• Particle and aerosol research
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• v.9 no.4
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• pp.209-219
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• 2013

We have used the modified diffusion flame burner to synthesize silica coated iron oxide nanoparticles having enhanced superparamagnetic property. Silica-encapsulated iron oxide particles were directly observed using a high resolution transmission electron microscope. From the energy dispersive X-ray spectroscopy (EDS) and zeta potential measurements, the iron oxide particles were found to be completely covered by a silica coating layer. X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) measurements revealed that the iron oxide core consists of ${\gamma}-Fe_2O_3$ rather than ${\alpha}-Fe_2O_3$. Our magnetization measurements support this conclusion. Biocompatibility test of the silica-coated iron oxide nanoparticles is also conducted using the protein adsorption onto the coated particle.

• Bulletin of the Korean Chemical Society
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• v.33 no.7
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• pp.2224-2228
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• 2012

This study describes the ability of capillary electrochromatography (CEC) for the determination of imidacloprid and carbendazim in tomato samples. A novel liquid crystal crown ether modified hybrid silica monolithic column was synthesized, characterized and developed as separation column for the first time. Baseline separation of imidacloprid and carbendazim could be achieved using a mobile phase containing 90% (v/v) 20 mmol/L phosphate buffer (pH 7.0) and 10% (v/v) acetonitrile. The matrix matched calibration curves were linear with correlation coefficient $r^2$ > 0.9998 in the range of 0.20-10.00 mg/L. The limits of detection for imidacloprid and carbendazim were 0.061 and 0.15 mg/kg, respectively, which were below the maximum residue limits established by the European Union as well as Codex Alimentarius. Average recoveries for imidacloprid and carbendazim varied from 101.6-108.0% with relative standard deviations lower than 6.3%. This method was applied to the analysis of tomatoes collected from local markets.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2013.11a
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• pp.68-71
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• 2013

Reactive Powder Concrete (RPC) is an ultra high strength and high ductility cement-based composite material and has shown some promise as a new generation concrete in construction field. It is characterized by a silica fume-cement mixture with very low water-binder (w/b) ratio and very dense microstructure, which is formed using various powders such as cement, silica fume and very fine quartz sand (0.15~0.4mm) instead of ordinary coarse aggregate. However, the unit weight of cement in RPC is as high as 900~1,000 kg/㎥ due to the use of very fine sand instead of coarse aggregate, and a large volume of relatively expensive silica fume as a high reactivity pozzolan is also used, which is not produced in Korea and thus must be imported. Since the density of RPC has a heavy weight at 2.5~3.0 g/㎤. In this study, the modified RPC was made by the combination of ternary pozzolanic materials such as blast furnace slag and fly ash, silica fume in order to economically and practically feasible for Korea's situation. The fire resistance and structural behavior of the modified RPC exposed to high temperature were investigated.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.5
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• pp.1-6
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• 2019

Organic dye-doped silica nanoparticles are used as a promising nanomaterials for bio-labeling, bio-imaging and bio-sensing. Fluorescent silica nanoparticles(NPs) have been synthesized by the modified $St{\ddot{o}}ber$ method. In this study, dye-free fluorescent silica NPs of various sized were synthesized by Sol-Gel process as the modified $St{\ddot{o}}ber$ method. The functional material of APTES((3-aminopropyl)triethoxysilane) was added as an additive during the Sol-Gel process. The as-synthesized silica NPs were calcined at $400^{\circ}C$ for 2 hours. The surface morphology and particle size of the as-synthesized silica NPs were characterized by field-emission scanning electron microscopy. The fluorescent characteristics of the as-synthesized silica NPs was confirmed by UV lamp irradiation of 365 nm wavelength. The photoluminescence (PL) of the as-synthesized silica NPs with different size was analyzed by fluorometry. As the results, the as-synthesized silica NPs exhibits same blue fluorescent characteristics for different NPs size. Especially, as increased of the silica NPs size, the intensity of PL was decreased. The blue fluorescence of dye-free silica NPs was attributed to linkage of $NH_2$ groups of the APTES layer and oxygen-related defects in the silica matrix skeleton.

• KCI Concrete Journal
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• v.14 no.2
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• pp.76-80
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• 2002

The role of high volume Class F fly ash in reducing expansion due to Alkali-Silica Reaction (ASR) was investigated. A series of modified ASTM C 1260 tests were performed under three different levels of NaOH normality, extending the test period to 28 days, using high- or low alkali cement, and Class F fly ash up to 58 ％ by mass of cement. A reactive siliceous fine aggregate was used. The test results confirm that HVFA replacement in a cementitious system significantly helps in controlling expansion caused by ASR.

• Structural Engineering and Mechanics
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• v.54 no.6
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• pp.1201-1216
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• 2015

This paper presents the details of size independent fracture energy and bi-linear tension softening relation for nano modified high strength concrete. Nano silica in powder form has been used as partial replacement of cement by 2 wt%. Two popular methods, namely, simplified boundary effect method of Karihaloo et al. (2003) and RILEM (1985) fracture energy with P-${\delta}$ tail correction have been employed for estimation of size independent fracture energy for nano modified high strength concrete (compressive strength ranges from 55 MPa to 72 MPa). It is found that both the methods gave nearly same values, which is an additional evidence that either of them can be employed for determination of size independent fracture energy. Bi-linear tension softening relation corresponding to their size independent fracture energy has been constructed in an inverse manner based on the concept of non-linear hinge from the load-crack mouth opening plots of notched three-point bend beams.

• Bulletin of the Korean Chemical Society
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• v.34 no.12
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• pp.3805-3810
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• 2013

The surface modification of silica particles (SPs) was systemically conducted by the treatment of 0.1-10 wt % phenylsilanetriol (PST) on the basis of SPs used through two step processes: 1) the PST coating of SPs via evaporation under reduced pressure and 2) their thermal condensation leading to Si-O-Si bond formation via heating at $130^{\circ}C$. The evaluation of the modified SPs was conducted by the simple floating test on water and the measurement of the contact angle (CA) of water droplet on the 2-dimensional layer of modified SPs on slide glass. When PST was used about 2 wt % or above on the basis of SPs (about average size: 50 nm) used, the modified SPs were fully floated on the water and all dispersed into upper organic solvent layer after a shaking with the mixture of the water and benzene, indicating that the modified SPs have hydrophobic properties. The modified SPs were characterized by $^{29}Si$ MAS NMR and physicochemical properties including SEM, TEM, BET, adsorption/desorption isotherms, etc. were measured and compared each other in details. This research demonstrates that the organosilanetriol is a good modifier applicable for the surface modification of inorganic oxide particles using a low amount of modifier on the basis of oxide particles used.

• Applied Chemistry for Engineering
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• v.8 no.5
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• pp.830-836
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• 1997

The surface modification of iron oxide particle produced from steel-pickled acid by sodium-contained materials was studied. The molar ratio of $SiO_2$ to $Na_2O$ of sodium silicate was 1, 2, 3.5, respectively. The dispersion stability of iron oxide suspension as functions of amount of silica and pH was evaluated by surface charge and sedimentation velocity of iron oxide particle. Then the amount of sodium silicate was determined to provide a dispersion stability of iron oxide particle above pH 7. Finally, the surface modification of iron oxide particle with sodium silicate as silica-contained materials was done by wet ball milling. In the results of study, the dispersion stability of silica modified iron oxide particle was largely depended on amount of silica and pH together. The untreated iron oxide was unstable at pH 8, i.e. isoelectric point, but, the surface modified iron oxide particle with 0.8wt% silica was stable above pH 5. The dispersion stability was enhanced with 0.2wt% of anionic polyelectrolyte.

• Transactions on Electrical and Electronic Materials
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• v.7 no.4
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• pp.167-172
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• 2006

Submicron colloidal silica coated with ceria were prepared by mixing of silica and nano ceria particles and modified by hydrothermal reaction. The polishing efficiency of the ceria coated silica slurry was tested over oxide film on silicon wafer. By changing the polishing pressure in the range of $140{\sim}420g/cm^2$ with the ceria coated silica slurries in $100{\sim}300nm$, rates, WIWNU and friction force were measured. The removal rate was in the order of 200, 100, and 300 nm size silica coated with ceria. It was known that the smaller particle size gives the higher removal rate with higher contact area in Cu slurry. In the case of oxide film, the indentation volume as well as contact area gives effect on the removal rate depending on the size of abrasives. The indentation volume increase with the size of abrasive particles, which results to higher removal rate. The highest removal rate in 200 nm silica core coated with ceria is discussed as proper combination of indentation and contact area effect.

• Journal of the Korean Ceramic Society
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• v.45 no.1
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• pp.48-53
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• 2008

In order to reduce signal delay in ULSI, an intermetal material of low dielectric constant is required. Ordered mesoporous silica film is proper to intermetal dielectric due to its low dielectric constant and superior mechanical properties. The ordered mesoporous silica film prepared by TEOS (tetraethoxysilane) / MTES (methyltriethoxysilane) mixed silica precursor and Brij-76 surfactant was surface-modified by HMDS (hexamethyldisilazane) treatment to reduce its dielectric constant. HMDS can substitute $-Si(CH_3)_3$ groups for -OH groups on the surface of silica wall. In order to modify interior silica wall, HMDS was treated by two different processes except the conventional spin coating. One process is that film is dipped and stirred in HMDS/n-hexane solution, and the other process is that film is exposed to evaporated HMDS. Through the investigation with different HMDS treatment, it was concluded that surface modification in evaporated HMDS was more effective to modify interior silica wall of nano-sized pores.