• Proceedings of the Materials Research Society of Korea Conference
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• 2003.11a
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• pp.131-131
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• 2003

The advent of photonic technologies in the field of communications and data transmission has been heavily increasing the demand in integrated optical (IO) circuits capable of accomplishing not only simple tasks like signal, but also more sophisticated functions like all-optical signal routing or active multiplexing/demultiplexing. In the last decade, sol-gel technology has been widely used to prepare optical materials. Sol-gel processes show many promises for the development of low-loss, high-performance glass integrated optical circuits. However, crack formation is likely to occur during heat treatment in thick gel films. In order to overcome the critical thickness limitation, the organic-modified silicate has been widely used. In this case coating matrices have been prepared from the organo-silanes of T structures, acidic catalyst and the as-prepared gel films have been heat-treated below 200$^{\circ}C$ to avoid the crack formation and the degradation of organic components. However, the films prepared in the acidic condition and the low heat temperature make the films contain high OH groups which is the major optical loss function. In this work, C$\sub$6/H$\sub$5/SiO$\sub$1.5/ films were prepared on silicon substrate by sol-gel method using base catalyst in a PTMS/NH$_4$OH/H$_2$O/C$_2$H$\sub$5/OH system. The sol showed spinable viscosity at 50 wt% of solid content, and neglectable viscosity change with time. The films were crack-free and transparent after curing at 450 $^{\circ}C$, and highly condensed to minimize OH content in C$\sub$6/H$\sub$5/SiO$\sub$1.5/ networks. The effects of heat treatment of the films are characterized on the critical thickness, the chemical composition and the refractive indices by means of SEM, FT-IR, TGA, prism coupler, respectively.

• Korean Chemical Engineering Research
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• v.45 no.6
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• pp.611-618
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• 2007

We demonstrate the sol-gel coating technique of colloidal clusters for producing hollow micro-particles with complex morphologies. Cross-linked amidine polystyrene (PS) microspheres were synthesized by emulsifier-free emulsion copolymerization of styrene and divinylbenzene. The amidine PS particles were self-organized inside toluene-in-water emulsion droplets to produce large quantities of colloidally stable clusters. These clusters were coated with thin silica shell by sol-gel reaction of tetraethylorthosilicate (TEOS) and ammonia, and the organic polystyrene cores were removed by calcination at high temperature to generate nonspherical hollow micro-particles with complex morphologies. This process can be used to prepare hollow particles with shapes such as doublets, tetrahedra, icosahedra, and others.

• Korean Journal of Materials Research
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• v.12 no.7
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• pp.573-579
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• 2002

Stoichiometric mullite ($3Al_2$$O_3$. $2SiO_2$) precursor sol has been prepared by sol-gel method. The effects of the precursor pH and sintering temperature on the synthesizing behavior and morphology of mullite have been studied. Mullite precursor sol was prepared by dissolution of aluminum nitrate enneahydrate (Al($NO_3$)$_3$.9H$_2O) into the mixture of silica sol. Precursor pH of the sols was controlled to acidic condition ($PH\leq$ 1~1.5) and to basic condition ($pH\geq$8.5~9). The synthesized aluminosilicate sols were formed under 20 MPa pressure after drying at $150^{\circ}C$ for 24 hours, and then sintered for 3hours in the temperature range of $1100~1600^{\circ}C$. From TGA/DTA analysis, total weight loss in the aluminosilicate gel of the acidic sample was (equation omitted) 56% and that of the basic sample was (equation omitted) 85%, indicating that the synthesizing temperature of mullite phase for acidic and basic samples was above $1200^{\circ}C$ and $1300^{\circ}C$, respectively. The morphologies of the synthesized mullite were fine and needle-like (or rod-like) for acidic sample, and granular for basic sample that has been sintered above $1300^{\circ}C$. It was found that the morphology of mullite particle was predominantly governed by precursor pH and sintering temperature.

• Journal of the Korean Ceramic Society
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• v.41 no.10 s.269
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• pp.766-770
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• 2004

High-transmittance film was coated by using spherical silica nano colloids. Silica colloid sol was preservred between two inclined slide glasses by capillary force, and particles were stacked to form a film onto the substrate as the upper glass was sliding. As the sliding speed increased, the thickness of the film decreased and light transmittance varied. The microstructure observed by SEM showed that silica particles were nearly close packed, which enabled the calculation of the effective refractive index of the film. The film thickness calculated from the wavelength of maximum transmittance and the effective refractive index was well coincided with the thickness observed by SEM and measured by profiler. The maximum transmittance of $94.7\%$ was obtained. This means that $97.4\%$ of transmittance or $1.3\%$ of reflectance can be achieved by simple process if both sides of the substrate are coated.

• Journal of the Korean Applied Science and Technology
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• v.31 no.1
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• pp.83-91
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• 2014

In this study, we synthesized two different silica monoliths by using sol-gel, solvent exchange, surface modification, ambient pressure drying processes, and surfactant-based templating technique followed by calcination process. All of the prepared two silica monoliths showed crack-free appearance with fairly good transparency, and furthermore were confirmed to have extremely high porosity, specific surface area, and mean pore size below 30 nm. The silica aerogel sample exhibited finer and more homogeneous nano-sized pore structure due to spring back effect caused by surface modification, which resulted in better thermal insulation performance. Based on measured thermal conductivities and theoretical relationship, multi-layered glass window system in which silica monolith prepared in this study was inserted as a middle layer was revealed to have superior thermal insulation performance compared to conventional air-inserted glass window system.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2015.11a
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• pp.263-263
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• 2015

절연층이 코팅된 연자성복합체(Soft magnetic composites) 분말 성형 시 발생하는 밀도와 강도 저하의 문제를 개선하기 위해 금속산화물 전구체로 표면 개질된 자성분말을 성형 후 경화시키는 방법으로 분말 자심을 제조하였다. 이를 통해 공정이 단순화 되면서 자심의 물리적 내구성을 향상시킬 수 있음을 확인하였다.

• Proceedings of the Korean Ceranic Society Conference
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• 2003.10a
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• pp.231.1-231
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• 2003

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.4 no.2
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• pp.199-209
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• 1994

$PbTiO_3$ thin films were prepared on soda-lime-silica slide glasses, Si-wafer and sapphire substrate by the dip-coating of precursor solution. As starting materials, titanium tetra iso-propoxide and lead acetate trihydrate were used. Then acetylacetone was added to prepare stable sol. The effect of the parameters such as viscosity and composition of sol were investigated. The optical transmittance at visible range, refractive index, IR spectra were measured in varying compositions, thickness and heat treatment temperature. The crystallization of $PbTiO_3$ films were measured by using XRD and SEM. Diffusion of compositions from slide glass to thin film were investigated by using EDX, too. These sols not precipitated for 20 days. Transmittance of $PbTiO_3$ films at visible range were decreased with the increase of thickness and heat treatment temperatures, and were exhibited flat spectra. Pyrochlore type appeared in the films on slide glass and perovskite type appeared in the films on Si-wafer or sapphire at $600^{\circ}C$. Perovskite crystals transformed to $PbTi_3O_7$ phase at $800^{\circ}C$.

• Polymer(Korea)
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• v.39 no.2
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• pp.323-328
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• 2015

Poly(${\varepsilon}$-caprolactone) (PCL) nanofibers and PCL/silica membranes were synthesized by sol-gel derived electrospinning and casting, respectively. Smooth PCL nanofibers were obtained from the precursor containing N,N-dimethylformamide (DMF). PCL/silica membranes were prepared by varying the tetraethyl orthosilicate (TEOS) contents from 0 to 40 vol% to investigate the effect of silica addition on mechanical properties and cytotoxicity of the membranes. Although the strength of the membranes decreased from 12 to 8 MPa with increasing the silica content, the strength remained almost constant 7 weeks after dipping in phosphate buffered saline solution (PBS). The strength reduction was attributed to the presence of a patterned surface pores and micro-pores present in the walls between pores. The crystal structure of the membranes was orthorhombic and the crystallite size decreased from 57 to 18 nm with increasing the silica content. From the agar overlay test, the PCL/silica membranes exhibited neither deformation and discoloration nor lysis of L-929 fibroblast cells.

• Applied Chemistry for Engineering
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• v.22 no.6
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• pp.631-635
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• 2011

Spherical and non-spherical silica particles prepared by the direct oxidation were studied for the effect of the particle size and shape of these particles on oxide CMP removal rate. Spherical silica particles, which have 10~100 nm in size, were prepared by the direct oxidation process from silicon in the presence of alkali catalyst. The 10 nm silica particles were aggregated by addition of an acid, an alcohol, or a silane as an aggregation inducer between the particles. Two or more aggregated silica particles were used as a seed to grow non spherical silica particles in the direct oxidation process of silicon in the presence of alkali catalyst. The oxide removal rate of spherical silica particles increased with increasing an average particle size for spherical silica abrasives in the oxide CMP. It further increased non-spherical particles, compared with the spherical particles in the similar average particle size.