• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.362-362
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• 2010

Today, vast attention has been paid to periodic arrays of nanostructures due to their potential for applications such as memory with huge storage density. Such application requires large-scale fabrication of well ordered nano-sized structures. One of the most widely used methods for the ordered nanostructures is lithography. This top-down process, however, has the limit to reduce size. Here the promising alternative is the self-organization of ordered nano-sized structures such as large scale 2d carbon-induced reconstructions on W(110). In the present study, we report on the first well-resolved atomic resolution STM studies of the well-known R($15{\times}3$) and R($15{\times}12$) carbon induced reconstruction of the W(110). From the atomic image of R($15{\times}3$) for different values of tunneling gap resistance, we can tell there are no missing atoms in unit cells of R($15{\times}3$) and some atomic displacements are substantial from the clean W(110), even though not all the imaged position of atoms correspond to tungsten, but may include those of carbon. We are considering two cases; First case is related to lattice deformation, or top layer of W(110) is deformed in the process of relief of strain caused by random inserting of carbon atoms possibly in the interstitial position. In the second case, R($15{\times}3$) unit cell results from a coincidence lattice between clean W(110) substrate and tungsten carbide overlayer which has rectangular atomic arrangement and giving R($15{\times}3$) coincidence lattice. beta-W2C showing rectangular unit cell should be a candidate. Further, we report on new reconstructions. Unlike the well-known R($15{\times}12$) consisting of two parts, two inner structures between two "Backbone" structures. The new reconstruction, which we found for the first time, contains more parts between the "Backbone"s. Sometimes we can observe the reconstruction consists of only inner parts without "Backbone" parts. Thus, the observed reconstruction can be built by constructing of two types of "Lego"-like block. Moreover, the rectangle shape of "Backbone" transform to parallelogram-like shape over time, the so-called wavy-R($15{\times}12$). Adsorption of hydrogen can be the reason for this transformation.

• Korean Chemical Engineering Research
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• v.60 no.4
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• pp.620-629
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• 2022

By varying various experimental conditions such as heating rate, molar hourly space velocity (MHSV), and nitridation reaction temperature, vanadium oxynitride was prepared through temperature programmed reduction/nitridation reaction (TPRN) of vanadium pentoxide and ammonia, and characterization were performed. In order to investigate the physico-chemical properties of the prepared catalyst, N₂ adsorption-desorption analysis, X-ray diffraction analysis (XRD), hydrogen temperature programmed reduction (H₂-TPR), temperature programmed oxidation (TPO), ammonia temperature programmed desorption (NH₃-TPD), transmission electron microscopy (TEM) was performed. Transformation of V₂O₅ with 5 m² g^-1 low specific surface area by reduction at 340 ℃ to V₂O₃ showed a high specific surface area value of 115 m² g^-1 by micropore formation. As the nitridation temperature increased beyond that, the specific surface area continued to decrease due to sintering. The nitridation reaction variable that had the greatest influence on the specific surface area was the reaction temperature, and the x + y value of VN_xO_y of a single phase approached from 1.5 to 1.0 as the nitridation reaction temperature increased. At a high reaction temperature of 680 ℃, the cubic lattice constant a was VN. close to the value. At 680 ℃, the highest nitridation temperature among the experimental conditions, the ammonia conversion rate was 93%, and no deactivation was observed.

• Analytical Science and Technology
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• v.19 no.5
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• pp.369-375
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• 2006

Calibration gas mixtures were prepared using dynamic volumetric method according to ISO 6145-5 and the uncertainty was evaluated. Ten identical capillaries with 0.25 mm in inner diameter and 50 cm in length were applied in this system. Dilution ratio of parent gas was determined by the number of capillaries that passes parent gas and that passes balance gas through. Capillaries were made of Teflon which had good chemical stability against adsorption of gaseous substances. Mechanical valves were introduced in this system in order to minimize the thermal effect of solenoid valves. Concentration of prepared gases were compared with master grade standard gases in cylinders made by RiGAS Co. and calibration of the instrument were completed using comparison method according to ISO 6143. Experimental results showed that the coefficient of variance of diluted oxygen standard gases showed less then 0.2% in most dilution range, that of diluted hydrogen sulfide standard gases showed less then 1.0%. Therefore, it is proven that the standard gases prepared by this system are appropriate to be used as a calibration standards in ambient monitoring, etc.

• Clean Technology
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• v.21 no.1
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• pp.68-75
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• 2015

In this study, we investigated the structure and properties of a highly heat conductive metal-ceramic core-shell CoAl₂O₄@Al micro-composite for heterogeneous catalysts support. The CoAl₂O₄@Al was prepared by hydrothermal surface oxidation of Al metal powder, which resulted in the structure with a high heat conductive Al metal core encapsulated by a high surface area CoAl₂O₄ shell. For comparison, CoAl₂O₄ was also prepared by co-precipitation method and also utilized for a catalyst support. Rh catalysts supported on CoAl₂O₄@Al and CoAl₂O₄ were prepared by incipient wetness impregnation and characterized by N₂ adsorption, X-ray diffraction (XRD), scanning electron microscopy (SEM), CO chemisorption, and temperature-programmed reduction (TPR). The properties of catalysts were investigated for glycerol steam reforming reaction for hydrogen production at 550 ℃. Rh/CoAl₂O₄@Al exhibited about 2.8 times higher glycerol conversion turnover frequency (TOF) than Rh/CoAl₂O₄ due to facilitated heat transport through the core-shell structure. The CoAl₂O₄@Al and CoAl₂O₄ also showed some catalytic activities due to a partial reduction of Co on the support, and a higher catalytic activity was also found on the CoAl₂O₄@Al core-shell than CoAl₂O₄. These catalysts, however, displayed deactivation on the reaction stream due to carbon deposition on the catalysts surface.

• Economic and Environmental Geology
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• v.55 no.6
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• pp.671-687
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• 2022

It has been reported that about 47% of groundwater wells within 10 km from the coastline in the western/southern coastal areas of Korea were affected by seawater. It has been interpreted that the cause of groundwater salinization is seawater intrusion. The Gilsan stream in the Seocheon area was a tidal stream until the Geumgang estuary dam was constructed and operated. Therefore, it is likely that the Gilsan stream catchment was deposited with sediments containing high-saline formation water prior to the use of landfill farmland at this catchment area. The groundwater in this study area showed EC values ranging from 111 to 21,000 µS/cm, and the water quality types were diverse including Ca(or Na)-HCO₃, Ca(or Na)-HCO₃(Cl), Na-Cl(HCO₃), Na-Cl types. It is believed that this diversity of water quality is due to the mixing of seawater and fresh groundwater generated by infiltration of precipitation and surface water through soil and weathered part. In this study, we discussed whether this water quality diversity and the presence of saline groundwater are due to present seawater intrusion or to remnant high-saline pore water in sediments during flushing out process. For this, rain water, surface water, seawater, and groundwater were compared regarding the water quality characteristics, tritium content, oxygen/hydrogen stable isotopic composition, and ⁸⁷Sr/⁸⁶Sr ratio. The oxygen/hydrogen stable isotopic compositions indicated that water composition of saline groundwaters with large EC values are composed of a mixture of those of fresh groundwater and surface water. Also, the young groundwater estimated by tritium content has generally higher NO₃ content. All these characteristics showed that fresh groundwater and surface water have continued to affect the high-saline groundwater quality in the study area. In addition, considering the deviation pattern in the diagrams of Na/Cl ratio versus Cl content and SAR (sodium adsorption ratio) versus Cl content, in which two end members of fresh surface-ground water and seawater are assumed, it is interpreted that the groundwater in the study area is not experiencing present seawater intrusion, but flush out and retreating from ancient saline formation water.