• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.5 no.3
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• pp.189-197
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• 2007

The solubility of U(VI) hydrolysis products was determined by using a laser-induced breakdown detection (LIBD) technique. The experiments were carried out at uranium concentrations in range from $2{\times}10^{-4}\;M\;to\;4{\times}10^{-6}\;M$, pH values between 3.8 and 7.0, the constant ionic strength of 0.1 M $NaClO_4$ and the temperature of $25.0{\pm}0.1^{\circ}C$. The solubility product of U(VI) hydrolysis products was calculated from LIBD results by using the hydrolysis constants selected in NEA-TDB. The solubility product extrapolated to zero ionic strength, ${\log}K^{\circ}_{sp}=-22.85{\pm}0.23$ was calculated by using a specific ion interaction theory (SIT). The spectral features of ionic species in uranium solutions were investigated by using a conventional UV-visible absorption spectrophotometer and a fluorophotometer, respectively, $(UO_2)_2(OH)_2^{2+}\;and\;(UO_2)_3(OH)_5^+$ were dominant species at uranium concentration of $2{\times}10^{-4}\;M$.

• The Korean Journal of Ceramics
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• v.2 no.1
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• pp.48-53
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• 1996

Ion beam assisted crystallization behavior of sol-gel derived $PbTiO_3$ thin films, deposited on bare silicon(100) substrates by spin-casting method, has been investigated. Ar ion bombardment was directly conducted on the spincoated film surface with or without heating the film from room temperature to $300^{\circ}C$. Ion dose was changed from $5{\times}10^{15}$ to $7.5{\times}10^{16}$ $Ar^-/cm^2$. Formation of (110) oriented perovskite phase was obseerved with ion dose above $5{\times}10^{16}\; Ar^+/cm^2$. Crystallization of $PbTiO_3$ thin film could be enhanced with increasing the Air ion dose, or heating the substrate during ion bombardment. Crystallization of the $PbTiO_3$ films by ion bombardment was related to the local heating effect during ion bombardment.

• Composites Research
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• v.22 no.6
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• pp.39-44
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• 2009

The effect of exposure times on the aging characteristics of carbon fiber/epoxy composite ring specimen was evaluated using an accelerating aging tester. Combined exposure conditions, such as temperature, moisture, and ultraviolet, were applied up to 3000 hours. Tensile properties and flexural properties including the effect of curvature were evaluated on the specimens subject to various exposure times through a material testing system. Their aging surfaces were observed through a scanning electron microscope. According to the results, tensile modulus was little affected by the exposure times. However, tensile strength, at the early stage of the exposure times, increased due to physical aging and curing reaction, but tensile strength slightly decreased due to degradation as the exposure times increased. The flexural modulus and flexural strength increased at the early stage of the exposure times, but slightly decreased as the exposure times increased. Aging surfaces of the specimens examined using the scanning electron microscope revealed a different morphology in various exposure times and provided useful information for identifying the degradation in mechanical properties of the composite subject to various exposure times.

• Applied Chemistry for Engineering
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• v.8 no.4
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• pp.602-609
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• 1997

The seed formation and growth of $\alpha$-ferric oxyhydroxide with aerial oxidative precipitation from aqueous solution of ferrous sulfate with KOH, NaOH, $Na_2CO_3$ and $K_2CO_3$ as precipitants have been studied by free pH drift experiment. It has been shown that all precipitants give same particle formation and growth path, and average particle length from KOH and NaOH as precipitants was about 1.5 times shorter than that of $K_2CO_3$ and $Na_2CO_3$. When initial mole ratio, $R_o=[Fe^{2+}]_o/[OH^-]_o$ of KOH was decreased the particle was grown oxyhydroxide seed growth from aqueous solution of ferrous sulfate with KOH has been studied. The influence of the air flow rate, reaction temperature and initial mole ratio, $R_o=[Fe^{2+}]_o/[OH^-]_o$, on the kinetics of seed growth are investigated by static pH experiment. The oxidation rate of seed growth increased with increase in the air low rate, reaction temperature and initial mole patio. The activation energy of seed growth is 16.16 KJ/mol and the rate equation of seed growth can be written as follows: $-\frac{d[Fe^{2+}]}{dt}=1.46{\times}10^4[P_{o2}]^{0.66}[OH^-]^{2.19}exp(-\frac{16.16}{dt})$.

• Journal of Korean Society of Environmental Engineers
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• v.30 no.10
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• pp.999-1005
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• 2008

The main reaction for soil washing with using sodium hydroxide(NaOH) and hydrogen peroxide(H$_2$O$_2$) was desorption and flotation of petrochemical contaminant by means of oxygen bubble. We found the rate of decomposition by rate constant according to various temperature. For the purpose of optimizing the operation factor, we examined the effect of concentration of NaOH and H$_2$O$_2$, washing time, and soil:water ratio. The rate of decomposition for H$_2$O$_2$ in liquid phase is the first order reaction by its concentration. The rate constant of k$_1$ was 0.9439 $\times$ exp(-1376.82/RT) when concentration of NaOH was lower than 0.1 M, and the rate constant of k$_2$ was 17.3588 $\times$ exp(-2320.06/RT) when it was higher than NaOH of 0.1 M. It found that NaOH was facilitated at the beyond of specific concentration. We confirmed the optimum concentration of NaOH/H$_2$O$_2$ by means of rate constants during soil washing. Also, the optimum conditions during soil washing were washing time of 15 min, soil : water ratio of 1 : 3, and NaOH/H$_2$O$_2$ concentration of 0.25 M/0.1 M.

• Korean Journal of Materials Research
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• v.26 no.10
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• pp.513-520
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• 2016

The effect of NaOH concentration on the properties of electrolytic plasma processing (EPP) coating formed on AZ61A Mg alloy is studied. Various types of EPP were employed on magnesium alloy AZ61A in a silicate bath with different concentrations of NaOH additive. Analysis of the composition and structure of the coating layers was carried out using an X-ray diffractometer (XRD) and a scanning electron microscope (SEM). The results showed that the oxide coating layer mainly consisted of MgO and $Mg_2SiO_4$; its porosity and thickness were highly dependent on the NaOH concentration. The Vickers hardness was over 900 HV for all the coatings. The oxide layer with 3 g/l of NaOH concentration exhibited the highest hardness value (1220 HV) and the lowest wear rate. Potentiodynamic testing of the 3 g/l NaOH concentration showed that this concentration had the highest corrosion resistance value of $2.04{\times}10^5{\Omega}cm^2$; however, the corrosion current density value of $5.80{\times}10^{-7}A/cm^2$ was the lowest such value.

• Bulletin of the Korean Chemical Society
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• v.25 no.12
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• pp.1907-1910
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• 2004

Generation of hydroxyl radical, one of their major active species in ozonation of water was directly observed with spin-trapping/electron spin resonance (ESR) technique using 5,5-dimethyl-pyrrolidine-1-oxyl (DMPO) as a spin-trapping reagent. Hydroxyl radical was trapped with DMPO as a stable radical, DMPO-OH. 80 mM of ozone produced $1.08{\times}10^{-6}$M of DMPO-OH, indicating that 1.4% of ${\cdot}$OH is trapped with DMPO if ${\cdot}$OH is produced stoichiometrically from ozone. Humic acid suppressed DMPO-OH generation in a dose-dependent manner. Generation rate of DMPO-OH was determined with ESR/stopped-flow measurement. Phenol derivatives increased the amount and generation rate of DMPO-OH, indicating that phenol derivatives enhance·OH generation during ozonation of water.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.10 no.1
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• pp.13-19
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• 2012

The long-lived fission products $^{79}Se$ and $^{99}Tc$ have been considered as the major concern nuclides for the disposal of radioactive waste because of their high solubilities and the existence of anionic species in natural water. In this study, the solubilities of $FeSe_2(s)$ and $TcO_2(s)$, known as respective Solubility Limiting Solid Phase (SLSP) of selenium and technetium, were measured in the KURT (KAERI Underground Research Tunnel) groundwater under various pH and redox conditions. And their solubilities and major species were also calculated using geochemical codes under conditions similar to experimental solutions. Experimental results and calculation for $FeSe_2$ show that the solubility of selenium was found to be below $1{\times}10^{-6}mol/L$ under the condition of pH 8~9.5 and Eh=-0.3~-0.4 V while the dominant species was identified as $HSe^-$. For $TcO_2$, the solubility of technetium was found to be $5{\times}10^{-8}{\sim}1{\times}10^{-9}mol/L$ in the solutions of pH 6~9.5 and Eh<-0.1 V, while the dominant species was $TcO(OH)_2$. However, when the Eh of the solution is -0.35 V, $TcO(OH)_3^-$ and $TcO_4^-$ are calculated as the dominant species at pH 10.5~12 and pH>12, respectively.

• Journal of the Korean Chemical Society
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• v.26 no.4
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• pp.218-223
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• 1982

The absorbance and fluorescence yields of chl-a vs. concentration of n-prOH in diethyl ether, benzene and iso-octane were shown the characteristic point which chl-a structures are changed to monomer by the solvation of oligomer, and the spectral differences of fluorescence excitation between oligomer and monomer were identified by fluorimetry. All the maximum wavelength of absorbance, fluorescence excitation and fluorescence emission were shifted to longer wavelength. The ratios of soret/red band were depended on the band intensions and the polarities of solution in organic solvents mixed with n-prOH.

• Journal of the Korean Chemical Society
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• v.29 no.2
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• pp.121-128
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• 1985

The electrochemical reduction of uranyl ion in aqueous basic media has been examined by d. c. polarography, differential pulsed polarography and cyclic voltammetry. From voltammograms obtained in uranyl solutions containing 0.1M sodium bicarbonate, either with or without the same amounts of sodium tripolyphosphate it is concluded that the first wave corresponds to the reduction of $UO_2^{2+}$ to $UO_2^+$. It is assumed that the uranyl ion undergoes appreciable hydrolysis in these media. The hydrolysis product $UO_2OH^+$ from $UO_2^{2+}$ is not reduced at the first wave, but is reduced at the second wave together with $UO_2^+$. The diffusion current was found proportional to the uranyl concentration in a range between $7.5 {\times} 10^{-4}$ and $3.75 {\times}10^{-3}$M.