• Journal of Welding and Joining
• /
• v.18 no.2
• /
• pp.105-111
• /
• 2000

The hydrogen attack characteristics of 3Cr-1Mo-V steel as simulated weld heat affected state were studied in this paper. The hydrogen attack susceptibility was evaluated by the ratios of Charpy impact absorbed energy at 0℃({TEX}$vE_{0} {HA}_/vE_{0}${/TEX}) and reduction of area by tensile test({TEX}$RA_{HA}/RA${/TEX}) before and after exposure to hydrogen at 600℃ under 450kgf/㎠ for 300hr. The values of {TEX}$vE_{0} {HA}_/vE_{0}${/TEX} and {TEX}$RA_{HA}/RA${/TEX} were aggravated as the peak temperature of the simulated heat affected zone(HAZ) raised. These results were due to the increase of the possession of bubbles along the grain boundaries, which were resulted in the reduction of grain boundary area to be precipitated carbides due to grain coarsening and the carbon dissolved in the martensite-austenite constituent near by the prior austenite grain boundary. The possession ratio of methane bubbles formed along prior austenite grain boundaries were increased with raising the peak temperature.

• Transactions of the Korean hydrogen and new energy society
• /
• v.12 no.1
• /
• pp.39-50
• /
• 2001

Vanadium based solid solution alloys have been studied as a potential negative electrode of Ni/MH battery due to their high hydrogen storage capacity. In order to improve the kinetic property of V-Ti alloy in KOH electrolyte, the ball-milling process with Ni, which has a catalytic effect of hydrogen absorption/desorption, was carried out to modify the surface properties of V-Ti-Cr alloys with high hydrogen storage capacity. Moreover, to overcome the problem of poor cycle life, V-Ti alloy substituted by Cr, V0.68 Ti0.20 Cr0.12, has been developed showing a good cycle performance (keeping about 80 % of initial discharge capacity after 200 cycles). The cycle life of surface-modified V0.68 Ti0.20 Cr0.12 alloy was improved by suppressing the formation of TiO2 layer on the alloy surface while decreasing the amount of dissolved vanadium in the KOH electrolyte. In order to promote the effect of Ni coating on the surface property of V0.68 Ti 0.20 Cr 0.12 alloy by ball-milling, filamentary-typed Ni, which has higher surface coverage area than sphere-typed Ni was used as a surface modifier. Consequently, the surface-modified V0.68 Ti0.20 Cr0.12 alloy electrode showed a improved discharge capacity of 460 mAh/g.

• Economic and Environmental Geology
• /
• v.51 no.2
• /
• pp.77-85
• /
• 2018

There would be a possibility of uranium contamination around the nuclear power plants and the underground waste disposal sites, where the uranium could further migrate and diffuse to some distant places by groundwater. It is necessary to understand the biogeochemical behaviors of uranium in underground environments to effectively control the migration and diffusion of uranium. In general, various kinds of microbes are living in soils and geological media where the activity of microbes may be closely connected with the redox reaction of nuclides resulting in the changes of their solubility. We investigated the adsorption and precipitation behaviors of dissolved uranium on some solid materials using hydrogen gas as an electron donor instead of organic matters. Although the effect of hydrogen gas did not appear in a batch experiment that used granite as a solid material, there occurred a reduction of uranium concentration by 5~8% due to hydrogen in an experiment using bentonite. This result indicates that some indigenous bacteria in the bentonite that have utilized hydrogen as the electron donor affected the behavior (reduction) of uranium. In addition, the bentonite bacteria have showed their strong tolerance against a given high temperature and radioactivity of a specific waste environment, suggesting that the nuclear-biogeochemical reaction may be one of main mechanisms if the natural bentonite is used as a buffer material for the disposal site in the future.

• Journal of Microbiology and Biotechnology
• /
• v.20 no.2
• /
• pp.346-349
• /
• 2010

Coenzyme $Q_{10}$ ($CoQ_{10}$) production from Rhizobium radiobacter T6102 was monitored under various oxygen supply conditions by controlling the agitation speeds, aeration rates, and dissolved oxygen levels. As the results, the $CoQ_{10}$ production was enhanced by limited oxygen supply. To investigate whether the $CoQ_{10}$ production is associated with its physiological functions of electron carrier and antioxidant, the effects of sodium azide and hydrogen peroxide on the $CoQ_{10}$ production were studied, showing that the $CoQ_{10}$ contents were slightly enhanced with increasing sodium azide (up to 0.4 mM) and hydrogen peroxide (up to $10\;{\mu}M$) concentrations. These results suggest the plausible mechanism where the limited electron transfer stimulating the environments of limited oxygen supply and oxidative stress could accumulate the $CoQ_{10}$, providing the relationship between the $CoQ_{10}$ physiological functions and its regulation system.

• Journal of the Korean Society of Safety
• /
• v.2 no.1
• /
• pp.17-29
• /
• 1987

The extraction mechanism of Zinc from aqueous solution with D2EHPA (Di-2-Ethylhexyl Phosphoric Acid) dissolved in Kerosene was studied by the single drop method. The effect of the concentrations of reactant species on the extraction rate, Zinc and hydrogen ion in the continuous phase and D2EHPA in the dispersed, was studied for the drop rise period by the experiment. Then a theoretical analysis on the basis of Handlos-Baron modle was carried out. It becomes clear that the extraction rate was controlled by the neutral complex forming reaction at the drop surface from both analysises. From effect of the concentrations of species on the reaction rate, the extraction rate at the drop surface is considered to be as follows. $${\gamma}_{pn}=9.42{\times}10^{-7}\;\frac{[Zn^{2+}][(HR)_2]^{3/2}}{[H^+]^{3/2}}$$

• Nuclear Engineering and Technology
• /
• v.40 no.3
• /
• pp.225-232
• /
• 2008

To understand the effect of the cyclic strain rate on the environmentally assisted cracking behaviors of SA508 Gr.1a low alloy steel in deoxygenated water at $310^{\circ}C$, the fatigue surface and a sectioned area of specimens were observed after low cycle fatigue tests. On the fatigue surface of the specimen tested at a strain rate of 0.008 %/s, unclear ductile striations and a blunt crack tip were observed. Therefore, metal dissolution could be the main cracking mechanism of the material at this strain rate. On the other hand, on the fatigue surfaces of the specimens tested at strain rates of 0.04 and 0.4 %/s, brittle cracks and flat facets, which are evidences of the hydrogen induced cracking, were observed. In addition, a tendency of linkage between the main crack and the micro-cracks was observed on the sectioned area. Therefore, at higher strain rates, the main cracking mechanism could be hydrogen induced cracking. Additionally, evidence of the dissolved MnS inclusions was observed on the fatigue surface from energy dispersive x-ray spectrometer analyses. Thus, despite the low sulfur content of the test material, the sulfides seem to contribute to environmentally assisted cracking of SA508 Gr.1a low alloy steel in deoxygenated water at $310^{\circ}C$.

• Transactions of the Korean hydrogen and new energy society
• /
• v.24 no.2
• /
• pp.172-178
• /
• 2013

This study examined the electrochemical deposition and dissolution of lithium on nickel electrodes in 1 mol $dm^{-3}$ (M) $LiPF_6$ dissolved in propylene carbonate (PC) containing different 1,2-dimethoxyethane (DME) concentrations as a co-solvent. The DME concentration was found to have a significant effect on the reactions occurring at the electrode. The poor cycleability of the electrodes in the pure PC solution was improved considerably by adding small amounts of DME. This results suggested that the dendritic lithium growth could be suppressed by using co-solvents. After hundredth cycling in the 1 M $LiPF_6$/PC:DME (67:33) solution, almost no dead lithium has been found from the disassembled cell, resulting from suppression of dendritic lithium growth. Scanning electron microscopy revealed that dendritic lithium formation was greatly affected by the ratio of DME. Raman spectroscopy results suggested that the structure of solvated lithium ions is a crucial important factor in suppressing dendritic lithium formation.

• Journal of Environmental Health Sciences
• /
• v.35 no.3
• /
• pp.201-208
• /
• 2009

Oxidation of phenol in aqueous media by electro-Fenton process using Ru-Sn-Sb/graphite electrode has been studied. Hydrogen peroxide was electrically generated by reaction of dissolved oxygen in acidic solutions containing supporting electrolyte and $Fe^{2+}$ was added in aqueous media. Phenol degradation experiments were performed in the presence of electrolyte media at pH 3. Effect of operating parameters such as current, electrolyte type (NaCl, KCl and $Na_2SO_4$) and concentration, $Fe^{2+}$ concentration, air flow rate and phenol concentration were investigated to find the best experimental conditions for achieving overall phenol removal. Results showed that current of 2 A, NaCl electrolyte concentration of 2g/l, 0.5M concentration of $Fe^{2+}$, air flow rate of 1l/min were the best conditions for mineralization of the phenol by electro-Fenton.

• Journal of Aquaculture
• /
• v.13 no.1
• /
• pp.39-46
• /
• 2000

Successive management of prawn farm is strongly dependent upon monitoring of pond seawater quality which is generally influenced by an excessive food supplied sediment type and phytoplankton composition in the pond. For good condition of seawater quality it must need exchangning of fresh seawater by tidal current. Two distinct shrimp ponds Galha and Yunho which were different in seawater exchanging system and sediment type were selected to understand how some factors affected to seawater and sediment qualities in the pond. Prawn growth was also determined. Galha pond characterized by sand bottom with water exchanging by turn of the tidal current accumulated 1.8 mgS/g-dry as sulfide in sediment while Yunho pond mud- bottomed with seawater exchanging of pumping system showed 4.7mgS/g-dry when it was highest, Ammonia-N and hydrogen sulfide measured in the seawater were 0.31mg/${\ell}$ and 21.2 ${\mu}$${\ell}$/${\ell}$in Yunho and 0.10mg/${\ell}$and 10.8${\mu}$${\ell}$/${\ell}$in Galha pond respectively. Dissolved oxygen remained below 6.0mg/${\ell}$ in Galha and 5.0mg/${\ell}$in Yunho pond from June through August. Less growth of prawn was found in Yunho pond than in Galha pond. Prawn growth expressed as body length and weight were 138.3mm 22.9g in Yunho pond while they were length 158.2mm and 28.9g in Galha pond respectively when they were harvested in October. These results indicate that higher levels of ammonia-N and hydrogen sulfide and lower dissolved oxygen in bottom seawater of Yunho pond might affect the growth of cultured prawn.

• Journal of Korean Society for Atmospheric Environment
• /
• v.29 no.6
• /
• pp.811-817
• /
• 2013

A two-stage bioreactor system using sulfur-oxidizing bacteria was studied to abate high strength hydrogen sulfide ($H_2S$) from biogas. The two-stage bioreactor consisted of a $H_2S$ absorption column (0.5 L) and a microbial oxidation column (1 L) in series, and the liquid medium was continuously recirculated through the columns. The objectives of this study were to determine the feasibility of the bioreactor for biogas desulfurization and to investigate the effect of the medium circulation rate on the system performance. An averaged concentration of $H_2S$ introduced to the bioreactor was 530 ppm, corresponding to an overall loading rate of $44.4g/m^3/hr$. During the initial 20 days period at the medium recirculation rate of 8 reactor volumes per hour (12 L/hr), the dissolved oxygen (DO) concentration in the oxidation column was 6 mg/L, while the DO in the absorption column was 0.5 mg/L showing that the oxygen contents of the biogas stream was not altered. Because of the biological oxidation of $H_2S$ in the oxidation column, the sulfate concentration increased from 200 mg/L to 5,600 mg/L in the liquid medium. The removal efficiency of $H_2S$ was greater than 99% in the initial operation period. After the initial period, the medium recirculation rate between the two columns was stepwise changed eight times from 1.0 to 40 vol/hr (1.5~60 L/hr). At the recirculation rate of faster than 4 vol/hr, the $H_2S$ removal efficiencies were found to be high, but the efficiency declined at the lower recirculation rates than the threshold.