• Corrosion Science and Technology
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• v.22 no.2
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• pp.90-98
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• 2023

In this study, cobalt oxide (Co₃O₄) and cobalt-doped magnetite (CoFe₂O₄) nanoparticles were synthesized by a hydrothermal method. They were then used as corrosion inhibitors for corrosion protection of AA2024-T3 aluminum alloys. These obtained nanoparticles were characterized by x-ray diffraction, field-emission scanning electron microscopy, and Zeta potential measurements. Corrosion inhibition activities of Co₃O₄ and CoFe₂O₄ nanoparticles were determined by performing electrochemical measurements for bare AA2024-T3 aluminum alloys in 0.05 M NaCl + 0.1 M Na₂SO₄ solution containing Co₃O₄ or CoFe₂O₄ nanoparticles. Corrosion protection for AA2024-T3 aluminum alloys by a water-based epoxy with or without the synthesized Co₃O₄ or CoFe₂O₄ nanoparticles was investigated by electrochemical impedance spectroscopy during immersion in 0.1 M NaCl solution. The corrosion protection of epoxy coating deposited on the AA2024-T3 surface was improved by incorporating Co₃O₄ or CoFe₂O₄ nanoparticles in the coating. The corrosion protection performance of the epoxy coating containing CoFe₂O₄ was higher than that of the epoxy coating containing Co₃O₄.

• Journal of the Korean Ceramic Society
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• v.46 no.4
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• pp.429-435
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• 2009

In this study, we investigated microstructure and the CO gas sensing properties of Ag-CuO-$SnO_2$ thin films prepared by co-evaporation and subsequently thermal oxidation at air atmosphere. The sensitivity of a Cu-Sn films, thermally oxidized at $600^{\circ}C$, is strongly affected by the amount of Cu. At Cu:7 wt%-Sn:93 wt%, the film exhibited a maximum sensitivity of ${\sim}2.3$ to CO gas of 1000 ppm at $300^{\circ}C$. In contrast, the sensitivity of a Sn-Ag film did not change significantly with the amount of Ag. An enhanced sensitivity of ${\sim}3.7$ was observed in the film with a composition of Ag:3 wt%-Cu:4 wt%-Sn:93 wt%, when thermally oxidized at $600^{\circ}C$. In addition, this thin film shows a response time of ${\sim}80$ sec and a recovery time of ${\sim}450$ sec to 1000 ppm CO gas. The results demonstrate that the CO sensitivity of the Ag-CuO-$SnO_2$ thin films may be closely associated with coexistence of $SnO_2$ and SnO phase, decrease in average particle size, and a porous microstructure. We also suggest that co-evaporation and followed by thermal oxidation is a very simple and effective method to prepare oxide gas sensor thin films.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.14 no.6
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• pp.267-271
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• 2004

Lithium cobalt oxide $(LiCoO_2)$ cathode powders for rechargeable battery have been successfully prepared using urea hydrolysis method. The obtained hydrolysis-derived precursors with different Li/Co molar ratio were calcined at various temperatures. Low temperature phase $(LT-LiCoO_2)$ and high temperature phase $(HT-LiCoO_2)$ were obtained after calcination at $500^{\circ}C$ for 2 hr, and phase transformation from $LT-LiCoO_2{\;}to{\;}HT-LiCoO_2$ was completely occurred over $700^{\circ}C$. The layered structure of $LiCoO_2$ was well developed with a rise in the calcination temperature. Charge-discharge test show that the lithium cobalt oxide with 1.2 molar ratio prepared at $800^{\circ}C$ has an initial discharge capacity as high as 152 mAh/g, and the relatively stable cycling characteristic with 9.2 % of capacity fading was obtained after 40th charge-discharge test.

• Journal of the Korean Ceramic Society
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• v.53 no.2
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• pp.134-138
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• 2016

Porous $Co_3O_4$ spheres with bimodal pore distribution (size: 2-3 nm and ~ 30 nm) were prepared by ultrasonic spray pyrolysis of aqueous droplets containing Co-acetate and polyethylene glycol (PEG), while dense $Co_3O_4$ secondary particles with monomodal pore distribution (size: 2-3 nm) were prepared from the spray solution without PEG. The formation of mesopores (~ 30 nm) was attributed to the decomposition of PEG. The responses of a porous $Co_3O_4$ sensor to various indoor air pollutants such as 5 ppm $C_2H_5OH$, xylene, toluene, benzene, and HCHO at $200^{\circ}C$ were found to be significantly higher than those of a commercial sensor using $Co_3O_4$ and dense $Co_3O_4$ secondary particles. Enhanced gas response of porous $Co_3O_4$ sensor was attributed to high surface area and the effective diffusion of analyte gas through mesopores (~ 30 nm). Highly sensitive porous $Co_3O_4$ sensor can be used to monitor various indoor air pollutants.

• Proceedings of the Materials Research Society of Korea Conference
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• 2003.11a
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• pp.226-226
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• 2003

The Commercial LiCoO$_2$ particles, which were 7.7${\mu}{\textrm}{m}$ in average diameter, were coated with $Al_2$O$_3$ by a gas suspension spray coating method. The coating amount of $Al_2$O$_3$ on the surface of LiCoO$_2$ was varied from 0.1 to 2 wt.% and compared their electrochemical characteristics with those of bare LiCoO$_2$. $Al_2$O$_3$ coating on the surface of LiCoO$_2$ increased surface area and electrical conductivity, and showed the better cycle and thermal stability even at the higher voltage. The observed optimum A1$_2$O$_3$ coating amount that exhibited the highest capacity retention was 0.2 wt.%.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2005.07a
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• pp.318-319
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• 2005

본 연구에서는 $LiCoO_2/LiNi_{1/3}Mn_{1/3}Co_{1/3}O_2$ 혼합 정극활물질로 사용하여 전극을 제작하고 성능을 평가하였다. $LiCoO_2/LiNi_{1/3}Mn_{1/3}Co_{1/3}O_2$와 $LiCoO_2$의 혼합비에 따른 충방전 거동 및 임피던스 변화를 측정하였다. 각 조성에서의 초기용량은 160 ~ 170 mAh/g 정도였으며, $LiNi_{1/3}Mn_{1/3}Co_{1/3}O_2$의 첨가 비율이 증가함에 따라 비용량이 증가하였으나 고율에서의 방전용량은 낮았다.

• Journal of the Korean institute of surface engineering
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• v.49 no.1
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• pp.75-80
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• 2016

$In_2O_3$ nanowires were coated with $Co_3O_4$ nanoparticles to investigate the improvement of ethanol gas sensing performance compared with as-synthesized $In_2O_3$ nanowires. Scanning electron microscopy showed that the nanowires synthesized by VLS mechanism had diameters and lengths of approximately 50-100 nm and a few micrometers, respectively. $Co_3O_4$ nanoparticles produced by hydrothermal method was in the size range of a few to a few tens nm. As-synthesized and $Co_3O_4$ nanoparticles coated $In_2O_3$ nanowires sensors exhibited responses of 1.96% and 4.57%, respectively for the ethanol gas concentration of 200 ppm at $200^{\circ}C$. The underlying mechanism for the improved responses of $Co_3O_4$ nanoparticles coated $In_2O_3$ nanowires sensors is discussed.

• The Journal of Natural Sciences
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• v.4
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• pp.85-93
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• 1991

In solid reaction of the eqimolecular mixture of $BaCO_3$ and $TiO_2$, $CO_2$ generates by the following reaction ; $BaCO_3 + TiO_2\longrightarrow$ $BaTiO_3 + CO_2$ The solid reaction is studied as the kinetics of decomposition reaction with DTA-TG. The results are as follows. 1. $BaCO_3$ with is coexisted with $TiO_2$ decompose at lower temperature than pure $BaCO_3$. The reason is decreasing free eneragy of products. 2. Carter's equation is more important than Jander's equation in solid reaction of $BaCO_3$ decomposi-tion. The activation energy obtained by Carte r's equation is 42.8 Kcal/mol.

• Korean Journal of Crystallography
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• v.6 no.2
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• pp.125-133
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• 1995

The crystal structure of dehydrated, partially Co(II)-exchanged zeolite X, stoichiometry Co2+Na+-X (Co41+Na10Si100Al92O384) per unit cell, has been determined from three-dimensional X-ray diffraction data gathered by counter methods. The structure was solved and refined in the cubic space group Fd3:α=24.544(1)Å at 21(1)℃. The crystal was prepared by ion exchange in a flowing stream using a solution 0.025 M each in Co(NO3)2 and Co(O2CCH3)2. The crystal was then dehydrated at 380℃ and 2×10-6 Torr for two days. The structure was refined to the final error indices, R1=0.059 and R2=0.046 with 211 reflections for which I > 3σ(I). Co2+ ions and Na+ ions are located at the four different crystallographic sites. Co2+ ions are located at two different sites of high occupancies. Sixteen Co2+ ions are located at the center of the double six-ring (site I; Co-O = 2.21(1)Å, O-Co-O = 90.0(4)°) and twenty-five Co2+ ions are located at site II in the supercage. Twenty-five Co2+ ions are recessed 0.09Å into the supercage from its three oxygen plane (Co-O = 2.05(1)Å, O-Co-O = 119.8(7)°). Na+ ions are located at two different sites of occupandies. Seven Na+ ions are located at site II in the supercage (Na-O = 2.29(1)Å, O-Na-O = 102(1)°). Three Na+ ions are statistically distribyted over site III, a 48-fold equipoint in the supercages on twofold axes (Na-O = 2.59(10)Å, O-Na-O = 69.0(3)°). Seven Na+ ions are recessed 1.02Å into the supercage from the three oxygen plane. It appears that Co2+ ions prefer sites I and II in order, and that Na+ ions occupy the remaining sites, II and III.

• Bulletin of the Korean Chemical Society
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• v.32 no.10
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• pp.3712-3719
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• 2011

Confined Pt and $CoFe_2O_4$ nanoparticles (NPs) in a mesoporous core/shell silica microsphere, Pt-$CoFe_2O_4$@meso-$SiO_2$, were prepared using a bi-functional linker molecule. A large number of Pt NPs in Pt-$CoFe_2O_4$@meso-$SiO_2$, ranging from 5 to 8 nm, are embedded into the shell and some of them are in close contact with $CoFe_2O_4$ NPs. The hydrogenation of cyclohexene over the Pt-$CoFe_2O_4$@meso-$SiO_2$ microsphere at $25^{\circ}C$ and 1 atm of $H_2$ yields cyclohexane as a major product. In addition, it gives oxygenated products. Control experiments with $^{18}O$-labelled water and acetone suggest that surface-bound oxygen atoms in $CoFe_2O_4$ are associated with the formation of the oxygenated products. This oxidation reaction is operative only if $CoFe_2O_4$ and Pt NPs are in close contact. The Pt-$CoFe_2O_4$@meso-$SiO_2$ catalyst is separated simply by a magnet, which can be re-used without affecting the catalytic efficiency.