• Journal of the Microelectronics and Packaging Society
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• v.22 no.2
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• pp.21-26
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• 2015

Mesoporous ceramic materials were applied in various fields such as adsorbent and gas sensor because of low thermal conductivity and high specific surface area properties. This structure could be divided into open-pore structure and closed-pore structure. Although closed-pore structure mesoporous ceramic materials have higher mechanical property than open-pore structure, it has a restriction on the application because the increase of specific surface area is limited. So, in this work, specific surface area of closed-pore structure $TiO_2$ was increased by anneal time. As increased annealing time, crystallization and grain growth of $TiO_2$ skeleton structured material in mesoporous structure induced a collapse and agglomeration of pores. Through this pore structural change, pore connectivity and specific surface area could be enhanced. After anneal for 24 hrs, porosity was decreased from 36.3% to 34.1%, but specific surface area was increased from $48m^2/g$ to $156m^2/g$. CO gas sensitivity was also increased by about 7.4 times due to an increase of specific surface area.

• Composites Research
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• v.37 no.4
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• pp.337-342
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• 2024

Thermosetting composite materials are applied in mobility and structural applications due to their high mechanical strength and thermal properties. Nevertheless, these materials are difficult to recycle or reprocess. Therefore, research is currently underway to introduce vitrimer as a solution to this challenge. In this study, to enable reprocessing and self-healing of structural epoxy, an epoxy containing disulfide bonds was synthesized and added. The addition of disulfide epoxy resulted in a decrease in tensile strength and Young's modulus, but an increase in tensile strain. Analysis of the fracture surface after tensile testing revealed that the addition of disulfide epoxy imparted characteristics of ductile materials. This is attributed to the structure of disulfide epoxy, which primarily involves alkyl chains and bond exchange occurring at the disulfide bonds. It was confirmed that the addition of disulfide epoxy enables self-healing through reprocessing. While reprocessing was not possible with disulfide epoxy content below 17 wt%, it was feasible up to four times with content above 0.25 wt%. This study is expected to contribute to extending the lifespan of structural composites and enhancing recycling possibilities through reprocessing.

• Journal of Korean Tunnelling and Underground Space Association
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• v.20 no.2
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• pp.255-268
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• 2018

Subsea tunnel can be highly vulnerable to seawater intrusion due to unexpected high-water pressure during construction. An artificial ground freezing (AGF) will be a promising alternative to conventional reinforcement or water-tightening technology under high-water pressure conditions. In this study, the freezing energy and required time was calculated by the theoretical model of the heat flow to estimate the total amount of refrigerant required for the artificial ground freezing. A lab-scale freezing chamber was devised to investigate changes in the thermal and mechanical properties of sandy soil corresponding to the variation of the salinity and water pressure. The freezing time was measured with different conditions during the chamber freezing tests. Its validity was evaluated by comparing the results between the freezing chamber experiment and the numerical analysis. In particular, the freezing time showed no significant difference between the theoretical model and the numerical analysis. The amount of refrigerant for artificial ground freezing was estimated from the numerical analysis and the freezing efficiency obtained from the chamber test. In addition, the energy ratio for maintaining frozen status was calculated by the proposed formula. It is believed that the energy ratio for freezing will depend on the depth of rock cover in the subsea tunnels and the water temperature on the sea floor.

• Polymer(Korea)
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• v.25 no.1
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• pp.78-89
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• 2001

Morphological changes of unsaturated polyester/polyvinylacetate semi-IPN were studied while the phase separation and the cure reaction occurred in a competing fashion. The light scattering and thermal analysis techniques were used to investigate the phase separation rates and mechanical properties resultantly induced by molecular diffusion of thermoplastic polymer during the curing process of thermosetting polymer. The reaction activation energy was calculated by using Flynn-Wall method and the semi-IPN structure exhibited various phase-separation morphological characteristics. When PVAc composition was 10 wt%, the phase separation was not observed during the curing reaction, but the phase separation occurred in a similar fashion to nucleation and growth(NG) mechanism at room temperature. On the other hand, when PVAc composition was over 11.65 wt%, the phase separation was generated in the middle of the curing process. Consequently, the phase separation seemed to influence the curing reaction rate, which was also supported by the changing activation energy with conversion and PVAc composition. Finally, the total scattered intensity was measured at various temperature, and subsequently the diffusion rates of phase separation R(${\beta}m$) were evaluated.

• Journal of the Korean Wood Science and Technology
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• v.39 no.3
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• pp.221-229
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• 2011

Due to the increase of oil price and the environmental issue such as the emission of volatile organic compounds, the necessity for developing alternative resins of petroleum-based adhesive resins, which have extensively been used for the manufacture of wood-based products, has been speculation since the early 1990. In our study, rapeseed flour (RSF), which is the by-product of bio-diesel produced from rapeseed, were hydrolyzed by enzymes. As a crosslinking agents of the RSF hydrolyzates, phenol-formaldehyde prepolymers (PF) were prepared. The RSF hydrolyzates and PF were mixed to complete the formulation of RSF-based adhesive resins, and the resins were applied to make the laminated veneer lumber (LVL). The physical and mechanical properties of the LVL were measured to examine whether RSF can be used as raw materials of adhesive resins for the fabrication of LVL or not. The average moisture content and soaking delamination rate of the LVL bonded with RSF-based adhesive resins exceeded the minimum requirement of KS standard. Moreover, thermal analysis of the RSF-based resins showed similar tendencies except for the RSF-based adhesive resins formulated with pectinase-hydrolyzed RSF. The bending strengths of the LVL were higher than that of the LVL made with commercial PF resins. These results showed the potential of RSF as a raw material of alternative adhesives for the production of LVL. Further works on the optimal conditions of RSF hydrolysis and spreading characteristics for RSF-based adhesive resins is required to improve the adhesive performance of RSF-based resins.

• Journal of the Korean Wood Science and Technology
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• v.42 no.6
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• pp.691-699
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• 2014

In order to improve the dimensional stability and durability of wood, this study attempted to impregnate bismuth (Bi) - tin (Sn) alloy metal with low melting temperature into solid woods of three species such as radiata pine, red oak and white oak, and investigated to determine an optimum condition of manufacturing the metal alloy-wood composites with natural wood grains. These Bi-Sn alloys were chosen for this study because they were harmless to human and melting at low temperatures. The composites resulted in high dimensional stability and low thickness swelling, and also showed much improved performance such as high bending strength, high hardness, high electric conductivity, and high thermal conductivity as floor materials. A proper impregnating condition of all specimens was determined as 10 minutes of the preliminary vacuum time, and $185^{\circ}C$ of the heating temperature. The proper processing condition for radiata pine wood was 2.5 minutes of the pressuring time at the pressure of $10kgf/cm^2$. For red oak wood, 10 minutes of the pressuring time at the pressure of $30kgf/cm^2$ were the proper condition. The proper manufacture conditions for white oak wood was determined as 10 minutes of the pressuring time at the pressure of $50kgf/cm^2$.

• Journal of the Korean Vacuum Society
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• v.20 no.2
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• pp.155-163
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• 2011

Carbon nanotubes (CNT) have been attracted much attention since they have been expected to be used in various areas by virtue of their outstanding physical, electrical, and chemical properties. In order to make full use of their prominent electric conductivity in some areas such as electron emission sources, device interconnects, and electrodes in energy storage devices, direct growth of CNT with vertical alignment is definitely beneficial issue because they can maintain mechanical stability and high conductivity at the interface between substrates. Here, we report direct growth of vertically aligned CNT (VCNT) on Cu foils using thermal chemical vapor deposition and characterize the field emission property of the VCNT. The VCNT's height was controlled by changing the growth temperature, growth time, and catalytic layer thickness. Optimum growth condition was found to be $800^{\circ}C$ for 20 min with acetylene and hydrogen mixtures on Fe catalytic layer of 1 nm thick. The diameter of VCNT grown was smaller than that of usual multi walled CNT. Based on the result of field emission characterization, we concluded that the VCNT on Cu foils can be useful in various potential applications where high conductivity through the interface between CNT and substrate is required.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.16 no.2
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• pp.243-260
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• 2018

A literature review on the effects of high temperature and radiation on radiation shielding concrete in Spent Fuel Dry Storage is presented in this study with a focus on concrete degradation. The general threshold is $95^{\circ}C$ for preventing long-term degradation from high temperature, and it is suggested that the temperature gradient should be less than $60^{\circ}C$ to avoid crack generation in concrete structures. The amount of damage depends on the characteristics of the concrete mixture, and increases with the temperature and exposure time. The tensile strength of concrete is more susceptible than the compressive strength to degradation due to high temperature. Nuclear heating from radiation can be neglected under an incident energy flux density of $10^{10}MeV{\cdot}cm^{-2}{\cdot}s^{-1}$. Neutron radiation of >$10^{19}n{\cdot}cm^{-2}$ or an integrated dose of gamma radiation exceeding $10^{10}$ rads can cause a reduction in the compressive and tensile strengths and the elastic moduli. When concrete is highly irradiated, changes in the mechanical properties are primarily caused by variation in water content resulting from high temperature, volume expansion, and crack generation. It is necessary to fully utilize previous research for effective technology development and licensing of a Korean dry storage system. This study can serve as important baseline data for developing domestic technology with regard to concrete casks of an SF (Spent Fuel) dry storage system.

• Journal of the Korean Ceramic Society
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• v.34 no.1
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• pp.102-108
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• 1997

ZrO2 powders stabilized with Y2O3 and CeO2 of various compositions were prepared by the coprecipitation of water-soluble ZrOCl2.8H2O, YCl3.6H2O and Ce(NO3)3.6H2O, and their compacts were pressurelessly sintered at 1400 and 150$0^{\circ}C$ for 2hrs in air. 2mol% Y2O3-ZrO3 showed the most superior strength (1003MPa) and microhardness (12.6GPa), while 10 mol%CeO2-ZrO2 had the hightest toughness (13.3 MPa.m1/2) after sintering at 140$0^{\circ}C$. The addition of Y2O3 into Y2O3-ZrO3 decreased mean grain size and increased strength and hardness but decrease toughness. On the other hand, the addition of CeO2 into Y2O3-ZrO2 enhanced the stability of tetragonal phase during low-temperature aging for a long time under hydrothermal atmosphere.

• KOREAN JOURNAL OF PACKAGING SCIENCE & TECHNOLOGY
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• v.23 no.2
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• pp.61-66
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• 2017

Poly lactic acid(PLA) and poly butylene adipate-co-terephthalate(PBAT) film was prepared using a twin extruder. PLA (25%) and PBAT (75%) were mixed with various ratio of chain extenders, such as $Joncryl^{(R)}$ and hexamethylene diisocyanate(HDI) to improve the mechanical and thermal properties of produced bio composite films. Tensile strengths of films were steadily increased with increasing ratio of chain extender. The tensile strength of control films was about 25 MPa, and the tensile strength of films with combined chain extenders was above 40 MPa. The films with $Joncryl^{(R)}$ resulted in improved tensile strength, while the film with HDI alone showed improved percent elongation at break. By adding chain extenders into PLA/PBAT resin, the cold crystallization temperature (Tcc) and decomposition temperature (Td) of the produced bio composite films increased. It revealed that the addition of two types of chain extenders was efficient way to get PLA/PBAT film with improved strength and elongation.