핫프레싱법에 의한 Zn₄Sb₃ 합금의 고상반응합성

어순철 忠州大學校 2004 한국교통대학교 논문집 Vol.39 No.1

Solid state synthesis by hot pressing has been used in order to produce high efficiency Zn4Sb3 bulk specimens. Single phase Zn4Sb3 with 98.5% of theoretical density were successfully produced by direct hot pressing of elemental powders containing 1.2 at.% excess Zn. Direct synthesis by hot pressing provides an optional processing route in this material.

기계적 합금화 Iron Silicide의 열간성형 및 열처리에 의한 상변화

어순철,김일호,황승준,조경원,최재화,Eo, Sun-Cheol,Kim, Il-Ho,Hwang, Seung-Jun,Jo, Gyeong-Won,Choe, Jae-Hwa 한국재료학회 2001 한국재료학회지 Vol.11 No.12

An n-type iron$silicide(Fe_{0.98}Co_{0.02}Si_2)$has been produced by mechanical alloying process and consolidated by vacuum hot pressing. Although as-milled powders after 120 hours of milling did not show an alloying progress,${\beta}-FeSi_2$phase transformation was induced by isothermal annealing at$830{\circ}C$for 1 hour, and the fully transformed${\beta}-FeSi_2$phase was obtained after 4 hours of annealing. Near fully dense specimen was obtained after vacuum hot pressing at$ 1100{\circ}C$with a stress of 60MPa. However, as-consolidated iron silicides were consisted of untransformed mixture of ${\Alpha}-Fe_2Si_5$and ${\varepsilon-FeSi$phases. Thus, 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, and XRD analysis. The phase transformation was shown to be taken place by a vacuum isothermal annealing at$830{\circ}C$and the transformation behaviour was investigated as a function of annealing time. The mechanical properties of${\beta}-FeSi_2$materials before and after isothermal annealing were characterized in this study.

기계적 합금화로 제조한 half-Heusler ZrNiSn1-xSbx 합금에서의 캐리어 이동 특성

어순철 忠州大學校 2011 한국교통대학교 논문집 Vol.46 No.-

Half-heusler ZrNiSn1-xSbx (0.02≤x≤0.08) alloys were prepared by mechanical alloying of elemental powders, and consolidated by vacuum hot pressing. Single phase of the Sb doped ZrNiSn was successfully produced in all doping ranges without subsequent annealing. Phase transformations during mechanical alloying and hot consolidation were investigated using XRD and SEM. Thermoelectric properties as functions of temperature and Sb contents were evaluated for hot pressed specimens. Their doping effect on the thermoelectric and the transport properties were examined. The Hall and Seebeck coefficients confirmed that all the Sb doped compositions exhibited n-type conduction. Relatively high carrier concentration and medium mobility were observed. Sb doping up to x=0.04 in ZrNiSn1-xSbx was shown to be effective on thermoelectric properties, and the figure of merit (ZT) was shown to reach to the maximum at x=0.02 in this study.

열간 압축 공정에 의한 Zn₄Sb₃의 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 Zn₄Sb₃의 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 $Zn_4Sb_3$.?

Electronic Transport Properties of Ni-doped CoSb3 Prepared by Hot Pressing

어순철,김일호 한국물리학회 2009 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.55 No.3

Ni-doped CoSb3 skutterudites (Co1−xNixSb3) were prepared by hot pressing, and their electronic transport properties were examined. Single-phase δ-(Co,Ni)Sb3 was successfully obtained, but it decomposed to δ-(Co,Ni)Sb2 and Sb when x ≥ 0.2, which means that the solubility limit of Ni in Co is x < 0.2. The negative signs of the Seebeck coefficients for all Ni-doped specimens revealed that Ni atoms acted as n-type dopants by substituting for Co atoms. The electrical resistivity and the thermal conductivity decreased with increasing Ni doping level. The ZT (dimensionless figure of merit) value was considerably enhanced by the Ni doping, and the optimum composition was found as Co0.9Ni0.1Sb3 for Ni-doped CoSb3 prepared by hot pressing.

기계적 합금화에 의한 Zn4Sb3 열전재료의 합성

어순철 忠州大學校 2003 한국교통대학교 논문집 Vol.38 No.4

Thermoelectric Zn4Sb3 bulk specimens were produced by mechanical alloying using elemental powders and consolidated by hot pressing. Single phase Zn4Sb3 was not obtained using a nominal stoichiometric composition, but near single phase Zn4Sb3 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 Properties of Tin-Filled Skutterudites Prepared by Mechanical Alloying Process

어순철,권준철,김일호 대한금속·재료학회 2008 METALS AND MATERIALS International Vol.14 No.5

Sn-filled (Fe,Co)Sb₃ skutterudites of the form of SnyFe3Co5Sb24 (0 ≤ y ≤ 1.5) were synthesized by the mechanical alloying of elemental powders followed by vacuum hot pressing. The phase transformations that occur during both mechanical alloying and vacuum hot pressing were examined by X-ray diffraction. Single-phase Sn-filled skutterudite was successfully produced by vacuum hot pressing using as-milled powders without subsequent annealing. The thermoelectric properties of the hot-pressed specimens were evaluated as a function of temperature and tin content. The void filling of tin (up to y = 1.0) in Fe₃Co5Sb24 appeared to increase the thermoelectric figure of merit.

기계적 합금화에 의한 Zn₄Sb₃ 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.

기계적 합금화로 제조한 N형 β의 상변화 및 열전 특성

어순철,Eo, Sun-Cheol 한국재료학회 2002 한국재료학회지 Vol.12 No.5

N-type ${\beta}-FeSi_2$ with a nominal composition of $Fe_{0.98}Co_{0.02}Si_2$ powders has been produced by mechanical alloying process and consolidated by vacuum hot pressing. As-milled powders were of metastable state and fully transformed to ${\beta}-FeSi_2$ phase by subsequent isothermal annealing. However, as-consolidated $Fe_{0.98}Co_{0.02}Si_2$ consisted of 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 transformation behavior of ${\beta}-FeSi_2$ was investigated by utilizing DTA, a modified TGA under magnetic field, SEM, and XRD analyses. Isothermal annealing at $830^{\circ}C$ in vacuum led to the thermoelectric semiconducting ${\beta}-FeSi_2$ phase transformation, but some residual metallic $\alpha$ and $\varepsilon$ phases were unavoidable even after prolonged annealing. Thermoelectric properties were remarkably improved by isothermal annealing due to the transformation from metallic $\alpha$ and $\varepsilon$ phases to semiconducting phases.