• Resources Recycling
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• v.15 no.4 s.72
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• pp.19-26
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• 2006

The preparation of Ag nano-powder from aqueous silver nitrate solution, which would be available for the recycling of silver bearing wastes, was investigated by a reductive precipitation reaction using hydrazine hydrate as a reducing agent. Silver solution was prepared by dissolving silver nitrate with distilled water, and then the dispersant, Tamol NN8906 or Tween 20, was also mixed to avoid the agglomeration of particles during the reductive reaction followed by the addition of hydrazine hydrate to prepare Ag nano-particles. Ag particles obtained from the reduction reaction from silver solution were characterized using the particle size analyzer and TEM to determine the particle size distribution and morphology. It was found that about 100% excess of hydrazine hydrate was required to reduce completely silver ions in the solution. Ag powders with very narrow distribution could be obtained when Tamol NN8906 was used as the dispersant. In case of Tween 20, the particle size distribution showed typically the bimodal or multimodal distribution and the morphology of Ag particles was found to be irregular shape in both cases.

• Korean Journal of Materials Research
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• v.34 no.1
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• pp.27-33
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• 2024

Al₂O₃ has excellent sintering properties and is important in semiconductor manufacturing processes that require high-temperature resistance and chemical inertness in a plasma environment. In this study, a comprehensive analysis of the chemical characteristics, physical properties, crystal structure, and dispersion stability of three commercially available Al₂O₃ powders was conducted. The aim was to provide a technological foundation for selecting and utilizing appropriate Al₂O₃ powders in practical applications. All powders exhibited α-Al₂O₃ as the main phase, with the presence of beta-phase Na₂O-11Al₂O₃ as the secondary phase. The highest Na⁺ ion leaching was observed in the aqueous slurry state due to the presence of the secondary phase. Although the average particle size difference among the three powders was not significant, distinct differences in particle size distribution were observed. ALG-1SH showed a broad particle size distribution, P162 exhibited a bimodal distribution, and AES-11 displayed a uniform unimodal distribution. High-concentration Al₂O₃ slurries showed differences in viscosity due to ion release when no dispersant was added, affecting the electrical double-layer thickness. Polycarboxylate was found to effectively enhance the dispersion stability of all three powders. In the dispersion stability analysis, ALG-1SH exhibited the slowest sedimentation tendency, as evidenced by the low TSI value, while P162 showed faster precipitation, influenced by the particle size distribution.

• Applied Chemistry for Engineering
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• v.7 no.2
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• pp.350-355
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• 1996

Poly(AA-co-EGDMA) microgels were prepared by precipitation polymerization in highly swollen polystyrene gel solution. The polymerization was carried out in selective solvent such as cyclohexane/acetone at $60^{\circ}C$. Poly(AA-co-EGDMA) microgels with various site of $0.18{\sim}0.55{\mu}m$ were obtained from different concentration of polystyrene(PS), concentration of crosslinking agent(EGDMA), ratio of Ps/monomer and volume ratio of solvents. The particle size of poly(AA-co-EGDMA) microgels decreased with increasing the concentration of PS and increased with that of EGDMA.

• Korean Journal of Materials Research
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• v.19 no.11
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• pp.588-595
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• 2009

The knowledge of grain growth of carbide particles is very important for manufacturing micrograined cemented carbides. In the present study, continuous and discontinuous grain growth in WC-Co and WC-VC-Co cemented carbides is investigated using the Monte Carlo computer simulation technique. The Ostwald ripening process (solution/re-precipitation) and the grain boundary migration process are assumed in the simulation as the grain growth mechanism. The effects of liquid phase fraction, grain boundary energy and implanted coarse grain are examined. At higher liquid phase content, mass transfer via solid/liquid interfaces plays a major role in grain growth. Growth rate of the implanted grain was higher than that of the matrix grains through solution/re-precipitation and coalescence with neighboring grains. The results of these simulations qualitatively agree with experimental ones and suggest that distribution of liquid phase and carbide particle/carbide grain boundary energy as well as contamination by coarse grain are important factors controlling discontinuous grain growth in WC-Co and WC-VC-Co cemented carbides. The contamination by coarse grains must by avoided in the manufacturing process of fine grain cemented carbides, especially with low Co.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.56 no.1
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• pp.151-155
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• 2007

A compact discharge plasma system with a photocatalyst has been proposed and investigated experimentally for application to air conditioners. It was found that there was intense ultra violet radiation with high energy of 3.2 eV from the corona discharge due to the DC-biased pulse voltage applied on a wire. An electrophotochemical reaction took place apparently on the surfaces of the photocatalyst of $TiO_2$ irradiated ultra violet front the discharge plasma in the proposed plasma system. The proposed discharge plasma system with the photocatalyst of $TiO_2$ showed very high removal efficiency of VOCs by tile additional electrophotochemical reactions on the photocatalyst. The proposed discharge plasma system also showed very high removal efficiency of particles such as smokes, suspended bacteria, and pollen and mite allergens by the electrostatic precipitation part. This type of corona discharge plasma system with a photocatalyst can be used as an effective means of removing both indoor pollutant gases and particles including suspended allergens.

• Advances in environmental research
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• v.4 no.2
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• pp.119-133
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• 2015

Water pollution means that the physical, chemical and biological properties of water are changing. In this study, adsorption was chosen as the treatment method because it is an eco-friendly and low cost approach. Magnetite is a magnetic material that can synthesize chemical precipitation. Magnetite was used for the removal of copper in artificial water samples. For this purpose, metal removal from water dependent on the pH, initial concentration of metal, amount of adsorbent and effect of sorption time were investigated. Magnetite was characterized using XRD, SEM and particle size distribution. The copper ions were determined by atomic absorption spectrometry. The adsorption of copper on the magnetite was studied in a batch process, with different aqueous solutions of Cu (II) at concentrations ranging from 10 to $50mg\;l^{-1}$. Optimum conditions for using magnetite were found to be concentration of $10mg\;L^{-1}$, pH: 4.5, contact time: 40 min. Optimum adsorbent was found to be 0.3 gr. Furthermore, adsorption isotherm data were analyzed using the Langmuir and Freundlich equations. The adsorption data fitted well with the Freundlich ($r^2=0.9701$) and Langmuir isotherm ($r^2=0.9711$) equations. Kinetic and equilibrium aspects of the adsorption process were studied. The time-dependent Cu (II) adsorption data were described well by a pseudo-second-order kinetic model.

• Bulletin of the Korean Chemical Society
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• v.26 no.4
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• pp.563-568
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• 2005

The Pt/C and Pd/C catalysts were prepared from conventional chloride precursors by adsorption or precipitation-deposition methods. Their activities for hydrogenation reactions of cyclohexene and acetophenone were compared with those of commercial catalysts. The Pt/C and Pd/C catalysts obtained from the adsorption procedure reveal higher hydrogenation activity than commercial catalysts and the catalysts prepared by the precipitation-deposition method. Their improved performances are attributed to the decreased metal crystallite sizes of Pt or Pd formed on the active carbon support upon the adsorption of the precursors probably due to the same negative charges of the chloride precursor and the carbon support. Under the preparation conditions studied, the reduction of the supported catalysts using borohydrides in liquid phase is superior to a gas phase reduction by using hydrogen in the viewpoint of particle size, hydrogenation activity and convenience.

• Journal of the Korean Ceramic Society
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• v.49 no.1
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• pp.118-123
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• 2012

GDC20($Ce_{0.8}Gd_{0.2}O_{1.9}$) powder was synthesized from Ce and Gd nitrate solutions using ammonium carbonate($(NH_4)_2CO_3$) as a precipitant. Attrition-milling of the powder, which had been calcined at $700^{\circ}C$ for 4 h, decreased an average particle size of 2.2 ${\mu}m$ to 0.5 ${\mu}m$. The milled powder consisted of nano-sized spherical primary particles. Due to the excellent sinterability of the powder, sintering of the powder compacts for 4 h showed relative densities of 80% at 1000 $^{\circ}C$ and 96.5% at $1200^{\circ}C$, respectively. Densification was found to almost complete at $1300^{\circ}C$, resulting in a dense and homogeneous microstructure with a relative density of 99.5%. The grains of ~0.2 ${\mu}m$ in size at $1200^{\circ}C$ grew to ~1 ${\mu}m$ in size at $1300^{\circ}C$ as a result of a rapid grain growth.

• Journal of environmental and Sanitary engineering
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• v.10 no.2
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• pp.79-88
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• 1995

The electrostatic precipitation of Auto- Bias has the advantages of a little of power consumption by the voltage to apply only at ionizer and the prevention of fire danger by current flow over. As this ionizer wire was used WXN- Pt material of diameter 90$\mu $m, that improved ion efficiency and safety, simplified a existing source of electric power by induced Auto- Bias voltage. Also, the new type collector used electric conductivity- film wag superior a electric safety and dust collection efficiency and was possible to wash it by water. As a experiment result of this Auto- Bias electrostatic collector, the induced Auto- Bias voltage by appling D.C 4.0∼6.0kV at ionizer was 1.3∼2.3kV and then the power consumption by applied voltage was 8- l8W. The pressure loss of collector by the amount of flowing was 6.1 OmmH$_{2}$O in 300m$^{3}$/hr and showed a safe state of the dust collection. The collection efficiency by particle size was 65.1-95.8% in 0.5∼5.0$\mu $m. After corona discharge of ionizer, the remains ozone concentration was found much lower than that of ACGIH or air pollution criteria in Korea.

• Korean Chemical Engineering Research
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• v.52 no.1
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• pp.40-44
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• 2014

For the purpose of development of an effective process for purified CHMI particles, a series of experimental researches on the synthesis of CHMI from CHMAIE, purification and precipitation of CHMI were preformed. It is turned out that n-heptane reflux imidation is more beneficial than toluene put-out imidation not only to the synthesis but to the precipitation of CHMI. By washing the synthetic CHMI with cold n-heptane twice, purified CHMI with 99.7% purity could be obtained at the cost of 11.7% weight loss. And CMHI particles were effectively prepared by spouting molten CHMI through the spiral nozzle with 3 mm diameter under the pressure of $1.5{\sim}2.0kg/cm^2$.