• Transactions of the Korean Society of Mechanical Engineers A
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• v.38 no.10
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• pp.1117-1123
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• 2014

This study sintered $Si_3N_4$ with different amounts of $SiO_2$ nano-colloid. The surface of a mirror-polished specimen was coated with $SiO_2$ nano-colloid, and cracks were healed when the specimen was treated at a temperature of 1273 K for 1 h in air. Wear specimen experiments were conducted after heat treatments for 10 min at 1073, 1273, and 1573 K. The heat-treated surface that was coated with the $SiO_2$ nano-colloid was slightly rougher than the noncoated surface. The oxidation state of the surface according to the heat treatment temperature showed no correlation with the surface roughness. Moreover, the friction coefficient, wear loss, and bending strength were not related to the surface roughness. $Si_3N_4$ exhibited an abrasive wear behavior when SKD11 was used as an opponent material. The friction coefficient was proportional to the wear loss, and the bending strength was inversely proportional to the friction coefficient and wear loss. The friction coefficient and wear loss increased with increasing amounts of the $SiO_2$ nanocolloid. In addition, the friction coefficient was slightly increased by increasing the heat treatment temperature.

• Journal of Power System Engineering
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• v.19 no.1
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• pp.45-49
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• 2015

This study focuses on the crack-healing behavior and bending strength of SiC ceramics with sintering additives of $SiO_2$colloid. Optimized crack-healing condition was found to be 1hr at an atmosphere of 1373 K. The maximum crack size that can be healed at the optimized condition was a semi-elliptical surface crack of $450{\mu}m$ in diameter. After heat treatment at the optimum temperature in air, the crack morphology almost entirely disappeared and the strength recovered to the value of the smooth specimens at room temperature for the investigated crack sizes up to $450{\mu}m$. The crack with width $1.4{\mu}m$ can be completely heal the surface crack.

• Advances in nano research
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• v.1 no.3
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• pp.159-169
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• 2013

A preparation method for gadolinium compound (GdC) nanoparticles coated with silica ($GdC/SiO_2$) is proposed. GdC nanoparticles were prepared with a homogeneous precipitation method at $80^{\circ}C$ using $1.0{\times}10^{-3}$ M $Gd(NO_3)_3$, 0.5 M urea and $0-3.0{\times}10^{-4}$ M ethylenediarinnetetraacetic acid disodium salt dihydrate (ETDA) in water. As a result of preparation at various EDTA concentrations, GdC nanoparticles with a size as small as $40.5{\pm}6.2$ nm, which were colloidally stable, were prepared at an EDTA concentration of $2.0{\times}10^{-4}$ M. Silica-coating of the GdC nanoparticles was performed by a St$\ddot{o}$ber method at $35^{\circ}C$ using $1.0-10.0{\times}10^{-3}$ M tetraethylorthosilicate (TEOS), 11 M $H_2O$ and $1.5{\times}10^{-3}$ M NaOH in ethanol in the presence of $1.0{\times}10^{-3}$ M GdC nanoparticles. Performance of preparation at various TEOS concentrations resulted in production of $GdC/SiO_2$ particles with an average size of $106.1{\pm}11.2$ nm at a TEOS concentration of $5.0{\times}10^{-3}$ M. The gadolinium (Gd) concentration of $1.0{\times}10^{-3}$ M in the as-prepared $GdC/SiO_2$ particle colloid solution was increased up to a Gd concentration of 0.2 M by concentrating with centrifugation. The core-shell structure of $GdC/SiO_2$ particles was undamaged, and the colloid solution was still colloidally stable, even after the concentrating process. The concentrated $GdC/SiO_2$ colloid solution showed images of X-ray and magnetic resonance with contrast as high as commercial Gd complex contrast agents.

• Journal of the Korean Ceramic Society
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• v.46 no.5
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• pp.472-477
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• 2009

Monodisperse spherical $SiO_2$ particles of various sizes ($\sim$350 nm and $\sim$800 nm) and size distributions were synthesized from TEOS and MTMS. The particle size and size distribution were controlled by changing the volume ratio of water to ethanol and the reaction temperature. Narrow-sized $SiO_2$ particles with $\sim$3% size distribution were obtained. Self-assembly of the $SiO_2$ particles for photonic crystals were performed by the solvent evaporation method. The number of ordered $SiO_2$ layers can be controlled by changing the amount of the dispersed $SiO_2$ volume fraction in the solvent.

• Journal of the Korean Institute of Telematics and Electronics A
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• v.29A no.4
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• pp.22-27
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• 1992

The cyclic voltammogram characteristics at the magnetized SrO${\cdot}6Fe_{2}O_{3}$ ceramics/(($10^{-3}$M KCI + p-Si powders) and /(($10^{-4}$M CsNO$_3$ + n-GaAs powders) suspension interfaces have been studied using the microelectrophoresis and the cyclic voltammetric method. The negatively charged ions are specifically absorbed on the virgin and the magnetized SrO${\cdot}6Fe_{2}O_{3}$ ceramics surfaces. The zeta potentials of the p-Si and n-GaAs colloidal semiconductors are + 41mV and -44.8mV, respectively. The magnetization effects act as potential barriers at the magnetized SrO${\cdot}6Fe_{2}O_{3}$ interfaces. The positivelely charged p-Si and the negatively charged n-GaAs colloidal semiconductors act as potential barriers at the virgin SrO${\cdot}6Fe_{2}O_{3}$ interfaces. On the other hand, the charged p-Si and n-GaAs colloidal semiconductors act as potential barrier scavengers at the magnetized SrO${\cdot}6Fe_{2}O_{3}$ interfaces. The magnetization effects and the charged colloidal semiconductor effects are irreversible and interdependent.

• Journal of the Korean Ceramic Society
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• v.41 no.4
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• pp.297-301
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• 2004

Nano-sized mullite (3Al$_2$O$_3$$.$2SiO$_2$) colloids were prepared by use of the spray combustion method. For combustion reaction, Al(NO$_3$)$_3$$.$9$H_2O$, and CH$_{6}$N$_4$O were used as an oxidizer and a fuel respectively, and then colloidal silica was also added as 2SiO$_2$source for mullite. The temperature of the reaction chamber was kept at 80$0^{\circ}C$ to initiate the ignition of droplets of the mixed precursors. For preventing droplet coagulation, the droplet number concentration was reduced using the metal screen filter, and the residence time of aerosol was kept at 2.5 seconds for laminar flow. The synthesized colloidal particles had an uniform spherical shape with 130 nanometer size and the crystalline phase showed the mullite with stoichiometry in the observations of XRD and TEM.

• Journal of Power System Engineering
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• v.17 no.4
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• pp.94-102
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• 2013

Manufactured $SiC_f/SiC$ composites by NITE method was investigated fracture characteristics according to the size of the surface crack. Coated surface crack with a $SiO_2$ colloid in several ways was evaluating the possibility of healing. The strength of CCS and UCS is 313 and 230MPa, respectively and it is about 1/3 of the SPS. Bending strength of $SiC_f/SiC$ composites has no effect with the pre-crack size to the critical crack size. $SiC_f/SiC$ composites can not generate large amount of $SiO_2$ oxides to the bottom of crack, and is only generated randomly on surfaces, and can not contribute to the recovery of bending strength.

• Corrosion Science and Technology
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• v.7 no.3
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• pp.179-181
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• 2008

With nano-$SiO_2$ and sulphate acid, a kind of colloid electrolyte is synthesized by sol-gel method. It is placed outside the reference electrode as a layer of gel electrolyte so as to decrease the leaching of $Cu^{2+}$ and increase the life of the reference electrode. The performance of the gel electrode in simulating soil solution is measured as follows: the potential of the electrodes ranging from 60 mV to 80 mV (vs. SCE) with potential variation no more than $\pm10mV$, enough resistance to polarization. The $Cu^{2+}$ effusion rate of the reference electrode without gel electrolyte is 3 times that with colloid electrolyte, which means that gel electrolyte can extend the life of the reference electrode significantly.

• Journal of the Korea Organic Resources Recycling Association
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• v.30 no.3
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• pp.5-12
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• 2022

This study suggests the effective recycling method of sludge waste from various industrial fields to synthesize uniform colloidal silica nanoparticles. In detail, polymers are removed from the sludge waste to attain sludge-extracted silica (s-SiO₂) micron-sized particles, and ammonia assisted sonication is applied to s-SiO₂, which has effectively extracted the silanol precursor. The nano-sized silica (n-SiO₂) particles are successfully synthesized by a typical sol-gel method using silanol precursor. Also, the yield amounts of n-SiO₂ are determined by the function of s-SiO₂ etching time. Finally, n-SiO₂-based slurry is synthesized for the practical CMP application. As a result, rough-surfaced semiconductor chip is successfully polished by the n-SiO₂-based slurry to exhibit the mirror-like clean surface. In this regard, sludge wastes are successfully prepared as valuable semicondutor grade materials.

• Bulletin of the Korean Chemical Society
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• v.35 no.1
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• pp.173-176
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• 2014

The hollow $SiO_2$ spheres with uniform size were synthesized by a modified Stober method under the control of polyelectrolytes (PSS and PAA) as templates. This synthetic route includes the formation of spherical colloid micelle in ethanol solution, hydrolysis of TEOS under control of ammonia, and the removal of polyelectrolyte by washing or calcination. Hollow silica spheres with controllable core diameters between 100 and 270 nm and wall thickness between 15 and 50 nm have been synthesized. The influence of template solution concentration and solvent and dispersant on the formation of silica hollow spheres is studied and reported in detail.