Investigation of the safety evaluation method of piping system

Journal of Mechanical Science and Technology - Plumbing is necessary for boilers and heat exchangers and in buildings and power plants, including those that produce green energy. Further, among all...     

An effective oxidation approach for luminescence enhancement in CdS quantum dots by H2O2

The effects of surface passivation on the photoluminescence (PL) properties of CdS nanoparticles oxidized by straightforward H₂O₂ injection were examined. Compared to pristine cadmium sulfide nanocrystals (quantum efficiency ≅ 0.1%), the surface-passivated CdS nanoparticles showed significantly enhanced luminescence properties (quantum efficiency ≅ 20%). The surface passivation by H₂O₂ injection was characterized using X-ray photoelectron spectroscopy, X-ray diffraction, and time-resolved PL. The photoluminescence enhancement is due to the two-order increase in the radiative recombination rate by the sulfate passivation layer.     

Enhanced electrochemical properties of SnO2 anode by AlPO4 coating

A SnO₂ anode material undergoes severe capacity loss, which is mainly associated with cracking/crumbling of the material by the large volume change between the Li_xSn and Sn phases, and the intensive reactions with the electrolyte solution. However, AlPO₄ nanoparticle coating showed drastically improved electrochemical properties with decreased surface cracks. The AlPO₄-coated SnO₂ exhibited a capacity of 781 mAh/g, approaching its theoretical capacity at the first cycle, with 44% capacity retention after 15 cycles between 2.5 and 0 V at a relatively high C rate of 105 mA/g. In contrast, the bare SnO₂ showed an initial capacity of 680 mAh/g, with only 8% capacity retention after 15 cycles.     

Evaluation of structural reliability of mems device in digital video disk systems

In this paper, we describe the reliability evaluation for MEMS devices, especially designed tbr DVD(Digital Video Disk) application. These MEMS devices are fabricated as a mirror plane (shutter plane) used in DVD data picking up. This micromachined annular shutter mirror (ASM) acts as an adjusting means of the numerical aperture. The electrostatic force can drive the upper plane up and down for focusing or defocusing of incident laser beam to the selected recording plane. So we need to evaluate the micromechanical properties of thin film structural materials to ensure the reliability of those MEMS devices. For those, we perfl)rm the fatigue tests onto the devices in the conditions of much accelerated than those of normal driving. The applied electrostatic force can induce the change of the thin film properties, and those are observed by direct and indirect methods (XRD and electrical system). And then, we compare the fatigue effects with electrical, optical data from the intentionally-fatigue-applied specimen and as-fabricated one under accelerated conditions. Consequently, we can estimate the structural reliability and will provide the effective suggestion data for the fabrication of stable mirror material before commercialization.     

Photoluminescence enhancement in CdS quantum dots by thermal annealing

ABSTRACT: The photoluminescence behavior of CdS quantum dots in initial growth stage was studied in connection with an annealing process. Compared to the as-synthesized CdS quantum dots (quantum efficiency approximately equal to 1%), the heat-treated sample showed enhanced luminescence properties (quantum efficiency approximately equal to 29%) with a narrow band-edge emission. The simple annealing process diminished the accumulated defect states within the nanoparticles and thereby reduced the nonradiative recombination, which was confirmed by diffraction, absorption, and time-resolved photoluminescence. Consequently, the highly luminescent and defect-free nanoparticles were obtained by a facile and straightforward process.     

Synthesis of vertically-aligned carbon nanotubes on stainless steel by water-assisted chemical vapor deposition and characterization of their electrochemical properties

We demonstrate synthesis of carbon nanotubes on stainless steel by water-assisted chemical vapor deposition using an Al/Fe bimetallic catalyst. A forest of vertically-oriented carbon nanotubes with a length of a few hundreds of micrometers were grown on the substrates. Electrical measurement confirmed that the carbon nanotubes were electrically connected to the stainless steel. Owing to the carbon nanotubes, electrochemical properties such as faradaic current and electron transfer were considerably improved. Carbon nanotubes grown on the stainless steel substrates would potentially be useful for various applications including electrochemical energy conversion and storage.     

Characterization of graphene-based supercapacitors fabricated on Al foils using Au or Pd thin films as interlayers

We demonstrate that an Au or Pd interlayer between graphene and an Al-foil current collector plays an important role in enhancing supercapacitor performance. Graphene was prepared by scalable chemical exfoliation and mild thermal reduction (～150 °C) processes. Working electrodes were prepared by coating the graphene on Au/Al or Pd/Al by drop-dry method. The graphene deposited on the noble metals Au and Pd demonstrated excellent supercapacitor performance. Estimated specific energy and specific power of supercapacitors were ～40 Wh/kg and ～40 kW/kg at the current density of ～33 A/g, when operated in organic solution. Altogether, we demonstrate that employing noble metals in the fabrication of graphene-based supercapacitors can lead to excellent performance, and this could be a critical basis for further development of graphene-based supercapacitors.     

Metal-phosphate coating on LiCoO2 cathodes with high cutoff voltages

Metal-phosphate coating on LiCoO₂ cathodes improved the cycle-life performance with high charge-cutoff voltages. The optimum annealing temperature and coating thickness for the excellent electrochemical properties of the metal-phosphate-coated LiCoO₂ cathodes were determined. Among the metal-phosphate-coating materials, the Al-P-O coating enhanced the electrochemical properties most efficiently. The EPMA results (after cycles) with a 4.8 V cutoff confirmed that most of the nanoscale coating layers, particularly the P component, had dissolved during cycling.