• Journal of Surface Science and Engineering
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• v.32 no.1
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• pp.49-60
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• 1999

The protective oxide scales and coatings formed on high temperature materials must be preserved in high temperature atmosphere. And the thermal stresses induced by thermal cycling and the growth stresses by the formation of oxide scales can cause the loss of adherence and spalling of the oxide scales and coated layers. Among the coating processes Al diffusion coating is favored due to thermochemical stability and superior adherence in an hostile atmosphere. In this study, protective oxide forming element, Al was coated on Ni, Inconel 600 and 690 by diffusion coating process varying coating temperature and time. And the surface stability and adherence of oxide scales formed on those Al diffusion coated materials were evaluated by thermal cycling test. Al diffusion coated specimens showed superior cyclic oxidation resistance compared to bare ones and specimens coated for longer period had better cyclic oxidation resistance, due to the abundant amount of Al in the coated layer. Meanwhile Al diffusion coated Inconel 600 and 690 showed improved cyclic oxidation resistance by the effect of Al in the coated layer and Cr in the substrate. Comparing both Al diffusion coated Inconel 600 and 690, Al diffusion coated Inconel 690 maintained better adhesion between coated layer and substrate by virtue of the bridging effect resulting from the segregation of Cr in the interdiffusion zone.

• Atmosphere
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• v.28 no.4
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• pp.383-392
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• 2018

This study investigates synoptic characteristics of cold surges over South Korea during winter season (December-February). A total of 63 cold events are selected by quantile regression analysis using daily mean temperature observations from 11 KMA stations for 38 years (1979/80-2016/17). Large-scale pressure pattern during the cold surges is well characterized by high over Siberia and low over Aleutian regions, which elucidates cold advection over the Korean peninsula. However, the large-scale pattern cannot successfully explain the observed sudden decrease of temperature during the cold surges. Composite analyses reveal that a synoptic-scale cyclone developing over the northern Japan is a key feature that significantly contribute to the enhancement of cold advection by increasing pressure gradient over the Korean peninsula. Enhanced sensible and latent heat fluxes are observed over the southern ocean of Korea and Japan during the cold surges due to temperature and humidity differences between the near surface and the lower atmosphere over the ocean. The evaporated water vapor transported toward the center of the surface cyclone and condenses in the lower-to-middle troposphere. The released energy likely promotes the development of the surface cyclone by inducing positive PV near the surface of the heating region.

• Journal of Ceramic Processing Research
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• v.13 no.spc1
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• pp.140-144
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• 2012

Ga-doped ZnO (GZO) was a limit of application on the photovoltaic devices such as CIGS, CdTe and DSSC requiring high process temperature, because it's electrical resistivity is unstable above 300 ℃ at atmosphere. Therefore, ZTO (zinc tin oxide) was introduced in order to improve permeability and thermal stability of GZO film. The resistivity of GZO (300 nm) single layer increased remarkably from 1.8 × 10-3Ωcm to 5.5 × 10-1Ωcm, when GZO was post-annealed at 400 ℃ in air atmosphere. In the case of the ZTO (150 nm)/GZO (150 nm) double layer, resistivity showed relatively small change from 3.1 × 10-3Ωcm (RT) to 1.2 × 10-2Ωcm (400 ℃), which showed good agreement with change of carrier density. This result means that ZTO upper layer act as a barrier for oxygen at high temperature. Also ZTO (150 nm)/GZO (150 nm) double layer showed lower WVTR compared to GZO (300 nm) single layer. Because ZTO has lower WVTR compared to GZO, ZTO thin film acts as a barrier by preventing oxygen and water molecules to penetrate on top of GZO thin film.

• KOREAN JOURNAL OF PACKAGING SCIENCE & TECHNOLOGY
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• v.19 no.1
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• pp.7-10
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• 2013

A packaging system integrated in primary and secondary packages to deliver consumers fresh peach in the produce supply chain was designed and its effectiveness on quality preservation was tested. The master packaging system was designed to contain 6 individual polypropylene film (PP, $30{\mu}m$ thickness) packages of 300 g peach fruit inside $35{\mu}m$ thick low density polyethylene (LDPE) bag located in a corrugated paperboard box. As a variable to attain the desired package atmosphere around the fruit during cold storage and subsequent retail display at higher temperature, different numbers (1, 3 and 7) of microperforations in $59{\mu}m$ diameter were tested on the individual PP packages. As control treatment, six fruits were placed without wrapping in a corrugated paperboard box. During the storage at $5^{\circ}C$, the control and individual packages were periodically separated from the box or master package, moved to the simulated retail shelf conditions of $20^{\circ}C$ and then stored for 3 more days with package atmosphere and fruit quality being measured. The package with 7 microperforations was the best in the ability to attain beneficial MA of 6~10% $O_2$ and 11~19% $CO_2$ around the fruit during the chilled storage at $5^{\circ}C$ and simulated retail display at $20^{\circ}C$. Packages with smaller number of microperforations resulted in anaerobic atmosphere at the low temperature storage and/or the subsequent high temperature display. Compared to control, all the treatments with master packaging system gave better retention of fruit firmness with significantly less weight loss.

• Proceedings of the Korean Vacuum Society Conference
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• 2015.08a
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• pp.169.2-169.2
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• 2015

$VO_2$ is a well-known a metal-to-insulator-transition (MIT) material, accompanied with a first order structural phase transition near room temperature. Because of the structural phase transition and the MIT occur near a same temperature, there is an ongoing argument whether the MIT is induced by the structural phase transition. $VO_2$ exhibits a relatively weak anti-oxidization ability and can be oxidized to higher-valence oxides (e.g., $V_4$ $O_7$ or $V_2$ $O_5$) when annealed at a high temperature in an oxygen-rich atmosphere. We fabricated $VO_2$ films on $Al_2$ $O_3$ (0001) substrates using a DC magnetron sputtering deposition process with carefully control the $O_2$ percentage in an atmosphere. X-ray diffraction measurements from the films showed only (0l0) peaks with no extra peaks, indicating b-oriented films. The temperature-dependent local structural properties of $VO_2$ films were investigated by using in-situ X-ray absorption fine structure (XAFS) measurements at the V K edge. XAFS revealed that the structural phase transition was occurred nearly $70^{\circ}C$ for heating process and reproducible. Resistance measurements as a function of temperature (R-T) demonstrated that the resistance of $VO_2$ films was changed by a factor of 4 near $75^{\circ}C$ which was higher than $68^{\circ}C$ reported from a $VO_2$ bulk. We will discuss the MIT of $VO_2$ films, comparing with the local structural properties determined by XAFS measurements.

• Proceedings of KOSOMES biannual meeting
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• 2003.11a
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• pp.181-185
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• 2003

the effect if atmosphere is more important in the West sea of Korea than in other seas because of shallow water and heat storage if the water. The serial oceanographic observation data and coastal station data from NFRID, and the atmosphere data from KMA were used in order to find out the relationship between them The highest water temperature, salinity and weather factor were recorded in Aug, and the lowest of them in Feb. As the water deepens, the maximum time leg in water temperature and the minimum time leg in salinity. Water temperature have the maximum in Oct, the minimum in Apr at 75m of the 311-07 station with 100m depth water temperature (WT)-air temperature, WT-precipitation (Preci.) and salinity (Sal)-wind speed (WS) were in direct proportion, but WT-WS, Sal-AT and Sal-Preci in inverse proportion Water temperature and salinity I-ave time leg at the same depth the maximum had more the delay of $2\~4$ months at a depth if 20 meters than at the surface in all stations except for salinity at 307-05.

• Journal of Powder Materials
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• v.4 no.3
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• pp.170-178
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• 1997

An investigation was performed to apply the M3/2 grade high speed steel for metal injection molding using both prealloyed and elementally blended powders. The injected samples were subjected to a debinding step in $H_2/N_2$ gas atmosphere at a ratio that affected the carbon content of the material. The carbon content ranged from 1.4wt.% to 1.43wt%. with increasing $H_2$ content up to 80% $H_2$ in $H_2/N_2$ atmosphere for the prealloyed powders. The carbon contents of the elementally blended powders exhibited 1.44wt.% and 1.62wt.% at 10% $H_2/N_2$ and 20% $H_2/N_2$ gas, respectively. This level decreased to 0.17wt.% upon increasing the $H_2$ content. The sintered density of both powders increased rapidly as the temperature reached the liquid phase forming temperature. After forming the liquid phase, the density rapidly increased to the optimum sintering temperature for the prealloyed powders, whereas the density of mixed elemental powders goes up slowly to the optimum sintering temperature. The optimum sintering temperature and density are 126$0^{\circ}C$ and 97.3% for the prealloyed powders and 128$0^{\circ}C$ and 96.9% for the elementally blended powders, respectively. The microstructure of the specimen at the optimum sintering temperature consisted of fine grains with primary carbides of MC and $M_6C$ type for the prealloyed powders. The elementally blended powders exhibited coarse grains with eutectic carbides of MC, $M_2C$ and $M_6C$ type.

• Composites Research
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• v.35 no.4
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• pp.242-247
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• 2022

This study has a different direction from the existing technology of applying recycled carbon fiber obtained by recycling waste CFRP to CFRP again. A study was conducted to utilize recycled carbon fiber as a raw material for manufacturing a carbon/carbon (C/C) composite material comprising carbon as a matrix. First, it was attempted to recycle a commonly used epoxy resin composite material through a thermal decomposition process. By applying the newly proposed oxidation-inert atmosphere conversion technology to the pyrolysis process, the residual carbon rate of 1~2% was improved to 19%. Through this, the possibility of manufacturing C/C composite materials utilizing epoxy resin was confirmed. However, in the case of carbon obtained by the oxidation-inert atmosphere controlled pyrolysis process, the degree of oxygen bonding is high, so further improvement studies are needed. In addition, short-fiber C/C composite material specimens were prepared through the crushing and disintegrating processes after thermal decomposition of waste CFRP, and the optimum process conditions were derived through the evaluation of mechanical properties.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.12 no.5
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• pp.170-175
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• 2013

For this study, the domestically developed bootstrap reservoir of the aircraft is set up in accordance with the temperature and humidity conditions depicted on the qualification test, and the variation in the internal pressure of the bootstrap reservoir of the aircraft is examined. The study shows that the bootstrap reservoir has less variation in the internal pressure at room temperature than at low temperature($-40^{\circ}C$). As a result, the internal pressure can be maintained stably when the temperature of working fluid in the bootstrap reservoir and the atmosphere environment is over room temperature($25^{\circ}C$). Therefore the keeping of temperature above room temperature is very important to operate the bootstrap reservoir of the aircraft properly.

• Journal of the Korean Society for Railway
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• v.9 no.6 s.37
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• pp.695-700
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• 2006

This study investigates the effects of the material properties and the fatigue behavior in the SM490A material specimens due to the low-temperature atmosphere. In the fatigue behavior, the low-temperature affects the fatigue life. As the temperature get low, the fatigue limit increase, also As the yield strength and the tensile strength increase, the impact absorbed energy decrease. The difference of fatigue lift represents to normal distribution and it is larger between the room temperature and the low temperature, but in the result of the cumulative density function, the effect of temperature is not too large on it.