• Applied Chemistry for Engineering
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• v.7 no.6
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• pp.1132-1141
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• 1996

Heterogeneous cation exchange membrane(HCEM) was prepared with LLDPE(Linear Low Density Poly-ethylene) as binder, powdered cation exchange resins($diameter{\leq}149{\mu}m$) as ion-exchange material and glycerol as additive for electrodialysis and electrodeionization system. The weight ratio of (binder/ion exchange)/glycerol was (60%/40%)/5%, (55%/45%)/5%, (50%/50%)/5% and (40%/60%)/5%. The characterization of prepared HCEM was evaluated on mechanical, electrochemical, morphology and ion permeable properties. It was compared with commercial membrane. Electrochemical properties of HCEM of (50%/50% )/5% were very similar to value of IONPURE(commercial membrane), in which ion exchange capacity, ion transfer number and membrane resistance were to be 1.733meq/g, 0.96 and $16.08{\Omega}/cm^2$, respectively. Ion permeability of the membrane was better than that of IONPURE membrane. Compared with IONPURE membrane, the HCEM had a higher tensile strength and lower elongation and modulus, in which HCEM had tensile strength of $62.33kg/cm^2$, elongation of 87.42% and modulus of $658.53kg/cm^2$. The HCEM of (50%/50% )15% was optimum combination.

• Korean Chemical Engineering Research
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• v.56 no.6
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• pp.901-908
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• 2018

Graphite is used as a sample anode active material. However, since the maximum theoretical capacity is limited to $372mA\;h\;g^{-1}$, a new anode active material is required for the development of a high capacity lithium ion battery. The maximum theoretical capacity of Si is $4200mA\;h\;g^{-1}$, which is higher than that of graphite. However, it is not suitable for direct application to the anode active material because it has a volume expansion of 400%. In order to minimize the decrease of the discharge capacity due to the volume expansion, the Si was pulverized by the dry method to reduce the mechanical stress and the volume change of the reaction phase, and the change of the volume was suppressed by coating the carbon layers to the particle size controlled Si particles. And carbon fiber is grown like a thread on the particle surface to control secondary volume expansion and improve electrical conductivity. The physical and chemical properties of the materials were measured by XRD, SEM and TEM, and their electrochemical properties were evaluated. In this study, we have investigated the synthesis method that can be used as anode active material by improving cycle characteristics of Si.

• Restorative Dentistry and Endodontics
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• v.18 no.2
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• pp.431-445
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• 1993

The purpose of this study was to observe corrosion characteristics of six dental amalgams and was to analyse corrosion products electrochemically. After each amalgam alloy and Hg was triturated as the direction of the manufacturer by using mechanical amalgamator, the triturated mass was inserted into the cylinderical metal mold ($12{\times}10mm$) and was condensed with 160kg/$cm^2$ by using the hydrolic press. The specimen was removed from the mold and was stored at room temperature for 1 week, and was polished with amalgam polishing kit. The anodic and cathodic polarization curve was obtained by using cyclic voltammetric method with 3-electrode potentiostat in saline for each amalgam and Ag, Sn, Cu plate specimen at $37{\pm}0.5^{\circ}C$. The potential sweep range was -1.7V~0. 4V(vs SCE) in working electrode and scan rate was 50mV/s and the exposed surface area of each specimen to the electrolytic solution was $0.79cm^2$. The results were as follows. 1. In anodic-cathodic polarization curve of amalgam specimens, two anodic current rising areas and two cathodic current peaks were obtained at the low Cu amalgam(CF, CS) specimen and three anodic current rising areas and three cathodic current peaks were obtained at the high Cu amalgam (TY, DS, HV) specimen. 2. As this compared with the anodic and cathodic current peak potentials of Sn, Cu and Ag specimen, the first cathodic current peak I c was caused by the reduction of divalent tin salt, second cathodic current peak IIIc results from the reduction of quadravalent tin salt, and third cathodic current peak me results from the reduction of copper salt. 3. As reverse potential sweeping was done repeatedly, anodic current was decreased slightly in all amalgam specimens.

• Corrosion Science and Technology
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• v.11 no.6
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• pp.280-285
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• 2012

Aluminum is on active metal, but it is well known that its oxide film plays a role as protective barrier which is comparatively stable in air and neutral aqueous solution. Thus, aluminum alloys have been widely applied in architectural trim, cold & hot-water storage vessels and piping etc., furthermore, the aluminum alloy of AC8A have been widely used in mold casting material of engine piston because of its properties of temperature and wear resistance. In recent years, the oil price is getting higher and higher, thus the using of low quality oil has been significantly increased in engines of ship and vehicle. Therefore it is considered that evaluation of corrosion resistance as well as wear resistance of AC8A material is also important to improve its property and prolong its lifetime. In this study, the effect of solution and tempering heat treatment to corrosion and wear resistance is investigated with electrochemical method and measurement of hardness. The hardness decreased with solution heat treatment compared to mold casting condition, but its value increased with tempering heat treatment and exhibited the highest value of hardness with tempering heat treatment temperature at $190^{\circ}C$ for 24hrs. Furthermore, corrosion resistance increased with decreasing of the hardness, and decreased with increasing of the hardness reversely. As a result, it is suggested that the optimum heat treatment to improve both corrosion and wear resistance is tempering heat treatment temperature at $190^{\circ}C$ for 16hrs.

• Journal of Advanced Marine Engineering and Technology
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• v.39 no.5
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• pp.536-541
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• 2015

Copper has been used extensively as an electric wire or as a base material in various types of machineries owing to its good electrical and thermal conductivity and good fabricating property, as well as its good corrosion resistance compared to iron. Furthermore, the copper-nickel alloy has significant corrosion resistance in severely corrosive environments. Although, cupro-nickel alloy shows better corrosion resistance than the brass and bronze series, this alloy also corroded in severely corrosive environments, including aggressive chloride ions, dissolved oxygen, and condition of fast flowing seawater. In this study, and annealing treatment at various annealing temperatures was carried out on the cupro-nickel (Cu-10%Ni) alloy, and the effects of annealing were investigated using electrochemical methods, such as measuring the polarization and impedance behaviors under flowing seawater conditions. The corrosion resistance increased by annealing compared to non heat treatment in the absence of flowing seawater. In particular, the sample annealed at $200^{\circ}C$ exhibited the best corrosion resistance. The impedance in the presence of flowing seawater showed higher values than in the absence of flowing seawater. Furthermore, the highest impedances was observed in the sample annealed at $800^{\circ}C$, irrespective of the present of flowing seawater. Consequently, the corrosion resistance of cupro-nickel (Cu-10%Ni) alloy in a severely corrosive environment can be improved somewhat by annealing.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2017.05a
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• pp.153-153
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• 2017

The application of the coating supports the mechanical characteristics of the implant, and various materials and coatings are currently being used in the implant in a way to accelerate adhesion. Especially, plasma electrolytic oxidation (PEO) coating has been proposed continually with good surface treatment of titanium alloys. Also, the PEO process can incorporate Ca and P ions on the titanium surface through variables varied factor. PEO process for bioactive surface has carried out in electrolytes containing Ca and P ions. Natural bone is composed of mineral elements such as Mg, Si, Zn, Sr, and Mn, etc. Especially, Mg and Si of these elements play role in bone formation and growth after clinical implantation of bio-implants. In this study, corrosion charateristics of PEO-treated Ti-6Al-4V alloy in solution containing Si and Mg ions has been investigated using several experimental techniques. The PEO-treated surfaces were identified by X-ray diffraction, using a diffractometer (XRD, Philips X' pert PRO, Netherlands) with Cu $K{\alpha}$ radiation. The morphology was observed by field-emission scanning electron microscopy (FE-SEM, Hitachi 4800, Japan) and energy-dispersive X-ray spectroscopy (EDX, Oxford ISIS 310, England). The potentiodynamic polarization and AC impedance tests for electrochemical degradations were carried out in 0.9% NaCl solution at similar body temperature using a potentiostat with a scan rate of 1.67mV/s and potential range from -1500mV to + 2000mV.

• International Journal of Ocean System Engineering
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• v.2 no.4
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• pp.209-213
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• 2012

Recently, the fuel using in the diesel engines of marine ships has been changed to a low quality of heavy oil because of the steady increase in the price of oil. Therefore, the wear and corrosion in all parts of the engine such as the cylinder liner, piston crown, and spindle and seat ring of exhaust valves has correspondingly increased. The repair welding of a piston crown is a unique method for prolonging its lifetime from an economic point of view. In this case, filler metals with a high corrosion and wear resistance are mainly being used for repair welding. However, often at a job site on a ship, a piston crown is actually welded with mild filler metals. Therefore, in this study, mild filler metals such as CSF350H, E8000B2, and 435 were welded to SS401 steel as the base metal, and the corrosion properties of the weld metals with and without post weld heat treatment were investigated using some electrochemical methods in a 0.1% $H_2SO_4$ solution. The weld metal welded with CSF350H filler metal exhibited the best corrosion resistance among these filler metals, irrespective of the heat treatment. However, the weld metal zones of the E8000B2 and 435 filler metals exhibited better and worse corrosion resistance with the heat treatment, respectively. As a result, it is suggested that in the case of repair welding with CSF350H and 435 filler metals, no heat treatment is advisable, while heat treatment is desirable if E8000B2filler metal is used with repair welding.

• Korean Journal of Metals and Materials
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• v.47 no.9
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• pp.586-590
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• 2009

The effects of additives on the surface morphology and physical properties of copper electrodeposited on polyimide(PI) film were investigated here. Two kinds of additives, an activator(additive A) and a leveler(additive B),were used in this study. Electrochemical experiments, in conjunction with scanning electron microscopy(SEM), X-ray diffraction(XRD) and a four-point probe, were performed to characterize the morphology and mechanical characteristics of copper electrodeposited in the presence of the additives. The surface roughness, crystal growth orientation and resistivity could be controlled using various quantities of additive B. High resistivity and lower peel strength were observed on the surface of the copper layer electroplated onto the electrolyte with no additive B. However, a uniform surface, lower resistivity and high flexibility were obtained with a combination of 20 ppm of additive A and 100 ppm of additive B.

• Korean Journal of Materials Research
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• v.18 no.9
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• pp.457-462
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• 2008

Through the electrostatic interaction between the poly-diallydimethylammonium chloride (PDDA) modified Multi-walled carbon nanotube (MWNT) and $SnO_2$ suspension in 1mM $NaNo_3$ solution, MWNT-$SnO_2$ nanocomposites (MSC) for anode electrodes of a Li-ion battery were successfully fabricated by colloidal heterocoagulation method. TEM observation showed that most of the $SnO_2$ nanoparticles were uniformly deposited on the outside surface of the MWNT. Galvanostatic charge/discharge cycling tests showed that MSC anodes exhibited higher specific capacities than bare MWNT and better cyclability than unsupported nano-$SnO_2$ anodes. Also, after 20 cycles, the MSC anode fabricated by heterocoagulation method showed more stable cycle properties than the simply mixed MSC anode. These improved electrochemical properties are attributed to the MWNT, which adsorbs the mechanical stress induced from volume change and increasing electrical conductivity of the MSC anode, and suppresses the aggregation between the $SnO_2$ nanoparticles.

• Journal of Powder Materials
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• v.14 no.6
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• pp.372-379
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• 2007

The microstructure, mechanical and electrochemical properties of plasma electrolytic coatings (PEO) coatings on Mg-4.3 wt%Zn-1.0 wt%Y and Mg-1.0 wt%Zn-2.0 wt%Y alloys prepared by gas atomization, followed by compaction at 320 for 10 min under the pressure of 700 MPa and sintering at 380 and 420 respectively for 24 h, were investigated, which was compared with the cast Mg-1.0 wt%Zn alloy. All coatings consisting of MgO and $Mg_2SiO_4$ oxides showed porous and coarse surface features with some volcano top-like pores distributed disorderly and cracks between pores. In particular, the surface of coatings on Mg-1.0 wt%Zn-2.0 wt%Y alloy showed smaller area of pores and cracks compared to the Mg-4.3 wt%Zn-1.0 wt%Y and Mg-1.0 wt%Zn alloys. The cross section micro-hardness of coatings on the gas atomized Mg-Zn-Y alloys was higher than that on the cast Mg-1.0 wt%Zn alloy. Additionally, the coated Mg-1.0 wt%Zn-2.0 wt%Y alloy exhibited the best corrosion resistance in 3.5%NaCl solution. It could be concluded that the addition of Y has a beneficial effect on the formation of protective and hard coatings on Mg alloys by plasma electrolytic oxidation treatment.