• Progress in Medical Physics
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• v.4 no.2
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• pp.49-58
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• 1993

The complex glow curves were split into isolated glow curves to be calculated the values of kinetic order, activation energy, escape frequency and density of initial trap from the independent glow curves using the mathematical method of thermally stimulated processes. The minimization of the intensity difference between measured and theoretical glow curve was done by the nonlinear least-square program. The results of the fitted curves were almost equal to the actual values of the parameters. Thermoluminescence from gamma ray irradiated ${\alpha}$-Al$_2$ $O_3$ over the range of 300K to 600K was split into six glow curves. The kinetic order, activation energy and escape frequency of first glow curve were obtained as 1, 1.12eV and 6.79X10$\^$12/sec$\^$-1/, respectively, which were similar to the results of other method. Also the parameters of the second and the third glow curve and so forth were calculated.

• Journal of the Korean Ceramic Society
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• v.34 no.1
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• pp.95-101
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• 1997

Using aluminum powder with average particle size of 22.1 $\mu$m, aluminum compact made by Pressureless Powder Packing Method showed 52% green density. The activation energy of aluminum oxidation was cal-culated from the weight change of TG, and it was varied in the range of 16~64 kJ/mol. It was found from the variation of the activation energy and the observation of the microstructure that oxidation was de-pendent on the destruction of oxide film and the melt-out of aluminum. Aluminum compact was reaction-bonded at 1000~140$0^{\circ}C$ for 4~60hrs, and oxidation was dependent on temperature rather than time. Reac-tion-bonded aluminum oxide at 140$0^{\circ}C$ for 60hrs showed 92% oxidation percent. It was sintered at 1$600^{\circ}C$ for 15hrs and the sintered body showed 62% relative density.

• Korean Journal of Materials Research
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• v.5 no.7
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• pp.765-774
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• 1995

The hot deformation behaviour of particulate reinforced aluminium 6061 Al composite were investigated by hot compression tests in the temperature range from 623K to 823K with strain rate of 10$^{-3}$ ~5.0 S$^{-1}$ . The effect of reinforced particulate volume fraction, mean diameter on the high temperature flow stress has also been studied. Experimental results showed that the increase in the volume fraction of reinforcement contributed to the rising of yield stress, but the stress above the yield point appeared to be steady state at all volume fractions. The apparent activation energy for deformation was 290KJ/mo1 for unreinforced 6061 Al, 327KJ/mo1 for 6061 Al-20vo1.% SiC composite and 531KJ/mo1 for 6061 Al-20vo1.%A1$_2$O$_3$composite. It appeared that $Al_2$O$_3$reinforced composites was more difficult to hot deform.

• Analytical Science and Technology
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• v.31 no.1
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• pp.7-13
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• 2018

In this study, we measured the time-resolved optically stimulated luminescence (TR-OSL) of Paleolithic paleosol quartz and evaluated its lifetime. Considering the lifetime dependence on the preheating applied after irradiation, the radiation exposure, and the optical pulse stimulation, we found that the optimum measurement condition for determining the lifetime of paleosol quartz was the optical pulse stimulation at a dwelling time of $250{\mu}s$, pulse width of $10{\mu}s$, and sweep number of 100,000, without preheating after 100 Gy of irradiation. Based on the dependence of the lifetime on the reading temperature, the thermal quenching activation energy ${\Delta}E$ and thermal assistance activation energy $E_a$ were evaluated as $0.60{\pm}0.14eV$ and $0.053{\pm}0.029eV$, respectively. These values were in good agreement with those reported in the literature. Therefore, we concluded that the resulting kinetic parameters for paleosol quartz are quite reliable.

• Journal of the Korean Magnetics Society
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• v.25 no.6
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• pp.185-188
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• 2015

We have investigated nuclear magnetic resonance of $^{23}Na$ nucleus in $NaMgCl_3$ single crystal in the temperature range 200 K~410 K using FT-NMR spectrometer. The spin-lattice relaxation times $T_1$ of $^{23}Na$ nucleus residing at cubic symmetry in the host crystal was measured as a function of temperature. The $T_1$ of $^{23}Na$ nucleus decreased with increasing temperature. The nuclear spin-lattice relaxation rate $1/T_1$ of $^{23}Na$ in $NaMgCl_3$ single crystal was proportional to the temperature T. This behavior is explained with the characteristic feature of the direct process between the nuclear spins and single phonon, $1/T_1$ being proportional to the absolute temperature. The activation energy calculated was $E_a=4.82J/mol$.

• Journal of Korean Society of Environmental Engineers
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• v.35 no.10
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• pp.703-709
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• 2013

Ozonation was performed under various experimental conditions that $Al_2O_3$ catalysts dosage and temperature for removal of DMP in laboratory scale batch reactor. Flow rate of ozone $1.0Lmin^{-1}$ and ozone concentration of $300{\pm}10mgL^{-1}$ were maintained constantly, and the pH, $COD_{Cr}$ and TOC was measured in 10 min intervals during the 60 min at oxidation processes. As a result, the presence of the $Al_2O_3$ than only ozonation increased the removal efficiency of both $COD_{Cr}$ and TOC in solution. The pseudo first-order rate constants for the elimination of $COD_{Cr}$ and TOC were $3.65{\times}10^{-4}sec^{-1}$, $2.52{\times}10^{-4}sec^{-1}$, and activation energy was $0.75kcal{\cdot}mol^{-1}$ and $0.70kcal{\cdot}mol^{-1}$ at $20^{\circ}C$, respectively.

• Applied Chemistry for Engineering
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• v.22 no.3
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• pp.296-300
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• 2011

In this work, various wood biomasses were used to determine the combustion characteristics for the fuel of cogeneration plant. Combustion characteristics of four types, i.e., (i) forest products, (ii) recycled wood, (iii) empty fruit bunch, and (iv) palm kernel shell, were examined via thermal gravimetric analyzer (TGA) in air atmosphere and coal was used as a comparison group. From the TGA results, the combustion of the wood biomass was occurred in the range of 280 to $420^{\circ}C$, which was lower than that of coal. Forest product showed the lowest activation energy (0.4 kJ/mol) compared to that of other wood biomasses (about 6 to 14 kJ/mol) and coal (64 kJ/mol). In addition, the reaction rate constant of the wood biomass was lower than that of coal. These results indicate the higher combustion initiation rate of wood biomass due to the high content of volatile matter, which had a low boiling point.

• Journal of the Korean Institute of Gas
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• v.26 no.5
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• pp.16-21
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• 2022

The reaction rate of a catalyst for producing hydrogen using the methanol steam reforming reaction was studied. It was prepared by impregnating copper, which is often used in methanol synthesis, as the main active metal, using hydrotalcite, which has excellent porosity and thermal stability, high specific surface area, weak Lewis acid point, and basicity, as a support. Activation energy and Pre-exponential factors were identified. In this study, the activation energy of the hydrotalcite catalyst impregnated with 20 wt% copper was calculated to be 97.4 kJ/mol and the Pre-exponential was 5.904 × 10¹⁰. Process simulation was performed using the calculated values and showed a similar tendency to the experimental results.

• Composites Research
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• v.21 no.1
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• pp.16-21
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• 2008

The cure behavior of epoxy resin with a conventional amide-type hardener(HD) was investigated in the presence of castor oil(CO), cashew nut shell liquid(CNSL) and CNSL-formaldehyde resin(CFR) by using a dynamic differential scanning calorimetry(DSC). The activation energy of curing reaction was also calculated based on the non-isothermal DSC thermograms at various heating rates. An one-stage curing was noted in the case of epoxy resin filled with CO, while the epoxy resin with CNSL and CFR showed a two-stage curing process. A competitive cure reaction was noted for the epoxy resin/CNSL(or CFR)/HD blends. In the absence of HD, the CFR showed lower values of curing enthalpy than that of CNSL. The activation energy of epoxy resin curing increased with increasing the CNSL and CFR loading.

• Korean Journal of Food Science and Technology
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• v.47 no.1
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• pp.56-62
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• 2015

Various pretreatment methods were evaluated to prevent tissue softening of heated onion. Changes in onion tissue firmness during heating were explained by 3-mechanism model consisting of texture hardening at low temperature ($60-80^{\circ}C$) and substrate softening at high temperature. Preheating of onion in a $Ca^{2+}$-containing solution significantly improved its texture after high-temperature heating. The improvement of firmness by preheating at low temperature was related to the formation of strong cross-linking between carboxyl groups and $Ca^{2+}$ by the action of pectin methylesterase in onion. The highest firmness was obtained by pre-heating at $70^{\circ}C$ for 120 min in 0.5% calcium solution. This result was supported by chemical analysis showing that the amount of bound calcium was the highest at $70^{\circ}C$. Further investigation should be carried out to establish the optimal conditions to prevent the softening of various vegetables.