• Journal of the Korean Ceramic Society
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• v.45 no.9
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• pp.556-560
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• 2008

The effects of Nb and Co ion substitution on the dielectric and magnetic properties of the multiferroic $BiFeO_3$ thin films have been investigated. Heteroepitaxial $BiFeO_3$ thin films were deposited by Pulsed Laser Deposition method. Nb substitution decreased the leakage current by 6 orders of magnitude and Co substituted $BiFeO_3$ thin films showed an enhanced magnetization, 2 times larger than that of un-substituted $BiFeO_3$. Through the co-substitution of Co and Nb, $BiFeO_3$ thin films with a low leakage current and an enhanced magnetization could be obtained.

• Journal of Powder Materials
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• v.18 no.4
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• pp.332-339
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• 2011

Cemented tungsten carbide has been used in cutting tools and die materials, and is an important industrial material. When the particle size is reduced to ultrafine, the hardness and other mechanical properties are improved remarkably. Ultrafine cemented carbide with high toughness and hardness is now widely used. The objective of this study is synthesis of nanostructured WC-Co powders by liquid phase method of tungstate. The precursor powders were obtained by freezen-drying of aqueous solution of soluble salts, such as ammonium metatungstate, cobalt nitrate. the final compositions were WC-10Co. In the case of liquid phase method, it can be observed synthesis of WC-10Co. The properties of powder produced at various temperature, were estimated from the SEM, BET and C/S analyser.

• Analytical Science and Technology
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• v.17 no.6
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• pp.532-535
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• 2004

A method on the determination of Co(II) after adsorbing of Co(II) on 2-mercaptobenzothiazole-loaded silica gel was studied. The conditions on the separation of Co(II) such as pH of solution, the amount of 2-mercaptobenzothiazole, the flow rate for adsorption, and the desorption solvent were optimized to 9.0, 0.05 g, $10mL\;min^{-1}$ and 1 M $HNO_3$ in ethanol, respectively. Under these optimum conditions, the calibration curve of Co(II) was obtained over concentration range of $2{\sim}120ng\;mL^{-1}$. The detection limit was $0.6ng\;mL^{-1}$. Recovery yields of Co(II) in various natural water samples were more than 90%.

• Journal of the Korean institute of surface engineering
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• v.40 no.1
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• pp.23-31
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• 2007

The objective of this study is to investigate the effect of Al addition on the reaction behavior of cobalt with molten zinc. Pure cobalt specimen was immersion tested in the three kinds of molten zinc (pure, 0.12%Al added and 0.24%Al added) baths at $460^{\circ}C,\;490^{\circ}C\;and\;520^{\circ}C$. For the understanding of degradation processes, specimens were analyzed with scanning electron microscope (SEM) and energy dispersive spectrum (EDS), and electrochemical stripping method. When 0.12% and 0.24% Al was added in molten zinc baths, three intermetallic compounds layers of ${\gamma},\;{\gamma}_1,\;and\;{\gamma}_2$ were formed on the Co matrix and ${\beta}_1$ layer was not formed between the Co matrix and the ${\gamma}$ layer. Particles of CoAl intermetallic compound were formed at the interface between the ${\gamma}_2$ layer and zinc melt and they did not adhere to the Co-Zn intermetallic layer. Weight loss of the Co specimen increased as Al content in the molten zinc increased and the relationship of weight loss vs. immersion time followed parabolic rate law. Rate controlling process for the reaction rate of Co with Al added molten zinc was analyzed as the diffusion process of Al atom through a boundary layer between the ${\gamma}_2$ layer and the Al added zinc melt.

• Korean Journal of Environmental Agriculture
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• v.29 no.1
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• pp.72-76
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• 2010

We have developed the bio-electrode measuring the variance of the amount of acetylcholine affected by residual pesticide. The working electrode of the biosensor was made by combination of cobalt phthalocyanine and carbon organic compounds. The biosensors were constructed by screen-printing method. The principle of working electrode is similar to thiocholine sensor. We have fabricated the biosensor using standard screen printing method. Generally, the biosensor made by printing method formed thick film biosensor. When the electrodes were made by electrochemical cells, the generation of current by the addition of enzyme substrate was inhibited by standard solutions of organo-phosphate pesticides. The detection limit of sensor is about 0.5 $\mu{g}/L$ for carbofuran. We could improve the responsibility of the sensor by controlling the cobalt phthalocyanine and thiocholine concentration ratio. Also we have tested the EPN and Chlorpyrifos pesticides and found that the biosensor is applicable to fast determination of residual pesticides.

• Journal of the Korean Chemical Society
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• v.47 no.4
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• pp.334-338
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• 2003

The crystal structure of $[Co(phen)_2(Cl)(H_2O)] Clㆍ2H_2O$(phen=1,10-phenanthroline) has been determined by X-ray crystallography. It crystallizes in the triclinic system, space group P1, with lattice parameters a=9.662(2), b=11.445(1), c=13.037(2)${\AA}$ ${\alpha}$=64.02(1), ${\beta}$=86.364(9), ${\gamma}=78.58(2)^°$, and Z=2. The coordinated cations contain a six-coordinated cobalt atom chelated by two phen ligands and one chloride anion and one water ligand in cis arrangement. In addition to the chloride coordinated to the cobalt, there are one chloride ion and four water molecules which complete the crystal structure. In the solid state, the title compound forms three dimensional network structure through hydrogen bonds, within which exists the strongest hydrogen bond (O(3)-O(4)=2.33${\AA}$). The intermolecular hydrogen bonds connect the $[Co(phen)_2(Cl)(H_2O)]1+,\;H_2O$ moieties and chloride ion.

• Resources Recycling
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• v.14 no.6 s.68
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• pp.28-36
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• 2005

A hydrometallurgical process to leach cobalt from the waste cathodic active material, $LiCoO_{2}$, and subsequently to separate it by solvent extraction was developed. The optimum leaching conditions for high recovery of colbalt and lithium were obtained: 2.0 M sulfuric acid, 5 $vol.\%$ hydrogen peroxide, $75^{\circ}C$ leaching temperature, 30 minutes leaching time and an initial pulp density of 100 g/L. The respective leaching efficiencies for Co and Li were $93\%$ and $94.5\%$. About $85\%$ Co was extracted from the sulfuric acid leach liquor containing 44.72 g/L Co and 5.43 g/L Li, using 1.5 M Cyanex272 as an extractant at the initial pH 5.0 and in organic to aqueous phase ratio of 1.6:1 under the single stage extraction conditions. The Co in the raraffinate was completely extracted by 0.5 M Na-Cyanex272 at the inital pH 5.0, and an organic to aqueous phase ratio of 1;1. The cobalt sulfate solution of higher than $99.99\%$ purity could be recovered from waste $LiCoO_{2}$, using a series of hydrometallurgical processes: sulfuric acid leaching of waste $LiCoO_{2}$- solvent extraction of Co by Na-Cyanex 271 - scrubbing of Li by sodium carbonate solution - stripping of Co by sulfuric acid solution.

• Korean Journal of Materials Research
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• v.10 no.9
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• pp.612-618
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• 2000

The WC/WC grain boundary structure and intergranular segregation in WC-Co and WC-VC-Co cemented carbides were investigated by high-resolution transmission electron microscopy and energy dispersive X-ray spectroscopy in order to elucidate whether contiguous boundaries were present or not at the atomic level. Some grain boundaries were separated by liquid phase, while others were contiguous at the atomic level. Cobalt was found to be segregated to WC/WC grain boundaries in WC-Co. Cobalt and vanadium were co-segregated to grain boundaries in WC-VC-Co. The segregation width in both materials was about 6 nm. These results suggest that the vanadium present in contiguous boundaries acts as an effective barrier to the migration of boundaries during sintering and annealing. This could explain the grain growth inhibiting mechanism of VC added to WC-Co.

• Journal of the Korean Applied Science and Technology
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• v.26 no.3
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• pp.279-287
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• 2009

Fisher-Tropsch synthesis for the production of hydrocarbon from syngas was investigated on 20% cobalt-based catalysts (20% Co/HSA, 20% Co/Si-MMS), which were prepared by home-made supports with high surface areas such as high surface alumina (HSA) and silica mesopores molecular sieve (Si-MMS). In the gas phase reaction by syngas only, 20% Co/Si-MMS catalyst was shown in higher CO conversion and lower carbon dioxide formation than 20% Co/HSA, whereas the olefin selectivity was higher in 20% Co/HSA than in 20% Co/Si-MMS. In the effect of n-hexane added in syngas, the selectivities of $C_{5+}$ and olefin were increased by comparing the supercritical phase reaction with the gas phase reaction in addition to reduce unexpected methane and carbon dioxide.

• Resources Recycling
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• v.19 no.4
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• pp.41-50
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• 2010

A fundamental study was carried out to develop a process for recycling tungsten and cobalt from WC-Co hardmetal sludge generated in the manufacturing process of hardmetal tools. The complete extraction of cobalt and simultaneous formation of tungstic was achieved by treating the sludge using aqua regia. The effect of aqua regia concentration, reaction temperature and time, pulp density on cobalt leaching and tungstic acid formation was investigated. The complete leaching of cobalt was attained at the optimum conditions: 100 vol.% aqua regia concentration, $100^{\circ}C$ temperature, 60 min. reaction time and 400 g/L pulp density. A complete conversion of tungsten carbide of the sludge to tungstic acid was however, obtained at the pulp densities lower than 150 g/L under the above condition. The progress of reaction during the aqua regia treatment of the sludge was monitored through the XRD phase identification of the residue. The metallic impurities in the tungstic acid so produced could be further removed as insoluble residues by dissolving the tungsten values in ammonia solution. The ammonium paratungstate($(NH_4)_{10}{\cdot}H_2W_{12}O_{42}{\cdot}4H_2O$) of 99.85% purity was prepared from the ammonium polytungstate solution by the evaporation crystallization method.