• Journal of the Korean Ceramic Society
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• v.53 no.2
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• pp.178-183
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• 2016

Ferroelectric relaxor ceramics with $BaTiO_3-NaNbO_3-Bi(Mg_{1/2}Ti_{1/2})O_3$ ternary compositions (BT-NN-BMT) have been prepared by sol-gel powder synthesis and consequent bulk ceramic processing. Through the modified chemical approach, fine and single-phase complex perovskite compositions were successfully obtained. Temperature and frequency dependent dielectric properties indicated typical relaxor characteristics of the BT-NN-BMT compositions. The ferroelectric-paraelectric phase transition became diffusive when NN and BMT were added to form BT based solid solutions. BMT additions to the BT-NN solid solutions affected the high temperature dielectric properties, which might be attributable to the compositional inhomogeneity of the complex perovskite and resulting weak dielectric coupling of the Bi-containing polar nanoregions (PNRs). The temperature stability of the dielectric properties was good enough to satisfy the X9R specification. The quasi-linear P-E response and the temperature- stable dielectric properties imply the high potential of this ceramic compound for use in high temperature capacitors.

• Korean Journal of Food Science and Technology
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• v.24 no.1
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• pp.54-58
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• 1992

The reological properties of commercial corn starch solutions at various concentrations($4{\sim}9%$) and temperatures($30{\sim}60^{\circ}C$) were investigated. The rheological behavior of corn starch solutions was illustrated by Herschel-Bulkley equation and exhibited pseudoplastic behavior with yield stress. The degree of pseudoplasticity of starch solution increased as the starch concentration increased but was independent on temperature. Apparent viscosity and yield stress of starch solutions were exponentially dependent on concentration and temperature. The critical concentrations for sol-gel transition and for the onset of close-packing of the starch granules were $6.22{\sim}6.52%\;and\;2.68{\sim}2.78%$ respectively.

• Proceedings of the KIEE Conference
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• 2006.10a
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• pp.5-6
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• 2006

Using the $(Ba_{0.5}Sr_{0.5}){TiO_3}$(BST) powders prepared by the Sol-Gel method, the EST thick films were fabricated on the ${Al_2}{O_3}$ substrates coated with Pt by the screen printing method. Compared with pure EST thick films, the structural and dielectric properties of the EST thick films doped with 1${\sim}$10 wt % MgO were investigated. It was observed that the Mg substitution into EST causes a shift in the cubic-tetragonal EST phase transition peak to a lower temperature. The microstructure of the EST substituted with Mg was homogeneous and dense. Mg substitution into EST had a significant effect on the grain size reduction. Dielectric constant was decreased with increasing the MgO content and temperature. In the case of EST thick films doped with 1 wt% MgO, the relative permittivity and dielectric loss were 158] and 1.4 % at 1 MHz.

• Journal of the Korean Solar Energy Society
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• v.22 no.4
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• pp.44-50
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• 2002

Photosynthesis of plants is effective in the range of 550 to 700 nm of the wavelength of solar irradiation. If the conversion of ultraviolet to the above mentioned region is possible, the photosynthesizing ability is expected to be enhanced. $Eu^{3+}$ doped soda-lime bulk and $TiO_2-SiO_2$ sol-gel coated glasses were prepared and their spectroscopic properties were studied. The absorption and emission spectra for the specimens were measured with the changes of wavelength and Eu ion concentration in the range of the wavelength of 300 to 700nm. The transmittance intensity of visible light through the bulk glass and the coated one was unchanged with the addition of Eu element. The emission spectrum intensity of $Eu^{3+}$ was found to be the maximum at 618 nm which is a transition of $^5DO{\rightarrow}^7F_2$. Additionally, it was shown that the intensity was linearly increased up to 10% of the Eu concentration.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09a
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• pp.487-488
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• 2006

Novel bisphenol-based wholly aromatic poly(ether sulfone-ketone) copolymer containing pendant sulfonate groups were prepared by direct aromatic nucleophilic substitution polycondensation of 4,4-difluorobenzophenone, 2,2'-disodiumsulfonyl-4,4'-fluorophenylsulfone (40mole% of bisphenol A) and bisphenol A. Polymerization proceeded quantitatively to high molecular weight in N-methyl-2-pyrrolidinone at $180^{\circ}C$. Organic-inorganic composite membranes were obtained by mixing organic polymers with hydrophilic $SiO_2$ (ca. 20nm) obtained by sol-gel process. The polymer and a series of composite membranes were studied by FT-IR, $^1HNMR$, differential scanning calorimetry (DSC) and thermal stability. The proton conductivity as a function of temperature decreased as $SiO_2$ content increased, but methanol permeability decreased. The nano composite membranes were found to posse all requisite properties; Ion exchange capacity (1.2meq./g), glass transition temperatures $(164-183\;^{\circ}C)$, and low affinity towards methanol $(4.63-1.08{\times}10^{-7}\;cm^2/S)$.

• Journal of Ceramic Processing Research
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• v.20 no.6
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• pp.603-608
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• 2019

In this study, the multilayered thin films of (Ba,Sr)TiO3/K(Ta,Nb)O3 were fabricated by the sol-gel and spin coating methods, and their structural and electrical properties were investigated. The specimen showed polycrystalline X-ray diffraction (XRD) characteristics with a tetragonal structure. The average grain size and film thickness for one coating were about 30~40nm and 60nm, respectively. The phase transition temperature of specimen was lower than 10 ℃. The dielectric constant and loss at 20 ℃ of the specimen coated six times were 1,231 and 0.69, respectively. The rate of change in dielectric constant at an applied direct current (DC) voltage of the six times coated thin films was 17.3%/V. The electrocaloric effect was the highest around the temperature at which the remanent polarization rapidly changed. When an electric field of 660kV/cm was applied to the triply coated thin films, the highest electrocaloric property of 4.41 ℃ was observed.

• The Korean Journal of Urological Oncology
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• 제15권3호
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• pp.178-186
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• 2017

Purpose: Poloxamer 407 (P407) thermo-sensitive hydrogel formulations were developed to enhance the retention time in the urinary bladder after intravesical instillation. Materials and Methods: P407 hydrogels (P407Gels) containing 0.2 w/w% fluorescein isothiocyanate dextran (FD, MW 4 kDa) as a fluorescent probe were prepared by the cold method with different concentrations of the polymer (20, 25, and 30 w/w%). The gel-forming capacities were characterized in terms of gelation temperature (G-Temp), gelation time (G-Time), and gel duration (G-Dur). Homogenous dispersion of the probe throughout the hydrogel was observed by using fluorescence microscopy. The in vitro bladder simulation model was established to evaluate the retention and drug release properties. P407Gels in the solution state were administered to nude mice via urinary instillation, and the in vivo retention behavior of P407Gels was visualized by using an in vivo imaging system (IVIS). Results: P407Gels showed a thermo-reversible phase transition at $4^{\circ}C$ (refrigerated; sol) and $37^{\circ}C$ (body temperature; gel). The G-Temp, G-Time, and G-Dur of FD-free P407Gels were approximately $10^{\circ}C-20^{\circ}C$, 12-30 seconds, and 12-35 hours, respectively, and were not altered by the addition of FD. Fluorescence imaging showed that FD was spread homogenously in the gelled P407 solution. In a bladder simulation model, even after repeated periodic filling-emptying cycles, the hydrogel formulation displayed excellent retention with continuous release of the probe over 8 hours. The FD release from P407Gels and the erosion of the gel, both of which followed zero-order kinetics, had a linear relationship ($r^2=0.988$). IVIS demonstrated that the intravesical retention time of P407Gels was over 4 hours, which was longer than that of the FD solution (<1 hour), even though periodic urination occurred in the mice. Conclusions: FD release from P407Gels was erosion-controlled. P407Gels represent a promising system to enhance intravesical retention with extended drug delivery.

• Journal of the Korean Magnetics Society
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• v.15 no.2
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• pp.96-99
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• 2005

Phase transition from normal- to inverse-spinel structure has been observed for $Fe_xCo_{3-x}O_4$ thin films as the Fe composition (x) increases from 0 to 2. The samples were fabricated as thin films by sol-gel method on Si(100) substrates. X-ray diffraction measurements revealed a coexistence of two phases, normal and inverse spinel, for $0.76{\le}x{\le}0.93$. The normal-spinel phase is dominant for $x{\le}0.55$ while the inverse-spinel phase for $x{\ge}l.22$. The cubic lattice constant of the inverse-spinel phase is larger than that of the normal-spinel phase. For both phases the lattice constant increases with increasing x. X-ray photoelectron spectroscopy measurements revealed that both $Fe^{2+}$ and $Fe^{3+}$ ions exist with similar strength in the x=0.93 sample. Conversion electron $M\ddot{o}ssbauer$ spectra measured on the same sample showed that $Fe^{2+}$ ions prefer the octahedral $Co^{3+}$ sites, indicating the formation of the inverse-spinel phase. Analysis on the measured optical absorption spectra for the samples by spectroscopic ellipsometry indicates the dominance of the normal spinel phase for low x in which $Fe^{3+}$ ions tend to substitute the octahedral sites.

• Journal of the Korean Magnetics Society
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• v.16 no.3
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• pp.168-172
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• 2006

We studied the magnetic and the related electronic properties of Ni-doped rutile $TiO_{2-{\delta}}$ films (including oxygen deficiency $\delta$) prepared using a sol-gel method. A room-temperature ferromagnetism was observed in the $TiO_{2-{\delta}}$ : Ni films with the saturation magnetization ($M_S$) decreasing with increasing Ni doping and remaining constant above 6 at% Ni doping. The observed ferromagnetism below 6 at% Ni doping is interpreted as due to magnetic polaron formed by a trapped electron in oxygen vacancy and magnetic impurity ions around it. For small Ni doping, $M_S$ up to $3.7{\mu}B/Ni$ was obtained. The ferromagnetism for Ni doping above 6 at% is interpreted as due to the existence of Ni clusters that can explain the p-n conductivity transition observed by Hall effect measurements.

• Clean Technology
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• v.24 no.1
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• pp.9-14
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• 2018

In this study, Material life cycle evaluation was performed to analyze the environmental impact characteristics of TiN-Zr membrane manufacturing process. The software of MLCA was Gabi. Through this, environmental impact assessment was performed for each process. Transition metal nitrides have been researched extensively because of their properties. Among these, TiN has the most attention. TiN is a ceramic materials which possess the good combination of physical and chemical properties, such as high melting point, high hardness, and relatively low specific gravity, high wear resistance and high corrosion resistance. With these properties, TiN plays an important role in functional materials for application in separation hydrogen from fossil fuel. Precursor TiN was synthesized by sol-gel method and zirconium was coated by ball mill method. The metallurgical, physical and thermodynamic characteristics of the membranes were analyzed by using Scanning Electron Microscope (SEM), Energy Dispersive X-ray (EDS), X-ray Diffraction (XRD), Thermo Gravimetry/Differential Thermal Analysis (TG/DTA), Brunauer, Emmett, Teller (BET) and Gas Chromatograph System (GP). As a result of characterization and normalization, environmental impacts were 94% in MAETP (Marine Aquatic Ecotoxicity), 2% FAETP (Freshwater Aquatic Ecotoxicity), 2% HTP (Human Toxicity Potential). TiN fabrication process appears to have a direct or indirect impact on the human body. It is believed that the greatest impact that HTP can have on human is the carcinogenic properties. This shows that electricity use has a great influence on ecosystem impact. TiN-Zr was analyzed in Eco-Indicator '99 (EI99) and CML 2001 methodology.