• Applied Chemistry for Engineering
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• v.10 no.3
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• pp.331-335
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• 1999

The transition metal oxides have been of interest as bifunctional electrocatalysts for bifunctional air electrodes. The amorphous citrate precursor (ACP) process has been optimized to prepare perovskite (La0.6Ca0.4CoO3) and pyrochlore (Pb2Ru2O6) powders with high surface area, and consequent improvement of The electrocatalytic performance in an air electrode with thermal treatment. PTFE -bonded gas diffusion electrodes loaded with perovskitc and pyrochlore catalysts showed good bifunctional performances. The electrodes were fairly stable up to 100 hour in the galvanostatic mode at ${\pm}25mA/cm^2$, from which these electrodes offer promise as practical bifunctional air electrodes.

• Journal of the Korean Society for Precision Engineering
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• v.28 no.5
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• pp.537-542
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• 2011

The thermo-mechanical interaction between brake block and wheel tread during braking has been found to cause thermal crack on the wheel tread. Due to thermal expansion of the rim material, the thermal cracks will protrude from the wheel tread and be more exposed to wear during the wheel/block contact than the rest of the tread surface. The wheel rim is in residual compression stress when is new. After service running, the region in the tread has reversed to tension. This condition can lead to the formation and growth of thermal cracks in the rim which can ultimately lead to premature failure of wheel. In the present paper, the thermal cracks of railway wheel, one of severe damages on the wheel tread, were evaluated to understand the safety of railway wheel in running condition. The residual stresses for damaged wheel which are applied to tread brake are investigated. Mainly X-ray diffusion method is used. Under the condition of concurrent loading of continuous rolling contact with rails and cyclic frictional heat from brake blocks, the reduction of residual stress is found to correlate well with the thermal crack initiation.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.490-490
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• 2011

Graphene, hexagonal network of carbon atoms forming a one-atom thick planar sheet, has been emerged as a fascinating material for future nanoelectronics. Huge attention has been captured by its extraordinary electronic properties, such as bipolar conductance, half integer quantum Hall effect at room temperature, ballistic transport over ${\sim}0.4{\mu}m$ length and extremely high carrier mobility at room temperature. Several approaches have been developed to produce graphene, such as micromechanical cleavage of highly ordered pyrolytic graphite using adhesive tape, chemical reduction of exfoliated graphite oxide, epitaxial growth of graphene on SiC and single crystalline metal substrate, and chemical vapor deposition (CVD) synthesis. In particular, direct synthesis of graphene using metal catalytic substrate in CVD process provides a new way to large-scale production of graphene film for realization of graphene-based electronics. In this method, metal catalytic substrates including Ni and Cu have been used for CVD synthesis of graphene. There are two proposed mechanism of graphene synthesis: carbon diffusion and precipitation for graphene synthesized on Ni, and surface adsorption for graphene synthesized on Cu, namely, self-limiting growth mechanism, which can be divided by difference of carbon solubility of the metals. Here we present that large area, uniform, and layer controllable graphene synthesized on Cu catalytic substrate is achieved by acetylene-assisted CVD. The number of graphene layer can be simply controlled by adjusting acetylene injection time, verified by Raman spectroscopy. Structural features and full details of mechanism for the growth of layer controllable graphene on Cu were systematically explored by transmission electron microscopy, atomic force microscopy, and secondary ion mass spectroscopy.

• Economic and Environmental Geology
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• v.26 no.1
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• pp.107-114
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• 1993

For the blue sapphires from Santung, China, the color change before and after has been investigated by UV-Visible spectrophotometry method. The blue sapphires from Shantung show four groups of absorption bands: the bands A (374, 386 and 450 nm) being attributed to single $Fe^{3+}$ ion, the band B (560, 579 and $704n{\breve{m}}$) to $Fe^{2+}$/$Ti^{4+}$ pairs, the band C (-800 nm) to $Fe^{2+}$/$Fe^{3+}$ pairs, and the D (528 nm) to $Ti^{3+}$ dd transitions. From those UV-VIS characteristics the origin of blue color of the sapphires is confirmed to be attributed by the factors such as $Fe^{2+}$/$Fe^{3+}$ and $Ti^{3+}$/$Ti^{4+}$. The absorption spectra of natural blue sapphires before and after heat treatment show distintive features, comparing with those of sapphires from other localities: the bands of 689 nm and of $Cr^{3+}$ are not recorded on the spectra of sapphires from Shantung. The band (492 nm), which resulted from $Ti^{3+}$, is not shown and the intensity of the band 528 nm decreases after the heat treatment. Decoloration of ink-blue sapphires are found to be successful by heat treatment with the control of annealing and atmosphere. During the diffusion process the excess components of impurities contained originally in the host crystal were expelled to the surface of crystals, enhancing the transparency of the crystals noticeably.

• Applied Chemistry for Engineering
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• v.10 no.8
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• pp.1099-1103
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• 1999

The surface of an ${\alpha}$-alumina tube was coated with zirconium modified polycarbosilane(PZC) by dip-coating method. Then the tube was pyrolyzed at 573~823 K. The prepared inorganic composite membrane was in $1{\mu}m$ thickness and had no pinholes larger than several nm. For the pyrolyzed inorganic composite membrane, the permeation test of He, $N_2$, $CO_2$, and $O_2$ was performed at 303~423 K. The gas permeation and separation factor were increased with increasing permeation temperature. The permeation for gases was controlled by the activated diffusion mechanism. The separation factor of $CO_2$, to $N_2$was 4.9 at 363 K on the composite membrane pyrolyzed at 823 K and its value was higher than that of He and $O_2$.

• Journal of the Korean Society for Heat Treatment
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• v.11 no.4
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• pp.305-314
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• 1998

This study has been performed to investigate into some effects of various amounts of $CO_2$ and CO gas added to the $50%NH_3-N_2$ based gas atmosphere on microstructure, hardness, chemical analysis and residual stress in the compound and diffusion layer of AISI H13 treated by gaseous nitrocarburising process. The compound layer formed in the surface is composed of mainly ${\varepsilon}-Fe_3$(N,C) and small amount of ${\gamma}^{\prime}-Fe_4N$ and cementite. The maximum hardness value obtainable from H13 steel is shown to be 1200 Hv and the effecvtive hardening depth increases with increasing CO content from 1% to 4%. In the case of CO content over 4%, however, it decreases with increasing CO content. The composition profiles of nitrogen and carbon are found to be within the ${\varepsilon}$-phase field located above the ${\varepsilon}+{\gamma}^{\prime}$ phase field in the Fe-N-C diagram. It is shown that the maximum value of compressive residual stress of H13 steel treated in atmospheres of $50%NH_3-(2,4)%CO_2-N_2-CO$ gas mixture is $48kg/mm^2$ and the depth to which residual stress is in Compressive state is $90{\mu}m$ for the atmosphere $50%NH_3-45%N_2-4%CO_2-1%CO$ gas mixture. It is consequently important to control the maximum value and size of compressive residual stress region in order to obtain desirable mechanical properties.

• Applied Chemistry for Engineering
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• v.7 no.3
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• pp.416-423
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• 1996

Electrochemical reduction of thionyl chloride in 1.5 M $LiAlCl_4/SOCl_2$ electrolyte solution containing tetradentate Schiff base Co(II), Ni(II), Cu(II), and Mn(II) complexes has been investigated at the glassy carbon electrode. The catalyst molecules of transition metal(II) complexes were adsorbed on the electrode surface and reduced thionyl chloride resulting in a generation of oxidized catalyst molecules. There was an optimum concentration for each catalyst compound. The current density of $SOCl_2$ reduction was enhanced up to 150% at the catalyst contained electrolyte solution. The reduction currents of thionyl chloride were increased and the reduction potentials were shifted to the negative potential as scan rates became faster. The reduction of thionyl chloride was proceeded to diffusion controlled reaction.

• International Journal of Fluid Machinery and Systems
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• v.2 no.2
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• pp.110-120
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• 2009

Generally the fluid flows within the centrifugal impeller passage as a decelerating flow with an adverse pressure gradient along the stream wise path. This flow tends to be in a state of instability with flow separation zones on the suction surface and on the front shroud. Hence several experimental attempts were earlier made to assess the efficacy of using boundary layer fences to trip the flow in the regions of separation and to make the flow align itself into stream wise direction so that the losses could be minimized and overall efficiency of the diffusion process in the fan could be increased. With the development of CFD, an extensive numerical whole field analysis of the effect of boundary layer fences in discrete regions of suspected separation points is possible. But it is found from the literature that there have been no significant attempts to use this tool to explore numerically the utility of the fences on the flow field. This paper attempts to explore the effect of boundary layer fences corresponding to various geometrical configurations on the impeller as well as on the diffuser. It is shown from the analysis that the fences located on the impellers near the trailing edge on pressure side and suction side improves the static pressure recovery across the fan. Fences provided at the radial mid-span on the pressure side of the diffuser vane and near the leading edge and trailing edge of the suction side of diffuser vanes also improve the static pressure recovery across the fan.

• Korean Journal of Materials Research
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• v.18 no.6
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• pp.307-312
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• 2008

In this study, a new cleaning process with a low cost of ownership (CoO) was developed with ozonated DI water ($DIO_3$). An ozone concentration of 40 ppm at room temperature was used to remove organic wax film and particles. Wax residues thicker than $200\;{\AA}$ remained after only a commercial dewaxer treatment. A $DIO_3$ treatment in place of a dewaxer showed a low removal rate on a thick wax layer of $8000\;{\AA}$ due to the diffusion-limited reaction of ozone. A dewaxer was combined with a $DIO_3$ rinse to reduce the wax removal time and remove wax residue completely. Replacing DI rinse with the $DIO_3$ rinse resulted in a surface with a contact angle of less than $5^{\circ}$, which indicates no further cleaning steps would be required. The particle removal efficiency (PRE) was further improved by combining a SC-1 cleaning step with the $DIO_3$ rinsing process. A reduction in the process time was obtained by introducing $DIO_3$ cleaning with a dewaxing process.

• Korean Journal of Materials Research
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• v.27 no.7
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• pp.392-397
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• 2017

Fluorine-doped tin oxide (FTO) coated NiCrAl alloy foam is fabricated using ultrasonic spray pyrolysis deposition (USPD). To confirm the influence of the FTO layer on the NiCrAl alloy foam, we investigated the structural, chemical, and morphological properties and chemical resistance by using USPD to adjust the FTO coating time (12, 18, and 24 min). As a result, when an FTO layer was coated for 24 min on NiCrAl alloy foam, it was found to have an enhanced chemical resistance compared to those of the other samples. This improvement in the chemical resistance of using USPD NiAlCr alloy foam can be the result of the existence of an FTO layer, which can act as a protection layer between the NiAlCr alloy foam and the electrolyte and also the result of the increased thickness of the FTO layer, which enhances the diffusion length of the metal ion.