• 한국재료학회:학술대회논문집
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• 한국재료학회 1998년도 IUMRS-ICEM ABSTRACT BOOK
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• pp.68.2-68
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• 1998

• 한국주조공학회지
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• 제17권6호
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• pp.608-614
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• 1997

The effect of mold preheating temperature on the microstructure such as grain size, eutectic silicon morphology was investigated for the Al-7wt%Si-0.3wt%Mg alloy. Microstructural variations have been characterized as a function of Sr addition and cooling rate during solidification. Microstructures were correlated with cooling rate, local solidification time and eutectic nucleation temperature, etc. In this study, Sr addition caused increase of local solidification time, undercooling and reduction of eutectic plateau temperature. In logarithmic scale, local solidification time was in inverse proportion to cooling rate. Eutectic nucleation temperature was in inverse proportion to cooling rate of logarithmic scale. Increasing the cooling rate refined dendrite arm spacing and eutectic silicon. Dendrite arm spacing was logarithmically in inverse proportion to cooling rate. Without modifier addition, eutectic silicon was modified at cooling rate of $7^{\circ}C/s$ or higher.

• 동력기계공학회지
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• 제10권3호
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• pp.51-57
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• 2006

The effect of grain size on corrosion resistance and high temperature oxidation behavior was studied in 22Cr-15Ni-5W super austenitic stainless steels for desulfurization equipment as a heat power station. In the high temperature oxidation test, oxidation rate was increased as the temperature increased from $600^{\circ}C\;to\;800^{\circ}C$. In vapor, oxidation rate was faster than that in air. Because the vapor was inhibited nucleation of $Cr_2O_3$ film. And the high temperature oxidation resistance at $600^{\circ}C{\sim}800^{\circ}C$ was excellent from all specimens and specimen of the smallest grain size was the most excellent. Because increasing of diffusion course through the grain-boundary was promoted nucleation and growth of $Cr_2O_3$ film. In the test temperature at $600^{\circ}C{\sim}800^{\circ}C$, Cr rich round particle oxide was formed in air, whereas Fe rich needle type oxide was developed in vapor.

• 한국결정성장학회지
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• 제6권2호
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• pp.275-285
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• 1996

The effect of heat-treatment on catalytic crystallization in $LI_2O-Al_2O_3-SiO_2$ glass system over its glass transition temperature was investigated. Glass composition $4Li_2O{cdot}22AL_2O_3{cdot}66SiO_2{cdot}2TiO_2{cdot}2.5ZrO_2{cdot}1.5P_2O_5{cdot}1.0Na_2O{cdot}1.0As_2O_3$ (wt%) was selected and heat-treated at different heating conditions to obtain transparent glass-ceramic. Nucleation and crystallization behaviour of this composition were estimated by differential thermal analysis (DTA) and X-ray diffractometer (XRD) and its thermal expansion coefficients were measured by Dilatometer. As a result, glass transition temperature was $730^{\circ}C$ and two maximum nucleation temperatures were estimated at $730^{\circ}C$ and 82$0^{\circ}C$ using JMA(Johson-Mehl-Avrami) equation by DTA. $ZrTiO_4$ $\beta$-Quartz solid solution and $\beta$-Spodumene crystals were identified by XRD. The optimum crystallization temperature was 92$0^{\circ}C$ and three step heating schedule was expected to be useful to obtain transparent glass-ceramic.

• 한국분말재료학회지
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• 제9권1호
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• pp.19-24
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• 2002

This paper reports the results of an investigation into the effect of Cu additions upon the nano-crystallization behaviour of an Al-Y-Ni alloy. 1 at.% Cu was added to a base alloy of Al/sub 88/Y₄Ni/sub 8/ either by substitution for Al to form Al/sub 87/Y₄Ni/sub 8/Cu₁, or by substitution for Ni to form Al/sub 88/Y₄Ni/sub 7/Cu₁. Consistent with previous findings in the literature, the substitution of Cu for Al was found to increase the thermal stability of the amorphous phase whereas the substitution of Cu for Ni was found to decrease its thermal stability. Comparing the microstructures of these alloys after heat treatment to produce equivalent volume fractions of Al nanocrystals showed average grain sizes of 14 nm, 12 nm and 9 nm for the alloys Al/sub 88/Y₄Ni/sub 8/, Al/sub 87/Y₄Ni/sub 8/Cu₁respectively. The effect of Cu in refining the size of the nanocrystals was attributed to enhanced nucleation increasing the number density of the nanocrystals, rather than diffusion limited or interface limited growth.

• 열처리공학회지
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• 제12권2호
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• pp.99-107
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• 1999

The graphitization is affected by the addition of small amount of the elements(such as Si, Al, Ni, B, Cr and Mn etc.) and the pre-treatment(such as cold rolling). Boron is well known element to accelerate the graphitization of cementite in high carbon steels. Also, cold rolling is known to accelerate the graphitization. But the graphitization nucleation mechanism by cold rolling is few reported. Therefore the effect of cold rolling in Fe-0.5%C-1.0%Si-0.47%Mn-0.005%B steel on the graphitization is investigated quantitatively using hardness test, optical microscope and scanning electron microscope, neutron induced microscopic radiography. The nucleation of graphite in cold-rolled Fe-0.5%C-1.0%Si-0.47%Mn-0.005%B steel is formed at void which is formed at pearlite/pearlite boundary by cold rolling. But the effect of cold rolling on graphitization in boron addition steel is more effective than that of no boron addition steel due to segregation of BN at void in boron addition steel.

• 한국식품과학회지
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• 제29권2호
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• pp.326-336
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• 1997

INP를 포함한 빙핵활성세균을 식품 가공 단계에 직접 이용하기 위해 빙핵활성을 최대한 유지시키면서 완전 살균하는 방법을 찾기 위해 가열, 고압, 방사선으로 처리한 후 생균수 및 빙핵활성을 측정하였다. 균주는 Pseudomonas syringae, Xanthomonas campestris와 INP유전자를 포함한 plasmid가 재조합된 Escherichia coli JM109/pEIN229, Gluconobacter oxydans/pKIN230를 사용하였다. 빙핵활성을 T90 (drop의 90%가 어는 온도)으로 나타내었을 때 방사선 조사시 $0.3^{\circ}C{\sim}0.7^{\circ}C$, 초고압 처리시 $1^{\circ}C{\sim}2^{\circ}C$, 가열 처리시 $4^{\circ}C{\sim}7^{\circ}C$가 감소하여 방사선 조사에 의한 살균시 빙핵활성의 감소가 가장 적은 것으로 나타났다. 각 살균점에서의 cumulative ice nucleation activity spectra를 측정한 결과 A부류의 빙핵($-5^{\circ}C$ 이상에서 빙핵으로 작용)의 수는 방사선처리시 거의 감소가 없었으며 초고압처리시 90% 이상 감소하였으며 가열처리시 존재하지 않았다. 증류수에 방사선조사로 살균된 빙핵활성세균을 첨가한 후 DSC를 이용해 thermogram을 얻었다. 빙핵활성세균을 첨가하지 않은 증류수보다 $11^{\circ}C{\sim}15^{\circ}C$ 정도 높은 온도에서 발열 피크가 형성되기 시작했으나 흡열 피크는 큰 차이를 보이지 않았으며, 발열량 및 흡열량은 감소했다. 한편, DSC를 이용해 측정된 빙핵활성은 drop freezing method에 의해 측정된 값과 높은 연관성$(R^{2}>0.993,\;p<0.0001)$을 보여 간편하고 정확한 빙핵활성 측정법으로의 사용 가능성을 제시했다.

• 한국재료학회지
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• 제2권2호
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• pp.110-118
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• 1992

형성방법이 다른 세종류의 TiN기판상에 CVD텅스텐막을 도포할 때의 W의 핵생성 양상을 비교조사하여 다음과 같은 결과를 얻었다. 반응성 스팟터법에 의하여 형성한 TiN과 $NH_3$분위기에서 RTP처리한 $SiH_4$환원에 의하여 CVD-W막을 증착할 때, 증착속도(deposition rate)는 sputtered TiN>RTP TiN>annealed TiN의 순서로 감소하며, W 핵생성에 대한 잠복기는 sputtered $TiN{\leq}RTP$ TiNTiO_{X}N_{Y}$로 바뀌기 때운에 그 위에서 W의 핵성성이 어려워지고, 증착속도도 낮아진 것이다. RTP-TiN의 미세한 결정립구조는 W의 핵성성과 성장에 유리한 효과를 미치지만, 그것의 높은 압축응력이 W의 핵생성과 성장에 미치는 불리한 효과가 더 크기 때문에, RTP-TiN 기판상에 W를 증착할 경우가 sputtered TiN 기판상에 W를 증착할 경우보다 증착속도가 더 낮고, 잠복기도 더 긴 것으로 사료된다.

• 한국응용과학기술학회지
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• 제23권1호
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• pp.54-62
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• 2006

Kelvin equation is revisited, which accounts for important phenomena observed frequently in nano-dispersion systems. They include vapor pressure increase for curved interfaces, nucleation, capillary condensation, Ostwald ripening and so on. The smaller the radius of curvature is, the more significant Kelvin equation becomes. Therefore, its meaning, curvature effect, and importance are examined and discussed.

• 한국결정성장학회지
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• 제6권3호
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• pp.360-367
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• 1996

실리콘 단결정에서 존재하는 산화저층결합(OISF)은 실리콘 웨이퍼의 전기적 성질에 많은 영향을 미치게 되는데 이 산화적층결함의 핵(nuclei)은 결정성장 과정에서 형성되며, 그 주요 원인으로는 초기 산소 농도, dopant의 종류 및 농도, 냉각속도 등이 있다. 본 연구에서는 냉각 속도에 따른 실리콘 단결정 내의 산화적층결함에 관하여 조사하였다. 수평관상로를 이용하여 실리콘 단결정괴를 Ar 분위기에서 $1400^{\circ}C$까지 승온후 각기 다른 냉각속도로 냉각하였다. 이후 $1150^{\circ}C$에서 산화처리를 한 후 실리콘 단결정 내의 산화적층결함의 농도를 조사하였으며, FTIR을 이용하여 산화석출물이 산화적층결함의 형성에 미치는 영향을 조사하였다. 그 결과 실리콘 단결정 내에서 산화적층결함이 가장 많이 형성되는 중간 단계의 냉각속도 범위가 있음을 확인하였으며 실리콘 단결정 내의 산소가 석출물의 형태로 존재할 때 산화적층결함이 많이 형성됨을 알 수 있었다.