• The Transactions of The Korean Institute of Electrical Engineers
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• v.57 no.11
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• pp.2015-2022
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• 2008

The effect of content of $Al_2O_3+Y_2O_3$ sintering additives on the densification behavior, mechanical and electrical properties of the pressureless-sintered $SiC-ZrB_2$ electroconductive ceramic composites was investigated. The $SiC-ZrB_2$ electroconductive ceramic composites were pressurless-sintered for 2 hours at 1,700[$^{\circ}C$] temperatures with an addition of $Al_2O_3+Y_2O_3$(6 : 4 mixture of $Al_2O_3$ and $Y_2O_3$) as a sintering aid in the range of $8\;{\sim}\;20$[wt%]. Phase analysis of $SiC-ZrB_2$ composites by XRD revealed mostly of $\alpha$-SiC(6H), $ZrB_2$ and In Situ YAG($Al_5Y_3O_{12}$). The relative density, flexural strength, Young's modulus and vicker's hardness showed the highest value of 89.02[%], 81.58[MPa], 31.44[GPa] and 1.34[GPa] for $SiC-ZrB_2$ composites added with 16[wt%] $Al_2O_3+Y_2O_3$ additives at room temperature respectively. Abnormal grain growth takes place during phase transformation from $\beta$-SiC into $\alpha$-SiC was correlated with In Situ YAG phase by reaction between $Al_2O_3$ and $Y_2O_3$ additive during sintering. The electrical resistivity showed the lowest value of $3.l4{\times}10^{-2}{\Omega}{\cdot}cm$ for $SiC-ZrB_2$ composite added with 16[wt%] $Al_2O_3+Y_2O_3$ additives at 700[$^{\circ}C$]. The electrical resistivity of the $SiC-TiB_2$ and $SiC-ZrB_2$ composite was all negative temperature coefficient resistance (NTCR) in the temperature ranges from room temperature to 700[$^{\circ}C$]. Compositional design and optimization of processing parameters are key factors for controlling and improving the properties of SiC-based electroconductive ceramic composites.

• Journal of the Korean Ceramic Society
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• v.52 no.3
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• pp.215-220
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• 2015

Phase evolution, microstructure, and microwave dielectric properties of $Li_2O$ and $Al_2O_3$ doped $Zn_{1.9}Si_{1.05}O_4$, i.e., $Zn_{1.9-2x}Li_xAl_x-Si_{1.05}O_4$, ceramics (x = 0.02 ~ 0.10) were investigated. The ceramics were densified by $SiO_2$-rich liquid phase composed of the Li-Al-Si-O system, indicating that doped Li and Al contributed to the formation of the liquid. As the secondary phase, ${\beta}$-spodumene solid solution with the composition of $LiAlSi_3O_8$ was precipitated from the liquid during the cooling process. The dense ceramics were obtained for the specimens of $$x{\geq_-}0.06$$ showing the rapid densification above $1000^{\circ}C$, implying that a certain amount of liquid is necessary to densify. The specimen of x = 0.06 sintered at $1050^{\circ}C$ exhibited good microwave dielectric properties; the dielectric constant and the quality factor ($Q{\times}f_0$) were 6.4 and 11,213 GHz, respectively.

• Journal of Korean Ophthalmic Optics Society
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• v.5 no.1
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• pp.61-65
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• 2000

${\beta}$-SiC powder and ${\alpha}$-SiC powders of different particle sizes, containing 5.7wt% $Al_2O_3$ and 4.3wt% $Y_2O_3$ as sintering aids, were hot-pressed at $1780^{\circ}C$ and subsequently annealed at $1950^{\circ}C$ to initiate grain growth. All the hot-pressed and annealed materials consisted of large SiC grains and elongated SiC grains. Typical hardness and fracture toughness of materials for spectacle lens cutting were 15.6 GPa and $5.7MPa{\cdot}m^{1/2}$, respectively.

• Journal of the Korean Ceramic Society
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• v.50 no.6
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• pp.364-371
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• 2013

The sintering behavior of monolithic SiC is examined using the binary sintering additive of $Al_2O_3$-rare earth oxide ($RE_2O_3$, where RE = Sc, Nd, Dy, Ho, or Yb). Through hot pressing at 20 MPa and $1750^{\circ}C$ for 1 h in an Ar atmosphere for 52 nm fine ${\beta}$-SiC powder added with 5 wt% sintering additive, a SiC density of > 97% is achieved, which indicates the effectiveness of $Al_2O_3-RE_2O_3$ system as a sintering of additive for SiC. Based on this result, 7 wt% of $Al_2O_3-Sc_2O_3$ is tested as an additive system for the fabrication of a continuous SiC fiber-reinforced SiC-matrix composite ($SiC_f$/SiC). Electrophoretic deposition combined with the application of ultrasonic pulses is used to efficiently infiltrate the matrix phase into the voids of $Tyranno^{TM}$-SA3 fabric. After hot pressing, a composite density of > 97% is obtained, along with a maximum flexural strength of 443 MPa.

• Natural Product Sciences
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• v.20 no.3
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• pp.160-169
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• 2014

44 compounds and 9 minerals were isolated from and detected in the New Zealand deer velvet antler Cervus elaphus var. scoticus L$\ddot{o}$nnberg. The chemical structures of (1 - 26) were identified on the basis of the spectroscopic methods and comparisons with literature, respectively. The structures were identified as cholesterol (CS, 6), 7-keto-CS (7), $7{\beta}$-hydroxy-CS (8), and $7{\alpha}$-hydroxy-CS (9), and included 12 steroid $3{\beta}$-O-(palmitic/stearic/myristic acid esters; PM/SA/MS) [CS-$3{\beta}$-O-PM (1 - 1), CS-$3{\beta}$-O-SA (1 - 2), CS-$3{\beta}$-O-MR (1 - 3), 7-keto-CS-$3{\beta}$-O-PM (2 - 1), 7-keto-CS-$3{\beta}$-O-SA (2 - 2), 7-keto-CS-$3{\beta}$-O-MR (2 - 3), $7{\beta}$-hydroxy-CS-$3{\beta}$-O-SA (3 -1), $7{\beta}$-hydroxy-CS-$3{\beta}$-O-PM (3 - 2), $7{\beta}$-hydroxy-CS-$3{\beta}$-O-MR (3 - 3), $7{\alpha}$-hydroxy-CS-$3{\beta}$-O-SA (4 - 1), $7{\alpha}$-hydroxy-CS-$3{\beta}$-O-PM (4 - 2), and $7{\alpha}$-hydroxy-CS-$3{\beta}$-O-MR (4 - 3)], dinonyl phthalate (5), 8 nucleic acids analogues [uracil (10), deoxyguanosine (11), deoxyuridine (12), uridine (13), deoxyadenosine (14), adenosine (15), inosine (16), and guanosine (17)], and the 9 free amino acids [L-phenylalanine (18), L-isoleucine (19), L-leucine (20), L-tyrosine (21), L-valine (22), L-proline (23), L-threonine (24), L-alanine (25), and L-hydroxyproline (26)]. Also, there are 8 kinds of amino acids [asparagine, serine, glutamine, glycine, histidine, arginine, methionine, and lysine], 2 sialic acids [N-acetylneuraminic acid (27), ketodeoxynonulosonic acid (28)], and 9 minerals [Na > K > Ca > Mg > Fe > Zn > B > Al > Cu] were detected from the autoaminoacid analyzer and ICP spectrometer, HPAEC-PAD/HPLC-FLD, respectively. 9 kinds of oxycholesterol-$3{\beta}$-O-fatty acid ester (2 - 1, 2 - 2, 2 - 3, 3 - 1, 3 - 2, 3 - 3, 4 - 1, 4 - 2, and 4 - 3) and 3 nucleic acids (12, 14, and 15) were isolated from the velvet antler for the first time. 6 kinds of steroids (7, 8, 9, 2 - 1, 3 - 1, and 4 - 1) were examined for their anti-proliferative effects against L1210, P388D1, K562, MEG-01, KG-1, MOLT-4, A549, HepG2, MCF-7, SK-OV-3, and SW-620 cancer cell lines. They showed anti-proliferative effects with $IC_{50}$ values of 0.06, 2.16, 2.42, > 50.0, 1.66 and $8.31{\mu}M$ against L1210, while the values were 24.05, 9.44, 5.22, 0.25. 9.48 and $49.77{\mu}M$ against P388D1, respectively. The others were inactive.

• Journal of Powder Materials
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• v.11 no.2
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• pp.118-123
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• 2004

A formation of aluminum hydroxide by hydrolysis reaction in the water has been studied by using nano aluminum powder fabricated by pulsed wire evaporation(PWE) method. The hydroxide type and morphology depending on temperature and pH were examined by structural analysis. The Boehmite($Al_2O_3$.$H_2O$ or AIO(OH)) was predominantly formed in high temperature region over 4$0^{\circ}C$, while the Bayerite($Al_2O_3$.$H_2O$ or $Al(OH)_3$) below $30^{\circ}C$ of hydrolysis temperature. The Boehmite formation was preferred to the Bayerite in acidic solution in the same hydrolysis temperature. The slowly formed Bayerite phase showed facet crystalline structure, while the fast formed Boehmite was fine fiber with a large aspect ratio of several nm in diameter and several hundred nm in length, and with much larger specific surface area(SSA) than that of Bayerite. The highest SSA was about $420m^2$/g.

• Journal of the Korean Ceramic Society
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• v.32 no.8
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• pp.865-872
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• 1995

Ultra-fine $\beta$-SiC powders were fabricated by self-propagating high temperature synthesis process (SHS) using microwave oven. The flexural strength, fracture toughness, and hardness of hot pressed sample at 200$0^{\circ}C$ for 60 min using synthesized SiC powders, which had 2 wt% of Al2O3 and 2.5 wt% of B4C content, showed 438 MPa, 4.15MPa.m1/2 and 28 GPa, respectively. The highest strength, fracture toughness, and hardness of composites containing 4wt% of Al2O3, which had highest relative density of 99.9%, showed 458 MPa, 4.6MPa.m1/2 and 36.2 GPa, respectively.

• Journal of the Korean Ceramic Society
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• v.28 no.2
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• pp.130-140
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• 1991

The powders of the system Si3N4-Y2O3-AlN were prepared using Si(OC2H5)4 and YCl3.6H2O together with commercial AlN powder. $\alpha$-Si3N4 was prepared by the carbothermal reduction and nitridation of the hydrolyzed gel at 135$0^{\circ}C$ for 10h in N2 atmosphere. YCl3.6H2O was observed to be changed to Y2O3 during the reaction. $\alpha$-Sialon(X=0.2, 0.4, 0.6) ceramics were obtained by hot-pressing the Si3N4-Y2O3-AlN mixture at 178$0^{\circ}C$ for 1h under 30 MPa. The content of $\alpha$-Sialon increased with increasing metal solubility(x value) and $\alpha$-Sialon single phase was obtained at the metal solubility of 0.6. With increasing metal solubility, flexural strength, fracture toughness and thermal shock resistence were decreased, while the microhardness was increased. Large elongated $\beta$-Si3N4 grains were mainly observed at lower metal solubility. Mechanical prorerties of the sintered ceramics with X=0.2 were measured as follows : flexural strength ; 650 MPa, fracture toughness ; 3.63 MN/m3/2, hardness ; 14.7 GPa, thermal shock resistence temperature ; 58$0^{\circ}C$.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.15 no.11
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• pp.6890-6897
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• 2014

EAF reduction slag has unstable properties of expansion and destruction. Therefore, it cannot be used as a construction material. The purpose of this study was to use EAF reduction slag as a concrete admixture. EAF reduction slag contains $11CaO{\cdot}7Al_2O_3{\cdot}CaF_2$ and ${\beta}-C_2S$ (calcium aluminate compounds). To confirm the properties of EAF reduction slag as a concrete admixture, the condensation, compressive strength and activity factor due to substitution rate of EAF reduction slag were measured. Originally, EAF reduction slag was cured rapidly because of its chemical composition ($11CaO{\cdot}7Al_2O_3{\cdot}CaF_2$). On the other hand, when 8% gypsum was added, its properties of condensation and compressive strength were similar to the plain specimen. When 6% gypsum was added, the quality of the KS F 2536 standards (quality standard number 3) were met in terms of activity factor. Overall, 8% gypsum addition is the most appropriate by considering the activity factor in the long-term compressive strength.

• Journal of the Korean Ceramic Society
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• v.26 no.6
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• pp.771-782
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• 1989

Synthesis of $\beta$-Sialon powder was attempted with carbothermal reduction of porous glass. The porous glass was prepared by heat and hydrothermal treatments of 9.32 Li2O.46.5B2O3.37.2SiO2.6.98Al2O3 glass. Carbon pyrolyzed from propane gas was deposited on the porous glass, thereafter activated carbon was added as reducing agents. The synthesized $\beta$-Sialon powder was pressureless sintered at 175$0^{\circ}C$ for 1hr in N2 atmosphere. The characterization of the $\beta$-Sialon powder was performed with XRD, BET, SEM and particle size analysis. The sinterability and mechanical properties of the sintered bodies were investigated in terms of bulk density, M.O.R., fracture toughness, morphology of microstructure and etc. The reduction effect of deposited carbon was better than that of activated carbon mechanically added. The formation of SiC was precominant over that of Si2ON2 and $\beta$-Sialon owing to low partial pressure of N2 inside the pore, wehreas on the surface of porous glass the formation of Si2ON2 and $\beta$-Sialon were predominant. Thereafter, SiC reduced unreacted glass to be $\beta$-Sialon. Single phase of $\beta$-Sialon(Z=1.92) was obtained from PGA porous glass having the largest pore radius by the simultaneous reduction and nitridation method at 145$0^{\circ}C$ for 5hrs. The bulk density, M.O.R., and KIC of the sitered body are 3.17g/cc, 434.4MPa and 4.1MPa.m1/2, respectively.