In this study, defects generated in the YSZ coating layer of the IN738LC turbine blade are investigated using an optical microscope and SEM/EDS. The blade YSZ coating layer is composed of a Y-Zr component top coat layer and a Co component bond coat layer. A large amount of Cr/Ni component that diffused from the base is also measured in the bond coat. The blade hot corrosion is concentrated on the surface of the concave part, accompanied by separation of the coating layer due to the concentration of combustion gas collisions here. In the top coating layer of the blade, cracks occur in the vertical and horizontal directions, along with pits in the top coating layer. Combustion gas components such as Na and S are contained inside the pits and cracks, so it is considered that the pits/cracks are caused by the corrosion of the combustion gases. Also, a thermally grown oxide (TGO) layer of several μm thick composed of Al oxide is observed between the top coat and the bond coat, and a similar inner TGO with a thickness of several μm is also observed between the bond coat and the matrix. A PFZ (precipitate free zone) deficient in γ' (Ni3Al) forms as a band around the TGO, in which the Al component is integrated. Although TGO can resist high temperature corrosion of the top coat, it should also be considered that if its shape is irregular and contains pore defects, it may degrade the blade high temperature creep properties. Compositional and microstructural analysis results for hightemperature corrosion and TGO defects in the blade coating layer used at high temperatures are expected to be applied to sound YSZ coating and blade design technology.

The present study analyzed the pore formation and development process in carbon black that was activated by CO2 gas and the effect of the burn-off (BO) ratio on the process, particularly based on changes in the surface shape and internal microstructure. The activation process was performed as follows. Carbon blacks were injected into a horizontal tube furnace when the inside temperature reached 1000 °C. Carbon black samples with different BOs, i.e., 7.2%, 15.4%, 30.4%, 48.2%, 59.9%, and 83.2%, were prepared by varying the activation time. The microstructure of the activated samples was observed and examined using SEM and TEM. The results showed that pore passages were first created on the surface of the primary particles of the carbon black, and then the inner portion of the carbon black with a lower degree of crystallinity started to be activated, thereby causing inner pores to be formed. These inner pores then started to grow and coalesce into larger pores, thereby causing the crystallite layers in the inner portion of the carbon black to be activated. The changes in the microstructure of the carbon black during the activation reaction were attributable to the carbon black manufacturing process, in which the nucleation and growth of the primary particles of the carbon black occurred within a very short period of time. Thus, the crystallization of the inner portion was suppressed, and therefore, the degree of crystallinity was lower in the inner portion than in the outer portion.

20 여 가지의 형태의 제올라이트 중에서 8-membered ring (8 MR) 구조를 지닌 제올라이트를 다공성 지지층 위에 연속적인 분리막 형태로 제작하고자 한다. 이 때, 궁극적인 분리막의 사용처에 해당되는 배가스 및 바이오가스 조건에서 이산화탄소를 분리하는 데 적합하도록 설계한 제올라이트 분리막에 대해 기술하고자 한다. 특히, 10% 정도의 수분에 의한 악영향을 최소화할 수 있는 방법에 대해 발표하고자 한다.

SiAlON-based ceramics are some of the most typical oxynitride ceramic materials, which can be used as cutting tools for heat-resistant super-alloys (HRSA). SiAlON can be fabricated by using gas-pressure reactive sintering from the raw materials, nitrides and oxides such as Si3N4, AlN, Al2O3, and Yb2O3. In this study, we fabricate Ybm/3Si12-(m+n)Alm+nOnN16-n (m=0.3, n=1.9, 2.3, 2.7) ceramics by using gas-pressure sintering at different sintering temperatures. Then, the densification behavior, phase formation, microstructure, and hardness of the sintered specimens are characterized. We obtain a fully densified specimen with β- SiAlON after gas-pressure sintering at 1820℃ for 90 min. under 10 atm N2 pressure. These SiAlON ceramic materials exhibited hardness values of ~92.9 HRA. The potential of these SiAlON ceramics for cutting tool application is also discussed.

Shale gas has become increasingly important as a viable alternative to conventional gas resources. However, one of the critical issues in the development of shale gas is the generation of produced water, which contains high concentration of ionic compounds (> TDS of 100,000 mg/L). Accordingly, membrane distillation (MD) was considered to treat such produced water. Experiments were carried out using a laboratory-scale direct contact MD (DCMD). Synthetic produced water was prepared to examine its fouling propensity in MD process. Antiscalants and in-line filtration were applied to control fouling by scale formation. Fouling rates (-dJ/dt) were calculated for in-depth analysis of fouling behaviors. Results showed that severe fouling occurred during the treatment of high range produced water (TDS of 308 g/L). Application of antiscalant was not effective to retard scale formation. On the other hand, in-line filtration increased the induction time and reduced fouling.

Gas hydrates are crystalline solids in which gas molecules (guests) are trapped in water cavities (hosts) that are composed of hydrogen-bonded water molecules. During the formation of gas hydrates in seawater, the equilibria and kinetics are then affected by salinity. In this study, the effects of salinity on the equilibria of CO2 and R134-a gas hydrates has been investigated by tracing the changes of operating temperature and pressure. Increasing the salinity by 1.75% led to a drop in the equilibrium temperature of about 2 oC for CO2 gas hydrate and 0.38 oC for R-134a gas hydrate at constant equilibrium pressure; in other words, there were rises in the equilibrium pressure of about 1 bar and 0.25 bar at constant equilibrium temperature, respectively. The kinetics of gas hydrate formation have also been investigated by time-resolved in-situ Raman spectroscopy; the results demonstrate that the increase of salinity delayed the formation of both CO2 and R134-a gas hydrates. Therefore, various ions in seawater can play roles of inhibitors for gas hydrate formation in terms of both equilibrium and kinetics.

The Galactic center uniquely provides opportunities to resolve how star clusters form in neutral gas overdensities engulfed in a large-scale accretion flow. We have performed sensitive Green Bank 100m Telescope (GBT), Karl G. Jansky Very Large Array (JVLA), and Submillimeter Array (SMA) mapping observations of molecular gas and thermal dust emission surrounding the Galaxy's supermassive black hole (SMBH) Sgr A*. We resolved several molecular gas streams orbiting the center on ≳10 pc scales. Some of these gas streams appear connected to the well-known 2-4 pc scale molecular circumnuclear disk (CND). The CND may be the tidally trapped inner part of the large-scale accretion flow, which incorporates in ow via exterior gas filaments/arms, and ultimately feeds gas toward Sgr A*. Our high resolution GBT+JVLA NH3 images and SMA+JCMT 0.86 mm dust continuum image consistently reveal abundant dense molecular clumps in this region. These gas clumps are characterized by ≳100 times higher virial masses than the derived molecular gas masses based on 0.86 mm dust continuum emission. In addition, Class I CH3OH masers and some H2O masers are observed to be well associated with the dense clumps. We propose that the resolved gas clumps may be pressurized gas reservoirs for feeding the formation of 1-10 solar-mass stars. These sources may be the most promising candidates for ALMA to probe the process of high-mass star-formation in the Galactic center.

The emission of carbon dioxide from the burning of fossil fuels has been identified as a major contributor to green house emissions and subsequent global warming and climate changes. For these reasons, it is necessary to separate and recover CO2 gas. A new process based on gas hydrate crystallization is proposed for the CO2 separation/recovery of the gas mixture. In this study, gas hydrate from CO2/H2 gas mixtures was formed in a semi-batch stirred vessel at a constant pressure and temperature. This mixture is of interest to CO2 separation and recovery in Integrated Coal Gasification (IGCC) plants. The impact of tetrahydrofuran (THF) on hydrate formation from the CO2/H2 was observed. The addition of THF not only reduced the equilibrium formation conditions significantly but also helped ease the formation of hydrates. This study illustrates the concept and provides the basic operations of the separation/recovery of CO2 (pre-combustion capture) from a fuel gas (CO2/H2) mixture.