• Journal of Adhesion and Interface
• /
• v.4 no.3
• /
• pp.33-40
• /
• 2003

In this work, diglycidyl ether of bisphenol A (DGEBA)/polyetherimide (PEI) blends were cured using 4,4-diaminodiphenyl methane (DDM). And the effects of addition of different PEI contents to neat DGEBA were investigated in the thermal properties and fracture toughness of the blends. The contents of contents of containing PEI were varied in 0, 2.5, 5, 7.5, and 10 phr. The cure activation energies ($E_a$) of the cured specimens were determined by Kissinger equation and the mechanical interfacial properties of the specimens were performed by critical stress intensity factor ($K_{IC}$). Also their surfaces were examined by using a scanning electron microscope (SEM) and the surface energetics of blends was determined by contact angles. As a result, $E_a$ and $K_{IC}$ showed maximum values in the 7.5 phr PEI. This result was interpreted in the increment of the network structure of DGEBA/PEI blends. Also, the surface energetics of the DGEBA/PEI blends showed a similar behavior with the results of $K_{IC}$. This was probably due to the improving of specific or polor component of the surface free energy of DGEBA/PEI blends, resulting in increasing the hydrogen bonding of the hydroxyl and imide groups of the blends.

• Journal of the Korea Concrete Institute
• /
• v.23 no.3
• /
• pp.321-330
• /
• 2011

Recently, the effects of high temperature and fiber content on the residual mechnical properties of high-strength concrete were experimentally investigated. In this paper, residual mechanical properties of concrete with water to cement (w/c) ratios of 0.55, 0.42 and 0.35 exposed to high temperature are compared with those obtained in fiber reinforced concrete with similar characteristics ranging from 0.05% to 0.20% polypropylene (PP) fiber volume percentage. Also, factors including pre-load levels of 20% and 40% of the maximum load at room temperature are considered. Outbreak time, thermal strain, length change, and mass loss were tested to determine compressive strength, modulus of elasticity, and energy absorption capacity. From the results, in order to prevent the explosive spalling of 50 MPa grade concretes exposed to high temperature, more than 0.05 vol. % of PP fibers is needed. Also, the cross-sectional area of PP fiber can influence the residual mechanical properties and spalling tendency of fiber reinforced concrete exposed to high temperature. Especially, the external loading increases not only the residual mechanical properties of concrete but also the risk of spalling and brittle failure tendency.

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.10 no.1
• /
• pp.66-72
• /
• 2000

The behavior of nucleation and crystallization in the $Li_2O_3-SiO_2$ glass heat-treated at different condition under the conventional and microwave processing was studied by differential thermal analysis (DTA), X-ray diffractometry (XRD), optical microscopy (OM), and electrical conductivity measurement. Nucleation temperature and temperature of maximum nucleation rate in both conventionally and microwave heat-treated samples were 460~$500^{\circ}C$ and $580^{\circ}C$, respectively. It was expected that the probability for bulk crystallization increased in microwave heat-treated sample, compared to conventionally heat-treated one. Degree of crystallization increased with increasing crystallization temperature in both conventionally and microwave heat-treated samples. However, pattern of crystallization growth under microwave processing appeared to be quite different from that under the conventional one due to its internal or volumetric heating. Electrical conductivity of conventionally and microwave heat-treated samples were 1.337~2.299, 0.281~~$0.911{\times}10^{-7}\Omega {\textrm}{cm}^{-1}$, respectively.

• The Transactions of the Korean Institute of Electrical Engineers C
• /
• v.51 no.8
• /
• pp.340-346
• /
• 2002

Capacitor material utilized in the downsizing passive devices and integration of passive devices requires the physical and electrical properties at given area such as capacitor thickness reduction, relative dielectric constant increase, low leakage current and thermal stability. common capacitor materials, $Al_2O_3$, $SiO_2$, $Si_3N_4$, $SiO_2$/$Si_3N_4$, TaN and et al., used until recently have reached their physical limits in their application to integration of passive devices. $Ta_2O_{5}$ is known to be a good alternative to the existing materials for the capacitor application because of its high dielectric constant (25~35), low leakage current and high breakdown strength. Despite the numerous investigations of $Ta_2O_{5}$ material, there have little been established the clear understanding of the annealing effect on capacitance characteristic and conduction mechanism. This study presents the dielectric properties $Ta_2O_{5}$ MIM capacitor structure Processed by $O_2$ RTA oxidation. X-ray diffraction patterns showed the existence of amorphous phase in $600^{\circ}C$ annealing under the $O_2$ RTA and the formation of preferentially oriented-$Ta_2O_{5}$ in 650, $700^{\circ}C$ annealing and the AES depth profile showed $O_2$ RTA oxidation effect gives rise to the $O_2$ deficientd into the new layer. The leakage current density respectively, at 3~1l$\times$$10_{-2}$(kV/cm) were $10_{-3}$~$10_{-6}$(A/$\textrm{cm}^2$). In addition, behavior is stable irrespective of applied electric field. the frequency vs capacitance characteristic enhanced stability more then $Ta_2O_{5}$ thin films obtained by $O_2$ reactive sputtering. The capacitance vs voltage measurement that, Vfb(flat-band voltage) was increase dependance on the $O_2$ RTA oxidation temperature.

• Korean Chemical Engineering Research
• /
• v.46 no.1
• /
• pp.106-111
• /
• 2008

Polypropylene (PP)/corn starch master batch (starch-MB)/silicate composites with different corn starch compositions of 10, 20, 30, 40 and 50 were prepared by melt compounding at $200^{\circ}C$, using lab scale Brabender mixer. The content of silicate was fixed at 5 wt%. The composition of starch-MB in composites was confirmed by the existence of hydroxy group and peak intensity in fourier-transform-infrared (FT-IR) spectrum. The thermal properties of the PP/starch-MB/silicate composites were investigated by differential scanning calorimetry (DSC), and thermogravimetric analyzer (TGA). There was no district change in melting temperature, and TGA curve indicates a decrease in degradation temperature with the increase of starch-MB content. The silicate dispersion of the composites was measured by X-ray diffraction (XRD) and transmission electron microscope (TEM). The degree of silicate dispersion in PP/starch-MB/silicate composites depended on the content of starch-MB. There was detectable change in d-spacing and peak intensity of the composite when the content of starch-MB was higher than 20 wt%. The rheological behavior of the composites was explained by both shear thinning effect and elastic property with the starch-MB amount. These effects were remarkable when the content of starch-MB was higher than 20 wt%. These were confirmed by an oscillatory viscometer at $200^{\circ}C$.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.27 no.7
• /
• pp.369-374
• /
• 2015

This study analyzed analyzes the energy performance of six houses in Daejeon completed which were built in 2011. Observed The observed houses, which were all designed and constructed inof the same size and structure, are were highly insulated with triple Low-E coating windows; the insulation level of the walls is was $0.13W/m^2K$ and that of the roof is was $0.10W/m^2K$. As electric houses, all of the energy supplied to the houses, including for cooking, is was supplied by electricity. A and 3~4 kWp of photovoltaic system and a 3~5 kW of ground source heat pump (GSHP) were installed in each house tofor providing provide space heating/and cooling and hot water are installed. We constructed a Web-based remote monitoring system in order to understand energy consumption and the dynamic behavior of the energy system. T, and the results of our metering data analysis of 2013 are as follows. First, the annual residential energy consumption is was 4,400 kWh (${\sigma}=1,209$) and GSHP energy consumption is was 5,182 kWh (${\sigma}=1,164$). Second, residential energy consumption ranked highest in average energy usage, with at 45% of the total, followed by heating with at 30%, hot water supply with at 17% and cooling with at 6%. Third, the average energy independence rate is was 51.8%, the GFA (Gross gross floor area) criteria average energy consumption unit is was $48.7kWh/m^2yr$ (${\sigma}=10.1$), and the net energy consumption unit (except the energy yield of the PV systems) is was $24.7kWh/m^2yr$ (${\sigma}=8.8$).

• Elastomers and Composites
• /
• v.44 no.1
• /
• pp.55-62
• /
• 2009

In this study, investigation on the polymerization characteristics of isoprene through nitroxide mediated controlled/"living" radical polymerization techniques was attempted. In the presence of acetol, linear increase of isoprene conversion with time and low polydispersities of the resulting polymers ($M_w/M_n$ < 1.5) were observed, which suggest successful controlled/"living" radical polymerization of isoprene. The microstructure of the resulting polyisoprene was composed of $\sim$ 22% of 3, 4, $\sim$30% of 1, 4-cis and $\sim$ 48% of 1, 4-trans. The optimum polymerization temperature was 145 $^{circ}C$, below which no significant polymerization behavior was observed. Non-cyclic nitroxide, such as di-tert-butyl nitroxide (DTBN) could not mediate the polymerization, whereas cyclic nitroxides (2, 2, 6, 6-tetramethyl-1-peperidine 1-oxyl (TEMPO) and 4-oxo-2, 2, 6, 6-tetramethyl-1-peperidine 1-oxyl (oxoTEMPO)) were successfully employed for the polymerization. However, isoprene dimerization reaction through Diels-Alder process was also observed at the given polymerization condition, which afforded a significant amount of limonene. Isoprene thermal autoinitiation was also possible, which was, however, considered to be not significant under the given polymerization condition.

• Bulletin of the Korean Chemical Society
• /
• v.30 no.11
• /
• pp.2691-2696
• /
• 2009

Effects of representative group II and transition metal ions on the stability of the $poly(dA){\cdot}[poly(dT)]_2$ triplex were investigated by the van’t Hoff plot constructed from a thermal melting curve. The transition, $poly(dA){\cdot}[poly(dT)]_2\;{\rightarrow}\;poly(dA){\cdot}poly(dT)\;+\;poly(dT)$, was non-spontaneous with a positive Gibb’s free energy, endothermic (${\Delta}H^{\circ}$ > 0), and had a favorable entropy change (${\Delta}S^{\circ}$ > 0), as seen from the negative slope and positive y-intercept in the van’t Hoff plot. Therefore, the transition is driven by entropy change. The $Mg^{2+}$ ion was the most effective at stabilization of the triplex, with the effect decreasing in the order of $Mg^{2+}\;>\;Ca^{2+}\;>\;Sr^{2+}\;>\;Ba^{2+}$. A similar stabilization effect was found for the duplex to single strand transition: $poly(dA){\cdot}poly(dT)\;+\;poly(dT)\;→\;poly(dA)\;+\;2poly(dT)$, with a larger positive free energy. The transition metal ions, namely $Ni_{2+},\;Cu_{2+},\;and\;Zn_{2+}$, did not exhibit any effect on triplex stabilization, while showing little effect on duplex stabilization. The different effects on triplex stabilization between group II metal ions and the transition metal ions may be attributed to their difference in binding to DNA; transition metals are known to coordinate with DNA components, including phosphate groups, while group II metal ions conceivably bind DNA via electrostatic interactions. The $Cd_{2+}$ ion was an exception, effectively stabilizing the triplex and melting temperature of the third strand dissociation was higher than that observed in the presence of $Mg_{2+}$, even though it is in the same group with $Zn_{2+}$. The detailed behavior of the $Cd_{2+}$ ion is currently under investigation.

• Journal of the Korean Chemical Society
• /
• v.64 no.5
• /
• pp.249-258
• /
• 2020

The potential use of egg shell and calcined egg shell as adsorbent was evaluated and compared to remove Cd²⁺ from aqueous solution. The samples were characterized using Thermogravimetry and Differential Thermal Analysis (TG/DTA), Scanning Electron Microscope (SEM), X-ray Diffractometer (XRD), Energy Dispersive X-ray Spectrometer (EDX) and BET Surface Analyzer. The batch-type adsorption experiment was conducted by varying diverse variables such as contact time, pH, initial Cd²⁺ concentrations and adsorbent dosage. The results showed that, under the initial Cd²⁺ concentrations ranged from 25 to 200 mg g^-1, the removal efficiencies of Cd²⁺ by egg shell powder (ESP) were decreased steadily from 96.72% to 22.89% with increase in the initial Cd²⁺ concentration at 2.5 g of dosage and 8 h of contact time. However, on the contrary to this, calcined egg shell powder (CESP) showed removal efficiencies above 99% regardless of initial Cd²⁺ concentration. The difference in the adsorption behavior of Cd²⁺ may be explained due to the different pH values of ESP and CESP in solution. Cd²⁺ seems to be efficiently removed from aqueous solution by using the CESP with a basicity nature of around pH 12. It was also observed that an optimum dosage of ESP and CESP for nearly complete removal of Cd²⁺ from aqueous solution is approximately 5.0 g and 1.0 g, respectively. Consequently, Cd²⁺ is more favorably adsorbed on CESP than ESP in the studied conditions. Adsorption data were applied by the pseudo-first-order and pseudo-second-order kinetics models and Freundlich and Langmuir isotherm models, respectively. With regard to adsorption kinetics tests, the pseudo-second-order kinetics was more suitable for ESP and CESP. The adsorption pattern of Cd²⁺ by ESP was better fitted to Langmuir isotherm model. However, by contrast with ESP, CESP was described by Freundlich isotherm model well.

• Clean Technology
• /
• v.18 no.4
• /
• pp.426-431
• /
• 2012

Carbon-rich coal can be utilized as a fuel for direct carbon fuel cell (DCFC). However, left-behind ash after the electrochemical oxidation may hinder the electrochemical reactions. In this study, we produced ash-free coal (AFC) by thermal extraction and then tested it as a fuel for DCFC. DCFC was built based on solid oxide electrolyte and the electrochemical performance of AFC mixed with $K_2CO_3$ was compared with AFC only. Significantly enhanced power density was found by catalytic steam gasification of AFC. However, an increase of the power density by catalytic pyrolysis was negligible. This result indicated that a catalyst activated the steam gasification reactions, producing much more $H_2$ and thus increasing the power density, compared to AFC only. Results of a quantitative analysis showed much improved kinetics in AFC with $K_2CO_3$ in agreement with DCFC results. A secondary phase of potassium on yttria-stabilized zirconia (YSZ) surface was observed after the cell operation. This probably caused poor long-term behavior of AFC with $K_2CO_3$. A thin YSZ (30 ${\mu}m$ thick) was found to be higher in the power density than 0.9 mm of YSZ.