• Bulletin of the Korean Chemical Society
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• v.9 no.6
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• pp.333-337
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• 1988

Spinel $CoFe_2O_4$ solid solutions containing up to 50 mol% CoO were synthesized with spectroscopically pure CoO and ${\alpha}-Fe_2O_3$ polycrystalline powders. The spinel structures of the $CoFe_2O_4$ solid solutions were analyzed from XRD patterns and the Mossbauer spectra showed that the quenched $CoFe_2O_4$ had a partially inversed spinel structure ($Co_{0.23}Fe_{0.77}$) < $Co_{0.77}Fe_{1.23}$ > $O_4$, while the slowly cooled $CoFe_2O_4$ was completely inversed spinel ($Co_{0.04}Fe_{0.96}$) <$Co_{0.96}Fe_{1.04}$ > $O_4$. The $CoFe_2O_4$ specimens containing 10, 20, 30 and 40 mol% CoO turned to be a mixture of corundum and spinel structures. Electrical conductivities were measured as a function of temperature from 300 to $900^{\circ}C$ under oxygen partial pressures from $10^{-3}$ to 1 atm. The temperature dependencies of the electrical conductivity show different behaviors in the low- and high-temperature regions. The average activation energies are 0.23 eV and 0.80 eV in the low- and high-temperature regions, respectively. It is suggested that $Co^{2+} {\to} CO^{3+} + e^-$ and $Fe^{2+} {\rightleftharpoons} Fe^{3+} + e^-$ are the main conduction mechanisms responsible for the electronic conduction in the low- and high-temperature regions, respectively.

• Journal of Electrochemical Science and Technology
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• v.14 no.1
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• pp.59-65
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• 2023

Sodium hydroxide solutions are often employed as sterilization agents in the pharmaceutical industry. Here, the chloride content is considered as a critical impurity. In this study, an electrochemical method was developed to remove chloride ions (Cl^-) through the oxidative deposition of AgCl on a Ag anode. The Cl^- content in the commercially available 50% w/w NaOH solution employed was approximately 100 mg Cl^-/kg NaOH. As the OH^- content is approximately 18,000 times higher than the Cl^- content, the formation of AgCl may be expected to be thermodynamically less favorable than the formation of Ag₂O. However, activation energies for AgCl and Ag₂O formation have been reported to be approximately 3.8 and 31.2 kJ/mol, respectively, and indicate that AgCl formation is favored. AgCl can be selectively produced by controlling the anode potential. Here, the Cl^- concentration was reduced to less than 50 mg Cl^-/kg NaOH when an anode potential of 0.18 or 0.19 V vs. Hg/HgO (reference electrode) was applied for one hour at 50℃. XRD analysis and visual monitoring of the Ag anode confirmed the oxidative deposition of AgCl on the anode surface as well as the electrochemical desalination of the concentrated NaOH solution.

• Journal of Electrochemical Science and Technology
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• v.13 no.2
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• pp.237-253
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• 2022

The methyl 2-(1,3-dithietan -2- ylidene)-3-oxobutanoate (MDYO) and 2-(1,3-dithietan-2-ylidene) cyclohexane -1,3-dione (DYCD) were synthesized and tested at various concentrations as corrosion inhibitors for 316L stainless steel in 1 M HCl using weight loss, electrochemical impedance spectroscopy (EIS), potentiodynamic polarization (PDP), surface analysis techniques (SEM / EDX and Raman spectroscopy) and Functional Density Theory (DFT) was also used to calculate quantum parameters. The obtained results indicated that the inhibition efficiency of MDYO and DYCD increases with their concentration, and the highest value of corrosion inhibition efficiency was determined in the range of concentrations investigated (0.01 × 10^-3 - 10^-3 M). Polarization curves (Tafel extrapolation) showed that both compounds act as mixed-type inhibitors in 1M HCl solutions. Electrochemical impedance spectra (Nyquist plots) are characterized by a capacitive loop observed at high frequencies, and another small inductive loop near low frequencies. The thermodynamic data of adsorption of the two compounds on the stainless steel surface and the activation energies were determined and then discussed. Analysis of experimental results shows that MDYO and DYCD inhibitors adsorb to the metal surface according to the Langmuir model and the mechanism of adsorption of both inhibitors involves physisorption. SEM-EDX results confirm the existence of an inhibitor protective film on the stainless steel surface. The results derived from theoretical calculations supported the experimental observation.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.4B
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• pp.427-432
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• 2006

The effects of free ammonia (FA) concentration and temperature on nitrite accumulation were studied. To estimate the most effective ammonium oxidation and nitrite build-up condition, nitrification tests were conducted in batch conditions at various FA concentrations, and at different ammonium concentration and temperature. The activation energies of ammonium oxidizer were 81.7 KJ/mol below $20^{\circ}C$, and 32.5 KJ/mol over $20^{\circ}C$, while that of nitrite oxidizer was 35.5 KJ/mol irrespective of temperature variations. The results of nitrification tests conducted at different FA concentrations and temperatures showed that temperature strongly affects nitrite accumulation, while effects due to FA concentrations were found negligible.

• Transactions of the Korean hydrogen and new energy society
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• v.34 no.6
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• pp.587-593
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• 2023

This research project focused on the production of hydrogen through ammonia decomposition reactions while investigating how the reactivity of this process varies when employing different catalysts. Several metal oxide supports (Al₂O₃, La₂O₃, CeO₂) were utilized as catalysts, with active metals from both the transition metal group (Co, Ni, Fe, Cr, Cu) and the noble metal group (Ru, Rh, Pd, Pt) impregnated onto these supports. Furthermore, the study examined how the reactivity evolves with changes in reaction temperature when employing the prepared catalysts. Additionally, the research delved into the distinctive activation energies associated with each of the catalysts. In this research, In the noble metal catalyst system, the order of high activity for ammonia decomposition reaction to produce hydrogen is Ru > Rh > Pt ≈ Pd. In the transition metal catalyst system, the order of high activity is Co > Ni > Fe > Cr > Cu.

• Korean Journal of Materials Research
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• v.34 no.6
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• pp.267-274
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• 2024

In this study, four different samples of Se₆₀Ge_40-xBi_x chalcogenides glasses were synthesized by heating the melt for 18 h in vacuum Pyrex ampoules (under a 10^-4 Torre vacuum), each with a different concentration (x = 0, 10, 15, and 20) of high purity starting materials. The results of direct current (DC) electrical conductivity measurements against a 1,000/T plot for all chalcogenide samples revealed two linear areas at medium and high temperatures, each with a different slope and with different activation energies (E₁ and E₂). In other words, these samples contain two electrical conduction mechanisms: a localized conduction at middle temperatures and extended conduction at high temperatures. The results showed the local and extended state parameters changed due to the effective partial substitution of germanium by bismuth. The density of extended states N(E_ext) and localized states N(E_loc) as a function of bismuth concentration was used to gauge this effect. While the density of the localized states decreased from 1.6 × 10¹⁴ to 4.2 × 10¹² (ev^-1 cm^-3) as the bismuth concentration increased from 0 to 15, the density of the extended states generally increased from 3.552 × 10²¹ to 5.86 × 10²¹ (ev^-1 cm^-3), indicating a reduction in the mullet's randomness. This makes these alloys more widely useful in electronic applications due to the decrease in the cost of manufacturing.

• The Korean Journal of Food And Nutrition
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• v.24 no.4
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• pp.559-566
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• 2011

The effects of pH and temperature on degradation of anthocyanin in purple-fleshed sweet potato cultivars(Mokpo No.62, Borami, Jami, Sinjami and Ayamurasaki) were determined at pH ranges of 1 to 5 and temperature ranges of 20 to $80^{\circ}C$. The anthocyanin contents of five sweet potato varieties were 3.9, 3.8, 4.7, 4.1, 4.2 mg/g of dried sweet potato, respectively. Degradations of anthocyanins at different pHs and temperatures followed the first-order reaction. Our results clearly showed that the anthocyanin stability of purple-fleshed sweet potato was dependent on the source of the sweet potato cultivars. Anthocyanin obtained from Borami showed the highest stability. The half-life of antocyanin degradation of purple sweet potato cultivars(Mokpo No.62, Borami, Jami, Sinjami and Ayamurasaki) at pH 3 were 22.2, 28.3, 26.3, 23.4, 22.7 days at $60^{\circ}C$, respectively. A significant decrease in anthocyanin stability was observed at temperatures above $40^{\circ}C$. Activation energies of purple-fleshed sweet potato cultivars at different temperatures were 54.67, 60.93, 71.73, 59.35, 62.28 kJ/mol, respectively.

• Korean Journal of Food Science and Technology
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• v.24 no.3
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• pp.256-260
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• 1992

This study was conducted to calculate and predict the shelf-life of meat sausage through physicochemical and biological analysis. Judging from physico-chemical components, it can be found out the most effective indicator in meat sausage. And also, the materials used for packaging is cellulose #23 in inner-packaging and CN/HDPE laminating film in outer-packaging. The changes of the most effective indicator were discussed through the method of kinetic analysis. Judging from physico-chemical components, VBN was the most available component in quality judgement of meat sausage and their upper limiting contents were 20 mg%. It is possible to calculate and predict the shelf-life of meat sausage through the regression equation and $Q_{10}$ value. As a result, the shelf-life prediction was $58{\sim}63$ days at $10^{\circ}C$, $47{\sim}51$ days at $20^{\circ}C$ and 26 days at $40^{\circ}C$, respectively, but the difference between two methods showed about $4{\sim}5$ days. $Q_{10}$ value on the changes contents was 1.35 at acceralated temperature $40^{\circ}C$. The reaction rate of VBN contents could be interpreted as a first order reaction that divided into 2 periods with different reaction rate constants. The corresponding Arrhenius activation energies were 2.959 Kcal/mole and 3.632 Kcal/mole, respectively.

• Journal of the Korean Society of Food Science and Nutrition
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• v.22 no.4
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• pp.458-464
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• 1993

In the present paper enzymatic properties of the trypsins from the four dark fleshed fish were compared with each other and thermal stabilities of the enzymes were also investigated. The trypsins from the dark fleshed fish showed their activity only in BA-p-NA substrate of the amide substrates such as BA-p-NA and SP-p-NA, and BAEE and TAME of the ester substrate such as ATEE, BAEE, BTEE, and TAME. The enzymes were strongly inhibited by the serine protease inhibitors such as antipain, leupeptin, TLCK, DFP and SBTI, and were also inhibited by such metal ions as Cu$^{2＋}$ and Hg$^{2＋}$, but fairly activated by $Mg^{2＋}$. Denaturation constants of the enzymes were 13.4$\times$10$^{-4}$ sec$^{-1}$ for anchovy trypsin, 47.18$\times$10$^{-4}$ sec$^{-1}$ for mackerel trypsin A, 34.06$\times$10$^{-4}$ sec$^{-1}$ mackerel trypsin B, 42.28$\times$10$^{-4}$ sec$^{-1}$ for yellowfin tuna trypsin and 16.6$\times$10$^{-4}$ sec$^{-1}$ for albacore trypsin at 55$^{\circ}C$. The activation energies of the trypsins at a temperature range of 3$0^{\circ}C$ to 5$0^{\circ}C$ were estimated to be 13.91 ㎉/mole for anchovy trypsin, 11.61㎉/mo1e and 8.43㎉/mole for mackerel trypsin A and for mackerel typsin B, 4.35㎉/mole for yellowfin tuna trypsin, and 3.76㎉/mole for albacore trypsin.

• Korean Chemical Engineering Research
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• v.52 no.4
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• pp.544-552
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• 2014

In this study, We have investigated the kinetics on the char-$CO_2$ gasification reaction. Thermogravimetric analysis (TGA) experiments were carried out for char-$CO_2$ catalytic gasification of an Indonesian Roto lignite. $Na_2CO_3$, $K_2CO_3$, $CaCO_3$ and dolomite were selected as catalyst which was physical mixed with coal. The char-$CO_2$ gasification reaction showed rapid an increase of carbon conversion rate at 60 vol% $CO_2$ and 7 wt% $Na_2CO_3$ mixed with coal. At the isothermal conditions range from $750^{\circ}C$ to $900^{\circ}C$, the carbon conversion rates increased as the temperature increased. Three kinetic models for gas-solid reaction including the shrinking core model (SCM), volumetric reaction model (VRM) and modified volumetric reaction model (MVRM) were applied to the experimental data against the measured kinetic data. The gasification kinetics were suitably described by the MVRM model for the Roto lignite. The activation energies for each char mixed with $Na_2CO_3$ and $K_2CO_3$ were found a 67.03~77.09 kJ/mol and 53.14~67.99 kJ/mol.