• Journal of the Korean Crystal Growth and Crystal Technology
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• v.5 no.2
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• pp.109-121
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• 1995

Reaction coulples of SiC with cobalt were annealed in an Ar/4 vol% $H_2$ atmosphere at temperatures between $950^{\circ}C$ and $1250^{\circ}C$for various times between 4 and 100 h. At temperatures above $950^{\circ}C$, solid state reactions lead to the formation of various silicides with carbon precipitates. The typical reaction layer sequence was $SiC/CoSi + C/CozSi + C/CozSi/CozSi + C/{\cdot\cdot\}/CO_2Si/CO$ in the reaction zone. The mechanism of the periodic band structure formation with the carbon precipitation behaviour was examined and discussed in terms of reaction kinetics and thermodynamic considerations. The growth of the reaction zone has a square root of time dependence. The reaction kinetics is proposed to estimate the effective reaction constant from the parabolic gowth of the reaction zone. The mechanical properties of the reaction zones were determined by the microhardness test.

• Journal of the Korean Ceramic Society
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• v.38 no.2
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• pp.158-165
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• 2001

고체산화물 연료전지용 밀봉재로서 전지 구성원과 열팽창계수가 유사하고 비젖음성 특성을 가지며 전지 작동온도에서 화학적 안정성을 갖는 밀봉유리를 개발하고자, BaO-Al$_2$O$_3$-La$_2$O$_3$-Ba$_2$O$_3$-SiO$_2$계 유리를 제조하여 조성 변화에 따른 열적 특성 변화와 접합후의 젖음성 및 반응성 등을 조사하였다. 유리망목 형성산화물인 B$_2$O$_3$와 SiO$_2$의 함량비 및 BaO의 망목 형성산화물(B$_2$O$_3$+SiO$_2$)에 대한 함량비 변화에 따른 유리의 열적 특성을 조사한 결과, 0.33~0.71의 B$_2$O$_3$/SiO$_2$함량비하에서 BaO/(B$_2$O$_3$+SiO$_2$)가 0.70일 때 유리의 열팽창계수는 106~111$\times$$10^{-7}$/K 이었으며 이때 연료전지 구성원인 YSZ(yttria stabilized zirconia)와의 열팽창 불일치(thermal expansion mismatch)가 가장 작았다. 또한 이러한 조성의 유리로부터 분말성형체를 제조하여 YSZ에 접합을 시도한 결과, 우수한 접합성 및 비젖음성을 확인할 수 있었으며, 800~8$50^{\circ}C$의 전지 작동온도에서 100시간까지 유지시에도 YSZ와의 계면반응이 일어나지 않음을 관찰할 수 있었다.

• Polymer(Korea)
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• v.30 no.1
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• pp.70-74
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• 2006

Plasticized cellulose diacetate(CDA) was prepared by homogenizing cellulose diacetate(CDA), triacetin(TA) and epoxidized soybean oil (ESO) in a high-speed mixer, then the CDA mixture was mixed with ramie fiber to produce a green composite material. In DMA analysis, the glass transition temperature of plasticized CDA and the composite was observed at $85\;^{\circ}C\;and\;140\;^{\circ}C$, respectively. A composite reinforced with alkali treated ramie fiber exhibited significantly higher mechanical properties, such as $15\;^{\circ}C$ increase in tensile strength as well as $41\;^{\circ}C$ increase in Young's modulus when compared with commercial polypropylene. In the SEM image analysis, much enhanced adhesion between plasticized CDA and alkali treated ramie fiber (AIRa) was observed.

• Polymer(Korea)
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• v.24 no.6
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• pp.820-828
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• 2000

In this study, biaxially oriented film process was used to improve barrier property of polypropylene (PP)/ethylene-vinyl alcohol copolymer (EVOH) blends by inducing a laminar morphology of the dispersed phase in the matrix phase. In order to examine the extent of deformation during melt extrusion process, the rheological properties of the resins were measured and the viscosity ratio of the dispersed phase to the continuous phase was determined. The effects of compatibilizer content, draw ratio, and draw temperature on the oxygen permeability and morphology of biaxially drawn blend films were studied. The laminar morphology of the EVOH phase with a larger area of thinner layer induced by biaxial orientation was found to result in a significant increase in oxygen barrier property of PP/EVOH (85/15) blends by about 10 times relative to the pure PP When both PP-g-MAH and ionomer were used as the compatibilizers, there existed an optimum level of compatibilizer content for obtaining improved barrier properties with a well developed laminar structure. In addition, higher draw ratio and draw temperature were found to be more favorable processing conditions in obtaining higher barrier blends.

• Journal of the Korea institute for structural maintenance and inspection
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• v.21 no.4
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• pp.110-115
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• 2017

This research was performed to investigate the mechanical performance of lightweight concrete including phase changing material(Low temperature PCM). Micro capsulised PCM consisted of wax type core and melamine based wall. Also, for PCM of one single kind, paraffin wax was inserted into Vermiculite and the surface was coated with melamine resin. Interfacial polymerization is based on the principle that macromolecule reaction takes place on the surfaces between 1-dodecanol(core material) and water (solvent) to form the wall material. Lightweight concrete has compressive strength of 10 MPa, tensile strength of 1.5 MPa, and oven dried density of 1.0kg/liter which included 10%, 20%, or 30% PCM by weight. To do so, this study fabricated light-weight foamed concrete ($1.0kg/m^3$) in pre-foaming method and mixed it with PCM micro capsule of 1-dodecanol and melamine to examine its physical properties.

• Composites Research
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• v.24 no.3
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• pp.1-5
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• 2011

Since the environmental problems and new stricter regulations are forcing the industries to introduce more ecological materials for their products, biodegradable materials have attracted increasing attention. Among these materials, Polylactic acid(PLA) is a promising candidate for its modulus, strength, chemical resistance. However, PLA could not be used for automobile industries for its low heat resistance and impact strength. In this study natural fibers were (jute fiber was) introduced as reinforcements in order to improve heat resistance and impact strength of PLA. Especially for improving the adhesion between PLA and jute, various surface treatments were tried. With each treatment, we verified that the impact strength of composite was improved. With annealing treatment, we found a remarkable increase of heat resistance of PLA composite.

• Applied Chemistry for Engineering
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• v.23 no.3
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• pp.339-343
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• 2012

Poly(olefin ketone) terpolymer having excellent mechanical properties was synthesized and composite materials of poly(olefin ketone) containing polyurethane/amino silane functionalized glass fibers were prepared. The compatibilities between the functionalized glass fiber and the polymer were characterized by observing the fracture surfaces of the composites using scanning electron microscopy (SEM). Mechanical properties of composites with different contents, diameters, lengths, and binders of glass fibers were also studied using universal testing machine (UTM). The introduction of suitably functionalized glass fiber into the poly(olefin ketone) produces composite materials having excellent mechanical properties and they are very promising alternative materials for the engineering plastic applications.

• Polymer(Korea)
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• v.35 no.2
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• pp.124-129
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• 2011

Wood plastic composites (WPCs) are attracting a lot of interest recently. In this study, wood flour/polyethylene (PE) composites panels comprised of a coupling agent and nanoclay were prepared by melt-blending followed by compression molding. Five maleic anhydride grafted polyethylene (MAPE) coupling agents were tested, and the best choice and its optimum content were determined. The mechanical properties of the WPCs were measured by UTM, and the thermal properties were measured by TGA, DMA, DSC, and TMA. Adding just a small amount (1 phr) of organoclay made the tensile and flexural strength and the crystallinity of the WPC somewhat increase and the storage modulus and dimensional stability of the WPC largely increase. SEM images showed that the coupling agent drastically improved wood flour/PE interfacial bonding. Selecting the best coupling agent optimized content and adding a small amount of organoclay resulted in a high performance wood flour/PE composite.

• Journal of the Korean Applied Science and Technology
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• v.6 no.1
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• pp.31-40
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• 1989

Five novel amphoteric surfactants of N-acyloxyethylcarboxybetaine series were synthesized via Schotten-Baumman reaction between five acid chlorides containing 10, 12, 14, 16 and 18 carbon atoms in their N-alkyl groups and dimethylaminoethanol to give the intermediate products, 2-dimethylaminoethylalkanoates(2). Quaternization of these products(2) was permitted to from 2-(acyloxyethyldimethylammonic)- acetates(3), whose structures were identified by elemental analysis, IR spectrophotometry and $^1Hnmr$ spectrometry. The yield of the final products was shown in the range of 77-80% based on the intermediate products. The surface tension of the aqueous solution of (3) was measured, and the critical micelle concentrations (cmc) were shown in the range of $2.1\;{\times}\;10^{-3}\;-\;3.3\;{\times}\;10^{-4}mol/l$, and the surface tension at cmc was 28-36 dyne/cm. Cmc was lowered gradually by the increment of the length of N-alkyl ester containing group. The isoelectric point was shown in the range of 4.44-5.20. It showed a tendency to lean toward the acidic site and its range was broadened as increase of the hydrophobic group length. A linear relationship between log cmc and the number of carbon atoms(N) in the hydrophobic alkyl chain was shown in the relative equation of log cmc=-1.75-0.1N, and the contribution rate of N on the standard free energy change in micellization, ${\bigtriangleup}({\bigtriangleup}G^{\circ}m)/{\bigtriangleup}N$, was calculated as -0.23 RT.

• Elastomers and Composites
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• v.40 no.3
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• pp.196-203
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• 2005

In this work, the engine oil resistant evaluation and breakdown analysis of room temperature vulcanizing silicone adhesives were performed through the surface properties, thermal stabilities, adhesive strength, and morphology measurements. As a result, the permeation of engine oil into adhesive specimens was carried out from surface to center in the specimens. And the oil content in the adhesive specimens was increased and the Si-O-Si bond of the adhesives was decomposed with increasing the aging time. The TGA results indicated that the thermal degradation was mainly occurred at under and surfaces of the specimens. The tensile strength, elongation, and adhesive strength of the adhesives were significantly decreased after the engine oil resistant tests, which could be attributed to the initial lose of adhesive properties resulting from the engine oil absorption and thermal aging. And the failure mode of the adhesive specimens was changed from cohesive failure to interfacial failure.