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Kumaran Vediappan,이창우 한국물리학회 2010 Current Applied Physics Vol.10 No.2
The millennium application of new hydrogen absorbing alloys as negative electrodes in rechargeable batteries has allowed the consideration of nickel/metal hydride (Ni–MH) batteries to replace the conventional nickel cadmium alkaline or lead acid batteries. In this study the mechanical alloying process was used for synthesizing nanocrystalline TiCo–Mg-type hydrogen storage materials. The pressing negative and positive electrode, polyethylene as a separator and 6 mol/l KOH as an electrolyte solution constructed the cells. The nanocrystalline alloys electrode was subjected to charge/discharge cycle for more than 200 cycles. The discharge capacities of the nanocrystalline alloys withstand at 240 mAh/g with a nominal fading in capacity on prolonged cycling. The results show that when using sealed batteries nanocrystalline Ti[Co0.65Mg0.35] alloy electrode shows two times more capacity than TiNi counterparts.
Vediappan, Kumaran,Park, Suk-Jun,Kim, Hyun-Soo,Lee, Chang Woo American Scientific Publishers 2011 Journal of Nanoscience and Nanotechnology Vol.11 No.1
<P>Novel cathode active materials, Li[Li(x)(Ni0.3Co0.1Mn0.6)1-x]O2 (x = 0.09, 0.11) composed of rod-like primary particles, but aggregated spherical shape in appearance, were synthesized. The newly Mn-rich cathode active materials were then adopted as cathodes to show the benefits for Li-ion rechargeable batteries. The results show that to use proper nano-scaled particles as a cathode and to make homogeneous particle sizes have great improvements on electrochemical performances, probably ascribed to enhancement of charge transfer kinetics and lower cell impedance at high voltage region (approximately 4.6 V). The electrochemical performances of Mn-rich cathodes were investigated by cycler (BT2000, Arbin), comparing electrochemical behaviors between room and elevated temperature, 55 degtees C. The morphology of cathodes having nano-scaled particles of active materials and the Mn-rich cathode active materials were investigated using field emission scanning electron microscope (FE-SEM) and field emission transmission electron microscope (FE-TEM), also the crystalline phase identification was analyzed by high power X-ray diffractometer (XRD).</P>
Vediappan, Kumaran,Kim, Woo-Sik,Lee, Chang Woo American Scientific Publishers 2011 Journal of Nanoscience and Nanotechnology Vol.11 No.2
<P>Mn-rich layered Li[Ni0.3M0.2Mn0.5]O2 (M = Mg, In, and Gd) cathode active materials were synthesized by a simple sol-gel method and comparative studies of those materials depending on doping elements were carried out.</P>
Vediappan, Kumaran,Kim, Hyun-Soo,Lee, Chang Woo American Scientific Publishers 2012 Journal of Nanoscience and Nanotechnology Vol.12 No.4
<P>High rate capable Mn-rich layered Li[Li(x)(Ni0.3Co0.1Mn0.6)1-x]O2 (x = 0.09, 0.11) cathode materials that are fully charged are investigated with respect to stability. Differential scanning calorimetry is used to determine the thermal stability of cathode material compositions together with PVdF binder and a conductive agent by heating from 30 degrees C to 400 degrees C at 10 degrees C/min. In the Li[Li(x)(Ni0.3Co0.1Mn0.6)1-x]O2 (x = 0.09, x = 0.11) cathode materials, the exothermic reaction started at 100 degrees C. Due to thermal runway, a sharp peak was observed at 279.25 degrees C for the material of x = 0.09 with exothermic heat generation of 168.4 J/g. For the Mn-rich cathode material, where x = 0.11, two relatively smaller peaks appeared at 250.72 degrees C and 268.60 degrees C with heat evolution of 71.49 J/g and 93.67 J/g, respectively. These layered cathode materials are thermally stable. The x = 0.09 composition shows huge heat flow occurrence when compared to the x = 0.11. It is concluded from a heat generation analysis that the two Mn-rich cathode materials are thermally stable for lithium rechargeable batteries.</P>
Vediappan, Kumaran,Lee, Chang Woo Royal Swedish Academy of Sciences 2010 Physica scripta Vol.2010 No.t139
<P>Lithium manganese oxide (LiMn<SUB>2</SUB>O<SUB>4</SUB>) is an inexpensive and pollution-free cathode material for Li-ion rechargeable batteries. In this study, spinel LiMn<SUB>2</SUB>O<SUB>4</SUB> cathode material was coated with biomineral powders by the mechano-chemical method. In the course of the material synthesis, citric acid and acryl amide were added to serve as a complexing agent and a gelling agent, respectively, followed by a calcination process at 700 °C for 6 h in a high-purity argon atmosphere. The spinel LiMn<SUB>2</SUB>O<SUB>4</SUB> and biominerals-coated spinel LiMn<SUB>2</SUB>O<SUB>4</SUB> cathode materials were, from diverse viewpoints, characterized by x-ray diffraction, field emission-scanning electron microscopy, Fourier transform infrared spectroscopy and the electrochemical cycling method to understand the mechanism of improvements in electrochemical performances. We suggest that the biominerals-coated spinel LiMn<SUB>2</SUB>O<SUB>4</SUB> is a good candidate as a low cost and environmentally friendly cathode material showing the enlarged capacity characteristic of Li-ion rechargeable batteries.</P>
Electrochemical approaches for the determination of ranitidine drug reaction mechanism
Kumaran Vediappan,이창우 한국물리학회 2011 Current Applied Physics Vol.11 No.4
The electrochemical reduction reaction of ranitidine, an antileprotic drug, was studied in an aqueous potassium chloride buffer with a stationary glassy carbon electrode. Cyclic voltammetric studies showed a well-defined reduction peak in the potential range from 0.0 to ―1.8 V at pH values ranging from 1.0 to 11.0. The reduction was irreversible and has exhibited a diffusion-controlled adsorption. Controlled potential coulometry revealed four electron reductions with a total charge consumption of 785 mC. A systematic study of the experimental parameters that affected the square wave stripping response was carried out, and the conditions were optimized. A calibration plot was derived for the determination of the compound. The best determination range was obtained between 0.033 and 3.33 mg/L ranitidine with a relative standard deviation (n = 10) of 3 ppt (0.3%). Analytical applicability of the method was verified by the determination of ranitidine in tablets, dosing of drugs, gene profiling, monitoring of biologically important metabolites and urine samples. Also these techniques could make easier many arduous procedures such as in-situ assessment of weapons or toxic substances, environment pollution and others.
강석현,조용남,K. Prasanna,P. Santhoshkumar,조윤철,Kumaran Vediappan,Ramasamy Gnanamuthu,이창우 한국공업화학회 2019 Journal of Industrial and Engineering Chemistry Vol.71 No.-
As a promising anode material, TiO2 x is prepared with a low bandgap by adding a zinc powder using asolvothermal reaction. It is homogeneous, spherical, and 30 nm in size, changing from anatase to rutile. Itshows a high discharge capacity, 253.8 mAh g 1, after 50 cycles at 100 mA g 1 whereas the pristine TiO2material delivers mere 81.1 mAh g 1. The improved electrochemical performance with cycling of theTiO2 x compared with the pristine TiO2 material is attributed to the presence of Ti3+ and/or oxygenvacancies.