• 한국분말재료학회지
• /
• 제13권5호
• /
• pp.360-365
• /
• 2006

The phase stability of tetragonal phase in Y-TZP was investigated in terms of the distribution of grain sizes and heat-treating atmosphere. Y-TZP with various grain sizes were prepared using duration time at $1600^{\circ}C$ as experimental parameter. Accumulated grain size distributions were built from the SEM micrographs and the amount of tetragonal phase were measured using XRD. Both results were compared to determine the critical grain size before and after heat-treatment in vacuum. The critical grain size drastically decreased compared with the small increase of average grain size due to the autocatalytic effect which critically affects the tetragonal to monoclinic phase transformation. After heat-treatment in reductive atmosphere critical grain size relatively increased due to the stabilization of tetragonal phase. The formation of oxygen vacancies during heat-treatment was ascribed to the increase of stability.

• 환경위생공학
• /
• 제19권4호
• /
• pp.1-8
• /
• 2004

This study has been investigated to analyze the thermal stability of cesium reacted with fly ash with changing mole ratio of Cs/Al in hydrogen atmosphere. When the $CsNO_3$ and fly ash were reacted at $1000^{\circ}C$ in hydrogen atmosphere, cesium $nepheline(CsAlSiO_4)$ Phase began to emerge in addition to $pollucite(CsAlSi_2O_6)$ phase when the cesium loading quantity was greater than $0.32(g-Cs_2O/g-fly\; ash)$. Cesium $nepheline(CsAlSiO_4)$ Phase increased with increasing cesium loading quantity. When cesium trapped on a fly ash was exposed to $1200^{\circ}C$ in hydrogen atmosphere, no weight loss due to the volatilization was shown until the cesium loading quantity was reached at $0.32(g-Cs_2O/g-fly\; ash)$. In the case of the cesium loading quantity of $0.48-0.74(g-Cs_2O/g-fly\;ash)$ in hydrogen atmosphere, the weight loss increased with increasing the cesium loading quantity. This is considered to be due to the cesium $nepheline(CsAlSiO_4)$ whose vapor pressure is higher than that of $pollucite(CsAlSi_2O_6)$.

• 한국세라믹학회지
• /
• 제34권5호
• /
• pp.467-472
• /
• 1997

Porous silicon was prepared by an anodic etching. The pore size was about 10 nm at an etching time of 20 sec and a current density of 20 mA/$\textrm{cm}^2$. The porous layer was composed of an micro-porous layer (0.6 ${\mu}{\textrm}{m}$) and a macro-porous layer (10 ${\mu}{\textrm}{m}$). Room temperature PL with maximum peak 6700$\AA$ appeared. The peak disappeared by an oxidation reaction when the porous silicon was heated to 100~20$0^{\circ}C$ in atmosphere. In order to avoid the oxidation a heat treatment was done in H2 atmosphere. The micro-pore and Si column, which formed quantum well, were collapsed by the high temperature. The PL maximum peak of heated sample was gradually red-shifted and showed about 300$\AA$ red-shift at 50$0^{\circ}C$. The intensity of PL was maintained to high temperatures in lower pressures. The porous Si was carbonized in C2H2+H2 gas in order to increase thermal stability. The carbonization of the porous Si prevented red-shift of the maximum PL peak caused by sintering effect at high temperatures, and the carbonized porous Si showed Pl signal at higher temperatures by above 20$0^{\circ}C$ than the sample in H2 atmosphere.

• 한국전기전자재료학회논문지
• /
• 제22권2호
• /
• pp.107-113
• /
• 2009

In order to improve air stability, we proposed a new active layer of an organic TFT by synthesizing P3HT/POSS conjugated polymer. P3HT/POSS OTFTs with the various P3HT/POSS volume ratios were fabricated and characterized. With the P3HT/POSS volume ratio of 1:1, we achieved the field-effect mobilities of ${\sim}1.19{\times}10^{-3}\;cm^2/v{\cdot}sec$ in the saturation region and the current on/off ratio of ${\sim}2.51{\times}10^2$. The resulting current on-off ratio was much higher than that of the P3HT-based OTFTs and resulted from the dramatic decrease of the off-current. Since the off-current can be reduced by preventing oxygen in atmosphere from doping the P3HT/POSS active layers, this new active layer shows its ability to avoid oxygen doping in atmosphere. Therefore, the improvement of the air stability can be achieved by employing the P3HT/POSS active layers.

• 농업생명과학연구
• /
• 제44권6호
• /
• pp.69-78
• /
• 2010

본 연구에서는 우리나라의 고층기상 관측자료와 수치모델(RDAPS 10km) 예상 자료를 활용하여 대기 불안정도와 건조도를 포함하는 산불잠재 위험지수인 Haines Index(HI)와 산불과의 관계를 분석하였고, 그 결과 산불 확산 잠재성이 높은 HI=5, 6은 4월에 가장 높게 나타났고, 대기의 안정도 보다는 건조도가 높게 나타났으며, 산불의 발생과 확산에 큰 영향을 주는 것으로 나타났다.

• Nuclear Engineering and Technology
• /
• 제34권4호
• /
• pp.323-330
• /
• 2002

Various types of compounds were tested with the aspects of decomposition and formation of residue in a $CO_2$ or 7H$_2$+93$N_2$ atmosphere. The evaporation temperature range of each compound was determined from thermogravimetric curve. Decomposition of dicarbon amide, stearic acid, acrowax and zinc stearate was studied by thermogravimetry in $CO_2$ or in 7H$_2$+93$N_2$ atmosphere. All compounds were decomposed in $CO_2$ atmosphere at lower than 40$0^{\circ}C$, but the residue, ZnO remained for zinc stearate. ZnO did not decompose in $CO_2$ atmosphere up to 130$0^{\circ}C$, but reduced into Zn metal and disappeared in the temperature range of $600^{\circ}C$ to 120$0^{\circ}C$ in 7H$_2$+93$N_2$ atmosphere. The effect of residue, which trapped in closed pores of sintered pellet, on the thermal stability was studied using the resintering test at 1$700^{\circ}C$ in 7H$_2$+93$N_2$ atmosphere. In the case of oxidative sintered pellet with admixing zinc stearate, the cavity formation accompanied with a density drop after resintering is due to the pressure of the Zn gases trapped in the isolated pores.

• 한국표면공학회지
• /
• 제55권4호
• /
• pp.215-221
• /
• 2022

In the present work, copper oxide thin films were formed by heat-treatment method with different temperatures and atmosphere, e.g., at 200 ~ 400 ℃; in air and Ar atmosphere. The morphological, electrical and optical properties of the thermally fabricated Cu oxide films were analyzed by SEM, XRD, and UV-VIS spectrometer. Thereafter, photoelectrochemical properties of the thermal copper oxide films were analyzed under solar light (AM 1.5, 100 mW/cm²). Conclusively, the highest photocurrent was obtained with Cu₂O formed under the optimum annealing condition at 300 ℃ in air atmosphere. In addition, EIS results of Cu oxide formed in air atmosphere showed relatively low resistance and long electron life-time compared with Cu Oxide fabricated in Ar atmosphere at the same temperature. This is because heat-treatment in Ar atmosphere could not form Cu₂O due to lack of oxygen, and thermally formed CuO at high temperature suppressed stability and conductivity of the Cu oxide.

• 한국환경과학회지
• /
• 제28권12호
• /
• pp.1133-1145
• /
• 2019

Successful launch requires state-of-the-art launch vehicle technology and constant test operations, However, the meteorological threat to the launch vehicle flight trajectory is also an important factor for launch success. Atmospheric stability above the Naro Space Center at the this time is very important, especially because the initial flight operation can determine the success of the launch. Moreover, during the flight of launch vehicle with rapid pressure and thrust into the atmosphere, convection activity in the atmosphere may create environmental conditions that cause severe weather threats such as thunderstorms. Hence, studies of atmospheric instability characteristics over the Naro Space Center are a necessary part of successful launch missions. Therefore, the main aims of this study were to (1) verify the atmospheric stability index and convection activity characteristics over the Naro Space Center using radiosonde data observed from 2007 to 2018 by the Naro Space Center, (2) analyze changes in the atmospheric stability index according to monthly and seasonal changes, and (3) assess how the calculated atmospheric stability index is related to actual thunderstorm occurrence using statistical analysis. Additionally, we aimed to investigate the atmospheric characteristics above the Naro Space Center through the distribution chart of the atmospheric stability index during summer, when convection activity is highest. Finally, we assessed the relationship between lightning occurrence and unstable atmospheric conditions, through predictability analysis performed using the lightning observation data of the Korea Meteorological Administration.

• 한국가스학회지
• /
• 제9권1호
• /
• pp.9-15
• /
• 2005

수소는 온실효과 가스배출을 저감하기 위한 다양한 연소장치에 이용되는 에너지 전달체로 가장 중요한 물질로 인식되고 있다. 그러나 에너지 전달체로 이용되기 위해서는 수소를 이용하는 장치와 관련된 안전의 문제점이 충분히 조사하고 이해되어야 한다. 따라서 누출된 수소가스와 공기의 혼합 가스운의 확산거동과 점화 가능성에 대한 연구가 필요하다. 본 연구에서는 대기 조건에 따라 대기 중에서 수소가스의 확산거동을 부력을 고려하여 살펴보았다. 풍하방향으로 위험범위는 대기안정도 및 풍속이 증가할수록 증가하게 되고, 지면에서 가스농도는 수소가스의 부력 때문에 거의 제로이다. 그러므로 누출된 수소가스 운의 점화 가능성은 낮고, 화재$\cdot$폭발 위험성은 타 연료가스 즉 부탄 및 프로판에 비하여 낮은 것으로 사료된다.

• Bulletin of the Korean Chemical Society
• /
• 제29권6호
• /
• pp.1121-1124
• /
• 2008

A carbon composite was synthesized by mechanical mixing of ball-milled graphite and PVC powders, followed by pyrolysis reaction of PVC. Natural graphite ball milled under atmosphere of argon or air leads to a disordered structure. It appears that the electrochemical lithium intercalation reaction is dependent on the atmosphere in which the graphite is ball milled. The carbon composite obtained using air-milled graphite shows a high reversible capacity and high initial coulombic efficiency compared to argon-milled graphite. This is attributed to the enhanced thermal stability of a disordered structure in the air milled sample. For the one with air-milled graphite, the disordered structure is maintained during heat treatment, while argon-milled graphite is partially crystallized.