• Korean Journal of Materials Research
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• v.21 no.6
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• pp.327-333
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• 2011

Nanostructured cobalt materials have recently attracted considerable attention due to their potential applications in high-density data storage, magnetic separation and heterogeneous catalysts. The size as well as the morphology at the nano scale strongly influences the physical and chemical properties of cobalt nano materials. In this study, cobalt nano particles synthesized by a a polyol process, which is a liquid-phase reduction method, were investigated. Cobalt hydroxide ($Co(OH)_2$), as an intermediate reaction product, was synthesized by the reaction between cobalt sulphate heptahydrate ($CoSO_4{\cdot}7H_2O$) used as a precursor and sodium hydroxide (NaOH) dissolved in DI water. As-synthesized $Co(OH)_2$ was washed and filtered several times with DI water, because intermediate reaction products had not only $Co(OH)_2$ but also sodium sulphate ($Na_2SO_4$), as an impurity. Then the cobalt powder was synthesized by diethylene glycol (DEG), as a reduction agent, with various temperatures and times. Polyvinylpyrrolidone (PVP), as a capping agent, was also added to control agglomeration and dispersion of the cobalt nano particles. The optimized synthesis condition was achieved at $220^{\circ}C$ for 4 hours with 0.6 of the PVP/$Co(OH)_2$ molar ratio. Consequently, it was confirmed that the synthesized nano sized cobalt particles had a face centered cubic (fcc) structure and with a size range of 100-200 nm.

• Animal Bioscience
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• v.35 no.2
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• pp.166-176
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• 2022

Objective: Sperm is particularly susceptible to reactive oxygen species (ROS) stress. Glutathione (GSH) is an endogenous antioxidant that regulates sperm redox homeostasis. However, it is not clear whether boar sperm could utilize cysteine for synthesis GSH to protect sperm quality from ROS damage. Therefore, the present study was undertaken to elucidate the mechanism of how cysteine is involved in protecting boar sperm quality during liquid storage. Methods: Sperm motility, membrane integrity, lipid peroxidation, 4-hydroxyIlonenal (4-HNE) modifications, mitochondrial membrane potential, as well as the levels of ROS, GSH, and, ATP were evaluated. Moreover, the enzymes (GCLC: glutamate cysteine ligase; GSS: glutathione synthetase) that are involved in glutathione synthesis from cysteine precursor were detected by western blotting. Results: Compared to the control, addition of 1.25 mM cysteine to the liquid storage significantly increased boar sperm progressive motility, straight-line velocity, curvilinear velocity, beat-cross frequency, membrane integrity, mitochondrial membrane potential, ATP level, acrosome integrity, activities of superoxide dismutase and catalase, and GSH level, while reducing the ROS level, lipid peroxidation and 4-HNE modifications. It was also observed that the GCLC and GSS were expressed in boar sperm. Interestingly, when we used menadione to induce sperm with ROS stress, the menadione associated damages were observed to be reduced by the cysteine supplementation. Moreover, compared to the cysteine treatment, the γ-glutamylcysteine synthetase (γ-GCS) activity, GSH level, mitochondrial membrane potential, ATP level, membrane integrity and progressive motility in boar sperm were decreased by supplementing with an inhibitor of GSH synthesis, buthionine sulfoximine. Conclusion: These data suggest that boar sperm could biosynthesize the GSH from cysteine in vitro. Therefore, during storage, addition of cysteine improves boar sperm quality via enhancing the GSH synthesis to resist ROS stress.

• Korean Chemical Engineering Research
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• v.53 no.5
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• pp.627-631
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• 2015

Various solid structures were prepared by electrospray technique. In this process, liquid flows out from a capillary nozzle under a high electrical potential and is subjected to an electric field, which causes elongation of the meniscus to form a jet. In our study, by controlling the amount of polyvinyl pyrrolydone in precursor solution, the jet either disrupted into droplets for the formation of spherical particles or was stretched in the electric field for the formation of fibers. During the electrospray process, the ethanol solvent was evaporated and induced the solidification of precursors, forming solid particles. The evaporation of ethanol solvent also enhanced the mass transport of solutes from the inner core to the solid shell, which facilitated fabrication of porous and hollow structure. The network structures were also prepared by heating the collector.

• Journal of the Korean Ceramic Society
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• v.30 no.5
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• pp.411-419
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• 1993

A process for the preparation of cobalt oxide powders was developed by the evaporaton of emulsion containing cobalt. The characteristics of powders were examined by means of DTA, X-ray diffracton, SEM, PSA. Cobalt oxide powders were produced by evaporating the emulsion prepared by mixing cobalt sulfate solution and organic phase consisted of kerosene, Span 80 and D2EHPA in the kerosene bath at 16$0^{\circ}C$, then the precursor obtained was calcined at 100$0^{\circ}C$. As the concentration of cobalt ions in the aqueous solution, Span 80 and the stirring speed increased, the mean size of cobalt oxide powders decreased and the size distribution was improved. At the volume ratio of one of the aqueous to organic phase, the finest mean size and the optimum size distribution was obtained. On the other hand the concentration of D2EHPA and liquid paraffin had little effect on the mean size as well as on the size distribution of powders.

• Journal of Powder Materials
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• v.6 no.3
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• pp.238-245
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• 1999

The preparation of $n-TiO_2$ powder by the Chemical Vapor Synthesis process (CVS) was studied using the liquid metal organic precursor (TTIP). The residence time and the collection methods were considered as main processing variables through the experiments. The CVS equipment consisted of a micropump and a flashvaporizer, a tube furnace and a tubular collection device. The synthesis was performed at $1000^{\circ}C$ with various sets of collection zone. The residence time and the total system pressure were controlled in the range of 3~20 ms and 10 mbar, respectively. Nitrogen adsorption, X-ray diffraction and electron microscopy were used to determine particle size, specific surface area and crystallographic structure. The grain size of the as-prepared $n-TiO_2$ powder was in the range of 2~8 nm for all synthesis parameters and the powder exhibited only little agglomeration. The relationship between particle characteristics and the processing variables is reviewed based on simple growth model.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2018.05a
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• pp.175-176
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• 2018

We have developed liquis precursotr delivery system (LDS) for ultra thin film preparation in semiconductor devices. The LDS concists of 3 major parts : aerosol generator, vaporizer and vapor storage. By uaing LDS which was attached to plasma enhanced chemical vapor deposition system, thin Al2O3 layer was prepared at extremely low temperature and characterized.

• Proceedings of the Korean Society Of Semiconductor Equipment Technology
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• 2006.10a
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• pp.14-17
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• 2006

This paper describes a novel processing technique for fabrication of polymer-derived SiCN (silicone carbonitride) microstructures for super-temperature MEMS applications. PDMS (polydimethylsiloxane) mold is fabricated on SU-8 photoresist using standard UV photolithographic process. Liquid precursor is injected into the PDMS mold. Finally, solid polymer structure is cross-linked using HIP (hot isostatic pressure) at $400^{\circ}C$, 205 bar Optimum pyrolysis and anneal ins conditions are determined to form a ceramic microstructure capable of withstanding over $1400^{\circ}C$. The fabricated SiCN ceramic microstructure has excel lent characteristics, such as shear strength (15.2 N), insulation resistance ($2.163{\times}10^{14}\;{\Omega}$) and BDV (min. 1.2 kV) under optimum process condition.

• Journal of the Korean Ceramic Society
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• v.34 no.11
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• pp.1182-1186
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• 1997

La0.8Ca0.2Cr0.98O3 powder was prepared using the modified Pechini process. Various crystalline phases formed during thermal decomposition were investigated. (La,Ca)CrO4 phase, first formed from the precursor, was transformed to (La,Ca)CrO3 and CaCrO4 above 80$0^{\circ}C$, which remained up to 110$0^{\circ}C$. However, only (La,Ca)CrO3 phase consisting of orthorhombic and intermediate rhombohedral polymorphs was observed after sintering at 125$0^{\circ}C$. The specimens sintered at 140$0^{\circ}C$ exhibited 98% of relative density and rather wide grain size distribution with average grain size of 3-4 ${\mu}{\textrm}{m}$. Densification and grain growth of the specimens observed above 125$0^{\circ}C$ were presumably attributed to liquid phase sintering resulted from melting of Ca3(CrO4)2 phase.

• Proceedings of the Korean Vacuum Society Conference
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• 2006.02a
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• pp.185-185
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• 2006

• Carbon letters
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• v.2 no.2
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• pp.91-98
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• 2001

Porous carbons have been prepared from different parts of banana stems using two different routes, viz., by pyrolysing the mass at different temperatures as well as by treating the dried mass with chemicals followed by pyrolysis. The pyrolysis behaviour of all these materials has been studied up to $1000^{\circ}C$. Samples treated with acids exhibit more increase in surface area as compared to those treated with alkalies or salts. Analysis of BET surface area shows that the carbon prepared at low temperature shows mixed porosity, i.e., micro and mesopores. Samples heated to high temperature above $700^{\circ}C$ show decrease in macroporosity and increase in microporosity. Liquid adsorption studies have been made using methylene blue and heavy oil. The activated carbons so prepared exhibit higher oil adsorption mainly in the macro and mesopores.