• Journal of the Korean Geotechnical Society
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• v.31 no.12
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• pp.17-27
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• 2015

In this study, we tried to precipitate calcium carbonate with carbonate ions decomposed from urea by plant extract and calcium ions dissolved in water. The clay particles carry a net negative charge on their surfaces. Such clay mineral was additionally mixed as a medium to improve soil strength and durability with environmentally-friendly way. The $1^{st}$ solution (plant extracts and urea) and the $2^{nd}$ solution (calcium chloride and clay) were mixed together with clean Nakdong River sand. Then, this mixed soil was compacted into a small cylindrical specimen and then air cured for 7 days in laboratory. The molar concentration of urea and calcium chloride was tested for three different conditions, 1, 5, and 7 mol. Three different clay contents (0, 1, and 3% per total weight) were mixed with sand. For each specimen, a series of unconfined compression test, a durability test, SEM, EDX and XRD analyses were carried out to evaluate its cementation and structure. As the molar concentration of the solution and clay content increased, the unconfined compressive strength and durability increased. The results of SEM, EDX and XRD analyses showed that calcite was precipitated around clay mineral. The thermogravimetry analysis indicated that calcium carbonate precipitated about 1~2% per total weight of the sample.

• Korean Chemical Engineering Research
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• v.49 no.6
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• pp.758-763
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• 2011

In this work, polymer composite electrolytes were prepared by a blend of poly(methyl methacrylate) (PMMA) and poly(ethylene oxide) (PEO) as a polymer matrix, propylene carbonate as a plasticizer, $LiClO_4$ as a salt, and by containing a different content of $TiO_2$, by using the solution casting method. The crystallinity and ionic conductivity of the polymer electrolytes was evaluated using X-ray diffraction(XRD) and AC impedance method, respectively. The morphology of composite electrolyte film was analyzed by SEM method. From the experimental results, by increasing the $TiO_2$ content, crystallinity of PEO was reduced, and ionic conductivity was increased. In particular, the ionic conductivity was dependent on the content of $TiO_2$ and showed the highest value 15 wt%. However, when $TiO_2$ content exceeds 15 wt%, the ionic conductivity was decreased. According to the surface morphology, the ionic conductivity was decreased because the polymer composite electrolytes showed a heterogenous morphology of fillers due to immiscibility or aggregation of the filler within the polymer matrix.

• Macromolecular Research
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• v.10 no.2
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• pp.91-96
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• 2002

To explore the effects of intramolecular interactions within the copolymer on the phase separation behavior of polymer blends, copolymers having two different types of intramolecular interactions, i.e., intramolecular repulsion and intramolecular attraction were prepared . In this study, poly(styrene-co-methylmethacrylate) (P(S-MMA)) having intramolecular repulsion caused by positive interaction between styrene and MMA and poly(styrene-co-ethyl-methacrylate) (P(S-EMA)) and poly(styrene-co-cyclohexylmethacrylate) (P(S-CHMA)) having intramolecular attraction caused by negative interaction between styrene and methacrylate were blended with tetramethyl poly-carbonate (TMPC). The phase behavior of blends was examined as a function of copolymer composition and blend composition. TMPC formed miscible blends with styrenic copolymers containing less than certain amount of methacrylate. The phase separation temperature of TMPC blends with copolymer such as P(S-MMA) and P(S-EMA), first increases with methacrylate content, goes through a maximum and then decreases just prior to the limiting content of methacrylate for miscibility, while that of TMPC blends with P(S-CHMA) always decreases. The calculated interaction energy for TMPC-P(S-EMA) pair is negative and monotonically increases with EMA content of the copolymer. Such behavior contradicted the general notion that systems with more favorable energetic interactions have higher LCST, The detailed inspection of the lattice-fluid theory related to the phase behavior was performed to explain such behavior.

• Bulletin of the Korean Chemical Society
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• v.30 no.2
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• pp.334-338
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• 2009

Trifunctional epoxy resin triglycidyl paraaminophenol (TGPAP)/$CaCO_3$ nanocomposites were prepared using the melt blending method. The effects of nano-$CaCO_3$ content on the thermal behaviors, such as cure behavior, glass transition temperature ($T_g$), thermal stability, and the coefficient of thermal extension (CTE), were investigated by several techniques. Differential scanning calorimetry (DSC) results indicated that the cure reaction of the TGPAP epoxy resin was accelerated with the addition of nano-$CaCO_3$. When the nano-$CaCO_3$ content was increased, the $T_g$ of the TGPAP/$CaCO_3$ nanocomposites did not obviously change, whereas the crosslinking density was linearly increased. The nanocomposites showed a higher thermal stability than that of the neat epoxy resin. This result could be attributed to the increased surface contact area between the nano-$CaCO_3$ particles and the epoxy matrix, as well as the high crosslinking density in the TGPAP/$CaCO_3$ nanocomposites. The CTE of the nanocomposites in the rubbery region was significantly decreased as the nano-$CaCO_3$ content was increased.

• The Korean Journal of Community Living Science
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• v.13 no.2
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• pp.53-61
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• 2002

This study is to find out how the 4 types of calcium salt such as calcium carbonate, calcium phosphate, calcium lactate and calcium citrate in soy protein diet, the vegetable protein source, affect the calcium utilization in the body. To do so, calcium, phosphate and creatinine concentration and ALP activity in blood as well as the content of calcium and ash, the length, weight strength, and the calcium utilization in the bone were measured. Four groups of Sprague-Dawley male rats with the weight of around 180g were fed for 3 weeks with the experimental diet. Each group was fed with the isolated soy protein containing 14% of the diet and the above mentioned 4 types of calcium salt as the calcium source. The results are as follows; 1. There were no differences of the feed intake, weight gain, and feed efficiency among groups. 2. ALP activity in blood was sinificantly high in calcium lactate group(P<0.05), but there were no differences of concentration of calcium, phosphates, and creatinine in blood among groups. 3. The weight, calcium content, calcium ratio in ash and the strength of bone were low when calcium lactate was provided(P<0.05). 4. The content of calcium in the liver was high in calcium lactate group and calcium citrate group(P<.0.05). 5. The exceretion of feces was low in calcium lactate group(P<0.05) and the excretion of urine was also relatively low. In addition, the ratio of absorption and the retention of calcium were high(P<0.05). In summary, out of four types of calcium salt such as calcium carbontate, calcium phosphate, calcium lactate and calcium citrate when calcium lactate was provided the ALP activity in blood was high and the weight, calcium content, calcium ratio in ash and the strength of bone were low. In calcium utilization, the ratio of absorption and retention of calcium were high, however it has lower effect than 3 other calcium types in improving weight, the content of calcium and the strength of bone.

• Journal of the Korean Geotechnical Society
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• v.32 no.8
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• pp.27-33
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• 2016

In this study, Polyvinyl alcohol (PVA) fiber was used to increase strength (unconfined compressive strength and tensile strength) of bio-cemented sand using microorganism. Ottawa sand was mixed with PVA fibers having three fiber contents (0, 0.4, and 0.8%). The fiber mixed sand was treated 14 times by using Microbially Induced Calcite Precipitation (MICP) which included culture (2 times per day) during 7 days to improve its engineering properties. The Bacillus Sporosarcina pasteurrii (Bacillus sp.) was used for urease activity. The specimen was prepared as a cylindrical specimen of 5 cm in diameter and 10 cm in height. Unconfined compressive strength and tensile strength were measured after cementation. Moreover, calcium carbonate content and SEM analyses were performed with a piece of sample. An average value of unconfined compressive strength increased and then slightly decreased but an average value of tensile strength ratio increased with increasing carbonate content the in same condition. Unconfined compressive strength and tensile strength increased about 30% and 160%, respectively. A strength ratio of unconfined compressive strength to tensile strength representing the brittleness decreased from 8 to 4 when fiber content increased from 0.0 to 0.8%. Such bio-cemented sand can be applied into slope area to prevent its shear failure or increase its tensile strength.

• The Journal of Engineering Geology
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• v.22 no.1
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• pp.123-134
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• 2012

Hydrochemical analyses, carbon isotopic (${\delta}^{13}C_{DIC}$) analyses, and noble gas isotopic ($^3He/^4He$ and $^4He/^{20}Ne$) analyses of the Dalki carbonate waters in the Chungsong area were carried out to elucidate their hydrochemical composition and to determine the source of $CO_2$ gas and noble gases. The carbonate waters have a pH of between 5.93 and 6.33, and an electrical conductivity 1950 to $3030{\mu}S/cm$. The chemical composition of all carbonate waters was Ca(Mg)-$HCO_3$, with a high Na content. The contents of Fe, Mn, and As in some carbonate waters exceed the limit stipulated for drinking water. The concentrations of major ions are slightly higher than those reported previously. The ${\delta}^{13}C_{DIC}$ values range from -6.70‰ to -4.47‰, indicating that the carbon originated from a deep-seated source. The $^3He/^4He$ and $^4He/^{20}Ne$ ratios vary from $7.67{\times}10^{-6}$ to $8.38{\times}10^{-6}$ and from 21.32 to 725.7, respectively. On the $^3He/^4He$ versus $^4He/^{20}Ne$ diagram, the noble gas isotope ratios plot in the field of a deep-seated source, such as mantle or magma. We therefore conclude that $CO_2$ gas and noble gas in the Dalki carbonate waters originated from a deep-seated source, rather than an inorganic $CO_2$ origin as suggested in a previous study.

• Food Science and Preservation
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• v.12 no.5
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• pp.501-506
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• 2005

This study was conducted to investigate the effect of organic acids on solubility of calcium. As a results, acetic and lactic acid showed the most excellent solubility of calcium. Calcium solubility was increased at initial total acid (4%) in citric acid but calcium was insoluble in tartaric acid. After solving, pH and residuals were decreased where as total acidity and calcium content were increased as increment of initial acidity of acetic and lactic acid. Calcium content in seaweed calcium and calcium carbonate were higher than that of nano calcium. Solubility of calcium was more conspicuous at lactic acid than acetic acid.

• Macromolecular Research
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• v.14 no.4
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• pp.456-460
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• 2006

The electrical, morphological, and mechanical properties of poly carbonate (PC)/multi-walled carbon nan-otube (MWNT) composites were studied by electrical conductivity, electromagnetic interference shielding efficiency (EMI SE), scanning electron microscopy, and tensile strength measurements. In the electrical property analysis of the PC/MWNT composites, the percolation threshold of the PC/MWNT composites was observed between 1.5 and 2.5 wt% MWNT content. From the electrical conductivity and EMI SE studies, the theoretical values of the EMI SE were in good agreement with the experimental values of the EMI SE. From the morphology of the PC/MWNT composites, it was observed that MWNT is dispersed homogenously in the PC matrix. From the electrical conductivity and morphological studies, it was suggested that the percolation threshold of the PC/MWNT composites is related with the morphological results in that MWNT is apparently interconnected to form an electrical pathway. The mechanical properties of the PC/MWNT composites peaked at the MWNT content of 2.5 wt%.

• Journal of Korean Society for Atmospheric Environment
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• v.18 no.E3
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• pp.153-163
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• 2002

A laboratory- scale dual-column biofilter system was used to study the biofiltration of dimethyl disulfide (DMDS). The gas flow rate and DMDS concentration to the biofilter were varied to study their effect on the remov-al of dimethyl disulfide. Operating parameters such as pH, temperature, and water content were monitored during the biofilter operation and necessary precautions were taken to keep these parameters within the acceptable limits. It was observed that the removal efficiency of DMDS was optimal at neutral pH values. After five month op-eration, the neutralization of the filter beds with sodium carbonate became necessary for the optimum operation of the biofilters. The microbial population already present in the compost mixtures was found to be adequate in treat-ing DMDS. The compost mixtures were found to be similar in terms of biofiltration efficiency of DMDS. However, pressure drops observed in the first column compost mixture (compost/ peat mulch) was extremely high, making this compost economically not feasible. The second mixture (compost/bark) provided pressure drops within accept-able limits. A minimum residence time of 30 seconds at the optimal operating conditions appeared to be adequate for achieving high removal efficiencies (>90%).