• Applied Chemistry for Engineering
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• v.21 no.5
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• pp.575-580
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• 2010

Forest fires in Korea, having forest coverage of 70%, have kept increasing in number and scale since the middle of 1990's. Although deposited fallen leaves in forests such as herbaceous plants, conifers, and broadleaf trees are used as a medium for forest fires, the pyrolysis and combustion characteristics of the various species of trees are hardly studied. Oriental oak is the representative broadleaf tree in domestic forests, and pyrolysis and combustion of oriental oak leaf were carried out by thermogravimetic analysis (TGA). The leaf of oriental oak was ignited at $239^{\circ}C$ whereas pyrolysis started at $250^{\circ}C$. The corresponding kinetic parameters including activation energy and pre-exponential factor were determined by differential method over the degree of conversions. The values of activation energies for pyrolysis were increased as the conversion increases from 10% to 80%, whereas those of values were decreased during combustion.

• Applied Chemistry for Engineering
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• v.19 no.2
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• pp.191-198
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• 2008

The thermal degradation characteristics of high molecular components obtained from pyrolysis of mixed waste plastics have been studied by thermogravimetric analysis (TGA) and gas chromatography spectrometry (GC-MS). The kinetics of thermal degradation has been studied by a conventional nonisothermal thermogravimetric technique at several heating rates between 10 and $50^{\circ}C/min$. The dynamic thermogravimetric analysis curve and its derivative have been analyzed using a variety of analytical methods reported in the literature to obtain information on the kinetic parameters such as activation energies and reaction orders. The yields of liquid products have been monitored by batch pyrolysis reactor under various reaction temperatures and reaction times. And the characteristic of liquid products with the increase in reaction temperature has been performed by GC-MS.

• Korean Journal of Food Science and Technology
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• v.12 no.4
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• pp.285-291
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• 1980

The hydration and cooking rate of two rice varieties, Akibare (Japonica) and Milyang 23 (Indica), were investigated in terms of mathematical rate equations. The hydration rate at temperatures of $10{\sim}40^{\circ}C$ was examined by weighing method. The absorption of liquid water by rice grain was directly proportional to the square root of the hydration time. The diffusion coefficient was given by the Arrhenius relation : $D=3.151{\times}10^{-3}\exp\;(-4000/RT)$ for Akibare and $D=5.853{\times}10^{-3}\exp\;(-5700/RT)$ for Milyang 23. Milyang 23 was cooked at a faster rate than Akibare. The activation energies for cooking were in the range of 18 000 cal/mole at $90{\sim}100^{\circ}C$ and 9,000cal/mole at $100{\sim}120^{\circ}C$. However, Milyang 23 showed slightly higher activation energy of cooking at $90{\sim}100^{\circ}C$. Adhesiveness and amylograph viscosities at all reference points for Milyang 23 were higher than those for Akibare.

• Journal of The Korean Astronomical Society
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• v.45 no.2
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• pp.39-48
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• 2012

We investigate non-LTE effects on the $H_3^+$ level populations to help the analysis of the observed 2 and 3.5 micron $H_3^+$ emissions from the Jovian ionosphere. We begin by constructing a simple three-level model, in order to compute the intensity ratio of the R(3,4) line in the hot band to the Q(1,0) line in the fundamental band, which have been observed in the Jovian auroral regions. We find that non-LTE effects produce only small changes in the intensity ratios for ambient $H_2$ densities less than or equal to $5{\times}10^{11}cm^{-3}$. We then construct two comprehensive models by including all the collisional and radiative transitions between pairs of more than a thousand known $H_3^+$ rovibrational levels with energies less than 10000 $cm^{-1}$. By employing these models, we find that the intensity ratios of the lines in the hot and fundamental bands are affected greatly by non-LTE effects, but the details depend sensitively on the number of collisional and radiative transitions included in the models. Non-LTE effects on the rovibrational population become evident at about the same ambient $H_2$ densities in the comprehensive models as in the three-level model. However, the models show that rotational temperatures derived from the intensities of rotational lines in the ${\nu}_2$ and $2{\nu}_2$ bands may differ significantly from the ambie temperatures in the non-LTE regime. We find that significant non-LTE effects appear near and above the $H_3^+$ peak, and that the kinetic temperatures in the Jovian thermospheric temperatures derived from the observed line ratios in the 2 and 3.5 micron $H_3^+$ emissions are highly model dependent.

• Polymer(Korea)
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• v.37 no.2
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• pp.240-248
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• 2013

The curing behaviors of diglycidyl ether of bisphenol A (DGEBA) with mercaptan hardener were studied by the comparison with amine-adduct type hardener. Curing behaviors were evaluated by DSC at dynamic and isothermal conditions. In the DSC, the dynamic experiments were based on the method of Kissinger's equation, and the isothermal experiments were fitted to the Kamal's kinetic model. Activation energy of epoxy/amine-adduct type hardener was ca. 40 kcal/mol. As the functional group of mercaptan hardener, -SH increased, on epoxy/mercaptan hardeners, the activation energies decreased from 28 to 19 kcal/mol. Epoxy/amine-adduct type hardener was initiated at $90^{\circ}C$ or higher. However, epoxy/mercaptan hardeners reduced the initiation temperatures below $80^{\circ}C$ and shortened the durations of curing reaction within 10 min. We found out that the reaction kinetics of epoxy with mercaptan hardener followed the autocatalytic reaction models, and the maximum reaction rates were shown at the conversions of 20~40%.

• Journal of the Korean Chemical Society
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• v.24 no.3
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• pp.183-192
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• 1980

Oxidation reactions of carbon monoxide on $SnO_2$, Sb-doped $SnO_2$, and Pt catalyst were studied. The oxidation reaction was found to be first order with respect to both CO and O$_2$ on $SnO_2$ and Sb-doped $SnO_2$ catalysts, and to be of half order on Pt catalyst. A small addition of Sb to $SnO_2$ (depant composition: 0.05∼0.1 mol %) increased the rate of oxidation. On the contrary, a large addition decreased the rate. From the rate expression of oxidation on Pt catalyst, the inhibition effect of carbon monoxide on the rate of oxidation was deduced. The experimentally obtained activatio energies were 5.7 kcal for the Sb doped $SnO_2$ catalyst (dopant composion: 0.05 mole%), and 6.4 kcal for the Pt catalyst. A possible reaction mechanism was proposed from the experimentally obtained kinetic data.

• Computational Structural Engineering
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• v.11 no.1
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• pp.191-204
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• 1998

The general formulation for free vibration and stability analysis of unsymmetric thin-wared space frames is presented in case where the shear deformation effects are neglected. The kinetic and total potential energies are derived by applying the extended virtual work principle, introducing displacement parameters defined at the arbitrarily chosen axis and including warping deformation and second order terms of finite semitangential rotations. In formulating the finite element procedure, cubic Hermitian polynomials are utilized as shape functions of the two node space frame element. Mass, elastic stiffness, and geometric stiffness matrices for the unsymmetric thin-walled section are evaluated, and load-correction stiffness matrices for off-axis distributed loadings are considered. In order to illustrate the accuracy and practical usefulness of this formulation, finite element solutions for the free vibration and stability problems of thin-walled beam-columns and space frames are presented and compared with available solutions.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.15 no.4
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• pp.609-617
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• 2002

A three-dimensional(3-D) method of analysis is presented for determining the free vibration frequencies and mode shapes of thick, circular rings with isosceles trapezoidal and triangular cross-sections. Displacement components u/sub s/, u/sub z/, and u/sub θin the meridional, normal, and circumferential directions, respectively, are taken to be sinusoidal in time, periodic in θ, and algebraic polynomials in the ψ and z directions. Potential(strain) and kinetic energies of the circular ring are formulated, and upper bound values of the frequencies we obtained by minimizing the frequencies. As the degree of the polynomials is increased, frequencies converge to the exact values. Novel numerical results are presented for the circular rings with isosceles trapezoidal and equilateral triangular cross-sections having completely free boundaries. Convergence to four-digit exactitude is demonstrated for the first five frequencies of the rings. The method is applicable to thin rings, as well as thick and very thick ones.

• Korean Journal of Materials Research
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• v.8 no.2
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• pp.173-178
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• 1998

$MgB_4O_7$: Tb, Tm, Dy, La, Ho and Nd phosphors have been prepared by sintering around $580^{\circ}C$ for 2 hours followed by flowing Ar gas. Activation energy and kinetic order of main peak of glow curve were studied by two methods peak shape method and initial rise method. By these methods, the estimated activation energies were $0.76\pm0.02eV$(Tb doped), $0.94\pm0.03eV$(Tm doped), $0.72\pm0.02eV$(Dy doped), respectively. The TL phosphors prepared in this work may be utilized to radiation sensor elements becaue of their high sensitivity to low energy X-ray.

• Journal of Powder Materials
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• v.25 no.4
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• pp.322-326
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• 2018

The hydrogen reduction behavior of $MoO_3-CuO$ powder mixture for the synthesis of homogeneous Mo-20 wt% Cu composite powder is investigated. The reduction behavior of ball-milled powder mixture is analyzed by XRD and temperature programmed reduction method at various heating rates in Ar-10% $H_2$ atmosphere. The XRD analysis of the heat-treated powder at $300^{\circ}C$ shows Cu, $MoO_3$, and $Cu_2MoO_5$ phases. In contrast, the powder mixture heated at $400^{\circ}C$ is composed of Cu and $MoO_2$ phases. The hydrogen reduction kinetic is evaluated by the amount of peak shift with heating rates. The activation energies for the reduction, estimated by the slope of the Kissinger plot, are measured as 112.2 kJ/mol and 65.2 kJ/mol, depending on the reduction steps from CuO to Cu and from $MoO_3$ to $MoO_2$, respectively. The measured activation energy for the reduction of $MoO_3$ is explained by the effect of pre-reduced Cu particles. The powder mixture, hydrogen-reduced at $700^{\circ}C$, shows the dispersion of nano-sized Cu agglomerates on the surface of Mo powders.