• Proceedings of the KIEE Conference
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• 1996.07c
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• pp.1679-1681
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• 1996

ZnO varistor with composition of 89wt%-ZnO, 3.0wt%-$Bi_{2}O_{3}$, 3.6wt%-$Sb_{2}O_{3}$, 1.16wt%-CoO, 0.88wt%-NiO, 0.71wt%-$MnO_2$, 0.93wt%-$Cr_{2}O_{3}$, 0.013wt%-$Al_{2}O_{3}$ was fabricated by sintering methods. The effects of annealing on the J-E characteristics of ZnO varistors were investigated. These changes of electric properties were found to be caused by the variation of grains and grain boundary related to annealing. And the conductive mechanism and micostructure of ZnO varistor were researched using I-V meter, SEM and XRD.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.18 no.8
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• pp.714-719
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• 2005

NiCr thin film was deposited by DC magnetron sputtering on $A;_2O_3$/Si substrate with NiCr (80:20) alloy target. NiCr thin films were annealed at $300^{\circ}C,\;400^{\circ}C,\;500^{\circ}C,\;600^{\circ}C,\;and\;700^{\circ}C$ for 6 hr in $H_2$ after annealing at $500^{\circ}C$ for 6hr in air atmosphere, respectively. To analyze NiCr thin film properties, the changes of its micro structure were Investigated through field emission scanning electron microscope (FESEM). X-ray photoelectron spectroscopy (XPS) was used to analyze a surface of NiCr thin film. Resistance of NiCr thin film was measured by 4-point probe technique. The generated heats were measured by infrared thermometer through the application of DC voltage (5 V/l2 V). NiCr thin film treated by gradational double annealing process had uniform and small grains. Maximum temperature generated heat by NiCr micro heater was $173^{\circ}C$. We expect that our results will be a useful reference in the realization of NiCr micro heater.

• Journal of the Korean Magnetics Society
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• v.15 no.1
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• pp.1-6
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• 2005

In this study we investigate the electronic structure and magnetism of transition metal (TM = Ti, Cr, Mn, Fe, Co, Ni, Ru, Pd, Ag ) deped ZnO($TM_{0.25}Zn_{0.75}O$), which are expected to have Curie temperature. Full-potential Linearized Augmented Plane Wave(FLAPW) metod is adopted with exchange-correlation potential expressed as general gradient approximation(GGA). The calculated magnetic moments of ($TM_{0.25}Zn_{0.75}O$) are 0.83, 3.03, 4.03, 3.48, 2.47, 1.56, 0.43, 0.75, 0.01 ${\mu}_B$ for TM = Ti, Cr, Mn, Fe, Co, Ni, Ru, Pd, Ag, respectively. The nearest neighbor O atom to the transition metal is calculated to have a significant magnetic moment of about 0.1${\mu}_B$, ?? 새 strong hybridization between O-p and TM-d bands. As the results, the systems may have larger magnetic moments in total, compared to the corresponding isolated atoms. The 3d TM doped systems exhibit the half-metallic character except Co, wheres the 4d TM doped systems behave like normal metals and low spin polarization at the Fermi levels.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.10 no.2
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• pp.97-104
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• 2012

A porous $TiO_2$ pellet was electrochemically converted to the metallic titanium by using a $CaCl_2$ molten salt system at $850^{\circ}C$. Ni-$TiO_2$ and graphite electrodes were used as cathode and anode, respectively. The electrochemical behaviour of $TiO_2$ pellet was determined by a constant voltage control electrolysis. Various reaction intermediates such as $CaTiO_3$, $Ti_2O$ and $Ti_6O$ were observed by XRD analysis during electrolysis of the pellet. Once $TiO_2$ pellet was converted to a porous metallic structure, the porous structure disappeared by sintering and shrinking with increasing the reaction time at high temperature.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2000.07a
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• pp.365-368
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• 2000

We have studies on the Microstructures and densities as a function of forming pressures and the magnetic properties of the specimens with additive Bi$_2$O$_3$ that sintered at 95$0^{\circ}C$ for 4.5 hours for synthesizing optimal Ni-Cu-Zn ferrite. Green density rose generally as Forming pressure increased from 1.7 ton/cm$^2$to 2.5 ton/cm$^2$and Cold Isostatic Pressure(CIP) method was more effective than Die Pressure(DP) method to high green density. Forming pressure had no influence on apparent density but on the other hand Bi$_2$O$_3$contents were strongly dominant to appaernt density than forming pressure. Bi$_2$O$_3$liquid phases created during sintering process promoted sintering and grain growth so that apparent density, grain size and permeability increased compared to that of the specimens which were sintered with non-additive Bi$_2$O$_3$.

• Journal of the Korean Chemical Society
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• v.31 no.3
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• pp.271-279
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• 1987

A nitrate ion-selective PVC membrane electrode based on ammonia modified bakelite A-Ni$(NO_3)_2$ complex as ion exchanger was prepared. The electrode gave a linear response with a Nernstian slope of 60mV per decade within the concentration range $1{\sim}10^{-4}$ M $KNO_3$ but nonresponse to hydrogen ion and multivalent anions. The selectivity, response time and life time of the electrode were investigated and it was found that the electrode exhibited good selectivity for four univalent anions ($Cl^-,\;Br^-,\;I^-,\;{ClO_4}^-$). Analytical application to the determination of nitrate were also studied.

• Journal of Korean Society for Atmospheric Environment
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• v.23 no.1
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• pp.64-73
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• 2007

The catalytic activity of transition metals (Cu, Co, Mn, Fe and Ni) supported on ${\gamma}-Al_2O_3$ for the oxidation of toluene was investigated in the microreactor of fixed-bed type. The catalytic activity of transition metals for the oxidation of toluene turned out to be increasing in the order of Ni$Cu/{\gamma}-Al_2O_3$ catalysts for the oxidation of toluene increased with the increasing loadings of copper, reached the maximum activity at 5% loadings of copper, and decreased with higher loadings of copper in the catalysts. The activity of $Cu/{\gamma}-Al_2O_3$ catalysts for the oxidation of toluene decreased with the increasing calcination temperatures. This might result from the decreasing surface area of catalysts due to the sintering of copper oxide as well as ${\gamma}-Al_2O_3$ supports. The 5wt% $Cu/{\gamma}-Al_2O_3$ catalysts calcined at $400^{\circ}C$ for 4 hrs in the air showed the highest activity for the oxidation of toluene. Mutual inhibition was observed for the binary mixture of toluene and xylene. The activity of the easy-to-oxidize toluene was greatly decreased while the difficult-to-oxidize xylene was slightly decreased in the binary mixture of toluene and xylene. It might suggest that the inhibition of toluene and xylene in the binary mixture resulted from the competitive adsorption for the adsorbed oxygen on the catalytic surface.

• Journal of the Korean Magnetics Society
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• v.11 no.5
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• pp.202-210
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• 2001

Spin dependent tunneling (SDT) junction devices of Ta/NiFe/Ta/NiFe/FeMn/NiFe/AlOx/CoFe/NiFe/Al with in-situ naturally oxidized Al barrier were fabricated using ion beam deposition and dc sputtering in UHV chamber of 10$^{-9}$ Torr. The maximum tunneling magnetoresistance (TMR) and the product resistance by junction (R$_{j}$ A) are 16-17% and 50-60 $\Omega$${\mu}{\textrm}{m}$$^2$, respectively. The values of TMR and (R$_{j}$ A) with field annealing were slightly increased. The TMR and (R$_{j}$ A) dependence versus the junction area size was observed. These results were explained by using sheet resistance effect of bottom electrode and spin channel effects.

• Journal of the Korean Chemical Society
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• v.44 no.4
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• pp.322-327
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• 2000

A new absorption spectrometric method for the determination of the Cr$_2O_7^{2-}$ ionin acidic media has been developed. The new method is based on the oxidation-reduction reaction of the HCr$O_4^-$ ion with H$_2$O$_2$forming a deep blue CrO(O$_2$) $_2$ andis coupled with a technique of flow injection analysis(FIA). The new method provides a linear calibration curve which accurately follows the Beer's law over a wide range of the analytical concentrations(2.0 ${\times}$ $10^{-6}$M~8.0 ${\times}$ $10^{-3}$M) of K$_2$Cr$_2$O$_2$. The sensitivity of the new method is approximately two times greater than the current method and the effects of the interfering substances such as V, Co, Ni, Fe, and Mn are almost negligible except Cu.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.27 no.2
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• pp.70-74
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• 2017

Two milling methods, dry vibration milling and wet ball milling, were used to prepare $Na_{2/3}(Ni_{1/3}Mn_{2/3})O_2$ powders as a cathode material for sodium ion batteries. The morphology and electrochemical property of the two powders with different milling processes were compared to each other. The particle size is less than $1{\mu}m$ in the dry vibration milled powder, while lots of larger particles than $1{\mu}m$ were found in the wet ball milled one. The single phase of $Na_{2/3}(Ni_{1/3}Mn_{2/3})O_2$ was obtained in the temperature range of $875{\sim}900^{\circ}C$. The discharge capacity and discharge voltage of the powder prepared by the dry process were higher than those of one prepared by the wet process.