• Journal of the Korean Electrochemical Society
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• v.24 no.4
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• pp.106-112
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• 2021

Catalyst poisoning by ionomers in membrane electrode assemblies of alkaline membrane fuel cells has been reported recently. We tried to improve the membrane electrode assembly's performance by controlling the solvent's ratio during electrode manufacturing. 4 Different mixing ratios of N-Methyl-2-pyrrolidone (NMP) and ethylene glycol (EG) gave four different cathode electrodes with platinum and Fuma-Tech ionomers. The electrode with higher EG improved polarization performance by about 36% compared to the NMP-based commercial ionomer. The dependence of the ionomer's dispersibility on the solvent seems responsible for the difference, which means that the non-uniform distribution of ionomers improves the performance of the electrode. High-frequency resistance, internal resistance corrected polarization curve, Tafel slope, mass activity, and impedance spectroscopy characterized the electrode. We can find that the existence of poor solvent improves cathode electrode performance. It seems to be the result of reduced poisoning of the catalyst according to the particle size distribution of the ionomer.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.14 no.3
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• pp.127-133
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• 2009

In order to determine organic carbon oxidation by manganese and iron oxides, six core sediments were obtained in slope and basin sediments of Ulleung Basin in East Sea. The basin sediments show high organic carbon contents (>2%) at the water depths deeper than 2,000 m; this is rare for deep-sea sediments, except for those of the Black Sea and Chilean upwelling regions. In the Ullleung Basin, the surface sediments were extremely enriched by Manganese oxides with more than 2%. Maximum contents of Fe oxides were found at the depth of $1{\sim}4cm$ in basin sediments. However, the high level of Mn and Fe oxides was not observed in slope sediment. Surface manganese enrichments (>2%) in Ulleung Basin may be explained by two possible mechanisms: high organic carbon contents and optimum sedimentation rates and sufficient supply of dissolved Manganese from slope to the deep basin. Reduction rates of iron and manganese oxides ranged from 0.10 to $0.24\;mmol\;m^{-2}day^{-1}$ and from 0.30 to $0.57\;mmol\;m^{-2}day^{-1}$, respectively. In Ulleung Basin sediments, $13{\sim}26%$ of organic carbon oxidation may be linked to the reduction of iron and manganese oxides. Reduction rates of metal oxides were comparable to those of Chilean upwelling regions, and lower than those of Danish coastal sediments.

• Journal of Bio-Environment Control
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• v.21 no.3
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• pp.213-219
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• 2012

Improving the physico-chemical properties of used media by mixing ratio of new plug media (NPM), used plug media (UPM) and perlite is necessary to improve seedling quality. In this study, five treatments were designed to investigate mixing ratio of UPM and NPM by ratio of volume 0 : 100, 25 : 75, 50 : 50, 75 : 25, 100 : 0, respectively. On the other hand, nine treatments were designed to investigate of perlite volumes were added to UPM and mixed media (UPM : NPM (50 : 50)) with 0, 5, 10, and 20% of ratio volume. The physicochemical properties of all mediums and their effect on growth response of tomato and cucumber seedlings were determined. The result indicates that physical properties was improved when NPM was mixed with UPM and at mixed ratio of volume 50 : 50 (v : v) has similar pore spare, bulk density and water retention to NPM. Seedling quality of tomato and cucumber in mixed media (50 : 50) are better than other mixed ratio and similar to NPM. Addition perlite to UPM and mixed media 50 : 50 (v : v) increased the pore space and water retention. Physical properties such as particle density, pore space and bulk density were increased when perlite volume increased. However, the best of seedling quality was observed by the addition at 10% volume of perlite. These results suggested that optimum of mixed ratio for recycled used media is new media and used media 1 : 1 mixed.

• Journal of the Korean Geotechnical Society
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• v.26 no.12
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• pp.19-30
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• 2010

Bentonite-based grout has been widely used to seal a borehole constructed for a closed-loop vertical ground heat exchanger in a geothermal heat pump system (GHP) because of its high swelling potential and low hydraulic conductivity. Three types of bentonites were compared one another in terms of viscosity and thermal conductivity in this paper. The viscosity and thermal conductivity of the grouts with bentonite contents of 5%, 10%, 15%, 20% and 25% by weight were examined to take into account a variable water content of bentonite grout depending on field conditions. To evaluate the effect of salinity (i.e., concentration of NaCl : 0.1M, 0.25M, and 0.5M) on swelling potential of the bentonite-based grouts, a series of volume reduction tests were performed. In addition, if the viscosity of bentonite-water mixture is relatively low, particle segregation can occur. To examine the segregation phenomenon, the degree of segregation has been evaluated for the bentonite grouts especially in case of relatively low viscosity. From the experimental results, it is found that (1) the viscosity of the bentonite mixture increased with time and/or with increasing the mixing ratio. However, the thermal conductivity of the bentonite mixture did not increase with time but increased with increasing the mixing ratio; (2) If bentonite grout has a relatively high swelling index, the volume reduction ratio in the saline condition will be low; (3) The additive, such as a silica sand, can settle down on the bottom of the borehole if the bentonite has a very low viscosity. Consequently, the thermal conductivity of the upper portion of the ground heat exchanger will be much smaller than that of the lower portion.

• Korean Journal of Breeding Science
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• v.42 no.1
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• pp.75-86
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• 2010

End-use properties of 26 Korean wheat cultivars (KWC) were evaluated to assess consumer satisfaction with 6 imported wheat and 5 commercial wheat flours. In end-use quality testing of cooked noodles, Absorption of noodle dough sheet of ASW (Australian standard white) was similar to Anbaek, Eunpa, Gobun, Hanbaek, Jeokjoong, Jonong, Namhae, and Sukang. Thickness of noodle dough sheet of KWC was showed thin difference. In imported wheat and commercial flour, Commercial flour for baking cookie (Com5) with lower protein flour was lower than those flours. In lightness of prepared noodle dough sheet, Lightness value ($L^*$) of KWC was lower than those of Commercial flour for making white salted noodle (Com1), commercial flour for making for yellow alkaline noodle (Com2), and commercial flour for multi-purpose (Com4). Lightness value ($L^*$) showed significantly negative correlations with particle size of flour, ash, damaged starch, and protein content. Hardness of cooked noodles positively correlated with protein content. In texture of cooked noodles, Hardness of Com1 was similar to that of Alchan, Dahong, Jeokjoon, and Sukang. Also, hardness of Com2 was similar to that of Gobun, Jokyung, Jonong, Keumkang, and Namhae. In end-use quality of bread, bread loaf volume of commercial flour for making bread (Com3) was similar to Alchan, Jokyung, Keumkang, and Namhae but firmness was low. Bread volume showed better relationships with higher SDS-sedimentation volume, longer mixing time of mixograph, higher height of dough during development. Firmness of crumb was negatively correlated with bread volume. Diameter of cookie showed significantly negative correlations with particle size of flour, damaged starch, and protein content. Also, Top gain score became higher as the increase diameter of cookie. In end-use quality testing of cooked cookie, Cookie diameter of Com5 was similar to that of Dahong, Geuru, Olgeuru, Tapdong, and Uri but top grain was low.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.15 no.1
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• pp.41-50
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• 2010

We have developed an in-situ benthic chamber (BelcI) for use in coastal studies that can be deployed from a small boat. It is expected that BelcI will be useful in studying the benthic boundary layer because of its flexibility. BelcI is divided into three main areas: 1) frame and body chamber, 2) water sampler, and 3) stirring devices, electric controller, and data acquisition technology. To maximize in-situ use, the frame is constructed from two layers that consist of square cells. All electronic parts (motor controller, pA meter, data acquisition, etc.) are low-power consumers so that the external power supply can be safely removed from the system. The hydrodynamics of BelcI, measured by PIV (particle image velocimetry), show a typical "radial-flow impeller" pattern. Mixing time of water in the chamber is about 30 s, and shear velocity ($u^*$) near the bottom layer was calculated at $0.32\;cm\;s^{-1}$. Measurements of diffusivity boundary layer thickness showed a range of $180-230\;{\mu}m$. Sediment oxygen consumption rate, measured in-situ，was $84\;mmol\;O_2\;m^{-2}\;d_{-1}$, more than two times higher than on-board incubation results. Benthic fluxes assessed from in-situ incubation were estimated as follows: nitrate + nitrite = $0.18\;{\pm}\;0.07\;mmol\;m^{-2}\;d^{-1}$ ammonium $23\;{\pm}\;1\;mmol\;m^{-2}\;d^{-1}$ phosphate = $0.09\;{\pm}\;0.02\;mmol\;m^{-2}\;d^{-1}$ and silicate = $23\;{\pm}\;1\;mmol\;m^{-2}\;d^{-1}$.

• Journal of the Korean Geotechnical Society
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• v.36 no.11
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• pp.97-106
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• 2020

Swelling properties and shear strength behavior of MgO-Sand mixtures with hydration procese of MgO are compared according to different MgO contents (W_MgO/W_Total=0, 30, 50, 70, 100%) in this study. The specimens are prepared by mixing with crushed MgO refractory bricks and silica sand. After hydration, the particle size and the specific gravity of MgO were decreases. Through microstructure observation and X-ray diffraction analysis, it is confirmed that MgO changes from the cubic structure of Periclase to the hexagonal cubic structure of Brucite after hydration. As the MgO content increases, both swelling rate and swelling pressure of the mixtures increase. W_MgO/W_Total=30% specimen shows relatively low swelling pressure and swelling rate because produced Mg(OH)₂ mainly fills the pores between sand particles. However, in the case of MgO more than 50%, swelling pressure and swelling rate increase significantly because Mg(OH)₂ fills the pores of sand particles at first and then either pushes out sand particles or Mg(OH)₂ particles after filling the pores. As a result of the direct shear test, before hydration, the mixtures show a dilative behavior on high MgO contents and a contractive behavior on low MgO contents. However, after hydration, the behavior of all mixtures changes to contractive behavior. The threshold fraction of fine (i.e., Mg(OH)₂) contents of the hydrated MgO-Sand mixtures reveals approximately 60% compared with normalized shear strength.

• Korean Chemical Engineering Research
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• v.53 no.6
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• pp.783-791
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• 2015

A fluidized-bed reactor with an inside diameter of 0.1 m and a height of 1.2 m was used to study the effect of steam and catalyst additions to air-blown biomass gasification on the production of producer gas. The equipment consisted of a fluidized bed reactor, a fuel supply system, a cyclone, a condenser, two receivers, steam generator and gas analyzer. Silica sand with a mean particle diameter of $380{\mu}m$ was used as a bed material and calcined dolomite ($356{\mu}m$), which is effective in tar reduction and producer gas purification, was used as the catalyst. Both of Korea wood pellet (KWP) and a pellet form of EFB (empty fruit bunch) which is the byproduct of Southeast Asia palm oil extraction were examined as biomass feeds. In all the experiments, the feeding rates were 50 g/min for EFB and 38 g/min for KWP, respectively at the reaction temperature of $800^{\circ}C$ and an ER (equivalence ratio) of 0.25. The mixing ratio (0~100 wt%) of catalyst was applied to the bed material. Air or an air-steam mixture was used as the injection gas. The SBR (steam to biomass ratio) was 0.3. The composition, tar content, and lower heating value of the generated producer gas were measured. The addition of calcined dolomite decreased tar content in the producer gas with maximum reduction of 67.3 wt%. The addition of calcined dolomite in the air gasification reduced lower heating value of the producer gas. However The addition of calcined dolomite in the air-steam gasification slightly increased its lower heating value.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.33 no.5
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• pp.448-454
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• 2000

This study was to examine the physicochemical characteristics of coagulation reaction between ignited oyster shell powder (IOSP) and red tide organisms (RTO), and its feasibility, in developing a technology for the removal of RTO bloom in coastal sea,IOSP was made from oyster shell and its physicochemical characteristics were examined for particle size distribution, surface characteristic by scanning electron microscope, zeta potential, and alkalinity and pH variations in sea water. Two kinds of RTO that were used in this study, Cylindrotheca closterium and Skeletonema costatum, were sampled in Masan bay and were cultured in laboratory. Coagulation experiments were conducted using various c(Incentrations of IOSP, RTO, and a jar tester. The supernatant and RTO culture solution were analyzed for pH, alkalinity, RTO cell number, IOSP showed positive zeta potentials of $11.1{\~}50.1\;mV\;at\;pH\;6.2{\~}12.7$, A positive zeta potential of IOSP slowly decreased with decreasing pNa 4,0 to 2,0. When pNa reached zero, the zeta potential approached zero, When a pMg value was decreased, the positive zeta potential of IOSP increased until pMg 3.0 and decreased below pMg 3.0. IOSP showed 4.8 mV of positive zeta potential while RTO showed -9.2 mV of negative zeta potential in sea water. A positive-negative EDL (electrical double-layer) interaction occurred between $Mg(OH)_2$ adsorption layer of IOSP and RTO in sea water so that EDL attractive force always worked between them. Hence, their coagulation reaction occurred at primary minimum on which an extreme attractive force acted because of charge neutralization by $Mg(OH)_2$ adsorption layer of IOSP. As a result, the coagulation reaction was rapidly processed and was irreversible according to DLVO (Deriaguin-Landau-Verwey-Overbeek) theory. Removal rates of RTO were exponentially increased with increasing both IOSP concentration and G-value. The removal rates were steeply increased until 50 mg/l of IOSP and reached $100{\%}\;at\;400\;mg/l$ of IOSP. Removal rates of RTO were $70.5,\;70.5,\;81.7,\;85.3{\%}$ for G-values of $1,\;6,\;29,\;139\;sec^(-1)$at IOSP 100 mg/l, respectively. This indicated that mixing (i.e., collision among particles) was very important for a coagulation reaction.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.29 no.3
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• pp.332-344
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• 1996

The vertical profiles of the natural $^{210}Po,\;^{210}Pb\;and\;^{234}Th$, activities were measured at the upper 150 m or 200 m of water column from west-east intersection in the east-southern coastal area of the Korea Peninsula during the period from 26 to 29 April 1994 to compare the removal rates (residence time) and removal processes for $^{210}Po\;and\;^{234}Th$. At the inshore stations, the $^{210}Po$ activity was generally higher in the thermocline and its under layer than in the surface mixed layer, while represented the reversed pattern at the offshore stations. However, the $^{210}Pb$ activity decreased generally with depth. Also, the activity of $^{210}Po$ relative to its parent $^{210}Pb$ was deficient in the water column above the main thermocline, but was slightly excess or close to equilibrium in the thermocline and its under layer. The vertical profiles for the activity of $^{210}Pb$ relative to its parent $^{226}Ra$ showed the reversed pattern with the vertical variation of $^{210}Po$ excess (or deficiency). The $^{234}Th$ activity was significantly lower in the surface mixed layer and thermocline than in the deeper layer. The residence time of $^{210}Po$ ranged from 1 to 4 years at the five stations except station E8 that showed yet long residence time (approximately 10 years). The long residence time at the station E8 may resulted from the thicker surface mixed layer and subsequent the vertical mixing of $^{210}Po$ which was recycled in the lower surface mixed layer compared to at the other stations. Also, the residence time of $^{210}Po$ was shorter at the inshore stations than at the offshore stations. However, the residence time of $^{234}Th$ ranged from 52 to 74 days at all station without the significant variation, was very much shorter relative to the residence time of $^{210}Po$. The correlation between the removal rate of dissolved $^{234}Th$ and the concentration of total suspended matter (TSM) was generally positive. Therefore, it seems that the major route of the removal mechanism of $^{234}Th$ from seawater in the surface mixed layer is via adsorption onto suspended particle surfaces (most likely inorganic particles) and subsequent settling to the bottom layer. Between the removal rate of dissolved $^{210}Po$ and the concentration of chlorophyll-a was positively good correlation. Consequently, most likely the removal of $^{210}Po$ may be occurred by uptake to organisms (mainly such as planktonic debris or fecal pellets) and subsequent settling.