• Corrosion Science and Technology
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• v.22 no.3
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• pp.187-192
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• 2023

The use of biomass is increasing as a response to the convention on climate change. In Korea, a method applied to replace fossil fuels is using wood chips in a cogeneration plant. To remove air pollutants generated by burning wood chips, a selective denitrification facility (Selective catalytic reduction, SCR) is installed downstream. However, problems such as ash deposition and descaling of the equipment surface have been reported. The cause is thought to be unreacted ammonia slip caused by ammonia ions injected into the reducing agent and metal corrosion caused by an acidic environment. Element analysis confirmed that ash contained alkali metals and sulfur that could cause catalyst poisoning, leading to an increase in the size of ash particle and deposition. Measurement of the size of ash deposited inside the facility confirmed that the size of ash deposited on the catalyst was approximately three times larger than the size of generally formed ash. Therefore, it was concluded that a reduction in pore area of the catalyst by ash deposition on the surface of the catalyst could lead to a problem of increasing differential pressure in a denitrification facility.

• Korean Journal of Materials Research
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• v.20 no.10
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• pp.508-512
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• 2010

The optimum route to fabricate nano-sized Fe-50 wt% Co and hydrogen-reduction behavior of calcined Fe-/Conitrate was investigated. The powder mixture of metal oxides was prepared by solution mixing and calcination of Fe-/Co-nitrate. A DTA-TG and microstructural analysis revealed that the nitrates mixture by the calcination at $300^{\circ}C$ for 2 h was changed to Fe-oxide/$Co_3O_4$ composite powders with an average particle size of 100 nm. The reduction behavior of the calcined powders was analyzed by DTA-TG in a hydrogen atmosphere. The composite powders of Fe-oxide and Co3O4 changed to a Fe-Co phase with an average particle size of 40 nm in the temperature range of $260-420^{\circ}C$. In the TG analysis, a two-step reduction process relating to the presence of Fe3O4 and a CoO phase as the intermediate phase was observed. The hydrogen-reduction kinetics of the Fe-oxide/Co3O4 composite powders was evaluated by the amount of peak shift with heating rates in TG. The activation energies for the reduction, estimated by the slope of the Kissinger plot, were 96 kJ/mol in the peak temperature range of $231-297^{\circ}C$ and 83 kJ/mol of $290-390^{\circ}C$, respectively. The reported activation energy of 70.4-94.4 kJ/mol for the reduction of Fe- and Co-oxides is in reasonable agreement with the measured value in this study.

• Journal of Powder Materials
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• v.20 no.3
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• pp.197-202
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• 2013

A novel route to prepare Nd-Fe-B magnetic particles by utilizing both spray drying and reduction/diffusion processes was investigated in this study. Precursors were prepared by spray drying method using the aqueous solutions containing Nd salt, Fe salt and boric acid with stoichiometric ratios. Precursor particles could be obtained with various sizes from 2 to $10{\mu}m$ by controlling concentrations of the solutions and the average size of $2{\mu}m$ of precursors were selected for further steps. After heat treatment of precursors in air, Nd and Fe oxides were formed through desalting procedure, followed by reduction processes in Hydrogen ($H_2$) atmosphere and with Calcium (Ca) granules in Argon (Ar) successively. Moreover, diffusion between Nd and Fe occurred during Ca reduction and $Nd_2Fe_{14}B$ particles were formed. With Ca amount added to particles after $H_2$ reduction, intrinsic coercivity was changed from 1 to 10 kOe. In order to remove and leach CaO and residual Ca, de-ionized water and dilute acid were used. Acidic solutions were more effective to eliminate impurities, but Fe and Nd were dissolved out from the particles. Finally, $Nd_2Fe_{14}B$ magnetic particles were synthesized after washing in de-ionized water with a mean size of $2{\mu}m$ and their maximum energy product showed 9.23 MGOe.

• Clean Technology
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• v.20 no.1
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• pp.28-34
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• 2014

In this study, we synthesized $TiO_2$ supports with nanosized crystalline structure by solvothermal method and prepared $TiO_2$ supported Pd-Cu catalysts. It was shown that the crystalline size of $TiO_2$ support in the catalyst influenced on the catalytic activity of nitrate reduction in water. The catalyst with the smaller crystalline size of $TiO_2$ support presented faster nitrate reduction rate, but had low nitrogen selectivity due to high pH environment of reaction medium during the reaction. Through injection of carbon dioxide as a pH buffer, the nitrogen selectivity increased by about 60%. Furthermore, we investigated that the relationships between the catalytic performance and the physicochemical properties of the prepared catalysts characterized by $N_2$ adsoprtion-desorption, X-ray diffraction (XRD), $H_2$-temperature programmed reduction (TPR), X-ray photoelectron spectroscopy (XPS).

• The Journal of Korea Institute of Information, Electronics, and Communication Technology
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• v.11 no.5
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• pp.531-537
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• 2018

A novel PLL with a delta-sigma modulator and a spur reduction circuit is proposed. delta-sigma modulator makes the LF remove noise easily by moving the spur noise to a higher frequency band. Therefore, the magnitude of spur can be reduced the reasonable bandwidth. The spur reduction circuit reduces the spur size by reducing the LF voltage change generated during the period of reference signal. The spur reduction circuit is designed as simple as possible not to increase the size of PLL. The proposed PLL with the previous two techniques is designed with a supply voltage of 1.8V in a 0.18um CMOS process. Simulation results show an almost 20dB reduction in the magnitude of spur. The spur reduced PLL can be used in narrow bandwidth communication system.

• The Journal of Korea Institute of Information, Electronics, and Communication Technology
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• v.11 no.6
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• pp.651-657
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• 2018

A novel PLL with a delta-sigma modulator and a spur reduction circuit is proposed. delta-sigma modulator makes the LF remove noise easily by moving the spur noise to a higher frequency band. Therefore, the magnitude of spur can be reduced the reasonable bandwidth. The spur reduction circuit reduces the spur size by reducing the LF voltage change generated during the period of reference signal. The spur reduction circuit is designed as simple as possible not to increase the size of PLL. The proposed PLL with the previous two techniques is designed with a supply voltage of 1.8V in a 0.18um CMOS process. Simulation results show an almost 20dB reduction in the magnitude of spur. The spur reduced PLL can be used in narrow bandwidth communication system.

• Korean Journal of Materials Research
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• v.33 no.12
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• pp.530-536
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• 2023

The theoretical capacity of silicon-based anode materials is more than 10 times higher than the capacity of graphite, so silicon can be used as an alternative to graphite anode materials. However, silicon has a much higher contraction and expansion rate due to lithiation of the anode material during the charge and discharge processes, compared to graphite anode materials, resulting in the pulverization of silicon particles during repeated charge and discharge. To compensate for the above issues, there is a growing interest in SiO_x materials with a silica or carbon coating to minimize the expansion of the silicon. In this study, spherical silica (SiO₂) was synthesized using TEOS as a starting material for the fabrication of such SiO_x through heating in a reduction atmosphere. SiO_x powder was produced by adding PVA as a carbon source and inducing the reduction of silica by the carbothermal reduction method. The ratio of TEOS to distilled water, the stirring time, and the amount of PVA added were adjusted to induce size and morphology, resulting in uniform nanosized spherical silica particles. For the reduction of the spherical monodisperse silica particles, a nitrogen gas atmosphere mixed with 5 % hydrogen was applied, and oxygen atoms in the silica were selectively removed by the carbothermal reduction method. The produced SiO_x powder was characterized by FE-SEM to examine the morphology and size changes of the particles, and XPS and FT-IR were used to examine the x value (O/Si ratio) of the synthesized SiO_x.

• 한국생물공학회:학술대회논문집
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• 2000.11a
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• pp.250-253
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• 2000

We researched effects of growth on initial inoculum size, liquid volume, and medium feeding rate etc. Cell suspension inoculated at low cell concentrations showed a typical growth reduction, whereas root cultures showed an improvement in growth. In this paper, Hairy roots showed high growth rate at 0.4 % inoculum size and 100 mL liquid volume in 250 mL flask cultures.

• Proceedings of the IEEK Conference
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• 2003.11c
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• pp.327-330
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• 2003

A novel compact circular polarization operation of the microstrip antenna with four-slits and T-slits is proposed. The mechanism for compact size antenna is investigated with the behavior of the currents on the radiating patch. The equivalent surface current path due to the slits is lengthened, reducing the resonant frequency at a fixed patch size. The proposed compact CP design can have an antenna size reduction of about 33 ∼ 45％ as compared to the conventional microstrip antenna. Details of the experimental and measured results are presented and analysed.

• Proceedings of the Korea Concrete Institute Conference
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• 1991.10a
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• pp.1-4
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• 1991

Relationship between againg and characteristic change of asphalt is not well known through asphalt rheolopy. Therefore, this study was conducted to evaluate characteristic change of asphalt cement due to againg based on experimental results of chromatogram and selected physical properties. Currently, three virgin asphalt cements were tested for physical properties and chromatograms before and after artificially conditioning for againg. Results in the current study showed that againg caused significant changes of physical properties and increase of larger size molecules and approximately corresponding reduction of smaller size molecule in asphalt cement molecular size distribution.