• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.24 no.12
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• pp.969-976
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• 2011

In this study we aims to evaluate the effects of 1/3 mol% $Co_3O_4$ addition on the reaction, microstructure development, resultant electrical properties, and especially the bulk trap and grain boundary properties of $ZnO-Bi_2O_3-Sb_2O_3$ (Sb/Bi=2.0, 1.0, and 0.5) system (ZBS). The samples were prepared by conventional ceramic process, and characterized by XRD, density, SEM, I-V, impedance and modulus spectroscopy (IS & MS) measurement. In addition of $Co_3O_4$ in $ZnO-Bi_2O_3-Sb_2O_3$ (ZBSCo), the phase development, density, and microstructure were controlled by Sb/Bi ratio. Pyrochlore on cooling was reproduced in all systems. The more homogeneous microstructure was obtained in ZBSCo (Sb/Bi=1.0) system. In ZBSCo, the varistor characteristics were improved drastically (non-linear coefficient ${\alpha}$=23~50) compared to ZBS. Doping of $Co_3O_4$ to ZBS seemed to form $V^{\cdot}_o$(0.33 eV) as dominant defect. From IS & MS, especially the grain boundary of Sb/Bi=0.5 system is composed of electrically single barrier (0.93 eV) and somewhat sensitive to ambient oxygen with temperature.

• Bulletin of the Korean Chemical Society
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• v.35 no.9
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• pp.2630-2634
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• 2014

The surface of natural graphite was modified by the use of hydrogen peroxide and evaluated as an anode material for lithium ion capacitors (LICs). The surface treatment was carried out under various ultrasonic conditions of 200, 300, and 400W, which were applied to a mixture of natural graphite and hydrogen peroxide solution for 1 h. While the bulk structure was maintained, the hexagonal symmetry and physical properties of natural graphite, such as BET surface area, tap density, and particle size, were affected by the surface treatment. FT-IR and XPS measurements confirmed the signature of C=O on the surface of graphite samples after treatment. Both the pristine and surface-treated graphites showed a similar reversible capacity of $370mAhg^{-1}$, and the coulombic efficiency of surface-treated graphite decreased with higher ultrasonic energies (89.1%, 89.0%, and 88.0% for 200, 300, and 400 W) comparing with pristine graphite (89.4%). The capacity retention of LICs was greatly improved with the treated natural graphite. The graphite treated under the ultrasonic energy of 300 W and pristine natural graphite showed capacity retention of 77.5% and 42.9%, implying that the surface treatment was an effective method for the improvement of natural graphite as an anode material for LICs.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.139.1-139.1
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• 2016

Multiferroic materials are of great interest because of its potential applications in the design of devices combining magnetic, electronic and optical functionalities. Among various multiferroic materials, $BiFeO_3$(BFO) is known to be one of the intensively focused mainly due to the possibility of multiferroism at device working temperature (> $200^{\circ}C$). However, leakage current and weak polarization resulting from oxygen deficiency and crystalline defect should be resolved. Furthermore the magnetic ordering of pure BFO mainly prefers to have antiferromagnetic coupling. Up to now many attempts have been performed to improve the ferromagnetic and the ferroelectric properties of BFO by doping. In this work, we investigated the effects of Ni substitution on the multiferroism of bulk BFO. Four BFO samples (a pure BFO and three Ni-doped BFO's; $BiFe_{0.99}Ni_{0.01}O_3$, $BiFe_{0.98}Ni_{0.02}O_3$ and $BiFe_{0.97}Ni_{0.03}O_3$) were synthesized by the standard solid-state reaction and rapid sintering technique. The XRD results reveal that Ni atoms are substituted into Fe-sites and give rise to phase transition of cubic to rhombohedal. By using vibrating sample magnetometer and standard ferroelectric tester, the multiferroic properties at room temperature were characterized. We found that the magnetic moment of Ni-doped BFO turned out to be maximized for 3% of Ni dopant.

• Journal of the Korean Ceramic Society
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• v.50 no.2
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• pp.157-162
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• 2013

The need for lead-free piezoceramics has caused a renewal of interest in $BaTiO_3$-based systems. Recently, it was found that ceramics in the $(Ba,Ca)(Zr,Ti)O_3$ system have properties comparable to those of $Pb(Zr,Ti)O_3$. However, these ceramics require rather high sintering temperatures of $1450-1550^{\circ}C$. In this work, the effect of $TiO_2$ and CuO addition on the sintering behavior, microstructure, dielectric and piezoelectric properties of $(Ba_{0.85}Ca_{0.15})(Zr_{0.1}Ti_{0.9})O_3$ (BCTZ) ceramics will be discussed. BCTZ ceramics were prepared by the mixed oxide route and 1 mol % of $TiO_2$ or CuO was added. Undoped and doped ceramics were sintered at $1350^{\circ}C$ for 1-5 h. CuO was found to be a very effective sintering aid, with samples sintered for 1 h at $1350^{\circ}C$ having a bulk density of 95% theoretical density; however the piezoelectric properties were greatly reduced, probably due to the small grain size.

• Progress in Superconductivity
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• v.11 no.1
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• pp.25-29
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• 2009

Polycrystalline samples of $(R_{0.8}Ca_{0.2})Ba_2Cu_3O_{7-z}$ (R = Lu and Y) were synthesized by a solid-state reaction route, and the phase stabilities were examined by heating at temperatures between $800^{\circ}C$ and $900^{\circ}C$ in various atmospheres. A comparative analyses of the x-ray diffraction data of the $(Lu_{0.8}Ca_{0.2})Ba_2Cu_3O_{7-z}$ and $(Y_{0.8}Ca_{0.2})Ba_2Cu_3O_{7-z}$ compounds showed that the 123 phase of both compounds is stable under heating in air and $O_2$ of 1 atm. However, contrary to the $(Y_{0.8}Ca_{0.2})Ba_2Cu_3O_{7-z}$ compound, the $(Lu_{0.8}Ca_{0.2})Ba_2Cu_3O_z$ compound was found to become unstable when heated in the low oxygen partial pressure below about 8 % $O_2\;in\;N_2$, Considering the instability of parent $LuBa_2Cu_3O_z$ compound, this result suggests that the phase stability of Lu-based 123 compounds is sensitive to both the composition and the oxygen partial pressure.

• Journal of the Mineralogical Society of Korea
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• v.15 no.1
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• pp.78-84
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• 2002

New pyrochlore-type phases($A_2$$B_2$$O_{7}$) were synthesized in the systems: CaO-C$eO_2$-T$iO_2$, CaO-$UO_2$(T$hO_2$)-Z$rO_2$, CaO-$UO_2$(T$hO_2$)-$Gd_2$$O_3$-T$iO_2$-Z$rO_2$, 및 CaO-T$hO_2$-S$nO_2$. The starting materials were pressed with the pressure of 200~400 MPa and sintered at 1500~ 155$0^{\circ}C$ for 4~8 hours in air and at 1300~ 135$0^{\circ}C$ for 5 ~50 hours under oxygen atmosphere. The products were characterized using XRD, SEM/EDS and TEM. In the bulk compositions of CaCe$Ti_2$$O_{7}$, CaTh$Zr_2$$O_{7}$,($Ca_{0.5}$ Gd$Th_{0.5}$)(ZrTi)$O_{7}$) ($Ca_{0.5}$Gd$Th_{0.5}$)(ZrTi)$O_{7}$, ($Ca_{0.5}$G$dU_{0.5}$)(ZrTi)$O_{7}$ and CaTh$Sn_2$$O_{7}$ , pyrochlore was the major phase, together with other oxide phase $of_2$$O_{7}$ fluorite structure. In the samples with target compositions CaU$Zr_2$$O_2$및 $Ca_{0.5}$ G$dU_{0.5}$)$Zr_2$T$iO_{7}$ pyrochlore was not identified, but a fluorite-structured phase was detected. The formation factor as the stable phase depended on crystal chemical characteristics of the actinide and lanthanide elements of the system concerned.

• Proceedings of the Korean Society of Near Infrared Spectroscopy Conference
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• 2001.06a
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• pp.4111-4111
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• 2001

When a drug is prepared in a tablet, the active component represents only a small portion of the dosage form. The other components of the formulation include materials to assist in the dissolution, antioxidants, coloring agents and bulk fillers. The tablets are tested using approved testing methods usually involving separation and subsequent quantification of the active component. Tablets may also be tested by near-Infrared Reflectance spectrometry (NIRS). In the present study, based on NIRS and multivariate calibration methods, a novel and precise method is developed for direct determination of ascorbic acid in vitamin C tablet. Two different tablet formulations were powdered in three different sizes, 63-125 ${\mu}{\textrm}{m}$, and examined. Spectral region of 4750-4950 $cm^{-1}$ / was used and optimized for quantitative operations. Partial least squares (PLS) and multiple linear regression (MLR) methods were performed for this spectral region. The results of optimized PLS and MLR methods showed that reproducibility increase with decreasing grain size and standard error of calibration (SEP) of less than 1% w/w of ascorbic acid and a correlation coefficient of 0.998 can be achieved. The PLS method showed better results than MLR. Seven overdose and underdose samples (prepared in the laboratory to match marketed products) were tested by proposed and iodometric standard methods. A correlation between NIRS predicted ascorbic acid values and iodomet.ic values was calculated ($R^2$=0.9950). Finally, the direct analysis of individual intact tablets in their unit-dose packages (Blistering in aluminum and PVC foils) obtained from market were also carried out and a correlation coefficient of 0.9989 and SEP of 0.931% w/w of ascorbic acid were achieved.

• Carbon letters
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• v.12 no.2
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• pp.95-101
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• 2011

To investigate new applications for illite as an additive for carbon-based composites, the composites were prepared with and without illite at different heat-treatment temperatures. The effects of the heat-treatment temperature on the chemical structure, microstructure, and thermal oxidation properties of the resulting composites were studied. As the heat-treatment temperature was increased, silicon carbide SiC formation via carbothermal reduction increased until all the added illite was consumed in the case of the samples heat-treated at $2,300^{\circ}C$. This is attributed to the intimate contact between the $SiO_2$ in the illite and the phenol carbon precursor or the carbon fibers of the preform. Among composites prepared at all temperatures, those with illite addition exhibited fewer pores, voids, and interfacial cracks, resulting in larger bulk densities and lower porosities. A delay of oxidation was not observed in the illite-containing composites prepared at $2,300^{\circ}C$, suggesting that the illite itself absorbed energy for exfoliation or other physical changes. Therefore, if the illite-containing C/C composites can reach a density generally comparable to that of other C/C composites, illite may find application as a filler for C/C composites. However, in this study, the illite-containing C/C composites exhibited low density, even when prepared at a high heat-treatment temperature of $2300^{\circ}C$, although the thermal oxidation of the resulting composites was improved.

• Progress in Superconductivity
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• v.9 no.1
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• pp.80-84
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• 2007

Charcoal was used as a carbon source for improving the critical current density of $MgB_2$ and the effect of annealing temperature on the $J_c$ of $MgB_2$ was investigated. The charcoal powder used in this study was $1{\sim}2$ microns in size and was prepared by wet attrition milling. $MgB_2$ bulk samples with a nominal composition of $Mg(B_{0.95}C_{0.05})_2$ were prepared by in situ process of Mg and B powders. The powder mixture was uniaxially compacted into pellets and heat treated at temperatures of $650^{\circ}C\;-\;1000^{\circ}C$ for 30 minutes in flowing Ar gas. It was found that superconducting transition temperature of $Mg(B_{0.95}C_{0.05})_2$ decreased by charcoal additions which indicates the carbon substitution for boron site. $J_c$ of $Mg(B_{0.95}C_{0.05})_2$ was lower than that of the undoped $MgB_2$ at the magnetic fields smaller than 4 Tesla, while it was higher than that of the undoped sample especially at the magnetic field higher than 4 T. High temperature annealing seems to be effective in increasing $J_c$ due to the enhanced carbon diffusion into boron sites.

• Journal of Korean Society of Occupational and Environmental Hygiene
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• v.11 no.1
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• pp.70-77
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• 2001

This study was conducted to identify the current status of occupational safety and health by checklist and to evaluate the airborne exposure to chemicals and to provide the appropriate recommendation for safety and health of laundries. A total of 20 laundries located in tile Gyungi district area were surveyed from July 20 to September 15, 2000. The prevalence of laundries having a stove and gas range were found to be 25 % and 55 %, respectively. Smoking is not allowed in 60 % of the laundries. Only 10 % of dry-cleaners were isolated. Ventilation systems in laundries had not been annually inspected. Most of the workers didn't put on respirators, MSDS were not available, and storage bottles did not contain warning labels. The bulk samples of dry cleaning agent include many chemicals that are not controlled by the MOL in Korea. The detected airborne organic solvents in the laundries were benzene, toluene, p-xylene, m-xylene, o-xylene, perchloroethylene, and 2-butoxy ethanol. The airborne concentrations of organic solvents were much less than the occupational exposure limits proposed by the Ministry of Labor(MOL) in Korea. But the concentrations of benzene exceeded the TLV of ACGIH. This study showed that the current status of occupational safety and health was not appropriate for workers in laundries. It is recommended that laundry workers should be educated for the treatment and storage of hazardous organic solvents to improve the occupational safety and health of the working environment as well as MSDS usage. Also, extended research and survey for the organic solvents that are not controlled by the MOL has to be conducted.