• Journal of Ceramic Processing Research
• /
• 제13권spc1호
• /
• pp.145-148
• /
• 2012

Spherical silica aerogel powders were fabricated via an emulsion polymerization method from a water glass. A water-in-oil emulsion, in which droplets of a silicic acid solution are emulsified with span 80 (surfactant) in n-hexane, was produced by a high power homogenizer. After gelation, the surface of the spherical silica hydrogels was modified using a TMCS (trimethylchlorosilane)/n-hexane solution followed by solvent exchange from water to n-hexane. Hydrophobic silica wet gel droplets were dried at 80 ℃ under ambient pressure. A perfect spherical silica aerogel powder between1 to 12 ㎛ in diameter was obtained and its size can be controlled by mixing speed. The tapping density, pore volume, and BET surface area of the silica aerogel powder were approximately 0.08 g·cm-3, 3.5 ㎤·g-1 and 742 ㎡·g-1, respectively.

• The Korean Journal of Ceramics
• /
• 제6권3호
• /
• pp.229-235
• /
• 2000

The spherical silica powder was synthesized by varying the kinds of solvent and mixing energy in emulsion method. The stirring speed varied from 500 to 1000 r.p.m. at 5$0^{\circ}C$ for 2h. Toluene in benzyl groups and a series of alkanes were used as dispersant. The average size of spherical silica particles decreased with increasing the stirring speed and the chain length o solvents used in this work. The average size was controlled in the range of 134~28$\mu\textrm{m}$ by selecting a proper solvent and stirring speed. The optimum processing parameters were described in details.

• 한국재료학회지
• /
• 제33권12호
• /
• pp.530-536
• /
• 2023

The theoretical capacity of silicon-based anode materials is more than 10 times higher than the capacity of graphite, so silicon can be used as an alternative to graphite anode materials. However, silicon has a much higher contraction and expansion rate due to lithiation of the anode material during the charge and discharge processes, compared to graphite anode materials, resulting in the pulverization of silicon particles during repeated charge and discharge. To compensate for the above issues, there is a growing interest in SiO_x materials with a silica or carbon coating to minimize the expansion of the silicon. In this study, spherical silica (SiO₂) was synthesized using TEOS as a starting material for the fabrication of such SiO_x through heating in a reduction atmosphere. SiO_x powder was produced by adding PVA as a carbon source and inducing the reduction of silica by the carbothermal reduction method. The ratio of TEOS to distilled water, the stirring time, and the amount of PVA added were adjusted to induce size and morphology, resulting in uniform nanosized spherical silica particles. For the reduction of the spherical monodisperse silica particles, a nitrogen gas atmosphere mixed with 5 % hydrogen was applied, and oxygen atoms in the silica were selectively removed by the carbothermal reduction method. The produced SiO_x powder was characterized by FE-SEM to examine the morphology and size changes of the particles, and XPS and FT-IR were used to examine the x value (O/Si ratio) of the synthesized SiO_x.

• 한국세라믹학회지
• /
• 제26권5호
• /
• pp.682-690
• /
• 1989

Fine mullite powder was prepared by colloidal sol-gel route. Boehmite as a starting material of Al2O3 and silica sol or fumed silica as a starting material of SiO2 were used. $\alpha$-Al2O3, TiO2 and ZrO2 were used as seeding materials. The combination of boehmite and silica was found to be the stoichiometric mullite powder. Techniques for drying used were spray drying, freeze drying, reduced pressure evaporation and drying in a oven. The gelled powder was heated at 130$0^{\circ}C$ for 100min and was attrition-milled for 1~3hrs. The mullite powder obtained was composed of submicrometer, uniform and spherical particles with a narrow size distribution. The mullite powder was characterized by BET, SEM, XRD and IR spectroscopy.

• 한국재료학회지
• /
• 제15권11호
• /
• pp.717-721
• /
• 2005

Silica powders were synthesized using emulsion solution containing water, nonionic surfactant of Triton N-57, and cyclohexane. Silica powders were prepared at low cost using inexpensive starting material of sodium silicate and ammonium sulfate. Morphology, size and size distribution were observed and determined using SEM. The powder was identified as silica by FT-IR and XRD analysis. Particle size and size distributions were affected by concentration of reactants, reaction time, and concentration of surfactant. Particle size were increased with increasing concentration of reactants and particles became dense with increasing reaction time. As R value increased, tile particle size was increased, reached a certain value and then decreased again. The silica powders synthesized under optimum condition were spherical in shape, $0.8{\mu}m$ in average particle size, narrow in particles size distribution, and well dispersed.

• 한국분말재료학회지
• /
• 제23권6호
• /
• pp.442-446
• /
• 2016

The sol-gel method is the simplest method for synthesizing monodispersed silica particles. The purpose of this study is to synthesize uniform, monodisperse spherical silica nanoparticles using tetraethylorthosilicate (TEOS) as the silica precursor, ethanol, and deionized water in the presence of ammonia as a catalyst. The reaction time and temperature and the concentration of the reactants are controlled to investigate the effect of the reaction parameters on the size of the synthesized particles. The size and morphology of the obtained silica particles are investigated using transmission electron microscopy and particle size analysis. The results show that monodispersed silica particles over a size range of 54-504 nm are successfully synthesized by the sol-gel method without using any additional process. The nanosized silica particles can be synthesized at higher TEOS/$H_2O$ ratios, lower ammonia concentrations, and especially, higher reaction temperatures.

• 한국산업보건학회지
• /
• 제25권1호
• /
• pp.36-44
• /
• 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.

• 한국생물공학회:학술대회논문집
• /
• 한국생물공학회 2002년도 생물공학의 동향 (X)
• /
• pp.510-513
• /
• 2002

Iron is an essential nutrient for most organisms, which supplied to them in a protein-iron complex known as ferritin. Ferritins are multimeric proteins those are consisted of spherical shell of 24 subunits defining a cavity of about 8nm in diameter. Soluble form of ferritin was separated from disrupted cells, followed by silica powder adsorption. Ferritin was recovered from silica-poweder by distiiled water, which was applied to DEAE anion exchage chromatography. Collected fractions from the DEAE column were assayed to gain the amount and the purity of ferritin by using GF-HPLC.

• KSBB Journal
• /
• 제17권4호
• /
• pp.365-369
• /
• 2002

수용성 형태로 존재하는 융합 페리틴을 정제함에 있어서 실리카 분말을 이용한 전처리 공정은 전체 정제 공정효율 증가에 기여하였다. 전처리 공정을 통해 정제된 융합 페리틴의 순도를 높이기 위해 젤 여과 크로마토그래피를 통해 보다 정제된 응합 페리틴을 얻을 수 있었다. 이렇게 정제된 융합 페리틴의 철분결합능력을 분석해본결과 320 moles $F_{H}+F_{L}$ mole로 활성이 우수함을 알 수 있었으며, 분자량 분석을 통해 융합페리틴(40 k dalton)은 trimer와 monomer형태로 존재함을 확인할 수 있었다

• 대한화장품학회지
• /
• 제30권2호
• /
• pp.189-195
• /
• 2004

카본 블랙은 매우 낮은 밀도로 화장품에는 사용되지 않고 있지만 독성이 없고 안정한 물리적 특성과 검은색의 특성으로 이용 가치가 있다고 사료되는 바이다. 본 연구에서는 TEOS, a) PEO/ lecithin, b) PEO/polyethylene glycol, c) lecithin/polyethylene을 ethanol/water 수용액상에서 계면활성제를 탄화시켜 sol-gei반응에 의해 meso-porous silica샘플을 얻었고 N2 조건하 50$0^{\circ}C$에서 열처리된 organic-inorganic hybrid silica를 합성하였다. Pore안에 카본 블랙을 함유하는 meso-porous silica는 친수성, 소수성 용매에서 모두 좋은 분산성을 보여준다. 이 샘플은 BET에 의해 specific surface area (750$m^2$/g)과 pore size (4-6 nm)이고, XRD측정으로 pore structure (cylindrical type)를, 샘플의 SEM촬영으로 morphology(0.1-0.5$\mu\textrm{m}$ 입자 크기를 갖는 spherical powder)를 갖는다는 것을 알아냈다. 이렇게 합성한 카본-실리카 블랙 컬러를 마스카라에 적용하면 일반적으로 마스카라에 사용되던 블랙 컬러 사용시 보다 좀더 검은색을 보여주는 것은 물론이고 우수한 분산성도 갖는다. 무엇보다 이 파우더의 밀도 조절이 가능하여 마스카라 뿐 만 아니라 모든 화장품에의 사용이 가능하다.