• Proceedings of the Korean Vacuum Society Conference
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• 2000.02a
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• pp.103-103
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• 2000

강한 결정 방향 의존성과 낮은 항정계를 갖는 Bi4Ti3O12 강유전체 박막은 NDRO형 비휘발성 강유전체 메모리 분야에서 매우 유망한 재료이다. 이를 위해서는 실리콘 기판과의 계면조절과 실리콘 기판성에서 고품질의 강유전성 박막을 성장시키는 기술이 필수적이다. MOCVD에 의한 Bi4Ti3O12 의 증착에서는 Bi 성분의 강한 휘발 특성과 낮은 반응성으로 인하여 조성과 두께 등의 조절이 매우 어렵다. 따라서 화학기상증착의 기구를 이해하고 제어하는 기술이 양질의 박막을 얻는데 필수적이다. 본 연구에서는 유기금속 원료 TPB, TIP 과 산소를 이용하여 실리콘 기판위에 Bi4Ti3O12 강유전체 박막을 증착할 때, 증착 변수의 변화에 따른 박막의 증착 거동과 구조적, 전기적 특성을 연계하여 분석하였다. 특히 기판부착력이 낮고 휘발성이 강한 Bi의 특성으로 인한 문제를 개선하기 위하여 TIP원료를 주기적으로 공급, 중단을 반복하는 펄스주입법을 고안하여 그 효과를 살펴보았다. 실리콘 기판위에서 TiO2의 증착속도는 실험온도 영역에서 온도에 따라 변화하지 않는 전형적인 물질 전달에 의해 지배되는 양상을 나타내었다. 반면 Bi2O3 경우에는 50$0^{\circ}C$ 이상에서 급격하게 증착속도가 감소하는 특이한 경향을 나타내었으며 이는 Bi2O3의 높은 휘발성 때문일 것이다. Bi4Ti3O12 박막은 온도증가에 따라 증착속도가 증가한 후 $600^{\circ}C$ 이상에서 포화되는 경향을 보였다. 이로부터 실리콘 기판위에서의 Bi4Ti3O12 박막의 증착 모델을 제시하였다. Bi2O3에 비해 상대적으로 표면 부착력이 월등히 큰 TiO2가 우선적으로 실리콘 펴면에 형성된 후 TPB 유기금속 원료가 이 TiO2와 반응하는 과정으로 Bi4Ti3O12 박막이 증착된다. $600^{\circ}C$이상에서는 증착 변수들을 바꾸어도 물성이 변하지 않는 자기조절기능이 있음을 알 수 있었는데 이는 고온에서의 Bi2O3의 강한 휘발성 때문일 것이다. 실리콘 기판에서 층상 페로브스카이트 상은 58$0^{\circ}C$ 이상에서 형성되며, 매우 좁은 온도 변화에도 결정구조, 박막현상 및 성분이 크게 바뀌는 온도에 민감한 증착거동이 관찰되었다. 증착 모델에서 예견되는 Bi의 불리함을 개선하기 위해 펄스주입법을 실시한 경우 Bi의 성분량이 증가되었고 결정성이 향상되었다. 이로부터 펄스주입법이 박막내에 부족하기 쉬운 Bi를 보충하여 박막의 특성을 개선함을 확인하였다. Bi4Ti3O12 박막의 증착온도에 따른 누설전류 특성 측정 결과 증착온도가 감소할수록 누설전류가 감소함을 알 수 있었고 펄스주입법이 연속주입법보다 더 낮은 누설전류를 보임을 알았다. 펄스주입법의 경우 -2.5V 인가 시의 누설전류는 7.4$\times$10-8A/cm2에서 1.3$\times$10+7A/cm2의 매우 우수한 값을 가졌다. 연속 주입법에 의해 증착된 박막은 C-V 측정 결과 강유전성 이력이 나타나지 않았으나, $600^{\circ}C$ 이상에서 펄스주입법에 의해 증착된 박박은 강유전성 이력을 나타내었다.

• Journal of the Korean Society of Food Science and Nutrition
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• v.32 no.8
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• pp.1200-1205
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• 2003

Structured lipids (SL) were synthesized by transesterification of corn oil and conjugated linoleic acid (CLA) in the continuous type reactor using sn-1,3 specific Rhizomucor miehei lipase. The parameters of reaction were observed in terms of flow rate, temperature, and substrate molar ratios. The highest incorporation of CLA was obtained with 1 mL/min flow rate, 55$^{\circ}C$ and 1 : 3 (corn oil/CLA) molar ratio, showing 10.26 ㏖%. When different reaction temperatures and substrate ratios were studied, the highest incorporation was obtained at $65^{\circ}C$ (17.33 ㏖%) and 1 : 5 (corn oil/CLA) ratio (17.50 ㏖%), respectively. After pancreatic lipase analysis, most of all CLA were found at sn-1,3 position. The iodine values of obtained SLs ranged from 110 to 120. From the neutral lipid analysis by normal-phase HPLC, produced SLs composed of 99.35 ∼ 99.89% triacylglycerols, 0.11 ∼ 0.51% 1,2- and 1,3-diacylglycerols, and 0.06 ∼ 0.22% monoacylglycerols.

• Journal of the Korean Society for Heat Treatment
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• v.29 no.2
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• pp.56-61
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• 2016

Heating experiments using the Ti-3Al-2.5V tube materials in a vacuum furnace have been performed to investigate a pertinent range of working temperatures and holding times for the development of the successive or simultaneous operation of superplastic hydroforming and diffusion bonding. The specimens were heated at $820^{\circ}C$, $870^{\circ}C$ and $920^{\circ}C$ respectively. Holding times at each temperature were varied up to 4 hours. Holding times longer than 1 hour were selected to consider the diffusion bonding process after or during the hydroforming process in the superplastic state. Grain sizes were varied from $5.7{\mu}m$ of the as-received tube to $9.2{\mu}m$ after heating at $870^{\circ}C/4hours$. Homogeneus granular microstructures could be maintained up to $870^{\circ}C$, while microstructures at $920^{\circ}C$ showed no more granular type.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.18 no.2
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• pp.97-100
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• 1982

The phase differences of the omega were observed continuously for the A-C pair and the A-E pair from Sept. 1, 1980 to Feb. 28, 1981 and from Sept. 20, 1981 to Feb. 82, 1982 at Fisheries University of Busan350$^{\circ}$ 07'.9N, 129$^{\circ}$ 06'.3E)In this paper we deal with the reappearance of these phase differences by annual, month, day As a results, annual eappearance are in good condition both pairs and daily reappearance in day and night are better than an hour around the sunset, and very bad reappearance is found by month.

• Korean Journal of Materials Research
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• v.5 no.4
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• pp.397-404
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• 1995

반도체 세정공정에서 염기성 세정액(SCI, Standard cleaning 1, $NH_{4}$OH + $H_{2}$O_{2}$ + $H_{2}$O)은 공정상 발생되는 여러 오염물 중 파티클의 제거를 위해 널리 사용되고 있는데, SCI 조성중 $NH_{4}$OH양에 따라 세정 중 실리콘의 식각속도를 증가시킨다. 이 연구에서는 SCI 세정이 CZ(Czochralski)와 에피 실리콘 기판 표면에 미치는 영향을 단순세정과 연속적인 산화-HF 식각-SCI 세정공정을 통해 관찰되었다. CZ와 에피 기판을 8$0^{\circ}C$의 1 : 2 : 10과 1 : 1 : 5 SCI 용액에서 60분까지 단순 세정을 했을 때 laser particle scanner와 KLA사의 웨이퍼 검색장치로 측정된 결함의 수는 세정시간에 따라 변화를 보이지 않았다. 그러나 CZ와 에피 기판을 10분간 SCI 세정후 90$0^{\circ}C$에서 산화 HF식각공정을 4번까지 반복하였을 때 에피 기판 표면의 결함수는 감소하는 반면에 CZ기판에서는 직선적으로 증가하였다. 반복적인 산화-HF 식각-XCI 세정공정을 통해 생성된 CZ기판 표면의 결함은 크기가 0.7$\mu$m 이하의 pit과 같은 형상을 보여주었다. 이들 결함은 열처리 중 CZ 기판내와 표면에 산화 석출물들이 형성, 반복적인 HF 식각-SCI 세정공정을 통해 다른 부위에 비해 식각이 빨리 일어나 표면에 생성되는 것으로 여기어 진다.

• KSBB Journal
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• v.20 no.2 s.91
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• pp.112-115
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• 2005

E. coli in combination with bacteriophage $\lambda$ was used to overcome the intrinsic plasmid instability that is frequently found in recombinant fermentation especially in long-term operation. In order to enhance the stability and productivity, the bacteriophage ${\lambda}NM1070$ was used in this study. It is a $\lambda$ mutant, which is deficient in the synthesis of protein related to DNA packaging and cell lysis. The ${\lambda}NM1070$ is also a temperature-sensitive mutant. To optimize the production of recombinant protein in this temperature-sensitive system, the temperature effects on growth and cloned gene expression were investigated for stable and efficient recombinant gene expression. The induction to the lytic state was not complete at $36^{\circ}C$ while the temperature above $40^{\circ}C$ induced the lytic state completely. However, the productivity was decreased at $42^{\circ}C$ by temperature inhibition. The L-free cell concentration increased with the increase of temperature until $40^{\circ}C$. In conclusion, ${\lambda}NM1070$ has the optimal temperature at $38^{\circ}C$ for stability and at $40^{\circ}C$ for expression.

• Microbiology and Biotechnology Letters
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• v.7 no.3
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• pp.141-147
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• 1979

Naringinase from Atpergillus nidulans was immobillized on DEAE-Sephadex A-25 and its characteristics were studied. The optimal conditions for the preparation of the immobilized enzyme were as follow; optimal pH, incubation time and the suitable amount of enzyme were 6.0, 30 min. and 110 units per gram of the dried ion exchage resin, respectively. The optimal pH of the immobilized enzyme was higher than that of the native enzyme. The optimal temperature increased from 4$0^{\circ}C$ to 5$0^{\circ}C$. The heat and pH stability of the immobillized enzyme were better than those of the native enzyme. No significant difference in the Michaelis constant was detected. Activation energy of the immobilized enzyme was 7.96 Kcal/mole, and the apparent Michaelis rate equation was used to describe the action of this material. The degree of hydrolysis was dependant on the flow rate at low rate of perfusion through the column. As the flow rate increased, the value of the apparent Km decreased.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.30 no.2
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• pp.20-25
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• 2016

This paper describes the effectiveness of continuous water removal in oil immersed transformers. Insulation oil in which insulation papers were immersed were prepared for tests and water concentrations in oil with heating time were measured at five oil temperatures. Also, the tests that water dissolved in $100^{\circ}C$ oil was removed at once and continuously at $50^{\circ}C$ and $100^{\circ}C$ were performed for consideration of effective method for water removal. Test results indicated that the oils for water measurement have to be extracted at similar temperatures and water in oil has to be continuously removed at higher temperatures for more effective water management of transformers.

• Polymer(Korea)
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• v.29 no.1
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• pp.96-101
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• 2005

Fluoropolymer of PTFE and PFA etc. is a heat resistance polymeric material that it is known as that maximum continuous use temperature reaches for 260 $^{\circ}C$. It was observed that these polymers had the enough thermal stability so enough that it was kept by thermal aging of 280 $^{\circ}C$/7 weeks too in this study. However, such thermal stability means that bulk material property is kept such as mechanical strength, melting point and initial pyrolysis temperature etc. If these polymers are evaluate by coating property such as surface contact angle, surface morphology, surface scratch, thing that heat resistance is not enough was confirmed in this study. Thermal aging of flouropolymer coating was achieved by gear aging oven that the exchange rate of air was controlled, and the analysis results were indicating serious damage of surface morphology and adhesive strength on metal substrate.

• Journal of Life Science
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• v.20 no.11
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• pp.1656-1661
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• 2010

Alkaline protease for the hydrolysis of egg yolk protein was immobilized on five carriers - Duolite A568, Celite R640, Dowex-1, Dowex 50W and Silica gel R60. Duolite A568 showed a maximum immobilization yield of 24.7%. Optimum pH for the free and immobilized enzyme was pH 8 and 9, respectively. However, no change was observed in optimum temperature ($50^{\circ}C$). Thermal stability was observed in immobilized enzymes compared to free enzymes. The immobilized enzyme retained 86% activity after 10 cycle operations in a repeated batch process. The effect of flow rate on the stability of enzyme activity in continuous packed-bed reactor was investigated. Lowering flow rate increased the stability of the immobilized enzyme. After 96 hr of continuous operation in a packed-bed reactor, the immobilized enzyme retained 83 and 61% activity when casein and egg yolk were used as a raw materials, respectively.