• 한국재료학회지
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• 제22권6호
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• pp.280-284
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• 2012

Bismuth antimony telluride (BiSbTe) thermoelectric materials were successfully prepared by a spark plasma sintering process. Crystalline BiSbTe ingots were crushed into small pieces and then attrition milled into fine powders of about 300 nm ~ 2${\mu}m$ size under argon gas. Spark plasma sintering was applied on the BiSbTe powders at 240, 320, and $380^{\circ}C$, respectively, under a pressure of 40 MPa in vacuum. The heating rate was $50^{\circ}C$/min and the holding time at the sintering temperature was 10 min. At all sintering temperatures, high density bulk BiSbTe was successfully obtained. The XRD patterns verify that all samples were well matched with the $Bi_{0.5}Sb_{1.5}Te_{3}$. Seebeck coefficient (S), electric conductivity (${\sigma}$) and thermal conductivity (k) were evaluated in a temperature range of $25{\sim}300^{\circ}C$. The thermoelectric properties of BiSbTe were evaluated by the thermoelectric figure of merit, ZT (ZT = $S^2{\sigma}T$/k). The grain size and electric conductivity of sintered BiSbTe increased as the sintering temperature increased but the thermal conductivity was similar at all sintering temperatures. Grain growth reduced the carrier concentration, because grain growth reduced the grain boundaries, which serve as acceptors. Meanwhile, the carrier mobility was greatly increased and the electric conductivity was also improved. Consequentially, the grains grew with increasing sintering temperature and the figure of merit was improved.

• 공업화학
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• 제27권4호
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• pp.353-357
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• 2016

인구 증가와 문명 발전에 따른 에너지 고소비형 사회로 진행됨에 따라 기존에 사용하던 에너지원의 고효율화 방안이 강구되고 있다. 이 중 열에너지 고효율화 방안으로 열전발전 기술이 주목을 받고 있다. 현재 열전발전 분야는 나노기술 등이 발전함에 따라 폐열회수 분야 등에서 충분한 경쟁력을 가질 수 있는 ZT > 2를 도달하였고, 더 높은 효율을 갖는 소재 개발 연구가 진행되고 있다. 본 총설에서는 현재 진행되고 있는 온도영역별 열전발전 소재 개발 및 모듈기술에 대해 간략히 소개하고자 한다.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2009년도 춘계학술대회 논문집
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• pp.23-23
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• 2009

It has been challenging to increase the thermoelectric figure of merit ($ZT=S^2{\sigma}T/\kappa$) of materials, which determine the efficiency of thermoelectric devices, because the three parameters Seebeck coefficient (S), electrical conductivity ($\sigma$), and thermal conductivity ($\kappa$) of bulk materials are inter-dependent. With the development of nanotechnology, ZT values of nanostructured materials are predicted to be enhanced by classical size effects and quantum confinement effects. In particular, Bi nanowires were suggested as one of ideal thermoelectric materials due to the expected quantum confinement effects for the simultaneous increase in Sand. In this work, we have investigated the thermal conductivity of individual single crystalline Bi nanowires with d = 98 nm and d = 327 nm in the temperature range 40 - 300 K using MEMS devices. The for the Bi nanowire with d = 98 nm was observed to be ~ 1.6 W/m-K at 300 K, which is much lower than that of Bi bulk (8 W/m-K at 300 K). This indicates that the thermal conductivity of the Bi suppressed due to enhanced surface boundary scattering in one-dimensional structures. Our results suggest that Bi nanowires grown by stress-induced method can be used for high-efficiency thermoelectric devices.

• 한국분말재료학회지
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• 제24권5호
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• pp.357-363
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• 2017

In this study, Bi-Sb-Te thermoelectric materials are produced by mechanical alloying (MA) and spark plasma sintering (SPS). To examine the influence of the milling atmosphere on the microstructure and thermo-electric (TE) properties, a p-type Bi-Sb-Te composite powder is mechanically alloyed in the presence of argon and air atmospheres. The oxygen content increases to 55% when the powder is milled in the air atmosphere, compared with argon. All grains are similar in size and uniformly, distributed in both atmospheric sintered samples. The Seebeck coefficient is higher, while the electrical conductivity is lower in the MA (Air) sample due to a low carrier concentration compared to the MA (Ar) sintered sample. The maximum figure of merit (ZT) is 0.91 and 0.82 at 350 K for the MA (Ar) and MA (Air) sintered samples, respectively. The slight enhancement in the ZT value is due to the decrease in the oxygen content during the MA (Ar) process. Moreover, the combination of mechanical alloying and SPS process shows a higher hardness and density values for the sintered samples.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2013년도 제44회 동계 정기학술대회 초록집
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• pp.589-589
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• 2013

열전재료는 제백효과(Seebeck effect)에 의해 폐열을 전기에너지로 변환시킬 수 있는 소재로서, 기존의 열전재료가 나노수준으로 크기가 줄어들 경우 양자제한효과에 의한 제백계수의 증가와 표면산란에 의한 열전도도 감소로 인해 벌크재료에 비해 높은 에너지변환효율을 가질 수 있을 것으로 기대되고 있다. 에너지 변환효율은 열전성능계수인 $ZT=S2{\sigma}T/k$로 정의되며 따라서 우수한 열전재료는 높은 제백계수 S와, 높은 전기전도도 ${\sigma}$ 및 낮은 열전도도 k를 갖는 재료여야 한다. 그러나 나노소재는 낮은 측정 신호와 측정소자준비가 어려워 기존 측정시스템으로는 원활한 측정이 어렵다. 특히 열전도도의 경우 나노소재 자체의 열전도 보다 나노소재 주변 구조에 의한 열전도가 큰 경우 정확한 열전도도 평가가 어렵다. 본 연구에서는 나노선의 열전물성을 평가하기 위해 MEMS기반 기술을 이용하여 열전물성 측정플랫폼(MEMS-based thermoelectric measurement platform, MTMP)을 개발하였다. 개발 된 MTMP는 얇은 Si nitride 브릿지들이 허공에 떠 있는 두 개의 아일랜드 형태의 멤브레인 구조를 지지하는 형태로 제작되었으며, 한 쪽 아일랜드구조 위에는 나노히터가 있어 두 아일랜드 구조 사이에 온도구배를 만들 수 있도록 제작되었다. 제작된 멤브레인을 이용하여 전기화학적인 방법으로 합성한 Bi-Te계 나노선의 S, ${\sigma}$ 그리고 k를 측정하였다. 측정결과 화학양론적 미세구조를 갖는 단결정 Bi2Te3 나노선은 300 K의 측정온도에서 $S=-57{\mu}V/K$, ${\sigma}=3.9{\times}10^5S/m$, k=2.0 W/m-K의 측정 값으로 ZT=0.19였다. 본 연구에서 개발한 MTMP는 나노선 뿐만 아니라 나노플레이트의 열전 측정에도 활용할 수 있는 구조로서 나노열전소재 측정에 널리 활용될 수 있다.

• 대한치과기공학회지
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• 제37권3호
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• pp.107-113
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• 2015

Purpose: This study provided the basic data for selecting the zirconia blocks by comparing the mechanical properties of the all ceramic crown between the domestic, import, translucent and shade blocks that were used in clinically. Methods: Currently, the most commercial block of five types(one import and two domestic block which is the translucent and shade) were used. It were elucidated by means of three point bending test, hardness test, FE-SEM observations and EDX analysis. The results were analyzed using a one-way ANOVA and Scheffe post hoc test for significant findings. Results: For flexural strength, LT specimen was the highest as 733.1 MPa, followed by JT specimen(712.0 MPa), ZT specimen(646.0 MPa), LS specimen(553.1 MPa), JS specimen(429.0 MPa). One-way ANOVA showed statistically significant difference between groups for flexural strength(p<0.05). For hardness, ZT specimen was the highest as 1556.5 Hv, followed by JT specimen(1540.3 Hv), LT specimen(1512.3 Hv), JS specimen(1472.0 Hv), LS specimen(1353.3 Hv). One-way ANOVA showed statistically significant difference between groups for hardness(p<0.05). Conclusion: Domestic block was higher than import block for flexural strength, and translucent block was higher than shade block for flexural strength. However, all blocks showed clinically acceptable range. There was no significant difference in hardness between domestic and import blocks. And significant difference was observed in translucent and shade blocks.

• 한국세라믹학회지
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• 제36권1호
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• pp.61-68
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• 1999

층상구조를 이루는 재료의 소결시 형성되는 다양한 결함 및 잔류응력을 고찰하기 위해 TZP-SUS계 및 ZT/SUS계다층재료와 porcelain/alumina 및 porcelain/Y-TZP 이층재료를 소결법으로 제조하였다. 상압소결로 제조한 다층재료에서는 층간의 소결수축율 차이에 의해 warping, splitting, 균열 등의 소결결함이 관찰되었으며, 중간층수 및 두께의 조절과 출발물질의 제어를 통해 이러한 소결결함이 완화됨을 알 수 있었다. Tape casting법으로 제조한 다층재료에서는 소결시 가한 압력에 의해 소결결함, 특히 warping이 제어됨을 확인할 수 있었다. 이층재료에서 형성되는 잔류응력은 vickers 압입법으로 관찰하였다. Porcelain/alumina에서는 porcelain 측의 계면에 작은 인장응력이, porcelain/Y-TZP에서는 압축응력이 형성됨을 확인할 수 있었으며, 이러한 잔류응력은 이층재료의 강도에도 영향을 미침을 알수 있었다. 결국 다층재료의 소결결함 및 잔류응력은 재료설계와 출발물질 상수에 영향을 받는다는 것을 알 수 있었다.

• 한국분말재료학회지
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• 제12권5호
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• pp.357-361
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• 2005

Fe-doped skutterudite $CoSb_3$ with a nominal composition of $Fe_{x}Co_{4-x}Sb_{12}(0\;{\le}\;x\;{\le}\;2.5)$ has been synthesized by mechanical alloying (MA) of elemental powders, followed by hot pressing. Phase transformations during mechanical alloying and hot pressing were systematically investigated using XRD. Single phase skutterudite was successfully produced by vacuum hot pressing using as-milled powders without subsequent annealing. However, second phase in the form of marcasite structure $FeSb_2$ was found to exist in case of $x\;{\ge}\;2$, suggesting the solubility limit of Fe with Co in this system. Thermoelectric properties as functions of temperature and Fe contents were evaluated for the hot pressed specimens. Fe substitution up to x=1.5 with Co in $Fe_{x}Co_{4-x}Sb_{12}$ appeared to increase thermoelectric figure of merit (ZT) and the maximum ZT was found to be 0.78 at 525K in this study.

• Current Applied Physics
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• 제18권12호
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• pp.1540-1545
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• 2018

SiGe alloy is widely used thermoelectric materials for high temperature thermoelectric generator applications. However, its high thermoelectric performance has been thus far realized only in alloys synthesized employing mechanical alloying techniques, which are time-consuming and employ several materials processing steps. In the current study, for the first time, we report an enhanced thermoelectric figure-of-merit (ZT) ~ 1.1 at $900^{\circ}C$ in ntype $Si_{80}Ge_{20}$ nano-alloys, synthesized using a facile and up-scalable methodology consisting of rapid solidification at high optimized cooling rate ${\sim}3.4{\times}10^7K/s$, employing melt spinning followed by spark plasma sintering of the resulting nano-crystalline melt-spun ribbons. This enhancement in ZT > 20% over its bulk counterpart, owes its origin to the nano-crystalline microstructure formed at high cooling rates, which results in crystallite size ~7 nm leading to high density of grain boundaries, which scatter heat-carrying phonons. This abundant scattering resulted in a very low thermal conductivity ${\sim}2.1Wm^{-1}K^{-1}$, which corresponds to ~50% reduction over its bulk counterpart and is amongst the lowest reported thus far in n-type SiGe alloys. The synthesized samples were characterized using X-ray diffraction, scanning electron microscopy and transmission electron microscopy, based on which the enhancement in their thermoelectric performance has been discussed.

• 한국분말재료학회지
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• 제28권3호
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• pp.239-245
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• 2021

The SnSe single crystal shows an outstanding figure of merit (ZT) of 2.6 at 973 K; thus, it is considered to be a promising thermoelectric material. However, the mass production of SnSe single crystals is difficult, and their mechanical properties are poor. Alternatively, we can use polycrystalline SnSe powder, which has better mechanical properties. In this study, surface modification by atomic layer deposition (ALD) is chosen to increase the ZT value of SnSe polycrystalline powder. SnSe powder is ground by a ball mill. An ALD coating process using a rotary-type reactor is adopted. ZnO thin films are grown by 100 ALD cycles using diethylzinc and H₂O as precursors at 100℃. ALD is performed at rotation speeds of 30, 40, 50, and 60 rpm to examine the effects of rotation speed on the thin film characteristics. The physical and chemical properties of ALD-coated SnSe powders are characterized by scanning and tunneling electron microscopy combined with energy-dispersive spectroscopy. The results reveal that a smooth oxygen-rich ZnO layer is grown on SnSe at a rotation speed of 30 rpm. This result can be applied for the uniform coating of a ZnO layer on various powder materials.