• Journal of Korea Foundry Society
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• v.35 no.5
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• pp.114-119
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• 2015

This paper reports the effect of a refractory crucible type on the microstructure of duplex stainless steel (DSS) cast with the addition of gadolinium using air-induction melting. Grade 4A DSSs with 1 wt% of gadolinium (Gd) were fabricated in various crucibles including alumina ($Al_2O_3$), magnesia (MgO), calcia (CaO) coated with yttria ($Y_2O_3$) and graphite. The standard free energies of the formation of calcium and yttrium oxide were lower than those of gadolinium oxide and other crucible elements based oxide. The yield of Gd in DSS using $Al_2O_3$, MgO, CaO-coated $Y_2O_3$ and graphite was 5, 19, 83 and 96%, respectively. As Gd yield increased, the amount of Gd-based inclusions increased, the size of the inclusions were reduced, and the inclusions became evenly distributed.

• Carbon letters
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• v.15 no.1
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• pp.38-44
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• 2014

This paper reports the effect of adding reduced graphene oxide (RGO) as a conductive material to the composition of an electrode for capacitive deionization (CDI), a process to remove salt from water using ionic adsorption and desorption driven by external applied voltage. RGO can be synthesized in an inexpensive way by the reduction and exfoliation of GO, and removing the oxygen-containing groups and recovering a conjugated structure. GO powder can be obtained from the modification of Hummers method and reduced into RGO using a thermal method. The physical and electrochemical characteristics of RGO material were evaluated and its desalination performance was tested with a CDI unit cell with a potentiostat and conductivity meter, by varying the applied voltage and feed rate of the salt solution. The performance of RGO was compared to graphite as a conductive material in a CDI electrode. The result showed RGO can increase the capacitance, reduce the equivalent series resistance, and improve the electrosorption capacity of CDI electrode.

• Polymer(Korea)
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• v.35 no.3
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• pp.265-271
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• 2011

Graphene oxide (GO) was prepared by the Hummers and Offeman method from graphite. Reduced graphene oxide (EGO) and functionalized graphenes were synthesized from GO by using hydrazine hydrate and amine-functionalized alkyl groups, respectively. The structures of the GO, EGO, and functionalized graphenes were identified by FTIR and $^{13}C$ NMR. In addition, we examined the thermal stability, morphology and dispersibility of the materials in various organic solvents. AFM disclosed that GO and RGO consisted of one- or two-layer graphene regions throughout the film. However, the functionalized graphene films showed average thicknesses of 2.26~3.30 nm, The thermal stability of the functionalized graphenes was poorer than that of the EGO. The functionalized graphenes were well dispersed in toluene or chloroform, as evidenced by the lack of the characteristic graphite reflection in the solutions.

• Applied Chemistry for Engineering
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• v.18 no.3
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• pp.291-295
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• 2007

The oxidation treatment of needle cokes with 70 wt% of nitric acid and sodium chlorate ($NaClO_3$) was attempted to achieve an electrochemically active material with a large capacitance. The structure of needle cokes was changed to graphite oxide after oxidation treatment of needle cokes with acidic solution having the composition ratio, $NaClO_3$/needle cokes, of 7.5, and the inter-layer distance of the oxidized needle cokes was extended to $6.9{\AA}$with increasing oxygen content. On the other hand, the electrochemical performance of oxidized needle cokes as a polarized electrode for an Electric Double Layer Capacitor (EDLC) was examined with an electrolyte of 1.2 M $TEABF_4$ (tetraethylammonium tetrafluoroborate) and $TEABF_4$ (triethylmethylammonium tetrafluoroborate) in acetonitrile. The capacitor cell using 1.2 M $TEABF_4$/acetonitrile has exhibited smaller electric resistance of $0.05{\Omega}$, and larger capacitance per weight and volume of 32.0 F/g and 25.5 F/mL at the two-electrode system in the potential range 0~2.5 V than that of the capacitor cell using $TEABF_4$. The observed electrochemical performance was discussed with the correlation between the inter-layer distance in graphite oxide structure and the anionic size of electrolyte.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1995.10a
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• pp.181-187
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• 1995

The effet of glass fiber and graphite on the wear properies in tin-bronze alloy matrix composites was studied by a pin-on-disk type wear testing machine. The results obtained from the wear test were analized by SEM observations of worn surfaces of pins and disks and EPMA composition measurments. The amount of wear was devreased as increasing the content of glass fiber in matrix, since the alloy matrix was reinforced by glass fibers. The wear mechanism of the matrix specimen without glass fibers was proved as the contact area delamination. Oxide layer formed on sliding surface led to the increasing wear resistance. Specimens containing graphite particles showed an lubrication effect to counter disks.

• Transactions of the Society of Information Storage Systems
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• v.8 no.2
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• pp.56-60
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• 2012

Graphene oxide, which is exfoliated by oxidant from graphite, is the material for solving the problem of mass production and positioning. We made graphene oxide based devices by dielectrophoresis, studied and controlled factors which can affect the characteristic of graphene oxide channel. Graphene oxide channel assembled by dielectrophoresis can be constructed differently by various frequency options. We confirmed the change of gate characteristics and I-V characteristics in the range from 80K to 300K temperature.

• Transactions of the Society of Information Storage Systems
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• v.9 no.1
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• pp.22-27
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• 2013

In this paper we are presenting a architecture of Co ion decorated graphene oxide as an electrode for supercapacitor application. Graphene oxide, which is exfoliated by oxidant from graphite, is the material for solving the problem of mass production and coating on the surface of working electrode. The $Co^{2+}$ ions are coated by using layer by layer(LBL) method on graphene oxide foam. The metal ion decorated graphene oxide shows enhanced capacitance performance when tested as supercapacitor electrode, showing the specific capacitance of $827Fg^{-1}$.

• Applied Chemistry for Engineering
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• v.33 no.6
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• pp.600-605
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• 2022

In this study, nitrogen oxide (NO_x) removal experiments were performed using a graphene based ceramic filter coated with a V₂O₅-WO₃-TiO₂ catalyst. Graphene oxide (GO) was prepared by Hummer's method using graphite, and the reduced graphene oxide was produced by reducing with hydrazine (N₂H₄). Vanadium (V), Tungsten (W), and Titanium (Ti) were coated by the sol-gel method, and then a metal oxide-supported filter was prepared through a calcination process at 350 ℃. A NO_x removal efficiency test was performed for the catalytic ceramic filters with UV light in a humid condition. When graphene oxide (GO) and reduced graphene oxide (rGO) were present on the filter, the NOx removal efficiency was superior to that of the conventional ceramic filter. Most likely, this is due to an improvement in the adsorption properties of NOx molecules on graphene coated surfaces. As the concentration of graphene increased, higher NO_x removal efficiency was confirmed.

• Journal of Electrochemical Science and Technology
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• v.6 no.1
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• pp.16-25
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• 2015

Transition metal oxide nanocrystalline materials are playing major role in energy storage application in this scenario. Nickel oxide is one of the best antiferromagnetic materials which is used as electrodes in energy storage devices such as, fuel cells, batteries, electrochemical capacitors, etc. In this research work, nickel oxide nanoparticles were synthesized by combustion route in presence of organic fuels such as, glycine, glucose and and urea. The prepared nickel oxide nanoparticles were calcined at 600℃ for 3 h to get phase pure materials. The calcined nanoparticles were preliminarily characterized by XRD, particle size analysis, SEM and EDAX. To prepare nickel oxide electrode materials for application in supercapacitors, the calcined NiO nanoparticles were mixed with di-methyl-acetamide and few drops of nafion solution for 12 to 16 h. The above slurry was coated in the graphite sheet and dried at 50℃ for 2 to 4 h in a hot air oven to remove organic solvent. The dried sample was subjected to electrochemical studies, such as cyclic voltammetry, AC impedance analysis and chrono-coulometry studies in KOH electrolyte medium. From the above studies, it was found that nickel oxide nanoparticles prepared by combustion synthesis using glucose as a fuel exhibited resulted in low particle diameter (42.23 nm). All the nickel oxide electrodes have shown better good capacitance values suitable for electrochemical capacitor applications.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.175.2-175.2
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• 2014

Graphene (G) has been modified with palladium, copper, and manganese oxide nanoparticles (NPs), and their catalytic applications have been studied in C-C coupling reactions and methylmercaptan (CH3SH) decomposition reactions. In this research, graphite oxide (GO) sheets were exfoliated and oxidized from graphite powder and impregnated with metal precursors including Pd2+, Cu2+, and Mn2+. The thermal treatments of the metal impregnated GO in preferred gas environments produced Pd NPs on graphene (Pd/G), PdO NPs on GO (PdO/GO), and CuOx and MnOx NPs on graphene (CuOx/MnOx/G). In case of Pd/G and PdO/GO, the TEM images show that, although the mean size of the Pd NPs changed significantly before and after the C-C coupling reaction, that of the PdO NPs didn't, implying that the PdO/GO was superior to Pd/G in terms of the recyclability. Also, we demonstrate that the CuOx/MnOx/G exerts the excellent catalytic efficiency in CH3SH decomposition reaction comparing with conventional catalysts. The chemical and electronic structural changes were investigated using XRD and XPS.