Choi J.-H.,Kongju National University
Desalination | Year: 2014
In this study, the potential at which electrode reactions start and the effects of these reactions on membrane capacitive deionization (MCDI) were investigated. An adsorption experiment was conducted until the cell potential reached 1.2V, applying constant current to an MCDI unit cell. While varying the current density (5.0-20.0A/m2), the changes in cell potential, electrical conductivity and effluent pH were measured. The results of the experiment showed that the ion adsorption decreased significantly as the current density increased. Furthermore, the pH of the effluent rapidly decreased beyond a certain time in the adsorption process, which is judged to be the result of electrode reactions. When the electrode reactions started, the cell voltages were in the range of 0.62-0.90V, which varied greatly depending on the current density. Using a simple model for the MCDI cell, the electrode potential was calculated from the cell potential and current density. Regardless of the current density applied, the electrode reaction was started at the electrode potential of 0.25V. It is desirable to use the electrode potential instead of the cell potential to analyze the electrode reactions in MCDI operation. © 2014 Elsevier B.V.
Kang J.,Kongju National University
Journal of Sound and Vibration | Year: 2012
Squeal propensity of the in-plane modes and the constrained-layer type damping shims for disc brake system is investigated by using the finite element method. Theoretical formulation is derived for a rotating disc in contact with two stationary vibrating pads attached to the damping shim components. By the conversion from the theoretical to FE brake model, the full equations of motion for the actual disc brake system describes the disc rotation, the in-plane friction characteristics and damping shims in association with squeal vibration. It is concluded from the results that the in-plane torsion modes can be generated by the negative friction slope, but they cannot be controlled by the damping shims. The in-plane radial mode is also investigated and found to be very insensitive in squeal generation. © 2012 Elsevier Ltd. All rights reserved.
Kwon J.E.,Seoul National University |
Park S.,Kongju National University |
Park S.Y.,Seoul National University
Journal of the American Chemical Society | Year: 2013
A full-color molecular pixel system is realized for the first time using simple mixtures composed of RGB-emitting excited-state intramolecular proton transfer (ESIPT) dyes, each of which has delicately tailored Stokes shift and independent emission capability completely free from energy transfer crosstalk between them. It is demonstrated that the whole range of emission colors enclosed within the RGB color triangle on the CIE 1931 diagram is predictable and conveniently reproducible from the RGB molecular pixels not only in the solution but also in the polymer film. It must be noted that mixing ratios to reproduce the desired color coordinates can be precisely calculated on the basis of additive color theory according to their molecular pixel behavior. © 2013 American Chemical Society.
Shin H.-S.,Kongju National University
Journal of Chromatography A | Year: 2012
A sensitive gas chromatographic method has been established for the determination of bromate in ozonated and chlorinated water, and in sea water. With acidic conditions, bromate reacts with chloride to form bromine, which reacts with 2,6-dialkylphenol to form 4-bromo-2,6-dialkylphenol. The organic derivative was extracted with ethyl acetate after quenching remaining oxidants with ascorbic acid, and then measured by gas chromatography-mass spectrometry (GC-MS). The lowest detection limit and limit of quantification of bromate in drinking water were 0.02 and 0.07μg/L, respectively, and the calibration curve showed good linearity with r 2=0.998. The 32 common ions did not interfere even when present in 100-fold excess over the bromated ion. The accuracy was in a range of 102-106% and the precision of the assay was less than 6% in chlorinated and ozonated tap water, ozonated mineral water, and sea water. The method was sensitive, reproducible and simple enough to permit reliable analysis of bromate to the ng/L level in water. © 2011 Elsevier B.V..
Choi J.-H.,Kongju National University
Separation and Purification Technology | Year: 2010
A carbon electrode was fabricated in a simple and inexpensive manner through a drying process after casting an electrode slurry made of activated carbon powder (ACP) blended in a polymer solution on the current collector. The electrochemical characteristics of the fabricated electrode were analyzed, and the salt removal efficiency was studied by changing the electrode potential and flow rate after manufacturing a unit cell. An analysis of the characteristics of the fabricated electrode through cyclic voltammetry and impedance spectroscopy indicated a capacitance of 0.47 F/cm2. An electrochemical oxidation/reduction reaction occurred when the potential was applied under the influence of a functional group extant on the ACP surface. Salt removal tests using a 200-mg/L NaCl solution, conducted by preparing a CDI unit cell with the fabricated electrode, indicated a high average salt removal efficiency of 77.8% with an applied 1.5-V electrode potential and a 20-mL/min solution flow rate. The adsorbed ions were mostly desorbed within 1 min after applying a desorption potential, indicating that the desorption proceeded at a high speed. © 2009 Elsevier B.V. All rights reserved.