• Membrane Journal
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• v.28 no.2
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• pp.129-135
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• 2018

ZIFs (Zeolitic imdazolate frameworks) have attracted great attention as membrane materials in recent years due to their high chemical and thermal stability, high specific surface area and adjustable pore structure. In this study, ZIF-8 membranes were synthesized by in-situ growth method on two different support materials (${\alpha}$-alumina and YSZ) and their $H_2/CO_2$ gas permeation characteristics were investigated. In order to synthesize defect-free ZIF-8 layer, YSZ support required less synthesis time than ${\alpha}$-alumina support due to smaller pore size. After in-situ growth for 3 h, ZIF-8 membranes prepared on both YSZ and ${\alpha}$-alumina supports showed $H_2/CO_2$ selectivity of about 10.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.8 no.1
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• pp.83-90
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• 1998

Stage transformation characteristics of Li, K and Na-graphite deintercalation compounds (GDICs) were studied under consideration of a deintercalation mechanism of the intercalants between carbon layers. Li-graphite intercalation compounds (GICs) synthesized by a controlling temperatures and pressures have been spontaneously decomposed in the atmosphere. By X-ray differaction analysis the $d_{001}$-values of stage 1 and 2 were identified to be 3.71 and 7.06 $\AA$, respectively. After 6 weeks, the deintercalation reaction of the Li-GICs ceased and only residual compounds could be observed. K-GICs were synthesized by the modified two-bulb method resulting in structural stabilities and stage transitions. By X-ray diffraction analysis the very stable K-graphite residue compounds were observed after 10 weeks. Na-GICs with stage 1 and 2 were synthesized using the high temperature and pressure technique. The temperature dependence of a deintercalation reaction and a thermal stability of Na-GICs were discussed. The structure changes of the Na-GDICs depending on heating rates were identified by X-ray diffraction. According to the deintercalation process, the stage transformations could be attributed to irregular deintercalations of the GDICs with disordered stage.

• Journal of Energy Engineering
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• v.11 no.2
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• pp.166-177
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• 2002

The present study is described of the flame structure of one-dimensional, flat, premixed, laminar, coal-air flame with some addition of methane for the flame stability. A low pressure burner operating at a combustion pressure of 0.3 arm was employed in order to extend the reaction zone. Predicted results from the models considered in the present study are compared with experimental results. Comparisons are included gas temperatures, species concentrations, char analysis and measured burning velocity. Among the models, Model II $I^{*}$-d, which specified devolatilization rate constants and a char surface area factor S=4, resulted in good agreement within the present experimental ranges. The results of char analysis suggest that the extent of the reaction occurring on the panicle might be underestimated in the model so that the char surface area should be increased. A value of 4 for this factor was given by sensitivity analysis of change in char surface area. Again, model II $I^{*}$-d gave satisfactory predictions of burning velocities over most of the experimental range studied. It has been clearly shown that the particle diameter appreciably affects the rates of devolatilisation and char oxidation through the effects of thermal lag and volumetric reactive surface area, consequently laminar burning velocity.ity.

• Journal of Sensor Science and Technology
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• v.3 no.2
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• pp.74-80
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• 1994

Silicon direct bonding technology is very attractive for both silicon-on-insulator devices and sensor fabrication because of its thermal stress free structure and stability. The process of SDB includes hydration of silicon wafer and heat treatment in a wet oxidation furnace. After hydration process, hydroxyl groups of silicon wafer were analyzed by using Fourier transformation-infrared spectroscopy. In case of hydrophilic treatment using a ($H_{2}O_{2}\;:\;H_{2}SO_{4}$) solution, hydroxyl groups are observed in a broad band around the 3474 $cm^{-1}$ region. However, hydroxyl groups do not appear in case of diluted HF solution. The bonded wafer was etched by using tetramethylammonium hydroxide etchant. The surface of the self etch-stopped silicon dioxide is completely flat, so that it can be used as sensor applications such as pressure, flow and acceleration, etc..

• Applied Chemistry for Engineering
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• v.7 no.5
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• pp.832-842
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• 1996

TAME synthesis was studied in a fixed bed reactor with 3 different types of exchanged resins i.e, Amberlyst-15, Amberlyst-15(wet) and Amberlyst XN-1010. Amberlyst-15 has highest activity, presumably due to the higher reaction participation of the inner active sites of gel shape microparticular resin structure. The optimum reaction conditions for TAME synthesis were found as follows ; reaction temperature of $135^{\circ}C$, molar ratio(MeOH/I.A.A) of 1.0~4.0 and W/F of 2.0~4.0 gr.-cat. hr/gr.-mole. The cross-linking bond of styrene divinyl benzene was observed at $2{\theta}=20$ in XRD pattern. The DSC analysis showed that the thermal stability was in order of Amberlyst-15>Amberlyst-15(wet)>Amberlyst XN-1010. The apparent activation energies of TAME synthesis reaction with Amberlyst-15, Amberlyst-15(wet) and Amberlyst XN-1010 were 12.36, 12.46 and 14.72 kcal/mole, respectively.

• Polymer(Korea)
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• v.31 no.1
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• pp.37-46
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• 2007

Fully or nearly fully 6- [4- (4'- (nitrophenylazo)phenoxycarbonyl)]pentanoated polysaccharide derivatives were synthesized by reacting cellulose, amylose, chitosan, chitin, alginic acid, pullulan or amylopectin with 6- [4- (4'- (nitrophenylazo)phenoxy) ] pentanoyl chloride (NA6C) and their thermotropic liquid crystalline behaviors were investigated. Like in the case of NA6C, all the polysaccharide derivatives formed monotropic nematic phases, suggesting that the mesophase structure of the polysaccharide derivatives is dertermined by the mesogenic side groups and not by the polysaccharide backbone. This is the first report of polysaccharide derivatives, except cellulose derivative, that form thermotropic nematic phases. The thermal stability and degree of order of the nematic phases observed for poly saccharide derivatives were significantly different from those reported for the polymers in which the azobenzene groups are attached to flexible or rigid backbones through flexible spacers. The results were discussed in terms of the difference in the arrangement of the main and side chains and the flexibility of the main chain.

• Journal of the Mineralogical Society of Korea
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• v.15 no.4
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• pp.273-282
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• 2002

Al-pillared montmorillonite was synthesized from Na-saturated montmorillonite which was prepared by ionic substitution from Ca-montmorillonite of the Jabut mine, Gyeongiu City d(001), surface areas, and dehydration and ionic substitution properties have been compared for both Ca-montmorillonite and Al-pillared montmorillonite. d(001) spacings of Ca-montmorillonite and Al-pillared montmorillonite were 15.1 $\AA$ and $18.3\AA$, respectively. Dehydration took place before $350 ^{\circ}C$ in Ca-montmorillonite, whereas linealy up to $550^{\circ}C$ in Al-pillared montmorillonite. BET surface areas are 5～6 times larger in Al-pillared montmorillonite ($192 \m^2$/g) than Camontmorillonite. Ca-montmorilonite shows high selectivity for $Na^{＋}$ /, whereas Al-pillared montmorillonite for $Ca^{2＋}$ . The former shows decreasing d(001) spacing with increasing substitution of $Na^{＋}$ and irregular interstratified structure at high substitution of $Ca^{2＋}$ /, whereas the latter shows linear decreasing pattern in d(001) spacing with increasing $Ca^{ 2+}$.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.669-669
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• 2013

Hierarchical N doped TiO2 nanostructured catalyst with micro, meso and macro porosity have been synthesized by a facile self-formation route using ammonia and titanium isopropoxide precursor. The samples were calcined in different calcination temperature ranging from $300^{\circ}C$ to $800^{\circ}C$ at slow heating rate ($5^{\circ}C$/min) and designated as NHPT-300 to NHPT-800. $TiO_2$ nanostructured catalyst have been characterized by physico-chemical and spectroscopy methods to explore the structural, electronic and optical properties. UV-Vis diffuse reflectance spectra confirmed the red shift and band gap narrowing due to the doping of N species in TiO2 nanoporous catalyst. Hierarchical macro porosity with fibrous channel patterning was observed (confirmed from FESEM) and well preserved even after calcination at $800^{\circ}C$, indicating the thermal stability. BET results showed that micro and mesoporosity was lost after $500^{\circ}C$ calcination. The photocatalytic activity has been evaluated for methanol oxidation to formaldehyde in visible light. The enhanced photocatalytic activity is attributed to combined synergetic effect of N doping for visible light absorption, micro and mesoporosity for increase of effective surface area and light harvestation, and hierarchical macroporous fibrous structure for multiple reflection and effective charge transfer.

• Journal of Microbiology and Biotechnology
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• v.22 no.8
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• pp.1077-1083
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• 2012

Previously, an extracellular ${\alpha}$-amylase (BKA) had been purified from the culture of Bacillus sp. KR8104. Subsequently, the crystal structure of the active enzyme revealed a 422 amino acids polypeptide. In this study, the bka was cloned into E. coli, which encoded a polypeptide of 659 amino acids including two additional fragments: one 44 residues N-terminal fragment and another 193 residues C-terminal fragment. In order to investigate the role of the C-terminal fragment, two constructs with and without this region [$BKA{\Delta}$(N44) and $BKA{\Delta}$(N44C193)] were designed and expressed in E. coli BL21. The optimum pH, thermal stability, and the end-products of starch hydrolysis were found to be similar in both constructs. The $K_m$ and $V_{max}$ values for $BKA{\Delta}$(N44) were lower than $BKA{\Delta}$(N44C193), using either starch or ethylidene-blocked 4-nitrophenylmaltoheptaoside as a substrate.

• Journal of Conservation Science
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• v.36 no.1
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• pp.1-14
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• 2020

This study investigates the crystallinity distribution of ancient silk. Owing to the inherent multi-hierarchical structure of silk protein and the complicated structural changes that occur due to various burial environments, it is challenging but worthwhile to study ancient silk ageing behavior, which is based on the fact that ageing begins with a single fiber and then spreads to a whole fabric. Crystallinity was one of the most effective indicators found to reveal the ageing status of silk. Therefore, a synchrotron radiation-based X-ray diffraction(SR-XRD) method was employed to study the crystallinity distribution of single fibers of ancient silk unearthed from seven archaeological sites in China from historical periods including the warring states, Han dynasty, Song dynasty, and Ming dynasty. In comparison, the conventional X-ray diffraction method, which uses large amounts of samples, was also performed to determine the integral crystallinity of ancient silk. Thermal stability experiments by thermogravimetry(TG) as well as morphology observations by scanning electron microscopy(SEM) and optical microscopy(OM) all confirmed the deterioration of ancient silk. Moreover, the ageing mechanism of ancient silk was proposed with the assistance of an artificial ageing study. The results confirmed the effectiveness of SR-XRD as an ageing indicator, revealing the crystallinity distribution. This research could provide motivation to determine the deterioration status of ancient silk, and would also aid in explaining the fragility of ancient silk due to ageing.