• Corrosion Science and Technology
• /
• v.6 no.3
• /
• pp.103-111
• /
• 2007

The effect of stress factors on the growing process of stress corrosion cracking (SCC) of the sensitized 18-8 stainless steel in high temperature water was investigated using equations of crack growth rate derived from applying electric circuits to SCC corrosion paths. Three kinds of cross sections have to be considered when electric circuit is constructed using total current. The first is ion flow passage area, $S_{sol}$, of solution in crack, the second is total dissolving surface area, $S_{dis}$, of metal on electrode of crack tip and the third is dissolving cross section, $S_{met}$, of metal on grain boundary or in base metal or in welding metal. Stress may affect each area. $S_{sol}$ may depend on applied stress, $\sigma_{\infty}$, related with crack depth. $S_{dis}$ is expressed using a factor of $\varepsilon(K)$ and may depend on stress intensity factor, K only. SCC crack growth rate is ordinarily estimated using a variable of K only as stress factor. However it may be expected that SCC crack growth rate depends on both applied stress $\sigma_{\infty}$ and K or both crack depth and K from this consideration.$\varepsilon(K)$ is expressed as ${\varepsilon}(K)=h_2{\cdot}K^2+h_3{\cdot}K^3$ when $h_{2}$ and $h_{3}$ are coefficients. Also, relationships between SCC crack growth rate, da/dt and K were simulated and compared with the literature data of JBWR-VIP-04, NRC NUREG-0313 Rev.2 and SKIFS Draft. It was pointed out in CT test that the difference of distance between a point of application of force and the end of starter notch (starting point of fatigue crack) may be important to estimate SCC crack growth rate. An anode dissolution current density was quantitatively evaluated using a derived equation.

• Korean Journal of Materials Research
• /
• v.13 no.5
• /
• pp.333-337
• /
• 2003

We report a new fabrication process for carbon nanotube field emitters with high performance. The key of the fabrication process is trim-and-leveling the carbon nanotubes grown in trench structures by employing a planarization process, which leads to a uniform distance from the carbon nanotube tip to the electrode. In order to enable this processing, spin-on-glass liquid is applied over the CNTs grown in trench to have them stubborn adhesion among themselves as well as to the substrate. Thus fabricated emitters reveal an extremely stable emission and aging characteristics with a large current density of 40 ㎃/$\textrm{cm}^2$ at 4.5 V/$\mu\textrm{m}$. The field enhancement factor calculated from the F-N plot is $1.83${\times}$10^{5}$ $cm^{－1}$ , which is a very high value and indicates a superior quality of the emitter originating from the nature of open-tip and high stability of the carbon nanotubes obtained new process.

• Journal of Hydrogen and New Energy
• /
• v.7 no.1
• /
• pp.29-37
• /
• 1996

Alkaline water electrolysis has been commercialized as the only large-scale method for a long time to produce hydrogen and the technology is superior to other methods such as photochemical, thermochemical water splitting, and thermal decomposition method in view of efficiency and related technical problem. However, such conventional electrolyzer do not have high electric efficiency and productivity to apply to large scale hydrogen production for energy or chemical feedstocks. Solid polymer electrolyte water electrolysis using a perfluorocation exchange membrane as an $H^+$ ion conductor is considered to be a promising method, because of capability for operating at high current densities and low cell voltages. So, this is a good technology for the storage of electricity generated by photovoltaic power plants, wind generators and other energy conversion systems. One of the most important R&D topics in electrolyser is how to minimize cell voltage and maximize current density in order to increase the productivity of the electrolyzer. A commercialized technology is the hot press method which the film type electrocatalyst is hot-pressed to soild polymer membrane in order to eliminate the contact resistance. Various technologies, electrocatalyst formed over Nafion membrane surface by means of nonelectrolytic plating process, porous sintered metal(titanium powder) or titanium mesh coated with electrocatalyst, have been studied for preparation of membrane-electrocatalyst composites. In this study some experiments have been conducted at a solid polymer electrolyte water electrolyzer, which consisted of single cell stack with an electrode area of $25cm^2$ in a unipolar arrangement using titanium mesh coated with electrocatalyst.

• Journal of Electrochemical Science and Technology
• /
• v.2 no.2
• /
• pp.110-115
• /
• 2011

The effect of $TiO_2$ nanotube (TNT) and nanoparticle (TNP) composite photoelectrode and the role of TNT to enhance the photo conversion efficiency in dye-sensitized solar cell (DSSC) have investigated in this study. Results demonstrated that the increase of the TNT content (1-15 %) into the electron collecting TNP film increases the open-circuit potential ($V_{oc}$) and short circuit current density ($J_{sc}$). Based on the impedance analysis, the increased $V_{oc}$ was attributed to the suppressed recombination between electrode and electrolyte or dye. Photochemical analysis revealed that the increased Jsc with the increased TNT content was due to the scattering effect and the reduced electron diffusion path of TNT. The highest $J_{sc}$ (12.6 mA/$cm^2$), Voc (711 mV) and conversion efficiency (5.9%) were obtained in the composite photoelectrode with 15% TNT. However, $J_{sc}$ and $V_{oc}$ was decreased for the case of 20% TNT, which results from the significant reduction of adsorbed dye amount and the poor attachment of the film on the fluorine-doped tin oxide (FTO). Therefore, application of this composite photoelectrode is expected to be a promising approach to improve the energy conversion efficiency of DSSC.

• The Korean Journal of Ceramics
• /
• v.3 no.4
• /
• pp.263-268
• /
• 1997

RuO$_3$ thin films were deposited on Si(100) substrate at low temperatures by hot-wall metalorganic chemical vapor deposition. Bis(cyclopentadienyl) ruthenium, Ru$(C_5H_5)_2$, was used as the precursor RuO$_2$single phase was obtained at a low deposition temperature of 25$0^{\circ}C$ and the crystallinity of RuO$_2$thin films improved with increasing deposition temperature. RuO$_2$thin films grow perpendicularly to the substrate and show the columnar structure. The grain size of RuO$_2$films drastically increases with increasing the deposition temperature. The resistivity of the 180 nm-thick RuO$_2$thin films deposited at 27$0^{\circ}C$ was 136 $\mu$$\Omega$-cm and increased with decreasing film thickness. SrBi$_2Ta_2O_4$ thin films deposited by rf magnetron sputtering on the RuO$_2$bottom electrodes showed a fatigue-free characteristics up to ~10$^10$ cycles under 5 V bipolar square pulses and the remanent polarization, 2 P$_r$ and the coercive field, 2 E, were 5.2$\mu$C/$\textrm{cm}^2$ and 76.0 kV/cm, respectively, for an applied voltage of 5 V The leakage current density was about 7.0$\times$10$^{-6}$ A/$\textrm{cm}^2$ at 150 kV/cm.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.18 no.12
• /
• pp.1133-1138
• /
• 2005

In this study, we have prepared, as the pluse power source, a commercially supplied Li-ion battery with a capacity of 700 mAh and AC resistivity of 60 md at 1 kHz and nonaqeous asymmetric hybrid capacitor composed of an activated carbon cathode and MCMB anode, and have examined the electrochemical characteristics of hybrid capacitor and the pulse performances of parallel connected hybrid capacitor/Li-ion battery source. The nonaqueous asymmetric hybrid capacitors constituted with each stack number of pairs composed of the cathode, the porous separator and the anode electrode were housed in Al-laminated film cell. The 10 stacked hybrid capacitor, which was charged and discharged at a constant current at 0.25 $mA/cm^2$ between 3 and 4.3 V, has exhibited the capacitance of 108F and the lowest equivalent series resistance was 32 $m{\Omega}$ at 1 kHz. On the other hand, the enhanced run time of Li-ion battery assisted by the hybrid capacitor was obtained with increasing of current density and pulse width in Pulse mode. The best improvement, $84\;\%$ for hybrid capacitor/Li-ion battery was obtained in the condition of a 7C-rate pulse (100 msec)/0.5C-rate standby/$10\;\%$ duty cycle.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2003.07b
• /
• pp.624-627
• /
• 2003

The BLT thin-films were one of the promising ferroelectric materials with a good leakage current and degradation behavior on Pt electrode. The BLT target was sintered at $1100^{\circ}C$ for 4 hours at the air ambient. $Bi_{3.25}La_{0.75}Ti_3O_{12}$ (BLT) thin-film deposited on $Pt/Ti/SIO_2/Si$ wafer by rf magnetron sputtering method. At annealed $700^{\circ}C$, (117) and (006) peaks appeared the high intensity. The hysteresis loop of the BLT thin films showed that the remanent polarization ($2Pr=Pr^+-Pr^-$) was $16uC/cm^2$ and leakage current density was $1.8{\times}10^{-9}A/cm^2$ at 50 kV/cm with coersive electric field when BLT thin-films were annealed at $700^{\circ}C$. Also, the thin film showed fatigue property at least up to $10^{10}$ switching bipolar pulse cycles under 7 V. Therefore, we induce access to optimum fabrication condition of memory device application by rf-magnetron sputtering method in this report.

• Journal of the Korean Ceramic Society
• /
• v.44 no.10
• /
• pp.589-595
• /
• 2007

Physical properties of sputtered YSZ thin film electrolytes on anode thin film by spray pyrolisis has been investigated to realize the porous electrode and dense electrolyte multilayer structure for micro solid oxide fuel cells. It is shown that for better crystallinity and density, YSZ need to be deposited at an elevated temperature. However, if pure NiO anode was used for high temperature deposition, massive defects such as spalling and delamination were induced due to high thermal expansion mismatch. By changing anode to NiOCGO composite, defects were significantly reduced even at high deposition temperature. Further research on realization of full cells by processing hybridization and cell performance characterization will be performed in near future.

• Journal of the Korean Ceramic Society
• /
• v.47 no.6
• /
• pp.638-642
• /
• 2010

The spinel material $Li_4Ti_5O_{12}$ has attracted considerable attention as an anode electrode material for many battery applications owing to its light weight and high energy density. However, the real capacity of $Li_4Ti_5O_{12}$ powder as determined by the solid-state method is lower than the ideal capacity. In this study, we investigated the effect of the dopants in M-doped spinel $Ba_xLi_{4-2x}Ti_5O_{12}$(x=0.005, 0.05, 0.1) powders prepared by the solid-state reaction method and used as the anode material in lithiumion batteries. The results confirmed the effect of the Ba and Sr dopants on the powder properties of the spinel $Li_4Ti_5O_{12}$, which exhibited a pure spinel structure without any secondary phase in its XRD pattern. Moreover, the electrochemical properties of the spinel M-LTO materials were investigated using a half cell. The electrochemical data show that cells with anodes made of undoped $Li_4Ti_5O_{12}$ and Ba- and Sr-doped $Li_4Ti_5O_{12}$ have discharge capacities of 97, 130, and 112 mAh/g, respectively, at the first cycle. Moreover, the Ba- and Sr-doped spinel $Li_4Ti_5O_{12}$ demonstrated good properties in the mid-voltage range at 1.55 V, showing stable cyclic voltammogram properties which surpassed those of the same material without Ba or Sr at 1 C after 100 cycles.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2008.11a
• /
• pp.67-67
• /
• 2008

Application of organic materials with low cost, easy fabrication and advantages of flexible device are increasing attention by research work. Recently, one of them, organic solar cells were rapidly increased efficiency with regioregular poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61-butyricacidmethylester (PCBM) used typical material. To increased efficiency of organic solar cell has tried control of domain of PCBM and crystallite of P3HT by thermal annealing and solvent vapor annealing. [4-6] In those annealing effects, be made inefficiently efficiency, which is increased fill factor (FF), and current density by phase-separated morphology with blended P3HT and PCBM. In addition, increased conductivity by modified hole transfer layer (HTL) such as Poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS), increased both optical and conducting effect by titanium oxide (TiOx), and changed cathode material for control work function were increased efficiency of Organic solar cell. In this study, we had described effect of organic photovoltaics by conductivity of interlayer such as PEDOT:PSS and TCO (Transparent conducting oxide) such as ITO, which is used P3HT and PCBM. And, we have measured with exactly defined shadow mask to study effect of solar cell efficiency according to conductivity of hole transfer layer.