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산화물 환원공정에 의해 제조된 Bi<sub>2</sub>Te<sub>2.7</sub>Se<sub>0.3</sub> 분말의 열전특성
박배건,이길근,김우열,하국현,Park, Bae-Gun,Lee, Gil-Geun,Kim, Woo-Yeol,Ha, Gook-Hyun 한국분말야금학회 2011 한국분말재료학회지 (KPMI) Vol.18 No.5
The present study focused on the synthesis of Bi-Te-Se-based powder by an oxide-reduction process, and analysis of the thermoelectric properties of the synthesized powder. The phase structure, chemical composition, and morphology of the synthesized powder were analyzed by XRD, EPMA and SEM. The synthesized powder was sintered by spark plasma sintering. The thermoelectric properties of the sintered body were evaluated by measuring its Seebeck coefficient, electrical resistivity, and thermal conductivity. $Bi_2Te_{2.7}Se_{0.3}$ powder was synthesized from a mixture of $Bi_2O_3$, $TeO_2$, and $SeO_2$ powders by mechanical milling, calcination, and reduction. The sintered body of the synthesized powder exhibited n-type thermoelectric characteristics. The thermoelectric properties of the sintered bodies depend on the reduction temperature. The Seebeck coefficient and electrical resistivity of the sintered body were increased with increasing reduction temperature. The sintered body of the $Bi_2Te_{2.7}Se_{0.3}$ powder synthesized at $360^{\circ}C$ showed about 0.5 of the figure of merit (ZT) at room temperature.
산화물 환원공정에 의해 제작된 n-형 Bi2Te2.7Se0.3 화합물의 열전특성연구
임영수,박배건,이길근 대한금속·재료학회 2020 대한금속·재료학회지 Vol.58 No.5
We report the thermoelectric transport properties of n-type Bi2Te2.7Se0.3 compounds prepared by oxide-reduction process. The oxide-reduction process is a recently developed method that can synthesize Bi2Te3-based compounds using only oxide starting materials, which is advantageous in terms of the diversity of the starting materials and cost efficiency. In this study, starting materials of Bi2O3,TeO2 and SeO2 were ball-milled for homogenous mixing, and then oxidized to prepare mixed oxide powders. The mixed oxide powders were reduced at different reduction temperatures (573, 603, 633 and 663 K) for 7 h under hydrogen atmosphere. A single phase of Bi2Te2.7Se0.3 could be achieved when the reduction temperature was higher than 603 K, and the shape of the particles changed from granules to flakes with increasing reduction temperature. Furthermore, the formation of antisite defects of BiSe was promoted by increasing reduction temperature, which strongly affected the electrical and thermal transport properties of the Bi2Te2.7Se0.3 compounds, which were prepared by spark plasma sintering of the reduced powders. The anisotropic microstructures in the sintered bodies were significantly influenced by the shape of the reduced powders, which was also controlled by the reduction temperature. The thermoelectric transport properties were characterized at room temperature, and the detailed effects of the reduction temperature on these properties are discussed in terms of the anisotropic microstructure and antisite defects.
산화물 환원공정에 의한 n형 Bi2Te2.7Se0.3 화합물의 합성과 열전특성
임영수,박배건,이길근 대한금속·재료학회 2022 대한금속·재료학회지 Vol.60 No.6
We present a study on the synthesis of Bi2Te2.7Se0.3 powders through an oxide reduction process and also on the effect of the oxide reduction process on the thermoelectric transport properties of the resulting Bi2Te2.7Se0.3 compounds. Starting materials of Bi2O3, TeO2 and SeO2 were mechanical milled for homogeneous mixing, and then oxidized to prepare complex oxide powders. The complex oxide powders were reduced at different reduction temperatures under hydrogen atmosphere, and a single phase of Bi2Te2.7Se0.3 could be achieved in the reduced powder, with shorter reduction times as the reduction temperature was increased. The shape of the synthesized powder particles changed from granules to flakes with increasing reduction temperature and longer reduction time. Bi2Te2.7Se0.3 powders with different shapes were consolidated by spark plasma sintering (SPS). The SPSed Bi2Te2.7Se0.3 compounds exhibited anisotropic n-type thermoelectric transport properties along the vertical and parallel planes with respect to the pressing direction of the SPS. The degree of anisotropy in the thermoelectric properties was quite consistent with the degree of anisotropy in the microstructure, which originated from the anisotropic shapes in the Bi2Te2.7Se0.3 powders depending on the reduction conditions. Detailed thermoelectric transport properties of the n-type Bi2Te2.7Se0.3 compounds were interpreted in terms of anti-site defect formation and their structural anisotropy.
초고온·고압 소결 공정으로 제조된 다결정 다이아몬드 컴팩트(PDC)의 VTL 마모 특성에 미치는 Co 제거의 영향
백민석,김지원,박배건,박희섭,이기안 대한금속·재료학회 2020 대한금속·재료학회지 Vol.58 No.7
Polycrystalline diamond compact (PDC) has excellent wear resistance, high impact resistance, superior fatigue properties, and has been used in the oil and gas drilling industries. This study investigated the effect of Co leaching on the microstructure, vertical turning lathe (VTL) wear properties of PDCs manufactured by high-temperature and high-pressure (HTHP) sintering. The VTL wear test has the advantage of simulating the actual oil drilling environment by using granite as the workpiece. PDC sintered material that did not receive Co leaching was named HTHP sintered PDC-A, and the material subjected to Co leaching was called Co-leached PDC-B in this study. As a result of XRD analysis of both PDCs, diamond and WC peaks were detected, and only the HTHP sintered PDC-A exhibited some Co peaks. In the HTHP sintered PDC-A, the binder WC and Co were evenly distributed at the diamond interface. However, in the Co-leached PDC-B, some empty spaces were observed at the diamond interface. The HTHP sintered PDCA exhibited a similar or slightly higher VTL wear resistance than the Co-leached PDC-B, but only in the short sliding distance. In the long sliding distance after 9 km, Co-leached PDC-B showed significantly superior wear resistance compared to the HTHP sintered PDC-A. The HTHP sintered PDC-A exhibited both abrasive and adhesive wear behaviors, while the Co-leached PDC-B showed only abrasive wear. Based on the above results, the VTL wear mechanism of PDCs, and ways of improving wear resistance were also discussed.