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나상수 ( Na Sang Su ) 서울대학교 국어교육과 2022 先淸語文 Vol.50 No.-
Grammar is a variable system constructed by principal agents of language. Therefore, in order for grammar inquiry to contain the essential properties of grammar, it would be necessary to provide a process experience that allows learners to construct grammar themselves. Moreover, hypothesis generation experience is the experience that learners construct their own personal grammar, which is the core of the grammar inquiry experience. Thus, this study sought to establish the grammar inquiry as the process experience of constructing grammar, and in order to realize education on grammar inquiry as a grammar construction experience, it was intended to establish education on hypothesis generation experience in the grammar inquiry process. This can be the answer to what unique experience of grammar inquiry education is, and hypothesis generation experience shows a specific image of grammar inquiry experience. In conclusion, considering the originality of grammar inquiry, the hypothesis in grammar inquiry was defined as “a verifiable and tentative conclusion as an explanation of the mechanism of linguistic phenomena”. In addition, the thought process of generating hypothesis was examined in detail by classifying hypotheses in grammar inquiry as inductive hypothesis and abductive hypothesis, and the aspects of hypothesis generation education in grammar inquiry learning that allow us to experience this thought process were embodied.
Al-2Zn-1Cu-0.3Mg합금의 Sc첨가에 따른 미세조직, 전기전도도, 열전도도 및 기계적 특성 변화
나상수,김용호,손현택,이성희,Na, Sang-Su,Kim, Yong-Ho,Son, Hyeon-Taek,Lee, Seong-Hee 한국재료학회 2020 한국재료학회지 Vol.30 No.10
Effects of Sc addition on microstructure, electrical conductivity, thermal conductivity and mechanical properties of the as-cast and as-extruded Al-2Zn-1Cu-0.3Mg-xSc (x = 0, 0.25, 0.5 wt%) alloys are investigated. The average grain size of the as-cast Al-2Zn-1Cu-0.3Mg alloy is 2,334 ㎛; however, this value drops to 914 and 529 ㎛ with addition of Sc element at 0.25 wt% and 0.5 wt%, respectively. This grain refinement is due to primary Al<sub>3</sub>Sc phase forming during solidification. The as-extruded Al-2Zn-1Cu-0.3Mg alloy has a recrystallization structure consisting of almost equiaxed grains. However, the as-extruded Sc-containing alloys consist of grains that are extremely elongated in the extrusion direction. In addition, it is found that the proportion of low-angle grain boundaries below 15 degree is dominant. This is because the addition of Sc results in the formation of coherent and nano-scale Al<sub>3</sub>Sc phases during hot extrusion, inhibiting the process of recrystallization and improving the strength by pinning of dislocations and the formation of subgrain boundaries. The maximum values of the yield and tensile strength are 126 MPa and 215 MPa for the as-extruded Al-2Zn-1Cu-0.3Mg-0.25Sc alloy, respectively. The increase in strength is probably due to the existence of nano-scale Al<sub>3</sub>Sc precipitates and dense Al<sub>2</sub>Cu phases. Thermal conductivity of the as-cast Al-2Zn-1Cu-0.3Mg-xSc alloy is reduced to 204, 187 and 183 W/MK by additions of elemental Sc of 0, 0.25 and 0.5 wt%, respectively. On the other hand, the thermal conductivity of the as-extruded Al-2Zn-1Cu-0.3Mg-xSc alloy is about 200 W/Mk regardless of the content of Sc. This is because of the formation of coherent Al<sub>3</sub>Sc phase, which decreases Sc content and causes extremely high electrical resistivity.
브레이징용 Al 합금 분말의 미세조직에 미치는 Sn 함량의 영향
김용호,유효상,나상수,손현택,Kim, Yong-Ho,Yoo, Hyo-Sang,Na, Sang-Su,Son, Hyeon-Taek 한국분말야금학회 2020 한국분말재료학회지 (KPMI) Vol.27 No.2
The powder manufacturing process using the gas atomizer process is easy for mass production, has a fine powder particle size, and has excellent mechanical properties compared to the existing casting process, so it can be applied to various industries such as automobiles, electronic devices, aviation, and 3D printers. In this study, a modified A4032-xSn (x = 0, 1, 3, 5, and 10 wt.%) alloy with low melting point properties is investigated. After maintaining an argon (Ar) gas atmosphere, the main crucible is tilted; containing molten metal at 1,000℃ by melting the master alloy at a high frequency, and Ar gas is sprayed at 10 bar gas pressure after the molten metal inflow to the tundish crucible, which is maintained at 800℃. The manufactured powder is measured using a particle size analyzer, and FESEM is used to observe the shape and surface of the alloy powder. DSC is performed to investigate the change in shape, according to the melting point and temperature change. The microstructure of added tin (Sn) was observed by heat treatment at 575℃ for 10 min. As the content of Sn increased, the volume fraction increased to 1.1, 3.1, 6.4, and 10.9%.