• Korean Journal of Materials Research
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• v.15 no.3
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• pp.177-182
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• 2005

Large amounts of the waste SiC sludge containing small amounts of Si and organic lubricant were produced during the wire cutting process of the single silicon crystal ingots. The waste SiC sludge was purified by the washing process and the purified SiC powders were used to fabricate continuously porous $SiC-Si_3N_4$ composites using a fibrous monolithic process, in which carbon, $6wt\%\;Y_2O_3-2\;wt\%\;A1_2O_3$ and ethylene vinyl acetate were added as a pore-forming agent, sintering additives, and binder, respectively. In the burning-out process, carbon was fully removed and continuously porous $SiC-Si_3N_4$ composites were successfully fabricated. The green bodies containing SiC, Si particles and sintering additives were nitrided at $1410^{\circ}C$ in a flowing $N_2+10\%\;H_2$ gas mixture. Continuously porous composites were combined with SiC, ${\alpha}Si_3N_4,\;\beta-Si_3N_4$ and a few $\%$ of Fe phases. The pore size of the 2nd and the 3rd passed $SiC-Si_3N_4$ composites was $260\;{\mu}m$ and $35\;{\mu}m$ in diameter, respectively.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.15 no.2
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• pp.86-91
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• 2005

The layered structure of organic-inorganic perovskite hybrids, $(C_nH_{2n+1}NH_3)_2CuC1_4$ (n = 6, 8, 10, 12) have synthesized. In $(C_nH_{2n+1}NH_3)_2CuC1_4$ compounds, the long-chain protonated alkylammonium ions as tilted bilayer type are inserted into perovskite-type layers of corner sharing $CuCl_6$ octahedron. Three solid phases have been characterized in the perovskite layered compound $(C_nH_{2n+1}NH_3)_2CuC1_4$ using HT-XRD and DSC. The $(C_nH_{2n+1}NH_3)_2CuC1_4$ compounds shows solid-solid phase transitions with stepwise increasing of the layer distance. Three different structures are explained by the conformational change of the long-chain protonated alkylammonium ions.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.12 no.3
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• pp.133-137
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• 2002

$ZnWO_4$ nano-powders were successfully synthesized at low temperature by polymerized complex method using zinc acetate and tungstic acid as starting materials. The polymeric precursors were heat-treated at temperatures from 300 to $600^{\circ}C$ for 3 h. The precursors and heat-treated powders were evaluated for crystallization process, thermal decomposition, surface morphology and crystallite size. Crystallization of the $ZnWO_4$ powders were detected at $400^{\circ}C$ and entirely completed at a temperature of $600^{\circ}C$. The particles heat-treated at $400^{\circ}C$ showed primarily co-mixed morphology with spherical and silk-worm-like forms, while the particles heat-treated at $500^{\circ}C$ showed more homogeneous morphology. The average crystalline sizes were 17.62~24.71 nm showing an ordinary tendency to increase with the temperatures from 400 to $600^{\circ}C$.

• Korean Journal of Microbiology
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• v.28 no.4
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• pp.304-310
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• 1990

The conditions for protoplasts formation and regeneration of thermophilic anaerobic C. thermocellum and C. thermohydrosulfuricum were determined under the anaerobic growth conditions. The cells of C. thermocellum in initial exponential growth phase were identified to be the most suited for protoplast formation. The optimal conditions for protoplast formation were found to be at $37^{\circ}C$ for 2 hours with 0.5 mg/ml of lysozyme in TMG buffer (pH7.5). On the other hand, C. thermohydro-sulfuricum grown in the same medium but excluding glycine was optimally protoplasted at the same conditions but with 0.2 mg/ml of lysozyme. The protoplasts of both strains only subjected to lysozyme treatment of the short time were satisfactorily regenerated after 7-10 days incubation at $60^{\circ}C$ in regeneration medium containing 0.3-0.4 M sorbitol, 0.5% casamino acid, and high concentration of $CaCl_{2}$ and $MgCl_{2}$. The regeneration frequencies of the protoplasts of C. thermocellum and C. thermohydrosulfuricum were found to be very low level of $4.85{\times}10^{-3}$ and $4.23{\times}10^{-2}$, respectively. The nonregenerated L-form cells were also observed inregeneration medium together with regenerated cells.

• Nuclear Engineering and Technology
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• v.8 no.4
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• pp.203-207
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• 1976

Strain rate dependence of the flow stress of cold-worked and annealed Zircaloy-4 was studied by stress relaxation test in temperature range of 20$0^{\circ}C$ to 45$0^{\circ}C$. The In $\sigma$-ln i curves for various temperatures were straight in the eirange of 10$^{-5}$ to 10$^{-3}$ sec$^{-1}$ . From the slope of a curve strain rate sensitivity m was obtained. The m in cold-worked Zircaloy-4 had a minimum value at 30$0^{\circ}C$, while m in annealed Zircaloy-4 had two minimum values, one at 30$0^{\circ}C$ and the other at 45$0^{\circ}C$. It was found that the temperatures of the minimum m are consistent with the temperatures of strain ageing peaks. The minimum m at 30$0^{\circ}C$ is considered to be due to strain ageing owing to the pinning of glide dislocations by oxygen atoms, while the minimum m at 45$0^{\circ}C$ for annealed specimen is attributed to iron atoms.

• Journal of the Korean Ceramic Society
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• v.19 no.2
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• pp.121-126
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• 1982

This paper deals with the $Si_3N_4$-bonded SiC refractory in terms of its microstructure development during nitridation. When mixture of SiC grains and fine Si power is fired under nitrogen atmosphere, an interlocking network of $Si_3N_4$ whiskers is formed by nitridation of Si. It is found that the strength of $Si_3N_4$-bonded SiC refractory is soley due to the physical nature of this interlocking whiskers. At the initial stage of nitridation, $Si_3N_4$ whisker forms in very thin and long shape and, with further nitridation, it becomes thicker with diameters up to 0.35$\mu\textrm{m}$. It is found that the mechanical strength of $Si_3N_4$-bonded SiC refractory depends on the degree of nitridation and the development of microstructure.

• Tribology and Lubricants
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• v.12 no.3
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• pp.48-54
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• 1996

Examined in this paper, is the effect of B$_{4}$C addition on the frictional characteristics of Cu-Sn based sintered friction materials. For the specimens 1wt%, 2wt% and 4wt% of B$_{4}$C were added into the reference material. A pin-on-disk type friction tester was used to,measure the friction torque with respect to the surface temperature and sliding distance. Wear mechanism of each specimen is analyzed in the view point of the oxide film formation. The specimen containing 4wt% of B$_{4}$C showed stable friction and low wear since the oxide film was sustained up to higher surface temperature ranges.

• Journal of Microbiology
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• v.35 no.3
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• pp.188-192
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• 1997

The strain of S-47 degrading 4-chlorobenzoic acid (4CBA) was isolated from Ulsan chemical industrial complex by enrichment cultivation with 1 mM 4CBA. The strain was Gram-negative rod and grew optimally at 30.deg.C and pH 7 under aerobic condition, so that the organism was identified as a species of Pseudomonas. Pseudomonas sp. S-47 degraded 4-chlorobenzoic acid to produce a yellow-colored meta-cleavage product, which was confirmed to be 5-chloro-2-hydroxymuconic semialdehyde (5C-2HMS) by UV-visible spectrophotometry. 5C-3HMS was proved trometry. This means that Pseudomonas sp. S-47 degraded 4CBA via 4-chlorocatechol to 5C-2HMS by meta-cleavage reaction and then to 5C-2HMA by 5C-2HMS dehydrogenase.

• Korean Journal of Materials Research
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• v.22 no.5
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• pp.253-258
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• 2012

Activated magnetite ($Fe_3O_{4-{\delta}}$) was applied to reducing $CO_2$ gas emissions to avoid greenhouse effects. Wet and dry methods were developed as a $CO_2$ removal process. One of the typical dry methods is $CO_2$ decomposition using activated magnetite ($Fe_3O_{4-{\delta}}$). Generally, $Fe_3O_{4-{\delta}}$ is manufactured by reduction of $Fe_3O_4$ by $H_2$ gas. This process has an explosion risk. Therefore, a non-explosive process to make $Fe_3O_{4-{\delta}}$ was studied using $FeC_2O_4{\cdot}2H_2O$ and $N_2$. $FeSO_4{\cdot}7H_2O$ and $(NH_4)_2C_2O_4{\cdot}H_2O$ were used as starting materials. So, ${\alpha}-FeC_2O_4{\cdot}2H_2O$ was synthesized by precipitation method. During the calcination process, $FeC_2O_4{\cdot}2H_2O$ was decomposed to $Fe_3O_4$, CO, and $CO_2$. The specific surface area of the activated magnetite varied with the calcination temperature from 15.43 $m^2/g$ to 9.32 $m^2/g$. The densities of $FeC_2O_4{\cdot}2H_2O$ and $Fe_3O_4$ were 2.28 g/$cm^3$ and 5.2 g/$cm^3$, respectively. Also, the $Fe_3O_4$ was reduced to $Fe_3O_{4-{\delta}}$ by CO. From the TGA results in air of the specimen that was calcined at $450^{\circ}C$ for three hours in $N_2$ atmosphere, the ${\delta}$-value of $Fe_3O_{4-{\delta}}$ was estimated. The ${\delta}$-value of $Fe_3O_{4-{\delta}}$ was 0.3170 when the sample was heat treated at $400^{\circ}C$ for 3 hours and 0.6583 when the sample was heat treated at $450^{\circ}C$ for 3 hours. $Fe_3O_{4-{\delta}}$ was oxidized to $Fe_3O_4$ when $Fe_3O_{4-{\delta}}$ was reacted with $CO_2$ because $CO_2$ is decomposed to C and $O_2$.

• Journal of the Korean Ceramic Society
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• v.38 no.6
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• pp.531-536
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• 2001

SiCl$_4$/CH$_4$/H$_2$계를 사용한 플라즈마 화학증착법(PECVD)으로 실리콘(100) 기판 위에 3C-SiC막을 117$0^{\circ}C$~1335$^{\circ}C$의 온도범위에서 증착하였다. 증착온도, 유입가스비, R$_{x}$ [=CH$_4$/(CH$_4$+H$_2$)], 그리고 r.f. power를 변화시켜 증착막의 결정성에 대해 검토하였다. Thermal CVD에 비해 PECVD법은 박막의 증착속도를 향상시켰다. 증착된 3C-SiC은 (111) 면으로 최대의 우선배향성을 지님을 알 수 있었다. 실리콘 기판 위의 3C-SiC막의 결정성은 R$_{x}$값에 의존하였으며, R$_{x}$가 감소할수록 결정성이 더욱 향상되었다. Free Si가 3C-SiC막과 함께 증착되었으나, 증착온도와 r.f power가 증가함에 따라 free Si의 함량은 감소하였다. 증착온도 127$0^{\circ}C$, 유입가스비 R$_{x}$=0.04, r.f. power가 60W에서 비교적 결정성을 가진 3C-SiC막을 얻을 수 있었다.