• Journal of Ocean Engineering and Technology
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• v.24 no.6
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• pp.86-91
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• 2010

Superconductor material $Bi_2Sr_2Ca_2Cu_3O_x$(Bi-2223) powders were synthesized by ultrasonic spray pyrolysis method. It is clear that Bi-2223 phase more than Bi-2212 phase was acquired at sufficient synthesized time. Best condition for Bi-2223 phase was synthesizing temperature at $860^{\circ}C$. We also investigated the effects for concentrations and viscosities of starting liquid precursor as well as temperature distribution of reacting furnace. The size of synthesized powder was decreased by decreasing the concentration of starting liquid precursor. Modified reacting furnace with four different temperature heating zones gave us successful results for desirable nano-powder including $Bi_2Sr_2Ca_2Cu_3O_x$ phase. Citric acid addition to starting liquid precursor showed increasing of the size for synthesized powder. Bi-2223 single phase was acquired from Bi2223 and Bi-2212 mixed phases through heat treatment in box furnace at 24 hours.

• Journal of the Korean Ceramic Society
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• v.39 no.2
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• pp.164-170
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• 2002

Measurements of sedimentation, solid loading, zeta potential, and viscosity were employed to determine a proper dispersant and its amount for a well dispersed alumina powders in aqueous alumina tape casting using acrylate as a binder. Polycarboxylic acid was the most effective one among various dispersants considered in the present study and its amount was 0.23∼0.24 g per 100 g alumina for a dispersion. Better dispersion was obtained as an increase of dispersant addition. However, the dispersion was hindered as the amount of dispersant was higher than the optimum amount because of bridging or tangling of polymer chains. Excellent aqueous alumina tapes were prepared from the slurry containing the optimum amount of the polycarboxylic acid (0.2g), alumina powders(100 g), acrylate and Benzoflex as binder and plasticizer, respectively. The viscosity of the slurry was 570 cps and the alumina loading in the tape was 57 vol%.

• Journal of the Korean Ceramic Society
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• v.41 no.3
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• pp.253-258
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• 2004

Non-aggregated nanoscale $\alpha$-Al$_2$O$_3$ powders were prepared successfully by polyacrylamine (PAA) gel method. The method was very simple and polymer network inhibited the aggregate of $\alpha$-Al$_2$O$_3$ powders. In this investigation, nanoparticles of $\alpha$-Al$_2$O$_3$ with a diameter of about 8-15 nm were fabricated by calcining the gel precusors with various concentrations of aluminum sulfate, acrylamide and N,N'-methylene-bis-acrylamide (BIS) in air at 110$0^{\circ}C$ for 2 h. The molar ratio of aluminum sulfate to acrylamide did not have any influence on the size of particles. On the other hand, as the molar ratio of BIS to acrylamide increased, the size of nanoparticles decreased.

• Korean Journal of Materials Research
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• v.21 no.8
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• pp.468-475
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• 2011

[ $LaMeO_3$ ](Me = Cr, Co) powders were prepared using the polymeric precursor method. The effects of the chelating agent and the polymeric additive on the synthesis of the $LaMeO_3$ perovskite were studied. The samples were synthesized using ethylene glycol (EG) as the solvent, acetyl acetone (AcAc) as the chelating agent, and polyvinylpyrrolidone (PVP) as the polymer additive. The thermal decomposition behavior of the precursor powder was characterized using a thermal analysis (TG-DTA). The crystallization and particle sizes of the $LaMeO_3$ powders were investigated via powder X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), and particle size analyzer, respectively. The as-prepared precursor primarily has $LaMeO_3$ at the optimum condition, i.e. for a molar ratio of both metal-source (a : a) : EG (80a : 80a) : AcAc (8a) inclusive of 1 wt% PVP. When the as-prepared precursor was calcined at $700^{\circ}C$, only a single phase was observed to correspond with the orthorhombic structure of $LaCrO_3$ and the rhombohedral structure of $LaCoO_3$. A solid-electrolyte impedance-metric sensor device composed of $Li_{1.5}Al_{0.5}Ti_{1.5}(PO_4)_3$ as a transducer and $LaMeO_3$ as a receptor has been systematically investigated for the detection of NOx in the range of 20 to 250 ppm at $400^{\circ}C$. The sensor responses were able to divide the component between resistance and capacitance. The impedance-metric sensor for the NO showed higher sensitivity compared with $NO_2$. The responses of the impedance-metric sensor device showed dependence on each value of the NOx concentration.

• Korean Journal of Food Science and Technology
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• v.38 no.2
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• pp.304-308
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• 2006

This study was performed to understand the behavior of protein mobility and intensity of enzymatic hydrolysis according to crosslinking of sodium caseinate, whey protein isolate, skim milk and whole milk powders with or without transglutaminase (TGase, w/w = 200 : 1) at $38^{\circ}C$. Whey protein was limited to crosslinking and skim milk was relatively more increased in high molecular polymer than whole milk. The degree of crosslinking decreased in the order of sodium caseinate>skim milk>whole milk>whey protein isolate. The SDS-PAGE results indicated that main bands of TGase treated samples had a high mobility and formed bands of molecular weights below 15 kDa by hydrolysis with pepsin after 10 min of reaction time. However, ${\beta}-lactoglobulin$ showed remarkable stability against pepsin hydrolysis treated with and without TGase. The high molecular polymers were easily hydrolyzed with digestive enzymes in vitro experiment. These results suggested that novel dairy products using TGase would have no special digestive problem in human body.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2004.05a
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• pp.113-116
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• 2004

The materials showing high structure dispersion with functional properties were developed on the quartz base and those were obtained by mechano-chemical reaction technology. Depending on the processing conditions and subsequent applications the materials produced by mechano-chemical reaction show concurrently magnetic, dielectric and electrical properties. The obtained magnetic-electrical powders classified by aggregate complex of their features as segnetomagnetics, containing a dielectric material as a carrying nucleus, particularly the quartz on that surface one or more layers of different compounds were synthesized having thickness up to 10~50 nm showing magnetic, electrical properties and others. The similarity of the structure of surface layers of quartz particles subjected to mechano-chemical processing and nano-structure cluspol (clusters in a polymer matrics) material was also confirmed by the fact that the characteristics of ferromagnetic quartz of insulating nano-composite powder were changed with time, after its preparing process was completed. The magnetic permeability of the sample was decreasing within first two months down by 15~20 %. Then, the magnetic characteristics were almost stabilized steadily and continuously. The observed changes were related with defective structure of the particles, elastic stress relief, and changes of electron density and magnetic moment in deformation zones. This process of stabilization of the investigated properties could be intensified by the thermal annealing heat treatment in short time period of the nano-composite quartz powders at the temperature ranges of 100~15$0^{\circ}C$.

• Journal of Technologic Dentistry
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• v.29 no.1
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• pp.121-131
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• 2007

A preparation process's conditions of aqueous sol which contains anatase-type nano titania particles with photocatalyic properties was established by using Yoldas process, so called, DCS(Destabilization of Colloidal Solution) process in this study. And crystal size change and phase transformation of titania particles in aqueous titania sol depending on reaction conditions was investigated by a light scattering method and XRD analysis of frozen dried powders, respectively. This sol with photo catalytic nano titania particles was used to the following hydrophilic hybrid coating film's fabrication and its properties was evaluated. Subsequently, for coating film using the above mentioned aqueous titania sol, non-aqueous titania sol was prepared without any chemical additives and its time stability according to aging time was investigate. By using the above mentioned aqueous titania sol and non-aqueous sol, a complex oxide coating sol for metal and ceramic substrate and a organic-inorganic hybrid coating sol for polymer substrate was prepared and it's hydrophilicity depending on UV irradiation conditions was evaluated. As a conclusions, the following results were obtained. (1)Aqueous titania sol The average particle size of titania in formed aqueous titania sol was distributed between 20$\sim$90nm range depending on reaction conditions. And the crystal phase of titania powders obtained by frozen drying method was changed from amorphous state to anatase and subsequently transformed to rutile crystal phase and it is attributed to concentration gradient in aqueous sol. (2)Non-aqueous titania sol Non-aqueous titania sol was prepared using methanol as a solvent and a little distilled water for hydrolysis and nitric acid as a catalyst were used. The obtained non-aqueous titania sol was stable at room temperature for 20 days. Additionally, non-aqueous titania sol with addition of chealating reagent such as acethylaceton and ethylene glycol prolonged the stability of sol by six months. (3)Complex sol and hybrid sol with super hydrophilicity The above mentioned aqueous titania sol as a main photocataylic component and non-aqueous titania sol as a binder for coating process was used to prepare a complex sol used for metal, ceramic and wood material substrate and also to prepare the organic-inorganic hybrid sol for polymer substrate such as polycarbonate and polyethylene, in which process APMS(3-Aminopropyltrimethoxysilane), GPTS(3-Glycidoxypropyl-trimethoxysilane) as a hydrophilic silane compound and HEMA(2-Hydroxyethyl methacrylate) as a forming network in hybrid coating film were used. The hybrid coating film such as prepared through this process showed a superhydrophilicity below 1$10^{\circ}$ depending on processing conditions and a pencil's hardness over 6 H.

• Journal of Powder Materials
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• v.17 no.4
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• pp.312-318
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• 2010

High speed steels (HSS) were used as cutting tools and wear parts, because of high strength, wear resistance, and hardness together with an appreciable toughness and fatigue resistance. Conventional manufacturing process for production of components with HSS was used by casting. The powder metallurgy techniques were currently developed due to second phase segregation of conventional process. The powder injection molding method (PIM) was received attention owing to shape without additional processes. The experimental specimens were manufactured with T42 HSS powders (59 vol%) and polymer (41 vol%). The metal powders were prealloyed water-atomised T42 HSS. The green parts were solvent debinded in normal n-Hexane at $60^{\circ}C$ for 24 hours and thermal debinded at $N_2-H_2$ mixed gas atmosphere for 14 hours. Specimens were sintered in $N_2$, $H_2$ gas atmosphere and vacuum condition between 1200 and $1320^{\circ}C$. In result, polymer degradation temperatures about optimum conditions were found at $250^{\circ}C$ and $480^{\circ}C$. After sintering at $N_2$ gas atmosphere, maximum hardness of 310Hv was observed at $1280^{\circ}C$. Fine and well dispersed carbide were observed at this condition. But relative density was under 90%. When sintering at $H_2$ gas atmosphere, relative density was observed to 94.5% at $1200^{\circ}C$. However, the low hardness was obtained due to decarbonization by hydrogen. In case of sintering at the vacuum of $10^{-5}$ torr at temperature of $1240^{\circ}C$, full density and 550Hv hardness were obtained without precipitation of MC and $M_6C$ in grain boundary.

• Resources Recycling
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• v.24 no.2
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• pp.55-61
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• 2015

In this study, mechanical properties of waste ground rubber tire powder were investigated to evaluate the influence of pre-treatment process for recycling. The tensile test, fracture test and morphology observation were carried out using various kinds of waste ground tire powders, which were produced by grinding and devulcanization process, respectively. As a results, it was found that the produced rubber powder through grinding process increased its tensile strength and elongation with decreasing particle size because of decreasing surface area. Devulcanized rubber powder also increased its tensile strength and elongation by de-crosslink with sulfur. It could be also suggested that devulcanization treatment after grinding process was more efficient recycling process for both increasing tensile property and fracture elongation of waste ground rubber tire powders.

• Polymer(Korea)
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• v.29 no.5
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• pp.501-507
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• 2005

Small intestinal submucosa (SIS) had been widely used as a biomaterial without immune rejection responses. SIS sponges prepared by crosslinking with 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC). SIS powders dissolved in $3\%(v/v)$ acetic acid aqueous solution for 48hrs and freeze-dried. EDC solution ($H_2O$ : ethanol = 5 : 95) as a crosslink agent was used in concentration of 100mM. In vitro, rat-BMSCs seeded in SIS sponges and induced the osteogenesis for 28 days. We have characterized the osteogenic potential of rat-BMSCs in SIS sponges by alkaline phosphatase activity(ALP), n assay, SEM and RT-PCR for osteogenic phenotype. In SEM, all morphology of SIS sponges was regular and showed interconnected pore structure. By RT-PCR analysis, we observed type I collagen expression. These results demonstrate osteogenic differentiation of rat-BMSCs. In conclusion, we confirmed that the morphology of surface, cross-section, and side of SIS sponges were highly porous with good interconnections between each pores, which can support the surface of cell growth, proliferation, and differentiation. This result indicates that SIS sponge is useful for osteogenesis of BMSCs.