• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.17 no.6
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• pp.661-667
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• 2004

The control of tilt angle for nematic liquid crystal (NLC) with negative and positive dielectric anisotropy on the rubbed homeotropic polyimide (PI) using baking method by hot plate equipment was investigated. LC tilt angle decreased with increasing baking temperature and time. Especially, the low LC tilt angle of positive type NLC (Δ$\varepsilon$＞0) on the rubbed homeotropic PI surface by increasing temperature and time was measured. The tilt angle of positive type NLC(Δ$\varepsilon$＞0) is smaller than that of the negative type (Δ$\varepsilon$＞0) on rubbed PI with increasing baking temperature and time. We consider that the tilt angle of NLC is decreased due to increasing the steric interaction between horizon component of permittivity $\varepsilon$ = of NLC and the stress of polymer side chain by high temperature. As the increase of baking temperature, we obtain that AFM (atomic force microscope) image of rubbed PI surface using Hot-plate method has formed better solid micro-groove structure than oven method.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.28 no.9
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• pp.577-580
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• 2015

In this paper, in order to develop the composition ceramics with the outstanding piezoelectric properties, $Pb(Mg_{1/2}W_{1/2})_{0.03}(Ni_{1/3}Nb_{2/3})_{0.09}(Zr_{0.5}Ti_{0.5})_{0.88}O_3$ ceramics substituted with $BiFeO_3$ were prepared by the conventional solid-state reaction method. The addition of small amount of $Li_2CO_3$ and $CaCO_3$ as sintering aids decreased the sintering temperature of the ceramics. The effects of $BiFeO_3$ substitution on their piezoelectric and dielectric properties were investigated. when 0.015 mol $BiFeO_3$ was substituted, the optimal physical properties of $d_{33}=590pC/N$, $E_c=8.78kV/mm$ were obtained.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.14 no.11
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• pp.904-911
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• 2001

High-density lead zirconate titanate(Pb(Zr$\_$0.53/Ti$\_$0.47/)O$_3$, PZT) ceramics were fabricated by a new milling-precipitation(MP) process improved from the conventional solid state process. This process was progressed by a milling impregnation through mixing ZrO$_2$ and TiO$_2$ powders with lead nitrate(Pb(NO$_3$)$_2$) water solution in zirconia ball media, and then milling precipitation was induced from precipitation of PbC$_2$O$_4$ by adding ammonium of oxalate monohydrate((NH$_4$)$_2$C$_2$O$_4$$.$H$_2$O) as a precipitant. As a result of this process, single-phase perovskite structure was formed at the calcination temperature of 750$\^{C}$ for Pb(Zr$\_$0.53/Ti$\_$0.47/)O$_3$ powders. In addition, the highest density at the sintering temperature of 1100$\^{C}$ was obtained, because of the highly sinterable PZT Powders ground through the re-milling process. Piezoelectric and dielectric properties of sintered sample were improved by MP process.

• Explosives and Blasting
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• v.40 no.1
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• pp.17-28
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• 2022

Electrical pulse disintegration(ED) is known as an efficient technology for recovering valuable resources by inducing dielectric breakdown in solids to separate mineral interfaces in ores among the crushing technologies by high voltage discharge. In this study, ED crushing experiment and mechanical crushing experiment of sulfide minerals were performed, and SEM analysis and Microfocus X-Ray CT of the crushed product were performed in order to analyze the disintegration characteristics of zinc minerals exist in the sulfide minerals by the shock wave generated in the solid by high voltage discharge.

• Journal of the Korean Vacuum Society
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• v.2 no.2
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• pp.220-226
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• 1993

An investigation was made of the dependences of the lattice constants and the energy gap on the composition of $TlGa_xIn_{1-x}Se_2$ single cystals grown by Bridgman method. It was found that a discontinuity in $TlGa_xIn_{1-x}Se_2$ solid solutions occurred in the composition range 0.25$0.0{\leq}X{\leq}0.25$) to the monoclinic structure ($0.65{\leq}X{\leq}1.0$) was observed in this composition range. The temperature dependences of the energy gap and the dielectric constant in $TlGaSe_2$ single crystal have shown that the anomalies appeared at 107 K and 120 K corresponding to first-order and second-order phase transitions, respectively.

• Korean Journal of Materials Research
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• v.26 no.12
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• pp.721-725
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• 2016

This work focuses on the electrical conduction mechanism in a lead free ($Na_{0.5}K_{0.5}NbO_3$ ; NKN) ceramics system with $LiNbO_3$ content of approximately critical concentration $x{\geq}0.2$. Lead free $(1-x)(Na_{0.5}K_{0.5})NbO_3-x(LiNbO_3)$, $NKN-LN_x$ (x = 0.1, 0.2) ceramics were synthesized by solid-state reaction method. Crystal structures are confirmed by X-ray diffraction. The electric-mechanical bond coefficient $k_p$ decreases and the phase transition temperature $T_c$ increases with increasing x content, as determined by dielectric and piezoelectric measurements. The value of the real dielectric constants ${\varepsilon}^{\prime}$ and $k_BT{\varepsilon}^{\prime\prime}$ showed anomalies around $T_c$ ($462^{\circ}C$ in the NKN-LN0.1 and $500^{\circ}C$ in the NKN-LN0.2). For the ionic conduction of mobile ions, the activation energies are obtained as $E_I=1.76eV$ (NKN-LN0.1) and $E_I=1.55eV$ (NKN-LN0.2), above $T_c$, and $E_{II}=0.78$ (NKNL-N0.1) and $E_{II}=0.81$ (NKN-LN0.2) below $T_c$. It is believed that the conduction mechanisms of NKN-LNx ceramics are related to ionic hopping conduction, which may arise mainly due to the jumping of $Li^+$ ions.

• Journal of the Korean Professional Engineers Association
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• v.17 no.3
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• pp.22-31
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• 1984

Sardine ant mackerel so called dark muscled fish have been underutilized due to the disadvantages in bloody meat color, high content of fat, and postmortem instability of protein. Recent efforts were made to overcome these defects and develope new types of product such as texturized protein concentrates and dark muscle eliminated minced fish. Approach of this study is based on the rapicl dehydration of foamed fish-starch paste by dielectric heating. In process comminuted sardine meat was washed more than three times by soaking and decanting in chilled water and finally centrifuged. The meat was ground in a stone mortar added with adequate amounts of salt, foaming agent, and other ingredients for aid to elasticity and foam stability. The ground meat paste was extruded in finger shape and heated in a microwave oven to give foamed, expanded, and porous solid structure by dehydration. Dielectric constant ($\varepsilon$′) and dielectric loss ($\varepsilon$") vcalues of sardine meat paste were influenced by wavelength and moisture level. Those values at 100KHz and 15MHz were ranged 2.25∼9.86 ; 2.22∼4.18 for $\varepsilon$′ and 0.24∼19.24 ; 0.16∼1.25 for $\varepsilon$", respectively, at the moisture levels of 4.2∼13.8％. For a formula for fish-starch paste preparation, addition of 20∼30% starch (potato starch) to the weight of fish meat, 2∼4% salt, and 5∼10% soybean protein was adequate to yield 4∼5 folds of expansion in volume when heated. Addition of egg yolk was of benefit to micronize foam size and better crispness. In order to provide better foaming and dehydration, addition of 0.2∼0.5% sodium bicarbonate foaming agent, was proper to result in foam size of 0.5∼0.7mm and foam density of 200∼400/$\textrm{cm}^2$ which gave a good crispness.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.14 no.10
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• pp.796-801
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• 2001

Ferroelectric 0.05PZN-xPZT(90/10)-(0.95-x)PZT(10/90) (x=0.65, 0.85) specimens were fabricated by the solid-state reaction method, and especially PZT(90/10) and PZT(10/90) powders were derived by the sol-gel method. All specimens showed a uniform ferroelectric grain without the presence of the pyrocholre phase. Average grain size increased with an increased in sintering temperature, the values for the x=0.65 and x=0.85 specimens sintered at 125$0^{\circ}C$ were 14.4$\mu$m and 9.8$\mu$m, respectively. The dielectric constant and dielectric loss of the x=0.65 specimen sintered at 125$0^{\circ}C$ were 1247. 2.06%, respectively. The coercive field and the remanent polarization of x=0.65 and x=0.85 specimens sintered at 125$0^{\circ}C$ were 8.5kV/cm, 13$\mu$C/$\textrm{cm}^2$ and 17.2kV/cm, 28 $\mu$C/$\textrm{cm}^2$, respectively. The pyroelectric coefficient of the x=0.65 and x=0.85 specimens sintered at 125$0^{\circ}C$ were 5.64$\times$10$^{-8}$ C/$\textrm{cm}^2$K and 2.76$\times$10$^{-8}$ C/$\textrm{cm}^2$K, respectively.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.25 no.6
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• pp.420-425
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• 2012

Lead-free piezoelectric ceramic/epoxy composites with '0-3' connectivity were prepared by cold-pressing with a temperature controlled curing method. A ceramic powder with a composition of $(Na_{0.51}K_{0.47}Li_{0.02})(Nb_{0.8}Ta_{0.2})O_3$ was synthesized by a conventional solid state reaction route. The dielectric and piezoelectric properties of ceramic/epoxy composites were characterized as a function of the volume fraction (${\phi}$) of piezoelectric ceramics, which was varied from 70 to 95 vol%. The results indicated that the piezoelectric properties of composites were significantly affected by the volume fraction of ceramics. In terms of the piezoelectric properties, specimens showed the best performance at ${\phi}$= 85 vol%, resulting in the piezoelectric constant $d_{33}$ of 39 pC/N and the figure of merit as a piezoelectric energy harvester ($d_{33}{\cdot}g_{33}$) of 1.24 $pm^2/N$.

• Journal of the Korean Magnetics Society
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• v.15 no.2
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• pp.113-117
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• 2005

Multiferroic $HoMnO_3$ single crystal was prepared using 4-point focused floating zone furnace, and polycrystalline $HoMn_{1-x}\;^57Fe_xO_3$ (x=0.00, 0.01, 0.02, 0.05) powders have been prepared by solid state reaction. Their magnetic and crystallographic properties are studied using MPMS, PPMS, and $M\ddot{o}ssbauer$ spectroscopy. The crystal structure found to be a hexagonal and a magnetic easy-axis is (110) direction. As the external applied magnetic field increases, temperature of the dielectric constant anomaly is decreased. $HoMn_{0.95}\;^{57}Fe_{0.05}O_3$ shows huge quadrupole splitting value from the $M\ddot{o}ssbauer$ spectra.