• Bulletin of the Korean Chemical Society
• /
• 제32권7호
• /
• pp.2178-2182
• /
• 2011

Recently, the synthesis of ordered macroporous materials has received much attention due to its potential use as photonic band gap materials.$^1$ In this study, we have used the three-dimensional (3D) latex array template impregnated with benzenesulfonic acid (BSA), which is capable of catalyzing the reaction using tetraethyl orthosilicate (TEOS) as a precursor and distilled water. The polystyrene (PS) templates were reacted with TEOS in $scCO_2$ at 40 $^{\circ}C$ and at 80 bar. In the reactor, TEOS was filtrated into the PS particle lattice. After the reaction, porous silica materials were obtained by calcinations of the template. The stability test of the PS template in pure $CO_2$ was conducted before the main experiment. Scanning electron microscopy (SEM) images showed that the reaction in $scCO_2$ takes place only on the particle surface. This new method using $scCO_2$ has advantages over conventional sol-gel processes in its capability to control the fluid properties such as viscosity and interfacial tension. It has been found that the reaction in $scCO_2$ occurs only on the particle surface, making the proposed technique as more rapid and sustainable method of synthesizing inverse opal materials than conventional coating processes in the liquid phase and in the vapor phase.

• Journal of Electrochemical Science and Technology
• /
• 제10권1호
• /
• pp.22-28
• /
• 2019

To maximize the oxygen evolution reaction (OER) in the electrolysis of water, nano-grade $IrO_2$ powder with a low specific surface was prepared as a catalyst for a solid polymer electrolyte (SPE) system, and a membrane electrode assembly (MEA) was prepared with a catalyst loading as low as $2mg\;cm^{-2}$ or less. The $IrO_2$ catalyst was composed of heterogeneous particles with particle sizes ranging from 20 to 70 nm, having a specific surface area of $3.8m^2g^{-1}$. The anode catalyst layer of about $5{\mu}m$ thickness was coated on the membrane (Nafion 117) for the MEA by the decal method. Scanning electron microscopy (SEM) and electrochemical impedance spectroscopy (EIS) confirmed strong adhesion at the interface between the membrane and the catalyst electrode. Although the loading of the $IrO_2$ catalyst was as low as $1.1-1.7mg\;cm^{-2}$, the SPE cell delivered a voltage of 1.88-1.93 V at a current density of $1A\;cm^{-2}$ and operating temperature of $80^{\circ}C$. That is, it was observed that the over-potential of the cell for the oxygen evolution reaction (OER) decreased with increasing $IrO_2$ catalyst loading. The electrochemical stability of the MEA was investigated in the electrolysis of water at a current density of $1A\;cm^{-2}$ for a short time. A voltage of ~2.0 V was maintained without any remarkable deterioration of the MEA characteristics.

• 공업화학
• /
• 제34권2호
• /
• pp.180-185
• /
• 2023

물의 전기 분해 효율을 향상시키기 위해 산소발생반응(OER)의 반응 속도를 가속화하며 고성능과 장기 안정성을 가진 OER 전기촉매 개발이 필수적이다. 본 연구에서는 고효율의 OER 전기촉매를 합성하기 위해 중공 금속-유기골격체 (MOF)로부터 유도된 루테늄-코발트 산화물 촉매를 개발하였다. 합성된 촉매는 루테늄의 표면 노출을 증대시킴으로 낮은 Tafel 기울기와 10 mA/cm²의 전류밀도에서 386 mV의 낮은 과전위가 관찰되었다. 또한 상용 RuO₂ 촉매 대비 높은 질량 활성과 안정성을 보여, 귀금속 촉매를 대체할 수 있을 것으로 기대된다.

• Nuclear Engineering and Technology
• /
• 제56권3호
• /
• pp.893-899
• /
• 2024

In a secondary cooling system of a sodium-cooled fast reactor (SFR), rapid detection of hydrogen due to sodium-water reaction (SWR) caused by water leakage from a heat exchanger tube of a steam generator (SG) is important in terms of safety and property protection of the SFR. For hydrogen detection, the hydrogen detectors using atomic transmission phenomenon of hydrogen within Ni-membrane were used in Japanese proto-type SFR "Monju". However, during the plant operation, detection signals of water leakage were observed even in the situation without SWR concerning temperature up and down in the cooling system. For this reason, the study of a new hydrogen detector has been carried out to improve stability, accuracy and reliability. In this research, the authors focus on the difference in composition of hydrogen and the difference between the background hydrogen under normal plant operation and the one generated by SWR and theoretically estimate the hydrogen behavior in liquid sodium by using ultra-accelerated quantum chemical molecular dynamics (UA-QCMD). Based on the estimation, dissolved H or NaH, rather than molecular hydrogen (H₂), is the predominant form of the background hydrogen in liquid sodium in terms of energetical stability. On the other hand, it was found that hydrogen molecules produced by the sodium-water reaction can exist stably as a form of a fine bubble concerning some confinement mechanism such as a NaH layer on their surface. At the same time, we observed experimentally that the fine H₂ bubbles exist stably in the liquid sodium, longer than previously expected. This paper describes the comparison between the theoretical estimation and experimental results based on hydrogen form in sodium in the development of the new hydrogen detector in Japan.

• 대한화학회지
• /
• 제48권1호
• /
• pp.46-52
• /
• 2004

층상구조를 갖는 망간산화물에서 결정성과 구조적 안정도 간의 관계에 대해 조사하였다. 좋은 결정성을 갖는 망간산화물은 고상합성법-이온교환법을 이용하여 합성하였으며, 나노결정 망간산화물은 실온에서의 Chimie-Douce 반응을 통해 얻어졌다. 마이크로 라만 분광과 X선 흡수분광 결과는 결정성에 상관없이 이들 화합물에 존재하는 망간이온이 공통적으로 층상구조의 팔면체 자리에 안정화되어 있음을 보여준다. 미분전하용량 분석 결과는 나노결정 화합물의 층상구조가 전기화학적 충방전 과정 동안 안정하다는 사실을 보여주며, 이와는 대조적으로 좋은 결정성을 갖는 층상구조 화합물의 경우 현저한 구조변화를 겪는다는 사실을 보여준다. 마이크로 라만 분광 결과는 이러한 구조전이가 층상 구조로부터 스핀넬 타입 구조로의 변화에 해당함을 보여준다. 위 실험 결과로부터 나노결정성이 층상구조의 안정도를 향상시킨다는 결론을 얻을 수 있었다.

• 한국운동역학회지
• /
• 제25권1호
• /
• pp.85-94
• /
• 2015

Purpose : The purpose of this study was to investigate the influence on the ground reaction force parameters according to wearing positions of backpack for during stair ascending and descending. Methods : Participants selected as subject were consisted of young female(n=10) and performed stairs walks(ascending and descending) with 2 types of wearing position(front of trunk[FT], rear of trunk[RT]). Passive(Fz 1) and active(Fz 2) forces of the vertical GRF were determined from time function and frequency domain. Also shear forces(Fx, Fy 1, Fy 2), dynamic postural stability index(MLSI, APSI, VSI, DPSI), loading rate and center of pressure (${\Delta}COPx$, ${\Delta}COPy$, COP area) were calculated from time function and frequency domain. Results : Fx, Fy 1, Fy 2, and Fz 1 in GRF didn't show significant differences statistically according to the wearing positions of backpack(p>.05), but stair descending showed higher forces than that of stair ascending. Particularly, Fz 2 of stair ascending showed higher forces than that of stair descending(p<.001), RT types showed higher than that of FT types(p<.05). MLSI, APSI, VSI, and DPSI of stair descending showed the increased stability index than that of stair ascending(p<.05), MLSI of RT types showed the decreased stability index than that of FT types(p<.05). Loading rate didn't show significant differences statistically according to the wearing positions of backpack(p>.05), but stair descending showed higher loading rate than that of stair ascending(p<.001). Also, ${\Delta}COPx$ in stair descending showed the increased movement than that of stair ascending(p<.05). Conclusions : A backpack of 10 kg(10 kg(ratio of body weights $17.61{\pm}1.17%$) showed significantly change GRF parameters according to wearing positions during stair ascending and descending. If possible, we suggest that the dynamic stability, in case of stairs walking with a smaller weights can be further improved.

• 분석과학
• /
• 제11권2호
• /
• pp.92-95
• /
• 1998

변형된 two-bulb pyrex관을 사용하여 K-SGICs(인조흑연 층간화합물)를 합성하였다. 흑연과 칼륨을 반응시키기 위하여 two-bulb관내에 압력을 $10^{-3}$ torr로 유지하여 주었다. 변형된 방법에 의하여 얻어진 K-SGICs는 유동 파라핀 내에서 $25{\sim}1400^{\circ}C$ 사이에서 열처리하여 deintercalation을 시켰다. K-SGICs의 온도 의존성과 열적 안정성을 DSC 분석기에 의하여 특성화하였다. K-SGIC의 엔탈피와 엔트로피 형성은 여러 온도에 의존하는 열역학적 발열반응과 deintercalation을 확인하여 계산하였다. 칼륨이온의 deintercalation 반응이 얼어나는 동안 K-SGICs 의 구조변이와 열적 안정성을 XRD에 의하여 확인하였다.

• 한국재료학회지
• /
• 제28권6호
• /
• pp.324-329
• /
• 2018

Needle-like NiO protecting layers on NiCrAl alloy foam, used as support for hydrogen production, are introduced through electroplated Ni and subsequent microwave annealing. To improve the stability of the NiCrAl alloy foam, oxygen concentration of microwave annealing to form a needle-like NiO layer with good chemical stability and corrosion resistance is controlled in a range of 20 and 50 %. As the oxygen concentration increases to 50 %, needle-like NiO forms a dense coating layer on the NiCrAl alloy foam; this layer formation can be attributed to accelerated growth of the (200) plane. In addition, the increased oxygen concentration causes increased NiO/Ni ratio of the resultant coating layer on NiCrAl alloy foam due to improved rate of the oxidation reaction. As a result, the introduction of dense needle-like NiO layers formed at 50 % oxygen concentration improves the chemical stability of the NiCrAl alloy foam by protecting the direct electrochemical reaction between the electrolyte and the foam. Thus, needle-like NiO can be proposed as a superb protecting layer to improve the chemical stability of NiCrAl alloy form.

• Korean Chemical Engineering Research
• /
• 제53권6호
• /
• pp.802-807
• /
• 2015

본 논문에서는 글루코스산화제, polyethyleneimine(PEI) 및 탄소나노튜브 간 물리적 흡착으로 제조된 촉매(GOx/PEI/CNT)에 새로운 가교제인 terephthalaldehyde(TPA)를 첨가하여 민감도 및 안정성이 개선된 글루코스 센서 촉매를 합성하여, 감지능 및 안정성 개선효과를 확인하였다. 새로운 가교제를 포함한 바이오 촉매는, 글루코스산화제 및 polyethyeleneimine의 관능기와 TPA의 관능기간 알돌축합반응에 의해 생성되었고, 이를 통해 생성된 새로운 전자전달구조는 글루코스의 산화반응을 촉진시켰다. 이러한 촉매활성은 전기화학적 평가를 통해 정량적으로 평가하였으며 그 결과 $41.1{\mu}Acm^{-2}mM^{-1}$의 글루코스 민감도를 얻을 수 있었다. 또한 가교제와 글루코스산화제 및 polyethyeleneimine 간의 화학반응의 형성에 의해 글루코스 산화제의 외부 손실을 최소화 하여, 센서 안정성 향상에도 크게 기여하였다. 안정성 평가를 한 결과, 3주간의 주기적인 촉매 활성 측정후에 94.6% 활성이 유지됨을 확인하였다.

• 한국추진공학회:학술대회논문집
• /
• 한국추진공학회 2010년도 제35회 추계학술대회논문집
• /
• pp.294-299
• /
• 2010

본 연구의 목적은 열안정성을 향상시키는 첨가제 (열안정제)를 이용하여 exo-tetrahydrodicyclopentadiene (exo-THDCP, $C_{10}H_{16}$)의 열안정성을 향상시키는 것이다. 실험은 반응 진행 중 미량의 시료 추출이 가능한 회분식 반응기에서 수행되었다. 추출한 시료를 gas chromatography-mass spectrometry (GC-MS)를 이용해 성분 분석하여 첨가제 성능-exo-THDCP의 열분해성-을 확인하고, 반응시간에 따른 exo-THDCP의 분해생성물의 성분 및 조성 변화를 통해 첨가제의 작용 메커니즘을 규명하였다. 열안정제로써 수소공여체를 사용하여 실험한 결과 1,2,3,4-tetrahydroquinoline (THQ), benzyl alcohol (BnOH) 등을 첨가하였을 때 exo-THDCP의 열안정성이 향상되었다. 이러한 수소공여체 물질들은 개시반응이 진행된 exo-THDCP 라디칼에 수소원자 (hydrogen radical)를 제공함으로 라디칼의 반응성을 완화시켜 1차 생성물의 활성을 감소시키어 2차생성물질인 $C_{11}$ 이상 생성물의 발생을 감소시키는 것으로 밝혀졌다.