• Corrosion Science and Technology
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• v.13 no.1
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• pp.28-35
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• 2014

Recently, the fuel oil of diesel engines of marine ships has been increasingly changed to heavy oil of low quality as the oil price is getting higher and higher. Therefore, the spiral gear attached at the motor of the oil purifier which plays an important role to purify the heavy oil is also easy to expose at severe environmental condition due to the purification of the heavy oil in higher temperature. Thus, the material of the spiral gear requires a better mechanical strength, wear and corrosion resistance. In this study, the heat treatment(tempering) with various holding time at temperature of $500^{\circ}C$ was carried out to the alloy of Cu-7Al-2.5Si as centrifugal casting, and the properties of both hardness and corrosion resistance with and without heat treatment were investigated with observation of the microstructure and with electrochemical methods, such as measurement of corrosion potential, cathodic and anodic polarization curves, cyclic voltammogram, and a.c. impedance. in natural seawater solution. The ${\alpha}$, ${\beta}^{\prime}$ and ${\gamma}_2$ phases were observed in the material in spite of no heat treatment due to quenching effect of a spin mold. However, their phases, that is, ${\beta}^{\prime}$ and ${\gamma}_2$ phases decreased gradually with increasing the holding time at a constant temperature of $500^{\circ}C$. The hardness more or less decreased with heat treatment, however its corrosion resistance was improved with the heat treatment. Furthermore, the longer holding time, the better corrosion resistance. In addition, when the holding time was 48hrs, its corrosion current density showed the lowest value. The pattern of corroded surface was nearly similar to that of the pitting corrosion, and this morphology was greatly observed in the case of no heat treatment. It is considered that ${\gamma}_2$ phase at the grain boundary was corroded preferentially as an anode. However, the pattern of general corrosion exhibited increasingly due to decreasing the ${\gamma}_2$ phase with heat treatment. Consequently, it is suggested that the corrosion resistance of Cu-7Al-2.5Si alloy can be improved with the heat treatment as a holding time for 48 hrs at $500^{\circ}C$.

• Journal of the Korean Chemical Society
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• v.34 no.1
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• pp.51-62
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• 1990

Pentadentate Schiff base cobalt(II) complexes; Co(II)(Sal-DET) and Co(II)(Sal-DPT) were synthesized and these complexes were allowed to react with dry to form oxygen adducts of cobalt(II) complexes such as [Co(III)(Sal-DET)]$_2O_2$ and [Co(III)(DPT)]$_2O_2$ in aprotic solvents. These complexes have been identified by IR spectra, TGA, DSC, magnetic susceptibility measurements, and elemental analysis. It has been found that the oxygen adadduct complexes of $\mu$-peroxo type have hexaccordinated octahedral configuration with pentadentate schiff base cobalt(II) and oxygen, but the mole ratio of oxygen to cobalt(III) complexes of first step for oxygen adduct formation reaction of cobalt(II) complexes in aprotic solvents are 1:1. The redox reaction processes of Co(II)(Sal-DET), Co(II)(Sal-DPT), and oxygen adduct of cobalt(II) complexes were investigated by cyclic voltammetry and DPP method with glassy carbon electrode in 0.1M TEAP-DMSO and 0.1M TEAP-pyridine. As a result the reduction reaction processes of Co(III)/Co(II) and Co(II)/Co(I) for cobalt(II) complexes and oxygen adducts of cobalt(II) complexes are two irreversible steps of one eletron process, and reaction processes of oxygen for oxygen adducts complexes were quasireversible and redox range of potential was $E_{pc}$ = -0.97V∼-0.86V and $E_{pa}$ = -0.87V ∼ 0.64V.

• Journal of the Korean Chemical Society
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• v.31 no.6
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• pp.542-554
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• 1987

Tetradentate schiff base cobalt(II) complexes; Co(SED), Co(SND) and Co(SOPD) have been prepared, these complexes have react with dry oxygen in DMSO to form oxygen adducts cobalt(III) complexes; $[Co(SED)(DMSO)]_2O_2,\;[Co(SND)(DMSO)]_2O_2$ and $[Co(SOPD)(DMSO)]_2O_2$. It seems to be that the oxygen adducts cobalt(Ⅲ) complexes have heexa coordinated octahedral configration with tetradentate schiff base cobalt (III), DMSO and oxygen, and the mole ratio of oxygen to cobalt(II) complexes are 1 : 2, these complexes have been identified by IR-Spectra, T.G.A., magnetic susceptibilitis and elemental analysis of C.H.N. and Cobalt. The redox reaction process of Co(SED), Co(SND) and Co(SOPD) complexes was investigated by cyclic voltammetry with glassy carbon electrode in 0.1M TEAP-DMSO. The results of redox reaction process of Co(II) / Co(III) and Co(II) / Co(I) for cobalt(SED) and cobalt(SOPD) complexes and Co(II) / Co(III) process for cobalt(SND) complex are reversible process but Co(II) / Co(I) process of Cobalt(SND) complex is irreversible, and oxygen adduct complexes to quasi reversibly with oxygen should be very closed related to the redox potentials of range, $E_{pc}$ = -0.80~-0.89V and $E_{pa}$ = -0.70~-0.76V.

• Journal of the Korean Chemical Society
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• v.31 no.6
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• pp.509-519
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• 1987

The tetradentate Schiff base ligand, 3,4-bis(salicylidene diimine) toluene, have been prepared by the reaction of salicylaldehyde with 3,4-diaminotoluene by Duff method. The Schiff base ligand reacts with Ni(II), Co(II), and Cu(II) ions to form new complexes, [Ni(o-BSDT)${\cdot}(H_2O)_2$], [Co(o-BSDT)${\cdot}(H_2O)$], and [Cu(o-BSDT)]. It seems that Ni(II) and Ni(II) complexes are hexacoordinated with the Schiff base ligand and two molecules of water, while the Cu(II) complexes are tetracoordinated with the Schiff base. The mole ratio of tetradentate Schiff base ligand to metals was found to be 1 : 1. The redox chemistry of these complexes was investigated by polarography and cyclic voltammetry with glassy carbon electrode in DMSO with 0.1M TEAP${\cdot}$[Ni(o-BSDT)${\cdot}(H_2O)_2$] hav EC reaction mechanisms which undergo a irreversible electron transfer followed by a fast chemical reaction. [Co(o-BSDT)${\cdot}(H_2O)_2$] undergoes a reduction of Co(II) to Co(I) and a oxidation of Co(II) to Co(III), and [Cu(o-BSDT)] undergoes a reduction of Cu(II) to Cu(I).

• Journal of the Korean Chemical Society
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• v.35 no.1
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• pp.24-37
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• 1991

We synthesized the binuclear Tetradentate Schiff base nickel(II) and copper(II) complexes ; [Ni(II)$_2$(SMPO)$_2$(L)$_2$], [Ni(II)$_2$(SPPD)$_2$(L)$_2$] and [Cu(II)$_2$(SMPD)$_2$] and [Cu(II)$_2$(SPPD)$_2$] (where, L : Py, DMSO and DMF). We identified the structure of these complexes by elemental analysis, IR-spectrum, T.G.A, D.S.C and ESR measurements. According to the results of cyclic voltammetry and DPP measurements in aprotic solvent included 0.1M TEAP as supporting electrolyte, we knew that diffusional controlled redox process of one step with one electron was irreversible process in 0.1M TEAP-Py solution. Also it was reversible or quasi reversible process in 0.1M TEAP-DMSO solution and reversible or E.C reaction mechanism in 0.1M TEAP-DMF solution at mononuclear complexes ; [Cu(II)(SOPD)] and [Ni(II)(SOPD)(L)$_2$]. But, we knew that diffusional controlled redox process of two step for one electron of binuclear complexes was as follows. The values of redox potential for dimeric complexes in 0.1M TEAP-L solution (where, L ; Py, DMSO and DMF) with scan rate 100mV/sec.

• Membrane Journal
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• v.21 no.1
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• pp.1-12
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• 2011

Partially fluorinated poly(arylene ether sulfone) block ionomer membranes with different branch degree for fuel cell applications were investigated. A sulfonable monomer, a non-sulfonable monomer and a trifunctional branching agent were synthesized and the sulfonable monomer was oligomerized to obtain block structures. The oligomer was then further polymerized with the non-sulfonable monomer and the branching agent. The mole ratio of oligomer : non-sulfonable monomer was fixed at 4:6 and the content of the branching agent was varied from 0 to 2 mol% (BBC-40Bx). Post-sulfonation of BBC-40Bx was carried out using chlorosulfonic acid (CSA) (SBBC-40Bx). All the synthesized compounds were characterized by $^1H$-NMR, $^{19}F$-NMR and FT-IR. It was confirmed that the ion exchange capacity (IEC), water uptake and ion conductivity of SBBC-40Bx increased with the increment of branching agent content.

• Membrane Journal
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• v.26 no.5
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• pp.337-350
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• 2016

Lithium-ion rechargeable batteries (LIBs) have garnered increasing attention with the rapid advancements in portable electronics, electric vehicles, and grid-scale energy storage systems which are expected to drastically change our future lives. This review describes a separator membrane, one of the key components in LIBs, in terms of porous structure and physicochemical properties, and its recent development trends are followed. The separator membrane is a kind of porous membrane that is positioned between a cathode and an anode. Its major functions involve electrical isolation between the electrodes while serving as an ionic transport channel that is filled with liquid electrolyte. The separator membranes are not directly involved in redox reactions of LIBs, however, their aforementioned roles significantly affect performance and safety of LIBs. A variety of research approaches have been recently conducted in separator membranes in order to further reinforce battery safeties and also widen chemical functionalities. This review starts with introduction to commercial polyolefin separators that are currently most widely used in LIBs. Based on this understanding, modified polyolefin separators, nonwoven separators, ceramic composite separators, and chemically active separators will be described, with special attention to their relationship with future research directions of advanced LIBs.

• Transactions of the Korean hydrogen and new energy society
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• v.30 no.6
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• pp.523-530
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• 2019

For the low-Pt electrodes for polymer electrolyte fuel cells (PEMFCs), the optimization of ionomer content for anode catalyst layers was carried out. A commercial catalyst of 20 wt.% Pt/C was used instead of 50 wt.% Pt/C which is commonly used for PEMFCs. The ionomer content varies from 0.6 to 1.2 based on ionomer to carbon ratio (I/C) and the catalyst layer is formed over the electrolyte by the ultrasonic spray process. Evaluation of the prepared MEA in the unit cell showed that the optimal ionomer content of the air electrode was 0.8 on the I/C basis, while the hydrogen electrode was optimal at the relatively high ionomer content of 1.0. In addition, a large difference in cell performance was observed when the ionomer content of the hydrogen electrode was changed. Increasing the ionomer content from 0.6 to 1.0 by I/C in a hydrogen electrode with 0.05 mg/㎠ platinum loading resulted in more than double cell performance improvements on a 0.6 V. Through the analysis of various electrochemical properties in the single cell, it was assumed that the change in ionomer content of the hydrogen electrode affects the water flow between the hydrogen and air electrodes bounded by the membrane in the cell, which affects the overall performance of the cell. A more specific study will be carried out to understand the water flow mechanism in the future, and this study will show that the optimization process of hydrogen electrode can also be a very important cell design variable for the low-Pt and high-performance MEA.

• Korean Chemical Engineering Research
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• v.54 no.2
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• pp.157-162
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• 2016

Porous $Co(OH)_2$ nano-flake thin films were prepared by a potential-controlled electro-deposition technique at various deposition voltage (-0.75, -1.0, -1.2, and -1.4 V) on Ti-mesh substrates for supercapacitor application. The potential of electrode was controlled to regulate the film thickness and the amount of $Co(OH)_2$ nano-flake on the titanium substrate. The film thickness was shown to reach the maximum value of $34{\mu}m$ at -1.4 V of electrode potential, where 17.2 g of $Co(OH)_2$ was deposited on the substrate. The specific discharge capacitances were measured to be 226, 370, 720, and $1008mF\;cm^{-2}$ in the 1st cycle corresponding to the films which were formed at -0.75, -1.0, -1.2, and -1.4 V of electrode potentials, respectively. Then the discharge capacities were decreased to be 206, 349, 586 and $866mF/cm^{-2}$, where the persistency rates were 91, 94, 81, and 86%, respectively.

• Resources Recycling
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• v.25 no.3
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• pp.55-62
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• 2016

Steel structures exposed to extremely corrosive environment like marine environments and industrial area are generally manufactured by applying various protection treatment to increase their lifetime. Metal spraying is one of the protection methods to overcome some drawbacks of the widely employed technologies. Therefore, lots of research needs to be done to improve the corrosion resistance of steel structures. In this study, the corrosion resistance of steel structures was evaluated with the variation in the type and thickness of metal spray by measuring the corrosion potential and current density. As a raw material for spraying, Zn, Al and their mixture were employed to obtain coating thickness of $30{\sim}100{\mu}m$. Our data indicated that the pure zinc coating with $100{\mu}m$ showed the lowest corrosion potential. In the case of pure Al and Zn 85%-Al 15%, the corrosion potential and current density was decreased compared to pure zinc. It was found that the corrosion potential was decreased with the increase of coating thickness irrespective of the type of the coating.