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열간 압축 공정에 의한 Zn<sub>4</sub>Sb<sub>3</sub>의 직접 고상 반응 합성 및 열전특성
어순철,Ur Soon-Chul 한국분말야금학회 2005 한국분말재료학회지 (KPMI) Vol.12 No.4
Direct solid state synthesis by hot pressing has been applied in order to produce high efficiency $Zn_4Sb_3$ bulk specimens. Single phase $Zn_4Sb_3$ with 98.5% of theoretical density was successfully produced by direct hot pressing of elemental powders containing 1.2 at.% excess Zn. Thermoelectric properties as a function of temperature were investigated from room temperature to 600 K and compared with results of other studies. Transport properties at room temperature were also evaluated. Thermoelectric properties of single phase $Zn_4Sb_3$ materials produced by direct synthesis were measured and are comparable to the published data. Direct solid state synthesis by hot pressing provides a promising processing route in this material.
고상 합성과 진공 압축성형에 의한 Zn<sub>4</sub>Sb<sub>3</sub>의 제조 및 열전특성
어순철,Ur Soon-Chul 한국재료학회 2005 한국재료학회지 Vol.15 No.7
Thermoelectric $Zn_4Sb_3$ alloys were synthesized by a conventional powder metallurgy process consisting of solid state reaction and hot pressing. Single phase $Zn_4Sb_3$ was successfully produced by the annealing of cold compact starting with the mixed elemental powders, and subsequent hot pressing yielded single phase bulk specimens without microcracks. Phase transformations in this alloy system during synthesis were investigated using XRD, SEM and EDS. Thermoelectric properties as a function of temperature were investigated from room temperature to 600 K and compared with results of analogue studies. Transport properties at room temperature were also evaluated. Thermoelectric properties of single phase $Zn_4Sb_3$ materials produced by this process are comparable to the published data. Synthesis by solid state reaction and hot pressing offers a potential processing route to produce a bulk $Zn_4Sb_3$.?
기계적 합금화에 의한 Skutterudite계 Fe<sub>x</sub>Co<sub>4-x</sub>Sb<sub>12</sub>의 합성 및 열전특성
권준철,김일호,어순철,Kwon, Joon-Chul,Kim, Il-Ho,Ur, Soon-Chul 한국분말야금학회 2005 한국분말재료학회지 (KPMI) Vol.12 No.5
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.
Processing and Properties of Mechanically Alloyed Iron-Silicide
어순철,김일호,Ur, Soon-Chul,Kim, Il-Ho Materials Research Society of Korea 2001 한국재료학회지 Vol.11 No.2
기계적 합금화 공정을 이용하여 열전재료$FeSi_2$분말을 제조하여 열간압축법을 사용하여 성형하였다. 열간압축 성형된 $FeSi_2$는 열전특성을 나타내는 $\beta$-$FeSi_2$ 상 및 상변태가 완료되지 않은 $\alpha$-$Fe_2$$Si_{5}$와 $\varepsilon$-FeSi의 혼합상으로 이루어져 있음이 확인되었다. 열전재료로의 $\beta$-$FeSi_2$ 상변태 유도를 위해 항온열처리를 행하여 상변태 조건을 조사하였다. SEM, TEM, XRD, DTA 등을 이용하여 상변태 거동을 분석한 결과, $830^{\circ}C$에서 24시간 진공 항온열처리 후 단상의 $\beta$-FeSi$_2$ 상을 얻을 수 있었다. 항온열처리 전의 열간압축 성형체와 상변태가 완료된 $\beta$-FeSi$_2$의 기계적 성질과 열전 특성을 측정하여 비교 분석하였다. Iron- silicide has been produced by mechanical alloying process and consolidated by hot pressing. As-consolidated iron silicides were consisted of $\beta$-FeSi$_2$ phase, and untransformed mixture of $\alpha$-$Fe_2Si_5$ and $\varepsilon$-FeSi phases. Isothermal annealing has been carried out to induce the transformation to a thermoelectric semiconducting $\beta$-$FeSi_2$ phase. The condition for $\beta$-FeSi$_2$ transformation was investigated by utilizing DTA, SEM, TEM and XRD analysis. The phase transformation was shown to be taken place by a vacuum isothermal annealing at $830^{\circ}C$ for 24 hours. The mechanical and thermoelectric properties of $\beta$-FeSi$_2$ materials before and after isothermal annealing were characterized in this study.
잔류 자성원소 검출에 의한 금속간화합물의 기계적 합금화 공정에서의 합금화 정도 해석
어순철,Ur, Soon-Chul 한국재료학회 2003 한국재료학회지 Vol.13 No.9
Mechanical alloying(MA) process using elemental powders followed by hot pressing has been applied to some intermetallic alloy system containing ferromagnetic elements, such as NiAl and $FeSi_2$. A modified thermogravimetric analysis (TGA) technique was used to investigate the degree of alloying in milled powders and hot consolidated specimens as well as heat-treated bulk specimens. It is shown that the measurement of Curie temperatures in MA intermetallic powders and consolidated specimens containing ferromagnetic components, when determined as a function of milling and heat treatment parameters, can give some insight into the progress and mechanism of alloying.
Graphite-Ni계 분말의 제조 및 용사 코팅 특성에 미치는 공정변수의 영향
권준철,최문관,김일호,홍태환,권순용,이영근,박순옥,어순철,Kwon Joon-Chul,Cho Mun-Kwan,Kim Il-Ho,Hong Tae-Whan,Kweon Soon-Yong,Lee Young-Geun,Park Soon-Wook,Ur Soon-Chul 한국분말야금학회 2005 한국분말재료학회지 (KPMI) Vol.12 No.2
Graphite-Ni composite powders were synthesized by mechanical alloying(MA) and spray drying(SD). Fabricated powders as well as commercial graphite-Ni powders were thermally sprayed on mild steel substrates using high velocity oxygen fuel (HVOF) thermal spray process and flame thermal spray process. The effects of several process parameters on related properties in thermally sprayed coatings have been investigated and correlated with microstructures in this study. The results indicated that the desired properties can be obtained when commercial powders were applied using HVOF process, while coating properties in case of MA powder application were inferior to those in HVOF process in so far. However, it is suggested that property enhancement can be obtained if the fraction of hexagonal graphite phase can be increased in mechanically alloyed powders.
기계적 합금화에 의한 Zn<sub>4</sub>Sb<sub>3</sub> 열전소재의 합성 및 열전 특성
어순철,Ur Soon-Chul 한국재료학회 2004 한국재료학회지 Vol.14 No.8
Thermoelectric $Zn_{4}Sb_3$ alloy powders were synthesized from elemental powders by mechanical alloying process and consolidated by hot pressing under controlled atmosphere. Single phase $Zn_{4}Sb_3$ was not obtained using a nominal stoichiometric composition, but near single phase $Zn_{4}Sb_3$ with remnant elemental Zn having a relatively high density was produced using a nominally 11.7 $at.\%$ Zn rich powders. Phase transformations during mechanical alloying were systematically investigated using XRD and SEM. Thermoelectric and transport properties were evaluated for the hot pressed specimens and compared with results of analogous studies.
열간압축성형으로 제조한 Co<sub>1-x</sub>Fe<sub>x</sub>Sb<sub>3</sub>의 열전특성
박관호,어순철,김일호,Park, Kwan-Ho,Ur, Soon-Chul,Kim, Il-Ho 한국재료학회 2006 한국재료학회지 Vol.16 No.7
The hot pressing was employed to prepare Fe-doped $CoSb_3$ skutterudites and their thermoelectric properties were investigated. Single phase ${\delta}-CoSb_3$ was successfully obtained by the hot pressing under 60MPa at 773 K for 2 hrs. Iron atoms acted as electron acceptors by substituting cobalt atoms. Thermoelectric properties were remarkably improved by the appropriate doping. $Co_{0.7}Fe_{0.3}Sb_3$ was found as an optimum composition for the best thermoelectric property in this work.
Skutterudite CoSb<sub>3</sub>의 열전특성에 미치는 Sn의 충진효과
정재용,어순철,김일호,Jung, Jae-Yong,Ur, Soon-Chul,Kim, Il-Ho 한국재료학회 2006 한국재료학회지 Vol.16 No.9
Sn-filled $Co_8Sb_{24}$ skutterudites were synthesized by the encapsulated induction melting process. Single ${\delta}-phase$ was successfully obtained by subsequent annealing and confirmed by X-ray diffraction analysis. Temperature dependences of Seebeck coefficient, electrical resistivity and thermal conductivity were examined from 300 K to 700 K. The positive Seebeck coefficient confirmed the p-type conductivity of the Sn-filled $Co_8Sb_{24}$. Electrical resistivity increased with increasing temperature, which shows that the Sn-filled $Co_8Sb_{24}$ skutterudite is a highly degenerate semiconductor. Thermal conductivity was reduced by Sn-filling because the filler atoms acted as phonon scattering centers in the skutterudite lattice. Thermoelectric figure of merit was enhanced by Sn filling and its optimum filling content was considered to be $z{\leq}0.5$ in the $Sn_zCo_8Sb_{24}$ system.