Yong Shin Kim

Effects of Sn and Nb on massive hydriding kinetics of Zr–XSn–YNb alloy

Kinetic studies on the massive hydriding of Zr–0.4Nb–XSn (X=0.5, 0.8, 1.5, 2.0) and Zr–0.8Sn–YNb (Y=0.2, 0.4, 0.8, 1.0) ternary alloys are carried out at 400°C under atmospheric pressure by in situ weight gain measurements with thermo-gravimetric apparatus (TGA) and transmission electron microscope/energy dispersive X-ray spectrometer (TEM/EDX) analysis. It is confirmed that the hydriding kinetics follow a linear rate law after incubation time. It is found that the hydriding reaction rate decreases with increasing Sn content up to 1.5% and then sharply increases in the case of Zr–0.4Nb–XSn while it steadily increases with Nb content in the case of Zr–0.8Sn–YNb. The rate does not seem to be affected by the grain size in the XSn alloys, but is influenced in the YNb alloys. TEM/EDX analysis shows that there is no strong relationship between the intermetallic precipitates and the kinetic rate in the Zr–XSn–YNb alloy system. It is revealed in this study that the solubility limit of Sn in the Zr–0.4Nb–XSn ternary system becomes higher than that in the Zr–Sn binary system. On the other hand, the Nb solubility limit remains unchanged in the Zr–0.8Sn–YNb ternary system. Optimized compositions in the Zr–XSn–YNb ternary alloy are suggested to be about 1.5% Sn and as low Nb as possible in order to minimize hydrogen uptake.

Fabrication of Pt-MWNT/Nafion Electrodes by Low-Temperature Decal Transfer Technique for Amperometric Hydrogen Detection

A Pt nanoparticle-decorated multiwall carbon nanotube (Pt-MWNT) electrode was prepared on Nafion by a hot-pressing at relatively low temperature. This electrode exhibited an intricate entangled, nanoporous structure as a result of gathering highly anisotropic Pt- MWNTs. Individual Pt nanoparticles were confirmed to have a polycrystalline face-centered cubic structure with an average crystal size of around 3.5 nm. From the cyclic voltammograms for hydrogen redox reactions, the Pt-MWNT electrode was found to have a similar electro- chemical behavior to polycrystalline Pt, and a specific electrochemical surface area of 2170 cm 2 mg �1 . Upon exposure to hydrogen analyte, the Pt-MWNT/Nafion electrode demon- strated a very high sensitivity of 3.60 µA ppm �1 and an excellent linear response over the con- centration range of 100-1000 ppm. Moreover, this electrode was also evaluated in terms of response and recovery times, reproducibility, and long-term stability. Obtained results revealed good sensing performance in hydrogen detection.

Laminated and infused Parafilm® − paper for paper-based analytical devices

Numerous fabrication methods have been reported for microfluidic paper-based analytical devices (μPADs) using barrier materials ranging from photoresist to wax. While these methods have been used with wide success, consistently producing small, high-resolution features using materials and methods that are compatible with solvents and surfactants remains a challenge. Two new methods are presented here for generating μPADs with well-defined, high-resolution structures compatible with solvents and surfactant-containing solutions by partially or fully fusing paper with Parafilm® followed by cutting with a CO2 laser cutter. Partial fusion leads to laminated paper (l-paper) while the complete fusion results in infused paper (i-paper). Patterned structures in l-paper were fabricated by selective removal of the paper but not the underlying Parafilm® using a benchtop CO2 laser. Under optimized conditions, a gap as small as 137 ± 22 μm could be generated. Using this approach, a miniaturized paper 384-zone plate, consisting of circular detection elements with a diameter of 1.86 mm, was fabricated in 64 × 43 mm2 area. Furthermore, these ablation-patterned substrates were confirmed to be compatible with surfactant solutions and common organic solvents (methanol, acetonitrile and dimethylformamide), which has been achieved by very few μPAD patterning techniques. Patterns in i-paper were created by completely cutting out zones of the i-paper and then fixing pre-cut paper into these openings similar to the strategy of fitting a jigsaw piece into a puzzle. Upon heating, unmodified paper was readily sealed into these openings due to partial reflow of the paraffin into the paper. This unique and simple bonding method was illustrated by two types of 3D μPADs, a push-on valve and a time-gated flow distributor, without adding adhesive layers. The free-standing jigsaw-patterned sheets showed good structural stability and solution compatibility, which provided a facile alternative method for fabricating complicated μPADs.

Synthesis of Hybrid Reduced Graphene Oxide Decorated with Ru(bpy)3(2+)-Doped Silica Nanoparticles.

Hybrid materials consisting of electrically conductive reduced graphene oxide (RGO) and Ru(bpy)3(2+)-doped silica (Ru@SiO2) nanoparticles were synthesized by hydrolysis of TEOS in the presence of Ru(bpy)3Cl2 and RGO. Many spherical Ru@SiO2 nanoparticles, of an average size of 96 nm, were observed to be strongly anchored on a planar RGO surface in SEM and TEM images. FTIR and EDS analyses confirmed the chemical compositions and functional groups of Ru@SiO2 and partially reduced RGO. The RGO prepared by 200 degrees C thermal treatment of GO in N2 was probed to have a multilayered sheet structure by XRD. An absorption spectrum of the hybrid exhibited a considerable red-shift in the characteristic visible peak of free Ru(bpy)3(2+) centered at 452 nm due to electrostatic interactions between Ru(bpy)3(2+) and negatively charged silica, indicating strong immobilization of Ru(bpy)3(2+) in the silica matrix.

Fabrication of Methanol Sensors Using Conductive Polypyrrole Nanofibers with a Core-Shell Structure

Electrically conductive polypyrrole-polyvinylpyrrolidone (PPy-PVP) nanofiber mats with a core-shell structure have been successfully fabricated by a two-step process: the formation of FeCl3-containing PVP nanofiber mat by electrospinning, and the vapor-phase polymerization (VPP) of pyrrole monomer on the mat in a sealed chamber at room temperature. Surface morphology and chemical composition of the PPy-PVP mat were characterized by SEM, EDX and FTIR analyses. The as-prepared nonwoven mat was composed of PPy-PVP nanofibers with an average diameter of 300 nm. The sheet conductivity of the nanofiber mat was measured to be approximately 0.01 S/cm by a four-point probe. We have also investigated gas-sensing properties of PPy-PVP nanofiber mat upon exposure to methanol vapor. The PPy-PVP nanofiber sensors were observed to have excellent methanol-sensing performance. The nanofiberbased core-shell nanostructure could give an opportunity to fabricate a highly sensitive and fast response sensor due to its high surfaceto-volume ratio.