• Korean Chemical Engineering Research
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• v.49 no.3
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• pp.367-371
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• 2011

TBAB (tetra-n-butyl ammonium bromide) forms a semi-clathrate with water under atmospheric pressure conditions and recently has attracted great attention due to its usage as a thermodynamic promoter in gas storage and separation process using gas hydrate formation. In this study, we measured the three-phase (hydrate (H) - liquid water ($L_{w}$)-vapor (V)) equilibria of the ternary $CH_{4}$+TBAB+water and $CO_{2}$+TBAB+water mixtures at the TBAB concentrations of 5 and 32 wt% to investigate promoting characteristics of TBAB. The greater promotion effect of TBAB was observed at 32 wt% than at 5 wt%. This result was in good agreement with that from pure TBAB semi-clathrate phase diagram under atmospheric pressure conditions. Through $^{13}C$ NMR analysis of the $CH_{4}$+TBAB semi-clathrate, it was found that $CH_{4}$ molecules are enclathrated in the cages of the double semi-clathrate and the position of resonance peak from encaged $CH_{4}$ molocules in the double semi-clathrate is the same as that from encaged $CH_{4}$ molocules in the pure $CH_{4}$ hydrate of structure I.

• Journal of the Architectural Institute of Korea Structure & Construction
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• v.33 no.12
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• pp.63-70
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• 2017

When industrial by-products like slag and fly ash are using in concrete with cement, it improves strength and durability against external deterioration factors by densifying the structure through potential hydraulic and pozzolanic reaction. But it has been pointed out that high dependence on the quality variation and the curing condition using a admixure material for concrete. In this study, the characteristics of internal micropore structure according to curing condition were analyzed for pastes and mortar specimens under using blast furnace slag powder. As a result, the variation of compressive strength and the internal microstructure were observed according to curing conditions by binder type. Particularly, using blast furnace slag powder, decrease in compressive strength were clearly observed in indoor and carbonation curing compared with water curing. The pore structure analysis also clearly observed the decrease of the gel pore existing in the CSH hydrate layer and the increase of the capillary pore in indoor and carbonation curing compared with water curing condition.

• International Journal of Concrete Structures and Materials
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• v.5 no.1
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• pp.3-10
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• 2011

Theoretical models for prediction of the mechanical properties of cement mortar are developed based on the morphology and interactions of cement hydration products, capillary pores and microcracks. The models account for intermolecular interactions involving the nano-scale calcium silicate hydrate (C-S-H) constituents of hydration products, and consider the effects of capillary pores as well as the microcracks within the hydrated cement paste and at the interfacial transition zone (ITZ). Cement mortar was modeled as a three-phase material composed of hydrated cement paste, fine aggregates and ITZ. The Hashin's bound model was used to predict the elastic modulus of mortar as a three-phase composite. Theoretical evaluation of fracture toughness indicated that the frictional pullout of fine aggregates makes major contribution to the fracture energy of cement mortar. Linear fracture mechanics principles were used to model the tensile strength of mortar. The predictions of theoretical models compared reasonably with empirical values.

• Proceedings of the Korea Concrete Institute Conference
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• 2004.11a
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• pp.777-780
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• 2004

Recently, the use of structure compound waterproof agent (hereinafter referred to as 'SCWA') that is used when manufacturing concrete for concrete structures, increases in quantity. However, while it is expected that the SCWA that is mixed in the concrete inside can significantly affect the change of physical properties that lift the internal force of a structure. This study has been conducted through an experiment for the effects of cement hardener on the formation of microscopic texture, and newly generated hydrates from that result were not confirmed in the. present experiment. It was found that at the hydrate reaction it has the property that can be hardened within the limit of pore diameterar a specific size rather than there is the internal gap filling capacity due to generating other hydrates.

• Archives of Pharmacal Research
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• v.26 no.9
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• pp.686-696
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• 2003

Ethyl (coumarin-4-oxy)acetate 1 was prepared through the reaction of 4-hydroxycoumarin with ethyl bromoacetate. Compound 1 was allowed to react with hydrazine hydrate to produce coumarin-4-oxyacetic hydrazide 2. The synthesis of N-(arylidene and alkylidene)-coumarin-4-oxyacetic hydrazones 3-20 was performed. The preparation of 2-substituted-3-[(coumarin-4-oxy) acetamido]thiazolidinones 21-26 and 2-[(coumarin-4-oxy )methyl]-4-acetyl-5-substituted-$\Delta^2$-1,3,4-oxadiazolines 27-33 was performed by the reaction of the hydrazones 3, 4, 7, 9, 12, 14 with mercaptoacetic acid and the hydrazones 3, 4, 5, 7, 12, 15, 16 with acetic anhydride, respectively. The antiviral activities, cytotoxicities and structure-activity relationship (SAR) towards different microorganisms of the prepared compounds were studied.

• Journal of the Korean Ceramic Society
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• v.28 no.9
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• pp.721-729
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• 1991

SnO2-TiO2(Pt or Pd), as raw material for hydrocarbon gas sensors, was prepared by a coprecipitation method. The SnO2-TiO2-based thick film gas sensors were made by screen printing technique. The titanium dioxide synthesized was shown to be anatase structure from XRD peaks and was transformed to rutile structure between 700$^{\circ}C$ and 1000$^{\circ}C$. Titanium dioxide in SnO2-TiO2 thick films devices plays a very important role in the enhancement of the sensitivity to CH4 and C4H10. In the case of SnO2-TiO2(Pt) sensors, titanium dioxide that was rutile structure enhanced the sensitivity of the thick film to CH4. Platinum added to the raw powder at coprecipitation (as chloroplatinic acid VI hydrate) improved the gas sensitivity to hydrocarbon gases. Therefore, it is expected that the SnO2-TiO2(Pt) thick film sensors fabricated in this experiment could be put into practical use as LPG (primary component : C4H10 and C3H8) and LNG (primary component : CH4) sensors.

• Journal of the Korean Ceramic Society
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• v.52 no.1
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• pp.48-55
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• 2015

Hardened cement-based materials exposed to the high temperatures of a fire are known to experience change in the pore structure as well as microstructural changes that affect their mechanical properties and tend to reduce their durability. In this experimental investigation, hardened Portland cement pastes were exposed to elevated temperatures of 200, 400, 600, 800, and $1000^{\circ}C$ for 60 minutes, and the resulting damage was studied by thermogravimetry (TG), mercury intrusion porosimetry (MIP) and density measurements. These results revealed that the residual compressive strength is increased at temperatures greater than $400^{\circ}C$ due to a small pore size of 3 nm and/or rehydration of the dehydrated cement paste. However, a loss of the residual strength occurs at temperatures exceeding 500 and $600^{\circ}C$. This can be attributed to the decomposition of hydrates such as portlandite and to an increase in the total porosity.

• Korean Journal of Materials Research
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• v.14 no.11
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• pp.790-794
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• 2004

Ultra-fine Copper particles for a conductive paste in electric-electronic field were prepared using wet-reduction process with hydrazine hydrate ($N_{2}H_4{\cdot}H_{2}O$) as a reductor. The effect of reaction conditions such as the amount of dispersion ($Na_{4}O_{7}P_2{\cdot}10H_{2}O$) and reductor ($N_{2}H_4{\cdot}H_{2}O$) on the particle size and shape for the prepared Cu powders was investigated. The quantity of dispersion and reductor varied from 0 to 0.0025 M and from 5 to 40 ml at a reaction temperature of $70^{\circ}C$, respectively. The particle size, shape, and structure for the obtained Cu particles were characterized by means of XRD, SEM, TEM, EDS and TGA. The aggregation of Cu particles was reduced with relatively increasing of the amount of dispersion at fixed other reaction conditions. The smaller Cu particle with size of approximately 300nm was obtained from 0.032 M $CuSO_4$ with adding of 0.0025 M $Na_{4}O7P_2{\cdot}10H_{2}O$ and 40ml $N_{2}H_4{\cdot}H_{2}O$ at a reaction temperature of $70^{\circ}C$.

• Polymer(Korea)
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• v.39 no.2
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• pp.235-239
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• 2015

In this work, we evaluated catalytic activity of LiOH, $Cu(acac)_2$ and n-butyltin hydroxide oxide hydrate in the early stage of the melt transesterification of isosorbide and bisphenol A as diol monomers and diphenylcarbonate for the melt polymerizaiton of polycarbonate. $Cu(acac)_2$ proved to be the most active catalyst for homopolymerization process, while the catalytic activity of LiOH was higher than the others in case of melt copolymerization depending on the catalytic mechanism and chemical structure of catalyst. We suggested that evaluation of catalytic activity can be used for selection of catalyst system in bio-based copolymerization of polycarbonate.

• Journal of the Korean Recycled Construction Resources Institute
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• v.10 no.1
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• pp.74-79
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• 2022

In this study, the effect of a sudden decrease in internal humidity and a decrease in hydration level due to the tight internal structure of high-strength concrete and cement composites was investigated. To verify the change in the internal Si hydration, waste glass foam beads were used as a lightweight aggregate, and the internal unreacted hydrate reduction and hydrate formation tendency were identified over the mid- to long-term. Waste glass foam beads were mixed with 5, 10, and 20 %, and were used by pre-wetting. As the mixing rate of the waste glass foamed beads increased, the strength showed a tendency to decrease. In addition, when the mixing amount of pre-wetted waste glass foam beads increases inside through XRD analysis, TGA analysis, and Si NMR analysis, it is judged that the hydration degree of internal Si is different because moisture is supplied to the paste.