Reduction characteristics of CuFe2O4 and Fe3O4 by methane; CuFe2O4 as an oxidant for two-step thermochemical methane reforming

The reduction characteristics of CuFe₂O₄ and Fe₃O₄ by methane at 600–900 °C were determined in a thermogravimetric analyzer for the purpose of using CuFe₂O₄ as an oxidant of two-step thermochemical methane reforming. It was found that the addition of Cu to Fe₃O₄ largely affected the reduction kinetics and carbon formation in methane reduction. In the case of CuFe₂O₄, the reduction kinetics was found to be faster than that of Fe₃O₄. Furthermore, carbon deposition and carbide formation from methane decomposition were effectively inhibited. In case of Fe₃O₄, Fe metal formed from Fe₃O₄ decomposed methane catalytically, that lead to the formation of graphite and Fe₃C phases. It is deduced that Cu in CuFe₂O₄ enhanced reduction kinetics, decreased reduction temperature and prevented carbide and graphite formation. Additionally, methane conversion and CO selectivity in the syngas production step with CuFe₂O₄ were in the range of 33.5–55.6% and 54.9–59.6%, respectively.     

Modelling of the thermal behaviour of an ultracapacitor for a 42-V automotive electrical system

A three-dimensional modelling approach is used to study the effects of operating and ambient conditions on the thermal behaviour of a NESSCAP 2.7 V/3500 F ultracapacitor cell for a 42-V automotive electrical system. The rate of heat generation of the ultracapacitor during charge and discharge is measured with a calorimeter. The transient temperature distribution of the ultracapacitor during cycling is obtained by using the finite element method with an implicit predictor-multicorrector algorithm. The results show that the temperature of the ultracapacitor cell increases during the first 50 cycles after which it reaches a periodic steady-state value that increases with increasing ambient temperature.     

Establishment of risk-based accident scenarios using the master logic diagram related to LILW management in the temporary storage facility

The initiating event, which is the first step in the establishment of risk-based accident scenarios, was derived by master logic diagram (MLD) method based on the fault tree analysis (FTA), and then the risk-based accident scenarios were developed by the event tree analysis (ETA) through the derived initiating events. The main initiating events led to the arbitrary operational accident: the dropping of a drum and fire were derived from the MLD method. Consequently, based on two main initiating events, four heading events were derived, and then the 12 risk-based accident scenarios concerning the LILW management in the temporary storage facility were finally established by the ETA method.     

Synthesis of high-purity silver colloids using a thermal decomposition method

A thermal decomposition method was employed to produce high purity Ag particles. Silver carbonate was dispersed in an H₂O solvent that was heated above 80°C, followed by rapidly injecting H₂O₂ into the solvent. Then, the silver carbonate was decomposed into nanosized Ag particles using the decomposition heat of hydrogen peroxide as follows: Ag₂CO₃→2Ag+CO₂+1/2O₂. The size of the synthesized Ag particles is approximately 100 nm. This method can be used to produce high-purity Ag colloids withuut impurities, unlike other methods.     

Luminescence properties of Nd-doped (Y,Gd)BO3 phosphors

A system of 0.03 mol Nd³⁺-doped (Y,Gd)BO₃ phosphors were prepared by the conventional solid state reaction method for different concentrations of Gd³⁺ ions and were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and NIR emission measurements. The emitted radiation was dominated by 1057 nm peak in the NIR region as a result of ⁴F_3/2 → ⁴I_11/2 transitions of Nd³⁺ ions. As the concentration of Gd³⁺ ions increases from 0.00 to 0.57 mol, the grain sizes and the intensity of NIR emission peaks were improved. The results are discussed in comparison with similar reported works.     

Effect of carrier concentration on optical bandgap shift in ZnO:Ga thin films

The Ga-doped ZnO thin films were deposited on glass substrate by sputtering and annealed at 350 °C in hydrogen atmosphere for 1 h. The optical bandgap of thin films showed the lower blueshift than the theoretical value of the Burstein-Moss (BM) effect. The shift of bandgap was dependent on the carrier concentration and acquired by combining the nonparabolic BM effect and bandgap narrowing (BGN). The modified BM effect equation was proposed to substitute the nonparabolic BM effect and BGN. The exponent in the modified BM equation was affected by carrier concentration and it was decreased with carrier concentration.     

Effect of high-energy electron beam irradiation on the properties of AZO thin films prepared by rf magnetron sputtering

We investigated that high-energy electron beam irradiation (HEEBI) performed in air at room temperature affected remarkably the properties of Al-doped ZnO (AZO) films grown on SiO₂ substrates by radio frequency magnetron sputtering techniques. Hall and photoluminescence measurements revealed that the n-type conductivity was preserved in HEEBI treated films with low dose up to 10¹⁵ electrons/cm² and converted to p-type conductivity with further increase in the amount of dose. X-ray photoelectron spectroscopy confirmed the conversion of conductivity by showing that in-diffusion of O₂ from the ambient as well as out-diffusion of Zn from the films took place as a result of HEEBI treatment at high dose of 10¹⁶ electrons/cm². X-ray diffraction analysis indicated that all as-grown films were found to have compressive stress, which was enhanced by HEEBI treatment with the increase of doses. It was also found that worse crystallinity with a smaller grain size was observed in HEEBI treated films with a higher dose, which was correlated with rougher surface morphologies of films observed by an atomic force microscope.     

Water photolysis by NaTaO3-C composite prepared by spray pyrolysis

Spherical powders of NaTaO₃-C composite were prepared by a step process in a continuous spray pyrolysis reactor and tested their photocatalytic activity in a continuous slurry reactor for the production of hydrogen from water. Effects of carbon contents in the composite on the crystal, surface property, shape, optical absorption response and efficiency of hydrogen production of the composite were examined. The crystal of NaTaO₃-C composite was analyzed by XRD analysis. From the analysis of SEM images, the prepared composite powder was found to be spherical with rough surface. The roughness of the composite surface became noticeable with increasing carbon content in the composite. The concentrations of all elements in the composite were determined by energy dispersive spectra (EDS). From the analysis of optical response, which was analyzed by diffuse reflectance spectra (DRS), the absorption edge of NaTaO₃-C composite was extended to the whole visible light range. The extension to the visible light absorption edge became drastic with increasing carbon content in the composite up to 8.98 wt.%. However, this shift is not directly related to the band change because there is no evidence that carbon is incorporated in the lattice of NaTaO₃.     

Thermal behavior of a quantum dot nanocomposite as a color converting material and its application to white LED

We present a novel nanocomposite, a mixture of a CdSe/CdS/ZnS red quantum dot (QD), an Sr(2)SiO(4):Eu green phosphor and silicone resin for a color converting material. The temperature rise and the optical characteristics of the nanocomposite due to the addition of the QD have been investigated in terms of QD content ratio and the mixing components. The experimental results suggested that a small addition of QDs generated a large amount of heat during light conversion at the wavelength of QD emission. Considering the temperature rise in a nanocomposite, we applied 0.2 wt% QDs on an InGaN blue LED chip. As a result, we could achieve a white LED device with a high color rendering index of 83.2, a high luminance of 65.86 lm W(-1) and a moderate temperature increase of 94?°C. The white LED converted by the newly developed QD-phosphor nanocomposite has great potential in future illumination.     

Annealing behavior of TiO<Subscript>2</Subscript>-sheathed Ga<Subscript>2</Subscript>O<Subscript>3</Subscript> nanowires

TiO₂-sheathed Ga₂O₃ one-dimensional (1D) nanostructures were synthesized by thermal evaporation of GaN powders and then sputter-deposition of TiO₂. Transmission electron microscopy (TEM) and X-ray diffraction (XRD) analysis results indicate that the Ga₂O₃ cores are of a single crystal nature with a monoclinic structure while the TiO₂ shells are amorphous. Photoluminescence (PL) emission is slightly decreased in intensity by TiO₂ coating, but it is significantly increased by thermal annealing in an oxygen atmosphere. The emission peak is also shifted from ~500 to ~550 nm by oxygen annealing. The increase in the green emission is due to the increase in the concentration of the Ga vacancies in the cores by the inflow of oxygen during oxygen annealing. On the other hand, annealing in a nitrogen atmosphere leads to a red shift of the emission to ~700 nm originating from nitrogen doping.