• Journal of Microbiology and Biotechnology
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• 제23권1호
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• pp.56-63
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• 2013

We have characterized the putative ${\alpha}$-glucosidase gene (st2525) selected by total genome analysis from the acidothermophilic crenarchaeon Sulfolobus tokodaii strain 7. The ORF was cloned and expressed as a fusion protein in Escherichia coli, and recombinant ST2525 was purified by Ni-NTA affinity chromatography. Maximum activity was observed at $95^{\circ}C$ and pH 4.0, and the enzyme exhibited stability with half-lives of 40.1 min and 7.75 min at extremely high temperatures of $100^{\circ}C$ and $105^{\circ}C$, respectively. The enzyme retained at least 85% of its maximal activity in the pH range of 4.0-11.0. ST2525 exclusively hydrolyzed ${\alpha}$-1,4-glycosidic linkages of oligosaccharides in an exo-type manner, with highest catalytic efficiency toward maltotriose. The enzyme also displayed transglycosylation activity, converting maltose to isomaltose, panose, maltotriose, isomaltotriose, etc. From these results, ST2525 could be potentially useful for starch hydrolysis as well as novel synthesis of oligosaccharides in industry.

• 자원리싸이클링
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• 제25권5호
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• pp.57-63
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• 2016

본 연구는 호주산 저품위 동광의 선광실험결과로 얻은 고품위 광물의 황산화 배소 및 선택적 침출반응 조건 확립을 통해 유가 광물 중에 함유된 성분을 선별적으로 용해해냄으로써 철 성분을 비롯한 불순물을 줄이거나, 동 및 니켈 성분을 용해 혹은 잔사에 잔류시킴으로써 유가금속회수를 효과적으로 회수하고자 하는데 목적이 있다. 본 연구실험결과 얻은 최적조건은 황산화 배소시 $450^{\circ}C$, $Na_2SO_4$ 2 mole ratio 및 1.5 h이었고, 배소산물의 침출온도는 상온 및 침출제는 $H_2O$ 혹은 1M $H_2SO_4$이었다. 최적조건 하에서 Cu 성분은 90 wt.% 침출율을 Fe성분은 20 wt.%내외, Ni성분은 15 wt.% 정도를 나타내는 것으로 보아 선택적 분해침출이 가능하다.

• 한국자원리싸이클링학회:학술대회논문집
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• 한국자원리싸이클링학회 1999년도 제6회 산화철국제워크샵 DIGESTS OF THE INTERNATIONAL WORKSHOP ON IRON OXIDES
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• pp.1-63
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• 1999

Generation of abnormally large grains in the microstructure of small grains has been investigated on some ferrites. Some fractions of large grains were observed in the microstructure of sintered ZnFe$_2$O$_4$, Mn-ZnFe$_2$O$_4$, Fe$_3$O$_4$(in N$_2$) and MnFe$_2$O$_4$(in air). On the other hand, the large grains were not observed in NiFe$_2$O$_4$ and CoFe$_2$O$_4$, independent of calcining and sintering conditions. The large grains seem to be generated in such ferrites that are easy to vary their compositions or valencies at high temperatures. As the sintering proceeded, the number of large grains was increasing to form a continuous structure consisting of large grains, while the size of large grains did not increase remarkably. In addition, the growth of small grains was also very slow during the generation of the large grains. The large grains appeared to be suddenly generated after some induction periods. Avrami equation could be applied to the relation between net volume of large grains and sintering time. Thus, the grain boundaries may be strongly stabilized when the large grains are generated. The large grain in generated by the local activation of the stabilized grain boundaries, which is caused by the variation of compositions or valencies during sintering. It is concluded that the essence of the abnormal grain growth is not the generation of abnormally large grains, but the abnormal stabilization and the local activation of the grain boundaries.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2010년도 제39회 하계학술대회 초록집
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• pp.210-210
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• 2010

ABO2 형태를 가진 delafossite 구조 산화물은 p-type 투명전도체 소재로 유명하다. Delafossite 구조가 p-type 투명전도체에 적합한 결정적인 이유는 밴드갭이 넓고 공유결합에 유리하기 때문이다. 투명전도체는 가시광선의 흡수가 없도록 band gap을 넓히는 것이 우선인데 이러한 band gap이 넓은 구조가 delafossite이다. 또한 delafossite 구조는 구조적으로 각각의 산화물 이온들이 유사 사면체 배위(pseudo-tetrahedral coordination)을 갖는다. 이러한 사면체 배위결합구조에서 산소이온은 비결합면이 없기 때문에 더욱더 공유결합성을 향상시킬 것으로 생각된다. 여기서 A는 +1가 cation, B은 +3가 cation으로 구성되어 있다. A자리에는 1가 원소인 팔라듐, 플래티늄, 은, 구리 등을 가질 수 있고. B자리에 3가 원소이면서도 크기가 알루미늄보다는 크고 란타늄보다는 작은 금속이 들어갈 수 있다. Delafossite 구조는 상온에서 2종류의 polytype (상온에서 Rhombohedaral 구조와 hexagonal 구조)이 존재하며 이들은 각각 3R(Rm) 및2H (P63/mmc)의 결정 구조를 가지고 있다. CuCrO2는 일반적으로 3R결정구조를 가지는 것으로 알려져 있다. delafossite 구조는 전기적 이방성을 띄고 있는데 c-축 방향으로의 전기적 특성이 a-축 방향으로의 전기적 특성보다 약 1000배 높은 물성을 띈다고 한다. 이는 c-축 방향의 원자 위치 때문인데 CuCrO2의 경우 Cu-O-Cr-O-Cu로서 3d-2p-3d-2p-3d 궤도를 가지기 때문인 것으로 알려져 있다.[ref] 반면 c-축으로 에피성장된 박막의 경우 +3가 이온이 위치한 layer에서 hole hopping에 의해 캐리어가 전도된다고 알려져 있기도 하다. 본 연구에서는 PLD를 이용하여 c-plane 사파이어 기판위에 성장된 delafossite구조인 CuCrO2박막의 특성을 알아보았다. p-type 특성을 위하여 CuCrO2에 Ni를 첨가하였으며 그에 따른 구조적 전기적 특성을 조사하였다. 성장온도와 도핑농도를 변화시켜 특성을 연구하였다. 결정구조적 특성과 전기적 특성을 분석하려 한다.

• 대한금속재료학회지
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• 제49권1호
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• pp.58-63
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• 2011

The grain size and growth direction of a directionally solidified turbine blade were evaluated by the initial nucleation condition at the start block of directional solidification. The initial nucleation condition was controlled by inserting a Ni foil on the directional solidification plate of the directional solidification furnace. Fine grains with good orientation were obtained in the faster cooling condition at the start block. The nucleus number was compared with the cooling rate of the start block by electron back scattered diffraction (EBSD). DSC (differential scanning calorimeter) analysis was performed to compare the melting point and undercooling for nucleation of the coarse nuclei and fine nuclei of the start block. The faster cooling condition at the start block showed more undercooling for nucleation and smaller size of nuclei which resulted in a fine grain with good orientation in the directional turbine blade.

• Nuclear Engineering and Technology
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• 제54권3호
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• pp.959-964
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• 2022

Lead is an important material, both for fusion or fission reactors. The cross sections of natural lead should be validated because lead is a main component of lithium-lead modules suggested for fusion power plants and it directly affects the crucial variable, tritium breeding ratio. The presented study discusses a validation of the lead transport libraries by dint of the activation of carefully selected activation samples. The high emission standard ²⁵²Cf neutron source was used as a neutron source for the presented validation experiment. In the irradiation setup, the samples were placed behind 5 and 10 cm of the lead material. Samples were measured using a gamma spectrometry to infer the reaction rate and compared with MCNP6 calculations using ENDF/B-VIII.0 lead cross sections. The experiment used validated IRDFF-II dosimetric reactions to validate lead cross sections, namely ¹⁹⁷Au(n, 2n)¹⁹⁶Au, ⁵⁸Ni(n,p)⁵⁸Co, ⁹³Nb(n, 2n)^92mNb, ¹¹⁵In(n,n')^115mIn, ¹¹⁵In(n,γ)^116mIn, ¹⁹⁷Au(n,γ)¹⁹⁸Au and ⁶³Cu(n,γ)⁶⁴Cu reactions. The threshold reactions agree reasonably with calculations; however, the experimental data suggests a higher thermal neutron flux behind lead bricks. The paper also suggests ²⁵²Cf isotropic source as a valuable tool for validation of some cross-sections important for fusion applications, i.e. reactions on structural materials, e.g. Cu, Pb, etc.

• 방사성폐기물학회지
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• 제20권1호
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• pp.43-63
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• 2022

The aim of this review is to communicate some essential knowledge of the underlying mechanism of the corrosion of structural containment alloys during molten salt reactor operation in the context of prospective online monitoring in future MSR installations. The formation of metal halide species and the progression of their concentration in the molten salt do reflect containment corrosion, tracing the depletion of alloying metals at the alloy salt interface will assure safe conditions during reactor operation. Even though the progress of alloying metal halides concentrations in the molten salt do strongly understate actual corrosion rates, their prospective 1^st order kinetics followed by near-linearly increase is attributed to homogeneous matrix corrosion. The service life of the structural containment alloy is derived from homogeneous matrix corrosion and near-surface void formation but less so from intergranular cracking (IGC) and pitting corrosion. Online monitoring of corrosion species is of particular interest for molten chloride systems since besides the expected formation of chromium chloride species CrCl₂ and CrCl₃, other metal chloride species such as FeCl₂, FeCl₃, MoCl₂, MnCl₂ and NiCl₂ will form, depending on the selected structural alloy. The metal chloride concentrations should follow, after an incubation period of about 10,000 hours, a linear projection with a positive slope and a steady increase of < 1 ppm per day. During the incubation period, metal concentration show 1^st order kinetics and increasing linearly with time^1/2. Ideally, a linear increase reflects homogeneous matrix corrosion, while a sharp increase in the metal chloride concentration could set a warning flag for potential material failure within the projected service life, e.g. as result of intergranular cracking or pitting corrosion. Continuous monitoring of metal chloride concentrations can therefore provide direct information about the mechanism of the ongoing corrosion scenario and offer valuable information for a timely warning of prospective material failure.

• 한국재료학회지
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• 제34권1호
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• pp.34-43
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• 2024

New piezoelectric and triboelectric materials for energy harvesting are being widely researched to reduce their processing cost and complexity and to improve their energy conversion efficiency. In this study, BaTiO₃ films of various thickness were deposited on Ni foams by R.F. magnetron sputtering to study the piezoelectric and triboelectric properties of the porous spongy structure materials. Then piezoelectric nanogenerators (PENGs) were prepared with spongy structured BaTiO₃ and PDMS composite. The output performance exhibited a positive dependence on the thickness of the BaTiO₃ film, pushing load, and poling. The PENG output voltage and current were 4.4 V and 0.453 ㎂ at an applied stress of 120 N when poled with a 300 kV/cm electric field. The electrical properties of the fabricated PENG were stable even after 5,000 cycles of durability testing. The triboelectric nanogenerators (TENGs) were fabricated using spongy structured BaTiO₃ and various polymer films as dielectrics and operated in a vertical contact separation mode. The maximum peak to peak voltage and current of the composite film-based triboelectric nanogenerator were 63.2 V and 6 ㎂, respectively. This study offers new insights into the design and fabrication of high output nanogenerators using spongy structured materials.

• 한국토양비료학회지
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• 제45권3호
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• pp.393-398
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• 2012

지형 특성에 따른 논토양 화학성변화를 조사하기 위해 전북지역 논 300개 지점에서 토양 물리화학성 및 중금속함량을 조사하였다. 논토양 분포 지형은 곡간 및 선상지 43.0%, 하해혼성평탄지 39.3%, 하성평탄지 15.0%, 홍적대지 2.7% 순이었다. 토양성분별 적정비율은 pH 65.3%, CEC 48.3%, 유효인산 22.3%이었고, 부족비율은 유기물 63.3%, 치환성 $K^+$ 61.3%, $Ca^{2+}$ 51.0%, $Mg^{2+}$ 59.3%, 유효규산 75.7%이었다. 곡간 및 선상지의 논토양 유형은 미숙답과 사질답이 각각 34.4과 33.6%이었고, 하성평탄지는 사질답 57.8%, 하해혼성평탄지는 보통답 47.4%, 홍적대지는 미숙답이 75.7%이었다. 곡간 및 선상지형의 토성은 양토가 53.5%를 차지하고, 하성평 탄지는 사양토 37.8%, 하해혼성평탄지에서는 미사질양토가 55.1%를 차지하고 있었다. 지형에 따라 pH와 유기물함량은 차이가 없었고, 유효인산은 홍적대지에서 224 mg $kg^{-1}$로 적정범위를 초과하였고, 치환성양이온은 곡간 및 선상지에서 $Ca^{2+}$을 제외하고 모두 적정범위에 분포하였다. 유효규산은 112~127 mg $kg^{-1}$ 수준으로 모든 지형에서 적정수준에 미치 지 못하였다. 토양 pH는 유효규산, 치환성 $Ca^{2+}$, $Mg^{2+}$, $Na^+$, CEC, 치환성 $K^+$ 순으로 정의 상관관계, 토양유기물 함량은 CEC, 유효인산, 치환성 $Ca^{2+}$, 유효규산과 정의 상관관계를 보 였다. 논토양의 Cd, Cr, Cu, Ni, Pb, Zn은 토양오염우려기준의 약 10%, As는 약 20~30%수준으로 분포하고 있어 전북지역 논토양은 안전한 것으로 조사되었다.

• 한국환경생태학회지
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• 제26권5호
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• pp.694-706
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• 2012

본 연구는 주남저수지의 수질, 퇴적물, 저서성 무척추대형동물, 어류, 수생식물을 조사 및 분석함으로서 수생태계의 보전과 복원을 위한 기초자료 제공에 그 목적이 있다. 수질분석 결과, 수소이온농도(pH)는 8.2~8.4, 화학적 산소요구량(COD)은 6.0~7.5mg/L, 부유물질량(SS)은 10.0~10.3mg/L, 용존산소량(DO)은 8.3~11.5mg/L, 총인량(T-P)은 0.1mg/L, 총질소량(T-N)은 1.2~1.3mg/L로 나타났다. 퇴적물의 경우 Cd(카드뮴)는 0.47~0.52mg/kg, Cu(구리)는 7.08~7.43 mg/kg, As(비소)는 0.22~0.32mg/kg, Hg(수은)는 0.02~0.03mg/kg, Pb(납)는 6.20~7.45mg/kg, Ni(니켈)는 32.80~39.70mg/kg, F(불소)는 513.0~543.0mg/kg, Zn(아연)은 137.0~140.0mg/kg으로 나타났으며, $Cr^{6+}$(6가크롬)은 검출되지 않았다. 저서성 대형무척추동물은 3문 5강 9목 26과 33속 39종 432개체가 있는 것으로 확인되었으며, 저서성 대형무척추동물의 생태점수(ESB)는 25로 나타났다. 어류는 8과 14종으로 나타났으며, 생태계교란야생동식물은 큰입배스와 파랑볼우럭 등 2분류군이었다. 수생식물은 28과 42속 56종 1아종 6변종 등 총 63분류군으로 확인되었으며, 정수식물은 38분류군(60.3%), 부엽식물은 5분류군(7.9%), 부유식물 및 침수식물은 각 10분류군(15.9%)로 나타났다.