• Nuclear Engineering and Technology
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• 제52권9호
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• pp.2041-2046
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• 2020

The present article investigates the influence of hydrogen concentration on the creep performance of cold-worked stress-relieved unirradiated Zircaloy-4 cladding tube using nanoindentation technique. The as-received Zircaloy-4 tube is hydrided to the concentrations of 600 ppm and 900 ppm using gaseous hydrogen charging method. Constant load indentation creep tests are performed for a dwell period of 600 s in the temperature range of 300℃-500 ℃ at 1000 μN, 2000 μN, and 3000 μN. The impact of hydrogen is evaluated in terms of steady state power law creep exponent and activation energy. The power law creep exponent decreases with increase in hydrogen concentration, however, it remains fairly constant with increase in temperature up to 500 ℃. Moreover, activation energy too decreases significantly with increase in hydrogen concentration. The mean stress exponent and activation energy are found to be 3.58 and 28.67 kJ/mol, respectively, for as-received sample.

• Preventive Nutrition and Food Science
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• 제2권1호
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• pp.6-10
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• 1997

The reaction mechanisms and kinetics of tertiary butylhydroquinone(TBHQ) as an antioxidant in soybean oil oxidation were studied. The oxidation reaction of soybean oil at 55, 60 and $65^{\circ}C$ was a first order. The activation energies of soybean oil containing 0, 25, 50, and 75ppm TBHQ were 12.15, 6.05, 6.15 and 6.17kcal/mole. respectively. The addition of THQ to soybean oil containing 0, 25, 50, and 75ppm TBHQ were 1.88$\times${TEX}$10^{7}${/TEX}, 4.10$\times${TEX}$10^{2}${/TEX}, 4.32 $\times${TEX}$10^{2}$p/TEX} and 3.97$\times${TEX}$10^{2}${/TEX}, respectively. The decrease of frequency factor rather than the activation energy. The effects of antioxidants on the temperature dependecy of lipid oxidation could be effectively evaluated by measuring their effects on the activation energy of lipid oxidation.

• 열처리공학회지
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• 제23권5호
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• pp.239-244
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• 2010

Influence of Zr addition on grain stability at elevated temperatures has been investigated for extruded pure Mg and Mg-0.25%Zr alloy. The grain size of pure Mg increases rapidly with increasing annealing temperature when isochronally annealed for 60 min from 573 to 773 K, whereas the grains are stable up to 723 K for the Zr-containing alloy. The activation energies for grain growth ($E_g$) at this temperature range were determined as 75.3 and 105.9 kJ/mole for the pure Mg and Mg-0.25%Zr alloy, respectively. TEM observations on the annealed Mg-Zr samples revealed that higher thermal stability and higher activation energy for grain growth resulting from Zr addition in Mg may well be associated with the restriction of grain growth by nano-sized Zr particles distributed in the microstructure.

• 한국표면공학회지
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• 제40권3호
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• pp.131-137
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• 2007

The typical MCFC (molten carbonate fuel cell) anode is made of Ni-10%Cr alloy. The work of this paper is focused concerning long life of anode because Ni-10% Cr anode is suffering from sintering and creep behavior during cell operation. Therefore, Ni-coated Alumina powder($20{\mu}m$) was developed by electroless nickel plating. Optimum condition of electroless nickel coation on $20{\mu}m$ alumina is as follows: pH 11.7, temperature $65{\sim}80^{\circ}C$, powder amount $100cm^2/l$. The deposition rate for Ni-electroless plating was as a function of temperature and activation energy was evaluated by Arrhenius Equation thereby activation energy calculated slope of experimental data as 117.6 kJ/mol, frequency factor(A) was $6.28{\times}10^{18}hr^{-1}$, respectively.

• Journal of Magnetics
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• 제19권2호
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• pp.116-120
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• 2014

The spin-lattice relaxation time, $T_1$, for $^{69}Ga$, $^{71}Ga$, and $^{75}As$ nuclei in GaAs:$Mn^{2+}$ single crystals was measured as a function of temperature. The values of $T_1$ for $^{69}Ga$, $^{71}Ga$, and $^{75}As$ nuclei were found to decrease with increasing temperature. The $T_1$ values in GaAs:$Mn^{2+}$ crystal are similar to those in pure GaAs crystal. The calculated activation energies for the $^{69}Ga$, $^{71}Ga$, and $^{75}As$ nuclei are 4.34, 4.07, and 3.99 kJ/mol. It turns out that the paramagnetic impurity effect of $Mn^{2+}$ ion doped in GaAs single crystal was not strong on the spin-lattice relaxation time.

• 한국염색가공학회지
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• 제10권3호
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• pp.36-42
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• 1998

The dyeabilities of C.I. Reactive Blue 19(B19, MW ; 626), C.I. Reactive Blue 4(B4, MW ; 637) and C.I. Reactive Black 5(B5, MW : 991) were investigated. Initial dyeing rates were increased and the amount of dye on the fabric at equilibrium was decreased with temperature like other ordinary dyeing processes. Activation entropy$(\Delta{S}^*)$ was decreased because of loose bonding between dyestuffes and fiber molecules at transition state. It can be clarified that the entire reaction is exothermic and the number of molecular species at transition state becomes greater from decrease in activation enthalpy$(\Delta{H}^*)$ and the increase in activation free energy$(\Delta{G}^*)$ with temperature, respectively. The amount of B19 on the fabric at equilibrium was greater than that of B4, because B4 became unreactive towards textile substrates through hydrolysis. Due to the biggest size of the dye molecule, the reaction rate of B5 was the slowest but its difunctional group played an important role in achieving the greatest amount of dye on the fabric at equilibrium.

• 멤브레인
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• 제7권4호
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• pp.183-190
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• 1997

Composite membranes were prepared by the deposition of pentafluoropyridine(PFP) or pentafluorotoluene(PFT) plasma films onto porous Celgard and nonporous poly(dimethylsiloxane) [PDMS] films. Gas permeation measurements for the composite membranes were made in the temperature range of 35$^{\circ}$C to 75 $^{\circ}$C and the solubilities in plasma polymers were measured using a Cahn Microbalance. The permeability coefficients of plasma polymers obeyed the Arrhenius relationship fairly wall. Activation energies for permeation in the plasma films increased with the size of penetrant molecules. The activation energy of plasma polymers was much lower than that of commonly used perfluoropolymers. This difference was proved to be attributable to the much lower heat of solutions of the plasma polymers compared to perfluoropolymers. The diffusion activation energies were comparable with each other.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2021년도 봄 학술논문 발표대회
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• pp.78-79
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• 2021

It is necessary to calculate Apparent Activation Energy(Ea) in order to apply the equivalent age formula to predict compressive strength using the maturity method. For carbon reduction, it is necessary to consider the change of Ea by condition of GGBFS concrete, which is widely used today. In this study, as a basic study for the design of the compressive strength model of GGBFS concrete, the apparent activation energy of the GGBFS mixed paste was calculated through a calorimeter. The experiment was carried out at a hydration temperature of 10 to 30℃ with a paste test specimen having a GGBFS content of 0 to 80%. As a result, the GGBFS replacement rate of the paste increased, and Ea tended to increase as the temperature decreased.

• 산업기술연구
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• 제39권1호
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• pp.7-14
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• 2019

Carbon nanotubes (CNT) on metal substrates are definitely beneficial because they can maintain robust mechanical stability and high conductivity between CNT and metal interfaces. Here, we report direct growth of CNT on Ni-based superalloy, Inconel 600, using thermal chemical vapor deposition (CVD) with acetylene feedstock in the growth temperature range of $400-725^{\circ}C$. Furthermore, we studied the effect of substrate pretreatment on the growth yield enhancement and growth temperature decrease of CNT on Inconel 600. Activation energy (AE) for CNT growth was estimated from the CNT height change with respect to the growth temperature. The AE values significantly decreased from 205.03 to 24.35 kJ/mol by the pretreatment of thermal oxidation of Inconel substrate at $725^{\circ}C$ under ambient. Higher oxidation temperature tends to have lower activation energy. The results have shown the importance of pretreatment temperature on CNT growth yield and growth temperature decrease.

• 한국화재소방학회:학술대회논문집
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• 한국화재소방학회 1996년도 학술발표회
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• pp.15-18
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• 1996

A general description of sprinkler activation time in compartment-fire-generated smoke layers is made. For calculation of the time hot layer temperature is obtained from two-layer zonal model and time constant of sprinkler is measured. Upper-layer thickness at the instant of sprinkler activation is also presented with changes of opening area. The outputs of the present study provide inputs for the interaction modeling of sprinkler spray and compartment fire environment, which simulates fire suppression phenomena.