• 한국결정성장학회지
• /
• 제27권1호
• /
• pp.47-56
• /
• 2017

본 연구에서는 Alumina 골재를 사용한 fly ash-blast furnace slag계 Geopolymer의 내열성 건축자재로서의 사용 가능성을 검토하기 위하여 고온조건에서의 열적 특성에 대하여 조사하였다. 모든 배합조건에서 Geopolymer 경화체의 표면 크랙은 $800^{\circ}C$까지는 관찰되지 않았으며, 이것은 열처리 전후 강도의 변화가 작은 것과 일치한다. 또한, $800^{\circ}C$까지 고로슬래그의 혼합비율이 60 wt%일 때 잔존압축강도가 가장 우수한 것으로 나타났다. Geopolymer 경화체의 주요 수화 생성물은 $20{\sim}35^{\circ}$(2theta) 범위의 비정질 halo 패턴과 원재료의 mullite($3Al_2O_3{\cdot}2SiO_2$)와 quartz($SiO_2$)가 확인되었다. 비정질 halo 패턴은 Geopolymer 축중합 반응에 의해서 생성된 aluminosilicate gel이며, $800^{\circ}C$까지는 aluminosilicate gel의 halo 패턴이 유지되고 있음을 알 수 있다. $1,000^{\circ}C$에서 aluminosilicate gel의 패턴은 사라지며 열처리온도의 증가와 함께 gehlenite, calcium silicate, calcium aluminum oxide, microcline와 같은 결정상이 관찰되었다.

• 폴리머
• /
• 제25권4호
• /
• pp.558-567
• /
• 2001

피라진염의 치환기를 변화시킨 열잠재성 양이온 촉매를 합성하고, 이관능성 에폭시(diglycidylether of bisphenol-A, DGEBA)에 개시제로서 1 wt% 촉매를 혼합하여 동적 DSC방법을 이용한 경화 거동과 열잠재 특성에 대해 연구하였다. 그 결과 합성된 촉매들은 에폭시 시스템에서 우수한 열잠재성을 가지고 있음을 확인하였다. 치환기의 염기도(basicity)가 높을수록 경화온도와 활성화 에너지는 높아지고 활성은 낮아졌는데 이는 활성과 경화거동이 링 스트레인(ring strain) 및 도입된 치환기의 염기도(basicity)에 의해 조절되기 때문인 것으로 사료된다. 결론적으로, 전자공여 그룹인 메틸기를 도입한 촉매의 활성은 경화시 개시단계에서 염기도 증가로 인한 피라진의 이탈능과 벤질 양이온의 안정성이 감소되었기 때문에 낮아졌으며, 전자수용 그룹인 시아노기를 도입한 촉매의 활성은 유기효과와 공명에 인해서 벤질 양이온의 안정성이 증가됨으로써 높아졌다.

• Smart Structures and Systems
• /
• 제12권1호
• /
• pp.41-54
• /
• 2013

Concrete is known as a heterogeneous product which is composed of complex chemical composition and reaction. The development of concrete thermal effect during early age is critical on its future structural health and long term durability. When cement is mixed with water, the exothermic chemical reaction generates hydration heat, which raises the temperature within the concrete. Consequently, cracking may occur if the concrete temperature rises too high or if there is a large temperature difference between the interior and the exterior of concrete structures during early age hydration. This paper describes the contribution of novel Fabry-Perot (FP) fiber optic temperature sensors to investigate the thermal effects of concrete hydration process. Concrete specimens were manufactured under various water-to-cement (w/c) ratios from 0.40 to 0.60. During the first 24 hours of concreting, two FP fiber optic temperature sensors were inserted into concrete specimens with the protection of copper tubing to monitor the surface and core temperature change. The experimental results revealed effects of w/c ratios on surface and core temperature developments during early age hydration, as well as demonstrating that FP fiber optic sensors are capable of capturing temperature variation in the concrete with reliable performance. Temperature profiles are used for calculating the apparent activation energy ($E_a$) and the heat of hydration (H(t)) of concrete, which can help us to better understand cement hydration.

• 한국분말재료학회지
• /
• 제16권5호
• /
• pp.363-369
• /
• 2009

The amorphization process and the thermal properties of amorphous Ti$_{40}$Cu$_{40}$Ni$_{10}$Al$_{10}$ powder during milling by mechanical alloying were examined by X-ray diffractometry (XRD), differential scanning calorimetry (DSC), and transmission electron microscopy (TEM). The chemical composition of the samples was examined by an energy dispersive X-ray spectrometry (EDX) facility attached to the scanning electron microscope (SEM). The as-milled powders showed a broad peak (2$\theta$ = 42.4$^{\circ}$) with crystalline size of about 5.0 nm in the XRD patterns. The entire milling process could be divided into three different stages: agglomeration (0 < t$_m$ $\leq$ 3 h), disintegration (3 h < t$_m$ $\leq$ 20 h), and homogenization (20 h < t$_m$ $\leq$ 40 h) (t$_m$: milling time). In the DSC experiment, the peak temperature T$_p$ and crystallization temperature T$_x$ were 466.9$^{\circ}C$ and 444.3$^{\circ}C$, respectively, and the values of T$_p$, and T$_x$ increased with a heating rate (HR). The activation energies of crystallization for the as-milled powder was 291.5 kJ/mol for T$_p$.

• 한국대기환경학회지
• /
• 제30권6호
• /
• pp.577-585
• /
• 2014

A series of experiments using atmospheric-pressure non-thermal plasma coupled with transition metal catalysts were performed to remove ethylene from agricultural storage facilities. The non-thermal plasma was created by dielectric barrier discharge, which was in direct contact with the catalyst pellets. The transition metals such as Ag and $V_2O_5$ were supported on ${\gamma}-Al_2O_3$. The effect of catalyst type, specific input energy (SIE) and oxygen content on the removal of ethylene was examined to understand the behavior of the hybrid plasma-catalytic reactor system. With the other parameters kept constant, the plasma-catalytic activity for the removal of ethylene was in order of $V_2O_5/{\gamma}-Al_2O_3$ > $Ag/{\gamma}-Al_2O_3$ > ${\gamma}-Al_2O_3$ from high to low. Interestingly, the rate of plasma-catalytic ozone generation was in order of $V_2O_5/{\gamma}-Al_2O_3$ > ${\gamma}-Al_2O_3$ > $Ag/{\gamma}-Al_2O_3$, implying that the catalyst activation mechanisms by plasma are different for different catalysts. The results obtained by varying the oxygen content indicated that nitrogen-derived reactive species dominated the removal of ethylene under oxygen-lean condition, while ozone and oxygen atoms were mainly involved in the removal under oxygen-rich condition. When the plasma was coupled with $V_2O_5/{\gamma}-Al_2O_3$, nearly complete removal of ethylene was achieved at oxygen contents higher than 5% by volume (inlet ethylene: 250 ppm; gas flow rate: $1.0Lmin^{-1}$; SIE: ${\sim}355JL^{-1}$).

• 방사성폐기물학회지
• /
• 제4권3호
• /
• pp.209-216
• /
• 2006

중성자가 조사된 흑연에 내재되어 있는 Wigner 에너지를 배출시키는 방법의 하나인 가열냉각공정의 적용 예로 DSC(미분 주사선 열량계) 측정을 통해 흑연으로부터 Wigner 에너지가 배출되는 열 배출 특성을 연구하였다. 일정온도 상승 방법 에 의한 DSC 운전에서 중성자가 조사된 흑연을 가열냉각(annealing)하는 동안 배출되는 Wigner 에너지의 총량과 처리온도에 따른 배출속도를 측정하였다. 연구로 2호기(KRR-2) thermal column 내에 위치별로 중성자의 조사량에 차이가 나는 흑연 시료를 분말로 만들어 상온에서 $500^{\circ}C$까지의 온도 범위에서 DSC를 운전하고 이로부터 Wigner 에너지의 배출 속도를 측정하였다. 가열냉각 동안 중성자가 조사된 흑연에서 배출되는 Wigner 에너지의 배출 특성은 가변적 활성화 에너지 속도 식으로 잘 상관시킬 수 있었다.

• The Korean Journal of Physiology
• /
• 제24권1호
• /
• pp.171-180
• /
• 1990

In 19 cats anesthetized with ${\alpha}-chloralose$ effects of taurine and ${\beta}-alanine$ on the responses of wide dynamic range (WDR) cells to mechanical, chemical and thermal stimuli were investigated in the lumbar spinal cord of the cat. Also studied was an interaction of strychnine with taurine in affecting the activities of WDR cells. Following intravenous administration of taurine, the responses of WDR cells to all types of mechanical stimuli were markedly enhanced, demonstrating that the response to pressure was most sensitive to taurine action. When the receptive field was exposed to thermal stimuli ($50^{\circ}C$) for 20 sec. taurine increased activity of WDR cell to 169.5% of the control value. The $K^{+}$-induced activation of WDR cells was invariably suppressed after taurine administration. Intravenously administered strychnine remarkably reduced the enhanced response of WDR cell to natural stimuli resulting from intravenous administration of taurine. Also ${\beta}-alanine$ markedly activated the response of spinal dorsal horn cell to natural mechanical stimuli. These findings suggest that neutral amino acid and its derivative such as ${\beta}-alanine$ and taurine can enhance the response of WDR cells to different stimuli in cats.

• 한국결정성장학회지
• /
• 제6권2호
• /
• pp.185-193
• /
• 1996

(100) Si wafer를 $2.5^{\circ},\;5^{\circ}$ 기울인 뒤, dry $O_{2}$ 분위기에서 산화시킴으로써, 시편들 간의 산화 거동 및 산화에 의한 적층 결함 특성의 차이를 알아보았다. 시편을 $900~1200^{\circ}C$에서 산화시키고 ellipsometer로 두께를 측정한 결과 저탈각 (100) Si이 (100) Si보다 산화 속도가 빨랐으며, $5^{\circ}$ off면이 $2.5^{\circ}$ off면보다 더 빨랐다. 결정방향에 따른 산화속도 차이는 산화 온도가 높아질수록 줄어들었다. 각 시편의 속도 상수에 대한 활성화 에너지는 포물 성장 속도 상수의 경우 (100) Si, $2.5^{\circ}$ off (100) Si, $5^{\circ}$ off Si이 각각 27.3, 25.9, 27.6 kcal/mol이였고, 선형 성장 속도 상수는 58.6, 56.6, 57.4 kcal/mol이였다. 또한, 두 시편에 대해 산화막을 선택 식각하 고 광학 현미경으로 관찰하여, (100) Si에 비해 $5^{\circ}$ off된 면의 산화에 의한 적층 결함 밀도가 훨씬 낮음을 확인하였고, 적층 결함 간의 각도가 달라짐을 확인하였다.

• Nuclear Engineering and Technology
• /
• 제38권6호
• /
• pp.585-590
• /
• 2006

This paper describes the results of an irradiation test and the specifications of the pneumatic transfer system (PTS) in the NAA #3 irradiation hole at the HANARO research reactor, which was reinstalled after some modifications of the operation mode at the end of 2004. The outer and inner diameters of the PE transfer tube are 34.1 and 27.5 mm, respectively. PE rabbit was used for sample irradiation. The $N_2$ gas pressure of the PTS lines was adjusted to 0.75 bar. The average sending time to the reactor was $8.5{\pm}0.3$ s and the average receiving time back to the receiver was $3.2{\pm}0.2$ s. The internal and external temperature of the irradiation tube was measured in a range of 50 to $80^{\circ}C$ for a 40 s to 80 s irradiation time, respectively. The optimum irradiation time was estimated to be less than 80 s. The thermal, epithermal and fast neutron flux at 30 MW thermal power were $1.42{\pm}0.01{\times}10^{14},\;1.51{\pm}0.04{\times}10^{13}$ and $9.48{\pm}0.69{\times}10^{11} n{\cdot}cm^{-2}{\codt}s^{1-}$, respectively. The cadmium ratio was approximately 9.40. The data obtained will be applied to supplement user information and for reactor management.

• BMB Reports
• /
• 제43권1호
• /
• pp.46-51
• /
• 2010

Thermal burn injury induces inflammatory cell infiltrates in the dermis and thickening of the epidermis. Following a burn injury, various mediators, including reactive oxygen species (ROS), are produced in macrophages and neutrophils, exposing all tissues to oxidative injury. The anti-oxidant activities of flavonoids have been widely exploited to scavenge ROS. In this study, we observed that several flavonoids-kaempferol, quercetin, fisetin, and chrysin-inhibit LPS-induced IL-8 promoter activation in RAW 264.7 cells. In contrast with quercetin and fisetin, pretreatment of kaempferol and chrysin did not decrease cell viability. Inflammatory cell infiltrates in the dermis and thickening of the epidermis induced by burn injuries in mice was relieved by kaempferol treatment. However, the injury was worsened by fisetin, quercetin, and chrysin. Expression of TNF-a induced by burn injuries was decreased by kaempferol. These findings suggest the potential use of kaempferol as a therapeutic in thermal burn-induced skin injuries.