• Proceedings of the Materials Research Society of Korea Conference
• /
• 2012.05a
• /
• pp.70.1-70.1
• /
• 2012

In-situ X-ray photoelectron spectroscopy (XPS) and infrared (IR) spectroscopy studies of SOFC cathode materials will be discussed in this presentation. The mixed conducting perovskites (ABO3) containing rare and alkaline earth metals on the A-site and a transition metal on the B-site are commonly used as cathodes for solid oxide fuel cells (SOFC). However, the details of the oxygen reduction reaction are still not clearly understood. The information about the type of adsorbed oxygen species and their concentration is important for a mechanistic understanding of the oxygen incorporation into these cathode materials. XPS has been widely used for the analysis of adsorbed species and surface structure. However, the conventional XPS experiments have the severe drawback to operate at room temperature and with the sample under ultrahigh vacuum (UHV) conditions, which is far from the relevant conditions of SOFC operation. The disadvantages of conventional XPS can be overcome to a large extent with a "high pressure" XPS setup installed at the BESSY II synchrotron. It allows sample depth profiling over 2 nm without sputtering by variation of the excitation energy, and most importantly measurements under a residual gas pressure in the mbar range. It is also well known that the catalytic activity for the oxygen reduction is very sensitive to their electrical conductivity and oxygen nonstoichiometry. Although the electrical conductivity of perovskite oxides has been intensively studied as a function of temperature or oxygen partial pressure (Po2), in-situ measurements of the conductivity of these materials in contact with the electrolyte as a SOFC configuration have little been reported. In order to measure the in-plane conductivity of an electrode film on the electrolyte, a substrate with high resistance is required for excluding the leakage current of the substrate. It is also hardly possible to measure the conductivity of cracked thin film by electrical methods. In this study, we report the electrical conductivity of perovskite $La_{0.6}Sr_{0.4}CoO_{3-{\delta}}$ (LSC) thin films on yttria-stabilized zirconia (YSZ) electrolyte quantitatively obtained by in-situ IR spectroscopy. This method enables a reliable measurement of the electronic conductivity of the electrodes as part of the SOFC configuration regardless of leakage current to the substrate and cracks in the film.

• Nuclear Engineering and Technology
• /
• v.48 no.4
• /
• pp.847-858
• /
• 2016

An overview is given on the work of the Laboratory of Nuclear Energy Systems at ETH, Zurich (ETHZ) and of the Laboratory of Thermal Hydraulics at Paul Scherrer Institute (PSI), Switzerland on tight-lattice bundles. Two-phase flow in subchannels of a tight triangular lattice was studied experimentally and by computational fluid dynamics simulations. Two adiabatic facilities were used: (1) a vertical channel modeling a pair of neighboring sub-channels; and (2) an arrangement of four subchannels with one subchannel in the center. The first geometry was equipped with two electrical film sensors placed on opposing rod surfaces forming the subchannel gap. They recorded 2D liquid film thickness distributions on a domain of $16{\times}64$ measuring points each, with a time resolution of 10 kHz. In the bubbly and slug flow regime, information on the bubble size, shape, and velocity and the residual liquid film thickness underneath the bubbles were obtained. The second channel was investigated using cold neutron tomography, which allowed the measurement of average liquid film profiles showing the effect of spacer grids with vanes. The results were reproduced by large eddy simulation + volume of fluid. In the outlook, a novel nonadiabatic subchannel experiment is introduced that can be driven to steady-state dryout. A refrigerant is heated by a heavy water circuit, which allows the application of cold neutron tomography.

• Korean Journal of Materials Research
• /
• v.8 no.6
• /
• pp.526-531
• /
• 1998

A hydride vapor phase epitaxy (HVPE) method was performed to grow the $10~240\mu{m}$ thick GaN films on (111) spinel $MgAl_2O_4$ substrate. The GaN films on $MgAl_2O_4$ substrate revealed a photoluminescence (PL) characteristics of the impurity doped GaN by the out-diffusion and auto-doping of Mg from $MgAl_2O_4$ substrate during GaN growth. The PL spectrum measured at 10K consists of free and bound excitons related recombination transitions and impurity-related donor-acceptor pair recombination and its phonon replicas. However, the deep-level related yellow band emission was not observed. The peak energy of neutral donor bound excitonic emission and the frequency of Raman $E_2$ mode were exponentially decreased with increasing the GaN thicknesses. and the frequency of E, Raman mode was shifted with the relation of $\Delta$$\omega$=3.93$\sigma$($cm^{-1}$/GPa), where l1 (GPa) is the residual strain in the GaN epilayers.

• Journal of Powder Materials
• /
• v.20 no.3
• /
• pp.197-202
• /
• 2013

A novel route to prepare Nd-Fe-B magnetic particles by utilizing both spray drying and reduction/diffusion processes was investigated in this study. Precursors were prepared by spray drying method using the aqueous solutions containing Nd salt, Fe salt and boric acid with stoichiometric ratios. Precursor particles could be obtained with various sizes from 2 to $10{\mu}m$ by controlling concentrations of the solutions and the average size of $2{\mu}m$ of precursors were selected for further steps. After heat treatment of precursors in air, Nd and Fe oxides were formed through desalting procedure, followed by reduction processes in Hydrogen ($H_2$) atmosphere and with Calcium (Ca) granules in Argon (Ar) successively. Moreover, diffusion between Nd and Fe occurred during Ca reduction and $Nd_2Fe_{14}B$ particles were formed. With Ca amount added to particles after $H_2$ reduction, intrinsic coercivity was changed from 1 to 10 kOe. In order to remove and leach CaO and residual Ca, de-ionized water and dilute acid were used. Acidic solutions were more effective to eliminate impurities, but Fe and Nd were dissolved out from the particles. Finally, $Nd_2Fe_{14}B$ magnetic particles were synthesized after washing in de-ionized water with a mean size of $2{\mu}m$ and their maximum energy product showed 9.23 MGOe.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.19 no.6
• /
• pp.1-9
• /
• 2015

Transverse steel bars are used in the plastic hinge zone of columns to insure adequate confinement, prevention of longitudinal bar buckling and ductile behavior. Fabrication and placement of rectangular hoops and cross-ties in columns are difficult to construct. Details of reinforcement for rectangular section require a lot of rectangular hoops and cross-ties. In this paper, to solve these problems, the new lateral confinement method using oblong hoop is proposed for the transverse confinement of the flared column. It can be the alternative for oblong cross-section and flared column with improved workability and cost-efficiency. The final objectives of this study are to suggest appropriate oblong hoop details and to provide quantitative reference data and tendency for seismic performance or damage assessment based on the drift levels such as residual deformation, elastic strain energy. This paper describes factors of seismic performance such as ultimate displacement/drift ratio, displacement ductility, response modification factor, equivalent viscous damping ratio and effective stiffness.

• Journal of the Institute of Electronics Engineers of Korea TC
• /
• v.45 no.7
• /
• pp.62-66
• /
• 2008

In this paper we have proposed a power aware location based routing protocol for wireless ad hoc network. The existing greedy perimeter stateless routing (GPSR) has some problems which are certain node overloaded and void situation. The proposed power aware greedy perimeter stateless routing (PAGPSR) protocol gives a solution for these problems in GPSR. PAGPSR uses power aware and geographically informed neighbor selection to route a packet towards the destination. It also gives a solution for the fundamental problem in geographical routing called communication void. It considers residual energy of battery and distance to the destination for the next hope node selection. When it encounters a void it starts limited-flooding to select next hop node. To evaluate the performance of our protocol we simulated PAGPSR in ns-2. Our simulation results show that our protocol achieves longer network lifetime compared with greedy perimeter stateless routing (GPSR).

• Proceedings of the Korean Vacuum Society Conference
• /
• 1999.07a
• /
• pp.154-154
• /
• 1999

금속산화막은 전자부품 및 광학적 응용에 널리 사용되고 있다. 특히 알루미늄의 산화막은 유전체의 재료로 커패시터에 많이 사용되고 있다. 이러한 알루미늄 산화막을 plasma를 이용한 ion plating에 의해 형성하였다.Activated Reactive Evaporation은 화합물의 증착율을 높이는데 좋은 증착법이다. 이러한 증착법에는 reactive ion plating와 ion-assisted deposition 그리고 ion beam sputtering 등이 있다. 본 연구에서는 알루미늄 산화막을 증착시키기 위해 plasma를 이용한 electron-beam법을 사용하였다. Turbo molecular pump로 챔버 내의 진공을 약 10-7torr까지 낸린 후 5$\times$10-5torr까지 O2와 Ar을 주입시켰다. 각 기체의 분압은 RGA(residual gas analyzer)로 조사하여 일정하게 유지시켰다. plasma를 발생시키기 위해 filament에서 열전자를 방출시키고 1kV 정도의 electrode에 의해 가속시켜 이들 기체들과 반응시켜 plasma를 발생시켰다. 금속 알루미늄을 5kV정도의 고전압과 90mA의 전류로 electron beam에 의해 증발시켰다. 기판의 흡착율을 높ㅇ기 위해 기판에 500V로 bias 전압을 걸어 주었다. 증발된 금속 알루미늄 증기들이 plasmaso의 산소 이온들과 활성 반응을 이루어 알루미늄 기판 위에 Al2O3막을 형성하였다. 알루미늄 산화막을 분석하기 위해 XPS(X-ray Photoelectron Spectroscopy)로 화학적 조성을 조사하였는데, 알루미늄의 2p전자의 binding energy가 76.5eV로 측정되었다. 이는 대부분 증착된 알루미늄이 산소 이온과 반응하여 Al2O3로 형성된 것이다. SEM(Scanning electron Microscopy)과 AFM(Atomim Force microscopy)으로 증착박 표면의 topology와 roughness를 관찰하였다. grain의 크기는 10nm에서 150nm이었고 증착막의 roughness는 4.2nm이었다. 그리고 이 산화막에 전극을 형성하여 유전 상수와 손실률 등을 측정하였다. 이와 같이 plasma를 이용한 3-beam에 의한 증착은 금속의 산화막을 얻는데 유용한 기술로 광학 재료 및 유전 재료의 개발 및 연구에 많이 사용될 것으로 기대된다.

• Journal of Microbiology and Biotechnology
• /
• v.26 no.6
• /
• pp.1067-1076
• /
• 2016

The gene encoding lipase (Lip98) from Aeromicrobium sp. SCSIO 25071 was cloned and functionally expressed in Escherichia coli. Lip98 amino acid sequence shares the highest (49%) identity to Rhodococcus jostii RHA1 lipase and contains a novel motif (GHSEG), which is different from other clusters in the lipase superfamily. The recombinant lipase was purified to homogeneity with Ni-NTA affinity chromatography. Lip98 showed an apparent molecular mass of 30 kDa on SDS gel. The optimal temperature and pH value for enzymatic activity were recorded at 30℃ and 7.5, respectively. Lip98 exhibited high activity at low temperatures with 35% maximum activity at 0℃ and good stability at temperatures below 35℃. Its calculated activation energy was 4.12 kcal/mol at the low temperature range of 15-30℃. Its activity was slightly affected by some metal ions such as K⁺, Ca²⁺, and Na⁺. The activity of Lip98 was increased by various organic solvents such as DMSO, ethanol, acetone, and hexane with the concentration of 30% (v/v) and retained more than 30% residual activity in neat organic solvent. The unique characteristics of Lip98 imply that it is a promising candidate for industrial application as a nonaqueous biocatalyst and food additive.

• Journal of the Korean institute of surface engineering
• /
• v.41 no.3
• /
• pp.121-128
• /
• 2008

High strength 7xxx aluminum alloys have been applied to automotive bump back beam of the some limited model for light weight vehicle. The aluminum bump back beam is manufactured through extrusion, bending and welding. The residual stress given on these processes combines with the corrosive atmosphere on the road spreaded with corrosive chemicals to melt snow to occur the stress corrosion cracking. The composition of commercial 7xxx aluminum has Zn/Mg ratio about 3 and Cu over 2 wt% for better strength and stress corrosion cracking resistivity. But this composition isn't adequate for appling to the automotive bump back beam with high resistance to extrusion and bad weldability. In this study the composition of 7xxx aluminum alloy was modified to high Zn/Mg ratio and low Cu content for better extrusion and weldability. To estimate the resistivity against stress corrosion cracking of this aluminum alloy by slow strain rate test, the corrosion atmosphere and strain rate separate the stress corrosion cracking from conventional corrosion must be investigated. Using 0.6 Mol NaCl solution on slow strain rate test the stress corrosion cracking induced fracture was not observed. By adding 0.3% $H_2O_2$ and 0.6M $Na_2SO_4$ to 1M NaCl solution, the corrosion potential and current density of polarization curve moved to active potential and larger current density, and on the slow strain rate test the fracture energy in solution was lower than that in pre-exposure. These mean the stress corrosion cracking induced fracture can be estimated in this 1M NaCl + 0.3% $H_2O_2$ + 0.6M $Na_2SO_4$ solution. When the strain rate was below $2{\times}10^{-6}$, the stress corrosion cracking induced fracture start to be observed.

• Macromolecular Research
• /
• v.11 no.1
• /
• pp.9-13
• /
• 2003

Poly (vinylidene fluoride) (PVDF) samples were implanted by using high energy (MeV)F$^{2+}$ and Cl$^{2+}$ ions. We observed that AC dielectric constant of the ion-implanted PVDF samples decreased from 10.5 to 2.5 at 1 kHz as the ion dosage increased from 10$^{11}$ to 3 $\times$ 10$^{14}$ ions/$\textrm{cm}^2$. From differential scanning calorimetry experiments, we observed that PVDF samples become more disordered state through the ion implantation. The decrease of the number of bonding of C-H and C-F and the increase of unsaturated bonding were observed from X-ray photoelectron spectroscopy experiments. The emission of HF and H$_2$ molecules during the ion implantation was detected by residual gas analyzer spectrum. Based upon the results, we analyzed that the low AC dielectric constant of the MeV ion-implanted PVDF samples originated from the reduction of polarization due to the structural change of the CF$_2$ molecules in the MeV ion-implanted PVDF samples.les.