• Bulletin of the Korean Chemical Society
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• v.31 no.5
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• pp.1295-1300
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• 2010

The $CO_2-CH_4$ reaction catalyzed by Ni/silicon wafers was kinetically studied by using a photoacoustic technique. The catalytic reaction was performed at various partial pressures of $CO_2$ and $CH_4$ (50 Torr total pressure of $CO_2/CH_4/N_2$) in the temperature range of 500 - $650^{\circ}C$ in a static reactor system. The photoacoustic signal that varied with the $CO_2$ concentration during the catalytic reaction was recorded as a function of time. Under the reaction conditions, the $CO_2$ photoacoustic measurements showed the as-prepared Ni thin film sample to be inactive for the reaction, while the $CO_2/CH_4$ reactions carried out in the presence of the sample pre-treated in $H_2$ at $600^{\circ}C$ were associated with significant time-dependent changes in the $CO_2$ photoacoustic signal. The rate of $CO_2$ disappearance was measured from the $CO_2$ photoacoustic signal data in the early reaction period of 50 - 150 sec to obtain precise kinetic data. The apparent activation energy for $CO_2$ consumption was determined to be 6.9 kcal/mol from the $CO_2$ disappearance rates. The partial reaction orders, determined from the $CO_2$ disappearance rates measured at various $PCO{_2}'S$ and $PCH{_4}'S$ at $600^{\circ}C$, were determined to be 0.33 for $CH_4$ and 0.63 for $CO_2$, respectively. Kinetic data obtained in these measurements were compared with previous works and were discussed to construct a catalytic reaction mechanism for the $CO_2-CH_4$ reaction over Ni/silicon wafer at low pressures.

• Smart Structures and Systems
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• v.12 no.1
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• pp.41-54
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• 2013

Concrete is known as a heterogeneous product which is composed of complex chemical composition and reaction. The development of concrete thermal effect during early age is critical on its future structural health and long term durability. When cement is mixed with water, the exothermic chemical reaction generates hydration heat, which raises the temperature within the concrete. Consequently, cracking may occur if the concrete temperature rises too high or if there is a large temperature difference between the interior and the exterior of concrete structures during early age hydration. This paper describes the contribution of novel Fabry-Perot (FP) fiber optic temperature sensors to investigate the thermal effects of concrete hydration process. Concrete specimens were manufactured under various water-to-cement (w/c) ratios from 0.40 to 0.60. During the first 24 hours of concreting, two FP fiber optic temperature sensors were inserted into concrete specimens with the protection of copper tubing to monitor the surface and core temperature change. The experimental results revealed effects of w/c ratios on surface and core temperature developments during early age hydration, as well as demonstrating that FP fiber optic sensors are capable of capturing temperature variation in the concrete with reliable performance. Temperature profiles are used for calculating the apparent activation energy ($E_a$) and the heat of hydration (H(t)) of concrete, which can help us to better understand cement hydration.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.25 no.12
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• pp.961-968
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• 2012

In this study, we have investigated the effects of Mn and Co co-doping on defects, J-E curves and grain boundary characteristics of ZnO-$Bi_2O_3$ (ZB) varistor. Admittance spectra and dielectric functions show two bulk defects of $Zn_i^{{\cdot}{\cdot}}$ (0.17~0.18 eV) and $V_o^{\cdot}$ (0.30~0.33 eV). From J-E characteristics the nonlinear coefficient (${\alpha}$) and resistivity (${\rho}_{gb}$) of pre-breakdown region decreased as 30 to 24 and 5.1 to 0.08 $G{\Omega}cm$ with sintering temperature, respectively. The double Schottky barrier of grain boundaries in ZB(MCo) ($ZnO-Bi_2O_3-Mn_3O_4-Co_3O_4$) could be electrochemically single type. However, its thermal stability was slightly disturbed by ambient oxygen because the apparent activation energy of grain boundaries was changed from 0.64 eV at lower temperature to 1.06 eV at higher temperature. It was revealed that a co-doping of Mn and Co in ZB reduced the heterogeneity of the barrier in grain boundaries and stabilized the barrier against an ambient temperature (${\alpha}$-factor= 0.136).

• Journal of the Korean Chemical Society
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• v.52 no.2
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• pp.124-132
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• 2008

effect of some furfural hydrazone derivatives (I -V) as corrosion inhibitors for C-steel in 3M H3PO4 solution in which M indicates mol/l has been studied using weight-loss and galvanostatic polarization techniques. A significant decrease in the corrosion rate of C-steel was observed in the presence of the investigated compounds. This study revealed that, the inhibition efficiency increases with increasing the inhibitor concentration, and the addition of iodide and thiocynate ions enhances it to a considerable extent. The effect of temperature on the corrosion behavior of C-steel was studied in the range from 30-60oC with and without 510-6 M investigated compounds using weight-loss method. Apparent activation corrosion energy (Ea*) and other thermodynamic parameters for the corrosion process were calculated and discussed. The polarization measurements show that the investigated compounds act as mixed-type inhibitors, but the cathode is more polarized when an external current was applied. The adsorption of these compounds on the surface of C-steel in 3M H3PO4 obeys Frumkins adsorption isotherm. The mechanism of inhibition was discussed in the light of the chemical structure of the investigated compounds.

• Korean Chemical Engineering Research
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• v.52 no.6
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• pp.821-825
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• 2014

Steam gasification of sawdust char was performed in a thermobalance reactor at high temperature. Gasification temperature was changed from $850^{\circ}C$ to $1400^{\circ}C$ and steam partial pressure was 0.3, 0.5 and 0.7 atm. Three models of gas-solid reaction were applied to the reaction kinetics analysis and modified volumetric model was an appropriate model. Reaction control regime and diffusion control regime were distinct depending on the temperature. Apparent activation energy and pre-exponential factors for both of the regimes were evaluated and the effects of steam partial pressure were examined. $H_2$ concentration in the produced gas was two times higher than that of CO due to the gasification accompanying by the water gas shift reaction.

• Applied Chemistry for Engineering
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• v.8 no.5
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• pp.749-755
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• 1997

Molybdenum phosphate(P/Mo = 0.6) has been synthesized with ammonium molybdate and phosphoric acid under aqueous solution. The kinetics of the ammoxidation of methylpyrazine over molybdenum phosphate catalyst was investigated with the variation of reaction temperature and partial pressure of methylpyrazine, oxygen and ammonia, respectively at atmospheric pressure. The catalytic activity was constant for 300hrs operation under our experimental conditions. Under the steady-state condition, the rate equation of methylpyrazine was shown as $-r=kP_{MP}P_{NH3}{^0}P_{O2}{^{\gamma}}({\gamma}=2.2;1.3{\leq}P_{O2}(kPa){\leq}4)$. The apparent activation energy was 29.6kcal/mol below 623K. The main product obtained in the ammoxidation of methylpyrazine is cyanopyrazine whose selectively was kept always over 90% regardless of conversion.

• Korean Journal of Food Science and Technology
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• v.24 no.3
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• pp.261-265
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• 1992

To improve preservation and utilization of radish juice concentrates, radish juice were concentrated by reverse osmosis(RO) and thin layer evaporator(TLE) and their rheological properties were investigated. Radish juice concentrates were considered as nowtonian fluids. The apparent viscosity of conc. 1 (Heat treatment radish juice, concentrated by TLE), conc. 2 (Raw radish juice, concentrated by TLE), conc. 3 (Heat treatment radish juice, concentrated by RO) were 0.0503, 0.0578 and 0.0655 Pa.s at 10(1/s), respectively. The yield stress of these concentrates were ranged from 0.0001 to 0.0580 Pa. The activation energy for the flow of the radish juice conc. 1 were increased from 2.7057 to $4.1159{\times}10^4KJ/kg.mol$ by increasing concentration of radish juice.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.23 no.12
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• pp.936-941
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• 2010

In this study, we have investigated the effects of Mn dopant on the bulk trap levels and grain boundary characteristics of $Bi_2O_3$-based ZnO (ZB) varistor using admittance spectroscopy and dielectric functions (such as $Z^*,\;Y^*,\;M^*,\;\varepsilon^*$, and $tan\delta$). Admittance spectra and dielectric functions show two bulk traps of $Zn_i^{..}$ (0.20 eV) and $V^{\bullet}_o$ (0.29~0.33 eV) in ZnO-$Bi_2O_3-Mn_3O_4$ (ZBM). The barrier of grain boundaries in ZBM could be electrochemically single type. However, its thermal stability was slightly disturbed by ambient oxygen because the apparent activation energy of grain boundaries was changed from 0.79 eV at lower temperature to 1.08 eV at higher temperature. The grain boundary capacitance $C_{gb}$ was decreased slightly with temperature as 1.3~1.8 nF but resistance $R_{gb}$ decreased exponentially. The relaxation time distribution can result from the heterogeneity of the barriers constituting the varistor. It is revealed that Mn dopant in ZB reduced the heterogeneity of the barrier in grain boundaries and stabilized the barrier against the ambient temperature.

• Microbiology and Biotechnology Letters
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• v.14 no.2
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• pp.169-174
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• 1986

Cytosine deaminase was partialy purified about 10 fold from the ceil-free extract of Aspergillus fumigatus. The partialy purified enzyme was relatively stable in a pH 5.5 to 8.0, but thermo-unstable. The enzyme activity was found in a pH optimum of 7.0 and temperature optimum of 30 to 35$^{\circ}C$. The activation energy calculated to be 13,240 cal/mol. The apparent Michaelis constants Km for cytosine was found to be 1.53 mM and the molecular weight was determined to be approximately 32,000. The enzyme was strongly inhibited by 0.1 mM of Hg$^^{2+}$, Pb$^{2+}$, Cd$^{2+}$ and Fe$^{2+}$, furthermore inhibited by 1mM of ATP, UTP, o-phenanthroline and p-chloromercuribenzoate.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.40 no.1
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• pp.1-7
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• 2007

The chemical and rheological properties of deproteinated porphyrans from laver Porphyra yezoensis were investigated to obtain basic data for the production of food materials with biological functionality. Deproteinated porphyran was prepared by acid extraction (pH 4.0, $80^{\circ}C$, 4 hr) and successive hydrolysis with 0.5% Alcalase and 0.5% Flavourzyme. The porphyran constituted 10.7% of the dry laver and consisted of 0.6% protein, 14.8% ester sulfate, 3.2% 6-O-methyl galactose, 16.0% 3,6-anhydro-L-galactose, and 67.3% galactose. The effects of concentration and temperature on the apparent viscosity were examined by applying the power law and Arrhenius equations. The porphyran solution showed the typical behavior of a pseudoplastic liquid and the flow behavior index decreased with increasing concentration. The activation energy of the deproteinated porphyran solution at a 1,000 L/s shear rate also increased from $1.4954{\times}10^{4}\;to\;1.9544{\times}10^{4}\;J/kg$ mol with the concentration.