• Journal of the Korean Ceramic Society
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• v.39 no.10
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• pp.912-918
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• 2002

Ni-Mn-Co-Fe oxide thick films were coated on an alumina substrate by screening printing technique. The microstructure and electrical properties of the thick films, as a function of composition and sintering temperature, were investigated. The components of the NTC thick films sintered at 1150${\circ}C$ were distributed homogeneously. On the other hand, in the case of the NTC thick films sintered at 1200 and 1250${\circ}C$, Co element was distributed homogeneously, but Ni, Mn and Fe elements were distributed heterogeneously, resulting in the formation of Ni rich and Mn-Fe rich regions. All the thick film NTC thermistors prepared showed a linear relationship between log resistance (log R) and the reciprocal of absolute temperature (1/T), indicative of NTC characteristics. At a given NiO and $Mn_3O_4$ content, the resistance, B constant and activation energy of $(Ni_{1.0}Mn_{1.0}Co_{1-x}Fe_x)O_4$ (0.25${\le}$x${\le}$0.75) and $(Ni_{0.75}Mn_{1.25}Co_{1-x}Fe_x)O_4$ (0.25${\le}$x${\le}$0.75) thermistors increased with increasing $Fe_2O_3$ content.

• Journal of the Korean Geophysical Society
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• v.4 no.4
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• pp.257-266
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• 2001

The properties of electrical resistance of Mn-Co-Ni-Fe oxide-based therrnistor with various Fe contents in sintering process at 1200 to 1400℃ for 4 hours in air atmosphere for fabricating therrnistor materials were investigated. The results were as follows: all samples showed single cubic spinel crystal structures in all region. The electrical conductivinity is the highlest thermistor sintered at 1300℃ for 4 hours. In general when the Fe content is increased except F-2, the resistivity increases and relatively the conductivity decreases. Particularly F-2 composition exhibited the highlest electrical conductivity(1.4x $10^-3$$Ω$cm) and relatively low B constant(2906K)

• The Journal of Engineering Research
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• v.5 no.1
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• pp.63-72
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• 2004

The properties of electrical resistance of Mn-Co-Ni-Fe oxide-based thermistor with various Fe contents in sintering process at $1200^{\circ}$ to $1400^{\circ}C$ for 4 hours in air atmosphere for fabricating thermistor materials were investigated. The results were as follows: all samples showed single cubic spinel crystal structures in all region. The electrical conductivity is the highest thermistor sintered at $1300^{\circ}C$ for 4 hours. In general when the Fe content is increased except F-2, the resistivity increases and relatively the conductivity decreases. Particularly F-2 composition exhibited the highest electrical conductivity (1.4${\times}$$10^-3$${\textohm}cm) and relatively low B constant(2906K)

• Proceedings of the Materials Research Society of Korea Conference
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• 2002.11a
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• pp.154-154
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• 2002

• Journal of the Korean Magnetics Society
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• v.9 no.6
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• pp.291-295
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• 1999

$NiFe/Co/Al_2O_3/Co/IrMn$ tunneling junctions were grown on (100)Si wafer and their spin-valve tunneling magnetoresistance (TMR) was studied. The tunneling junctions were grown by using a 5-gun RF/DC magnetron sputter. $Al_2O_3$ barrier layer was formed by exposing Al layer to oxygen atmosphere at 6$0^{\circ}C$ for 72 hours. Strong exchange coupling interaction is observed between the ferromagnetic Co and the antiferromagnetic IrMn of Co/IrMn bilayer when IrMn is 100$\AA$ thick. $NiFe(183\;{\AA})/Co(17\;{\AA})/Al_2O_3(16\;{\AA})/Co(100\;{\AA})/IrMn(100\;{\AA})$ tunneling junction shows best TMR ratio of about 10% in the applied magnetic field range of $\pm$20 Oe. The TMR ratio is improved about 23% and electrical resistance is decreased about 34% when annealed at 200 $^{\circ}C$ for 1 hour in magnetic field of 330 Oe, parallel to the bottom electrode. With increasing the active area of junction the TMR ratio increases while electrical resistance decreases.

• Journal of the Korean Ceramic Society
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• v.44 no.11
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• pp.639-644
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• 2007

Spinel pigments, developing black color in high temperature glazes at oxidation or reduction atmosphere, without CoO because of its high price were synthesized by solid solution method. Ten mixed compositions consisted of NiO, MnO, $Fe_2O_3 and $Mn_2O_3$ were fired at $1250^{\circ}C$ for 1h. The resulting pigments were characterized by using XRD, FT-IR, SEM and UV-vis spectrometer. Structure of the pigments are spinel and particles' shape are spherical or cubic. Glazed tiles containing 5 wt% pigments were fired at $1260^{\circ}C$ and $1240^{\circ}C$ in reduction atmosphere. Color in glazes were analyzed by UV-vis spectrometer. Colors of NiO 0.875 MnO $0.125{\cdot}Fe_2O_3$ $0.4875{\cdot}Cr_2O_3$ $0.50{\cdot}Mn_2O_3$ 0.0125 mole% and NiO 0.875 MnO $0.125{\cdot}Fe_2O_3$ $0.3875{\cdot}Cr_2O_3$ $0.50{\cdot}Mn_2O_3$ 0.1125 mole% in lime glaze showed black in oxidation, in reduction NiO 0.875 MnO $0.125{\cdot}Fe_2O_3$ $0.4875{\cdot}Cr_2O_3$ $0.50{\cdot}Mn_2O_3$ 0.0125 mole% and NiO 0.875 MnO $0.125{\cdot}Fe_2O_3$ $0.4375{\cdot}Cr_2O_3$ $0.55{\cdot}Mn_2O_3$ 0.0125 mole% showed black. In case of lime-barium glaze, NiO 0.875 MnO $0.125{\cdot}Fe_2O_3$ $0.3875{\cdot}Cr_2O_3$ $0.50{\cdot}Mn_2O_3$ 0.1125 mole%, NiO 0.975 MnO $0.075{\cdot}Fe_2O_3$ $0.4375{\cdot}Cr_2O_3$ $0.50{\cdot}Mn_2O_3$ 0.0625 mole% and NiO 0.925 MnO $0.075{\cdot}Fe_2O_3$ $0.4375{\cdot}Cr_2O_3$ $0.50{\cdot}Mn_2O_3$ 0.0625 mole% showed black color in oxidation and NiO 0.875 MnO $0.125{\cdot}Fe_2O_3$ $0.3875{\cdot}Cr_2O_3$ $0.50{\cdot}Mn_2O_3$ 0.1125 mole%, NiO 0.925 MnO $0.075{\cdot}Fe_2O_3$ $0.4375{\cdot}Cr_2O_3$ $0.50{\cdot}Mn_2O_3$ 0.0625 mole% and NiO 0.725 MnO $0.275{\cdot}Fe_2O_3$ $0.4375{\cdot}Cr_2O_3$ $0.50{\cdot}Mn_2O_3$ 0.0625 mole% showed black one in reduction.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.12 no.10
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• pp.4660-4665
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• 2011

New precursors as a Li adsorbent, $Li_{1.6}(MnM)_{1.6}O_4$ (M=Cu, Ni, Co, Fe), were synthesized by hydrothermal method and their physicochemical properties were discussed. XRD and HRTEM results revealed that the original spinel structure was stabilized by cobalt-doping while Cu-, Ni- and Fe-doping led to structural changes. Such a structural stabilization by Cobalt-doping was maintained after lithium leaching by acid treatment. Li absorption efficiency from seawater was significantly enhanced by using the Cobalt-doped spinel manganese oxide, $Li_{1.6}[MnCo]_{1.6}O_4$, compared to the commercially available $Li_{1.33}Mn_{1.67}O_4$; the adsorbed amount of Li from 1g-adsorbent was 35 and 16 mg by $Li_{1.6}[MnCo]_{1.6}O_4$, and $Li_{1.33}Mn_{1.67}O_4$, respectively.

• Transactions of Materials Processing
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• v.17 no.4
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• pp.240-248
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• 2008

The effect of alloying elements(Mn, S, Mo, B) on the high temperature deformation behavior of Fe-29%Ni-17%Co (Kovar) alloy were investigated. And the effect of high temperature oxidation on the hot ductility was also studied. The hot ductility of Kovar alloy was drastically increased with the addition of Mn and lowering of S content. It has been found that the brittle intergranular fracture at high temperature cracking is closely associated with the FeS sulfide along the grain boundary. When Mn was added, the type of sulfide was changed to MnS from FeS and ductile intergranular fracture and transgranular fracture were promoted. The formation of oxide layer was found to have minimized the hot ductility of the Kovar alloy significantly. Grain boundary micro-cracks in the internal oxide region were noted following deformation due to high temperature, one of which acting as a notch that caused the poor hot workability of the oxidized specimen. The addition of Mo to the Kovar alloy could also retard the decrease in the hot ductility of the oxidized specimen through the prevention of notching due to internal oxidation. Hot ductility was remarkably improved by the addition of Boron. The improvement of hot ductility results from the grain boundary migration mainly due to the dynamic recrystallization at lower temperature range ($900{\sim}1000^{\circ}C$).

• Transactions of the Korean hydrogen and new energy society
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• v.14 no.3
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• pp.268-275
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• 2003

The water-splitting process by the metal oxides using solar heat is one of the hydrogen production method. The hydrogen production process using the metal oxides (NiFe2O4/NiAl2O4,CoFe2O4/CoAl2O4, CoMnNiFerrite, CoMnSnFerrite, CoMnZnFerrite, CoSnZnFerrite) was carried out by two steps. The first step was carried out by the CH4-reduction to increase activation of metal oxides at operation temperature. And then, it was carried out the water-splitting reaction using the water at operation temperature for the second step. Hydrogen was produced in this step. The production rates of H2 were 110, 160, 72, 29, 17, $21m{\ell}/hr{\cdot}g-_{Metal\;Oxide}$ for NiFe2O4/NiAl2O4, CoFe2O4/CoAl2O4, CoMnNiFerrite, CoMnSnFerrite, CoMnZnFerrite, CoSnZnFerrite respectively in the second step. CoFe2O4/CoAl2O4 had higher H2 production rate than the other metal oxides.

• Metals and materials international
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• v.24 no.6
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• pp.1285-1292
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• 2018

Microstructural properties of as-grown and annealed CoCrFeMnNi high entropy alloy (HEA) oxynitride thin films were investigated. The CoCrFeMnNi HEA oxynitride thin film was grown by magnetron sputtering method using an air gas, and annealed under the argon plus air flow for 5 h at $800^{\circ}C$. The as-grown film was homogeneous and uniform composed of nanometer-sized crystalline regions mixed with amorphous-like phase. The crystalline phase in the as-grown film was face centered cubic structure with the lattice constant of 0.4242 nm. Significant microstructural changes were observed after the annealing process. First, it was fully recrystallized and grain growth happened. Second, Ni-rich region was observed in nanometer-scale range. Third, phase change happened and it was determined to be $Fe_3O_4$ spinel structure with the lattice constant of 0.8326 nm. Hardness and Young's modulus of the as-grown film were 4.1 and 150.5 GPa, while those were 9.4 and 156.4 GPa for the annealed film, respectively.