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M-type Sr-Hexaferrite에서 MnCO<sub>3</sub> 첨가에 따른 소결 거동
정민석,유창재,조중영,문경석,Jeong, MinSeok,You, Changjae,Cho, Jung Young,Moon, Kyoung-Seok 한국분말야금학회 2020 한국분말재료학회지 (KPMI) Vol.27 No.2
The grain growth behavior of M-type Sr hexaferrite (SrM) grains is investigated with the addition of MnCO<sub>3</sub>. First, the SrM powder is synthesized by a conventional solid-state reaction. The powder compacts of SrM are sintered at 1250℃ for 2 h with various amounts of MnCO<sub>3</sub> (0, 0.5, 1.0, and 4.0 mol%). There is no secondary solid phase in any of the sintered samples. Relative density increases when MnCO<sub>3</sub> is added to the SrM. Obvious abnormal grain growth does not appear in any of the SrM samples with MnCO<sub>3</sub>. The average grain size increases when 0.5 mol% MnCO<sub>3</sub> is added to the SrM. However, as the amount of MnCO<sub>3</sub> increase to over 0.5 mol%, the average grain size decreases. These observations allow us to conclude that the growth of SrM grains is governed by the two-dimensional nucleation grain growth mechanism, and the critical driving force for the growth of a grain decreases as the amount of MnCO<sub>3</sub> increases.
남우현(Woo Hyun Nam),조중영(Jung Young Cho) 한국세라믹학회 2021 세라미스트 Vol.24 No.2
To solve the global energy problems, investigating renewable and environmentally friendly energy resources has considerable significance. Thermoelectric materials and modules have gained considerable attention because they can directly convert waste heat into electric power while leaving no environmental pollution. The performance of the thermoelectric materials can be determined using the dimensionless figure of merit, ZT. However, trade-off relationships between the thermoelectric parameters (electrical conductivity, Seebeck coefficient, and thermal conductivity) have hindered significant improvement of ZT over the decades. Therefore, independent control of the charge and phonon transports is of great importance. In this respect, CoSb3–based skutterudites showing PGEC (phonon-glass electron-crystal) properties are considered to be promising thermoelectric materials for mid-temperature power generation. In this paper, we review the current status of research in the fields of CoSb3-based thermoelectric materials and modularization techniques.
Fe/Co 비율 제어를 통한 P형 Nd-Fe-Co-Sb계 Skutterudite 소재의 열전특성 향상
남우현(Woo Hyun Nam),조중영(Jung Young Cho) 한국환경에너지공학회 2023 한국열환경공학회 학술대회지 Vol.2023 No.2
본 연구는 Fe/Co 비율 제어를 통한 P 형 Nd-Fe-Co-Sb계 skutterudite 합금의 열전 특성 향상에 대해 보고한다. 유도 용해 및 급속 응고법을 통해 분말을 제작한 후 방전 플라즈마 소결법 (903 K, 50 MPa, 15 min)으로 Ndo_9fe4-~oxSb12(x = 0.5, 0.75, 1, 1.25, 1.5) 소결체를 합성하였다. 소결체의 XRD 분석을 통해 skutterudite 단일상이 형성되었으며, Fe/Co 비율 조절에 따른 주요 회절 피크의 이동을 통해 Co가 Fe 자리로 효과적으로 치환된 것을 확인하였다. Co 치환량 중가에 따른 캐리어 농도 감소로 전기전도도는 감소하고 제벡계수는 중가하는 경향을 보였으며, 캐리어 농도 최적화에 따라 X = 0.75 샘플에서 최대출력인자(28.9 x 10-4 wm-1K-2 @ 769 K)를 얻었다. 또한, 열전도도는 Co 치환량 중가에 따른 전자 전도 기여분의 저하로 감소하는 경향을 보였다 결과적으로 Fe/Co 비율 조절을 통해 p 형 skutterudite 소재의 전기적 및 열적특성을 동시에 제 어하여 열전성능이 향상되는 것을 확인하였으며. X = 0.75 샘플(Nd0.9Fe3.25CO0.7Sb12.2)에서 1.0(@ 769 K)의 최대 열전성능지수를 보였다.
심일운,노원태,권지운,조중영,김경수,강동희 대한화학회 2002 Bulletin of the Korean Chemical Society Vol.23 No.4
Copper complexes have been directly incorporated into cellulose acetate (CA) and the resulting light blue colored homogeneous films of 5-20 wt.% copper acetate complex concentrations are found to be thermally stable up to 200 °C. The reaction chemistry of Cu in CA has been investigated by reacting them with small gas molecules such as CO, H2, D2, O2, NO, and olefins in the temperature range of 25-160 °C, and various Cuhydride, -carbonyl, -nitrosyl, and olefin species coordinated to Cu sites in CA are characterized by IR and UV/ Vis spectroscopic study. The reduction of Cu(II) complexes by reacting with H2 gas at the described conditions results in the formation of Cu2O and copper metal nanoparticles in CA, and their sizes in 30-120 nm range are found to be controlled by adjusting metal complex concentration in CA and/or the reduction reaction conditions. These small copper metal particles show various catalytic reactivity in hydrogenation of olefins and CH3CN; CO oxidation; and NO reduction reactions under relatively mild conditions.
매트랩/시뮬링크 simulation model을 이용한 열전 모듈의 효율 예측
이나영,예성욱,Rahman Jamil Ur,탁장렬,조중영,서원선,신원호,Walter Commerell,남우현,노종욱 대한금속·재료학회 2021 대한금속·재료학회지 Vol.59 No.11
Development new high-performance thermoelectric materials for more efficient power generation systems and eco-friendly refrigerating systems has been challenging. Over the past few decades, thermoelectric studies have been focused on increasing the thermoelectric properties of materials. However, for conventional applications, developing of thermoelectric devices or modules with lower cost and simpler fabrication processes is also important. Simulation models that can predict the thermoelectric efficiency of modules using the thermoelectric properties of materials are needed for this purpose. In this study, we developed a simple model for calculating the efficiency of thermoelectric modules using MATLAB/Simulink. In this model, the temperature difference between the hot source and heat sink was fixed to ensure the precise comparisons of thermoelectric efficiency. The electric resistivity and Seebeck coefficient of thermoelectric materials was used in order to predict the efficiency of the thermoelectric modules. Then, the efficiency of the thermoelectric modules was verified using measured values which had been reported in prior experimental works. In this study, the simulated values were higher than the real thermoelectric effiency values. To address this, the simulations should consider the thermal resistance or electric contact resistance between the thermoelectric materials and electrodes.
Grain 크기 조절을 통한 n-Type Bi2Te3 열전 소재 특성 향상
이나영,예성욱,Rahman Jamil Ur,탁장렬,조중영,서원선,신원호,남우현,노종욱 한국마이크로전자및패키징학회 2021 마이크로전자 및 패키징학회지 Vol.28 No.4
The enhancement of thermoelectric figure of merit was achieved by the simple processes of sieving and high energy ball milling, respectively, which are enable to reduce the grain size of n-type Bi2Te3 thermoelectric materials. By optimizing the grain size, the electrical conductivities and thermal conductivities were controlled. In this study, spark plasma sintering was employed for hindering the grain growth during the sintering process. The thermoelectric figure of merit was measured to be 0.78 in the samples with 30 min high energy ball milling process. Notably, this value was 40 % higher than that of pristine Bi2Te3 sample. This result shows the properties of thermoelectric materials can be readily controlled by optimization of grain size via simple ball milling process. 본 연구에서는 체가름과 고에너지 볼 밀링 공정이 n-type Bi2Te3 열전 재료의 전기적 및 열적 수송 특성에 미치는 영향을 검토하였다. 입자 크기가 감소한 분말의 특성을 유지하기 위하여 짧은 시간 안에 소결이 가능한 방전 플라즈마 소결 공정 (spark plasma sintering, SPS)을 진행하였다. 그 결과, 밀링 처리를 진행한 소결체의 열전 성능지수가 향상되었으며, 30분동안 고에너지 볼 밀링 공정을 거친 샘플이 425 K에서 0.78의 최대 열전 성능지수를 가지는 것을 확인하였다. 이는 손쉬운 공정을 이용하여 결정립 크기 감소를 통한 phonon의 격자 산란을 효과적으로 유도한 결과이다. 동시에 n-type Bi2Te3에서 anti-site defect와 같은 결함을 제어함으로써 캐리어 농도를 증가시킬 수 있음을 본 연구를 통하여 확인하였다.
Sb가 결핍된 N형 Skutterudite Co<sub>4</sub>Sb<sub>12</sub>의 열전 특성
탁장렬,정민석,이나영,남우현,서원선,조중영,Tak, Jang-Yeul,Van Du, Nguyen,Jeong, Min Seok,Lee, NaYoung,Nam, Woo Hyun,Seo, Won-Seon,Cho, Jung Young 한국전기전자재료학회 2019 전기전자재료학회논문지 Vol.32 No.6
In this study, we investigate the effect of an Sb-deficiency on the thermoelectric properties of double-filled n-type skutterudite ($In_{0.05}Yb_{0.15}Co_4Sb_{12-x}$). Samples were prepared by encapsulated induction melting, consecutive long-time annealing, and finally spark plasma sintering processes. The Sb-deficient sample contained a $CoSb_2$ secondary phase. Both the double-filled n-type skutterudite pristine and Sb-deficient samples showed metallic behavior in electrical conductivity with increasing temperature. The carrier concentration of the Sb-deficient sample decreased compared with that of the pristine sample. Due to a decrease in carrier concentration, the Sb deficient sample showed decreased electrical conductivity and an increased Seebeck coefficient compared with the conductivity and coefficient of the pristine sample. Furthermore, the Sb deficient sample showed an increase in the power factor (${\sigma}{\cdot}S^2$); the power factor maximum shifted to athe lower temperature side than ones of the pristine sample. As a result, the Sb-deficient sample represents an improved average figure of merit (ZT) and a $ZT_{max}$ temperature lower than that of the pristine sample. Therefore, we propose that Sb-deficient double-filled n-type skutterudite thermoelectric material ($In_{0.05}Yb_{0.15}Co_4Sb_{12-x}$) be used in the 573~673 K temperature range.