• Applied Chemistry for Engineering
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• v.2 no.2
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• pp.165-174
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• 1991

The kinetics and the mechanism for the selective oxidation of ethylene on the supported monolithic silver catalyst were experimentally investigated in a fixed bed tubular reactor. The formation rates of ethylene oxide and carbon dioxide were measured at the atmospheric pressure with various combinations of partial pressures of ethylene and oxygen at temperature range of $225-300^{\circ}C$, conversion with 1.2-7.5 %, and then the mechanism of the selective oxidation of ethylene was verified. Their formation rates fitted with the Langmuir-Hinshelwood mechnism. The ethylene oxide and carbon dioxide are produced by reation of adsorbed ethylene with monoatomic oxygen adsorbed on the active sites of Ag-surface, and their formation rate equation are expressed as : $R_{EO}={\frac{k_1K_0{^{1/2}}K_EK_SP_{02}{^{3/2}}P_E}{(1+{\sqrt{K_0P_{02}}}+K_EP_E+K_PP_P)^2(1+{\sqrt{K_SP_{02}})^2}}$ $R_C={\frac{k_2K_0{^3}K_EK_S{^{7/2}}P_{02}{^{13/2}}P_E}{(1+{\sqrt{K_0P_{02}}}+K_EP_E+K_PP_P)^7(1+{\sqrt{K_SP_{02}})^7}}$ The activation energies of ethylene oxide and dioxide and carbon dioxide formations can be estimated to be 12.25 and 17.85 Kcal/mol, respectively.

• BMB Reports
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• v.40 no.1
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• pp.100-106
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• 2007

The wound-inducible lipoxygenase obtained from maize is one of the nontraditional lipoxygenases that possess dual positional specificity. In this paper, we provide our results on the determination and comparison of the kinetic constants of the maize lipoxygenase, with or without detergents in the steady state, and characterization of the dependence of the kinetic lag phase or initial burst, on pH, substrate, and detergent in the pre-steady state of the lipoxygenase reaction. The oxidation of linoleic acid showed a typical lag phase in the pre-steady state of the lipoxygenase reaction at pH 7.5 in the presence of 0.25% Tween-20 detergent. The reciprocal correlation between the induction period and the enzyme level indicated that this lag phenomenon was attributable to the slow oxidative activation of Fe (II) to Fe (III) at the active site of the enzyme as observed in other lipoxygenase reactions. Contrary to the lagging phenomenon observed at pH 7.5 in the presence of Tween-20, a unique initial burst was observed at pH 6.2 in the absence of detergents. To our knowledge, the initial burst in the oxidation of linoleic acid at pH 6.2 is the first observation in the lipoxygenase reaction. Kinetic constants (Km and kcat values) were largely dependent on the presence of detergent. An inverse correlation of the initial burst period with enzyme levels and interpretations on kinetic constants suggested that the observed initial burst in the oxidation of linoleic acid could be due to the availability of free fatty acids as substrates for binding with the lipoxygenase enzyme.

• Journal of the Korean Electrochemical Society
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• v.11 no.3
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• pp.147-153
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• 2008

Improvement of the selectivity of nonenzymatic glucose based on mesoporous platinum ($H_1$-ePt) by using A.C. impedance is reported. The idea of the present work is based on the novel effect of the mesoporous electrode that the apparent exchange current due to glucose oxidation remarkably grows although the reaction kinetics on the surface is still sluggish. It is expected that the enlarged apparent exchange current on the mesoporous electrode can raise the sensitivity of admittance in A.C. impedance to glucose concentration. At a low frequency, A.C. impedance could become more powerful. The admittance at 0.01 Hz is even more sensitive to glucose than to ascorbic acid while amperometry exhibits the inverse order of sensitivity. This is the unique behavior that is neither observed by A.C. impedance on flat platinum electrode nor obtained by amperometry. The study shows how the combination of A.C. impedance and nano-structured surface can be applied to the detection of sluggish reaction such as electrochemical oxidation of glucose.

• Journal of the Korean Chemical Society
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• v.38 no.12
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• pp.885-890
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• 1994

Kinetics of electrochemical polymerization of aniline on a tungsten electrode in acidic aqueous solution was studied by means of cyclic voltammetry and kinetic measurements of anodic oxidation. Aniline molecule appeared to be intially oxidized via two-electron transfer to produce oxidized deprotonated aniline ion, which subsequently undergoes nucleophilic attack to the parent aniline and results in head to tail coupling to yield a dimerized species. But, being contrary to the case of Pt electrode, the propagation of polymerization occured through attack of the monomer by the oxidized aniline monomer to polymer. The growth rate of polyaniline was slow in comparison with the growth on Pt electrode. The degradation products were confirmed to be not p-benzoquinone(BQ) but p-phenylenediamine(p-PDA) by spectrophotometry, which agrees with the fact that oxidation of p-PDA was not observed below 1.0 V.

• Bulletin of the Korean Chemical Society
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• v.33 no.9
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• pp.3009-3016
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• 2012

This study evaluated the use of iron-impregnated SBA-15 (Fe/SBA-15) as a catalyst for the oxidative degradation of persistent phenol analogues, such as 2-chlorophenol (2-CP), 4-chlorophenol (4-CP), 2-nitrophenol (2-NP), 4-nitrophenol (4-NP) and 2,4,6-trichlorophenol (2,4,6-TCP) in water. The oxidation reactions were carried out with reaction time, concentration of the phenols, amount of the catalysts, reaction temperature, pH of the reaction mixture as the process variables with or without using hydrogen peroxide as the oxidizing agent. The conversion achieved with Fe/SBA-15 at 353 K for 2-CP, 4-CP, 2-NP, 4-NP, 2,4,6-TCP was 80.2, 71.2, 53.1, 62.8, 77.3% in 5h with a reactant to $H_2O_2$ mole ratio of 1:1, and 85.7, 65.8, 61.9, 63.7, 78.1% in the absence of $H_2O_2$, respectively. The reactions followed pseudo first order kinetics. The leachability study indicated that the catalyst released very little iron into water and therefore, the possibility of secondary pollution is negligible.

• Journal of the Korean Society for Heat Treatment
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• v.18 no.1
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• pp.24-28
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• 2005

New post plasma nitriding can achieve a high uniformity that have been difficult in DC nitriding and have a high productivity comparable to gas nitriding. However, it has not a enough high nitriding potential for a rapid nitriding, because surface activation or ion etching in the general plasma nitriding cannot be expected. Thus, in this study, the effects of pre-treatments with oxidation and reduction gas have been investigated to improve the nitriding kinetics of post plasma nitriding. An effective pre-treatment consisting of oxidation and reduction resulted in the increase of surface energy of STD 11. This induced the surface hardness and the effective nitriding depth of STD 11. It is thought that the increase of the surface energy and the surface area with pre-treatment promote the nucleation of nitriding layer.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.18 no.6
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• pp.515-520
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• 2005

CMP(chemical mechanical polishing) process has been attracted as an essential technology of multi-level interconnection. Also CMP process got into key process for global planarization in the chip manufacturing process. In this study, potentiodynamic polarization was carried out to investigate the influences of $H_2O_2$ concentration and metal oxide formation through the passivation on tungsten and titanium. Fortunately, the electrochemical behaviors of tungsten and titanium are similar, an one may expect. As an experimental result, electrochemical corrosion of the $5\;vol\%\;H_2O_2$ concentration of tungsten and titanium films was higher than the other concentrations. According to the analysis, the oxidation state and microstructure of surface layer were strongly influenced by different oxidizer concentration. Moreover, the oxidation kinetics and resulting chemical state of oxide layer played critical roles in determining the overall CMP performance. Therefore, we conclude that the CMP characteristics tungsten and titanium metal layer including surface roughness were strongly dependent on the amounts of hydrogen peroxide oxidizer.

• Journal of Electrochemical Science and Technology
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• v.8 no.2
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• pp.96-100
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• 2017

Iridium(III) bis(2-phenylpyridinato-$N,C^{2^{\prime}}$)acetylacetonate ($(ppy)_2Ir(acac)$), a green dopant used in organic light-emitting devices (OLEDs), was subjected to electrochemical characterization to estimate its formal oxidation potential ($E^{o^{\prime}}$), HOMO energy level ($E_{HOMO}$), electron transfer rate constant ($k^{o^{\prime}}$), and diffusion coefficient ($D_o$). The employed combination of voltammetric methods, i.e., cyclic voltammetry (CV), chronocoulometry (CC), and the Nicholson method, provided meaningful insights into the electron transfer kinetics of $(ppy)_2Ir(acac)$, allowing the determination of $k^{o^{\prime}}$ and $D_o$. The quasi-reversible oxidation of $(ppy)_2Ir(acac)$ furnished information on $E^{o^{\prime}}$ and $E_{HOMO}$, allowing the latter parameter to be easily estimated by electrochemical methods without relying on expensive and complex ultraviolet photoemission spectroscopic (UPS) measurements.

• Nuclear Engineering and Technology
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• v.50 no.2
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• pp.237-245
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• 2018

Potential air ingress scenarios during accidents in nuclear reactors or spent fuel pools have raised the question of the influence of air, especially of nitrogen, on the oxidation of zirconium alloys, which are used as fuel cladding tubes and other structure materials. In this context, the reaction of zirconium with nitrogen-containing atmospheres and the formation of zirconium nitride play an important role in understanding the oxidation mechanism. This article presents the results of analysis of the interaction of the oxygen-preloaded niobium-bearing alloy $M5^{(R)}$ with nitrogen over a wide range of temperatures ($800-1400^{\circ}C$) and oxygen contents in the metal alloy (1-7 wt.%). A strongly increasing nitriding rate with rising oxygen content in the metal was found. The highest reaction rates were measured for the saturated ${\alpha}-Zr(O)$, as it exists at the metal-oxide interface, at $1300^{\circ}C$. The temperature maximum of the reaction rate was approximately 100 K higher than for Zircaloy-4, already investigated in a previous study. The article presents results of thermogravimetric experiments as well as posttest examinations by optical microscopy, scanning electron microscopy (SEM), and microprobe elemental analyses. Furthermore, a comparison with results obtained with Zircaloy-4 will be made.

• Korean Journal of Metals and Materials
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• v.47 no.2
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• pp.107-113
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• 2009

Molten iron with 2 mass % carbon content was decarbonized at 1823 K~1923 K by bubbling $Ar+O_2$ gas through a submerged nozzle. The reaction rate was significantly influenced by the oxygen partial pressure and the gas flow rate. Little evolution of CO gas was observed in the initial 5 seconds of the oxidation; however, this was followed by a period of high evolution rate of CO gas. The partial pressure of CO gas decreased with further progress of the decarbonization. The overall reaction is decomposed to two elementary reactions: the decarbonization and the dissolution rate of oxygen. The assumptions were made that these reactions are at equilibrium and that the reaction rates are controlled by mass transfer rates within and around the gas bubble. The time variations of carbon and oxygen contents in the melt and the CO partial pressure in the off-gas under various bubbling conditions were well explained by the mathematical model. Based on the present model, it was explained that the decarbonization rate of molten iron was controlled by gas-phase mass transfer at the first stage of reaction, but the rate controlling step was transferred to liquid-phase mass transfer from one third of reaction time.