• Journal of the Korean Ceramic Society
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• v.24 no.5
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• pp.500-506
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• 1987

In order to synthesize monodispersed spherical silica fine particles, we investigated the reaction of hydrolysis of 0.05∼4.0 mole Si(OC2H5)4-0.01∼7.60mole NH3 -0.24∼38.40 mole H2O-2.62∼16.88mole C2H5OH systems. The range of the composition of solution which spherical silica particles were formed was enlarged according to an increase in concentration of Si(OC2H5)4. Larger particles were obtained at higher molar ratios of Si(OC2H5)4/C2H5OH, NH3/H2O and H2O/Si(OC2H5)4 and at a lower reaction temperature.

• Journal of IKEEE
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• v.22 no.4
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• pp.1230-1233
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• 2018

$Al_2O_3$ films with the thickness of 50 nm were fabricated on 4H-SiC by aerosol deposition, and their electrical properties were characterized with different post annealing conditions. As a result, the $Al_2O_3$ film annealed in $N_2$ atmosphere showed decreased fixed charge density at the interface area between the $Al_2O_3$ and SiC, and increased leakage currents due to the generation of oxygen vacancies. From this result, it was confirmed that proper $N_2$ and $O_2$ ratio for the post annealing process is important.

• Clean Technology
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• v.25 no.1
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• pp.91-97
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• 2019

Oxidative desulfurization (ODS) has received much attention in recent years because refractory sulfur compounds such as dibenzothiophenes can be oxidized selectively to their corresponding sulfoxides and sulfones, and these products can be removed by extraction and adsorption. In this work, The oxidative desulfurization of marine diesel fuel was performed in a batch reactor with hydrogen peroxide ($H_2O_2$) in the presence of various supported heteropoly acid catalysts. The catalysts were characterized by XRD, XRF, XPS and nitrogen adsorption isotherm techniques. Based on the sulfur removal efficiency of promising silica supported heteropoly acid catalysts, the ranking of catalytic activity was: $30\;H_3PW_{12}/SiO_2$ > $30\;H_3PMo_{12}/SiO_2$ > $30\;H_4SiW_{12}/SiO_2$, which appears to be related with their intrinsic acid strength. The $30\;H_3PW_{12}/SiO_2$ catalyst showed the highest initial sulfur removal efficiency of about 66% under reaction conditions of $30^{\circ}C$, $0.025g\;mL^{-1}$ (cat./oil), 1 h reaction time. However, through the recycle test of the $H_3PW_{12}/SiO_2$ catalyst, significant deactivation was observed, which was attributed to the elution of the active component $H_3PW_{12}$. By introducing cesium cation ($Cs^+$) into the $H_3PW_{12}/SiO_2$ catalyst, the stability of the catalyst was improved with changing the solubility, and the $Cs^+$ ion exchanged catalyst could be recycled for at least five times without severe elution.

• Proceedings of the KIEE Conference
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• 1998.11c
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• pp.853-855
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• 1998

The electrical resistivity and mechanical properties of the hot-pressed and annealed ${\beta}$-SiC+39vol.%$ZrB_2$ electroconductive ceramic composites were investigated as a function of the liquid forming additives of $Al_{2}O_{3}+Y_{2}O_{3}$(6:4wt%). In this microstructures. no reactions were observed between $\beta$-SiC and $ZrB_2$, and the relative density is over 97.6% of the theoretical density. Phase analysis of composites by XRD revealed mostly of a $\alpha$-SiC(6H, 4H), $ZrB_2$ and weakly $\beta$-SiC(15R) phase. The fracture toughness decreased with increased $Al_{2}O_{3}+Y_{2}O_{3}$ contents and showed the highest for composite added with 4wt% $Al_{2}O_{3}+Y_{2}O_{3}$ additives. The electrical resistivity increased with increased $Al_{2}O_{3}+Y_{2}O_{3}$ contents because of the increasing tendency of pore formation according to amount of liquid forming additives $Al_{2}O_{3}+Y_{2}O_{3}$. The electrical resistivity of composites is all positive temperature coefficient resistance(PTCR) against temperature up to $700^{\circ}C$.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.14 no.2
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• pp.117-122
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• 2001

In this paper, we report on photoelectrochemical etching process of 6H-SiC semiconductor wafer. The etching was performed in two-step process; anodization of SiC surface to form a deep porous layer and thermal oxidation followed by an HF dip. Etch rate of about 615${\AA}$/min was obtained during the anodization using a dilute HF(1.4wt% in H$_2$O) electrolyte with the etching potential of 3.0V. The etching rate was increased with the bias voltage. It was also found out that the adition of appropriate portion of H$_2$O$_2$ into the HF solution improves the etching rate. The etching process resulted in a higherly anisotropic etching characteristics and showed to have a potential for the fabrication of SiC devices with a novel design.

• Journal of the Korean Ceramic Society
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• v.42 no.3 s.274
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• pp.178-181
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• 2005

Silicon oxynitride (SiON) layers deposited upon a $SiO_2/Si$ buffer layer placed upon silicon wafers have been obtained by using PECVD from $SiH_4,\;N_2O$, and $N_2$. It can be seen that the refractive index, measured by using a prism coupler, for the SiON films can be varied between 1.4480 and 1.4958 at a wavelength of 1552 nm by changing the process parameters. Optical planar waveguides with a thickness of $6{\mu}m$ and a refractive index contrast ($\Delta$n) of $0.36\% have been deposited. Also, etching experiments were performed using ICP dry etching equipment on thick SiON films grown onto Si substrates covered by a thick $SiO_2$ buffer layer. A polarization maintaining single-mode fiber was used for the input and a microscope objective for the output at $1.55{\mu}m$. As a result, a low index contrast SiON based waveguide is fabricated with easily adjustable refractive index of core layer. It illustrates that the output intensity mode is a waveguiding single-mode.

• Korean Chemical Engineering Research
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• v.47 no.4
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• pp.424-429
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• 2009

The effects of $Na_2O$, $SiO_2$ and $H_2O$ contents of the synthetic mixtures prepared from water glass on the crystallinity and crystallite size of sodalite were studied. The composition of the synthetic mixtures described by $x\;Na_2O{\cdot}y\;SiO_2{\cdot}Al_2O_3{\cdot}z\;H_2O$ was varied within x=2.5~7.5, y=1.4~3.0, z=140~400. The hydrothermal reaction was carried out at $140^{\circ}C$ for 2 days. High content of $Na_2O$ resulted in the high crystallinity and small crystallite of sodalite. The $SiO_2/Al_2O_3$ molar ratios of around 2 were suitable for the synthesis of sodalite, and produced zeolite species were varied by the $H_2O$ content. Sodalite was mainly obtained with a high crystallinity from the synthetic mixtures with $SiO_2/Al_2O_3$ molar ratio of around 2 and high content of $Na_2O$. The high content of sodium ions caused a decrease in the particle sizes because of their role of structure directing agent.

• Journal of the Korean Vacuum Society
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• v.19 no.3
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• pp.230-235
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• 2010

In this paper, we controlled the deposition rate and reflective index with process conditions that are TCP power, gas flow ratio and bias for optical properties of $SiO_2$ thin film using TCP-CVD equipment. We obtained a excellent $SiO_2$ thin film which has a excellent uniformity (<1 [%]), deposition rate (0.28 [${\mu}m$/ min]) and reflective index (1.4610-1.4621) within 4" wafer with process conditions ($SiH_4:O_2$=50 : 100 [sccm], TCP power 1 [kW], bias 200 [W]) at [$300^{\circ}C$].

• Journal of the Korean Ceramic Society
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• v.30 no.6
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• pp.485-491
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• 1993

Porous glass in the ZrO2.SiO2 system containning up to 30mol% zirconia were prepared by the sol-gel method from metal alkoxides and their pore characteristics with reaction parameters were investigated. The gels were made by hydrolyzing and condensation of the mixed metla alkoxides and were converted into the porous glass by heating up to $700^{\circ}C$. As a results, the mean pore radius became larger with increasing contents of HCl, H2O and hydrolysis temperature, and an alcohol with a large molecular weight for making the porous glass. In the case of 20ZrO2.80SiO2 porous glass with heated at $700^{\circ}C$, HCl and H2O content was 0.3mol and 4mol, the specific surface area was 284$m^2$/g, average mean pore radius was about 19.4$\AA$, porosity was 22.55% and pore characteristics depended on heating temperature.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.07a
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• pp.151-154
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• 2003

AlN/Al/SiO$_2$/Si thin films for application to FBAR(Film Bulk Acoustic Resonator) devices were prepared by FTS(Facing Targets sputtering system) apparatus which provides a stable discharge at low gas pressures and can deposit high quality thin films because of the substrate located apart from the plasma. The AlN thin films were deposited on a $SiO_2(1{\mu}m)/Si(100)$ substrate using an Al bottom electrode. The process parameters were fixed such as sputering power of 200W, working pressures of 1mTorr and AlN thin film thickness of 800nm, respectively and crytallographic characteristics of AlN thin films were investigated as a function of $N_2$ gas flow rate$[N_2/(N_2+Ar)]$. Thickness of AlN thin films were measured by $\alpha$-step, the crystallographic characteristics and c-axis preferred orientation were evaluated by XRD.