• 전기화학회지
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• 제23권4호
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• pp.97-104
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• 2020

전기 물 분해 기술 중 주요 과제 중 하나는 귀금속의 Ir과 Ru 기반의 촉매를 대체할 수 있는 고성능, 저비용의 산소 발생 반응 (OER) 촉매를 개발하는 것이다. 본 연구에서는 CoSO₄와 Fe(NO₃)₃ 수용액을 1차 가열 후 KNO₃와 NaOH 추가 반응을 이용한 침전법을 이용하여 OER 촉매로 사용 가능한 역스피넬 구조의 약 44 nm 크기를 갖는 CoFe₂O₄ 나노 입자를 합성하였다. CoFe₂O₄ 나노 입자의 합성 시간을 조절하여 입자 및 결정립 크기를 제어하였다. CoFe₂O₄ 나노 입자의 합성 시간이 6시간일 때, 높은 전도성과 전기 화학 표면적을 가졌다. 이 CoFe₂O₄ (6 h)는 전류 밀도 10 mA/㎠의 과전압 및 Tafel slope는 각각 395 mV 및 52 mV/dec으로 나타났다. 또한, 이 촉매는 10 mA/㎠에서 18시간 동안 우수한 내구성을 나타냈다.

• 한국응용과학기술학회지
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• 제34권4호
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• pp.883-891
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• 2017

고분자 전해질 연료전지의 연료에 포함된 일산화탄소의 선택적 산화를 위하여, 귀금속 촉매를 대체하기 위한 CuO-$CeO_2$ 복합 산화물 촉매를 졸-겔법과 공침법으로 제조하였다. 졸-겔법으로 촉매 제조 시 Cu/Ce의 비와 가수분해 비를 변화시켰다. 제조한 촉매의 활성은 귀금속 촉매($Pt/{\gamma}-Al_2O_3$)와 비교하였다. Cu/Ce의 비를 변화시키면서 제조한 촉매 중 Cu/Ce의 비가 4:16인 촉매가 가장 높은 CO 전환율(90%)과 선택도(60%)를 나타내었다. 촉매의 제조에서 가수분해 비가 증가할수록 촉매 표면적이 증가하였고, 아울러 촉매 활성 또한 증가하였다. 공침법으로 제조한 촉매와 1wt% $Pt/{\gamma}-Al_2O_3$ 촉매의 가장 높은 CO 전환율은 각각 82% 및 81%인 반면, 졸-겔법으로 제조한 촉매의 경우는 90%가 얻어졌다. 이는 졸-겔법으로 제조한 촉매가 공침법으로 제조한 촉매나 귀금속 촉매보다 더 높은 촉매활성을 보임을 의미한다. CO-TPD 실험을 통하여, 낮은 온도($140^{\circ}C$)에서 CO를 탈착하는 촉매가 본 반응에서 더 높은 촉매활성을 보임을 알 수 있었다.

• 센서학회지
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• 제20권6호
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• pp.406-411
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• 2011

$Co_3O_4$ thick film gas sensor using the powder prepared by hydrothermal reaction method(HRM) was fabricated. For comparison study, we also prepared the sensor using commercial $Co_3O_4$ powder under the same fabrication conditions. Sensitivity, time response, and selectivity of them to variable gases such as iso-$C_4H_{10}$, CO, $NH_3$, and $CH_4$ were investigated. The sensor from the powder prepared by HRM showed higher sensitivity to every gas than those from commercial powder. For iso-$C_4H_{10}$ gas, the sensitivities of both sensor to 100 ppm are 160 % and 40 %, respectively. Time response and selectivity of the sensor using the powder prepared by HRM were better than those of the sensor using commercial powder.

• 한국자기학회지
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• 제17권1호
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• pp.47-50
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• 2007

최근 geometrical frustration 현상 및 멀티페로익 효과가 Cr 이온의 나선 스핀 구조에 기인하는 것으로 해석되고 있다. 이에 본 연구에서는 Cr 이온 자리에 Fe을 치환하여 $CoCrFeO_4$를 제조하였고, $M\"{o}ssbauer$ 분광법에 의해 자기적 미세 구조의 상관관계를 연구하였다. 졸겔법을 이용하여 Fd3m의 cubic 스피넬 구조를 갖는 $CoCr_2O_4,\;CoCrFeO_4$ 단일상을 합성하였고, Rietveld 법에 의한 분석결과 격자상수는 $a_0=8.340$에서 $8.377{\AA}$로 증가 하였으며, Cr, Fe 이온은 모두 팔면체 구조에 위치하는 것으로 분석되었다. 자기 상전이 온도는 $T_N=97K$에서 320 K로 증가하였으며, 상호작용의 변화에 따라서 field cooled 온도에 따른 자화 곡선의 변화를 관측하였다. $M\"{o}ssbauer$ 스펙트럼 분석결과 4.2 K에서 공명흡수선에 대한 초미세자기장($H_{hf}$) 값은 각각 507, 492 kOe 정도로 나타났으며, 이성질체 이동치($\delta$)는 0.33, 0.34 mm/s 정도로 Fe 이온상태가 둘 다 +3 가의 이온상태임을 알 수 있었다.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2004년도 하계학술대회 논문집 Vol.5 No.1
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• pp.110-113
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• 2004

ZnO varistor ceramics which were fabricated with variation of added of $0.5{\sim}1.0mol%\;Co_3O_4$ sintered at $1150^{\circ}C$. In the specimen added $0.7mol%\;Co_3O_4$, sintered density was $6.03g/cm^3$ and electrical peoperties were superior to any other components. The nonlinear coefficient a was 83, and clamping voltage ratio was 1.35. But, endurence surge current in the specimen added $0.5mol%\;Co_3O_4$ was $7000A/cm^2$, and deviation of varistor voltage was ${\Delta}-3.23%$. As P.C.T and T.C.T environment test were succeed in all specimens, and deviation of varistor voltage in the specimen added $0.6mol%\;Co_3O_4$ was ${\Delta}-0.81%$. All specimens showed a good leakage current property in the High Temperature Continuous Load Test for 1000hr, at $85^{\circ}C$, and variation rate of the varistor voltage was ${\Delta}-2%$.

• 한국재료학회지
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• 제22권11호
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• pp.620-625
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• 2012

A general synthetic method to make $Fe_3O_{4-{\delta}}$ (activated magnetite) is the reduction of $Fe_3O_4$ by $H_2$ atmosphere. However, this process has an explosion risk. Therefore, we studied the process of synthesis of $Fe_3O_{4-{\delta}}$ depending on heat-treatment conditions using $FeC_2O_4{\cdot}2H_2O$ in Ar atmosphere. The thermal decomposition characteristics of $FeC_2O_4{\cdot}2H_2O$ and the ${\delta}$-value of $Fe_3O_{4-{\delta}}$ were analyzed with TG/DTA in Ar atmosphere. ${\beta}-FeC_2O_4{\cdot}2H_2O$ was synthesized by precipitation method using $FeSO_4{\cdot}7H_2O$ and $(NH_4)_2C_2O_4{\cdot}H_2O$. The concentration of the solution was 0.1 M and the equivalent ratio was 1.0. ${\beta}-FeC_2O_4{\cdot}2H_2O$ was decomposed to $H_2O$ and $FeC_2O$4 from $150^{\circ}C$ to $200^{\circ}C$. $FeC_2O4$ was decomposed to CO, $CO_2$, and $Fe_3O_4$ from $200^{\circ}C$ to $250^{\circ}C$. Single phase $Fe_3O_4$ was formed by the decomposition of ${\beta}-FeC_2O_4{\cdot}2H_2O$ in Ar atmosphere. However, $Fe_3C$, Fe and $Fe_4N$ were formed as minor phases when ${\beta}-FeC_2O_4{\cdot}2H_2O$ was decomposed in $N_2$ atmosphere. Then, $Fe_3O_4$ was reduced to $Fe_3O_{4-{\delta}}$ by decomposion of CO. The reduction of $Fe_3O_4$ to $Fe_3O_{4-{\delta}}$ progressed from $320^{\circ}C$ to $400^{\circ}C$; the reaction was exothermic. The degree of exothermal reaction was varied with heat treatment temperature, heating rate, Ar flow rate, and holding time. The ${\delta}$-value of $Fe_3O_{4-{\delta}}$ was greatly influenced by the heat treatment temperature and the heating rate. However, Ar flow rate and holding time had a minor effect on ${\delta}$-value.

• 한국자기학회지
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• 제5권5호
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• pp.552-555
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• 1995

The magnetic properties of Mg-Mn ferrites were investigated in the composition range of $Mg_{a}Mn_{b}Fe_{c}O_{4\pm\delta}$ (a+b+c=3) with the addition of $Al_{2}O_{3}$. In $MgO-MnO-Fe_{2}O_{3}$ ternary system, the spinel single phase existed within the composition range of MgO-50 mol%, MnO-70 mol% and $Fe_{2}O_{3}-60\;mol%$. The saturation magnetic flux density increased with the increase of $Fe_{2}O_{3}$ content and showed the maximum at the stoichiometric composition of $(Mg,Mn)Fe_{2}O_{4}$. In $Mg_{x}Mn_{1-x}Fe_{2}O_{4}(x=0.2~0.8)$ system, the saturation magnetic flux density showed the maximum at $Mg_{0.2}Mn_{0.8}Fe_{2}O_{4}$. The addition of $Al_{2}O_{3}$ resulted in the decrease of saturation magnetic flux density but increased the electrical resistivity.

• 한국재료학회지
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• 제11권8호
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• pp.685-689
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• 2001

Sr 페라이트 자석의 자기적 특성을 향상시키기 위하여 화학량론적 조건인 $SrFe_{ 12}$$O_{19}$ [SrM]에서 $_{11.7}$Co$SrFe_{0.3}$ $O_{19}$[$Co_{0.3}$ -SrM]/ 및 $Sr_{0.7}$ $La_{0.3}$F $e_{11.7}$ $Co_{0.3}$ $O_{19}$ /[(La-Co)$_{0.3}$-SrM] 조성으로 혼합후 공기중 하소를 실시하여 하소분의 특성을 조사하였고, 소결조제와 함께 미분쇄한 후 공기 중에서 소결하여 페라이트 자석을 제조한 후 자기특성 변화를 조사하였다. 화학량론적인 조성에서 (La-Co)$_{0.3}$-SrM 조성으로 원소치환을 실시한 하소분말을 사용하여 제조한 페라이트 자석의 소결특성은 포화자화 ($M_{s}$ ) 71.08 emu/g, 보자력 ($iH_{c}$ ) 4.38 kOe 및 잔류자속밀도 ($B_{r}$ ) 4.18 kG, 보자력 ($iH_{c}$ ) 4.35 kOe, 최대에너지적($BH_{max}$ ) 4.3 MGOe으로 화학량론적인 조건에 비해 B $H_{max}$가 10% 이상 더 큰 자기특성값을 나타내었다.나타내었다.다.

• 한국작물학회:학술대회논문집
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• 한국작물학회 2017년도 9th Asian Crop Science Association conference
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• pp.4-4
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• 2017

Atmospheric carbon dioxide enrichment ($eCO_2$) often increases soil nitrous oxide ($N_2O$) emissions, but the underlying mechanisms are not fully understood. Emerging evidence suggests that $eCO_2$ alters plant N preference in favor of ammonium ($NH_4{^+}-N$) over nitrate ($NO_3{^-}-N$). Yet, whether and how this attributes to the enhancement of $N_2O$ emissions has not been investigated. We examined the effects of $eCO_2$ on soil $N_2O$ emissions in the presence of two N forms ($NH_4{^+}-N$ or $NO_3{^-}-N$), using wheat (Triticum aestivum L.) as a model plant. Our results showed that N forms dominated $eCO_2$ effects on plant and microbial N utilization, and thus soil $N_2O$ emissions. Elevated $CO_2$ significantly increased the rate and the sum of $N_2O$ emissions by three to four folds when $NO_3{^-}-N$, but not $NH_4{^+}-N$, was supplied. Enhanced $N_2O$ emission was related to the reduced plant $NO_3{^-}-N$ uptake in wheat. We propose a new conceptual model in which $eCO_2$-inhibition of plant $NO_3{^-}-N$ uptake and/or $CO_2$-enhancement of soil labile C enhances the N and/or C availability for denitrifiers and increases the intensity and/or the duration of $N_2O$ emissions. Together, these findings suggest that to enhance plant N use efficiency and reduce $N_2O$ emission, crop breeding and management need to consider altered plant preference of N sources under future $CO_2$ scenarios.

• 한국응용과학기술학회지
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• 제20권1호
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• pp.33-43
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• 2003

$LiMn_2O_4$ catalyst for $CO_2$ decomposition was synthesized by oxidation method for 30 min at 600$^{\circ}C$ in an electric furnace under air condition using manganese(II) nitrate $(Mn(NO_3)_2{\cdot}6H_2O)$, Lithium nitrate ($LiNO_3$) and Urea $(CO(NH_2)_2)$. The synthesized catalyst was reduced by $H_2$ at various temperatures for 3 hr. The reduction degree of the reduced catalysts were measured using the TGA. And then $CO_2$ decomposition rate was measured using the reduced catalysts. Phase-transitions of the catalysts were observed after $CO_2$ decomposition reaction at an optimal decomposition temperature. As the result of X-ray powder diffraction analysis, the synthesized catalyst was confirmed that the catalyst has the spinel structure, and also confirmed that when it was reduced by $H_2$, the phase of $LiMn_2O_4$ catalyst was transformed into $Li_2MnO_3$ and $Li_{1-2{\delta}}Mn_{2-{\delta}}O_{4-3{\delta}-{\delta}'}$ of tetragonal spinel phase. After $CO_2$ decomposition reaction, it was confirmed that the peak of $LiMn_2O_4$ of spinel phase. The optimal reduction temperature of the catalyst with $H_2$ was confirmed to be 450$^{\circ}C$(maximum weight-increasing ratio 9.47%) in the case of $LiMn_2O_4$ through the TGA analysis. Decomposition rate(%) using the $LiMn_2O_4$ catalyst showed the 67%. The crystal structure of the synthesized $LiMn_2O_4$ observed with a scanning electron microscope(SEM) shows cubic form. After reduction, $LiMn_2O_4$ catalyst became condensed each other to form interface. It was confirmed that after $CO_2$ decomposition, crystal structure of $LiMn_2O_4$ catalyst showed that its particle grew up more than that of reduction. Phase-transition by reduction and $CO_2$ decomposition ; $Li_2MnO_3$ and $Li_{1-2{\delta}}Mn_{2-{\delta}}O_{4-3{\delta}-{\delta}'}$ of tetragonal spinel phase at the first time of $CO_2$ decomposition appear like the same as the above contents. Phase-transition at $2{\sim}5$ time ; $Li_2MnO_3$ and $Li_{1-2{\delta}}Mn_{2-{\delta}}O_{4-3{\delta}-{\delta}'}$ of tetragonal spinel phase by reduction and $LiMn_2O_4$ of spinel phase after $CO_2$ decomposition appear like the same as the first time case. The result of the TGA analysis by catalyst reduction ; The first time, weight of reduced catalyst increased by 9.47%, for 2${\sim}$5 times, weight of reduced catalyst increased by average 2.3% But, in any time, there is little difference in the decomposition ratio of $CO_2$. That is to say, at the first time, it showed 67% in $CO_2$ decomposition rate and after 5 times reaction of $CO_2$ decomposition, it showed 67% nearly the same as the first time.