• Journal of the Korean Chemical Society
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• v.50 no.4
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• pp.328-337
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• 2006

purpose of this study was to find out problems in experiments for electrolysis of an aqueous CuCl2 solution in high school science textbooks and to suggest an improved experiment considering students' capability of experimenting and laboratory safety in high schools. For this study, the experiments for electrolysis of an aqueous CuCl2 solution presented in 11 high school science textbooks were classified by their experimental methods. After high school chemistry teachers performed the experiments as presented in the high school science textbooks, an analysis was performed on problems of the experiments, and an improved experiment was devised. According to the results of this study, in the experiments for electrolysis of an aqueous CuCl2 solution using a U type tube and a U type tube with branch, reaction velocity of the electrolysis was slow, therefore, a side reaction was generated. In the experiment using a beaker, reaction of each electrode could not be observed separately. And in the experiment using an electrolysis instrument, it was difficult to identify property of the reaction product. In the improved experiment using a reaction vessel of ㅂshape, reaction velocity of the electrolysis was fast, reaction of each electrode could be observed separately, and the side reaction decreased. From these results, it was suggested that the improved experiment would help high school students understand scientific conception regarding electrolysis.

• Journal of Korean Society of Environmental Engineers
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• v.27 no.7
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• pp.726-731
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• 2005

Sedimentation is treated as the most important unit process in waterworks, and plays great role on turbidity removal efficiency. Rectangle sedimentation basin is the most widely accepted sedimentation process. But it has some problems with short-circuit flow and density flow caused by temperature and influent turbidity variation. To solve these problems, installation of rectification wall was suggested, but not generally fully accepted in field. Because hole of rectification wall cause jet flow. In this research, use of moving baffle was investigated. Moving baffle was designed to induce uniform velocity at every section of water flow. The baffle walls was made from soft fiber materials. The baffle walls with flow of sedimentation basin moves at same speed. It is like that it controls density flow and short-circuit flow and induce uniform velocity at every section of water flow in sedimentation basin. When moving baffle was operated retention time of sedimentation basin was extended to 1 hours. When it talked again and the effluent time of highest concentration of the chlorine ion from 100 minutes was extended to 160 minutes. Turbidity removal efficiency was tested with different operation modes(continuous and batch) with influent turbidity and retention time. It was revealed that turbidity removal efficiency carl be improved up to 36%(continuous mode) and 58%(batch mode) respectively. Consequently if moving baffle introduces in Rectangle sedimentation basin, it forecasts that the turbidity improvement above 30% will be possible.

• Journal of Korean Society of Environmental Engineers
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• v.27 no.2
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• pp.170-176
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• 2005

This study was conducted to investigate the level of PCBs and distribution of PCB congeners in the ambient air of Korea and Japan. The source of PCBs were also studied by a statistical method. The TEQ concentration of PCB in the ambient air of Korea and Japan were between 0.003 and $1.01\;pgTEQ/m^3$(mean value : $0.22\;pgTEQ/m^3$) and between 0.002 and $0.014\;pgTEQ/m^3$ (mean value: $0.007\;pgTEQ/m^3$), respectively. The ambient air of industrial area of Korea showed a fluctuation in PCB concentration than other sampling area. The isomer distribution patterns in the ambient air was more or less similar in all sampling places. In addition, highly chlorinated homologues ($7{\sim}10CB$) were detected in the only Korea industrial area. This observation suggests that there is a possibility of specific source of PCBs in the industrial area. The source identification of PCB in ambient air was performed using multivariate statistical analysis(principal component analysis). As a result, it is estimated that the Korean ambient air was more influenced by combustion process than the ambient air of Japan and also the effect of PCB commercial products was relatively a small.

• Economic and Environmental Geology
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• v.49 no.3
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• pp.167-179
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• 2016

Water quality of Oseepchun, Dogye area, was investigated quantitatively for its origin and hydrogeochemistry in relation to the influence of groundwater. Groundwater appears to be the principal source of Oseepchun from the water-quality monitoring data including redox potentials, composition of dissolved ions and their correlations, hydrogen and oxygen stable isotopic ratios, and the distribution and occurrence of contaminants. Water-quality type of the surface water was grouped by the water-rock interactions as $Ca-HCO_3$ type originated from carbonated bed-rocks in the Joseon Supergroup, (Ca, Mg)-$SO_4$ type related with dissolution of surfide minerals in coal beds of Pyeongan Supergroup, and (Ca, Mg)-($HCO_3$, $SO_4$) type of the mixed one. Locally water pollution occurs by high $SO_4$ from mine drainage and $NO_3$ from waste-treatment facility. Intensive precipitation in summer has no effect on the water type of Oseepchun, but increases the inflow of nitrate and chloride originated from land surface. Results of this study direct that groundwater-surface water interaction is intimate, and thus surface-water resource management should begin with groundwater characterization.

• Journal of the Korea Institute of Building Construction
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• v.22 no.6
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• pp.553-564
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• 2022

Concrete is a representative composite material that shows excellent performance in the construction field. However, it is a brittle and nonhomogeneous material and exhibits weak behavior against bending and tensile forces. To compensate for such weakens, fiber reinforcement has been utilized, and steel fiber has been recognized as one of the best material for such purpose. However, steel fiber can seriously affect the durability of concrete exposed to the marine environment due to the corrosion caused by chlorine ions. This study intended to evaluate the mechanical performance of steel fiber reinforce concrete during and after repeated wet/dry cycles in salt solution. According to the experimental results, there was no reduction in the relative dynamic modulus of concrete during the repeated wet/dry cycles in salt solution for 37 weeks. Flexural strength was not decreased after completion of repeated wet/dry cycles in salt solution. There was no sign of corrosion in steel fibers after visual observation of fractured surface. However, the flexural toughness was decreased, and this is because about half of the concrete specimen showed failure before reaching the maximum displacement of 3 mm. Although repeated wet/dry cycles in salt solution did not cause cracks in concrete through corrosion of steel fibers, specific attention is required because it can reduce flexural toughness of steel fiber reinforced concrete.

• Journal of the Korean Chemical Society
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• v.39 no.7
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• pp.513-523
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• 1995

Polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs) are the most concerned toxic organic pollutants to human. Because of their extremely high toxicity and uncertain genotoxic potential, their determination in environmental and biological samples is of great interest. Municipal solid waste incinerator facilities have been reported as the major contributors of dioxins and furans to the environment, and their formation from combustion is a universal phenomenon, everywhere. In this study dioxins and furans were analyzed from the bottom ash produced during combustion in an municipal waste incinerator located in Seoul. The EPA method was modified for sample pretreatment: the soxhlet method was used for extraction and clean-up procedures were performed by using silica and basic alumina, excluding active-carbon. The extract was then analyzed by HRGC/HRMS. A general trend of increase in the amounts of 6∼7 chlorine-substituted dioxins and furans was observed. Total dioxins, furans and 2,3,7,8-TCDD were determined as 8.05 ng/g, 4.75 ng/g, and 6.93 pg/g, respectively.

• Journal of the Korean GEO-environmental Society
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• v.13 no.7
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• pp.49-54
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• 2012

This study focuses on the decomposition of pentachlorophenol(PCP) by an electron beam (E-beam) process. To attain this objective, we investigated the reactive species generated from E-beam process during irradiation (reaction time 0.6 s) and G-values of PCP decomposition and effects of pH and $H_2O_2$ as an additive. The effect of pH values was independent on the decomposition of PCP. However, during E-beam irradiation a scavenging effect of added $H_2O_2$ (> 1mM) for the decomposition of PCP was shown, which was supported by the decreased amounts of $Cl^-$ produced by the decomposition of PCP. Meanwhile, oxalic acid and unidentified organic chlorine compounds as by-products were increased by the addition of $H_2O_2$. Thus, in order to enhance the efficiency of PCP decomposition, the E-beam process has to consider a proper concentration of $H_2O_2$ as a well-known source of strong oxidant hydroxyl radical.

• Journal of the Korea institute for structural maintenance and inspection
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• v.9 no.4
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• pp.235-242
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• 2005

This study is on the evaluation of performance of polymer cement mortar which is used for pre-wetting spray method. Pre-wetting spray method is an epoch-making method to repair concrete structures damaged, which is added a small quantity water preciously to dry mortar to reduce dust and rebound and spray mortar mixed with fixed quantity water at nozzle before spray. The result showed that physical performance such like compressive, flexural and adhesive strength of polymer cement mortar, TS 100 used for pre-wetting spray method was superior to other repair mortar. Also durable performance such as resistance on permeability of chloride ion, carbonation, chemical and freezing-thawing was excellent.

• Journal of the korean veterinary medical association
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• v.32 no.4
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• pp.206-219
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• 1996

동물의 전염성 해면형 뇌증에는 양과 염소의 스크래피, 사슴과 엘크의 만성소모형, 밍크의 전염성 밍크 뇌증, 소 및 소과 야생동물의 소 해면형 뇌증 그리고 고양이의 고양이 해면형 뇌증등이 알려져 있다. 전염성 해면형 뇌증의 원인은 알려져 있지 않으며, 스트레인간의 차이는 숙주의 프리온 유전자에 있어서의 대립유전자의 차이에 의존되는 것으로 추정되고 있다. 이러한 동물의 전염성 해면형 뇌증들은 우리나라에서의 발생보고가 없는 해외 가축전염병이며 현재 영국에서 문제되고 있는 소 해면형 뇌증 즉 일명 광우병은 영국에서 1986년 최초로 확인된 새로운 가축전염병으로서 사람의 크로이츠휄트-야콥병과의 어떤 연관 가능성 때문에 수의학계의 관심의 대상이 되고 있는 질병이다. 영국정부 보건장관 스티픈 도렐은 최근(1996년 3월 20일)에 과거 10년 동안 영국의 소에 감염되어 온 소 해면형 뇌증이 사람의 희귀한 뇌 질환인 크로이츠휄트-야콥병의 새로운 스트레인과 관련성이 있는 증거가 있을 수 있는 것으로 과학자문위원회가 믿고 있다고, 영국하원에서 보고한 바 있다. 한편, 영국의 농업장관 더글러스 호그는 영국에서 30개월 이상된 소를 도살할 때에는 모든 뼈를 제거하여야 하며, 모든 포유동물의 조직은 농업용 사료로 사용해서는 아니된다는 새로운 규정을 공표하였다. 그러나 영국의 쇠고기는 안심하고 먹을 수 있다고 발표하면서 만일 문제가 된다면, 영국에서 사육하는 1천 1백만 마리의 소를 전부 도살할 용의가 있다고 하였다. 이러한 영국정부 견해는 다음 날 CNN News 등 세계 각 매스컴을 통하여 보도되었으며, 아직까지 과학적인 증거가 확립된 바는 없지만, 수의학이나 의학적인 사실 확인의 여부를 떠나, 사회 경제적인 문제로 큰 놀라움과 많은 의문사항을 남겨둔 채, 영국산 소와 쇠고기의 수입금지 조치 등 국제적인 문제로 확대되었다. 본편에서는 동물의 전염성 해면형 뇌증에 대하여 종합적으로 고찰해 보고자 한다.

• Magazine of the Korea Concrete Institute
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• v.11 no.2
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• pp.221-230
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• 1999

Corrosion of rebars can occur if there are cracks, moisture and availability of oxygen or carbonation proceeds, chloride penetrates and diffuses in concrete. Once rebars in concrete corrodes, subsequently accompanied with scaling, spalling in concrete cover. As a result of them, the RC structure is seriously deteriorated. In this study, theoretical review and experiments for cathodic protection(CP) have been performed to control corrosion of rebars in concrete contained chlorides and pre-crack. For CP the impressed current system was applied, the protection effect was investigated when rebars was directly contacted with salt water due to crack and open to much chlorides in concrete. In order to investigate the effect of protection, when CP was energized for 1 year, half-cell potential, potential-decay with current density, corrosion ratio, etc. were measured. With the cathodic protection by impressed current system, the depolarized values of all specimen were met NACE Standard, the effect of 34~84% of the ratio of corrosion area and 84~86% of cross-section reduction were calculated.