• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2001.07a
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• pp.554-557
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• 2001

In this work, we had synthesis the GaN powder by direct reaction between Ga and NH$_3$at the temperature range of 1000∼1150$^{\circ}C$, and investigated the reaction condition dependence of the GaN yield and some properties of GaN powder. The synthesized powder had Platelet and prismatic shape and showed hexagonal crystalline structure with the lattice constants of a= 3.1895 ${\AA}$, c= 5.18394 ${\AA}$, and the ratio of c/a = 1.6253. The GaN powder synthesis processes were examined based on the oxidation process of mater, and found as combined with mass transport process for the initial stage and diffusion-limited reaction for the extended reaction.

• Journal of the Korean Ceramic Society
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• v.31 no.11
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• pp.1346-1354
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• 1994

In this study, the formation of magnetite using Fe(II) and Fe(III) hydroxides was investigated; The effects of hydroxide synthesizing pH and temperature, reaction temperature, and total water volume of hydroxide suspensions on the magnetite formation were studied. And the basic reaction behaviors of magnetite formation was discussed in the view of hydroxide formation reaction of Fe(II) and Fe(III) by titration. The characteristics of products were examined by TEM, VSM, XRD. From these experimental data, solid-solid reaction between Fe(II) and Fe(III) hydroxides is proposed as a new ferrite formation mechanism.

• Journal of the Korean Ceramic Society
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• v.32 no.1
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• pp.37-44
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• 1995

TiO2 fine powders were synthesized using oxygenolysis and hydrolysis reaction of TiCl4 vapor in gas phase. The TiO2 powder synthesized showed morphological differences depending on reaction system as follows: TiCl4-O2 reaction system produced the monosized particles having polyhedral shape with well-defined crystal planes and the particles did not agglomerate into secondary particles. TiCl4-H2O reaction system, whereas, produced the spherical secondary particles which consisted of fine primary particles. Other powder characteristics such as particle size, impurity content and rutile content are also reported in this study.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.30 no.11 s.254
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• pp.1123-1130
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• 2006

This study discusses about research efforts of hydrogen generation from hydrocarbon(e.g., diesel, gasoline, natural gas, and LPG), especially, butane reforming by using Autothermal Reforming Reaction (ATR) technology. Several catalysts were selected for butane ATR. Thermodynamic reactor conditions (temperature, $O_2$/C, S/C) are varied and reforming characteristics of 2 catalysts (Pt and Rh on ceramic supports) and 1 commercial catalyst (FCR-HC35) have been examined. To understand reaction behaviors in an ATR reactor comprehensively, temperature profiles of reactor were observed. By mass transfer limitation, fuel conversion decreases when GHSV increases. Significant temperature variation along the reactor was observed and it was mainly due reaction kinetics difference between exothermic oxidation and endothermic reforming reaction.

• Journal of Aerospace System Engineering
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• v.10 no.1
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• pp.74-81
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• 2016

Space propulsion system produces required thrust for satellites and space launch vehicles by using chemical reactions of a liquid fuel and a liquid oxidizer typically. Among several liquid propellants, the monomethylhydrazine-dinitrogen tetroxide is expecially preferred for a GEO satellite propellants due to their better storability in liquid phase during a long mission life under a freezing space environment. Recently, a development of the monomethylhydrazine-dinitrogen tetroxide bipropellant system becomes important as the national space program requires the heavier and the more efficient space system. Thus, the objective of the present study is to review a foreign research trend of a chemical reaction between the monomethyhydrazine fuel and the dinitrogen tetroxide oxidizer to understand a fundamental basis of their characteristics to prepare for domestic development in future.

• Nuclear Engineering and Technology
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• v.47 no.4
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• pp.424-433
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• 2015

The operating characteristics of hydrogen iodide (HI) decomposition for hydrogen production were investigated using the commercial computational fluid dynamics code, and various factors, such as hydrogen production, heat of reaction, and temperature distribution, were studied to compare device performance with that expected for device development. Hydrogen production increased with an increase of the surface-to-volume (STV) ratio. With an increase of hydrogen production, the reaction heat increased. The internal pressure and velocity of the HI decomposer were estimated through pressure drop and reducing velocity from the preheating zone. The mass of $H_2O$ was independent of the STV ratio, whereas that of HI decreased with increasing STV ratio.

• Journal of the Korean Ceramic Society
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• v.35 no.1
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• pp.1-4
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• 1998

SiC whisker reinforced Al2O3-SiC composite was fabricated by reaction synthesis method whish is cost ef-fective and allows good dispersion of whiskers. Fracture strength at room temperature showed the highest value with 150$0^{\circ}C$ reaction temperature because a lot of SiC whiskers was formed. Fracture strength at 135$0^{\circ}C$ did not show big differences with reaction temperature due to agglomeration of whiskers and formation of sil-icon oxynitride during hot MO(modulus of rupture) test probably promoting grain boundary sliding.

• Journal of Korean Society of Environmental Engineers
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• v.29 no.9
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• pp.989-996
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• 2007

In this study, abiotic transformation of 1-naphthol(1-NP) via oxidative-coupling reaction and its reaction products were investigated in the presence of Mn oxides. The reaction products were characterized for their relative polarity using solvent extraction experiment and reverse-phase HPLC, and for structure using CCMS and LC/MS, and for absorption characteristics using UV-Vis spectrometry. The reaction products present in aqueous phase were more polar than parent naphthol and comprised of 1,4-naphthoquinon(1,4-NPQ) and oligomers such as dimers and trimers. Hydrophilic component present in water phase after solvent$(CH_2Cl_2)$ extractions was identified as naphthol polymerized products having molecular weight(m/z) ranging from 400 to 2,000, and showed similar UV-Vis. absorption characteristics to that of foil fulvic acid. Transformation of 1,4-NPQ, which is non-reactive to Mn oxide, to the polymerized products via cross-coupling reaction in the presence of 1-NP was also verified. In this experimental conditions(20.5 mg/L, 1-NP, 2.5 g/L $MnO_2$, pH 5), the transformation of 1-NP into the oligomers and polymerized products were about 83% of initial 1-NP concentrations, and more than 30% of the reaction products was estimated to be water insoluble fractions, not extracted by $H_2O$ methanol. Results from this study suggest that Mn oxide-mediated treatment of naphthol contaminated soils can achieve risk reduction through the formation of oligomers md polymer precipitation.

• Korean Chemical Engineering Research
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• v.54 no.3
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• pp.299-304
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• 2016

Characteristics of self-propagating reaction for the preparation of ZnO powder from precursors composed of nitrate and citrate compounds were examined. The ratio of C/N was maintained in range of 0.7~0.8 to initiate the self-propagating reaction between the reducing citrate and oxidizing nitrate groups. The samples were decomposed thermally by using TGA. The sudden decomposition occurred in the range of X > 0.5 in a very short time with a very sharp decrease of mass, indicating that the self-propagating reaction would occur. Friedman, Ozawa-Flynn-Wall and Vyazovkin methods were employed to predict the activation energy, reaction order and frequency factor of the reaction rate in the rate determining step of X < 0.5 range. The activation energy increased with increasing fractional conversion in the range of 46~130 (kJ/min). The reaction order decreased in the range of 2.9~0.9, while the frequency factor increased in the range of 85~278 ($min^{-1}$), respectively, with increasing the rate of temperature increase.

• Journal of Korean Society of Environmental Engineers
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• v.22 no.3
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• pp.547-556
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• 2000

A study have been conducted for the adsorption and desorption characteristics of Cu ion using manganese nodule as adsorbent. For 100 ppm Cu ion solution, the adsorbed amount of Cu ion was more than 90 % at equilibrium state. Adsorption was equilibrated in 42 hours the adsorption reaction was shown to be first order reaction. For the desorption reaction of Cu ion in the region of solution pH 3.5~9.5, the desorption was completed in the acidic region, but it has been decreased as the pH was raised. Also, the desorption rate was higher in the acidic region compared with alkaline region. The desorbed amount was decreased as the reaction temperature increased, therefore, the desorption reaction was thought to be exothermic. Also, several thermodynamic properties were calculated based on experimental results and compared with theoretically driven values. To see the effect of complexing agent on the desorption of Cu ion, EDTA was introduced and the des orbed amount increased in the presence of EDTA.