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Electronic Transport and Thermoelectric Properties of Te-Doped Tetrahedrites Cu12Sb4-yTeyS13
곽성규,이고은,Il-Ho Kim 대한금속·재료학회 2021 대한금속·재료학회지 Vol.59 No.8
Tetrahedrite is a promising thermoelectric material mainly due to its low thermal conductivity, a consequence of its complicated crystal structure. However, tetrahedrite has a high hole concentration; therefore, optimizing carrier concentration through doping is required to maximize the power factor. In this study, Te-doped tetrahedrites Cu12Sb4-yTeyS13 (0.1 ≤ y ≤ 0.4) were prepared using mechanical alloying and hot pressing. The mechanical alloying successfully prepared the tetrahedrites doped with Te at the Sb sites without secondary phases, and the hot pressing produced densely sintered bodies with a relative density >99.7%. As the Te content increased, the lattice constant increased from 1.0334 to 1.0346 nm, confirming the successful substitution of Te at the Sb sites. Te-doped tetrahedrites exhibited p-type characteristics, which were confirmed by the positive signs of the Hall and Seebeck coefficients. The carrier concentration decreased but the mobility increased with Te content. The electrical conductivity was relatively constant at 323–723 K, and decreased with Te substitution from 2.6 × 104 to 1.6 × 104 Sm-1 at 723 K. The Seebeck coefficient increased with temperature and Te content, achieving values of 184–204 μVK-1 at 723 K. The thermal conductivity was <1.0 Wm-1K-1, and decreased with increasing Te content. Cu12Sb3.9Te0.1S13 exhibited the highest dimensionless figure of merit (ZT = 0.80) at 723 K, achieving a high power factor (0.91 mWm-1K-2) and a low thermal conductivity (0.80Wm-1K-1).
곽성규,이고은,김일호 대한금속·재료학회 2019 대한금속·재료학회지 Vol.57 No.5
Tetrahedrite Cu12Sb4S13 has low lattice thermal conductivity because of the lone-pair electrons of Sb, which cause the Cu atoms to vibrate at a low frequency and high amplitude. When the Cu atoms of Cu12Sb4S13 are partially substituted with a transition metal, changes in the Cu vibrations can intensify phonon scattering, thereby enhancing the thermoelectric properties. The synthesis of tetrahedrite compounds by conventional melting methods requires sophisticated reactions because the S element vaporizes at low temperature and its homogenization requires a long time. However, a homogeneous and solid-state synthesis can be carried out in a short time using mechanical alloying, because the volatilization of the constituent elements is inhibited and the subsequent heat treatment is not necessary. In this study, Zn-doped Cu12- xZnxSb4S13 tetrahedrites were prepared by mechanical alloying (MA) and hot pressing (HP), and their electronic transport and thermoelectric properties were examined. A single tetrahedrite phase was successfully obtained by the MA-HP process without subsequent heat treatment. The lattice constant increased with the Zn content, confirming that Zn was substituted for Cu. Zn doping led to p-type conduction characteristics; however, it did not effectively increase the power factor. However, the thermal conductivity showed a marked decrease upon Zn doping, due to decrease in carrier contribution. A dimensionless figure of merit of 0.76 was obtained at 723 K for Cu11.6Zn0.4Sb4S13.
Solid-State Synthesis and Thermoelectric Properties of Tetrahedrites Cu12Sb4-yBiyS13
곽성규,피지희,이고은,김일호 대한금속·재료학회 2020 대한금속·재료학회지 Vol.58 No.4
Tetrahedrite has low lattice thermal conductivity because of the lone-pair electrons of Sb, which cause the Cu atoms to vibrate at a low frequency and high amplitude. The synthesis of tetrahedrite compounds by conventional melting methods requires a long-time reaction and annealing. However, a homogeneous and solid-state synthesis can be conducted in a short time using mechanical alloying (MA) because the volatilization of the constituent elements is inhibited and a subsequent heat treatment is not necessary. In this study, Bi-doped tetrahedrites Cu12Sb4-yBiyS13 (y = 0-0.4) were prepared by MA and hot pressing. X-ray diffraction analyses revealed that all specimens consisted of single-phase tetrahedrite. However, with increasing Bi content, skinnerite Cu3SbS3 was detected. The electrical conductivity increased and the Seebeck coefficient deceased with increasing Bi content as result of the substitution of Bi at Sb sites. In addition, the thermal conductivity increased as the Bi content increased because of the increase in electronic thermal conductivity. A high dimensionless figure of merit of 0.88 was obtained at 723 K for Cu12Sb3.9Bi0.1S13.
김일수,김학형,장한기,김희진,곽성규,유회수,심지연,Kim, Ill-Soo,Kim, Hak-Hyoung,Jang, Han-Kee,Kim, Hee-Jin,Kwak, Sung-Kyu,Ryoo, Hoi-Soo,Shim, Ji-Yeon 대한용접접합학회 2009 대한용접·접합학회지 Vol.27 No.4
In the process to manufacture for metallic structures, control of welding deformation is one of an important problems connected with reliability of the manufactured structures so that welding deformation should be measured and controlled with quickly and actively. Also, welding parameters which have as lot of effects on welding deformation such as arc voltage, welding current and welding speed can also be controlled. The objectives for this study were to develop a simple 2-D FEM to calculate not only the transient thermal histories but also the sizes of fusion and heat-affected zone (HAZ) in multi pass arc welds including the butt and fillet weld type with dissimilar thickness, and to concentrate on a developed model for the finding the parameters of Godak's moving heat source model based on a GA. The developed model includes a GA program using MATLB and GA toolbox, and a batch mode thermal model using ANSYS software. Not only the thermal model was verified by comparison with Goldak's work but also the developed model was validated with molten zone section experimental data.
등가구조응력법을 이용한 전단하중이 고려된 굴착기 용접부 수명 예측 연구
안영동(Yeongdong An),박병화(Byunghwa Park),곽성규(Sungkyu Kwak) 한국자동차공학회 2019 한국자동차공학회 학술대회 및 전시회 Vol.2019 No.11
It is difficult to predict fatigue life of welded structures in construction equipment, because they undergo a variety of working environment and working conditions. We conduct verification process such as proto test and numerical analysis reflecting actual vehicle operating conditions measured at major sites. Nevertheless, after our standard verification process has been passed, unexpected field issues sometimes occur. In this paper, the industrial case study was conducted to figure out field cracks in our excavators using the equivalent structural stress method, rather than the nominal stress method. The structural stress method can reproduce field cracks that were not predictable by conventional methods. Through this study, the prediction results improved quantitatively and qualitatively.