• Korean Journal of Food Science and Technology
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• v.15 no.4
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• pp.404-408
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• 1983

Some properties of malic enzyme (EC 1.1.1.40) prepared from malate-decomposition yeast, Schizosac-charomyces japonicus var. japonicus St-3 were investigated. The activity of malic enzyme was maximum when it was cultured for 24 hours. The optimum conditions for the enzyme reaction were pH 10.0 and temperature of $25^{\circ}C$. The crude enzyme was very stable at the range of pH 7.0-8.4, and almost 50 percent of enzyme activity was lost by heating at $60^{\circ}C$ for 10 minutes. The malic enzyme activity was enhanced by the addition of $Mn^{++}$. But the enzyme activity was not affected by the addition of organic acids, amino acids and ethanol, respectively.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2018.06a
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• pp.105-105
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• 2018

스테인리스강은 내식성과 내구성이 우수하여 파이프 및 일반 구조용 고온재료에 널리 사용된다. 그러나 선박 및 해양플랜트 등의 고부가가치 산업에 사용될 경우 내피로성, 내구성 및 내식성이 더욱 요구되고 있다. 특히 해수 환경 하에서 스테인리스강은 재료 표면의 부동태 피막 파괴로 공식 또는 틈부식에 의한 국부부식을 초래하여 해양환경용 재료로 사용하는데 제한적이다. 플라즈마 이온질화는 저온에서 열처리가 가능하며 재료의 변형이 없어 스테인리스강에 널리 적용되는 열화학적 표면처리 기술이다. 플라즈마 이온질화는 일반적으로 고온에서 실시하여 스테인리스강의 기계적 특성을 향상시키는 목적으로 주로 적용하였으나, 저온-플라즈마 이온질화 처리 시 질소의 확산계수 증가로 표면에 S-phase 생성에 기인하여 부식 저항성이 향상된다고 알려져 있다[1-2]. 그러나 해수 펌프, 밸브, 스트레이너(Strainer) 등의 해양 환경용 기자재로 널리 사용되고 있는 주조 스테인리스강에 대한 플라즈마 이온질화 적용과 그 연구는 미비하다. 따라서 본 연구에서는 주조용 스테인리스강에 대하여 플라즈마 이온질화 기술을 적용하여 공정온도에 따른 해수 내 전기화학적 부식 특성을 규명하였다. 플라즈마 이온질화 공정은 $25%N_2$와 $75%H_2$ 비율로 $350^{\circ}C{\sim}500^{\circ}C$의 공정온도에서 10시간 동안 실시하였다. X-선 회절분석을 통해 공정온도 변수에 따른 표면에 형성된 질화층의 상변화를 분석하였다. 또한 비커스 경도계를 이용하여 표면경도를 측정하여 기계적 특성 향상을 확인하였다. 전기화학적 부식 실험 후 표면 손상 형상 관찰, 무게 감소량 및 손상 깊이 계측을 통해 공정 온도와 부식 저항 특성을 규명하였다. 또한 타펠 분석을 통해 모재와 플라즈마 이온질화 온도 변수에 따른 부식 속도를 비교 분석하였다.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2018.06a
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• pp.114-114
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• 2018

탄소 재료는 뛰어난 물성에서 다양한 재료로의 응용이 기대되고 있다. 특히, 이종 원소 함유 카본 재료는 전기적 특성과 촉매성의 발현 등 새로운 기능을 카본 재료에 부여할 수 있어서 연료 전지, 에너지 저장, 태양 전지 등에의 응용이 기대되고 있다. 최근, 용액 중의 저온 플라즈마인 솔루션 플라즈마(solution plasma process)를 이용하여 벤젠 용액 등에서 탄소 재료 합성에 성공하였다. 그러나 기존의 연구에서는 솔루션 플라즈마 프로세스를 이용하여 합성한 이종원소 카본은 전도성이 낮아 이종원소의 함유량을 낮추는 고온의 열처리가 필요했다. 따라서 본 연구에서는 우수한 물리적 전기적 특성을 갖는 그래핀(graphene)과 같은 이종 원소 카본 나노시트(heteroatom carbon nanosheets)의 합성 및 메커니즘(mechanism)에 대해 검토하였다. 다양한 이종원소를 포함한 유기용매 안에 바이폴라 펄스 전원에 의한 전압을 두 텅스텐 전극 간에 인가하고, 솔루션 플라즈마를 생성하여 이종원소 카본 재료를 합성했다. 플라즈마 생성은 텅스텐 봉을 전극으로 사용하고 전압을 2.0 kV, 펄스 주파수를 200 kHz, 펄스 폭을 $1.0{\mu}s$, 전극 간 거리를 1.5 mm에서 일정하게 유지하며 200 mL 유기용매 중에서 방전시키는 것으로 재료를 합성했다. 플라즈마 방전 후, 필터을 이용하여 흡인 여과한 뒤 $200^{\circ}C$에서 1 시간 동안 건조 시켰다. 건조 후의 이종원소 카본의 물리적 특성을 원소 분석, X선 회절 법(XRD), 저항률 측정, 투과형 전자 현미경(TEM) 및 라만 분광법, 전자 현미경(SEM), X-선광전자분광기(XPS)등을 이용하여 카본의 형상 및 특성을 분석하였다. 그 결과 다양한 이종원소를 포함한 유기용매 중 2-pyrrolidone을 사용했을 때, 이종 원소 카본 나노시트를 합성하는데 성공하였다. 또한, 이 연구방법을 통해서 솔루션 플라즈마 프로세스를 통한 카본 나노시트 합성의 메커니즘을 규명하였다.

• Applied Chemistry for Engineering
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• v.17 no.5
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• pp.539-546
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• 2006

A study on the polymerization of polyethylenedioxythiophene (PEDOT) and the carbonization process of a separator was carred out in order to apply conductive polymer PEDOT to the winding typed aluminum condenser as a solid electrolyte and a negative electrode. PEDOT was polymerized with ethylenedioxythiophene (EDOT) as a monomer and ferric-p-toluenesulfonate as an oxidizing agent. The separator of condenser element was carbonized to control its fibrous tissue for the purpose of making it easy to impregnate the PEDOT solution into the microporous etched pit of aluminum foil by preventing separator from concentrating the PEDOT solution on itself. The characteristics of condenser such as capacitance, dissipation factor, equivalent series resistance, and thermal resistance depended on a carbonization temperature and a carbonization time. It was found that a thickness and a density of the used separator were major parameters of carbonization process and the characteristics of condenser were affected by these parameters.

• Korean Journal of Food Science and Technology
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• v.27 no.1
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• pp.97-100
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• 1995

The pigments of acetylshikonin and isobutylshikonin isolated from the roots of Lithospermum erythrorhizon were determined over a period of storage for their stabilities influenced by temperatures and metal ions. In dark condition, both pigment solution were unstable at 488 and 560 nm; alcoholic solutions of acetylshikonin pigment were stable at $25^{\circ}C$ and $50^{\circ}C$ for 1 hour, but isobutylshikonin showed severe discoloration within 1 hour at $95^{\circ}C$ . Buffered solutions of acetylshikonin tended to be discolored with the addition of $Fe^{++}$, while those of isobutylshikonin with $Fe^{++}$ and $Cu^{++}$. These studies indicated that acetylshikonin and isobutylshikonin can be used in foods as the natural colorant under selected conditions in case of considering storage temperature and metal ions.

• Korean Journal of Food Science and Technology
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• v.32 no.3
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• pp.610-617
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• 2000

The indigestible dextrin with high indigestible fraction was prepared by treating the enzyme hydrolysate of pyrodextrin with ethanol or strongly acidic cation exchange resin(UBK 530). Optimum conditions of ethanol treatment for preparing the indigestible dextrin from $\alpha-amylase$ and amyloglucosidase treated hydrolysate were determined based on the indigestible fraction, dietary fiber content, and yield. Ethanol was added 5-fold by weight to 30%(w/w) enzyme hydrolysate, and the mixture was kept at room temperature for 3 hr. Low molecular weight saccharides containing glucose and high molecular weight saccharides were separated by strongly acidic cation exchange resin. While initial enzyme hydrolysate by $\alpha-amylase$ and amyloglucosidase showed 43.6% of DPI(glucose) and 51.1% of DP4+(maltotetraose and over), the indigestible dextrin collected to 50% of initial enzyme hydrolysate by treatment of cation exchange resin showed 7.1% of DPI(glucose) and 91.2% of DP4+(maltotetraose and over). In conclusion, 44.5% of indigestible fraction of initial enzyme hydrolysate increased to 78.9% after separation of low molecular weight saccharides.

• Korean Chemical Engineering Research
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• v.46 no.6
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• pp.1119-1123
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• 2008

Tin oxide was prepared by microwave heating for anode material of lithium ion battery. The samples were heated at 300, 500 and $700^{\circ}C$ for 3h under flowing oxygen after microwave heating. The effect of microwave heating on the electrochemical performance of the manufactured tin oxide and the reversible capacity performance were investigated. Tin oxide heated at $500^{\circ}C$ showed higher capacity than those at $300^{\circ}C$ and $700^{\circ}C$ under microwave heating condition. Comparing microwave and furnace heating, microwave heating condition showed higher capacity. The discharge capacity after microwave heating and $500^{\circ}C$ heating showed 1,500 mAh/g.

• Journal of the Korean Ceramic Society
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• v.41 no.7
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• pp.508-512
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• 2004

For abutment of dental implants, (Y, Nb)-TZP/Alumina composites were prepared by addition of 10-90 vol% alumina at an interval of 10 vol％ into tetragonal zirconia solid solution which consists of 90.24 mol% Zr $O_2$, 5.31 mol% Y$_2$ $O_3$, and 4.45 mol% Nb$_2$O$\_$5/. Biaxial flexure strength and fracture toughness of composite were optimized by adding 10 vol% alumina, which resulted in 900 MPa and 8.9 MPam$\^$1/2/, respectively. The composite did not undergo low temperature degradation even after autoclave treatment at 200$^{\circ}C$ for 10 h. 65 of (Y, Nb)-TZP/Alumina composite abutments were employed into 40 patients and any adverse reaction, screw loosing, or fracture of abutments was not observed for the span of 2 years, indicating that the ceramic abutments can be safely used for restorations.

• Polymer(Korea)
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• v.24 no.5
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• pp.664-672
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• 2000

It is generally agreed that transesterification provides the, copolymer in the melt blending of poly(ethylene naphthalate) (PEN) and poly($\varepsilon$-caprolactone) (PCL). Effects of the conditions of transesterification reaction and catalyst on the degree of randomness and average sequence length of PEN/PCL blends were investigated and results were used to interpret the biodegradability of PEN/PCL blends. It was found that degree of randomness values of obtained copolymer lied between 0 and 1, and it indicated that this blend consisted with physical blends of PEN/PCL and PEN/PCL block copolymers. The degree of randomness reached almost 1 which is the theoretical value of random copolymers and the average sequence length became shorter by the further transesterification reaction. In additions, it was found that the increase of copolymers, especially random copolymers reduced the biodegradability in PEN/PCL blends.

• Polymer(Korea)
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• v.24 no.5
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• pp.638-645
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• 2000

Linear and star-shaped, poly(lactic acid) (PLA) stereo-block copolymers were synthesized by sequential polymerization of DL-lactic acid and L-lactide in the presence of diol or polyol compounds. The molecular weight of block copolymers could be controlled to some extent by the variation of alcohol content. These block copolymers had relatively narrow molecular weight distributions. The glass transition temperature and melting temperature of block copolymers appeared at around 5$0^{\circ}C$ and 100~14$0^{\circ}C$, respectively. The block copolymers were found to crystallize even at the high D-stereoisomer concentration of 35 mol%, in contrast to the amorphous nature of the random copolymer with similar composition. Also we could observe the crystallinity of PLA stereo-block copolymers varying with annealing temperature and time.