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동적재료모델을 활용한 STS 321 스테인리스강의 고온성형성 평가와 초기 미세조직의 영향
조평석,이재관,황효운,이용재,이동근 대한금속·재료학회 2022 대한금속·재료학회지 Vol.60 No.12
General austenitic stainless steel has a problem with intergranular corrosion due to volatilizingchromium, which forms chromium carbide in a high temperature environment. By adding titanium as analloying element, STS 321 stainless steel has excellent creep resistance and intergranular corrosion resistanceat high temperatures, because the formation of chromium carbide is suppressed. It is important to find theoptimal process conditions for STS 321 stainless steel used in the aerospace field, because high temperatureprocessing is mainly applied, and defects or inhomogeneity of materials that occur during high temperatureprocessing lowers the yield of products. In this study, to investigate the effect of the initial microstructure onthe high-temperature deformation behavior of STS 321 stainless steel, a high-temperature compression testwas performed on two types of STS321 alloys with different initial microstructures. The temperature rangewas set at 50°C intervals from 800°C to 1100°C, and the strain rate was set at 10-1/sec intervals from 1 × 100/sec to 1 × 10-3/sec. Based on the experimental results, the thermal activation energy, which differed dependingon differences in the initial microstructure, was calculated. In addition, by deriving flow stress and processingmaps, the difference in energy dissipation efficiency depending on temperature and strain rate was explained,along with the initial microstructure and high-temperature deformation mechanism.
LTCC 를 이용한 SnO<sub>2</sub> 가스 센서
조평석,강종윤,김선중,김진상,윤석진,이종흔,Cho, Pyeong-Seok,Kang, Chong-Yun,Kim, Sun-Jung,Kim, Jin-Sang,Yoon, Seok-Jin,Hieu, Nguyen Van,Lee, Jong-Heun 한국재료학회 2008 한국재료학회지 Vol.18 No.2
A sensor element array for combinatorial solution deposition research was fabricated using LTCC (Low-temperature Co-fired Ceramics). The designed LTCC was co-fired at $800^{\circ}C$ for 1 hour after lamination at $70^{\circ}C$ under 3000 psi for 30 minutes. $SnO_2$ sol was prepared by a hydrothermal method at $200^{\circ}C$ for 3 hours. Tin chloride and ammonium carbonate were used as raw materials and the ammonia solution was added to a Teflon jar. 20 droplets of $SnO_2$ sol were deposited onto a LTCC sensor element and this was heat treated at $600^{\circ}C$ for 5 hours. The gas sensitivity ($S\;=\;R_a/R_g$) values of the $SnO_2$ sensor and 0.04 wt% Pd-added $SnO_2$ sensor were measured. The 0.04 wt% Pd-added $SnO_2$ sensor showed higher sensitivity (S = 8.1) compared to the $SnO_2$ sensor (S = 5.95) to 200 ppm $CH_3COCH_3$ at $400^{\circ}C$.
수열합성법을 이용한 ZnO 나노로드의 제조 및 이산화질소 감응 특성
조평석,김기원,이종흔,Cho, Pyeong-Seok,Kim, Ki-Won,Lee, Jong-Heun 한국진공학회 2006 Applied Science and Convergence Technology Vol.15 No.5
$Zn(NO_3)_2{\cdot}6H_2O$, 수산화나트륨, cyclohexylamine, 에탄올, 물이 혼합된 용액을 수열합성하여 ZnO 나노로드를 합성하고, 합성한 물질의 이산화 질소$(NO_2)$와 일산화 탄소(CO)에 대한 감응특성을 조사하였다. 혼합 용액에 첨가되는 물의 양을 변화시켜 ZnO 나노로드의 형상과 응집현상을 조절할 수 있었다. 이는 물과 cyclohexylamine의 반응에 의해 발생되는 $OH^-$ 이온의 농도변화에 의한 것으로 해석된다. 물의 함량이 낮을 때에는 뭉쳐진 성게모양의 ZnO 나노로드를, 물의 함량이 많을 때에는 잘 분산된 ZnO 나노로드를 각각 합성할 수 있었다. 잘 분산된ZnO 나노로드는 공기 중에서 50 ppm 의 CO에 노출되었을 때 주목할 만한 반응을 보이지 않는 반면, 1 ppm 의 $NO_2$에 노출되었을 때에는 저항이 1.8배 증가하였다. 이러한 선택적 반응을 보이는 ZnO 나노로드는 자동차용 자동환기 시스템의 핵심부품인 매연센서의 감응물질로 사용될 수 있다. ZnO nanorods were prepared by the hydrothermal reaction of a solution containing $Zn(NO_3)_2{\cdot}6H_2O$, NaOH, cyclohexylamine, ethanol and water, and their $NO_2$ and CO sensing behaviors were investigated. By the control of water concentration in solution, the morphology and agglomeration of ZnO nanorods could be manipulated, which is associated with the variation of $[OH^-]$ resulted from an interaction between water and cyclohexylamine. Sea-urchin-like and well-dispersed ZnO nanorods were prepared at low and high water content, respectively. Well-dispersed ZnO nanorods showed 1.8 fold change in resistance at 1 ppm $NO_2$ while there was no significant change in resistance at 50 ppm CO. This selective detection of $NO_2$ in the presence of CO can be used in automated car ventilation systems.
타이타늄-구리 폭발압접 이종 클래드 판재의 TIG 용접 건전성 평가
조평석 ( Pyeong-seok Jo ),윤창석 ( Chang-seok Youn ),황효운 ( Hyo-woon Hwang ),이동근 ( Dong-geun Lee ) 한국열처리공학회 2021 熱處理工學會誌 Vol.34 No.2
Cladding material, which can selectively obtain excellent properties of different metals, is a composite material that combines two or more types of dissimilar metals into one plate. The titanium-copper cladding material between titanium which has excellent corrosion resistance and copper which has high thermal and electrical conductivity, are highly valuable composite materials. It can be used as heat exchangers with high conductivity under severe corrosion conditions. In order to apply the clad plate to the heat exchanger, it must be manufactured in the form of a tube and additional welding is required. It is important to select the cladding material manufacturing process and the welding process. The process of manufacturing the cladding material includes extrusion, rolling, and explosive bonding. Among them, the explosive bonding process is suitable for additional welding because no heat-affected zone is formed. In this study TIG welding of the explosive-bonded dissimilar clad plates was successfully performed by butt welding. The microstructures and bonding interface of the welded part were observed, and the effect of the bonding layer at the welding interface and the intermetallic compounds on the mechanical properties and tensile plastic deformation behaviors were analyzed. And also the integrity of TIG-welded dissimilar part was evaluated. (Received February 25, 2021; Revised March 4, 2021; Accepted March 9, 2021)
용액적하법으로 제조된 WO<sub>3</sub> 첨가 SnO<sub>2</sub> 박막의 가스감응 특성
최중기,조평석,이종흔,Choi, Joong-Ki,Cho, Pyeong-Seok,Lee, Jong-Heun 한국재료학회 2008 한국재료학회지 Vol.18 No.4
$WO_3$-doped $SnO_2$ thin films were prepared in a solution-deposition method and their gas-sensing characteristics were investigated. The doping of $WO_3$ to $SnO_2$ increased the response ($R_a/R_g,\;R_a$: resistance in air, $R_g$: resistance in gas) to $H_2$ substantially. Moreover, the $R_a/R_g$ value of 10 ppm CO increased to 5.65, whereas that of $NO_2$ did not change by a significant amount. The enhanced response to $H_2$ and the selective detection of CO in the presence of $NO_2$ were explained in relation to the change in the surface reaction by the addition of $WO_3$. The $WO_3$-doped $SnO_2$ sensor can be used with the application of a $H_2$ sensor for vehicles that utilize fuel cells and as an air quality sensor to detect CO-containing exhaust gases emitted from gasoline engines.
하이드라진을 이용한 용액환원법에 의한 Ni-GDC 미분말 합성과 전기적 특성
김선중,김강민,조평석,조윤호,이충용,박승영,강윤찬,이종흔,Kim, Sun-Jung,Kim, Kang-Min,Cho, Pyeong-Seok,Cho, Yoon-Ho,Lee, Choong-Yong,Park, Seung-Young,Kang, Yun-Chan,Lee, Jong-Heun 한국재료학회 2008 한국재료학회지 Vol.18 No.12
Ni-GDC (gadolinia-doped ceria) composite powders, the anode material for the application of solid oxide fuel cells, were prepared by a solution reduction method using hydrazine. The distribution of Ni particles in the composite powders was homogeneous. The Ni-GDC powders were sintered at $1400^{\circ}C$ for 2 h and then reduced at $800^{\circ}C$ for 24 h in 3% $H_2$. The percolation limit of Ni of the sintered composite was 20 vol%, which was significantly lower than these values in the literature (30-35 vol%). The marked decrease of percolation limit is attributed to the small size of the Ni particles and the high degree of dispersion. The hydrazine method suggests a facile chemical route to prepare well-dispersed Ni-GDC composite powders.