• Journal of the Korean Ceramic Society
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• v.55 no.3
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• pp.285-289
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• 2018

We synthesized silicon carbide (${\beta}-SiC$) nanowires with nano-scale diameter (30 - 400 nm) and micro-scale length ($50-200{\mu}m$) on a porous body using low-grade silica and carbon black powder by carbothermal reduction at $1300-1600^{\circ}C$. The SiC nanowires were formed by vapor-liquid-solid deposition with self-evaporated Fe catalysts in low-grade silica. We investigated the characteristics of the SiC nanowires, which were grown on a porous body with Ar flowing in a vacuum furnace. Their structural, optical, and electrical properties were analyzed with X-ray diffraction (XRD), transmission electron microscopy (TEM), and selective area electron diffraction (SAED). We obtained high-quality SiC single crystalline nanowire without stacking faults that may have uses in industrial applications.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.21 no.6
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• pp.855-859
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• 2012

Silicon nanowires (SiNWs) were fabricated by a metal-assisted chemical etching of Si and the porous structure on their surfaces was controlled by changing the volume ratio of the etching solution composed of hydrofluoric acid, hydrogen peroxide, and deionized water. The concentration of hydrogen peroxide as the oxidant was varied for controlling the porosity of SiNWs. The optical properties of porous SiNWs were unique and very different from those of single-crystalline Si, as characterized by measuring their photoluminescence and Raman spectra for different porosities.

• Korean Chemical Engineering Research
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• v.54 no.4
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• pp.459-464
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• 2016

In this study, the electrochemical characteristics of porous silicon/carbon composite anode were investigated to improve the cycle stability and rate performance in lithium ion batteries. In this study, the effect of TEOS and $NH_3$ concentration, mixing speed and temperature on particle size of nano silica was investigated using $St{\ddot{o}}ber$ method. Nano porous Si/C composites were prepared by the fabrication processes including the synthesis of nano $SiO_2$, magnesiothermic reduction of nano $SiO_2$ to obtain nano porous Si by HCl etching, and carbonization of phenolic resin. Also the electrochemical performances of nano porous Si/C composites as the anode were performed by constant current charge/discharge test, cyclic voltammetry and impedance tests in the electrolyte of $LiPF_6$ dissolved inorganic solvents (EC:DMC:EMC=1:1:1vol%). It is found that the coin cell using nano porous Si/C composite has the capacity of 2,006 mAh/g and the capacity retention ratio was 55.4% after 40 cycle.

• Journal of Sensor Science and Technology
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• v.20 no.3
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• pp.168-171
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• 2011

Porous 3C-SiC(pSiC) samples with different pore diameters were prepared from poly crystalline N-type 3C-SiC by electrochemical anodization. The pSiC surface was chemically modified by the sputtering of Pd and Pt nano-particles as a hydrogen catalyst. Changes in resistance were monitored with hydrogen concentrations in the range of 110 ppm - 410 ppm. The variations of the electrical resistance in the presence of hydrogen demonstrated that Pd and Pt-deposited pSiC samples have the ability to detect hydrogen at room temperature. Regardless of the catalyst, the 25 nm pore diameter samples showed good response and recovery properties. However, the 60 nm samples showed unstable and slow response. It was found that the pore size affects the catalyst reaction and consequently, results in changes of the sensitivity to hydrogen.

• Korean Journal of Materials Research
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• v.16 no.3
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• pp.188-192
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• 2006

The microstructures and mechanical properties of continuously porous $SiC-Si_3N_4$composites fabricated by multi-pass extrusion were investigated at different Si levels added. Si-powder with different weight percentages (0%, 5%, 10%, 15%, 20%) was added to the SiC powder to make the raw mixture powders, with $6wt%Y_2O_3-2wt%Al_2O_3$ as sintering additives, carbon ($10-15{\mu}m$) as a pore-forming agent, ethylene vinyl acetate as a binder and stearic acid ($CH_3(CH_2)_{16}COOH$) as a lubricant. In the continuously porous $SiC-Si_3N_4$ composites, $Si_3N_4$ whiskers like the hairs of nostrils were frequently observed on the wall of the pores. In this study, the morphology of the $Si_3N_4$ whiskers was investigated with the silicon addition content. In the composites containing of 10 wt% Si, a large number of $Si_3N_4$ whiskers was found at the continuous pore regions. In the sample to which 15 wt% Si powder was added, maximum values of about 101 MPa bending strength and 57.5% relative density were obtained.

• Journal of Powder Materials
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• v.24 no.1
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• pp.24-28
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• 2017

Silicon alloys are considered promising anode active materials to replace Li-ion batteries by graphite powder, because they have a relatively high capacity of up to 4200 mAh/g, and are environmentally friendly and inexpensive ECO-materials. However, its poor charge/discharge properties, induced by cracking during cycles, constitute their most serious problem as anode electrode. In order to solve these problems, Si-Ge-Al alloys with porous structure are designed as anode alloy powders, to improve cycling stability. The alloys are melt-spun to obtain the rapidly solidified ribbons, and then ball-milled to make fine powders. The powders are etched using 1 M HCl solution, which gives the powders a porous structure by removing the element Al. Subsequently, in this study, the microstructures and the characteristics of the etched powders are evaluated for application as anode materials. As a result, the etched porous powder shows better electrochemical properties than as-milled Si-Ge-Al powder.

• Journal of the Korean Ceramic Society
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• v.17 no.4
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• pp.197-202
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• 1980

The oxidation mechanism of the not sintered pellets and sintered bodies of $Si_3N_4$ was investigated. in air over the temperature range of 800~130$0^{\circ}C$. The $\beta$-cristobalite was instantaneously formed and covered the particles of powder packed in the not sintered and weakly sintered porous $Si_3N_4$ bodies by molecular diffusion of oxygen through the porous Si3N4 bodies and an immediate oxidation. The diffusion of oxygen ion through the formed $\beta$-cristobalite surface layer is assumed to control the further oxidation of the $Si_3N_4$ particles of the porous $Si_3N_4$ bodies. The diffusion coefficients and activation energies of oxygen ion through the $\beta$-cristobalite layer were obtained by the use of a derived equation.

• Journal of the Korean Ceramic Society
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• v.56 no.2
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• pp.191-196
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• 2019

This study assessed the feasibility of a Ti₃AlC₂ MAX phase as an Al-source for the formation of a mullite bond in the fabrication of porous SiC tubes with high strength. The as-received Ti₃AlC₂ was partially oxidized at 1200℃ for 30 min before using to minimize the abrupt volume expansion caused by oxidation during sintering. Thermal treatment at 1100-1400℃ for 3 h in air led to the formation of Al₂O₃ by the decomposition of Ti₃AlC₂, which reacted further with oxidation-derived SiO₂ on the SiC surface to form a mullite phase. The fabricated porous SiC tubes with a relative density of 48 - 62 % exhibited mechanical strengths of 80 - 200 MPa, which were much higher than those with the Al₂O₃ filler material. The high mechanical strength of the Ti₃AlC₂-added porous SiC was explained by the rigid mullite neck formation along with the retained Ti₃AlC₂ with good mechanical properties.

• Journal of the Korean Ceramic Society
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• v.46 no.5
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• pp.520-524
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• 2009

Porous self-bonded silicon carbide (SBSC) ceramics were fabricated at temperatures ranging from 1750 to $1850^{\circ}C$ using SiC, Si, C as starting materials and Al as an optional sintering additive. The effect of Al addition on the porosity and strength of the porous SBSC ceramics were investigated as functions of sintering temperature and Si:C ratio. The porosity increased with decreasing the Si:C ratio and increasing the sintering temperature. It was possible to fabricate SBSC ceramics with porosities ranging from 37% to 44% by adjusting the Si:C ratio and the sintering temperature. Addition of Al additive promoted densification and necking between SiC grains, resulting in improved strength. Typical flexural strengths of SBSC ceramics with and without Al addition were 44 MPa and 34MPa, respectively.

• Journal of the Korean Ceramic Society
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• v.29 no.1
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• pp.35-40
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• 1992

Porous glass in the ZrO2-SiO2 system containing up to 30 mol% zirconia were prepared from the mixed solutions of Zr(O.nC3H7)4 and partially prehydrolyzed TEOS by the sol-gel method. Pore characteristics, physical properties and alkali resistance were investigated. The gels converted into the porous glass by heating at $700^{\circ}C$, it was found that the glass like skeleton was already made up in lower temperature regions. The specific surface area of the porous glass was 227 $m^2$/g, average mean pore size was about 19$\AA$ and porosity was 19.2%, pore characteristics and physical properties depended on heating temperature. Alkali resistance of the porous glass increased as the zirconia content increased, because of the appearance of Zr-enriched layer at glass surface.