• Corrosion Science and Technology
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• 제9권3호
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• pp.122-128
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• 2010

The corrosion of the flexible tube in the automobile exhaust system is caused by the ambient water and chloride ions. Since welding is one of the key processes for the flexible tube manufacturing, it is required to select a proper welding method to prevent the flexible tube corrosion and to increase its lifetime. There are many studies about the efficiency of the welding method, but no systematic study is performed for the effect of welding method on the corrosion property of the austenitic stainless weldment. The aim of the present study is to provide information on the effect of two different welding methods of TIGW (tungsten inert gas welding) and PAW (plasma arc welding) on the corrosion property of austenitic stainless steel weldment. Materials used in this study were two types of the commercial austenitic stainless steel, STS321 and XM15J1, which were used for flexible tube material for the automotive exhaust system. Microstructure was observed by using optical microscopy (OM) and scanning electron microscopy (SEM). To evaluate the corrosion behavior, potentiodynamic and potentiostatic tests were performed. The chemical state of the passive film was analyzed in terms of XPS depth profile. Metallurgical analysis show that the ferrite content in fusion zone of both STS321 and XM15J1 is higher when welded by PAW than by TIGW. The potentiodynamic and potentiostatic test results show that both STS321 and XM15J1 have higher transpassive potential and lower passive current density when welded by PAW than by TIGW. XPS analysis indicates that the stable $Cr_2O_3$ layer at the outermost layer of the passive film is formed when welded by PAW. The result recommends that PAW is more desirable than TIGW to secure corrosion resistance of the flex tube which is usually made of austenitic stainless steel.

• 열처리공학회지
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• 제20권2호
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• pp.65-71
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• 2007

Microstructural changes and hardness variations in STS 304 steel have been investigated during the processes of carbide dispersion (CD) carburization; carburization, austenitization, subzero treatment and tempering. The carbon content of the surface layer increased up to maximum 4.0% after carburization, and the content was homogenized with the value of 2.3% to the $95{\mu}m$ from the surface after austenitization. The carbide appeared during CD carburization process was $Cr_7C_3$ type, which was composed network carbides along the austenite grain boundaries, square type carbides in the interior of the grain and fine nano-sized carbides. The fine nano-sized carbides precipitated at the austenitization stage and possibly subzero treatment stage were coarsened after tempering at $200^{\circ}C$, resulting the hardness decrease. The tempered steel without subzero treatment increased hardness with increasing time due to the continuous precipitation of fine carbides during tempering. The nano-sized carbide appeared square type morphology.

• 한국과학교육학회지
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• 제25권3호
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• pp.327-335
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• 2005

이 연구에서는 STS 가설 연역적 수업 전략을 고등학교 화학 I의 물 단원의 수업 전략에 사용하여 학생들의 과학 학업 성취도와 과학에 관련된 태도를 알아보았다. 연구의 대상은 경기도에 있는 남녀 공학 고등학교 2학년 자연 계열 학생들이다. 본 연구는 사전 검사로 실험반과 통제반 학생들의 물 단원 관련 과학 학업 성취도와 과학에 관련된 태도를 조사한 후 STS 가설 연역적 수업 전략과 교과서 위주의 전통적 강의식 수업 전략을 총 10차시에 걸쳐 시행한 후에, 학생들이 수업 후 형성된 과학 학업 성취도와 과학과 관련된 태도를 사후 검사를 통해 실시하였으며 얻어진 결과는 다음과 같다. 첫째, 물과 관련하여 STS 가설 연역적 수업 전략을 도입한 실험반의 학생들과 교과서 위주의 강의식 수업 방식을 도입한 통제반의 학생들은 과학 학업 성취도 변화에 있어서 실험반의 교정 평균이 통제반의 교정 평균보다 4.26점 높게 나타났으나, 통계적으로 유의미한 차이는 나타나지 않았다(p>05). 둘째, STS 가설 연역적 수업 전략을 도입한 실험반의 학생들이 교과서 위주의 강의식 수업 방식을 도입한 통제반의 학생들보다 과학/기술/사회와 관련된 태도 변화에 있어서 통계적으로 유의미한 차이를 나타내었다 (p<.05).과학에 관련된 태도의 하위 영역에서 실험반이 통제반 에 비해 통계적으로 유의미한 차이가 있는 영역은 과학 수업 내용(II영역), 과학 공부(III영역), 과학의 가치(IV영역)이였다.

• 한국초등과학교육학회지:초등과학교육
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• 제33권2호
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• pp.207-216
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• 2014

Understanding the nature of science (NOS) has been a major component of scientific literacy and an important learning goal in science education (American Association for the Advancement of Science, 1990, 1993; Millar & Osborne, 1998; National Research Council, 1996, 2013). To achieve this goal, it is necessary to include appropriate views of the nature of science in science curriculum such as a textbook. The aim of this study was to conduct a content analysis of the elementary science textbooks to examine the presentation of the nature of science (NOS) using the four themes of scientific literacy, which are (1) nature of scientific knowledge, (2) nature of scientific inquiry, (3) nature of scientific thinking, and (4) nature of interactions among science, technology, and society (STS). Findings show while $3^{rd}$ and $4^{th}$ grade levels of science textbooks heavily emphasize on the Theme I, nature of scientific knowledge and the Theme II, the nature of scientific inquiry, the upper grade levels such as $5^{th}$ and $6^{th}$ grades of science textbooks are well balanced with the four themes of the nature of science. In addition, most of elementary science textbooks little focus on the Theme IV, nature of interactions among science, technology, and society (STS) among the four themes of the nature of science. It might be a shortcoming because the understanding the nature of interacions among science, technology and society (STS) is one of the key components in order for students to be a scientific literate person.

• 한국수소및신에너지학회논문집
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• 제23권3호
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• pp.207-212
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• 2012

This study was performed to observe the change of stainless steel pipe interacting with alkaline solution. We used STS316L and STS304 as samples which were soaked in alkaline solution. We measured the samples by use of FE-SEM, EDX, SIMS to observe the surface and depth profile of both samples. The result showed that the precipitate appeared on the surface of both samples from 5 days. but the precipitate was confirmed to be decreased as time passes. but the quantitative change of precipitates at both samples was different as time passed. The EDX showed that the precipitate is Potassium from solution of Electrolysis. The result also showed that the primary elements of stainless steel pipeline and of Alkaline Solution were changed. The change of primary elements was severe between 5 days to 16 days and was stable around 40 days at both samples. The reaction of STS316L with alkaline solution was lower than STS304. We hoped that this study would be the foundation of developing the electrode of the alkaline hydrogen generator.

• 한국과학교육학회지
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• 제19권3호
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• pp.409-427
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• 1999

본 논문의 목표는 영국의 과학교육이라는 맥락 속에서 STS교육과 관련된 아이디어의 역사적 발전과정을 - 특히, 19세기와 20세기 전반 동안 - 살펴보는 것이다. STS교육은 구성주의와 함께 20세기 후반의 세계 과학교육을 특징짓는 양대 패러다임으로 간주되고 있다. 그리고 많은 사람들은 STS교육의 역사를 Science in Society 와 SISCON 이 개발되었던 1980년대 이후를 중심으로만 생각하는 경향이 있다. 하지만, 영국에서 STS교육과 관련하여 생각해 볼 수 있는 최초의 움직임으로는 19세기 초반의 노동자를 대상으로 과학의 기초 내용과 그 응용적 측면을 교육하고자 하였던 '노동자학교' 운동과 초등학교에서 '일상사물의 과학' 을 활발히 교육하였던 Dawes 등의 활동을 들 수 있겠다. 19세기 중반을 지나면서, 이러한 움직임은 초등학교의 '실물학습'이라는 교과를 통해 이어지게 되는데, 그 시기 동안 학교 과학 과목들은 정식으로 교육과정에 포함되고 이 과정에서 과학은 점차 순수 학문적이고 전문가 양성을 위한 준비과정으로 그 성격이 확립되게 되었다. 20세기에 접어들면서 이러한 협소한 관점의 학교 과학교육에 대한 비판과 반성이 점차 제기되었고, 특히 제 1차 세계대전의 경험을 통해 일반인 전체를 대상으로 하는 과학과 사회의 관계에 대한 교육의 필요성이 점차 널리 인식되게 되었다. 이러한 배경에서 1920-40년대 영국에서는 '일반과학'과 '시민과학'의 운동이 활발하게 전개되었으며, 이중에서 특히 '시민과학' 운동의 일환이었던 Hogben의 Science for the Citizen의 집필은 대표적인 STS교육의 사례라고 할 수 있겠다. 20세기 중반까지의 영국의 과학교육사는 기본적으로 학교 과학교육이 실용성과 학문성. 전문가양성과 일반 교육, 정신훈련과 과학지식교육, 개별과학과 일반과학 등 과학교육의 목표와 기능에 대한 상치되는 관점들 간의 투쟁의 단면들임을 보여주고 있다.

• Food Science and Biotechnology
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• 제17권5호
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• pp.1066-1073
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• 2008

Sensitivity to 6-n-propylthiouracil (PROP) tasting predicts sensitivity to food qualities as well as rejection of some strong tasting foods. Using consumer rejection threshold (CRT) method, this study aimed to assess whether systematic changes in the taste intensities of familiar foods would lead to earlier rejection of these products by PROP tasters than by PROP non-tasters. Subjects rated the intensity of PROP solution and were divided into tasters (Ts) and non-tasters (NTs). And Ts were further divided into medium-tasters (MTs) and super-tasters (STs). Difference thresholds and CRTs were then evaluated for caffeine in coffee, citric acid in orange juice, and for NaCl in beef soup. For each food, Ts were more sensitive to variations in tastants than NTs. Ts also rejected more bitter coffee, more sour orange juice, and less salty beef soup more readily than did NTs. Comparisons among NTs, MTs, and STs gave fewer clear differences.

• 공학교육연구
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• 제15권1호
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• pp.79-83
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• 2012

I argue that STS education for engineers, despite its prima facie usefulness in demystifying the conventional image of science and technology, should deal with a few challenges in order to cultivate 'responsible' engineers. The challenges come from the fact that there are more than one legitimate way of understanding 'responsible' in the engineering contexts depending on how wide the range of responsibility is intended and on how the relevant reference class is defined. In order to tackle these issues, I suggest that we should take into account more seriously the 'value-laden' nature of the engineering design.

• 한국수소및신에너지학회논문집
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• 제20권6호
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• pp.455-463
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• 2009

코발트 보호막 코팅이 적용된 페라이트계 스테인리스 스틸인 STS 430과 STS 444 소재에 대해 고체산화물 연료전지용 금속연결재로서의 고온 산화 특성에 대해 살펴보았다. 코발트 코팅층은 $800^{\circ}C$ 고온 산화 후 코발트 산화물 및 $Co_2CrO_4$, $CoCr_2O_4$, $CoCrFeO_4$ 등과 같은 코발트가 함유된 스피넬 상을 형성하였다. 또한 페라이트계 스테인리스 스틸과 코발트 코팅의 계면에서 크롬과 철이 함유된 치밀한 산화층을 형성하여 금속연결재 표면의 스케일 성장속도를 감소시키고 금속연결재 내에 함유된 크롬의 외부 확산을 효과적으로 억제하였다. 한편 STS 430은 고온 산화 후 표면에 형성된 스케일 하부에 $SiO_2$와 같은 내부 산화물이 형성된 반면 STS 444는 표면 스케일 이외에 다른 내부 산화물은 확인되지 않았으며 고온에서의 면저항 측정 결과, 코발트가 코팅된 STS 444의 전기 전도성이 STS 430 보다 우수한 것으로 나타났다.

• 한국재료학회지
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• 제28권3호
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• pp.174-181
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• 2018

Three kinds of STS304-Zr alloys were fabricated by varying the Zr content, and their microstructure and fracture properties were analyzed. Moreover, we performed heat treatment to improve their properties and studied their microstructure and fracture properties. The microstructure of the STS304-Zr alloys before and after the heat treatment process consisted of ${\alpha}-Fe$ and intermetallics: Zr(Cr, Ni, Fe)2 and Zr6Fe23. The volume fraction of the intermetallics increased with an increasing Zr content. The 11Zr specimen exhibited the lowest hardness and fine dimples and cleavage facets in a fractured surface. The 15Zr specimen had high hardness and fine cleavage facets. The 19Zr specimen had the highest hardness and large cleavage facets. After the heat treatment process, the intermetallics were spheroidized and their volume fraction increased. In addition, the specimens after the heat treatment process, the Laves phase (Zr(Cr, Ni, Fe) 2) decreased, the Zr6Fe23 phase increased and the Ni concentration in the intermetallics decreased. The hardness of all the specimens after the heat treatment process decreased because of the dislocations and residual stresses in ${\alpha}-Fe$, and the fine lamellar shaped eutectic microstructures changed into large ${\alpha}-Fe$ and spheroidized intermetallics. The cleavage facet size increased because of the decomposition of the fine lamellar-shaped eutectic microstructures and the increase in spheroidized intermetallics.