• E2M - 전기 전자와 첨단 소재
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• 제7권3호
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• pp.187-199
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• 1994

In order to find an effect of structural changes due to variation of addition ratio of anhydride hardener and postcuring herat-treatments upon electrical properties of epoxy composites, the dielectric properties over a frequency range from 30[Hz] to l[MHz] were investigated in the temperature range of 20-180[.deg. C]. From the dielectric properties, the a peaks related with glass-transition phenomena of epoxy network appeared near 130[.deg. C], the conduction loss in high temperature region above 150[.deg. C] due to thermal dissociation of hardener started off with the low frequency side and the .betha. peak concerned with contribution of movable unreacted terminal epoxy groups and curing agents in the glass states concurred with the high-frequency side below 20[.deg. C]. And an effect of an hydride hardener upon structural changes and of postcuring heat treatments upon structural stability in epoxy composites would be explained through the estimation of the distribution of relaxation times and the activation energy for a .alpha. peak according to the WLF equations.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2006년도 하계학술대회 논문집 Vol.7
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• pp.232-233
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• 2006

In recent years the interest in organic/inorganic hybrid materials has increased at a fast rate. Nano organic-inorganic hybrid composites have shown advantages for preparing hard coating layers. Especially, nano hybrid composite has low environmental pollution. It has high transparency, hardness, toughness, thermal dissociation temperature, hydrophobicity by using nano sized inorganic material. There are many ways in which these materials may be synthesized, a typical one being the use of silica and silanes using the sol-gel process. The structure of sol-gel silica evolves as a result of these successive hydrolysis and condensation reactions and the subsequent drying and curing. The sol-gel reactions are catalyzed by acids and produce silica sol solutions. The silica sol grows until they reach a size where a gel transition occurs and a solid-like gel is formed. Colloidal silica(CS)/silane sol solutions were synthesized in variation with parameters such as different acidity and reaction time. In order to understand their physical and chemical properties, sol-gel coating films were fabricated on glass. From all sol-gel solutions, seasoning effect of sol-gel coating layer on glass was observed.

• Bulletin of the Korean Chemical Society
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• 제19권8호
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• pp.830-835
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• 1998

The characteristics of the ablation plume generated by 532 nm Nd: YAG laser irradiation of a Pb(Zr0.52Ti0.48)O3 (PZT) target have been investigated using a pulsed-field time-of-flight mass spectrometer (TOFMS). The relative abundance of O+, Ti+, Zr+, Pb+, TiO+, and ZrO+ ions has been measured and discussed. TiO+ and ZrO+ ions were also found to be particularly stable within the laser ablation plasma with respect to PbO+ species. The behavior of the temporal distributions of each ionic species was studied as a function of the delay time between the laser shot and the ion extraction pulse. The most probable velocity of each ablated ion is estimated to be Vmp=1.1-1.6x 105 cm/s at a laser fluence of 1.2 J/cm2, which is typically employed for the thin film deposition of PZT. The TOF distribution of Ti+ and Zr+ ions shows a trimodal distribution with one fast and two slow velocity components. The fast velocity component (6.8x 10' cm/s) appears to consist of directly ablated species via nonthermal process. The second component, originated from the thermal evaporation process, has a characteristic velocity of 1.4-1.6 x 105 cm/s. The slowest component (1.2 x 105 cm/s) is composed of a dissociation product formed from the corresponding oxide ion.

• Bulletin of the Korean Chemical Society
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• 제35권5호
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• pp.1479-1484
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• 2014

Based on the full optimized molecular geometric structures at B3LYP/cc-pvtz method, a new designed compound, 4,6,8-trinitro-4,5,7,8-tetrahydro-6H-furazano[3,4-f ]-1,3,5-triazepine was investigated in order to look for high energy density compounds (HEDCs). The analysis of the molecular structure indicates that the seven-membered ring adopts chair conformation and there exist intramolecular hydrogen bond interactions. IR spectrum and heat of formation (HOF) were predicted. The detonation velocity and pressure were evaluated by using Kamlet-Jacobs equations based on the theoretical density and condensed HOF. The bond dissociation energies and bond orders for the weakest bonds were analyzed to investigate the thermal stability of the title compound. The results show that $N_1-N_6$ bond is the trigger bond. The crystal structure obtained by molecular mechanics belongs to $Pna2_1$ space group, with lattice parameters Z = 4, a = 15.3023 ${\AA}$, b = 5.7882 ${\AA}$, c = 11.0471 ${\AA}$, ${\rho}=2.06gcm^{-3}$. In addition, the analysis of frontier molecular orbital shows the title compound has good stability and high chemical hardness.

• 한국진공학회지
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• 제9권4호
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• pp.335-340
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• 2000

코발트실리사이드형성에 있어서 Capping layer로써의 Ti의 역할에 대한 연구를 수행하였다. 실리콘 산화막이 제거된 Si(100)기판과 $H_2SO_4$에 의한 chemical oxide를 형성한 Si(100)기판 위에 Co와 Ti를 증착한 후 열처리 온도 증가에 따른 계면반응과 상변화 등의 미세구조와 면저항 특성의 변화를 four point prove, XRD, TEM, SIMS등의 분석을 통하여 TiN capping, capping layer가 없는 경우에 대하여 비교하였다. 실리콘 산화막이 제거된 Si 기판 상에서 Ti capping의 경우 TiN capping, capping layer가 없는 경우보다 높은 온도에서 $CoSi_2$상이 형성되었으며, chemical oxide가 형성된 Si 기판 상에서는 Ti capping의 경우 코발트 실리사이드 박막을 형성 할 수 있었다. 이것은 capping layer인 Ti가 1차 RTA(Rapid Thermal Annealing)동안 Si 기판 방향으로 확산 침투하여 Co와 Si 사이에 존재하는 실리콘 산화막을 분해하는 역할을 하기 때문이다.

• Journal of Microbiology and Biotechnology
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• 제22권6호
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• pp.818-825
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• 2012

Keratinases are exciting keratin-degrading enzymes; however, there have been relatively few studies on their immobilization. A keratinolytic protease from Chryseobacterium sp. kr6 was purified and its partial sequence determined using mass spectrometry. No significant homology to other microbial peptides in the NCBI database was observed. Certain parameters for immobilization of the purified keratinase on chitosan beads were investigated. The production of the chitosan beads was optimized using factorial design and surface response techniques. The optimum chitosan bead production for protease immobilization was a 20 g/l chitosan solution in acetic acid [1.5% (v/v)], glutaraldehyde ranging from 34 g to 56 g/l, and an activation time between 6 and 10 h. Under these conditions, above 80% of the enzyme was immobilized on the support. The behavior of the keratinase loading on the chitosan beads surface was well described using the Langmuir model. The maximum capacity of the support ($q_m$) and dissociation constant ($K_d$) were estimated as 58.8 U/g and 0.245 U/ml, respectively. The thermal stability of the immobilized enzyme was also improved around 2-fold, when compared with that of the free enzyme, after 30 min at $65^{\circ}C$. In addition, the activity of the immobilized enzyme remained at 63.4% after it was reused five times. Thus, the immobilized enzyme exhibited an improved thermal stability and remained active after several uses.

• Bulletin of the Korean Chemical Society
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• 제34권1호
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• pp.95-98
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• 2013

The photoluminescence (PT) properties of Al-doped ZnO thin films grown by the sol-gel dip-coating method have been investigated. At 12 K, nine distinct PL peaks were observed at 2.037, 2.592, 2.832, 3.027, 3.177, 3.216, 3.260, 3.303, and 3.354 eV. The deep-level emissions (2.037, 2.592, 2.832, and 3.027 eV) were attributed to native defects. The near-band-edge (NBE) emission peaks at 3.354, 3.303, 3.260, 3.216, and 3.177 eV were attributed to the emission of the neutral-donor-bound excitons ($D^0X$), two-electron satellite (TES), free-to-neutral-acceptors (e,$A^0$), donor-acceptor pairs (DAP), and second-order longitudinal optical (2LO) phonon replicas of the TES (TES-2LO), respectively. According to Haynes' empirical rule, we calculated the energy of a free exciton (FX) to be 3.374 eV. The thermal activation energy for $D^0X$ in the nanocrystalline ZnO thin film was found to be ~25 meV, corresponding to the thermal dissociation energy required for $D^0X$ transitions.

• 공업화학
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• 제10권1호
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• pp.35-40
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• 1999

Hard segment 함량이 35%와 53%로 서로 다른 두 개의 열가소성 폴리우레탄 시료 (각각 TPU-35와 TPU-35)와 이들을 70/30, 50/50, 30/70 wt%로 용융 블렌딩한 조성들이 annealing 온도와 시간에 따라 변화할 수 있는 유리전이온도와 용융피이크, 분자량 및 분자량 분포도의 변화를 관찰하였다. TPU의 $T_g$는 hard segment 함량이 많을수록 높은 값을 보였으며 annealing 온도와 시간에 따라 hard microdomain 구조의 미약한 관계에 의한 용융피이크의 크기와 온도 등이 변하였다. 이는 annealing에 의한 열이 long-range 혹은 short-range segmental motion의 거동, 비결정 microphase 구조의 order-disorder 전이, domain의 크기 및 결정구조의 질서도 등 여러 가지 복합적인 영향을 끼친 결과로 사료된다. 미세 결정의 용융 결과로 나타나는 $T_3$단일 피이크만이 존재하는 annealing 온도는 TPU-35, TPU-44와 TPU-53에 대해 각각 130, 170 및 $180^{\circ}C$이었다. Annealing 온도와 시간에 따른 분자량 및 분자량 분포도 변화 측정에서 TPU-35는 $135^{\circ}C$에서, TPU-44(TPU-35/TPU-53=50/50 블랜드)는 $170^{\circ}C$, 그리고 TPU-53은 $180^{\circ}C$에서 수평균 및 중량평균 분자량의 증가와 더불어 polydispersity(PI)는 감소를 보였다. 이 변화는 같은 조건의 annealing 온도에 따른 용융피이크 변화에서 $T_3$단일 피이크만 남게 되는 annealing온도와 일관성을 보이고 있는데, 이는 이들 시료가 특정한 annealing 온도에서 chain dissociation과 recombination이 동시에 일어나므로써 빚어진 결과로 추측된다.

• 방사성폐기물학회지
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• 제7권4호
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• pp.207-212
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• 2009

본 연구에서는 산화조건하 LiCl-KCl 공융염내에서 란탄계 염화물의 하나인 $PrCl_3$의 열적거동을 살펴보았다. 먼저 산소를 주입하면서 $PrCl_3$의 열중량분석(TGA; thermogravimetric analysis)을 실시하였고, 이 때 얻어진 결과들을 바탕으로, 산소분산법을 이용하여 온도에 따른 LiCl-KCl 공융염내 $PrCl_3$의 산화실험을 수행하였다. $PrCl_3$의 열중량분석 결과에 따르면, 약 $380^{\circ}C$까지 $PrCl_3$에서 염소의 해 리가 급격하게 발생되었고 약 $600^{\circ}C$에서 $PrCl_3$가 PrOCl로 전환되는 반응이 종료되는 것으로 확인되었다. 산소분산법에 의한 LiCl-KCl 공융염내 $PrCl_3$의 열적거동은 산화조건에서 열중량분석시 나타난 $PrCl_3$의 열적거동과 유사하였고, 발생된 PrOCl은 공융염내에서 불용성 화합물로써 바닥으로 침전하였다. 산소분산법에 의한 공융염내 $PrCl_3$의 PrOCl로의 전환은 $650^{\circ}C$ 이상의 온도에서 활발하게 진행되었고, 이 때 발생되는 배기가스내 $Cl_2$의 농도분석을 통해 공융염내 $PrCl_3$의 전환상태를 예측할 수 있을 것으로 판단된다.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2011년도 제40회 동계학술대회 초록집
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• pp.407-408
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• 2011

Natural boron consists of two stable isotopes 10B and 11B with natural abundance of 18.8 atom percent of 10B and 81.2 atom percent of 11B. The thermal neutron absorption cross-section for 10B and 11B are 3837 barn and 0.005 barn respectively. 10B enriched specific compounds are used for control rods and as a reactor coolant additives. In this work 2 methods for boron enrichment were analysed: 1) Gas irradiation in static conditions. Dissociation occurs due to multiphoton absorption by specific isotopes in appropriately tuned laser field. IR shifted laser pulses are usually used in combination with increasing the laser intensity also improves selectivity up to some degree. In order to prevent recombination of dissociated molecules BCl3 is mixed with H2S 2) SILARC method. Advantages of this method: a) Gas cooling is helpful to split and shrink boron isotopes absorption bands. In order to achieve better selectivity BCl3 gas has to be substantially rarefied (~0.01%-5%) in mixture with carrier gas. b) Laser intensity is lower than in the first method. Some preliminary calculations of dissociation and recombination with carrier gas molecules energetics for both methods will be demonstrated Boron separation in SILARC method can be represented as multistage process: 1) Mixture of BCl3 with carrier gas is putted in reservoir 2) Gas overcooling due to expansion through Laval nozzle 3) IR multiphoton absorption by gas irradiated by specifically tuned laser field with subsequent gradual gas condensation in outlet chamber It is planned to develop software which includes these stages. This software will rely on the following available software based on quantum molecular dynamics in external quantized field: 1) WavePacket: Each particle is treated semiclassicaly based on Wigner transform method 2) Turbomole: It is based on local density methods like density of functional methods (DFT) and its improvement- coupled clusters approach (CC) to take into account quantum correlation. These models will be used to extract information concerning kinetic coefficients, and their dependence on applied external field. Information on radiative corrections to equation of state induced by laser field which take into account possible phase transition (or crossover?) can be also revealed. This mixed phase equation of state with quantum corrections will be further used in hydrodynamical simulations. Moreover results of these hydrodynamical simulations can be compared with results of CFD calculations. The first reasonable question to ask before starting the CFD simulations is whether turbulent effects are significant or not, and how to model turbulence? The questions of laser beam parameters and outlet chamber geometry which are most optimal to make all gas volume irradiated is also discussed. Relationship between enrichment factor and stagnation pressure and temperature based on experimental data is also reported.