• KSCE Journal of Civil and Environmental Engineering Research
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• v.43 no.5
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• pp.555-566
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• 2023

In this study, a composite phase change material (CPCM) produced using the SOL-GEL technique was developed as a thermal energy storage medium for low-temperature applications. Tetradecane and activated carbon (AC) were used as the core and supporting materials, respectively. The tetradecane phase change material (PCM) was impregnated into the porous structure of AC using the vacuum impregnation method, and a thin layer of silica gel was coated on the prepared composite using the SOL-GEL process, where tetraethyl orthosilicate (TEOS) was used as the silica source. The thermal performance of the CPCM was analysed using differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). DSC results showed that the pure tetradecane PCM had melting and freezing temperatures of 6.4℃ and 1.3℃ and corresponding enthalpies 226 J/g and 223.8 J/g, respectively. The CPCM exhibited enthalpy of 32.98 J/g and 27.7 J/g during the melting and freezing processes at 7.1℃ and 2.4℃, respectively. TGA test results revealed that the AC is thermally stable up to 500℃, which is much higher than the decomposition temperature of the pure tetradecane, which is around 120℃. Moreover, in the case of AC-PCM and CPCM thermal degradation started at 80℃ and 100℃, respectively. The chemical stability of the CPCM was studied using Fourier-transform infrared (FT-IR) spectroscopy, and the results confirmed that the developed composite is chemically stable. Finally, the surface morphology of the AC and CPCM was analysed using scanning electron microscopy (SEM), which confirmed the presence of a thin layer of silica gel on the AC surface after the SOL-GEL process.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.11a
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• pp.224-224
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• 2009

본 연구는 여러종류의 에폭시 나노콤포지트의 절연파괴 강도에 대한 와이블 특성을 연구하였다. 여러 종류 나노콤포지트는 나노입자 형상의 변화 즉, 층상실리케이트(Layered Silicate)와 구상 입자(SiO2)의 충진함량변화를 통한 절연파괴특성을 연구하였다. 나노+마이크로입자에대한 두 개의 체적비를 통한 멀티-나노복합물을 구현하였고, 그 절연파괴 특성의 결과와 기계적특성으로 굴곡강도특성을 Weibull Plot을 통하여 분석하였다. 순수한 나노콤포지트보다 멀티나노콤포지트가 기계적특성에서 월등하게 나타내었고, 절연파괴강도역시 형상파리미터가 대단히 큰 결과를 얻었다.

• Journal of the Korean Ceramic Society
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• v.47 no.3
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• pp.216-222
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• 2010

Portland cement has been restricted in applications to ecological area because of its environmental harmfulness and the $CO_2$ emission during a production process. Geopolymer materials attract some attention as an inorganic binder due to their superior mechanical and eco-friendly properties. In this study, geopolymer-based cement was prepared by using aluminosilicate minerals (flyash, meta-kaolin) with alkaline-activators and its compressive strength with concentration of alkaline-activators was investigated. Aluminosilicate-based geopolymers were obtained by mixing aluminosilicate minerals, alkaline solution (NaOH or KOH with different concentration) and water-glass under the vigorous stirring for 20 min. Compressive strength after curing at $30^{\circ}C$ for 3 days increased with the concentration of alkaline-activator due to the enhanced polymerization of the aluminosilicate materials and dense microstructure. Aluminosilicate-based geopolymer cement using KOH as an alkaline-activator showed high compressive strength compared with NaOH activator. In addition, geopolymer cement using fly-ash as a raw material showed higher compressive strength than that of meta-kaolin.

• Polymer(Korea)
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• v.26 no.3
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• pp.375-380
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• 2002

Diamines (p-phenylenediamine , m-phenylenediamine , and n-hexamethylenediamine) were intercalated into sodium montmorillonite for the further reaction with the anhydride end groups of polyamic acid. The anhydride terminated polyamic acid was synthesized using a mole ratio of 4,4'-oxydianilline : 1,2,4,5-benzene tetracarboxylic dianhydride = 1.50 : 1.53. The modified montmorillonite was reacted with polyamic acid terminated with anhydride group in N-methyl-2-pyrrolidone (polyamic acid/clay nanocomposite). After imidization, thin films of the polyimide/clay nanocomposite were prepared. From the results of XRD and TEM, we found that mono layered silicates were dispersed in polyimide matrix and those resultants were exfoliated nanocomposites. Mechanical properties of exfoliated polyimide nanocomposite were better than both those of pure polyimide and those of intercalated polyimide nanocomposite.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.5 no.3
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• pp.291-298
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• 1995

Abstract The growth and dissolution behaviour of reaction phase was studied during dissolution reaction between sintered alumina and $CaMgSiO_4$ at $1600^{\circ}C$ for various times. The formation of $CaO{\cdot}6Al_2O_3$ an intermediate reaction phase, and $CaMgSiO_4$ spinel, the final reaction product were observed during dissolution reaction of alumina into $CaMgSiO_4$ liquid phase. The growth and dissolution shape of $CaO{\cdot}6Al_2O_3$, an intermediate phase, was quite different.

• Magazine of the Korea Concrete Institute
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• v.6 no.2
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• pp.108-117
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• 1994

This study was performed to investigate the Alkali-Silica Reaction(ASR) of crushed stones using chemical analysis, polarization microscope, XRD, chemical method(KS F 2545, ASTM C 289), mortar-bar method( KS F 2546, ASTM C 227) and Scanning Electron Microscope (SEM ) and Energy Dispersive X-ray Analysis(EDXA) of reaction products by ASK in the mortar bars and to investigate the influence on alkali content and kind of added alkali to the ASR. Test results show that one kind of domestic crushed stone is estimated as deleterious by ASTM chemical method and mortar bar method, and reaction product is proved as alkali silicate gel by EDXA.

• Journal of the Korea Institute of Military Science and Technology
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• v.16 no.3
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• pp.358-364
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• 2013

Borosilicate glass(GVB-Solutions in glass, 2mm, Germany) was prepared in the composition of $80.4SiO_2-4.2Na_2O-2.4Al_2O_3-13.0B_2O_3$. The 2-step crystallization was performed around $584^{\circ}C$ of glass transition temperature ($T_g$), and $774^{\circ}C$ of crystallization temperature($T_c$). The maximum nucleation rate was $8.8{\time}10^9/mm^3{\cdot}hr$ at $600^{\circ}C$ and the maximum crystal growth rate was 3.5nm/min at $750^{\circ}C$. The maximum mechanical properties were observed at 22.8% of volume fraction, the strength, hardness and fracture toughness was 555MPa, $752kg/mm^2$, $1.082MPa{\cdot}mm^{1/2}$. The crystal size of 177nm which has volume fraction of 22.8% showed maximum strength of 562MPa, it is about 157% higher than parent borosilicate glass. From these results, the crystallized borosilicate glass can be applied weight lighting of bullet proof materials.

• Journal of Powder Materials
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• v.23 no.3
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• pp.189-194
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• 2016

We report a facile method for preparing KIT-1 mesoporous silicates with two different macroporous structures by dual templating. As a template for macropores, polystyrene (PS) beads are assembled into uniform three dimensional arrays by ice templating, i.e., by growing ice crystals during the freezing process of the particle suspension. Then, the polymeric templates are directly introduced into the precursor-gel solution with cationic surfactants for templating the mesopores, which is followed by hydrothermal crystallization and calcination. Later, by burning out the PS beads and the surfactants, KIT-1 mesoporous silicates with macropores are produced in a powder form. The macroporous structures of the silicates can be controlled by changing the amount of EDTANa4 salt under the same templating conditions using the PS beads and inverse-opal or hollow structures can be obtained. This strategy to prepare mesoporous powders with controllable macrostructures is potentially useful for various applications especially those dealing with bulky molecules such as, catalysis, separation, drug carriers and environmental adsorbents.

• Proceedings of the Korean Institute of Resources Recycling Conference
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• 2005.10a
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• pp.330-334
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• 2005

본 연구에서는 유해 중금속을 다량 함유하고 있는 산업폐기물의 고화 처리에 사용되는 칼슘설포알루미네이트(4CaO $3Al_2O_3\;SO_4$ 이후부터 CSA로 기입)의 제조를 위해 철강부산물인 압연 슬러지를 활용하여 그 특성에 대해 조사하였다. 본 연구에서는 철강 부산물인 압연슬러지 외에 석회석 미분물, 인산부산 석고를 혼합하여 칼슘알루미네이트 상을 합성하였다. 합성 결과 소성온도 $1250^{\circ}C$에서부터 CSA가 합성되었고, 이와 함께 칼슘실리케이트$(2CaO\;SiO_2)$와 칼슘알루미노페라이트($4CaO\;Al_2O_3\;Fe_2O_3$)도 함께 합성되었다. CSA 합성에 미치는 중금속 영향을 관찰한 결과 원료의 중금속이 CSA 합성 온도를 낮추는 효과가 있는 것으로 나타났다. CSA를 이용한 철강산업 폐기물의 중금속 고용 처리 연구에서도 본 실험에서 합성된 CSA가 폐기물의 중금속 고화 처리에 효과가 있는 것으로 나타났다.

• Polymer(Korea)
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• v.27 no.2
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• pp.129-134
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• 2003

It has been known that the intercalation of long alkyl chains in montmorillonites (MMT) increased the hydrophobicity as well as gallery spacing of UT, which has influenced on the exfoliation behavior of various polymers. A series of organophilic MMTs were synthesized from the water/isopropyl alcohol solution of MMT with ammonium salts of various alkyl amines. The properties of obtained MMTs such as thermal decomposition temperature, gallery spacing as well as hydrophobic property were investigated. The X-ray diffraction experiments on organophilic montmorillonite demonstrated that the increase of length of alkyl substituent resulted in increase in the spacing between silicate layers, which was ranged from 13.1 to 29.4 $\AA$. On the other hand, introduction of (di-, tri-) alkyl substituents in ammonium salts decreased water absorption of organophiplic montmorillonite to 2.7%.