• Journal of Powder Materials
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• v.24 no.6
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• pp.437-443
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• 2017

SiC-based composite materials with light weight, high durability, and high-temperature stability have been actively studied for use in aerospace and defense applications. Moreover, environmental barrier coating (EBC) technologies using oxide-based ceramic materials have been studied to prevent chemical deterioration at a high temperature of $1300^{\circ}C$ or higher. In this study, an ytterbium silicate material, which has recently been actively studied as an environmental barrier coating because of its high-temperature chemical stability, is fabricated on a sintered SiC substrate. $Yb_2O_3$ and $SiO_2$ are used as the raw starting materials to form ytterbium disilicate ($Yb_2Si_2O_7$). Suspension plasma spraying is applied as the coating method. The effect of the mixing method on the particle size and distribution, which affect the coating formation behavior, is investigated using a scanning electron microscope (SEM), an energy dispersive spectrometer (EDS), and X-ray diffraction (XRD) analysis. It is found that the originally designed compounds are not effectively formed because of the refinement and vaporization of the raw material particles, i.e., $SiO_2$, and the formation of a porous coating structure. By changing the coating parameters such as the deposition distance, it is found that a denser coating structure can be formed at a closer deposition distance.

• Journal of the Microelectronics and Packaging Society
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• v.9 no.2
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• pp.19-25
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• 2002

Glass composed of $Li_2$O.MgO. $MgF_2$.$SiO_2$.$B_2O_3$ for the fabrication of green sheet was prepared by melting process, and glass ceramics was prepared by the process of nucleation and grystal growth for the glass of $Li_2$O.MgO. $MgF_2$.$SiO_2$.$B_2O_3$ system with Lithium fluorhectorite and Lithium boron fluorphlogopite crystal phase. Powderization of the glass ceramics was carried out by water swelling. The average particle size at this point was 2.574 $\mu\textrm{m}$. Slurry was prepared for green sheet using high viscous sol fabricated by water swelling, which shows cleavage phenomenon in prepared glass ceramics. The optimum ratio of powder to water for the tape casting was 18:100, and its viscosity was 11,000~14,000 cps.

• Journal of the Korean Ceramic Society
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• v.26 no.5
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• pp.705-711
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• 1989

The glass-ceramics was prepared with the scoria(CaO-MgO-Al2O3-SiO2 system) of the locally occurring volcanic ejecta containing 10-13w/o of (FeO＋Fe2O3) by melting at 140$0^{\circ}C$ for 4 hours and thermally treated for nucleation and crystallization. The sucrose was added to the scoria to adjust the Fe2+/Fe3+ ratio during the melting process. The addition of 1-2w/o of sucrose showed the glass-ceramics body with the finest particle developed and dispersed over the entire range. It is concluded that the impurity content of iron oxide and titanium oxide play the most-influencial effect on the crystallization. When 1-2w/o of sucrose was added to the scoria, the value of Fe2+/Fe3+ ratio was 0.93-1.32 and showed the best result of crystallization. The nucleation temperature and time were calculated by the measurements of exothermic peak temperatures of DTA for quenched and thermally treated glasses. The nucleation temperature of scoria glass without the addition of sucrose was estimated as 75$0^{\circ}C$, but the addition of sucrose by 2w/o showed the nucleation temperature 6$25^{\circ}C$. The nucleation time was calculated with the same DTA curves. The nucleation times estimated were about 150min. for both of glasses without and with sucrose added. Finally, the activation energies for crystallization were calculated with the DTA data. The calculated activation energies were 143 Kcal/mole for the glass without addition of sucrose and 90Kcal/mole, 87Kcal/mole, 85Kcal/mole and 71Kcal/mole for the glasses of 1w/o, 2w/o, 3w/o and 4w/o addition respectively.

• Journal of the Korean Institute of Gas
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• v.26 no.2
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• pp.1-8
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• 2022

The purpose of this study is to prepare GPTMS((3-Glycidoxypropyl) trimethoxysilane)-SiO₂ nanofluid and analyze the effect of nanofluid injection on carbonate reservoirs. Structural analysis of silica nanoparticles modified by GPTMS was investigated by FTIR(Fourier transform infrared spectroscopy). C-H stretching vibrations at 2,950 cm^-1 indicating the silica surface modification with GPTMS were observed when the silane feed was over 0.5 mmol/g. Also, the coreflooding test by nanofluid injection on the aged limestone and dolomite plug samples was carried out with different particle concentration and flow rate. The incremental oil recovery was up to 18.9%, and contact angle and permeability of carbonate samples were changed by the effect of nanoparticle adsorption on pore which caused wettability alteration and pore size change. Therefore, the prepared nanofluid will be utilized as an injection fluid for enhancing oil recovery and modifying fluid flow properties such as change of rock wettability and permeability in carbonate reservoirs.

• Composites Research
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• v.20 no.4
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• pp.9-17
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• 2007

Powder metallurgy has been employed for the development of SiC particle reinforced aluminum metal matrix composites by means of hot isotropic pressing and vacuum hot pressing. A material model based on micro-mechanical approach then has been presented for the processes. Densification occurs by the inelastic flow of matrix materials during the consolidation, and consequently it depends on many process conditions such as applied pressure, temperature and volume fraction of reinforcement. The model is implemented into finite element software so that the process simulation can be performed enabling the predicted relative density to be compared with experimental data. In order to determine the performance of finished products, further tensile test has been conducted using the developed specimens. The effect of internal void of the materials on mechanical properties therefore can be investigated.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.22 no.4
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• pp.200-206
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• 2012

The artificial aggregate composing of coal bottom ash and waste catalyst slag (7 : 3, wt%) were fabricated using direct sintering method and, the bloating properties of aggregates were investigated as a function of raw material particle size and sintering temperature. Most of the artificial aggregates sintered at over $1150^{\circ}C$ showed the bloating phenomenon regardless of particle size of the raw materials. Consequently, the specific gravity of the aggregates was drastically decreased to below 1.4. The aggregates containing waste catalyst slag of $90{\mu}m$ under among the W-series specimens, however, did not show the noticeable bloating phenomenon. For the aggregates sintered at lower temperature as $1050{\sim}1150^{\circ}C$, the specific gravity increased with particle size of raw materials. Also, the water absorption of all aggregates decreased with the sintering temperature. The aggregates fabricated in this study met the lightweight aggregate standard showing the specific gravity 1.7~1.4 and water absorption 8~19 % and, therefore, can be applicable for the various fields.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.11 no.6
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• pp.1943-1948
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• 2010

Two kind of $\beta$-SiC powders of different particle sizes (${\sim}1.7\;{\mu}m$ and ${\sim}30\;nm$), containing 7 wt% $Y_2O_3$, 2 wt% $Al_2O_3$ and 1 wt% MgO as sintering additives, were prepared by hot pressing at $1800^{\circ}C$ for 1 h under applied pressures, and then were hot-forged at $1950^{\circ}C$ for 6 h under 40 MPa in argon. All the hot-pressed specimens consisted of equiaxed grains and were developed grain growth after hot-forging. The smaller starting powder was developed the finer microstructure. The microstructures on the surfaces parallel and perpendicular to the pressing direction of the hot-forged SiC were similar to each other, and no texture development was observed because of the lack of massive $\beta$ to $\sigma$ phase transformation of SiC. The fracture toughness (${\sim}3.9\;MPa{\cdot}m^{1/2}$), hardness (~ 25.2 GPa) and flexural strength (480 MPa) of hot-forged SiC using larger starting powder were higher than those of the other.

• Journal of the Korean Ceramic Society
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• v.31 no.9
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• pp.1076-1086
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• 1994

This study covers synthetic effect of the various hydrothermal treatments on formation of artificially made kaolinite mineral. The hydrothermal treatment includes the temperature treatment with time duration, addition of seeds, particle size of the starting material used, pH variation and the different types of organic acids. A colloidal silica and alumina sol which are commercially available are used for this study. A colloidal silica and alumina sol are mixed by the atomic ratio of Al/Si = 1, based on the theoretical kaolinite composition and calcined at $600^{\circ}C$ for 8 hours duration. It was found that the kaolinitic clay mineral was well developed; thereby, the different patterns of crystalline mineral are appeared. Spherical type as a crystal form was distinctively formed at the temperature of 20$0^{\circ}C$ to 25$0^{\circ}C$ with short duration time, while platy type as a crystal was highly yielded at 300~35$0^{\circ}C$. Moreover, by adding more than 20 wt% of seed as the natural kaolinitic clay to the starting material is widely distributed and developed when 2 ${\mu}{\textrm}{m}$ or less particle size of the starting material is used; also, when they are heat-treated at the temperature of 25$0^{\circ}C$ with 5 hours duration. With respect of the effect of pH variation on formation of the synthetic kaolinite minerals, the crystalline minerals are highly yielded at less than pH 2 and gradually diminished at more than pH9. Regarding to the effect of different acids on development of the kaolinite mineral, the organic acids with high chelating capacity produces good formation of crystalline minerals; whereas, amine radical-(NH2) is not an effective agent to generate the crystalline minerals.

• Korean Journal of Materials Research
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• v.11 no.3
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• pp.227-235
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• 2001

In this work, Zn$_2$SiO$_4$:Mn phosphors were prepared by solid state reaction. The effect of sintering/reduction temperature, flow rate of H$_2$-5%/$N_2$-95% mix gas, and ball milling conditions have been investigated on the sake of PDP(Plasma Display Panel) application. The characteristics such as particle morphology and photoluminescence of prepared phosphors were compared to those of commercial Zn$_2$SiO$_4$:Mn Phosphors. It was found that the Phosphor synthesized at 130$0^{\circ}C$ with 0.08 Mn concentration had a maximum brightness, This brightness was increased more 20% by reduction treatment under 100me/min flow rate of 5%H$_2$-95%$N_2$ mixed gas. The size of particles decreased under 3$\mu\textrm{m}$ after ball milling. Especially, higher luminescence was obtained in our Zn$_2$SiO$_4$:Mn phosphors than commercial Zn$_2$SiO$_4$:Mn phosphors, so that they are able to be applied for PDP.

• Journal of the Korea Institute of Military Science and Technology
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• v.20 no.6
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• pp.752-757
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• 2017

Analysis has been performed for the penetration of a long-rod into MMC/Ceramic layered armour system with several shot test and a series of simulations. Two types of MMC plate have been fabricated by a liquid pressing method; A356/45%vol.%SiCp with a uniform distribution of SiC particle and Al7075/45%vol.B4Cp with B4C particle. The mechanical properties were measured with the high-speed split Hopkins bar test, hardness test and compression test. The popular Simplified Johnson-Cook model was adopted to represent the material characteristics for FEM simulations. The performance of the MMC applied armour system has been made by comparing with the semi-infinite mild steel target using the depth of penetration(DOP). The results show that placing ceramic front layer provides a certain gain in protection, and that placing another ductile front layer provides a further gain. The application of MMC is found to be attractive.