as N2 gas incorporation into the S-cage of structure-II hydrate preformed by the SF6 gas. Raman analysis confirmed the N2 gas incorporation into the S-cage of structure-II hydrate. The compositions in the hydrate phase were found to be 71, 79, 80, and 81% of SF6 when the feed gas compositions were 40, 65, 70, and 73% of SF6, respectively. The present study provides basic information for the separation and purification of SF6 from mixed SF6 gas containing inert gases.

Fabrication of Volmer-Weber type ZnO nanorods by combining RF sputtering and hydrothermal methods.

We fabricated Volmer-Weber type ZnO nanorods by using a hydrothermal method combing with an RF sputtering system. Volmer-Weber type ZnO seed nanocrystals were formed on Pt(111)/TiO2/SiO2/Si(100) substrates by using RF sputtering method and then the seeded substrates were soaked in an aqueous chemical solution, which was mixed with Zn(NO3)2 x 6H2O and NaOH. We found that ZnO nanorods were perpendicularly grown along the [002] direction by using X-ray diffraction (XRD) and scanning electron microscopy (SEM) methods. We also confirmed that fabricated ZnO nanorods were Volmer-Weber type by using an energy dispersive X-ray spectrometer (EDX) method.

The fabrication of TiO2 mesoporous thick films by employing a pre-embedded ZnO nanorods support.

TiO2 mesoporous films with a thickness more than 2 microm were synthesized through the evaporation-induced self-assembly approach. In order to prevent the formation of cracks due to the strain during the calcination, we employed the ZnO nanorod arrays as a pre-embedded support, which were obtained from an aqueous solution method. The spaces between ZnO nanorods were filled with TiO2 sol-gel by a dip-coater. Then ZnO nanorods embedded in the thick film were eliminated by a wet chemical etching method and the left spaces were refilled by the TiO2 sol-gel. As a result, a dense and thick TiO2 mesoporous film was obtained. The resultant materials were characterized in detail by using small angle X-ray diffraction (SAXRD), field-emission scanning electron microscopy (FESEM) and transmission electron microscopy methods (TEM).

The growth mechanism and optical properties of ultralong ZnO nanorod arrays with a high aspect ratio by a preheating hydrothermal method.

Well-aligned ultralong ZnO nanorod arrays with a length of 10 microm have been synthesized on glass substrates using a preheating hydrothermal method. The diameter of the nanorods is in the range from 50 to 80 nm, and the aspect ratio and alignment can be simply controlled by varying the preheating time. Based on the evolution of aspect ratio with preheating time, a possible growth mechanism was proposed. X-ray diffraction (XRD) and scanning electron microscopy (SEM) show that the nanostructures are well oriented with the c-axis perpendicular to the substrate. The photoluminescence (PL) spectrum of the as-grown ZnO nanostructure reveals a near-band-edge (NBE) emission peak and a yellow emission, and the origin of yellow emission was confirmed to be from the absorbed hydroxyl group. The ultralong nanorod arrays made in solution have a desirable diameter, length, density and orientation for ordered nanodevice applications.

Surfactant effects on SF6 hydrate formation.

Sulfur hexafluoride (SF(6)) has been widely used in a variety of industrial processes, but it is one of the most potent greenhouse gases. For this reason, it is necessary to separate or collect it from waste gas streams. One separation method is through hydrate crystal formation. In this study, SF(6) hydrate was formed in aqueous surfactant solutions of 0.00, 0.01, 0.05, 0.15 and 0.20 wt% to investigate the effects of surfactants on the hydrate formation rates. Three surfactants, Tween 20 (Tween), sodium dodecyl sulfate (SDS) and linear alkyl benzene sulfonate (LABS), were tested in a semi-batch stirred vessel at the constant temperature and pressures of 276.2 K and 0.78 MPa, respectively. All surfactants showed kinetic promoter behavior for SF(6) hydrate formation. It was also found that SF(6) hydrate formation proceeded in two stages with the second stage being the most rapid. In situ Raman spectroscopy analysis revealed that the increased gas consumption rate with the addition of surfactant was possibly due to the increased gas filling rate in the hydrate cavity.