• Korean Journal of Materials Research
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• v.10 no.6
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• pp.385-391
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• 2000

A kinetic study on the preparation of iron powder by hydrogen reduction of ferrous chloride vapor has been carried out both experimentally and theoretically. For the preparation of iron powder, ferrous chloride was vaporized and transported to a reaction zone by Ar gas used as carrier. Ferrous chloride vapor and hydrogen were mixed and subject to a reduction reaction at high temperature to produce iron powder and HCI gas. Iron powder was collected with organic solvent at the end of reaction zone and HCI gas was also absorbed in a caustic soda solution to determine the conversion ratio of ferrous chloride. For the development of rate equations, a 1st-order reaction and equilibration of ferrous chloride vapor with Ar gas were assumed. According to the results, the rate constant, k could be expressed as $k=7,879exp(-53,840/RT)\textrm{dm}^3/mole.sec$ and the activation energy was found to be 53.84kJ/mole. From TEM observation, the particle size distribution of iron powder produced was found to be in the range of $0.1~1.0{\mu\textrm{m}}$ which was not significantly influenced by reaction temperature or gas flow rates.

• Economic and Environmental Geology
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• v.46 no.1
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• pp.29-37
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• 2013

In order to apply the silver cementation method using Fe powder from pregnant thiourea leaching solution. Parameters such as the amount of Fe powder addition, agitation speed, and temperature were investigated. The silver cementation rate was increased by the increasing of Fe powder addition, agitation speed, and temperature. The highest silver cementation rate was found when the addition of Fe powder was 50 g/L at the agitation speed of 500 rpm. The silver cementation rate increase with increasing temperature according to the Arrhenius equation and obeys $1^{st}$ order kinetics. The activation energy from the kinetics data was found to be between 13.73 KJ/mol and 17.02 KJ/mol. In the XRD analysis, goethite was detected in the precipitate of the thiourea leach solution. This indicates that an oxidation-reduction reaction had occurred in the thiourea solution due to the addition of the Fe powder.

• Journal of Energy Engineering
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• v.23 no.3
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• pp.157-162
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• 2014

In this research, we investigate electrical performance and electrochemical properties of carbon supported Pt (Pt/C) that is synthesized by polyol method. With the Polyol_Pt/C that is adopted for oxygen reduction reaction (ORR) as cathode of proton exchange membrane fuel cells (PEMFCs), their catalytic activity and ORR performance and electrical performance are estimated and compared with commercial Pt/C(Johnson Mattey) catalyst. Their electrochemically active surface (EAS) area are measured by cyclic voltammetry (CV), respectively. On the other hand, regarding ORR activity and electrical performance of the catalysts, (i) linear sweeping voltammetry by rotating disk electrode and (ii) PEMFC single cell tests are used. The CV measurement demonstrate EAS of Polyol_Pt/C is compared with commercial JM_Pt/C. In case of Polyol_Pt/C, its half-wave potential, kinetic current density are excellent. Based on data obtained by half-cell test, when PEMFC single cell tests are carried out, current density measured at 0.6V and maximum power density of the PEMFC single cell employing Polyol_Pt/C are better than those employing commercial Pt/C. Conclusively, Polyol_Pt/C synthesized by modified polyol process shows better ORR catalytic activity and PEMFC performance than other catalysts.

• Wind and Structures
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• v.28 no.1
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• pp.1-17
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• 2019

Internal ring beams are primary components of new ring-stiffened cooling towers. In this study, numerical simulation of the internal flow field of a cooling tower with three ring beams under wind-thermal coupling effect is performed. The studied cooling tower is a 220-m super-large hyperbolic indirect natural draft cooling tower that is under construction in China and will be the World's highest cooling tower, the influence of peripheral radiators in operating cooling tower is also considered. Based on the simulation, the three-dimensional effect and distribution pattern of the wind loads on inner surface of the cooling tower is summarized, the average wind pressure distributions on the inner surface before and after the addition of the ring beams are analyzed, and the influence pattern of ring beams on the internal pressure coefficient value is derived. The action mechanisms behind the air flows inside the tower are compared. In addition, the effects of internal ring beams on temperature field characteristics, turbulence kinetic energy distribution, and wind resistance are analyzed. Finally, the internal pressure coefficients are suggested for ring-stiffened cooling towers under wind-thermal coupling effect. The study shows that the influence of internal stiffening ring beams on the internal pressure and flow of cooling towers should not be ignored, and the wind-thermal coupling effect should also be considered in the numerical simulation of cooling tower flow fields. The primary conclusions presented in this paper offer references for determining the internal suction of such ring-stiffened cooling towers.

• Journal of Electrochemical Science and Technology
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• v.12 no.1
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• pp.82-91
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• 2021

This study was conducted to investigate the effect of initial pH, current density, and electrolysis time on process performance in terms of decolorization and chemical oxygen demand (COD) removal from disperse dyebath wastewater (DDW) by mono-polar parallel laboratory scale electrocoagulation (EC) process. COD reduction of 51.3% and decolorization of 92.8% were obtained with operating cost of 0.19 €/㎥ treated wastewater for Al-Al electrode pair, while 90.5% of decolorization and 49.2% of COD reduction were obtained with operating cost of 0.20 €/㎥ treated wastewater for an Fe-Fe electrode pair. The amount of sludge production were highly related to type of the electrode materials. At the optimum conditions, the amount of sludge produced were 0.18 kg/㎥ and 0.28 kg/㎥ for Al-Al and Fe-Fe electrode pairs, respectively. High decolorization can be explained by the hydrophobic nature of the disperse dye, while limited COD removal was observed due to the high dissolved organic matter of the DDW based on auxiliary chemicals. Energy, electrode, and chemical consumptions and sludge handling were considered as major cost items to find a cost-effective and sustainable solution for EC. The contribution of each cost items on operating cost were determined as 10.0%, 51.1%, 30.5% and 8.4% for Al-Al, and they were also determined as 9.0%, 38.0%, 40.5% and 12.5% for Fe-Fe, respectively. COD reduction and decolorization were fitted to first-order kinetic rule.

• Korean Journal of Metals and Materials
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• v.49 no.2
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• pp.167-173
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• 2011

Nickel cobalt ferrite($Ni_{0.5}Co_{0.5}Fe_2O_4$) powder was prepared through the ceramic route by the calcination of a stoichiometric mixture of NiO, CoO and $Fe_2O_3$ at $1100^{\circ}C$. The pressed pellets of $Ni_{0.5}Co_{0.5}Fe_2O_4$ were isothermally reduced in pure hydrogen at $800{\sim}1100^{\circ}C$. Based on the thermogravimetric analysis, the reduction behavior and the kinetic reaction mechanisms of the synthesized ferrite were studied. The initial ferrite powder and the various reduction products were characterized by X-ray diffraction, scanning electron microscopy, reflected light microscope and vibrating sample magnetometer to reveal the effect of hydrogen reduction on the composition, microstructure and magnetic properties of the produced Fe-Ni-Co alloy. The arrhenius equation with the approved mathematical formulations for the gas solid reaction was applied to calculate the activation energy($E_a$) and detect the controlling reaction mechanisms. In the initial stage of hydrogen reduction, the reduction rate was controlled by the gas diffusion and the interfacial chemical reaction. However, in later stages, the rate was controlled by the interfacial chemical reaction. The nature of the hydrogen reduction and the magnetic property changes for nickel cobalt ferrite were compared with the previous result for nickel ferrite. The microstructural development of the synthesized Fe-Ni-Co alloy with an increase in the reduction temperature improved its soft magnetic properties by increasing the saturation magnetization($M_s$) and by decreasing the coercivity($H_c$). The Fe-Ni-Co alloy showed higher saturation magnetization compared to Fe-Ni alloy.

• Food Science of Animal Resources
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• v.40 no.5
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• pp.813-830
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• 2020

In this study, the potential of infrared assisted freeze-drying (IRAFD) was tested for the production of shelf-stable edible insects: Protaetia brevitarsis larva (larva of white-spotted flower chafer). The IRAFD system was customized using an infrared lamp, K-type thermocouple, controller, and data acquisition system. The infrared lamp provided the sublimation energy for rapid freeze-drying (FD). The IRAFD conditions were continuous IRAFD-5.0 kW/㎡ and IRAFD-5.0 kW/㎡ at different weight reduction (WR) (10%, 20%, and 30%). The continuous IRAFD reduced the drying time to 247 min compared to the 2,833 min duration of FD (p<0.05). The electrical energy could be reduced by more than 90% through infrared radiation during FD (p<0.05). The Page model resulted in the best prediction among the tested drying kinetic models. In terms of quality, IRAFD showed significantly lower hardness, chewiness, and higher protein levels than hot air drying and FD (p<0.05). IRAFD better preserved the glutamic acid (6.30-7.29 g/100 g) and proline (3.84-5.54 g/100 g). The external product appearance after IRAFD exhibited more air pockets and volume expansion, which might result in a good consumer appeal. In conclusion, this study reports the potential of IRAFD in producing shelf-stable and value-added edible insects.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.27 no.10
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• pp.1393-1400
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• 2003

Ignition of hydrogen and oxygen in the "third limit" is theoretically investigated in the stagnation point flow with activation energy asymptotics. With the steady-state approximations of H, OH, O and HO$_2$, a two-step reduced kinetic mechanism is derived for the regime lower than the crossover temperature T$_{c}$ at which the rates of production and consumption of all radicals are equal. Appropriate scaling of Damkohler number successfully provides the explicit relationship between pressure, temperature and strain rate at ignition. It is shown that, compared with those for the counterflow, ignition temperatures for the stagnation point flow are considerably increased with increasing the system pressure. This is because ignition in the "third limit" is characterized by the production of reduction of $H_2O$$_2$, which is reduced by wall effect. Strain rate substantially affects ignition temperature because key reaction rates of $H_2O$$_2$ are comparably with its transport rate, while the mixture temperature and the hydrogen composition do not significantly affect ignition temperature.e.

• Journal of Mechanical Science and Technology
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• v.16 no.9
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• pp.1040-1053
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• 2002

This research deals with the influence of nonlinearities associated with impact and sliding upon the rocking behavior of a rigid block, which is subjected to two-dimensional horizontal and vertical excitation. Nonlinearities in the vibration were found to depend strongly on the effect of the impact between the block and the base, which involves an abrupt reduction in the system's kinetic energy. In particular, when sliding occurs, the rocking behavior is substantially changed. Response analysis using a non-dimensional rocking equation was carried out for a variety of excitation levels and excitation frequencies. The chaos responses were observed over a wide response region, particularly, in the cases of high vertical displacement and violent sliding motion, and the chaos characteristics appear in the time histories, Poincare maps, power spectra and Lyapunov exponents of the rocking responses. The complex behavior of chaotic response, in phase space, is illustrated by the Poincare map. The distribution of the rocking response is described by bifurcation diagrams and the effects of sliding motion are examined through the several rocking response examples.

• Journal of Photoscience
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• v.1 no.1
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• pp.9-14
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• 1994

Exposure of isolated intact mitochondria to near UV to visible light resulted in not only loss of respiration, the most well-documented phenomenon regarding phototoxic effects in the respiring organelles, but also lipid peroxidation of membranes and mitochondrial swelling; these turned out to be O$_2$-dependent and thus prevented by anaerobiosis, enhanced by a partial deuteration of the suspension medium, and suppressed by the presence of a singlet oxygen ($^1O_2$) scavenger. Measurements of the spectral dependence of such detrimental effects of light on mitochondrial structure and function revealed that all the resulting spectra bear a significant resemblance to the action spectrum for photogeneration of $^1O_2$ from mitochondrial membranes, which in turn carries the spectral characteristics of light absorption by mitochondrial Fe-S centers. Futhermore, destructing the Fe-S centers by a mercurial treatment of mitochondria brought about a striking reduction of the light-induced membrane peroxidation and swelling of mitochondria. These results are consistent with the suggestion that the impairment of functional, structural integrity of mitochondria caused by strong irradiation is directly related to the production of $^1O_2$ in mitochondria, photosensitized by the Fe-S centers. This paper also presents kinetic data which indicate that, among various membrane-bound protein systems associated with mitochondrial energy metabolism, the respiratory chain is the primary target for photodamage.