• Nuclear Engineering and Technology
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• v.28 no.5
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• pp.458-466
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• 1996

The effects of dopants on the modification of microstructure of UO$_2$ and UO$_2$-4wt%CeO$_2$ sintered pellets have been studied in hydrogen and $CO_2$/CO mixture atmospheres by using $Ta_2O_5$, TiO$_2$ and $Nb_2O_5$ as sintering additives. The dopant were added as oxide powders and homogenized by attrition milling. The mixed powders were pressed, and then sintered in hydrogen at 1$700^{\circ}C$ , or in oxidizing atmosphere using Controlled $CO_2$/CO mixtures at 125$0^{\circ}C$. Both density and microstructure of UO$_2$ are modified by the addition of dopants in reducing atmosphere. The sintered density is increased with $Ta_2O_5$ addition up to 0.33wt% and subsequently decreased with higher content of the additive. The effect on the densification and the gain growth are apparent with the addition of 0.24wt% $Nb_2O_5$. With 0.lwt% titania and 0.6wt% $Ta_2O_5$, the sintered density is decreased, but the grain size is increased. In oxidizing atmosphere, the grain sizes for UO$_2$ doped with the above additives are smaller than that for pure UO$_2$. The grain size of Ta or Nb-doped UO$_2$ is decreased with increasing $CO_2$/CO ratio, but that of pure UO$_2$or T-doped UO$_2$ is increased. A large portion of second phases is observed in UO$_2$ doped with 0.lwt% TiO$_2$ sintered in hydrogen atmosphere, while, in $CO_2$/CO atmospheres, the second phases or dopant agglomerates are not observed. For UO$_2$-4wt%CeO$_2$ mixed oxide, the effect of additives on the gain growth is not so much as that for the pure UO$_2$. This is attributed to the formation of clusters by dopant cations and Ce ions, so that the additives contribute to a lesser exent to the grain growth for the mixed oxide.

• Journal of the Mineralogical Society of Korea
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• v.29 no.2
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• pp.79-87
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• 2016

Asian dust (Hwangsa) interacts with light, atmospheric gas, aerosol, and marine ecosystem, affecting Earth climate. Mineralogical properties are essential to understand the interaction between the dust and environments. In this study, we examined the mineralogical properties of Asian dust collected at Deokjeok Island, Incheon, Korea in February 22, 2015. X-ray diffraction (XRD) analyses showed that phyllosilicate minerals (62 wt%) dominate the Asian dust. Illite-smectite series clay minerals (55%) were common with minor chlorite (5%) and kaolinite (2%). Non-phyllosilicate minerals were quartz (18%), plagioclase (10%), K-feldspar (4%), calcite (4%), and gypsum (1%). Similar results were obtained by mineral quantification using scanning electron microscopy (SEM) and energy dispersive X-ray spectrometry (EDS). Transmission electron microscopy combined with EDS confirmed illite-smectite series clay minerals as the dominant phyllosilicate type. Morphological analyses using SEM showed clay agglomerates, clay-coated quartz, feldspars, and micas. Gypsum grains were common on the particle surface, while calcite nanofibers, previously reported as common on the surface, were rare, indicating the reaction of calcite and acidic atmospheric pollutants to form gypsum. The analytical result of 2015 Asian dust would contribute to the establishment of mineralogical base for the modeling of the interaction between Asian dust and environments.

• Journal of the Korean Association of Oral and Maxillofacial Surgeons
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• v.27 no.6
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• pp.491-497
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• 2001

Polymethylmethacrylate(PMMA) is currently commonly used material for the reconstruction of bone defects and fixation of joint prosthetics following congenital and acquired causes. Although PMMA has widespread use, it does not possess the ideal mechanical characteristics with osteoconductivity and osteoinductivity required. In order to overcome these problem, addition of bovine bone drived defatting demineralized bone(BDB) powders to a PMMA bone cement was done for improvement of physical property and bone forming characteristics of composite. In order to investigate the influence of BDB reinforcement on the PMMA, we measured physical property of compressive, tensile, flexural strength, and scanning electron microscopic examinations. The results were obtained as follows: 1. The PMMA forms a solid cellular matrix with open cells about $100{\mu}m$ in variable size and incorporating BDB. BDB aggregates inside the cells form a porous network that is accessible from the outer surface. 2. The physical properties were compressive strength of mean $22.74{\pm}1.69MPa$, tensile strength of mean $22.74{\pm}1.69MPa$, flexural strength of mean $77.53{\pm}6.93MPa$. Scanning electron microscopic examinations were revealed that there was DBD particles form a highly porous agglomerates. BDB can be added PMMA in the form of dried powders, the composites are applicable as bone substitutes. BDB and PMMA mixture is shown to produce a class of composites that due to their microstructure and improved mechanical properties may be suitable for application as bone subsitutes. The mechanical and material properties of the BDB-PMMA bone substitute composites are competitive with those properties of a porous ceramic matrix of other hydroxyapatite and with those of natural bones.

• Journal of the Korean Ceramic Society
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• v.40 no.6
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• pp.577-582
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• 2003

BaTiO$_3$ fine powders were synthesized by hydrothermal process from peroxo-coprecipitate precursors. The peroxo-coprecipitates were obtained by addition of the BaCl$_2$, TiCl$_4$, and $H_2O$$_2$ aqueous solution to an ammonium solution. Hydrothermal reaction was conducted at various reaction temperatures, times and pH ranges. Unlike the conventional hydrothermal synthesis which needs highly alkaline condition over pH 13 with KOH or NaOH, the present method offered well-developed crystalline (perovskite) BaTiO$_3$ powders synthesized below pH 12 with use of ammonium solution. It was found that the phase-pure fine powders were formed at temperatures as low as 11$0^{\circ}C$ and the properties of the powders synthesized over 13$0^{\circ}C$ were almost same regardless of the reaction time. BET surface area of the prepared powder was as high as 76 $m^2$/g and the calculated particle (particulate) size was below 20 nm. The ultrafine particulates formed weak agglomerates. The microstructure and dielectric properties of BaTiO$_3$ ceramics sintered at the temperature range of 1150~125$0^{\circ}C$ were evaluated.

• Journal of the Korean Society of Marine Environment & Safety
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• v.22 no.5
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• pp.547-553
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• 2016

Black carbon (BC) contained in particulate matter (PM) originating from the exhaust gases of ships' diesel engines has been receiving great attention as a cause of glacial melting and warming in the polar regions. In this study, we took samples from various locations of PM emitted from the training ship (T/S) HANBADA's main engine, in cooperation with the Korea Maritime and Ocean University. We analyzed the structure and characteristics of these samples using high-resolution transmission electron microscopy (HR-TEM) and applied our findings as fundamental research for developing PM reduction technology. We also employed our results to determine appropriate preemptive action to meet upcoming PM/BC regulations. In addition, we confirmed the emission trend of pollutants from exhaust gases under various engine operating conditions using an exhaust gas analyzer. Results obtained from the analysis of HR-TEM images showed that the structure of the PM is chain-like wispy agglomerates consisting of a number of individual spherical particles. As the sampling location was moved away from the turbo charger (T/C) towards the funnel, more condensates were observed at a low temperature and the molecular structure of the PM lost its characteristic BC structure as an amorphous structure gradually appeared. Furthermore, through the analysis of exhaust gases, we predicted a decrease in PM concentration in the exhaust stream as engine rpm increase.

• Korean Journal of Materials Research
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• v.8 no.9
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• pp.813-818
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• 1998

Ultrafine powders of $\textrm{In}_{2}\textrm{O}_{3}$-doped $\textrm{SnO}_{2}$ were synthesized by a coprecipitation method and the effects of pH value and the amount of In2Q addition on particle size were investigated. The influence of pH value on particle size could be negligible, whereas the amount of $\textrm{In}_{2}\textrm{O}_{3}$ has influenced on particle size and specific surface area. The gas sensitivity to hydrocarbOn($\textrm{C}_{3}\textrm{H}_{8}$, $\textrm{C}_{4}\textrm{H}_{10}$) increased with $\textrm{In}_{2}\textrm{O}_{3}$ addition and reached a maximum at 3wt.% addition. From the results of impedance analysis and I-V characteristics. it was showed that the agglomeration structure of particles and the boundaries between agglomerates were the important factors to determine the gas sensing mechanism.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.9
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• pp.474-481
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• 2018

The policy-making and technological development of eco-friendly automobiles designed to increase their supply is ongoing, but the internal combustion engine still accounts for approximately 95% of automobiles in use. To meet the stricter emission regulations of internal combustion engines based on fossil fuels, the proportion of after-treatments for vehicles and (ocean going) vessels is increasing continuously. As diesel engines have high power and good fuel economy in addition to less CO2 emissions, their market share is increasing not only in commercial vehicles, but also in passenger cars. Because of the characteristics of the diesel combustion, however, NOx is generated in localized high-temperature combustion regions, and particulates are formed in the zones of diffusion combustion. LNT and urea-SCR catalysts have been developed for the after-treatment of exhaust gas to reduce NOx in diesel vehicles. This study examined the effect of a containing promoter on SCR catalysts to cope with the severe exhaust gas regulation. The de-NOx performance of the Mn-SCR catalyst was the best, and the de-NOx performance was improved as the ion exchange rate between Mn ion and Zeolyst was good and the activation energy was low. The de-NOx performance of the 7Cu-15Ba/78Zeoyst catalyst was 32% at $200^{\circ}C$ and 30% at $500^{\circ}C$, and showed the highest performance. The NOx storage material of BaO loaded as a promoter was well dispersed in the Cu-SCR catalyst and the additional de-NOx performance of BaO was affected by the reduction reaction of the Cu-SCR catalyst. Among the three catalysts, the 7Cu-15Ba/Zeolyst SCR catalyst was resistant to thermal degradation. The same type of CuO due to thermal degradation migrates and agglomerates because BaO reduces the agglomeration of the main catalyst CuO particles.

• Composites Research
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• v.25 no.4
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• pp.93-97
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• 2012

Carbon nano fibers (CNFs) reinforced magnesium alloy (AZ91) matrix composites have been fabricated by liquid pressing process. In order to improve the dispersibility of CNFs and the wettability with magnesium alloy melt, CNFs were mixed with submicron sized SiC particles ($SiC_p$). Also, the mixture of CNFs and $SiC_p$ were coated with Ni by electroless plating. In liquid pressing process, AZ91 melts have been pressed hydrostatically and infiltrated into three reinforcement preforms of only CNFs, the mixture of CNFs and $SiC_p$ (CNF+$SiC_p$), and Ni coated CNFs and $SiC_p$ ((CNF+$SiC_p$)/Ni). Some CNFs agglomerates were observed in only CNFs reinforced composite. In cases of the composites reinforce with CNF+$SiC_p$ and (CNF+$SiC_p$)/Ni, CNFs were dispersed homogeneously in the matrix, which resulted in the improvement of mechanical properties. The compressive strengths of CNF+$SiC_p$ and (CNF+$SiC_p$)/Ni reinforced composites were 38% and 28% higher than that of only CNFs composite.

• Fire Science and Engineering
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• v.28 no.1
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• pp.44-51
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• 2014

Smoke from fire is a mixture of combustion gases and particles which include micro-droplets formed from condensed organic vapors and carbonaceous agglomerates. The inhalation of smoke particles causes adverse health effects, and it is prerequisite for the hazard and risk analysis of the smoke particles to know how they behaviour in the respiratory tract. The characteristics of the absorption and adsorption of toxic gases and the amount and location of the particle deposition within the respiratory tract that determine the adverse health effects are related to the morphology and the size distribution of smoke particles. In the present work, as a preliminary study for the adverse health effects of smoke particles, the morphologies of the smoke particles from combustible materials were investigated for each fire stage: smouldering, well-ventilated flaming, small under-ventilated flaming, fully-developed under-ventilated fire. The steady-state tube furnace method given in ISO/TS 19700 was used for the generation of smoke particles. The fire stages were controlled by changing furnace temperature and equivalent ratio. The morphologies were analyzed by using Transmission Electron Microscope (Bio-TEM) by collecting the particles on TEM grids put on each stage of a cascade impactor.

• Journal of the Korean association of regional geographers
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• v.9 no.1
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• pp.53-65
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• 2003

The aim of this study is to examine the regional features of shipbuilding-allied industries comprehensively. Inaddition, this study would offer groundwork to construct spatial networks of shipbuilding-allied industries. Relatively in short term, large modem shipbuilding firms of South Korea have developed under the national strategic support, around southeast coast region. Although small shipbuilding firms and marine equipment firms have supported regional economy, these firms have scaled down their functions and roles due to the national policy. In the long tenn, Korean shipbuilding-allied industries have limitations in stable development, because they have separated their roles. Consequently it is necessary the balanced development of large, medium, and small shipbuilding firms and linkage system with marine equipment firms for overall development of shipbuilding-allied industries. This study suggests two spatial strategy for shipbuilding-allied industries development. First, we need to construct a shipbuilding specialization area which agglomerates competent parts firms adjacent to large shipyards. Second, in national strategy, a long term strategy is required to utilize extremely synergy and external effects induced from a shipbuilding duster of southeast coast region which systematically combines shipbuilding-allied industries, universities, the government authorities, and research institutions.