• Korea-Australia Rheology Journal
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• v.17 no.4
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• pp.199-205
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• 2005

Carbon dioxide was absorbed into aqueous polyethylene oxide (PEO) solution containing AMP in a flat-stirred vessel to investigate the effect of non-Newtonian rheological behavior of PEO on the rate of chemical absorption of $CO_2$, where the reaction between $CO_2$ and AMP was assumed to be a first-order reaction with respect to the molar concentration of $CO_2$ and AMP respectively. The liquid-side mass transfer coefficient, which was obtained from the dimensionless empirical equation containing the properties of viscoelasticity of the non-Newtonian liquid, was used to estimate the enhancement factor due to chemical reaction. PEO with elastic property of non-Newtonian liquid made the rate of chemical absorption of $CO_2$ accelerate compared with Newtonian liquid based on the same viscosity of the solution.

• Bulletin of the Korean Chemical Society
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• v.20 no.4
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• pp.395-396
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• 1999

• Corrosion Science and Technology
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• v.15 no.2
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• pp.84-91
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• 2016

The transport and deposition of corrosion products in pressurized water nuclear reactor (PWR) steam generators have led to corrosion (SCC, denting etc.) problems. Lancing, mechanical cleaning and chemical cleaning have been used to reduce these problems. The methods of lancing and mechanical cleaning have limitations in removing corrosion products due to the structure of steam generator tubes. But high temperature chemical cleaning (HTCC) with EDTA is the most effective method to remove corrosion products regardless of the structure. However, EDTA in chemical cleaning aqueous solution and chemical cleaning environments affects the integrity of materials used in steam generators. The nuclear power plants have to perform the pre-test (also called as qualification test (QT)) that confirms the effect on the integrity of materials after HTCC. This is one of the series studies that assess the effect, and this study determines the effects of 20 % EDTA aqueous solution on defective tubes in high temperature chemical cleaning environments. The depth and magnitude of defects in steam generator (SG) tubes were measured by eddy current test (ECT) signals. Surface analysis and magnitude of defects were performed by using SEM/EDS. Corrosion rate was assessed by weight loss of specimens. The ECT signals (potential and depth %) of defective tubes increased marginally. But the lengths of defects, oxides on the surface and weights of specimens did not change. The average corrosion rate of standard corrosion specimens was negligible. But the surfaces on specimens showed traces of etching. The depth of etching showed a range on the nanometer. After comprehensive evaluation of all the results, it is concluded that 20 % EDTA aqueous solution in high temperature chemical cleaning environments does not have a negative effect on defective tubes.

• Geomechanics and Engineering
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• v.17 no.5
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• pp.465-473
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• 2019

Biocementation due to the microbially induced calcium carbonate precipitation (MICP) process is a potential technique that can be used for soil improvement. However, the effect of biocementation may be affected by many factors, including nutrient concentration, bacterial strains, injection strategy, temperature, pH, and soil type. This study investigates mainly the effect of chemical concentration on the formation of calcium carbonate (e.g., quantity, size, and crystalline structure) and unconfined compressive strength (UCS) using different treatment time and chemical concentration in the biotreatment. Two chemical concentrations (0.5 and 1.0 M) and three different treatment times (2, 4, and 8 cycles) were studied. The effect of chemical concentrations on the treatment was also examined by making the total amount of chemicals injected to be the same, but using different times of treatment and chemical concentrations (8 cycles for 0.50 M and 4 cycles for 1.00 M). The UCS and CCC were measured and scanning electron microscopy (SEM) analysis was carried out. The SEM images revealed that the sizes of calcium carbonate crystals increased with an increase in chemical concentrations. The UCS values resulting from the treatments using low concentration were slightly greater than those from the treatments using high concentration, given the CCC to be more or less the same. This trend can be attributed to the size of the precipitated crystals, in which the cementation efficiency increases as the crystal size decreases, for a given CCC. Furthermore, in the high concentration treatment, two mineral types of calcium carbonate were precipitated, namely, calcite and amorphous calcium carbonate (ACC). As the crystal shape and morphology of ACC differ from those of calcite, the bonding provided by ACC can be weaker than that provided by calcite. As a result, the conditions of calcium carbonate were affected by test key factors and eventually, contributed to the UCS values.

• Journal of the Society of Cosmetic Scientists of Korea
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• v.22 no.2
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• pp.70-75
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• 1996

DMHF (2.5-dimethyl-4-hydroxy-3[2H]-furanone), an antioxidative compound from the reaction of L-cysteine/D-glucose scavenged efficiently 1,1-diphenyl-2-picryl hydrazyl free radicals. It exhibited an inhibitory effect on the autoxidation of linolenic acid, and the protective effect against UV cytotoxicity in cultured human fibroblast. In addition, DMHF appeared to prevent the cellular melanogenesis in the cultured murine melanoma cells more effectively than kojic acid, a well known inhibitor of melanogenesis, while the former was not so effective as the latter for the inhibition of the tyrosinase. Considering that cellular melanogenesis is a metabolic process triggered by oxidative stress, it ovas tentatively deduced that the antioxidative property of DMHF might afford the effect against cellular pigmentation by alleviating the causative stress. In toxicological tests such as irritation and sensitization, this compound turned out to be safe. The results of this study suggest that DMHF may be a novel inhibitor of melanogenesis, and that night be useful for application in cosmetics.

• YAKHAK HOEJI
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• v.40 no.3
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• pp.347-350
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• 1996

The post-antibiotic effect (PAE), which is defined as the period of time lag that the target organisms resume normal growth rate after complete removal of the antibiotics, of LB 20304 and ciprofloxacin was evaluated against Staphylococcus aureus 6538p and Escherichia coli 3190Y, respectively. The PAE was estimated by adding each antibiotic to a log phase of growth and incubating at $37^{\circ}$C for 1 h.Antibiotic was removed by centrifugation, and total viable cell counts were determined hourly for a further 10 h. The PAEs of LB20304 against S. aureus at concentrations of $1{\times}MIC\;and\;2{\mu}g/ml$ were 10 min and 93min, respectively. LB20304 showed a comparable PAE to ciprofloxacin. Against E. coli, the PAE of LB20304 was also similar to that of ciprofloxacin at concentration of $4{\times}MIC$ but it was much longer than that of ciprofloxacin at concentration of 2${\mu}g/ml$. LB20304 showed higher lethality than ciprofloxacin against both S. aureus and E. coli strains.

• Bulletin of the Korean Chemical Society
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• v.33 no.7
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• pp.2378-2380
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• 2012

• Journal of the Korean Ceramic Society
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• v.50 no.1
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• pp.25-30
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• 2013

The pore volume of hardened cement with waterproofing materials is lower compared to that of hardened cement without waterproofing materials. Thus, fewer gaps will appear by means of chemical reactions between $Ca^{2+}$ ions in hardened cement and water, solutes, and other ions. Due to the selective permeability, the osmotic pressure of hardened cement can change due to physical effects such as the reduction of the pore volume and the reduction in the number of pores, as well as by the electrochemical reaction between water, solutes, other ions and $Ca^{2+}$ ions in hardened cement. Of course, these factors do not have independent effects but instead a combined complex effect. Accordingly, we studied changes in the osmotic pressure due to the difference in the pore structure of hardened cement. A pore size smaller than 1 nm in hardened cement had only a slight effect on the osmotic pressure, whereas a pore size larger than 1 nm had a direct effect on the osmotic pressure.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1997.10a
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• pp.907-910
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• 1997

With increasing the needs for micro and precision parts, micro machining technology has been studied to fabricate a small part with high density such as electronics, optics, communications, and medicine industry more than before. But there are many problems to be solved requiring a high-level technology. So this research presents the new method to fabricate a small part through applying chemical mechanical micro machining (C3M) for the Al wafer. Al(thickness I ,u m) was sputtered on the Si substrate. Al is widely used as a lightweight material. However form defect such as burr has a bad effect on products. To improve machinability of ductile material, oxide layer was formed on the surface of AI wafcr before grooving by chemical reaction with HN03(10wt%). And then workpieces were machined to compare conventional micro-machining process with newly suggested method at different machining condition such as load and feed rate. To evaluate whether or not the machinability was improved by the effect of chemical condition, such as the size, the width of grooves 'and burr generation were measured. Finally, it is confirmed that C3M is one of the feasible tools for micro machining with the aid of effect of the chemical reaction.

• Korean Journal of Soil Science and Fertilizer
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• v.48 no.2
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• pp.146-152
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• 2015

Heavy metal pollution has been a critical problem in agricultural field near at the abandoned metal mines and chemical amendments are applied for remediation purpose. However, biological activity can be changed depending on chemical amendments affecting crop productivity. Main purpose of this research was to evaluate biological parameters after applying chemical amendments in heavy metal polluted agricultural field. Result showed that soil respiration (SR) and microbial biomass carbon (MBC) were changed after chemical amendments were applied. Among three different amendments, lime stone (LS), steel slag (SS), and acid mine drainage sludge(AMDS), AMDS had an effect to increase SR in paddy soil. Comparing to control ($93.98-170.33mg\;kg^{-1}day^{-1}$), average of 30% increased SR was observed. In terms of MBC, SS had an increased effect in paddy soil. However, no significant difference of SR and MBC was observed in upland soil after chemical amendment application. Overall, SR can be used as an indicator of heavy metal remediation in paddy soil.