• Macromolecular Research
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• 제17권1호
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• pp.37-43
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• 2009

To fabricate dental nanocomposites containing finely dispersed silica nanoparticles, nearly monodispersed silica nanoparticles smaller than 25 nm were synthesized without forming any aggregates via a modified sol-gel process. Since silica nanoparticles synthesized by the Stober method formed aggregates when the particle size is smaller than 25 nm, the synthetic method was modified by changing the reaction temperature and adding poly(1-vinyl-2-pyrrolidinone) (PVP) to the reaction mixture. The size of the formed silica nanoparticles was reduced by increasing the reaction temperature or adding PVP. Furthermore, the formation of aggregates with primary silica nanoparticles smaller than 25 nm was prevented by increasing the amount of PVP added to the reaction mixture. To enhance the dispersion of the silica particles in an organic matrix, the synthesized silica nanoparticles were treated with 3-methacryloxypropyltrimethoxysilane ($\gamma$-MPS). A dental nanocomposite containing finely dispersed silica nanoparticles could be produced by using the surface-treated silica nanoparticles.

• 한국세라믹학회지
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• 제15권4호
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• pp.193-198
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• 1978

Test-bricks were prepared from an artifically graded Ham Kang sand and a commercial CaO and autoclaved for 6 hours at $16 kg/cm^2$ pressure $(203^{\circ}C)$. Bricks were tested for compressive strength, free lime, saluble silica and amount of water absorption. Physical properties of bricks were very much depended on the size distribution of sand particle and the amount of soluble silica in bricks.

• 대한기계학회논문집B
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• 제23권9호
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• pp.1151-1162
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• 1999

The effects of radial heat and $H_2O$ diffusion on the evolution of silica particles in coflow diffusion flames have been studied experimentally. The evolution of silica aggregate particles in coflow diffusion flames has been measured experimentally using light scattering and thermophoretic sampling techniques. The measurements of scattering cross section from $90^{\circ}$ light scattering have been utilized to calculate the aggregate number density and volume fraction using with combination of measuring the particle size and morphology through the localized sampling and a TEM image analysis. Aggregate or particle number densities and volume fractions were calculated using Rayleigh-Debye-Gans and Mie theory for fractal aggregates and spherical particles, respectively. Flame temperatures and volumetric differential scattering cross sections have been measured for different flame conditions such as inert gas species, $H_2$ flow rates, and burner injection configurations to examine the relation between the formation of particles and radial $H_2O$ diffusion. The comparisons of oxidation and flame hydrolysis have also been made for various $H_2$ flow rates using $N_2$ or $O_2$ as a carrier gas. Results indicate that the role of oxidation becomes dominant as both carrier gas($O_2$) and $H_2$ flow rates increases since the radial heat diffusion precedes $H_2O$ diffusion in coflow flames used in this study. The effect of carrier gas flow rates on the evolution of silica particles have also been studied. When using $N_2$ as a carrier gas, the particle volume fraction has a maximum at a certain carrier gas flow rate and as the flow rate is further increased, the hydrolysis reaction Is delayed and the spherical particles finally evolves into fractal aggregates due to decreased flame temperature and residence time.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2001년도 The 6th International Symposium of East Asian Resources Recycling Technology
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• pp.84-87
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• 2001

A demand for the aggregates is increasing in the field of civil and architectural industry and so on. In these industries, the particle size and shape of aggregates are important factors and especially spherical or rounded particles are desired. In Japan, waste glass is used as one of the aggregate materials for the pavement or the construction. In this study based on the frictional action of material on each other, an autogenous grinding of silica glass with a stirred mill were carried out in order to eliminate flakelike or squarish particles and get spherical or rounded ones for aggregate materials. The autogenous grinding experiments were conducted by applying loads to the particle layer of silica glass. The particle shape was evaluated by the shape index, N/T and the degree of circularity, Ψ$_{ci}$ . The unfractured particles (20~13mm) were evaluated by N/T and Ψ$_{ci}$ , and the products (finer than 10${\mu}{\textrm}{m}$) by Ψ$_{ci}$ . As a result, N/T of the unfractured particles decreased with an increase of grinding time. Ψ$_{ci}$ of the unfractured particles and the products increased with an increase of grinding time (; progress of grinding), and became almost constant in the long time grinding. These tendencies were not changed by the applied load on the particle layer, but the limit value of Ψ$_{ci}$ at the products were varied with the applied load.plied load.

• The Journal of Advanced Prosthodontics
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• 제12권5호
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• pp.291-298
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• 2020

PURPOSE. The aim of this study is to evaluate the influence of repeated surface treatments on wettability and surface roughness for zirconia surface and bond strength of zirconia-based ceramics to resin cement. MATERIALS AND METHODS. Seventy blocks (10 × 10 × 3 mm) of zirconia-based ceramics were fabricated and divided into two groups according to the surface treatments: (A) 110 ㎛ Al₂O₃ airborne-particle abrasion and (R) 110 ㎛ silica modified Al₂O₃ airborne-particle abrasion. At stage 2, each group was subdivided into 5 groups according to the surface retreatments: (a) 110 ㎛ Al₂O₃ airborne-particle abrasion, (r) 110 ㎛ silica modified Al₂O₃ airborne-particle abrasion, (D) diamond bur, (Da) diamond bur + 110 ㎛ Al₂O₃ airborne-particle abrasion, and (Dr) diamond bur + 110 ㎛ silica modified Al₂O₃ airborne-particle abrasion. Cylinders of self-adhesive resin cement were cemented onto each treated ceramic surface and subjected to micro-shear bond strength test. Additional specimens were prepared for roughness and wettability analyses. The data were subjected to t-test and One-way ANOVA followed by Tukey's post hoc test (α=.05). RESULTS. At stage 1, group R presented higher bond strength values than group A (P=.000). There was a statistically significant increase of bond strength at stage 2 for group A (P=.003). The diamond bur influenced the surface roughness, increasing the values (P=.023). Group R provided better wettability. Regardless of the applied surface treatment, most of failures were adhesive. CONCLUSION. The combination of application and reapplication of Rocatec Plus showed the best results of bond strength. Surface retreatment and recementation might be an indicated clinical strategy.

• 한국입자에어로졸학회지
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• 제8권2호
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• pp.89-95
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• 2012

Spherical mesoporous silica particles, of which main pore diameter was 3.8 nm, were successfully prepared by spray pyrolysis from aqueous silicic acid. The effect of precursor concentration, reaction temperature, and the addition of urea and PEG on the particle diameter and pore properties such as pore diameter, total pore volume, and specific surface area were investigated by using FE-SEM, particle size analyzer, and nitrogen absorption-desorption analysis. With an increase of the precursor concentration from 0.2 M to 0.7 M, the average particle diameter, total pore volume, and specific surface area of the porous silica particles increased from 0.56 to $0.96\;{\mu}m$, 0.434 to $0.486\;cm^3/g$, 467.8 to $610.4\;m^2/g$, respectively. Within the temperature range $(600\;^{\circ}C{\sim}800\;^{\circ}C)$, there was no significant difference in the pore diameter, total pore volume, and specific surface area. In addition, the addition of urea as an expansion aid led to slight increases in particle diameter, pore diameter, and specific surface area. However, when the polyethylene glycol (PEG) as an organic template was used, the total pore volume of porous particles increased dramatically.

• 공업화학
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• 제10권8호
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• pp.1180-1185
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• 1999

본 연구에서는 입경 제어가 용이하며 입자의 배열 상태가 치밀화된 매우 단분산된 실리카 미립자를 합성키 위하여 회분과 반회분의 적용 순서를 달리한 혼합 공정을 이용, TEOS(Tetraethylorthosilicate)의 가수분해로부터 실리카 미립자를 제조하였다. 실험은 회분과 반회분 각각의 공정을 회분-회분, 회분-반회분, 반회분-회분, 반회분-반회분의 네가지 형태로 순서를 바꾸어 혼합 적용하였으며, 각각의 공정에서 생성된 실리카 입자에 대하여 평균 입경, 입도분표, 수율, 그리고 입자의 치밀화 등을 측정, 비교하였다. 실험결과 최종 평균 입경과 수율은 반회분-반회분>회분-반회분>회분-회분>반회분-회분 공정의 순서로 컸으며, 입도 분포와 입자의 치밀화 정도는 회분-반회분>회분-회분>반회분-회분>반회분-반회분의 순서로 단분산되고 치밀한 결과를 보였다. 이중 반회분-회분, 반회분-반회분과 같이 반회분식으로 먼저 실험하여 입자를 생성한 경우는 두 번째 공정의 종류에 관계없이 모두 2차 핵 생성이 일어나는 결과를 보였으며, 이중 반회분-회분의 혼합 공정에 의해서 생성된 입자는 2차의 회분식 공정 단계에서 반응물이 첨가된 후 시간이 경과함에 따라 오히려 입자가 감소하는 결과를 보였다. 결과적으로 상기 네 가지 공정 중 회분-반회분 순서의 혼합 공정에 의해 생성된 실리카 미립자가 가장 단분산되고 입자의 치밀화가 양호한 상태로 쉽게 입경 제어를 할 수 있음을 알 수 있었다.

• 한국안전학회지
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• 제34권3호
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• pp.28-35
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• 2019

Dry water is a core-shell structured powder which comprises a very fine water core covered with hydrophobic silica particles. Recently, the dry water has attracted attention as a new type of fire extinguishing agents. However, characteristics of the dry water as a fire extinguishing agent have not been revealed until now. To our best knowledge, this is the first work to uncover effects of particle size of the dry water on the fire extinguishing performance. Pristine dry water, which has heterogeneous particle size distribution, was carefully separated by sieving method into three fractions which were a small size (ca. $110{\mu}m$) fraction, a medium size (ca. $220{\mu}m$) fraction and a large size (ca. $400{\mu}m$) fraction. Microscopic observations confirmed the effective separation of dry water's particle size. In extinguishing tests of wood cribs fire, the medium size dry water showed most excellent fire extinguishing performance, as compared to other dry waters having small (ca. $110{\mu}m$) and large (ca. $400{\mu}m$) particle size. The good performance of the medium size (ca. $220{\mu}m$) dry water may be attributed to the balance between cooling effect of the water core and smothering effect of the silica particles. It is also revealed that small size dry water has poor flowability than large size dry water.

• 한국산학기술학회논문지
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• 제17권1호
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• pp.181-187
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• 2016

실리카는 다양한 산업용 소재로 이용되고 있으며, 특히 불순물의 함량이 적은 고품위 실리카는 전자소재인 LCD 및 OLED 등의 원재료로 큰 주목을 받고 있다. 본 연구에서는 물리적 정제방법인 자력선별 방식에 의한 실리카의 고순도화 연구를 위해 세 가지 형태의 자력 선별기를 고려하여 $SiO_2$와 $Fe_2O_3$를 대상으로 전산모사를 실시하였다. 전산모사 결과, $Fe_2O_3$ 입자를 끌어당길 수 있는 유효면적이 자력선별의 매우 중요한 변수로 작용함을 확인하였으며, $SiO_2$ 입자의 손실율 및 $Fe_2O_3$ 입자의 제거율은 입자의 크기와 유속에 매우 큰 영향을 받음을 알 수 있었다. 본 연구에서는 입자크기 $10{\mu}m$, 유속 0.2 m/s의 조건에서 가장 우수한 분리효율의 확보가 가능하였으며, 자력선별기의 구성에 있어 입자의 크기, 유속, 자속 밀도가 매우 핵심적인 변수임을 증명하였다.

• 대한기계학회논문집A
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• 제38권9호
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• pp.1037-1041
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• 2014

반도체 연마용 슬러리를 이온교환법, 가압방법 및 다단계 주입방법으로 제조하여 입자 크기와 형상에 따른 화학적 기계적 연마에 미치는 영향을 연구하였다. 이온교환법을 이용하여 구형의 콜로이달실리카를 크기별로 입자로 제조하였다. 이렇게 제조한 구형의 실리카를 다시 가압방법을 이용해 입자간의 결합을 유도해 비구형의 형상을 가진 콜로이달 실리카를 제조하였고, 이온교환법과 가압방법의 특징을 살려 실리식산을 다단계로 주입하여 입자 표면과 실리식산의 반응으로, 2~3 개의 입자가 결합한 형상의 콜로이달 실리카를 제조하였다. 이렇게 제조한 입자를 CMP 에 적용하여 콜로이달 실리카의 입자 형상에 따른 연마율을 기존의 상용 슬러리와 비교하였다. pH 가 높을수록 연마율은 높아졌고, 입자가 결합한 비구형의 콜로이달 실리카는 가장 높은 연마율과 양호한 비균일도를 나타내었다.