• Journal of the Korean institute of surface engineering
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• v.56 no.6
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• pp.443-450
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• 2023

SiC/SiC_f CMC is vulnerable to water vapor corrosion at a high temperature of 1500℃. So, EBC (Environmental Barrier Coating) materials are required to protect Si-based CMCs. Ytterbium silicates are reported to have coefficient of thermal expansion (CTE) similar to that of the base material, such as SiC/SiC_f CMC. When the EBC are materials exposed to high temperature environment, the interface between ytterbium silicates and SiC/SiC_f CMC is not separated, and the coating purpose can be safely achieved. For the perspective of EBC applications, thermally grown oxide (TGO) layer with different CTE is formed by the reaction with water vapor in EBC, which leads to a decrease in life time. In this study, we prepare two types of ytterbium silicates to observe the corrosion behavior during the expose to high temperature and water vapor. In order to observe this behavior, the steam-jet furnace is prepared. In addition, phase formation of these ytterbium silicates is analyzed with microstructures by the before/after steam-jet evaluation at 1500℃ for 100 h.

• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.19 no.2
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• pp.109-116
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• 2023

This study presents a CRUD modelling to simulate the thermal resistance behavior of CRUD, deposited on the surface of a cladding tube of a fuel assembly. When heat produced from fuels transfers to a coolant through a cladding tube, the CRUD acting as an additional thermal resistance is expressed as two layers, i.e., a solid oxide layer and an imaginary fluid layer, which are added to the experimental tube's heat structure of the MARS-KS input data. The validation calculation for the experiments performed in UNIST-DISNY facility showed that the center and surface temperatures of the cladding tube increased as the porosity and the steam amount inside pores of the CRUD got higher. In addition, the temperature gradient in the imaginary fluid layer was calculated to be larger than that in the solid oxide part, indicating that the steam amount inside the layer acted more largely as thermal resistance. It was also evaluated through sensitivity calculations that the cladding tube temperature was more sensitive to the CRUD porosity and the steam amount in pores than to the inlet flow rate of the coolant.

• Journal of the Korean earth science society
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• v.41 no.1
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• pp.75-91
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• 2020

The purposes of this study are 1) to develop a pre-education program for teaching the basic concepts of systems thinking and STEAM program based on systems thinking and 2) to investigate the effects of the program on middle school students' systems thinking. The subjects were 4 seventh-graders and 4 ninth-graders in a middle school located in the province of Gyeongsangbuk-do. Data related to students' systems thinking was analyzed using the rubrics developed by Hung(2008). The results were reviewed by experts to verify the validity of the rubrics and the reliability of students' system thinking. In addition, the data analyzed with the rubrics, students' awareness of systems thinking, word associations, causal maps and interviews were systematically analyzed to investigate the effects of the program on students' systems thinking. The findings of this study were as follows: First, a pre-education program and teachers' guidebook for teaching and learning the concept of systems thinking and causal maps were developed. The pre-education program consisted of familiar TV entertainment program-Infinite Challenge (Muhandojeon)-with a theme of Global Warming. Second, a STEAM education program based on systems thinking which was composed of 5 steps: Analysis-Design-Build-Assessment-Systems thinking. The major theme of the program was an air extinguisher. The developed STEAM education program had positive effects on improving middle school students' systems thinking abilities such as understanding systems, relations within a system and system generalization. Therefore, it was concluded that the STEAM program could be instrumental for cultivating students' STEAM literacy with improved systems thinking.

• 대한공업교육학회지
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• v.40 no.2
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• pp.239-258
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• 2015

The purpose of this study is to provide basic data that can be used in a reasonable assessment of the learning outcomes of STEAM. It presented a learning outcome evaluation method, relative weights of key competencies standard that a learner should cultivate. For this study, a pairwise comparison questionnaire about the key competencies was conducted on the STEAM professionals, and AHP was applied to analyze the priority of main factors of key competencies. The results of this study are as follows. First, the importance of capabilities of convergence accomplishment and capabilities of convergent cognition, in the first layer of key competencies, were 39.4% and 36.8%, respectively. In the education evaluation of the STEAM, capabilities of convergence accomplishment and capabilities of convergent cognition showed similar level of importance, and were considered more important factor than capabilities of convergence attitude (23.8%). Second, the relative importance of capabilities of problem solving (20.0%) was highest in the second layer of key competencies, and followed by capabilities of creative thinking (18.3%), responsibility (15.3%), and understanding convergence knowledge (11.0%). Third, it will be a foundation of a competency evaluation, which reasonably evaluates, based on the relative weights, whether to accomplish educational objectives of the STEAM program In addition, this results is expected to become a guide to develop an education program that can improve the teaching and learning process and raise the learning outcome, as well as an education evaluation of the STEAM.

• Journal of Korean Elementary Science Education
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• v.40 no.1
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• pp.113-125
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• 2021

In this study, a problem-centered learning based STEAM field experience learning program was developed and the effects of applying it were investigated. The program was composed of 8 sessions by using problem-centered learning education method and integrating STEAM elements between disciplines. The contents of program are as follow. In the step of sharing problems and making a problem-solving plan, they understood the various examples and meanings of endangered species, explored the project activities, and made an inquiry plan. In the search and re-exploration phase, a smart device was used to investigate the appearance, habitat environment and cause of extinction for Clithon retropictus, and a site inquiry plan was established for each group. Then, they moved to the field to explore brackish-headed gallops and discuss ways to protect endangered species. In the step of creating a solution, a web-based report was produced as the final product using smart devices based on the results of the inquiry. In the presentation and evaluation stage, the produced web-based report was used to present each group, conduct mutual evaluation, and organize project activities. The developed program was applied to 6th grade 29 students enrolled in the J University Gifted Education Center. In order to find out the effectiveness of the program, tests of science process skill, creative problem-solving ability, and scientific attitude were conducted before and after of program learning, and the results were statistically analyzed by t-test. In addition, a STEAM program satisfaction test was conducted after project in order to find out the satisfaction of the class. As a result of application of the program, the results were significantly improved in openness, criticism, and creativity among the sub-factors of creative problem-solving ability and scientific attitude. Satisfaction with the STEAM program was also high, but no significant result was found in science process skill. Therefore, the program of this study could be influenced on improvement of creative problem-solving ability and scientific attitude of gifted students in elementary science.

• Clean Technology
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• v.28 no.1
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• pp.1-8
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• 2022

To confirm the applicability of the water gas shift reaction for the production of high purity hydrogen for petroleum cokes, an unutilized low grade resource, Cu/ZnO/MgO/Al₂O₃ (CZMA), catalyst was prepared using the co-precipitation method. The prepared catalyst was analyzed using BET and H₂-TPR. Catalyst reactivity tests were compared and analyzed in two cases: a single LTS reaction from syngas containing a high concentration of CO, and an LTS reaction immediately after the syngas passed through a HTS reaction without condensation of steam. Reaction characteristics in accordance with steam/CO ratio, flow rate, and temperature were confirmed under both conditions. When the converted low concentration of CO and steam were immediately injected into the LTS, the CO conversion was rather low in most conditions despite the presence of large amounts of steam. In addition, because the influence of the steam/CO ratio, temperature, and flow rate was significant, additional analysis was required to determine the optimal operating conditions. Meanwhile, carbon deposition or activity degradation of the catalyst did not appear under high CO concentration, and high CO conversion was exhibited in most cases. In conclusion, it was confirmed that when the Cu/ZnO/MgO/Al₂O₃ catalyst and the appropriate operating conditions were applied to the syngas composition containing a high concentration of CO, the high concentration of CO could be converted in sufficient amounts into CO₂ by applying a single LTS reaction.

• Korea Trade Review
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• v.44 no.2
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• pp.127-141
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• 2019

In this study, the relationship between Baltic Dry Index(BDI) and maritime trade volume in the dry cargo market was verified using the vector autoregressive (VAR) model. Data was analyzed from 1992 to 2018 for iron ore, steam coal, coking coal, grain, and minor bulks of maritime trade volume and BDI. Granger causality analysis showed that the BDI affects the trade volume of coking coal and minor bulks but the trade volume of iron ore, steam coal and grain do not correlate with the BDI freight index. Impulse response analysis showed that the shock of BDI had the greatest impact on coking coal at the two years lag and the impact was negligible at the ten years lag. In addition, the shock of BDI on minor cargoes was strongest at the three years lag, and were negligible at the ten years lag. This study examined the relationship between maritime trade volume and BDI in the dry bulk shipping market in which uncertainty is high. As a result of this study, there is an economic aspect of sustainability that has helped the risk management of shipping companies. In addition, it is significant from an academic point of view that the long-term relationship between the two time series was analyzed through the causality test between variables. However, it is necessary to develop a forecasting model that will help decision makers in maritime markets using more sophisticated methods such as the Bayesian VAR model.

• Corrosion Science and Technology
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• v.14 no.2
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• pp.76-84
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• 2015

The components in ultra super critical (USC) steam turbine, which is under development for high efficient power generation, are encountering harsher solid particle erosion by iron oxide scales than ones in the existing steam turbines. Therefore, the currently used boride coating will not be able to hold effective protection from particle erosion in USC system and should be replaced by new particle erosion resistant coatings. One of the best protective coatings developed for USC steam turbine parts was found to be vanadium-boride (V-boride) coating which has a hardness of about 3000 HV, much higher than that of boride, 1600~2000 HV. In order to evaluate particle erosion resistance of the various coatings such as V-boride, boride and Cr-carbide coatings at high temperature, particle erosion test equipments were designed and manufactured. In addition, erosion particle velocity was simulated using FLUENT software based on semi-implicity method for pressure linked equations revised (SIMPLER). Based on experimental results of this work, the vanadium-boride coating was found to be superior to others and to be a candidate coating to replace the boride coating.

• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.16 no.1
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• pp.74-83
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• 2020

A number of so-called 'Type IV' cracking was reported to occur at the welded joints of the P91 steel or P92 steel reheat steam piping systems in Korean supercritical thermal power plants. The reheat steam piping systems are subjected to severe thermal and pressure loading conditions of coolant higher than 570℃ and 4MPa, respectively. In this study, piping analyses and design evaluations were conducted for the piping system of a specific thermal plant in Korea and suggestions were made how structural integrity could be improved so that type IV cracks at the welded joints could be prevented. Integrity evaluations were conducted as per ASME B31.1 code with implicit consideration of creep effects which was used in original design of the piping system and as per nuclear-grade RCC-MRx code with explicit consideration of creep effects. Comparisons were made between the evaluation results from the two design rules. Another approach with modification or reduction of the redundant supports in the piping systems was investigated as a tool to mitigate thermal stresses which should essentially contribute to prevention of Type IV cracking without major modification of the existing piping systems. In addition, a post weld heat treatment method and repair weld method which could improve integrity of the welded joint of P91 steel were investigated.

• Applied Chemistry for Engineering
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• v.26 no.6
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• pp.648-658
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• 2015

Extraction of phytoncide oil from korea pine cone waste without damaging the pine cone tree itself was investigated using a steam distillation method. Also various components in the extracted phytoncide oil were separated using a column chromatography method. The extraction of phytoncide oil was effectively proceeded, and the maximum production yield of phytoncide oil could be obtained under $100^{\circ}C$ of distillation temperature and within 30 minute of distillation time. According to chemical analysis, it was found that the phytoncide oil from korea pine cone waste was consisted of more than 12 components such as ${\alpha}$-pinene, ${\beta}$-pinene, D-limonene, as main components. In addition, the aqueous hydrogel containing other components such as verbenone, ${\alpha}$-terpinieol, fenchol, different from components of phytoncide oil itself could be obtained through the steam distillation.