• Bulletin of the Korean Chemical Society
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• v.32 no.12
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• pp.4382-4386
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• 2011

$TiO_2$ hollow spheres were fabricated by using $SiO_2$ as an inorganic template. Spherical $SiO_2$ particles were coated by $TiO_2$ through the nucleation process, and then the core $SiO_2$ part was eliminated by using HF solution. Finally, $TiO_2$ hollow spheres were obtained. The size of the $TiO_2$ hollow spheres was about 300-400 nm and the thickness of the hollow wall was about 20-30 nm. The hollow has several holes whose diameters were within 100-200 nm. Dye-sensitized solar cells fabricated by using the $TiO_2$ hollow spheres were characterized. The solar conversion efficiency of the cell was 8.45% when $TiO_2$ hollow spheres were used as a scattering material, while it was 4.59% when $TiO_2$ hollow spheres were used as a normal electrode material.

• Korean Journal of Materials Research
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• v.22 no.10
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• pp.531-538
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• 2012

Hollow silica spheres were prepared by spray drying of precursor solution of colloidal silica. The precursor solution is composed of 10-20 nm colloidal silica dispersed in a water or ethanol-water mixture solvent with additives of tris hydroxymethyl aminomethane. The effect of pH and concentrations of the precursor and additives on the formation of hollow sphere particles was studied. The spray drying process parameters of the precursor feeding rate, inlet temperature, and gas flow rate are controlled to produce the hollow spherical silica. The mixed solvent of ethanol and water was preferred because it improved the hollowness of the spheres better than plain water did. It was possible to obtain hollow silica from high concentration of 14.3 wt% silica precursor with pH 3. The thermal conductivity and total solar reflectivity of the hollow silica sample was measured and compared with those values of other commercial insulating fillers of glass beads and $TiO_2$ for applications of insulating paint, in which the glass beads are representative of the low thermal conductive fillers and the $TiO_2$ is representative of infrared reflective fillers. The thermal conductivity of hollow silica was comparable to that of the glass beads and the total solar reflectivity was higher than that of $TiO_2$.

• Membrane Journal
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• v.17 no.4
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• pp.381-386
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• 2007

Hollow fibers were made using the nickel slurry containing nickel particles and polymers by phase inversion method. And then, metallic filters were fabricated by sintering method at $1,150^{\circ}C$ under reduction condition. Metallic microfiltration membranes were prepared by coating nickel particles on the metallic filter. The properties of the metallic hollow fiber filters and microfiltration membranes such as pore size and strength were investigated. The metallic membrane showed good resistance against acid, base and chlorine. It was observed that the membrane exhibited good recovery rate by back washing.

• Journal of the Korean Electrochemical Society
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• v.14 no.3
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• pp.184-190
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• 2011

$LiMn_2O_4$ with mesoporous hollow sphere shape was synthesized by precipitation method with silica template. The synthesized $LiMn_2O_4$ has nanosized first particle and mesoporous hollow sphere shape. Silica template was removed by chemical etching method using NaOH solution. When the concentration of NaOH solution was increased, first particle size of manganese oxide was decrease and confirmed mesoporous hollow shpere shape. X-ray diffraction(XRD) patterns revealed that the synthesized samples has spinel structure with Fd3m space group. In case the ratio of silica and maganese salt increased, the size of first particles was decreased. The tetragoanal $LiMn_2O_4$ with micron size was synthesized at ratio of silica and manganese salt over 1 : 9. The prepared samples were assembled as cathode materials of Li-ion battery with 2032 type coin cell and their electrochemical properties are examined by charge-discharge and cyclic performance. Electrochemical measurements show that the nano-size particles had lower capacity than micron-size particles. But, cyclic performance of nano-size particles had better than that of micron-size particles.

• Bulletin of the Korean Chemical Society
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• v.32 no.5
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• pp.1534-1538
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• 2011

Uniform, hollow nanosilica spheres were prepared by the chemical coating of cationic polystyrene (cPS) with tetraethylorthosilicate (TEOS), followed by calcination at 600 $^{\circ}C$ under air. cPS was synthesized by surfactant-free emulsion polymerization using 2,2'-azobis (2-methyl propionamidine) dihydrochloride as the cationic initiator, and poly(vinyl pyrrolidone) as a stabilizer. The resulting cPS spheres were 280 nm in diameter, and showed monodispersion. After coating, the hollow silica product was spherically shaped, and 330 nm in diameter, with a narrow distribution of sizes. Dispersion was uniform. Wall thickness was 25 nm, and surface area was 96.4 $m^2/g$, as determined by BET. The uniformity of the wall thickness was strongly dependent upon the cPS surface charge. The effects of TEOS and ammonia concentrations on shape, size, wall thickness, and surface roughness of hollow $SiO_2$ spheres were investigated. We observed that the wall thicknesses of hollow $SiO_2$ spheres increased and that silica size was simultaneously enhanced with increases in TEOS concentrations. When ammonia concentrations were increased, the irregularity of rough surfaces and aggregation of spherical particles were more severe because higher concentrations of ammonia result in faster hydrolysis and condensation of TEOS. These changes caused the silica to grow faster, resulting in hollow $SiO_2$ spheres with irregular, rough surfaces.

• Journal of the Korean Ceramic Society
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• v.35 no.11
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• pp.1171-1181
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• 1998

$SrZr_{0.95}$$Y_{0.05}$$O_{2.975}$ powder was synthesized by ultrasonic spray pyrolysis using a solution that Sr carbonate and Zr and Y nitrates were dissolved in a citric acid solution. The processes of particle formation were in-vestigated with respect to solution properties and pyrolysis temperature. With changing the solution con-centration form 0.1M to 0.01M there was a tendency that average sizes of droplets and particles were de-creased and their size distributions were narrowed. Citrate functional groups converted the droplets into gel particles which prevented an inhomogeneous precipitation of the metal ions and facilitated the diffusion of gases during thermal decomposition. As a result the powder having spherical particles without hollow par-ticles could be prepared. Low pyrolysis temperature led to amorphous particles due to incomplete pyrolysis and made the particles difficult to maintain spherical shape due to retarded gelation of the droplets. Whereas higher pyrolysis temperature produced hollow and broken particles because the droplets un-derwent rapid gelationand decomposition. The particles obtained at two pyrolysis temperature $500^{\circ}$and $1000^{\circ}C$ consisted of a perovskite phase and a very small amount of $SrCO_3$ However after calcination at $1000^{\circ}C$ the particles contained a single perovskite phase having an average particle size of 0.63${\mu}{\textrm}{m}$ and an apparent density near to the theoretical density.

• Journal of the Korean Ceramic Society
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• v.54 no.5
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• pp.429-437
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• 2017

Micro hollow plate type silica with low refraction properties was synthesized and its hollow structure was applied as an optical structure to develop a light diffusion material that simultaneously satisfies the requirements of good light diffusibility, high transmissibility, and high luminance. The developed light diffusion material was applied to a light diffusion film and the film's optical properties were assessed. Hollow silica was synthesized by precipitation method using $Mg(OH)_2$ core particles, sodium silicate, and ammonium sulfate as the silica precursors. The concentration of the silica precursor was adjusted to control hollow silica shell thickness. The total light transmittance of the light diffusion film composed of the hollow silica was 94.55%, which was 4.57% higher than that of the PC film; new film's haze was 71.20%, which was 70.9% higher. Furthermore, the luminance increased by 5.34% compared to that of the light source. The reason for the results is not only that the micro plate type hollow silica, which has a low refractive property, played a role in reducing the difference in refractive index between the medium boundaries, but also that there was a light-concentrating effect due to the changing of light paths to the front direction inside the hollow structure. Optical simulation verified the enhanced optical properties when hollow silica was applied to the light diffusion film.

• Applied Chemistry for Engineering
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• v.10 no.8
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• pp.1186-1191
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• 1999

By using a liquid-mix precursor, we prepared the hollow glass spheres(HGS) as an additive of polymer compound which are used in the field of modifier, promoter, filler, and reinforcement. Liquid-mix precursor is a mixture of 40% sodium silicate aqueous solution, boric acid as a insolubilizing agent, and urea as a blowing agent. To obtain the precursor particles which are fed into a gas flame furnae, the above liquid-mix precursor was dried in oven and crushed with ball mill. We assumed the size of precursor particles ($53{\sim}63{\mu}m$, $63{\sim}180{\mu}m$), temperature of furnace($800{\sim}1200^{\circ}C$), and amount of urea(0~30 g) as the parameters affecting on the properties of HGS. As a result mean particle size of HGS increases with increasing the temperature of furnace and the amount of urea and with decreasing the size of precursor particles. Also, we found that incresing the amount of urea is related to a decrease of the crush strength of HGS.

• Applied Chemistry for Engineering
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• v.17 no.6
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• pp.648-652
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• 2006

Demand for $MnO_{2}$ has been increased with interest for its various applications in the fields of battery, catalyst, and capacitor. In this study, $MnO_{2}$ hollow microspheres were synthesized by sacrificial core method. $MnO_{2}$ nano particles were produced by the hydrolysis and condensation of manganese acetate. The stable $MnO_{2}$ hollow microspheres can very well be synthesized with mixing 0.2% of water, 0.65 mM of manganese acetate, and 0.02 mM catalyst at a room temperature.

• 한국정보디스플레이학회:학술대회논문집
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• 2002.08a
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• pp.803-806
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• 2002

Flame spray pyrolysis was applied to improve the photoluminescence characteristics of blue-emitting $Sr_5(PO_4)_3Cl:Eu^{2+}$ phosphor particles with high brightness for the application to LED phosphor. $Sr_5(PO_4)_3Cl:Eu^{2+}$ prepared from conventional spray pyrolysis had poor PL intensity than that of commercial products under long-wavelength ultraviolet(UV). $Sr_5(PO_4)_3Cl:Eu^{2+}$ phosphor particles prepared by flame spray pyrolysis had PL intensity as same as that of commercial products under long-wavelength UV. Hollow morphology and porous structure of the particles prepared by the flame spray pyrolysis disappeared after posttreatment. Even though the $Sr_5(PO_4)_3Cl:Eu^{2+}$ phosphor particles prepared by the flame spray pyrolysis had irregular shape, the particles had dense structure and clear surface property.