• Journal of the Korean Ceramic Society
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• v.51 no.3
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• pp.170-176
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• 2014

Effective glass frit compositions enabled to absorb laser energy, and to seal a commercial dye-sensitized solar-cell-panel substrate were developed by using $V_2O_5$-based glasses with various amounts of $TeO_2$ substitution. The latter was intended to increase the lifetime of the solar cells. Substitution of $V_2O_5$ by $TeO_2$ provided a strong network structure for the glasses via the formation of tetrahedral pyramids in the glass, and changed the various glass properties, such as glass transition temperature ($T_g$), dilatometric softening point ($T_d$), crystallization temperature, coefficient of thermal expansion (CTE), and glass flowage without any detrimental effect on the laser absorption property of the glasses. The thermal expansion mismatch (${\Delta}{\alpha}$) between the glass frit and the substrate could be controlled within less than ${\pm}5%$ by addition of 10 wt% of ${\beta}$-eucryptite. An 810 nm diode laser was used for the sealing test. The laser sealing test revealed that the VZBT20 glass frit with 10 wt% ${\beta}$-eucryptite was successfully sealed the substrates without interfacial cracks and pores. The optimum sealing conditions were provided by a beam size of 3 mm, laser power of 40 watt, scan speed of 300 mm/s, and 200 irradiation cycles.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1993.11a
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• pp.75-79
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• 1993

The Thermally Stimulated Current(TSC) method has been allied to study the influence of the structural change and interface on the electrical properties of epoxy composites. Three DGBA- MeTHPA matrix model samples mixed different ratios arts silica(SiO$_2$) filled sample and silaln treating-filled sample have been studied. Above room temperature, the relaxation mode ${\alpha}$ peak associated with T$\_$g/ has been located at 110$^{\circ}C$. Below glass transition temperature(T$\_$g/), three relaxation modes are observed in all samples : a ${\beta}$ mode situated at 10$^{\circ}C$, a ${\gamma}$ mode located at -40$^{\circ}C$ and a $\delta$mode appeared in -120$^{\circ}C$, which may be due to segmental motion, side chains, substitution and terminal groups. The analysis of its fine structure indicates that constitution of elementary processes is characterized by the activation energy and relaxation time. Also the change of the molecular structure and their thermal motion are compared with the relaxation mode and conduction mechanism in TSC spectra through the dielectric properties and FTIR measurements.

• Carbon letters
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• v.16 no.2
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• pp.101-106
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• 2015

We report a covalent functionalization of graphene nanoparticles (GnPs) employing 2,3,4-Tri-O-acetyl-${\beta}$-D-xylopyranosyl azide followed by fabrication of an epoxy/functionalized graphene nanocomposite and an evaluation of its thermo-mechanical performance. Successful functionalization of GnP was confirmed via thermal and spectroscopic study. Raman spectroscopy indicated that the functionalization was on the edge of the graphene sheets; the basal plane was not perturbed as a result of the functionalization. The epoxy/functionalized GnP composite system exhibited an increase in flexural modulus (~18%) and glass transition temperature (${\sim}10^{\circ}C$) compared to an un-functionalized GnP based epoxy composite.

• Korean Journal of Materials Research
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• v.23 no.2
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• pp.104-111
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• 2013

In this study, GaN powders were synthesized from gallium oxide-hydroxide (GaOOH) through an ammonification process in an $NH_3$ flow with the variation of $B_2O_3$ additives within a temperature range of $300-1050^{\circ}C$. The additive effect of $B_2O_3$ on the hexagonal phase GaN powder synthesis route was examined by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and Fourier transformation infrared transmission (FTIR) spectroscopy. With increasing the mol% of $B_2O_3$ additive in the GaOOH precursor powder, the transition temperature and the activation energy for GaN powder formation increased while the GaN synthesis limit-time ($t_c$) shortened. The XPS results showed that Boron compounds of $B_2O_3$ and BN coexisted in the synthesized GaN powders. From the FTIR spectra, we were able to confirm that the GaN powder consisted of an amorphous or cubic phase $B_2O_3$ due to bond formation between B and O and the amorphous phase BN due to B-N bonds. The GaN powder synthesized from GaOOH and $B_2O_3$ mixed powder by an ammonification route through ${\beta}-Ga_2O_3$ intermediate state. During the ammonification process, boron compounds of $B_2O_3$ and BN coated ${\beta}-Ga_2O_3$ and GaN particles limited further nitridation processes.

• BMB Reports
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• v.35 no.2
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• pp.155-164
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• 2002

The structural aspects of ervatamin B have been studied in different types of alcohol. This alcohol did not affect the structure or activity of ervatamin B under neutral conditions. At a low pH (3.0), different kinds of alcohol have different effects. Interestingly, at a certain concentration of non-fluorinated, aliphatic, monohydric alcohol, a conformational switch from the predominantly $\alpha$-helical to $\beta$-sheeted state is observed with a complete loss of tertiary structure and proteolytic activity. This is contrary to the observation that alcohol induces mostly the $\alpha$helical structure in proteins. The O-state of ervatamin B in 50% methanol at pH 3.0 has enhanced the stability towards GuHCl denaturation and shows a biphasic transition. This suggests the presence of two structural parts with different stabilities that unfold in steps. The thermal unfolding of ervatamin B in the O-state is also biphasic, which confirms the presence of two domains in the enzyme structure that unfold sequentially. The differential stabilization of the structural parts may also be a reflection of the differential stabilization of local conformations in methanol. Thermal unfolding of ervatamin B in the absence of alcohol is cooperative, both at neutral and low pH, and can be fitted to a two state model. However, at pH 2.0 the calorimetric profiles show two peaks, which indicates the presence of two structural domains in the enzyme with different thermal stabilities that are denatured more or less independently. With an increase in pH to 3.0 and 4.0, the shape of the DSC profiles change, and the two peaks converge to a predominant single peak. However, the ratio of van't Hoff enthalpy to calorimetric enthalpy is approximated to 2.0, indicating non-cooperativity in thermal unfolding.

• Bulletin of the Korean Chemical Society
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• v.32 no.12
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• pp.4347-4351
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• 2011

The nucleophilic substitution reactions of ethylene phosphorochloridate (2) with X-pyridines are investigated kinetically in acetonitrile at $-20.0^{\circ}C$. The free energy correlations for substituent X variations in the nucleophiles exhibit biphasic concave upwards with a break point at X = 3-Ph. Unusual positive ${\rho}_X$ (= +2.49) and negative ${\beta}_X$ (= -0.41) values are obtained with the weakly basic pyridines, and rationalized by the isokinetic relationship with isokinetic temperature at $t_{ISOKINETIC}=6.6^{\circ}C$. The pyridinolysis rate of 2 with a cyclic five-membered ring is forty thousand times faster than its acyclic counterpart (3: diethyl chlorophosphate) because of great positive value of the entropy of activation of 2 (${\Delta}S^{\neq}$ = +49.2 eu) compared to negative value of 3 (${\Delta}S^{\neq}$ = -44.1 eu) over considerably unfavorable enthalpy of activation of 2 (${\Delta}H^{\neq}=28.4\;kcal\;mol^{-1}$) compared to 3 (${\Delta}H^{\neq}=6.3\;kcal\;mol^{-1}$). Great enthalpy and positive entropy of activation are ascribed to sterically congested transition state (TS) and solvent structure breaking in the TS. A concerted mechanism involving a change of nucleophilic attacking direction from a frontside attack with the strongly basic pyridines to a backside attack with the weakly basic pyridines is proposed.

• Journal of the Korean Vacuum Society
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• v.1 no.1
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• pp.88-95
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• 1992

Abstract-Using a high resolution low energy electron diffraction(HRLEED), we report an exponent study of 2d continuous phase transition from an ordered ~ ( 2 x 1 )ox ygen overlayer on a W(110) surface. Temperature dependence of a (% 0) superlattice diffraction spot, characteristic of the p(2X 1) structure, shows power-law like divergence of the susceptibility and the fluctuation correlation length at T,=708.765 K. By fitting the intensities as well as the line-shapes, we obtained exponents P=0.19* 0.05, y=1.48+ 0.34, v= 1.23i 0.27 and q=0.38+ 0.12. The non-universal character of the exponents are understood in terms of a 2d XY model with cubic anisotropy as suggested previously.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.48 no.5
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• pp.296-302
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• 1999

$CdIn_2S_4 and CdIn_2S_4 : Co^{2+}$ singlecrystals of thenormal spinel structure were grown by the C.T.R. method. The optical energy band structure of these compounds had a indirect band gap at the fundamental optical absorption band edge. The direct and the indirect energy gaps are found to be 2.325 and2.179eV for $Cdln_2S_4$ , and 2.303 and 2.169eV for $CdIn_2S_4 and CdIn_2S_4 : Co^{2+}$ at 5K, respectivly. The fundamental absorption band edge of these single crystals shift to a shorter wavelength region with decreasing temperature, and the temperature dependence of the optical energy gaps in these compounds satisfy Varshni equation. The Varshni constants$\alpha and \beta$ of the direct energy gap are given by $13.39{\times}10_{-4}eV/K$ and 509 K for $Cdln_2S_4$ and $29.73{\times}10_{-4} eV/K$ and 1398K for $CdIn_2S_4 and CdIn_2S_4 : Co^{2+}$. The Varshni constants ${\alpha}and {\beta}$ of the indirect energy gap are given by 9.68${\times}10^{-4}$ eV/K 308K for $Cdln_2S_4$ and $13.33{\times}10_{-4}eV/K$ and 440K for $CdIn_2S_4 : Co^{2+}$ respectivly. The impurity optical absorption peaks due to cobalt dopant are observed in $CdIn_2S_4 : Co^{2+}$ single crystal. These impurity optical absorption peaks can be attributed to the electronic transitions between the split energy levels of $Co_{2+}$ ions located at $T_d$ symmetry site of $Cdln_2S_4$ host lattece.