• Polymer(Korea)
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• v.29 no.6
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• pp.605-612
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• 2005

This study investigates the isothermal crystallization behaviors of polypropylene-polyethylene-(1-butene) terpolymer and the adiabatically expanded polyolefin structured foams. For this purpose, butane gas was used as a physical blowing agent. Avrami equation has been used to interpret theoretically the experimental results obtained by either DSC or polarized optical microscope. It is believed that elongation induced crystallization occurring during the adiabatic expansion process has resulted in an increase in crystallization rate, eventually leading to a faster growth rate of spherulites and an increase in the nucleation density. An analysis of the foam by SEM images showed that the structure of foam is uniform (below diameter 30 $\mu$m closed cell) In addition, the thermal conductivity and the compressive strength of the polyolefin structured foams was measured. The thermal conductivity of foamed resin with excellent insulation characteristics is reduced compared with unfoamed resin. The compressive strength is decreased with increase in the expansion ratio.

• Korean Journal of Materials Research
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• v.4 no.8
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• pp.847-854
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• 1994

An amorphous single phase and coexistent amorphous and hcp-Mg phases in Mg-Zn-Ce system were found to form in the composition ranges of 20 to 40% Zn, 0 to 10% Ce and 5 to 20% Zn, 0 to 5% Ce, respectively. A $Mg_{85}Zn_{12}Ce_{3}$ amorphous alloy containing nanoscale hcp-Mg particles was found to form either by melt spinning or by heat treatment of melt -spun ribbon. The particle size of the hcp-Mg phase can be controlled in the range of 4 to 20 nm. The mixed phase alloy prepared thus has a good bending ductility and exhibits high ultimate tensile strength($\sigma_{B}$) ranging from 670 to 930 MPa and fracture elongation($\varepsilon_{f}$) of 5.2 to 2.0%. The highest specific strength($\sigma_{B}$/density =$\sigma_{s}$)$3.6 \times 10^5N \cdot m/kg$. It should be noted that the highest values of flB, US and ？1 are considerably higher than those (690MPa,$2.5 \times 10^5N \cdot m/kg$and 2.5%) for amorphous Mg-Zn-Ce alloys. The increase of the mechanical strengths by the formation of the mixed phase structure is presumably due to a dispersion hardening of the hcp supersaturated solution which has the hardness higher than that of the amorphous phase with the same composition.

• Nuclear Engineering and Technology
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• v.18 no.3
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• pp.218-227
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• 1986

Studies were conducted to determine the extent of oxidation and same of the mechanical property changes of Zircaloy-4 fuel cladding after it was exposed to hot steam environment. The purpose of these tests was to provide some informations on the embrittlement behavior of CANDU type fuel cladding, which could be experienced under the loss-of-coolant accident conditions. The Zircaloy fuel cladding tubes were exposed in a steam environment at the temperature of 90$0^{\circ}C$, 1,00$0^{\circ}C$. The growth of the ZrO$_2$ layer combined with an oxygen rich $\alpha$-phase layer into the Zircaloy tube material was found as a function of time t and temperature of steam exposure, E=1.1√Dt+0.002 where D is a temperature dependent diffusion coefficient. The tensile strength of the specimens exposed for a short period increased but decreased continuously with further exposure. The circumferential elongation was drastically changed with the exposure time while the hoop strength did't decrease greatly. The X-ray measurement of preferred orientation of the Zircaloy tube material indicated that grains in the as received tube were oriented such that the poles of the basal (0001) planes were predominantly radial, while the poles of the basal plane in the tube materials heattreated at 1,00$0^{\circ}C$ were oriented tangentially. It appears that this reoriented texture may contribute to lessening the decrease of the hoop strength of the heat treated Zircaloy tube material.

• Korean Journal of Materials Research
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• v.7 no.2
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• pp.129-135
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• 1997

This study has investigated the effects of aging treatment on thc nlechanical propcrries of blg-iiAl-x%nix - 0.1.2) alloys fabricated by the squeeze castmg process. The microstructurcs of as-squeeze cast were composed of pro eurectic $\alpha$ magnesium solid solution, super saturated $\alpha$ solid solution and $\beta(Mg_{17}AI_{12}$) compund. Agcd at both $200^{\circ}C$ and $240^{\circ}C$, Mg--6AixZn alloys showed the peak hardness due to the formation of $\beta(Mg_{17}AI_{12}$) precipitates. The tiiscontinuous precipitates of the lamella r\.pe are predominant at $200^{\circ}C$ aging tredrment. tvhilc. the finely dispersed continu ous precipitates were major type at $240^{\circ}C$ treatment. Mg-- GAI-xZn a1loi.s fabricated hy the squeeze casting process had the hetter combination of tensile strength and elongation compared to the conventionally cast alloys. As increascci zinc: contents. the tensile strength was increased 11y the soiid solutirin strengthening effect of zinc,.

• Journal of Adhesion and Interface
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• v.13 no.3
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• pp.131-136
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• 2012

In this study, commercial poly(vinyl alcohol) (PVA) film was dyed with reactive dichroic dyes under mild conditions using organic solvents in stead of strong basic aqueous solution. After drawing of 500% of this PVA film, the polarizing efficiency and the single piece transmittance were measured. The degree of saponification of the commercialized PVA film was determined by using NMR and FT-IR spectromety. The commercial PVA film, with ca. 100% of the degree of saponification determined by NMR spectrometry, was dyed with the reactive dichroic dyes, which have 3,5-dichloro-2,4,6-triazine moiety. As a result, we found that the PVA film dyed with the reactive congo red showed relatively good polarization efficiency, and the PVA film dyed with the reactive direct black 22 exhibited relatively good single piece transmittance.

• Journal of Korean Society of Steel Construction
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• v.22 no.5
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• pp.399-409
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• 2010

Steel structures are threatened to reduce load-carrying capacity as the cross section is decreased by corrosion. However, there has been no method in definitely evaluating residual load-carrying capacity and the effect of corrosion to the load-carrying capacity of steel. This study evaluated tensile residual load-carrying capacity of corroded steel plates by using tensile tests of specimens, which were selected from the web of temporary structure's main beam. After the surface shapes were measured and tensile tests were examined, the rust of 21 corroded specimens was, first of all, removed using a chemical method. From the tensile test result, which of reference specimens that was picked off at the flange of the same main 13-mm-thick beam and corroded specimens were based, surface geometry and correlation with the reduction of corroded thickness and strain, yield strength or tensile strength was established as constant numbers. Effective thickness of corroded steel with irregular cross sections could be calculated using average residual thickness and standard deviation. The irregular cross sections could be the evaluated tensile strength that is equalized to non-corroded uniform steel's regardless of corrosion. Also, reasonable measuring intervals of residual thickness could be proposed by using this result to apply for executive work.

• Journal of the Korean Electrochemical Society
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• v.17 no.1
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• pp.7-12
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• 2014

There is increasing demand on the reducing the weight and the volume of the major components in lithium secondary battery to improve energy density. Separator not only provides pathway for lithium ion movement but also prevents direct contact between anode and cathode. Herein we fabricated polyethylene separator by varying biaxial stretching ratio to obtain membrane thickness of 16, 12, and $9{\mu}m$. Mechanical and thermal properties of the separator with different thickness were investigated. Also rate capability and charge-discharge cycle property up to 500 cycles were studied using coin type full-cell with $LiCoO_2$ and graphite as a cathode and an anode, respectively. All the cells using separator with different thickness demonstrated excellent capacity retention after 500cycles (around 80%). Considering the rate capability, cell using separator with thickness of $9{\mu}m$ showed best performance. Interestingly, separator thickness of $9{\mu}m$ was more resistant to heat contraction compared to that of $16{\mu}m$ separator.

• Membrane Journal
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• v.28 no.2
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• pp.83-89
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• 2018

Hydrophobic porous PVDF hollow fiber membranes for Membrane Distillation (MD) were fabricated by a combination of thermally induced phase separation (TIPS) and stretching. The purpose of this study is to investigate the shape and operating conditions of the module and the effect of piping size on parallel connection. In the optimization experiment of the vacuum membrane distillation module, the flux decreased as the packing density and length of the membrane in the module increased. When the module was connected vertically, it was confirmed that the nearest to the inlet of the vacuum port was the highest flux. In selecting the size of the header pipe of the module, it was confirmed that the maximum flux is shown when the inner diameter area of the hollow fiber membrane and the inner diameter area of the header pipe are the same. Also, it is necessary to find the optimal linear velocity because the higher the linear velocity in the module, the higher the flux, but the pressure acting on the module also increases proportionally.

• Food Science and Preservation
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• v.21 no.6
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• pp.767-775
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• 2014

The shelf-life of fresh mushrooms is notably limited because their browning, texture change, and decay are too fast after immediately harvest. Especially, the best management for extending golden needle mushroom's shelf-life is modified atmosphere packaging under pressure vacuum at cold storage. In this study, three types of films, $20{\mu}m$ polyethylene+polypropylene (PE+PP), oriented polypropylene (OPP), and low density polyethylene (LDPE) were tested to extend the shelf-life of golden needle mushrooms. Mushrooms were packed under pressure vacuum and stored at $10^{\circ}C$ for 2 weeks. The golden mushrooms in LDPE film as a commercial packaging, were highly perishable and immediately proceed deterioration as browning, elongation, fluctuation of respiratory quotient (RQ) and softening within 7 days after packaging. On the other hand, the mushrooms in OPP and PE+PP film shown that shelf-life were extend to 14 days from 7 days, causing delay breakup of vacuum and maintenance of color, length, and RQ during storage. The breakup of vacuum in PE+PP film was faster few days than OPP film packaging. This present study indicated that the golden needle mushrooms by OPP packaging under pressure vacuum treatment might be extended the shelf-life until approximately 14 days during cold storage.

• KOREAN JOURNAL OF PACKAGING SCIENCE & TECHNOLOGY
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• v.21 no.2
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• pp.55-60
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• 2015

Packaging of export cut lilies reduces physical damage during distribution like dropping, shock, vibration, compression and serves to protect from necrosis, microbial contamination and decomposition. Study on which packaging materials must be selected is necessary because it serves to direct effect maintaining quality and the degree of freshness. newspaper, perforated OPP film, Oriented Nylon film (ON), punched OPP film, OPP films are used in this study. Plant senescence of lilies was happened rapidly during storage at $25^{\circ}C$ rather than at $5^{\circ}C$. Also, water absorption, fresh weight at during storage $25^{\circ}C$ rather than at $5^{\circ}C$ In addition, fresh weight of lilies storage at $25^{\circ}C$ appears higher than at $5^{\circ}C$ all of the packaging materials except OPP because water absorption of lily storage at $5^{\circ}C$ appears higher than at $25^{\circ}C$, thereby suppressing the fresh weight reducing Also, effect on biological activity of lilies from shape of packaging material appears higher during storage at $5^{\circ}C$ than at $25^{\circ}C$. Compared with each packaging materials, newspaper packaging is the smallest effect on changes in biological activity of cut lilies during storage. Thus, the results demonstrate that flowering date are affected mainly by the storage temperature rather than packaging materials.