• Journal of the Korean Ceramic Society
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• v.39 no.3
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• pp.245-251
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• 2002

We prepared γ-alumina beads using the amorphous alumina, obtained by fast calcination of gibbsite, and its were immersed in aqueous solution of the mixture of 21.87% nitric acid and 28.57% acetic acid. The beads thus were hydrothermaly treated at 200$^{\circ}$C for 3h, and were investigated changes of crystal, pore characteristics, $N_2$ adsorption and desorption isotherms, mechanical strengths and thermal resistance. Acicular platelet crystals of 0.1∼0.3${\mu}$m were transformed into acicular boehmite crystals of 1∼2${\mu}$m having the same crystal structure. Through this changes, we found that reversible phase transformation due to hydrothermal reaction took placed between boehmite and ${\gamma}$-alumina. In comparison to the ${\gamma}$-alumina bead before hydrothermal treatment, $N_2$ adsorption capacity was increased from 450㎖/g to 670㎖/g, and pore volume between 100${\AA}$ and 1000${\AA}$ was increased form 0.15㎖/g to 0.77㎖g, and mechanical strength was increased form 1.4MPa to 2.2MPa. Also, it showed the remarkable thermal resistance which sustained ${\theta}$-alumina crystal structure and pores between 100${\AA}$ and 1000${\AA}$ at 1000$^{\circ}$C in 40vol% steam.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2016.11a
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• pp.197-197
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• 2016

Commercially pure titanium (CP Ti) and Ti-6Al-4V alloys have been widely used for biomedical applications. However, the use of the Ti-6Al-4V alloy in biomaterial is then a subject of controversy because aluminum ions and vanadium oxide have potential detrimental influence on the human body due to vanadium and aluminum. Hence, recent works showed that the synthesis of new Ti-based alloys for implant application involves more biocompatible metallic alloying element, such as, Nb, Hf, Zr and Mo. In particular, Nb and Hf are one of the most effective Ti ${\beta}-stabilizer$ and reducing the elastic modulus. Plasma electrolyte oxidation (PEO) is known as excellent method in the biocompatibility of biomaterial due to quickly coating time and controlled coating condition. The anodized oxide layer and diameter modulation of Ti alloys can be obtained function of improvement of cell adhesion. Manganese(Mn) plays very important roles in essential for normal growth and metabolism of skeletal tissue in vertebrates and can be detected as minor constituents in teeth and bone. Radio frequency(RF) magnetron sputtering in the various PVD methods has high deposition rates, high-purity films, extremely high adhesion of films, and excellent uniform layers for depositing a wide range of materials, including metals, alloys and ceramics like a hydroxyapatite. The aim of this study is to research the Mn coatings on the micro-pore formed Ti-29Nb-xHf alloys by RF-magnetron sputtering for dental applications. Ti-29Nb-xHf (x= 0, 3, 7 and 15wt%, mass fraction) alloys were prepared Ti-29Nb-xHf alloys of containing Hf up from 0 wt% to 15 wt% were melted by using a vacuum furnace. Ti-29Nb-xHf alloys were homogenized for 2 hr at $1050^{\circ}C$. Each alloy was anodized in solution containing typically 0.15 M calcium acetate monohydrate + 0.02 M calcium glycerophosphate at room temperature. A direct current power source was used for the process of anodization. Anodized alloys was prepared using 270V~300V anodization voltage at room. Mn coatings was produced by RF-magnetron sputtering system. RF power of 100W was applied to the target for 1h at room temperature. The microstructure, phase and composition of Mn coated oxide surface of Ti-29Nb-xHf alloys were examined by FE-SEM, EDS, and XRD.

• Korean Chemical Engineering Research
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• v.53 no.6
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• pp.808-813
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• 2015

Boron is difficult to be removed from seawater by simple RO (reverse osmosis) membrane process, because the size of boric acid ($B(OH)_3$), the major form of aqueous boron, is as small as the nominal pore size of RO membrane. Thus, the complexation of boric acid with polyols was suggested as an alternative way to increase the size of aqueous boron compounds and the complexation behavior was investigated with Raman spectroscopy. As a reference, the Raman peak for symmetric B-O stretching vibrational mode both in boric acid and borate ion (${B(OH)_4}^-$) was selected. A Raman peak shift ($877cm^{-1}{\rightarrow}730cm^{-1}$) was observed to confirm that boric acid in water is converted to borate ion as the pH increases, which is also correctly predicted by frequency calculation. Meanwhile, the Raman peak of borate ion ($730cm^{-1}$) did not appear as the pH increased when polyols were applied into aqueous solution of boric acid, suggesting that the boric acid forms complexing compounds by combining with polyols.

• Journal of the Korean Geotechnical Society
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• v.27 no.9
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• pp.87-98
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• 2011

In this study, the magnitude and phase variation of dynamic earth pressure acting on a pile in liquefiable soils were analyzed using a series of 1g shaking table tests. In the case of a pile in dry sand, the value of the dynamic earth pressure was the highest near the surface due to the inertia force of the upper load on the pile and it decreased as the depth of the pile got lower. On the other hand, for a pile in liquefiable sand, the magnitude and shape of the dynamic earth pressure were similar to those of the excess pore pressure and was largely affected by the deformation of soils. Furthermore, the inertia force of the upper load and the dynamic earth pressure acted in opposite directions in cases of dry sand and saturated sand where low excess pore pressure had developed. However, after liquefaction, those force components near surface acted unfavorably in the same direction. Finally, the Westergaard’s solution was modified and proposed as a method to evaluate the magnitude of dynamic earth pressure acting on a pile during liquefaction.

• Journal of the Korean Electrochemical Society
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• v.3 no.3
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• pp.146-151
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• 2000

So fine cobalt oxide xerogel powders were prepared by using a unique solution chemistry associated with the sol-gel process. The effect of thermal treatment on the crystalinity, particle structure, and corresponding electrochemical properties of the resulting xerogel remained amorphous as $Co(OH)_2$ up to $160^{\circ}C$ With an increase in the temperature above $200^{\circ}C$, both the surface area and pore volume decreased sharply, because the amorphous $Co(OH)_2$ decomposed to form CoO that was subsequently oxidized to form crystalline Co304. In addition, the changes in the crystallinity, and particle structure all had significant but coupled effects on the electrochemical properties of the xerogels. A maximum capacitance of 192F1g was obtained for an electrode prepared with the $CoO_x$ Xerogel calcined at$150^{\circ}C$, which was consistent with the maxima exhibited in both the surface area and pore volume. This capacitance was attributed solely to a surface redox mechanism.

• Korean Journal of Agricultural and Forest Meteorology
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• v.2 no.4
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• pp.190-197
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• 2000

Anions such as C $l^{[-10]}$ , N $O_3$$^{[-10]}$ , S $O_4$$^{2-}$, P $O_4$$^{3-}$, and organic anions, that do not become a part of the clay mineral crystal lattice, are of considerable interest in soils which are a potential sink caused by acid rain. In this paper, elution of native sulfate and breakthrough curves (BTC) were obtained from miscible displacement of non-specifically or specifically adsorbed anions through non-saturated or saturated Bt soil of Chungwon series. The shape and position of the BTC's could be affected by adsoprtion and ion exchange onto the soil particle surfaces. Measured BTC's for oxalic acid under unsaturated and saturated conditions showed that less pore volumes were required to displace the native S $O_4$$^{2-}$S from the soil column, and that maximum detection limit of oxalic acid reached earlier than under unsaturated. The retarded BTC's to the righthand side could be attributed by different adsorption behavior of each anion, although BTC's may be influenced by the smaller order of velocity change. The alternate breakthrough and elution curves show the rapid approach to the maximum detection limit of C/Co = 1, compared to progressive tailing of elution curve to reach to C/Co = 0. The probable explanation for asymmetric elution patterns for both anion is that the anion was selectively adsorbed on the positively charged soil surface from the solution passing in the soil column. On the other hand, the variations of pH in effluent showed that pH was increased to 7 in the first 6 pore volume and then gradually decreased to pH 4.

• Applied Chemistry for Engineering
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• v.29 no.6
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• pp.759-764
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• 2018

3D porous carbon electrodes (cNPIM), prepared by solution casting of a polymer of intrinsic microporosity (PIM-1) followed by nonsolvent-induced phase separation (NIPS) and carbonization are presented. In order to effectively control the pore size of 3D porous carbon structures, cNPIM was prepared by varying the THF ratio of mixed solvents. The SEM analysis revealed that cNPIMs have a unique 3D macroporous structure having a gradient pore structure, which is expected to grant a smooth and easy ion transfer capability as an electrode material. In addition, the cNPIMs presented a very large specific surface area ($2,101.1m^2/g$) with a narrow micropore size distribution (0.75 nm). Consequently, the cNPIM exhibits a high specific capacitance (304.8 F/g) and superior rate capability of 77% in an aqueous electrolyte. We believe that our approach can provide a variety of new 3D porous carbon materials for the application to an electrochemical energy storage.

• Journal of Korean Dental Science
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• v.11 no.2
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• pp.71-81
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• 2018

Purpose: The purpose of this study was to investigate the corrosion behaviors of dental implant alloy after microsized surface modification in electrolytes containing Mn ion. Materials and Methods: $Mn-TiO_2$ coatings were prepared on the Ti-6Al-4V alloy for dental implants using a plasma electrolytic oxidation (PEO) method carried out in electrolytes containing different concentrations of Mn, namely, 0%, 5%, and 20%. Potentiodynamic method was employed to examine the corrosion behaviors, and the alternatingcurrent (AC) impedance behaviors were examined in 0.9% NaCl solution at $36.5^{\circ}C{\pm}1.0^{\circ}C$ using a potentiostat and an electrochemical impedance spectroscope. The potentiodynamic test was performed with a scanning rate of $1.667mV\;s^{-1}$ from -1,500 to 2,000 mV. A frequency range of $10^{-1}$ to $10^5Hz$ was used for the electrochemical impedance spectroscopy (EIS) measurements. The amplitude of the AC signal was 10 mV, and 5 points per decade were used. The morphology and structure of the samples were examined using field-emission scanning electron microscopy and thin-film X-ray diffraction. The elemental analysis was performed using energy-dispersive X-ray spectroscopy. Result: The PEO-treated surface exhibited an irregular pore shape, and the pore size and number of the pores increased with an increase in the Mn concentration. For the PEO-treated surface, a higher corrosion current density ($I_{corr}$) and a lower corrosion potential ($E_{corr}$) was obtained as compared to that of the bulk surface. However, the current density in the passive regions ($I_{pass}$) was found to be more stable for the PEO-treated surface than that of the bulk surface. As the Mn concentration increased, the capacitance values of the outer porous layer and the barrier layer decreased, and the polarization resistance of the barrier layers increased. In the case of the Mn/Ca-P coatings, the corroded surface was found to be covered with corrosion products. Conclusion: It is confirmed that corrosion resistance and polarization resistance of PEO-treated alloy increased as Mn content increased, and PEO-treated surface showed lower current density in the passive region.

• Journal of the Korean GEO-environmental Society
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• v.12 no.12
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• pp.47-54
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• 2011

Consolidation behavior of soft clay is generally to be affected by its compressibility and deformation characteristics. Especially, soil permeability depends on soil characteristics including its type of anisotropy. Coefficient of permeability of soft clay is mostly estimated by using laboratory(Oedometer test) and in-stiu piezocone test. The permeability characteristics of soft clay is estimated by excess pore pressure dissipation test results. In this study, the tests were performed to find out the validity of the existing theoretical formula in clay by pore pressure dissipation test and laboratory test results. After grasping of variation the coefficient of permeability ratio(${k_{h}/k_{v}}$) in different clay soils, it was found out adequate solution of in-stiu permeability ratio(${k_{h}/k_{v}}$). Piezocone tests and laboratory tests were performed at the site of pilot project of ground improvement at Yangsan-Mulgeum, Gyeongsangnam-do. Comparisons of the estimated values of ${k_{h}/k_{v}}$ using piezocone tests results and those from laboratory consolidation tests were carried out. Test results show that values of ${k_{h}/k_{v}}$ by piezocone test result(5.85) is similar of it's laboratory test(5.28).

• Korean Journal of Environmental Agriculture
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• v.14 no.2
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• pp.135-143
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• 1995

This study was conducted to investigate the adsorption characteristics, distribution coefficients, and movement of alachlor(2-chloro-2', 6'-dimethyl-N-(methoxymethyl) acetanilide) and chlorothalonil(tetrachloroisophthalonitrile) for the 3 soils sampled from major soil groups in Cheju Island. Namwon, Jeju, and Mureng soils used in this study were classified as black volcanic ash soil, dark brown volcanic ash soil and dark brown nonvolcanic soil, respectively. Organic carbon content and CEC of Namwon soil were very high and those of Mureung soil were very low. Linear and Freundlich adsorption isotherms were the best to fit the adsorption of alachlor and chlorothalonil in the soils. K value, Freundlich coefficient, of alachlor for Namwon soil was 21.38, being 5.4 and 97.2 times higher than that for Jeju and Mureung soils respectively. The values of chlorothalonil for the soils were similar to those of alachlor but were much higher than them. When Mureung, Jeju and Namwon soil columns were leached with a solution containing 10.25 mg/l of alachlor and 1.50 mg/l of chlorothalonil, alachlor was first detected at 0.265, 0.47, and 1.86 pore volume (PV) and chlorothalonil was 3.71, 4.7 and 17.5 PV, respectively. The pore volumes at $C/C_o=1$ of alachlor in the leachates from Mureung, Jeju and Namwon soil columns were 1.1, 3.7 and 6.6 PV and those at $C/C_o=0.2$ of chlorothalonil were 7.5, 8.5 and 27.5, respectively. This means that the deceasing order of the mobility of the chemicals in soils was Mureung soil>Jeju soil${\gg}$Namwon soil. The pore volumes detecting $C/C_o=0.5$ of alachlor and $C/C_o=0.05$ of chlorothalonil in leachate were positively correlated with the distribution coefficients for the soils.