• Journal of the Korean Ceramic Society
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• v.27 no.1
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• pp.109-117
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• 1990

Magnetite for Water-based ferrofluid was synthesized by air oxidation of aqueous suspension in the pH range 7-12 at $65^{\circ}C$. The optimum condition of magneite formation was delineated by examining various physicochemcial properties such as Fe2+ content, phase characteristics, MHC and $\sigma$max. The point of zero charge of iron oxide powders obtained at various pH conditions were correlated with the oxidation state of Fe in the iron oxide. The magnetite powder prepared at pH 9 ws dispersed using sodium oleate and sodium dodecylbenzenesulfonate (SDBS) as dispersants, and the dispersion characteristics of the magnetite ferrofluid were examined by means of the fraction of solid dispersed, zeta potential data and FT-IR spectrum. A simple calculation on the potential energy of two interacting magnetite particles showed that the dispersion stability was directly correlated with height of the potential energy barrier or the shape of zeta potential.

• Journal of Korean Vacuum Science & Technology
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• v.6 no.4
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• pp.153-157
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• 2002

The electronic structures of Gd$_{5}$Si$_2$Ge$_2$ compound, which has a giant magnetocaloric effect, in the monoclinic and orthorhombic phases were calculated using the tight-binding linear-muffin-tin-orbital method within the atomic-sphere approximation. The calculated total energies of the monoclinic and orthorhombic structures in the paramagnetic phase confirm that the orthorhombic structure is more stable than monoclinic structure. The density of states (DOS) at the Fermi level of the orthorhombic phase is higher than that of the monoclinic phase in the paramagnetic phase, fulfilling the Stoner criterion. The calculated charge density verified the breaking of Ge(Si)-Ge(Si) bonding in the basal plane upon the orthorhombic-monoclinic phase transition. The DOS curve fairly well reproduces the photoemission spectrum.m.

• Proceedings of the Polymer Society of Korea Conference
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• 2006.10a
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• pp.21-22
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• 2006

Significant progress has been realized in the design and synthesis of light emitting polymers with emission over the whole range of the visible spectrum. However up to seventy-five percent of charge recombination events can lead to triplet states that decay non-radiatively. Following the pioneering work in the field of small molecule organic light emitting devices it has been found that solution processible iridium polymer complexes can be used to harness the wasted triplet energy. In this paper new results concerning electrophosphorescence of solution processible tethered iridium polymer derivatives will be presented. Furthermore our approaches to the design of new high triplet energy conjugated polymer hosts will be reported.

• Proceedings of the KIEE Conference
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• 1998.07d
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• pp.1255-1257
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• 1998

In this study,$ 5{\times}5$ dot-matrix display was implemented with powder electroluminescent device (PELD). Generally PELD which have a luminance from powder phosphor with electric field, inserted phosphor and dielectric layer between electrodes is basic structure. To make high brightness PELD compared to conventional device, new type of PELD was proposed as follows. New PELD had only one layer, which was mixed phosphor (ZnS:Cu) and dielectric (BaTiO3) material appropriately between electrodes. To compare and estimate the conventional and new type of PELD, the EL spectrum, transferred charge density, brightness and decay time was measured. As above result, we fabricated a hish brightness $ 5{\times}5$ dot-matrix display with new type of PELD. Its brightness was 6400 $cd/m^2$ at 200 V, 400Hz.

• Macromolecular Research
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• v.15 no.2
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• pp.129-133
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• 2007

Significant progress has been realized in the design and synthesis of light emitting polymers that emit over the entire visible spectrum. However, up to seventy-five percent of charge recombination events can lead to triplet states that decay non-radiatively. Following the pioneering work in the field of small molecule organic light emitting devices, it has been found that solution processible iridium polymer complexes can be used to harness the wasted triplet energy. In this paper, new results with respect to the electrophosphorescence of solution processible tethered iridium polymer derivatives are presented. Furthermore, our approaches to the design of new high triplet energy conjugated polymer hosts are also reported.

• Proceedings of the Korean Institute of IIIuminating and Electrical Installation Engineers Conference
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• 1998.11a
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• pp.9-11
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• 1998

A phenomenon of electroluminescent radiate as electric field applied in the phosphor, in this paper, we produced the Powder Electroluminescent Device(PELD) which was changing the structure and the thickness of phosphor and insulator for realization of the PELD with high brightness. We made PELD with structure that is WK-1(ITO film/Phosphor/Insulator/Electrode), WK-2(ITO film/Phosphor/Insulator/Electro de), WK-3(ITO film/Phosphor/Insulator/Electrode), WK-4(ITO film/Phosphor+Insulator/ Electrode). The property of the produced PELD are analyzed by measuring the spectrum which electrical and optical property, the brightness and the transferred charge density. In this result, the structure of WK-4 have good luminescence property than others, it's effective thickness is 60${\mu}{\textrm}{m}$. At 100V 400Hz, High brightness of 2700cd/m2 was performed.

• Proceedings of the KIEE Conference
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• 2000.07c
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• pp.1969-1971
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• 2000

This paper presents a data acquisition and analysis program modules that has been developed using the Labview program. These program modules can use to acquire and analyze leakage current data of insulator under different contamination conditions. The experimental hardware made up salt fog chamber, AC/DC power supply, transducer (shunt resistor), measurement devices and PC with the GPIB (General Purpose Interface Bus). And analysis program modules can calculate pulse level count, accumulated charge, average leakage current, power spectrum, and harmonics. The result of applying these analytical program modules to polymeric insulator is available for evaluation of leakage current characteristic of outdoor insulators.

• Journal of the Korean Magnetics Society
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• v.8 no.4
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• pp.198-202
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• 1998

We have studied $Al_xFe_{3-x}O_4$ produced by direct composition method using X-ray diffraction and Mssbauer spectroscopy. The cation distribution for $Al_xFe_{3-x}O_4$ was determined by the ratio of sub-spectra absorption area. The charge state of Fe atoms in octahedral site(B-site) is $Fe^{2.5+}$ based on electron hopping, $Fe^{2+}$ ↔ $(Fe^{3+},Al^{3+})$ without dependency of substituted Al amounts.

• 전기의세계
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• v.26 no.4
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• pp.68-72
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• 1977

The main purpose of this paper is to study on the nature of the traps in polymer. The polyethlene is typical of polymer material as to be selected for a sample. The current I$_{th}$ are obtained with an small external bias voltage from high density polyethylene which have been treated by the high-field application. Two peaks, P$_{1}$ and P$_{2}$ with maxima near 85.deg. C, respectively, appeared on the current I$_{th}$ spectrum. From the results of experiment, It is clear that The current I$_{th}$ arises from the drift, under the external field, of carriers released from the trap sites by the heating and the trap is surrounded by a potential barrier and trapping proceeds during the high-field treatment. The obtained results can suggest that polyethylene contains trap sites which have an important role in the electrical conduction and breakdown of polymeric materials.rials.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1999.11a
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• pp.582-585
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• 1999

Electroluminescence is occurred when phosphor is located in electric field. In this paper, we made powder electroluminescent device (PELD) with structured ITO film/Phosphor/Insulator/Silver paste. The transparent electrode was ITO film and green(2704-01) and orange(2702-02) and blue-preen(2703-01) were used as phosphor. The insulator was BaTiO$_3$ and $Y_2$O$_3$, bark electrode was silver paste. To investigate electrical and optical properties of PELDs, EL spectrum, Brightness . Transferred charge density using Sawyer-Towers circuit was measured.