• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.29 no.4
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• pp.225-230
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• 2016

Effect of electrolyte composition and concentration on PEO coating layer were investigated. Mg alloy, Surface of AZ31 and AZ91 were oxidized using PEO with different electrolyte system, Na-P and Na-Si. and applied voltage and concentration. We measured thickness, roughness, X-ray crystallographic analysis and breakdown voltage of the oxidized layer. When increasing concentration of electrolyte, the thickness of oxide layer also increased too. And roughness also increased as concentration of electrolyte increasing. Breakdown voltage of coated layer showed same behavior, the voltage goes high as increasing thickness of coating layer, as increasing concentration of electrolyte, and increasing applied voltage of PEO. $Mg_2SiO_4$ phase were observed as well as MgO.

• Transactions on Electrical and Electronic Materials
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• v.12 no.3
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• pp.119-122
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• 2011

A series of mesoporous silicalites was synthesized using different compositions of tetraethylorthosilicate and methyltriethoxysilane (MTES) as the silica source. Cetyltrimethylammonium bromide was used as the organic template. Their detailed pore structures were investigated by transmission electron microscopy, X-ray diffraction, and N2 adsorption method. The thermal properties of these silicalites were studied by thermogravimetric analysis. The increased amount of MTES destroyed mesoporous channels and reduced pore sizes from 3.4 nm to 2.8 nm in calcined silicalites. The calcined silicalite transformed completely into an amorphous state at 30% MTES loading. Methyl pending groups of MTES hindered the structural ordering of ≡Si-O- frameworks, resulting in an amorphous structure. This was caused by the insufficient formation of supramolecular assembly with the organic template. No capillary condensation step was found in MS 7/3 silicalite. The other capillary condensation steps shifted toward the lower relative pressure with increasing MTES content, indicating the reduction of pore sizes.

• Journal of Korea Foundry Society
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• v.16 no.2
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• pp.141-148
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• 1996

In high chromium cast iron, the control of matrix microstructure as well as carbide structure is important to the performance as a wear resistant material. In this study, 3.0% C-24.0% Cr white cast irons with various molybdenum contents(residual, 1.0%, 3.0% and 5.0%) were solidified conventionally and unidirectionally for studying their effects on the microstructure and hardness. In the conventional casting, two sets of castings were poured from each melt. One set of the castings consisted of cylindrical bars of 10 and 20mm by 155mm long. The second set of the castings was a cylindrical bar of 30mm by 200mm long. On the other hand, a pep-set mold set on the Cu plate was employed to make the solidification unidirectionally. X-ray diffraction method was used to observe retained austenite and carbides in the high chromium cast iron. The morphology of eutectic $M_7C_3$ carbides changed from needle-like type to nodular type with the increase of Mo content. And, the presence of $M_2C$ carbides was identified in the sample where Mo was added over 3.0 %. Primary and eutectic carbides appeared as rod type and corngrain type, respectively in the unidirectionally solidified samples which were cut to parallel to the solidification direction. In the EDX analysis, Cr concentration was higher in the primary and eutectic $M_7C_3$ carbides, Mo in the $M_2C$ carbides, and Fe in the matrix.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.272-272
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• 2014

SnO thin films, 100 nm in thickness, were deposited on glass substrates by RF magnetron sputtering. A stack structure of $SnO_2/SnO$, where few nanometers of $SnO_2$ were determined on the SnO thin film by X-ray photoelectron spectroscopy. In addition, XPS depth profile analysis of the pristine and heat treated thin films were introduced. The electrical behavior of the as-sputtered films during the annealing was recorded to investigate the working conditions for the SnO sensor. Subsequently, The NH3 sensing properties of the SnO sensor at operating temperature of $50-200^{\circ}C$ were examined, in which the p-type semiconducting sensing properties of the thin film were noted. The sensor shows good sensitivity and repeatability to $NH_3$ vapor. The sensor properties toward several gases like $H_2S$, $CH_4$ and $C_3H_8$ were also introduced. Finally, a sensing mechanism was proposed and discussed.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.445.1-445.1
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• 2014

Dye-sensitized solar cells (DSSCs) have been widely investigated as a next-generation solar cell because of their simple structure and low manufacturing cost. The $TiO_2$ film with thickness of $8{\sim}10{\mu}m$, which consists of nanoparticles, acts as both a scaffold with a high surface-to-volume ratio for the dye loading and a pathway to remove the electrons. However, charge carriers have to move across many particle boundaries by a hopping mechanism. So, one dimensional nanostructures such as nanotubes, nanorods and nanowires should improve charge carrier transportation by providing a facile direct electron pathway and lowering the diffusion resistance. However, the efficiencies of DSSCs using one dimensional nanostructures are less than the $TiO_2$ nanoparticle-based DSSCs. In this work, the patterned $TiO_2$ film with thickness of $3{\mu}m$ was deposited using photolithography process to decrease of electron pathway and increase of surface area and transmittance of $TiO_2$ films. Properties of the patterned $TiO_2$ films were investigated by various analysis method such as X-ray diffraction, field emission scanning electron microscopy (FESEM) and UV-visible spectrophotometer.

• Proceedings of the Materials Research Society of Korea Conference
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• 2010.05a
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• pp.42.2-42.2
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• 2010

Recently, highly porous bone substitutes, which have interconnected open pore structure, have been focused on improving their mechanical properties and modifying their functions. Especially, it is highly required to develop functional gradient structured bone substitute which is available for controlling their material properties such as bioresorption rate and elastic modulus. Porous $ZrO_2$ scaffold was fabricated by the sponge replica method using PU sponge. After 3 times of dip coating and the subsequent oven drying, burning out and microwave sintering were carried out. Various $ZrO_2$-BCP powder mixtures were prepared depending on the ratio and coated on the $ZrO_2$ scaffold by dip coating process. X-ray diffraction analysis was performed to characterize the phase identification of the scaffolds. Microstructures of the bone substitutes were observed using scanning electron microscopy.

• Korean Journal of Materials Research
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• v.27 no.2
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• pp.82-88
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• 2017

Ink-jet printing techniques with ceramic ink, which contains ceramic pigments as colorant, are in increasingly use in the ceramic industry. Generally, ceramic pigments that are produced by conventional method show diameters of several micrometers; these micrometer sized particles in the ink-jet printing process can cause undesirable behavior such as print head nozzle clogging. To prevent this problem, a particle size reduction process is required. In this study, CMYK (cyan, magenta, yellow, black) pigments were synthesized via solid state method. Each pigment particle was milled to submicron size by an attrition mill. The effects of micronizing on the morphology, mechanical property, crystal structure and color property of the CMYK ceramic pigments were investigated by field emission scanning electron microscopy (FE-SEM), particle size analysis (PSA), X-ray diffraction (XRD) and CIE $L^{\ast}a^{\ast}b^{\ast}$.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2005.11a
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• pp.340-341
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• 2005

Lithium titanium oxide as anode material for energy storage prepared by novel synthesis method. $Li_4Ti_5O_{12}$ based spinel-framework structures are of great interest material for lithium-ion batteries. We describe here $Li_4Ti_5O_{12}$ a zero-strain insertion material was prepared by novel sol-gel method and by high energy ball milling (HEBM) of precursor to from nanocrystalline phases. According to the X-ray diffraction and scanning electron microscopy analysis, uniformly distributed $Li_4Ti_5O_{12}$ particles with grain sizes of 100nm were synthesized. Lithium cells, consisting of $Li_4Ti_5O_{12}$ anode and lithium cathode showed the 173 mAh/g in the range of 1.0 $\sim$ 3.0 V. Furthermore, the crystalline structure of $Li_4Ti_5O_{12}$ didn't transfer during the lithium intercalation and deintercalation process.

• Journal of Powder Materials
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• v.17 no.5
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• pp.399-403
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• 2010

The effects of $MnO_2$ doping on the crystal structure, ferroelectric, and piezoelectric properties of (K,Na)$NbO_3$ (KNN) ceramics have been investigated. $MnO_2$ was found to be effective in enhancing the densification and grain growth during sintering. X-ray diffraction analysis indicated that Mn ions substituted B-site Nb ions up to 2 mol%, however, further doping induced unwanted secondary phases. In comparison with undoped KNN ceramics, the well developed microstructure and the substitution to B-sites in 2 mol% Mn-doped KNN ceramics resulted in significant improvements in both piezoelectric coupling coefficient and electromechanical quality factor.

• Journal of the Korean Electrochemical Society
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• v.5 no.2
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• pp.43-46
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• 2002

Commercial titanium rod was anodized in three types of electrolytes such as 0.06 mol/L $\beta-glycerophosphate+0.3mol/L$ calcium acetate, 0.06mol/L $\beta-glycerophosphate+0.3mol/L$ sodium acetate and 0.06 mol/L $\beta-glycerophosphate+5mol/L$ calcium phosphate. The titanium oxide layer $(TiO_2)$ was characterized by scanning electron microscope (SEM), X-ray diffraction (XRD) and electron spectroscopy chemical analysis (ESCA). Numerous micropores were observed on the titanium oxide layer by SEM. The diameter of micropores increased with the increase of electrolytic voltage. The titanium oxide layer was composed of anatase structure. The phosphorous element was detected at 130 eV binding energy, but calcium was not found in the oxide layer because of lower contents. After anodizing the oxide layer was etched in the 30g/L NaOH solution at $80^{\circ}C$ for 1hr. The surroundings of micropores were much more smoothed and rounded than before alkaline etching.