• KSBB Journal
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• v.17 no.4
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• pp.365-369
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• 2002

An iron-storage protein, ferritin is a spherical shell consisting of 24 H-and L-chain subunits. Soluble form of fused($F_{H}+F_{L}$ chain) ferritin was separated from disrupted recombinant E. coii cells, followed by silica powder adsorption. Ferritin was recovered from silica-poweder by distilled water, which was applied to gel filtration chromatography(GFC). Collected ferritin fractions from the GFC were assayed via iron-uptake and its molecular weight determined using GF-HPLC. Fused ferritin showed a higher activity than the M- or L- chain ferritin by two times.

• Bulletin of the Korean Chemical Society
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• v.21 no.12
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• pp.1193-1198
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• 2000

The preparation of nanocrystalline hematite, ${\alpha}-Fe_2O_3$, paricles and their surface coating with silica layers are described. The hematite particles with the size of 30~60 nm are firstly prepared by thermal decomposition of trinuclear acetate-hydroxo iron (III) nitrate complex, $[Fe_3$(OCOCH_3)_7$OH${\cdot}$2H_2O]NO_3$, at $400^{\circ}C$. Subsequently the hematite surfaces are coated with siliva layers by a controlled hydrolysis and condensation reaction of TEOS with varying the TEOS concentration and pH. Monodispersed and spherical $SiO_2-coatedFe_2O_3$ particles with the average particle diameter of ~90 nm and extremely narrow size distribution can be obtained at the pH of 11 and the TEOS concentration of 0.68M, which are found to be the optimum conditions in the present study in achieving the homogeneous deposition of silica layers on hematite surfaces. Diffuse reflectance UV-Vis spectra reveal that the characteristic optical reflectance of ${\alpha}-Fe_2O_3$ particles is preserved almost constant even after coating the surfaces, suggesting that the $SiO_2$ layers can be regarded as protecting layers without degrading the optical properties of hematite particles.

• Membrane Journal
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• v.24 no.3
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• pp.177-184
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• 2014

Silica membranes with high permeability were prepared using colloidal and polymeric silica sols on a porous stainless steel-tube support by a DRFF and SRFF method. Silica sols were derived with tetraethylorthosilicate (TEOS) by sol-gel method and analyzed with DLS, FE-SEM, and $N_2$ adsorption. The coating of the intermediate layer with colloidal silica sol on the stainless steel-tube support led to a denser surface morphology of the membrane along with a considerable reduction in the number of surface defect. As the polymeric silica sol enclosed the colloidal silica sol with spherical particles during the SRFF method, the separation-layer-coated silica membrane showed a denser surface than the intermediate layer. Moreover, the silica membranes showed high hydrogen gas permeability of $(6.63-9.21){\times}10^{-5}mol{\cdot}m^{-2}{\cdot}s^{-1}{\cdot}Pa^{-1}$ with low $H_2/N_2$ perm-selectivity (2.9-3.1) at room temperatures.

• Korean Journal of Materials Research
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• v.14 no.8
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• pp.600-606
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• 2004

$Zn_{2}SiO_{4}:Mn$ phosphor particles were prepared by a flame spray pyrolysis method. It has been generally known that the high-temperature flame enables fast drying and decomposition of droplets. In the present investigation, the morphology and luminescent property of $Zn_{2}SiO_{4}:Mn$ phosphor were controlled in a severe flame preparation condition. The particle formation in the flame spray pyrolysis process was achieved by the droplet-to-particle conversion without any evaporation of precursors, which made it possible to obtain spherical $Zn_{2}SiO_{4}:Mn$ particles of a pure phase from a droplet. Using colloidal solutions wherein dispersed nano-sized silica particles were adopted as a silicon precursor. $Zn_{2}SiO_{4}:Mn$ particles with spherical shape and filled morphology were prepared and the spherical morphology was maintained even after the high-temperature heat treatment, which is necessary to increase the photoluminescence intensity. The $Zn_{2}SiO_{4}:Mn$ particles with spherical shape, which were prepared by the flame spray pyrolysis and posttreated at $1150^{\circ}C$, showed good luminescent characteristics under vacuum ultraviolet (VUV) excitation.

• Journal of Korean Society of Occupational and Environmental Hygiene
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• v.25 no.1
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• pp.36-44
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• 2015

Objectives: This study aimed to elucidate the physicochemical properties of silica powder and airborne particles as by-products generated from fabrication processes to reduce unknown risk factors in the semiconductor manufacturing work environment. Materials and Methods: Sampling was conducted at 200 mm and 300 mm semiconductor wafer fabrication facilities. Thirty-two powder and airborne by-product samples, diffusion(10), chemical vapor deposition(10), chemical mechanical polishing(5), clean(5), etch process(2), were collected from inner chamber parts from process and 1st scrubber equipment during maintenance and process operation. The chemical composition, size, shape, and crystal structure of silica by-product particles were determined by using scanning electron microscopy and transmission electron microscopy techniques equipped with energy dispersive spectroscopy, and x-ray diffractometry. Results: All powder and airborne particle samples were composed of oxygen(O) and silicon(Si), which means silica particle. The by-product particles were nearly spherical $SiO_2$ and the particle size ranged 25 nm to $50{\mu}m$, and most of the particles were usually agglomerated within a particle size range from approximately 25 nm to 500 nm. In addition, the crystal structure of the silica powder particles was found to be an amorphous silica. Conclusions: The silica by-product particles generated from the semiconductor manufacturing processes are amorphous $SiO_2$, which is considered a less toxic form. These results should provide useful information for alternative strategies to improve the work environment and workers' health.

• Journal of Powder Materials
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• v.30 no.4
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• pp.346-355
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• 2023

Epoxy-based composites find extensive application in electronic packaging due to their excellent processability and insulation properties. However, conventional epoxy-based polymers exhibit limitations in terms of thermal properties and insulation performance. In this study, we develop epoxy-based siloxane/silica composites that enhance the thermal, mechanical, and insulating properties of epoxy resins. This is achieved by employing a sol-gel-synthesized siloxane hybrid and spherical fused silica particles. Herein, we fabricate two types of epoxy-based siloxane/silica composites with different siloxane molecular structures (branched and linear siloxane networks) and investigate the changes in their properties for different compositions (with or without silica particles) and siloxane structures. The presence of a branched siloxane structure results in hardness and low insulating properties, while a linear siloxane structure yields softness and highly insulating properties. Both types of epoxy-based siloxane/silica composites exhibit high thermal stability and low thermal expansion. These properties are considerably improved by incorporating silica particles. We expect that our developed epoxy-based composites to hold significant potential as advanced electronic packaging materials, offering high-performance and robustness.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.23 no.11
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• pp.1379-1389
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• 1999

A new technique for control of size and shape of flame-made particles is Introduced. The characteristic sintering time can be controlled Independently of collision time by heating the particles with irradiation of laser because the sintering time strongly depends on temperature. A coflow oxy-hydrogen diffusion flame burner was used for $SiCl_4$ conversion to silica particle. Nanometer sized aggregates irradiated by a high power CW $CO_2$ laser beam were rapidly heated up to high temperatures and then were sintered to approach volume-equivalent spheres. The sphere collides much slower than the aggregate, which results in reduction of sizes of particles maintaining spherical shape. Light scattering of Ar ion laser and TEM observation using a local sampling device were used to confirm the above effects. When the $CO_2$ laser was irradiated at low position from the burner surface, particle generation due to gas absorption of laser beam occurred and thus scattering intensity increased with $CO_2$ laser power. At high irradiation position, scattering intensity decreased with $CO_2$ laser power and TEM image showed a clear mark of evaporation and recondensation of particles for high $CO_2$ laser power. When the laser was irradiated between the above two positions where small aggregates exist, average size of spherical particles obviously decreased to 58% of those without $CO_2$ laser irradiation with the spherical shape. Even for increased carrier gas flow rate by a factor of three, TEM photograph also revealed considerable reduction of particle size.

• Bulletin of the Korean Chemical Society
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• v.34 no.1
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• pp.143-148
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• 2013

Novel titanium containing solid core mesoporous shell silica has been synthesized by using octadecyltrichloro silane and triethylamine. The synthesized material was characterized by various physicochemical techniques. The mesoporous character of the material has been revealed from PXRD studies. The presence of octadecyltrichloro silane and triethylamine in the sample has been confirmed from EDAX studies. TG/DTA analysis reveals the thermal characteristics of the synthesized material. The presence of titanium in the frame work and its coordination state has been studies by UV-vis DR studies and XPS analysis. Chemical environment of Si in the framework of the material has been studied by $^{29}SiMASNMR$ studies. The surface area of the material is found to be around $550\;m^2g^{-1}$ and pore radius is of nano range from BET analysis. The spherical morphology and particle size of the core as well as shell has been found to be 300 nm and 50 nm respectively from TEM analysis. The catalytic application of this material towards the synthesis of caprolactam from cyclohexanone in presence of hydrogen peroxide through ammoxidation reaction has been investigated. The optimum conditions for the reaction have been established. The plausible mechanism for the formation of core silica and conversion of cyclohexanone has been proposed.

• Applied Chemistry for Engineering
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• v.22 no.3
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• pp.328-331
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• 2011

ZnSe quantum dots (QDs) were prepared by employing water-containing Dioctyl sodium sulfosuccinate (AOT) reversed micelles (microemulsions) and the silica-encapsulated ZnSe QDs were obtained by a direct injection of tetraethyl orthosilicate (TEOS) into the microemulsion system. When the QDs were coated by silica, well-defined spherical shapes were formed and the average size of the QDs was near 7 nm. In addition, the photoluminescence (PL) efficiency of the QDs was reduced from 8.0 to 1.1% as they were encapsulated by silica. However, the solid layers of the silica-encapsulated ZnSe QDs on gold surfaces showed the excellent photostability. In particular, they are cadmium free and thus, less toxic. Moreover, the present method does not require a hot reaction temperature or extremely toxic H2Se gas as a Se precursor. Accordingly, the method can be a safer and more economical process for producing silica-encapsulated ZnSe QDs, which may be a potential media for biosensors.

• Korean Journal of Materials Research
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• v.26 no.10
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• pp.570-576
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• 2016

Using the ultrasonic pyrolysis method, spherical $SiO_2$ powders were synthesized from aqueous $SiO_2$ sol as a starting material. The effects of pyrolysis conditions such as reaction temperature, $SiO_2$ sol concentration, and physical properties of precursor were investigated for the morphologies of the resulting $SiO_2$ powders. The particle size, shape, and crystallite size of the synthesized $SiO_2$ powders were demonstrated according to the pyrolysis conditions. Generally, the synthesized $SiO_2$ particles were amorphous phase and showed spherical morphology with a smooth surface. It was revealed that increased crystallite size and decreased spherical $SiO_2$ particle size were obtained with increases of the pyrolysis reaction temperature. Also, quantity of spherical $SiO_2$ particles decreased with the decrease in the concentration and surface tension of the precursor.