• Journal of the Korean Ceramic Society
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• v.15 no.1
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• pp.16-20
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• 1978

The solubility of tobermorite was measured, and it was compaired with the resultswhich calculated by thermodynamic data. As the result, 1) The type of silisic acid species in liquid phase were the both type of $H_3SiO_4$-, $H_4SiO_4$. 2) The solubility product of tobermorite represented the maximum value at 18$0^{\circ}C$.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.32 no.11
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• pp.1003-1009
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• 2008

In this study, liquid phase sintered SiC (LPS-SiC) materials were made by hot pressing method. The particle size of nano-SiC powder was 30nm. Alumina ($Al_2O_3$), yttria ($Y_2O_3$) and silica ($SiO_2$) were used for sintering additives. To investigate effects of $SiO_2$, ratios of $SiO_2$ contents were changed by five kinds. Materials have been sintered for 1 hour at $1760^{\circ}C$, $1780^{\circ}C$ and $1800^{\circ}C$ under the pressure of 20MPa. The system of sintering additives which affects a property of sintering as well as the influence depending on compositions of sintering additives were investigated by measurement of density, mechanical properties such as flexural strength, vickers hardness and sliding wear resistance were investigated to make sure of the optimum condition which is about matrix of $SiC_f$/SiC composites. The abrasion test condition apply to load of 20N at 100RPM for 20min. Sintered density, flexural strength of fabricated LPS-SiC increased with increasing the sintering temperature. And in case of LPS-SiC with low $SiO_2$, sliding wear resistance has very excellent. Monolithic SiC $1800^{\circ}C$ sintering temperatures and 3wt% have excellent wear resistance.

• Journal of Convergence for Information Technology
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• v.7 no.5
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• pp.123-128
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• 2017

Nanostructured materials have received attention due to their unique electronic, optical, optoelectrical, and magnetic properties as a results of their large surface-to-volume ratio and quantum confinement effects. Thermal chemical vapor deposition process has attracted much attention due to the synthesis capability of various structured nanomaterials during the growth of nanostructures. In this study, silicon oxide nanowires were grown on Si\$SiO_2$(300 nm)\Pt(5~40 nm) substrates by two-zone thermal chemical vapor deposition with the source material $TiO_2$ powder via vapor-liquid-solid process. The morphology and crystallographic properties of the grown silicon oxide nanowires were characterized by field-emission scanning electron microscope and transmission electron microscope. As results of analysis, the morphology, diameter and length, of the grown silicon oxide nanowires are depend on the thickness of the catalyst films. The grown silicon oxide nanowires exhibit amorphous phase.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2004.11a
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• pp.266-270
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• 2004

SiC materials have been extensively studied for high temperature components in advanced energy system and advanced gas turbine because it has excellent high temperature strength, low coefficient of thermal expansion, good resistance to oxidation and good thermal and chemical stability etc. However, the brittle characteristics of SiC such as low fracture toughness and low strain-to fracture still impose a severe limitation on practical applications of SiC materials. For these reasons, SiC/SiC composites can be considered as a promising for various structural materials, because of their good fracture toughness compared with monolithic SiC ceramics. But, high temperature and pressure lead to the degradation of the reinforcing jiber during the hot pressing. Therefore, reduction of sintering temperature and pressure is key requirements for the fabrication of SiC/SiC composites by hot pressing method. In the present work, monolithic Liquid Phase Sintered SiC (LPS-SiC) was fabricated by hot pressing method in Ar atmosphere at $1800^{\circ}C$ under 20MPa using $Al_2O_3,\;Y_2O_3\;and\;SiO_2$ as sintering additives in order to low sintering temperature and sintering pressure. The starting powder was high purity $\beta-SiC$ nano-powder with all average particle size of 30mm. The characterization of LPS-SiC was investigated by means of SEM and three point bending test. Base on the composition of sintering additives-, microstructure- and mechanical property correlation, tire compositions of sintering additives are discussed.

• Proceedings of the KIEE Conference
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• 2004.11a
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• pp.191-193
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• 2004

The composites were fabricated, respectively, using 61vol.% SiC-39vol.% $TiB_2$ and using 61vol.% SiC-39vol.% $ZrB_2$ powders with the liquid forming additives of 12wt% $Al_2O_3+Y_2O_3$ by hot pressing annealing at $1650^{\circ}C$ for 4 hours. Reactions between SiC and transition metal $TiB_2$, $ZrB_2$ were not observed in this microstructure. The result of phase analysis of composites by XRD revealed SiC(6H, 3C), $TiB_2$, $ZrB_2$ and $YAG(Al_5Y_3O_{12})$ crystal phase on the SiC-$TiB_2$, and SiC-$ZrB_2$ composites. The ${\beta}\;{\alpha}$-SiC phase transformation was occurred on the $SiC-TiB_2$, $SiC-ZrB_2$ composites. The relative density, the flexural strength and Young's modulus showed respectively value of 98.57%, 226.06Mpa and $86.37{\times}10^3Mpa$ in SiC-$ZrB_2$ composites.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.49 no.9
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• pp.510-515
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• 2000

The mechanical and electrical properties of the hot-pressed and annealed $\beta-SiC-TiB_2$ electroconductive ceramic composites were investigated as a function of the liquid forming additives of Al_2O_3+Y_2O_34. The result of phase analysis of composites by XRD revealed $\alpha-SIC(6H)\;TiB_2,\; and YAG(Al5Y3O12) crystal phase. The relative density and the mechanical properties of composites were increased with increasing $Al_2O_3+Y_2O_34 contents because YAG of reaction between $Al_2O_3\; and\; Y_2O_3$ was increased. The Flexural strength showed the highest value of 432.5MPa for composites added with 12wt% $Al_2O_3+Y_2O_34 additives at room temperature. Owing to crack deflection crack bridging phase transition and TAG of fracture toughness mechanism the fracture toughness showed 7.1MPa.m1/2 for composites added with 12wt% $Al_2O_3+Y_2O_34 additives at room temperature. The electrical resistivity and the resistance temperature coefficient showed the lowest of $6.0\times10-4\Omega.cm\; and\; 3.1\times10-3/^{\circ}C4 respectively for composite added with 12wt% \Omega additives at room temperature. The electrical resistivity of the composites was all positive temperature coefficient resistance (PTCR) in the temperature range of $25^{\circ}C\; to\; 700^{\circ}C$.

• Nuclear Engineering and Technology
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• v.56 no.3
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• pp.812-818
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• 2024

The volume and toxicity of radioactive waste can be decreased by separating the components of high-level liquid waste according to their properties. An impregnated silica-based adsorbent was prepared in this study by combining N,N,N',N',N",N"-hexa-n-octylnitrilotriacetamide (HONTA) extractant, N',N'-di-n-hexyl-thiodiglycolamide (Crea) extractant, and macroporous silica polymer composite particles (SiO₂-P). The performance of platinum-group metals adsorption and separation on prepared (HONTA + Crea)/SiO₂-P adsorbent was then assessed together with that of co-existing metal ions by batch-adsorption and chromatographic separation studies. From the batch-adsorption experiment results, (HONTA + Crea)/SiO₂-P adsorbent showed high adsorption performance of Pd(II) owing to an affinity between Pd(II) and Crea extractant based on the Hard and Soft Acids and Bases theory. Additionally, significant adsorption performance was observed toward Zr(IV) and Mo(VI). Compared with studies using the Crea extractant, the high adsorption performance of Zr(IV) and Mo(VI) is attributed to the HONTA extractant. As revealed from the chromatographic experiment results, most of Pd(II) was recovered from the feed solution using 0.2 M thiourea in 0.1 M HNO₃. Additionally, the possibility of recovery of Zr(IV), Mo(VI), and Re(VII) was observed using the (HONTA + Crea)/SiO₂-P adsorbent.

• Proceedings of the KSME Conference
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• 2000.11b
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• pp.174-179
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• 2000

Ultrafine particles have been used widely in many high technology industrial areas. The spherical nonagglomerated and uniform nanometer-size $SiO_2$ particles are synthesized by the direct injection of TEOS(Tetraethyorthosilicate) using electro-hydrodynamic spray ins method. Electro-hydrodynamic spray can generate in the range of submicron-size TEOS particles with high electric charge by applying a high electric field between the liquid injection nozzle and the reaction tube. This TEOS particles are thermally decomposed or oxidized to produce nanometresized $SiO_2$ particles in the reaction tube. Spherical, nonagglomerated and ultrafine particle generated and examined at furnaced temperature, $800^{\circ}C$ and TEOS flowrate of 0.49 or $1.00cm^3/hr$ using SEM and SMPS. As the total gas flowrate changes from 1.51pm to 5.01pm, the mean diameter of $SiO_2$ particle decreases from 120 nm to 68nm.

• The Korean Journal of Ceramics
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• v.5 no.3
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• pp.255-259
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• 1999

The effects of $SiO_2$ and MnO addition on the sinterability and the electrical properties of 0.4mol% Nb-doped SrTiO3 varistor were investigated. The $SiO_2$ content was fixed at 0.3mol% and the MnO content varied from 0 to 1.0mol%. With 0.3 mol% $SiO_2$ and 0.3 mol% MnO addition, optimum density was obtained by sintering at $1200^{\circ}C$ without excess liquid phase. Impedance spectroscopy was performed on the sintered specimens with 0.3 mol% $SiO_2$ and various MnO contents. It was found that the resistivities of grains was increased with increasing MnO content. The dielectric constant was measured to be above 50000 in the specimen with 0.3~1.0mol% Mn content. The non-linear coefficient increased substantially with MnO addition, and it varied from 1 to 9 depending on the MnO content.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.50 no.12
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• pp.593-598
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• 2001

Transient liquid phase processing was investigated to decrease processing temperatures while maintaining useful piezoelectric properties in the lead zirconate titanate (PZT) system. Niobium oxide$(Nb_2O_5)$ modified crystalline PZT (PZTN) powder was combined with lead silicate $(PS; PbO-SiO_2)$ glass powder and crystalline titania, zirconia, and niobia. Firing above the melting temperature of the lead silicate $(PS; Tm \risingdotseq\; 714^{\circk}C)$ resulted in liquid phase densification of the PZTN followed by dissolution of the titania, zirconia, and niobia into the liquid phase, and crystallization of additional PZTN. The addition of crystalline titania, zirconia, and niobia to react with the lead oxide from the lead silicate phase resulted in an increase in the dielectric and Piezoelectric properties.