• Journal of the Korean Chemical Society
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• v.55 no.6
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• pp.919-925
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• 2011

A new series of manganese(II), iron(III) and cobalt(III) complexes of 14-membered macrocyclic ligand, (3,6,10,13,16,19-hexaazabicyclo[6.6.6]icosane-1,8-diamine) have been prepared and characterized by elemental analyses, IR, UV-VIS, $^1H$- and $^{13}C$- NMR spectra, magnetic susceptibilities, conductivities, and ESR measurements. Molar conductance measurements in DMF solution indicate that the complexes are electrolytes. The ESR spectrum for cobalt(III) complex in $CD_3OD+10%D_2O$ after exposure to $^{60}Co-{\gamma}$-rays at 77 K using a 0.2217 M rad $h^{-1}$ vicrad source showed $g_{\perp}$ > $g_{\parallel}$ > $g_e$, indicating that, the unpaired electron site is mainly present in the $d_z2$ orbital with covalent bond character. In this case, the ligand hyperfine tensors are nearly collinear with ${\gamma}$-tensors, so there is no major tendency to bend. Therefore, little extra delocalization via the ring lobe of the $dz^2$ orbital occurs. However, the ESR spectrum in solid state after exposure to $^{60}Co-{\gamma}$-rays at 77 K showed $g_{\parallel}$ > $g_{\perp}$ > $g_e$, indicating that, the unpaired electron site is mainly present in the $d_x2_{-y}2$ ground state as the resulting spectrum contains a large number of randomly oriented molecules provided that, the principle directions of g and A tensors. Manganese (II) complex 2, $[H_{12}LMn]Cl_4.2H_2O$, showed six isotropic lines characteristic to an unpaired electron interacting with a nucleus of spin 5/2, however, iron(III) complex 3, $[H_{12}LFe]Cl_5.H_2O$, showed spectrum of a high spin $^{57}Fe$ (I=1/2), $d^5$ configuration. The geometry of these complexes was supported by elemental analyses, IR, electronic and ESR spectral studies. Complex 1 showed exploitation in reducing the amount of electron adducts formed in DNA during irradiation with low radiation products.

• Journal of Korean Neurosurgical Society
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• v.56 no.5
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• pp.400-404
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• 2014

Objective : Clip artifacts limit the visualization of intracranial structures in CT scans from patients after aneurysmal clipping with cobalt alloy clips. This study is to analyze the parameters influencing the degree of clip artifacts. Methods : Postoperative CT scans of 60 patients with straight cobalt alloy-clipped aneurysms were analyzed for the maximal diameter of white artifacts and the angle and number of streak artifacts in axial images, and the maximal diameter of artifacts in three-dimensional (3-D) volume-rendered images. The correlation coefficient (CC) was determined between each clip artifact type and the clip blade length and clip orientation to the CT scan (angle a, lateral clip inclination in axial images; angle b, clip gradient to scan plane in lateral scout images). Results : Angle b correlated negatively with white artifacts (r=-0.589, p<0.001) and positively with the angle (r=0.636, p<0.001) and number (r=0.505, p<0.001) of streak artifacts. Artifacts in 3-D images correlated with clip blade length (r=0.454, p=0.004). Multiple linear regression analysis revealed that angle b was the major parameter influencing white artifacts and the angle and number of streak artifacts in axial images (p<0.001), whereas clip blade length was a major factor in 3-D images (p=0.034). Conclusion : Use of a clip orientation perpendicular to the scan gantry angle decreased the amount of white artifacts and allowed better visualization of the clip site.

• Journal of the Mineralogical Society of Korea
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• v.23 no.3
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• pp.227-234
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• 2010

We investigated the effect of dry grinding of laterite on the extraction of nickel and cobalt. The major chemical compositions of the sample for this work were $SiO_2$, $Fe_2O_3$ and MgO. The sample contained 0.81% Ni and 0.02% Co. The major minerals of the sample were lizardite and quartz with minor amounts of forsterite and enstatite. The mean particle size, specific surface area and density of the ground sample decreased with increasing grinding time, while the amorphization of lizardite increased as identified by XRD analysis. The grinding enabled the extraction ratio of Ni and Co to increase by the breakdown of Mg-OH bonding in the lizardite structure. However, physical properties of quartz were not changed by grinding. The extraction ratio of Ni and Co increased with increasing grinding time. Approximately 80% of Ni and Co were extracted regardless of the kind of acid solutions when the sample was ground for 60 minutes.

• Resources Recycling
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• v.30 no.5
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• pp.25-31
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• 2021

Smelting reduction of spent lithium-ion batteries results in the production of metallic alloys in which reduced cobalt, nickel and copper coexist. In this study, we investigated the leaching of the metallic alloys containing the above three metals together with iron, manganese, and silicon. The mixture of hydrochloric acid and hydrogen peroxide as an oxidizing agent was employed, and the effect of the concentration thereof, the reaction time and temperature, and pulp density was investigated to accomplish the complete leaching of cobalt, nickel, and copper. The effect of the hydrogen peroxide concentration and pulp density on the leaching was prominent, compared to that of reaction time and temperature, especially in the range of 20 to 80℃. The complete leaching of the metals present in metallic alloys, except silicon, was accomplished using 2 M HCl and 5% H₂O₂ with a pulp density of 30 g/L for 150 min at 60℃.

• Resources Recycling
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• v.19 no.5
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• pp.25-30
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• 2010

Leaching of CMSX-4 superalloy was done in hydrochloric acid solutions. The leaching behaviors of main alloy components, such as Ni, Co, Cr, Al, was investigated by controlling acid concentration, temperature, leaching time and pulp density. Increasing acid concentration enhanced the leaching rate till the rate decreased over 3 M acid concentration. Raising temperature increased the leaching amount of the metal components. After the leaching for 60 minutes at $90^{\circ}C$ and 10 g/L pulp density in 4 M acid solution, 93.2% nickel, 89.9% aluminum, 80.4% cobalt, and 79.1% chromium were leached. Nickel and aluminum were preferentially leached out, while the leaching rate of cobalt and chromium were relatively high only after 60 minutes, Increasing pulp density lowered the leaching rate and especially serious on cobalt and chromium, The optimum leaching condition for CMSX-4 was obtained at $90^{\circ}C$, 120 minutes, and less than 125 g/L in 4 M hydrochloric acid solution.

• Bulletin of the Korean Chemical Society
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• v.29 no.4
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• pp.736-740
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• 2008

The interaction of myelin basic protein (MBP) from bovine central nervous system with divalent calcium ion was studied by isothermal titration calorimetry at 27 ${^{\circ}C}$ in aqueous solution. The extended solvation model was used to reproduce the enthalpies of $Co^{2+}$-MBP interaction over the whole $Co^{2+}$ concentrations. The solvation parameters recovered from the solvation model were attributed to the structural change of MBP due to the metal ion interaction. It was found that there is a set of three identical and noninteracting binding sites for $Co^{2+}$ ions. The association equilibrium constant is 0.015 ${\mu}M^{-1}$. The molar enthalpy of binding is $\Delta$H = −14.60 kJ $mol^{-1}$.

• Journal of Technologic Dentistry
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• v.45 no.4
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• pp.87-94
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• 2023

Purpose: This study aimed to observed changes in the shape of dental barrels based on application time. Machinability measures the angle of alloy specimens. Polishing performance measures the surface roughness of alloy specimens. Methods: The dental barrel polishing equipment used in this study was a Snow Barrel (DK Mungyo). Three types of cobalt-chromium alloys for partial dentures were used as specimens (BC CAST R [BP]; Bukwang, Vera PDI [VP]; Aalbadent, and GM 800+ [GP]; Dentaurum). Specimens were prepared in the form of plates (10 mmx10 mmx2 mm). Dental barrel polishing was performed at 450 rpm for 60 minutes with intervals of 5 minutes. The processing angle was measured using a microscope (SZ61; Olympus). Results: For the angle measurement, the VPC specimen was measured at 78.64°, 36.00° for the VP60 specimen, 79.57° for the BP control (BPC) specimen, 28.07° for the BP60 specimen, 75.01° for the GPC specimen, and 39.92° for the GP60 specimen. For the surface roughness measurements, the average surface roughness of the VPC and VP15 specimens were 1.09 ㎛ and 0.26 ㎛, respectively. The average surface roughness of the BPC and BP20 specimens were 1.77 ㎛ and 0.29 ㎛, respectively. The average surface roughness of the GPC and GP15 specimens were 1.08 ㎛ and 0.27 ㎛. Conclusion: The results were excellent after about 20 minutes of dental barrel polishing conditions presented in this study.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.4
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• pp.1-7
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• 2017

Cobalt silicide was used as a counter electrode in order to confirm its reliability in dye-sensitized solar cell (DSSC) devices. 100 nm-Co/300 nm-Si/quartz was formed by an evaporator and cobalt silicide was formed by vacuum heat treatment at $700^{\circ}C$ for 60 min to form approximately 350 nm-CoSi. This process was followed by etching in $80^{\circ}C$-30% $H_2SO_4$ to remove the cobalt residue on the cobalt silicide surface. Also, for the comparison against Pt, we prepared a 100 nm-Pt/glass counter electrode. Cobalt silicide was used for the counter electrode in order to confirm its reliability in DSSC devices and maintained for 0, 168, 336, 504, 672, and 840 hours at $80^{\circ}C$. The photovoltaic properties of the DSSCs employing cobalt silicide were confirmed by using a simulator and potentiostat. Cyclic-voltammetry, field emission scanning electron microscopy, focused ion beam scanning electron microscopy, and energy dispersive spectrometry analyses were used to confirm the catalytic activity, microstructure, and composition, respectively. The energy conversion efficiency (ECE) as a function of time and ECE of the DSSC with Pt and CoSi counter electrodes were maintained for 504 hours. However, after 672 hours, the ECEs decreased to a half of their initial values. The results of the catalytic activity analysis showed that the catalytic activities of the Pt and CoSi counter electrodes decreased to 64% and 57% of their initial values, respectively(after 840 hours). The microstructure analysis showed that the CoSi layer improved the durability in the electrolyte, but because the stress concentrates on the contact surface between the lower quartz substrate and the CoSi layer, cracks are formed locally and flaking occurs. Thus, deterioration occurs due to the residual stress built up during the silicidation of the CoSi counter electrode, so it is necessary to take measures against these residual stresses, in order to ensure the reliability of the electrode.

• Journal of the Korean Electrochemical Society
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• v.23 no.3
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• pp.57-65
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• 2020

It is crucial to investigate the thermal degradation of lithium-ion batteries (LIBs) to understand the possible malfunction at high temperature. Herein, we investigated the effects of surface film formation on the thermal degradation of lithium cobalt oxide (LiCoO₂, LCO) cathode that is one of representative cathode materials. Cycling test at 60℃ exhibited poorer cycleability compared with the cycling at 25℃. Cathodes after the initial 5 cycles at 60℃ (60-LCO) exhibited higher impedance compared to the cathode after initial 5 cycles at 25℃ (25-LCO), resulting in the lower rate capability upon subsequent cycling at 25℃, although the capacity values were similar at the lowest C-rate of 0.1C. In order to understand degradation of the LCO cathode at the high temperature, we analyzed the cathodes surface using X-ray photoelectron spectroscopy (XPS). Among various peaks, intensity of lithium hydroxide (LiOH) increased substantially after the operation at 60℃, and the C-C signal that represents the conductive agent was distinctly lower on 60-LCO compared to 25-LCO. These results pointed to an excessive formation of cathode-electrolyte interphase including LiOH at 60℃, leading to the increase in the resistance and the resultant degradation in the electrochemical performances.

• Journal of Life Science
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• v.19 no.8
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• pp.1139-1144
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• 2009

It has been known that brassiolide (BL) increased the positive gravitropic response and ethylene production in maize roots. This study examined the relationship between the BL-induced gravitropic response and ethylene Production. The ethylene production was inhibited to about 90% of the control by the treatment of $10^{-4}$ M aminoethoxyvinylglycine (AVG), the ethylene synthesis inhibitor. However, the gravitropic response did not show any significant changes compared to the control at $10^{-4}$ M AVG. In the case of treatment of AVG with BL, the ethylene production decreased to 60% of the control. However, the gravitropic response increased to the level which was induced by BL. Cobalt ions, another ethylene biosynthesis inhibitor, inhibited ethylene production, but not gravitropic response. When roots were treated with BL and cobalt ions, they showed the inhibition of ethylene production and promotion of gravitropic response. To elucidate the possibility that the effect of BL is related to auxin transport, roots were treated with TIBA (2,3,5-triiodobenzoic acid), an auxin transport inhibitor. Both treatment of TIBA alone and TIBA with BL stimulated ethylene production to about 96% and 132%, respectively. However, gravitropic response was completely inhibited in both treatments. Further, roots treated with BL in the presence of TIBA and IAA showed a negative gravitropic response, which means that IAA accumulates in the upper side of horizontal roots. Root elongation was also stimulated in this treatment. Taken together, these results suggest that BL might affect the differential distribution of internal IAA on roots, causing the regulation of positive gravitropic response.