• Nuclear Engineering and Technology
• /
• v.27 no.4
• /
• pp.453-462
• /
• 1995

In connection with the safe storage of high level nuclear waste, effect of $H_2O$$_2$ on the corrosion behavior of 304L stainless steel was examined. Open circuit potentials and polarization curves were measured with and without $H_2O$$_2$. The experimental results show that $H_2O$$_2$ increased corrosion potential and decreased pitting potential. The passive range, therefore, decreased as $H_2O$$_2$ concentration increased, indicating that pitting resistance was decreased by the existence of $H_2O$$_2$ in the electrolyte. These effect of $H_2O$$_2$ on corrosion of 304L stainless steel are considered to be similar to those of ${\gamma}$-irradiation. To compare the effects of $H_2O$$_2$ with those of $O_2$, cathodic and anodic polarization curves ore made in three types of electrolyte such as aerated, deaerated, and stirred electrolyte. The experimental results show that the effects of $H_2O$$_2$ on the corrosion behavior were tory similar to those of $O_2$ such as increase of corrosion potential, decrease of pitting resistance, and increase of repassivation potential. In acid and alkaline media, the corrosion potential shifts by $H_2O$$_2$ were restricted by the large current density of proton reduction and by the le Chatelier's principle respectively.y.

• Membrane Journal
• /
• v.29 no.3
• /
• pp.173-182
• /
• 2019

Much research has been made for finding new and eco-friendly alternative sources of energy to solve the problems related with the pollution caused by emissions of greenhouse gases such as carbon dioxide as the use of fossil fuels increases worldwide. Among them, fuel cells draws particular interests as an eco-friendly energy generator because only water is obtained as a by-product. Anion exchange membrane-based alkaline fuel cell (AEMFC) that uses anion exchange membrane as an electrolyte is of increased interest recently because of its advantages in using low-cost metal catalyst unlike the PEMFC (potton exchange membrane fuel cell) due to the high-catalyst activity in alkaline conditions. The main properties required as an anion exchange membrane are high hydroxide conductivity and chemical stability at high pH. Recently we reported a chemically crosslinked poly(2-dimethyl-1,4-phenylene oxide) (PPO) by reacting PPO with N,N,N',N'-tetramethyl-1,6-hexanediamine as novel anion exchange membranes. In the current work, we further developed the same crosslinked polymer but having enhanced physicochemical properties, including higher conductivity, increased mechanical and dimensional stabilities by using the PPO with a higher molecular weight and also by increasing the crosslinking density. The obtained polymer membrane also showed a good cell performance.

• The Journal of Korean Academy of Prosthodontics
• /
• v.47 no.1
• /
• pp.39-45
• /
• 2009

Statement of problem: Recently precalcification treatment has been studied to shorten the period of the implant. Purpose: This study was performed to evaluate the effect of precalcification treatment of $TiO_2$ Nanotube formed on Ti-6Al-4V Alloy. Material and methods: Specimens of $20{\times}10{\times}2\;mm$ in dimensions were polished sequentially from #220 to #1000 SiC paper, ultrasonically washed with acetone and distilled water for 5 min, and dried in an oven at $50^{\circ}C$ for 24 hours. The nanotubular layer was processed by electrochemical anodic oxidation in electrolytes containing 0.5 M $Na_2SO_4$ and 1.0 wt% NaF. Anodization was carried out using a regulated DC power supply (Kwangduck FA, Korea) at a potential of 20 V and current density of $30\;㎃/cm_2$ for 2 hours. Specimens were heat-treated at $600^{\circ}C$ for 2 hours to crystallize the amorphous $TiO_2$ nanotubes, and precalcified by soaking in $Na_2HPO_4$ solution for 24 hours and then in saturated $Ca(OH)_2$ solution for 5 hours. To evaluate the bioactivity of the precalcified $TiO_2$ nanotube layer, hydroxyapatite formation was investigated in a Hanks' balanced salts solution with pH 7.4 at $36.5^{\circ}C$ for 2 weeks. Results: Vertically oriented amorphous $TiO_2$ nanotubes of diameters 48.0 - 65.0 ㎚ were fabricated by anodizing treatment at 20 V for 2 hours in an 0.5 M $Na_2SO_4$ and 1.0 NaF solution. $TiO_2$ nanotubes were composed with strong anatase peak with presence of rutile peak after heat treatment at $600^{\circ}C$. The surface reactivity of $TiO_2$ nanotubes in SBF solution was enhanced by precalcification treatment in 0.5 M $Na_2HPO_4$ solution for 24 hours and then in saturated $Ca(OH)_2$ solution for 5 hours. The immersion in Hank's solution for 2 weeks showed that the intensity of $TiO_2$ rutile peak increased but the surface reactivity decreased by heat treatment at $600^{\circ}C$. Conclusion: This study shows that the precalcified treatment of $TiO_2$ Nanotube formed on Ti-6Al-4V Alloy enhances the surface reactivity.

• KOREAN JOURNAL OF CROP SCIENCE
• /
• v.42 no.1
• /
• pp.68-78
• /
• 1997

Laboratory and greenhouse studies were conducted to determine differential sensitivities on absorption of $^{14}$ C-oxyfluorfen and the anatomical responses in wheat and barley to protoporphyrinogen oxidase-inhibiting herbicides [oxyfluorfen (2-chloro-1- (3-ethoxy -nitrophen-oxy)-4-(trifluoromethyl) benzene, acifluorfen(5-[2-chloro-4-(trifluoromethyl) phenoxy]-2-nitro-benzoic acid), bifenox(methyl-5-(2, 4-dichlorophenoxy)-2-nitrobenzoate) and oxadiazon(5-tert-butyl-3-(2, 4-dichloro-5-isopropoxyphenyl)-1, 3, 4-oxadiazol-2-one)]. I$_{50}$ value of the tolerant wheat cultivars to oxyfluorfen was about 10$^{-4}$ , whereas that of the susceptible barley cultivars was about 10$^{-6}$ M, showing significant difference between the two groups. When foliage were applied with acifluorfen, bifenox or oxadiazon, the oxyfluorfen-tolerant wheat showed less decreased in shoot fresh weight and chlorophyll content than the susceptible barley. Also, when soil-applied with these herbicides test plants showed similar tendency in foliar application. Electrolyte leakage from the tissue treated with these compounds was the more influenced in the barley than the wheat. Malondialdehyde(MDA) production as index of lipid peroxidation was greater in the barley than the wheat by treatment of these compounds. Therefore, the differential sensitivities of wheat and barley to protoporphyrinogen oxidaseinhibiting herbicides was showed by our greenhouse and in vitro experiment. The absorption rates of $^{14}$ C-oxyfluorfen were higher in the barley than the wheat. And this tendency was showed appararitly difference by increase of treatment durations. After the oxfluorfen and oxadiazon treatment, the tolerant wheat did not show the structural damage in leaf surface, but the susceptible barley was damaged in the leaf waxy layer. However, the acifluorfen and bifenox treatment showed no difference between wheat and barley. The anatomical changes by these compounds treatment were not observed in the tolerant wheat but epidermal cell and mesophyll cell were highly broken in the susceptible barley.

• Applied Chemistry for Engineering
• /
• v.7 no.6
• /
• pp.1078-1086
• /
• 1996

The peroxo-polytungstic acid was formed by the direct reaction of tungsten powder with the hydrogen peroxide solution. Peroxo-polytungstic powder were prepared by rotary evaporator using the fabricated on to ITO coated glass as substrate by dip-coating method using $2g/10mL(W-IPA/H_2O)$ sol solution. A substrate was dipped into the sol solution and after a meniscus had settled, the substrate was withdrawn at a constant rate of the 3mm/sec. Thicker layer could be built up by repeated dipping/post-treatment 15 times cycles. The layers dried at the temperature of $65{\sim}70^{\circ}C$ during the withdrawn process, and then tungsten oxides thin film was formed by final heating treatment at the temperature of $230{\sim}240^{\circ}C$ for 30min. A linear rotation between the thickness of thin film and the number of dipping/post-treatment cycles for tungsten oxides thin films made by dip-coating was found. The thickness of thin film had $60{\AA}$ after one dipping. From the patterns of XRD, the structure of tungsten oxides thin film identified as amorphous one and from the photographs of SEM, the defects and the moderate cracks were observed on the tungsten oxides thin film, but the homogeneous surface of thin films were mostly appeared. The electrochemical characteristic of the $ITO/WO_3$ thin film electrode were confirmed by the cyclic voltammetry and the cathodic Tafel polaization method. The coloring bleaching processes were clearly repeated up to several hundreds cycles by multiple cyclic voltammetry, but the dissolved phenomenon of thin film revealed in $H_2SO_4$ solution was observed due to the decrease of the current densities. The diffusion coefficient was calculated from irreversible Randles-Sevick equation from the data obtained by the cyclic voltammetry with various scan rates.

• Korean Chemical Engineering Research
• /
• v.59 no.4
• /
• pp.557-564
• /
• 2021

Sr_0.92Y_0.08Ti_1-xV_xO_3-δ (SYTV) with perovskite structure was investigated as an alternative anode to utilize H₂S containing fuels in solid oxide fuel cells. To improve the electrochemical performance of Sr_0.92Y_0.08TiO_3-δ (SYT), vanadium(V) was substituted to titanium(Ti) at the B-site of the SYT perovskites. The SYTV synthesized by the Pechini method was chemically compatible with the YSZ electrolyte without additional by-products formation under the cell fabricating conditions. As increasing V substitution amounts, the oxygen vacancies increased, resulting to increasing ionic conductivity of the anode. The cell performance in pure H₂ at 850 ℃ is 19.30 mW/cm² and 34.87 mW/cm² for a 1 mol.% and 7 mol.% of V substituted anodes, respectively. The cell performance using H₂ fuel containing 1000 ppm of H₂S at 850 ℃ was 23.37 mW/cm² and 73.11 mW/cm² for a 1 mol.% and 7 mol.% of V substituted anodes, respectively.

• Korean Journal of Mineralogy and Petrology
• /
• v.35 no.2
• /
• pp.101-109
• /
• 2022

The mobility and transport of radioactive cesium are crucial factors to consider for the safety assessment of high-level radioactive waste disposal sites in granite. The retardation of radionuclides in the fractured crystalline rock is mainly controlled by the hydrochemical condition of groundwater and surface reactions with minerals present in the fractures. This paper reports the experimental results of cesium sorption to the Wonju Granite, a typical Mesozoic granite in Korea, performed in an anaerobic chamber that mimics the anoxic environment of a deep disposal site. We measured the rates and amounts of cesium (¹³³Cs) removed by crushed granite samples in different electrolyte (NaCl, KCl, and CaCl₂) solutions and a synthetic groundwater solution, with variations in the initial cesium concentration (10^-5, 5×10^-6, 10^-6, 5×10^-7 M). The cesium sorption kinetic and isotherm data were successfully simulated by the pseudo-second-order kinetic model (r²= 0.99) and the Freundlich isotherm model (r²= 0.99), respectively. The sorption distribution coefficient of granite increased almost linearly with increasing biotite content in granite samples, indicating that biotite is an effective cesium scavenger. The cesium removal was minimal in KCl solution compared to that in NaCl or CaCl₂ solution, regardless of the ionic strength and initial cesium concentration that we examined, showing that K⁺ is the most competitive ion against cesium in sorption to granite. Because it is the main source mineral of K⁺ in fracture fluids, biotite may also hinder the sorption of cesium, which warrants further research.