• Journal of the Korean Crystal Growth and Crystal Technology
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• v.16 no.3
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• pp.116-120
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• 2006

We have investigated plasma spray coated $Al_2O_3$ layers on Al-60 series substrates for development of wafer electrostatic chuck in semiconductor dry etching system. Samples were prepared without/with cooling bar on backside of samples, at various distances, and with different powder feed rates. There were many cracks and pores in the $Al_2O_3$ layers coated on Al-60 series substrates without cooling bar on the backside of samples. But the cracks and pores were almost disappeared in the $Al_2O_3$ layers on Al-60 series substrates coated with cooling bar on the back side of samples, 15 g/min. powder feed rate and various 60, 70, 80 mm working distances. Then the surface morphology was not changed with various working distances of 60, 70, 80 mm. When the powder feed rate was changed from 15 g/min to 20 g/min, the crack did not appear, but few pores appeared. Also the $Al_2O_3$ layer was coated with many small splats compared with $Al_2O_3$ layer coated with 15 g/min powder feed rate. The deposited rate of $Al_2O_3$ layer was higher when the process was done without cooling bar on the back side of sample than that with cooling bar on the back side of sample.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.21 no.1
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• pp.47-53
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• 2011

The artificial aggregates (AAs) were manufactured from the parent batch powders consisting of bottom ash containing excess unburned carbon and dredged soil, 7 : 3 weight ratio by direct sintering method and those physical properties were evaluated. Especially, the effects of waste glass or frit (NWG) which was made by addition of 5 wt% $Na_2O$ to the waste glass upon the bloating phenomenon of AAs were analyzed. The AAs manufactured from the parent batch powders showed a lower specific gravity than that of specimens containing waste glass or NWG due to excess u$Na_2O$nburned carbon which usually obstructs a sintering process. But, the waste glass added on parent batch powders promoted the sintering and densification thus increased the specific gravity of AAs. Also the specific gravity of AAs added with 5 wt% NWG, was lowered compared to that of AAs added with as-received waste glass. This is because of bloating of shell which captures gases owing to the lowered viscosity of liquid formed at the specimen surface caused by $Na_2O$ addition. In conclusion, the AAs sintered at above $1100^{\circ}C$ in this study showed characters of lightweight aggregate of specific gravity 1.15~1.34 and water absorption 11~19 %, and the bloating phenomenon of AAs was occurred at the shell rather black core part.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.25 no.2
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• pp.62-67
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• 2015

The carbon microspheres of a core-shell type were grown by the method of mixed-source hydride vapor phase epitaxy (HVPE). The surface and the cross section of the carbon microsphere grown by a new method were observed by scanning electron microscope (SEM). The characteristics of the carbon microsphere were investigated by X-ray photoelectron spectroscopy (XPS) and a high resolution-transmission electron microscope (HR-TEM). From these measurements, the diameters of carbon sphere were about few hundred micrometers. Furthermore, we show that the carbon microsphere of the core-shell type by mixed-source HVPE method can be grown successfully with the larger size than those of the existing one. This mixed-source HVPE method is proposed a new method for making of carbon microsphere.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.19 no.5
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• pp.256-261
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• 2009

Hydrophilic and transparent $TiO_2$ thin film was fabricated by sol-gel method and the properties of contact angle, surface morphology, and transmittance were measured. In addition, surfactant Tween 80 was used for increasing the hydrophilic property of thin film. When the contents of Tween 80 in $TiO_2$ solution was 0, 10, 30, 50wt%, the contact angles of $TiO_2$ thin film were $41.4^{\circ}$, $18.2^{\circ}$, $16.0^{\circ}$, $13.2^{\circ}$, respectively. Fabricated $TiO_2$ thin film showed the photocatalytic property that decomposed methylene blue and decreased the absorbance of solution after UV irradiation. $TiO_2$ thin films fabricated with the solution of 30 wt% Tween 80 were deposited on glass (bare), antimony tin oxide (ATO), fluorine tin oxide (FTO), indium tin oxide (ITO) coated glass substrates, and the contact angle and transmittance of thin film was measured. The contact angles of thin films deposited on four substrates were $16.2\sim27.1^{\circ}$ and was decreased to the range of $13.2\sim17.6^{\circ}$ after UV irradiation, Especially, the thin films coated on ATO and FTO glass substrate showed high transmittance of 74.6% in visible range, respectively, and low transmittance of 54.2% and 40.4% in infrared range, respectively.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.27 no.1
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• pp.18-21
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• 2017

In this study, spherical monodispersed cerium-doped yttrium aluminum garnet (YAG : $Ce^{3+}$) phosphor particles were synthesized via homogeneous precipitation method using the mixed solution of yttrium nitrate, cerium nitrate, aluminum nitrate, ammonium aluminum sulfate, and urea as a precipitant. During the process of precursors of monodispersed YAG : $Ce^{3+}$, aluminum ions which form spherical aluminum compounds precipitated first and yttrium compounds precipitated onto the surface of the existing spherical aluminum compounds. Drying process using lyophilization could obtain monodispered spherical YAG : $Ce^{3+}$ particles compare to using oven. The thermal calcination process of YAG : $Ce^{3+}$ precursors under the temperature of $1200^{\circ}C$ for 6 h was enough to obtain 400~500 nm sized YAG particles with pure YAG phase.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.29 no.6
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• pp.345-351
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• 2019

Recently, ink-jet printing technology has been applied for various industries such as semiconductor, display, ceramic tile decoration. Ink-jet printing has advantages of high resolution patterning, fast printing speed, high ink efficiency and many attempts have been made to apply functional materials with excellent physical and chemical properties for the ink-jet printing process. Due to these advantages, research scope of ink-jet printing is expanding from conventional two-dimensional printing to three-dimensional printing. In order to expand the application of ink-jet printing, it is necessary to optimize the rheological properties of the ink and the interaction with the substrate. In this study, photo curable ceramic complex ink containing nano silica particles were synthesized and its printability was characterized. Contact angle of the photo curable silica ink were modified by control of the ink composition and the surface property of the substrate. Effects of contact angle on printing resolution and three-dimensional printability were investigated in detail.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.22 no.2
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• pp.92-98
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• 2012

The co-precipitation technique has been applied to synthesize biphasic calcium phosphate (BCP). $Ca(NO_3)_2{\cdot}4H_2O$, $(NH_4)_2HPO_4$, TEOS and $Mg(NO_3)_2{\cdot}6H_2O$ as the starting materials was used. After the heat treatment of powder crystalline phases HAp and ${\beta}$-TCP analysis showed a mixed phase. The overall spectra appear to have mainly two modes corresponding to characteristic $PO^{3-}_4$ and $OH^-$ groups. After immersion in Hanks' Balanced Salt Solution (HBSS) for 1 week a precipitation started to be formed with individual small granules on the specimen surface. An MTT assay indicated that ionic substituted BCP powders had no cytotoxic effects on MG-63 cells, and that they have good biocompatibility.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.29 no.2
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• pp.54-60
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• 2019

Recently, various composite materials for additive manufacturing are interested to expand the application field of 3D printing. 3D printing technique was mainly developed using polymer, and ceramic materials for 3D printing are still in the early stage of research due to the requirement of high solid content and post treatment process. In this study, silica particles with various diameters were surface treated with silane coupling agent, and synthesized as silica composite with photopolymer to apply DLP 3D printing process. DLP is an additive manufacturing technology, which has high accuracy and applicability of various composite materials. The rheological behavior of silica composite was analyzed with various solid contents. After DLP 3D printing was performed using silica composites, the printing accuracy of the 3D printed specimen was less than about 3 % to compare with digital data and he bending strength was 34.3 MPa at the solid content of 80 wt%.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.31 no.4
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• pp.159-165
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• 2021

The fiber composites have been investigated as lightweight structure material platforms for aerospace applications because their strength can be enhanced by adding reinforcement without a significant increase in weight. In this study, the fabrication and characterization of carbon nanotube (CNT) reinforced glass fiber composites are demonstrated to enhance the tensile strength of longitudinal direction along the glass fibers. Due to the reinforcement of CNT in epoxy layers, the yield strength of fiber/epoxy composites is enhanced by about 10 %. Furthermore, using scanning electron microscopy, analysis of fracture surfaces shows that mixed CNT in epoxy layers acts as necking agents between fractured surfaces of fiber/epoxy; thereby, initiation and evolution of crack across fiber composite can be suppressed by CNT necking between fractured surfaces.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.31 no.6
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• pp.282-286
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• 2021

Penetration depth and compressive residual stress of laser-carburized TiZrN coating by thickness of carbon paste were investigated in terms of carbon potential. The carbon paste was covered with a thickness of 1.1 mm using screen printing, and applied to a thickness of 0.4 mm using spin coating, and laser carburization was performed under the same conditions. As the thickness of carbon paste increased, the diffraction pattern of the laser-carburized TiZrN coating shifted to a lower angle, indicating solid solution strengthening and lattice distortion. For microstructure analysis using TEM, the defects and carbon concentration of the laser-carburized TiZrN coating increased as the carbon paste was thicker. It indicated that the variation of the carbon potential corresponds to the change in the paste thickness. In XPS depth profile analysis, high concentration of carbon and formation of carbide were observed in laser-carburized TiZrN coating with thick carbon paste. It revealed that the carbon concentration on the surface and carbon potential were changed by the thickness control of carbon paste. The compressive residual stress increased from 3.67 GPa to 4.58 GPa by the variation of carbon concentration.