• Journal of the Korean Electrochemical Society
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• v.16 no.4
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• pp.204-210
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• 2013

Thin pore-filled cation and anion-exchange membranes (PFCEM and PFAEMs, $t_m=25-30{\mu}m$) were prepared using a porous polymeric substrate for efficient all-vanadium redox flow battery (VRB). The electrochemical and charge-discharge performances of the membranes have been systematically investigated and compared with those of commercially available ion-exchange membranes. The pore-filled membranes were shown to have higher permselectivity as well as lower electrical resistances than those of the commercial membranes. In addition, the VRBs employing the pore-filled membranes exhibited the respectable charge-discharge performances, showing the energy efficiencies (EE) of 82.4% and 84.9% for the PFCEM and PFAEM, respectively (cf. EE = 87.2% for Nafion 1135). The results demonstrated that the pore-filled ion-exchange membranes could be successfully used in VRBs as an efficient separator by replacing expensive Nafion membrane.

• Bulletin of the Korean Chemical Society
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• v.25 no.1
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• pp.106-108
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• 2004

In this paper we have determined the thermodynamic parameters for the isomerization between the ${\alpha}$-cis and the ${\beta}$-cis isomers in vanadium(V)-propylenediaminetetraacetate complex in water by $^{51}V$ NMR spectroscopy. In addition, the effects of organic solvents (methanol, formamide and dimethylsulfoxide) and inorganic salts (NaCl, $NaClO_4\;and\;NH_4Cl$) on the isomerization in solution have been investigated.

• Proceedings of the Korean Vacuum Society Conference
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• 2015.08a
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• pp.125.2-125.2
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• 2015

The evolution of oxidation states of vanadium is monitored with ambient pressure X-ray photoemission spectroscopy. As the pressure of oxygen gas and surface temperature change, the formations of various oxidation states of vanadium are observed on the surface. Under 100mTorr of the oxygen gas pressure and 523K of sample temperature, VO2 and V2O5 are formed on the surface. The temperature-dependent resistance measurement on grown sample shows a clear metal-insulator transition near 350K. In addition, the measurement of Raman spectroscopy displays the structural change from monoclinic to rutile structures across the phase transition temperature.

• Korean Journal of Chemical Engineering
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• v.35 no.12
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• pp.2365-2378
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• 2018

We investigated the correlation between vanadium surface density and VOx structure species in the selective catalytic reduction of NOx by $NH_3$. The properties of the $VOx/TiO_2$ catalysts were investigated using physicochemical measurements, including BET, XRD, Raman spectroscopy, FE-TEM, UV-visible DRS, $NH_3-TPD$, $H_2-TPR$, $O_2-On/Off$. Catalysts were prepared using the wet impregnation method by supporting 1.0-3.0 wt% vanadium on $TiO_2$ thermally treated at various calcination temperatures. Through the above analysis, we found that VOx surface density was $3.4VOx/nm^2$, and the optimal V loading amounts were 2.0-2.5 wt% and the specific surface area was $65-80m^2/g$. In addition, it was confirmed that the optimal VOx surface density and formation of vanadium structure species correlated with the reaction activity depending on the V loading amounts and the specific surface area size.

• Korean Journal of Materials Research
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• v.8 no.10
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• pp.969-974
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• 1998

The effect of vanadium, which is known to decrease the stacking fault energy of Fe-base alloys, on the microstructure and elevated temperature sliding wear resistance of Fe-20Cr- 1.7C- 1Si alloy was investigated. The maximum amount of vanadium maintaining the austenitic matrix seems to be about 3wt.% in Fe-20Cr- 1.7C-1Si-xV (x = 0, 1, 3, 6. lOwt.%) alloys and the austenitic alloys showed better wear resistance than ferritic alloys. It was considered to be due to the low stacking fault energy and $\gamma->\alpha$ strain-induced phase transformation at rmm temperature. It was shown from elevated temperature sliding tests up to .$225^{\circ}C$ that the addition of vanadium increases the temperature, at which the transition from oxidative wear to adhesive wear occur, and the amount of d formed at $225^{\circ}C$. Thus, it was considered that the addition of vanadium improves the elevated temperature sliding wear resistance of Fe-20Cr- 1.7C - 1Si by reducing the increasing rate of stacking fault energy with temperature and by increasing Ma temperature.

• Resources Recycling
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• v.33 no.3
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• pp.3-11
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• 2024

This study addressed the cost structure of metallurgical plants for vanadium recovery or production, which were previously planned or implemented. Vanadium metallurgy consists of several sub-processes such as such as pretreatment, roasting, leaching, precipitation, and filtration, in order to finally produce vanadium pentoxide. Here, lots of costs should be spent for such plants, in which these costs are largely divided into CAPEX (Capital Expenditure) and OPEX (Operational Expenditure). As a result, the capacities (feed input rates) and vanadium contents are various along the target projects for this study. However, final production rates and grades of vanadium pentoxide showed relatively small differences. In addition, a noticeable correlation is found between capacities and specific operating costs, in that a steadily decreasing trend is described with a non-linear curve with around -0.3 power. Therefore, for the plant capacity below 100,000 tons per year, the specific operating cost rapidly decreases as the capacity increases, whereas the cost remains relatively stable in the range of 0.6 to 1.2 million tons per year of the capacity. From a technical perspective, effective optimization of the metallurgical process plant can be achieved by improving vanadium recovery rate in the pre-treatment and/or roasting-leaching processes. Finally, the results of this study should be updated through future research with on-going field verification and further detailed cost analysis.

• Journal of Power System Engineering
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• v.15 no.3
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• pp.52-57
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• 2011

440A martensitic stainless steels which were modified with reduced carbon content(~0.5wt.%) and addition of small amount of vanadium, tungsten and molybdenum 0.4wt.%, 0.4wt.% and 0.68wt.% respectively were manufactured. Effects of alloying elements and tempering temperatures on the intergranular corrosion were investigated through the method of DL-EPR(Double-electrochemical potentiodynamic reactivation). It was thought that the highest DOS(Degree of sensitization) of specimens was obtained at the tempering temperature of $450^{\circ}C$ regardless of types of alloy because of the precipitation of Cr7C3. Addition of vanadium lowered DOS a little above the tempering temperature of $550^{\circ}C$. It was considered to be effected by precipitation of VC carbides. Intergranular corrosion was influenced more by tempering temperature than by alloying elements of V, W and Mo.

• Corrosion Science and Technology
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• v.14 no.2
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• pp.76-84
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• 2015

The components in ultra super critical (USC) steam turbine, which is under development for high efficient power generation, are encountering harsher solid particle erosion by iron oxide scales than ones in the existing steam turbines. Therefore, the currently used boride coating will not be able to hold effective protection from particle erosion in USC system and should be replaced by new particle erosion resistant coatings. One of the best protective coatings developed for USC steam turbine parts was found to be vanadium-boride (V-boride) coating which has a hardness of about 3000 HV, much higher than that of boride, 1600~2000 HV. In order to evaluate particle erosion resistance of the various coatings such as V-boride, boride and Cr-carbide coatings at high temperature, particle erosion test equipments were designed and manufactured. In addition, erosion particle velocity was simulated using FLUENT software based on semi-implicity method for pressure linked equations revised (SIMPLER). Based on experimental results of this work, the vanadium-boride coating was found to be superior to others and to be a candidate coating to replace the boride coating.

• 한국신재생에너지학회:학술대회논문집
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• 2010.11a
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• pp.73.1-73.1
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• 2010

For the successful cold starting of a fuel cell engine, either internal of external heat supply must be made to overcome the formation of ice from water below the freezing point of water. In the present study, switchable vanadium oxide compounds as variable temperature-electrical resistance materials onto the surface of flat metallic bipolar plates have been prepared by a dip-coating technique via an aqueous sol-gel method. Subsequently, the chemical composition and micro-structure of the polycrystalline solid thin films were analyzed by X-ray diffraction, X-ray fluorescence spectroscopy, and field emission scanning electron microscopy. In addition, it was carefully measured electrical resistance hysteresis loop over a temperature range from $-20^{\circ}C$ to $80^{\circ}C$ using the four-point probe method. The experimental results revealed that the thin films was mainly composed of Karelianite $V_2O_3$ which acts as negative temperature coefficient materials. Also, it was found that thermal dissipation rate of the vanadium oxide thin films partially satisfy about 50% saving of the substantial amount of energy required for ice melting at $-20^{\circ}C$. Moreover, electrical resistances of the vanadium-based materials converge on an extremely small value similar to that of pure flat metallic bipolar plates at higher temperature, i.e. $T{\geq}40^{\circ}C$. As a consequence, experimental studies proved that it is possible to apply the variable temperature-electrical resistance material based on vanadium oxides for the cold starting enhancement of a fuel cell vehicle and minimize parasitic power loss and eliminate any necessity for external equipment for heat supply in freezing conditions.

• Journal of Powder Materials
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• v.30 no.6
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• pp.516-520
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• 2023

Highly safe lithium-ion batteries (LIBs) are required for large-scale applications such as electrical vehicles and energy storage systems. A highly stable cathode is essential for the development of safe LIBs. LiFePO₄ is one of the most stable cathodes because of its stable structure and strong bonding between P and O. However, it has a lower energy density than lithium transition metal oxides. To investigate the high energy density of phosphate materials, vanadium phosphates were investigated. Vanadium enables multiple redox reactions as well as high redox potentials. LiVPO₄O has two redox reactions (V⁵⁺/V⁴⁺/V³⁺) but low electrochemical activity. In this study, LiVPO₄O is doped with fluorine to improve its electrochemical activity and increase its operational redox potential. With increasing fluorine content in LiVPO₄O_1-xF_x, the local vanadium structure changed as the vanadium oxidation state changed. In addition, the operating potential increased with increasing fluorine content. Thus, it was confirmed that fluorine doping leads to a strong inductive effect and high operating voltage, which helps improve the energy density of the cathode materials.