• E2M - 전기 전자와 첨단 소재
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• 제4권3호
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• pp.201-210
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• 1991

본 논문에서는 (B $i_{1-x}$ P $b_{x}$)$_{2}$S $r_{2}$C $a_{2}$C $u_{3.6}$ $O_{y}$ (x=0~0.5)로 조성된 분말의 최적 하소온도를 결정하고 시편의 최적 소결온도를 규명하기 위하여 열분석을 하였다. 또 단일상의 고온 초전도체를 제작하기 위하여 열처리 온도, 시간 및 Pb 함량 변화에 따라 제작된 시편의 미세구조, 조성, 전기저항 및 전류밀도를 측정하여 상호 연관성을 종합적으로 분석, 검토하여 상변이에 관한 원인을 규명하고자 하였다. 또한 실용화 전 단계로서 임계특성 해석을 위하여 성형조건을 변화시켜 시편을 제작, 전류밀도값을 측정하였다.였다.다.

• Advances in environmental research
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• 제4권4호
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• pp.247-262
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• 2015

The few lignin biomarker studies conducted in tropical environments are hampered by having to use references signatures established for plants and soils characteristic of the temperate zone. This study presents a lignin biomarker analysis (vanillyls (V), p-hydroxyls (P), syringyls (S), cinnamyls (C)) of the dominant plant species and soil horizons as well as an analysis of the interrelated terrigenous organic matter (TOM) dynamics between vegetation and soil of the $Tapaj{\acute{o}}s$ river region, an active colonization front in the Brazilian Amazon. We collected and analyzed samples from 17 fresh dominant plant species and 48 soil cores at three depths (0-5 cm, 20-25 cm, 50-55 cm) from primary rainforest, fallow forest, subsistence agriculture fields and pastures. Lignin signatures in tropical plants clearly distinguish from temperate ones with high ratios of Acid/aldehyde of vanillyls ((Ad/Al)v) and P/V+S. Contrary to temperate environments, similarly high ratios in tropical soils are not related to TOM degradation along with pedogenesis but to direct influence of plants growing on them. Lignin signatures of both plants and soils of primary rainforest and fallow forest clearly distinguish from those of non-forested areas, i.e., agriculture fields and pastures. Attalea speciosa Palm trees, an invasive species in all perturbed landscapes of the Amazon, exhibit lignin signatures clearly distinct from other dominant plant species. The study of lignin signatures in tropical areas thus represents a powerful tool to evaluate the impact of primary rainforest clearing on TOM dynamics in tropical areas.

• 한국분말재료학회지
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• 제8권3호
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• pp.163-167
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• 2001

A bulk porous $CaZrO_3/MgO$ composite with plantinum nano-dispersion was synthesized in air atmosphere through the combination of several in situ reactions, including the pyrolysis of $PtO_2$. A mixture of $CaMg(CO_3)_2$(dolomite), $ZrO_2$, $PtO_2$ and LiF (0.5 wt%, as an additive) was cold isostatically pressed at 200 MPa and sintered at $1100^{\circ}C$ for 2 h. The porous $CaZrO_3/MgO/Pt$ composite ($CaZrO_3/MgO$ : Pt=99 : 1 in volume) had a uniformly open-porous structure (porosity: 56%) with three-dimensional (3-D) network and a narrow pore-size distribution, similarly to the porous $CaZrO_3/MgO$ composites reported before. Catalytic Properties (viz., NO direct decomposition and NO reduction by $C_2H_4$) of the $CaZrO_3/MgO/Pt$ composite were investigated up to $900^{\circ}C$. In the absence of oxygen, the NO conversion rate reached ~52% for the direct decomposition and ~100% for the reduction by $C_2H_4$, respectively. The results suggest the possibility of the porous composite as a multifunctional filter, i.e., simultaneous hot gas-filtering and $de-NO_x$ in one component.

• 한국세라믹학회지
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• 제40권12호
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• pp.1154-1158
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• 2003

Hydrothermal deposition of hydroxyapatite coatings on $Al_2$O$_3$ substrates was studied using aqueous solutions of Ca(NO$_3$)$_2$ㆍ4$H_2O$ and (NH$_4$)$_2$HPO$_4$ containing EDTA disodium salt as a chelating agent for $Ca^{2+}$. For the precipitation of the coatings the EDTA-Ca$^{2+}$ chelates were dissociated thermally at 20$0^{\circ}C$ or decomposed by oxidation with $H_2O$$_2$ at 9$0^{\circ}C$. Scanning electron microscopy and X-ray diffraction were used to investigate the deposition behavior and the phase of the coatings. Hydroxyapatite coatings were not deposited with the thermal dissociation method, whereas uniform deposition of the coatings (about 0.7 $\mu\textrm{m}$ thickness) was obtained with the oxidative decomposition method. The coatings consisted of fine rod-like hydroxyapatite crystals (hexagonal structure) with 60-80 nm diameters, having some preferred orientation with their length (i.e., the c axis) perpendicular to the substrate.ate.

• E2M - 전기 전자와 첨단 소재
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• 제8권5호
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• pp.611-618
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• 1995

The (Sr$_{1-x}$ .Ca$_{x}$)TiO$_{3}$+0.6[mol%]Nb$_{2}$O$_{5}$ (0.05.leq.x.leq.0.2) ceramics were fabricated to form semiconducting ceramics by sintering at about 1350[.deg. C] in a reducing atmosphere(N$_{2}$ gas). Metal oxides, CuO, was painted on the both surface of the specimens to diffuse to the grain boundary. They were annealed at 1100 [.deg. C] for 2 hours. The 2nd phase formed by thermal diffusing from the surface lead to a very high apparent dielectric constant. According to increase of the frequency as a functional of temperature, all specimens used in this study showed the dielectric relaxation, and the relaxation frequency was above 106 [Hz], it move to low frequency with increasing resistivity of grain. The specimens showed three kinds of conduction mechanisms in the temperature range 25-125 [.deg. C] as the current increased: the region I below 200 [V/cm] shows the ohmic conduction. The region rt between 200 [V/cm] and 2000 [V/cm] can be explained by the Poole-Frenkel emission theory, and the region III above 2000 [V/cm] is dominated by the tunneling effect.fect.

• 한국전기전자재료학회논문지
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• 제17권11호
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• pp.1167-1173
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• 2004

This paper reports the variations of varistor voltage, nonlinear exponent, leakage current, and dissipation factor against surge stress of ZnO-P $r_{6}$ $O_{11}$-CoO-C $r_2$ $O_3$-E $r_2$ $O_3$(ZPCCE)-based varistors manufactured with the variations of sintering temperature. It was found that the variations of electrical parameters against surge stressing current of 100 A/$\textrm{cm}^2$(8x20 ${\mu}\textrm{s}$) is not so large under the surge stress of 700 times. Among varistors, specially the varistor sintered at 134$0^{\circ}C$ exhibited the smallest variations, with %$\Delta$ $V_{lmA}$=+0.23%, %$\Delta$$\alpha$=+0.23%, %$\Delta$ $I_{L}$=0%, %$\Delta$tan$\delta$=-6.94%. The clamping voltage ratio( $V_{c}$/ $V_{lmA}$) of all varistors was less than 2.2.2.2.2.2.2.

• E2M - 전기 전자와 첨단 소재
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• 제10권2호
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• pp.97-104
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• 1997

In this paper, in order to investigate the behavior of charged particles on (Sr.Ca)TiO$_{3}$ ceramics with paraelectric properties, the characteristics of electrical conduction and thermally stimulated current was measured respectively. As a result, the conduction mechanism is divided into three regions having different mechanism as the current increased. The region I below 200[V/Cm] shows the ohmic conduction. The region B between 200[V/cm] and 2000[V/cm] can be explained by the Poole-Frenkel emission theory, and the region III above 2000[V/cm] is dominated by the tunneling effect. The three peaks of TSC were obtained at the temperature of -20[.deg. C], 20[.deg. C] and 80[.deg. C], respectively. The origins of these peaks are that the .alpha. peak observed at -20[.deg. C] looks like to be ascribed to the ionization excitation from donor level in the grain, and the .alpha.' peak observed at 20 [.deg. C] appears to show up by hopping conduction of the trapped carrier of border between the oxidation layer and the grain, and the .betha. peak observed at 80[.deg. C] seems to be resulted from hopping conduction of existing carrier in the trap site of the border between the oxidation and second phase.

• 한국재료학회지
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• 제17권1호
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• pp.1-5
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• 2007

GaN thin fan were grown by spin coated colloidal GaOOH precursor. Polycrystalline GaNs with crystalline size of $10{\sim}100nm$ were grown on $SiO_2$ substrate. The shape of crystallite above $900^{\circ}C$ had the hexagonal plate and column type. X-ray diffraction patterns for them correspond to those of the hexagonal wurtzite GaN. With increasing droplets. i.e, thickness of deposited layers, XRD intensity increased. PL (photoluminescence) spectrum consisted with an weak near band-edge emission at 3.45 eV and a broad donor-acceptor emission band at 3.32 eV. From the low temperature PL measurement on GaN grown at $800^{\circ}C$ that the shallow donor-acceptor recombination induced emission was more intense than the near band-edge excitonic emission.

• 한국초전도ㆍ저온공학회논문지
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• 제1권1호
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• pp.15-21
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• 1999

Textured bulk $YBa_2Cu_3O_x$ superconductors samples were grown directionally using different precursors of $YBa_2Cu_3O_x$ power. and a mixture of $YBa_2Cu_3O_5, BaCuO_2 and CuO$ powder. The microstructures and superconducting properties of the samples were compared. The mixture powder produced better microstructures i.e. dense and crack-free so that a higher critical current density was achieved at the same hot-zone temperature of 115$0^{\circ}C$ than the reacted powder does. When the reacted powder used as a precursor, as the hot-zone temperature increased upto 1215$^{\circ}C$, the texture of the sample improved and the critical current density increased. The amount of melt in the sample is of secondary importance for the growth of superconducting $YBa_2Cu_3O_x$ grains. The microstructures and superconductivity of good quality superconductors grown directionally were more strongly influenced by the kind of precursor rather than the amount og melt in a sample.

• Journal of Magnetics
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• 제14권3호
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• pp.117-119
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• 2009

Polycrystalline samples of LaFe$O_3$-BaTi$O_3$ were synthesized to examine the structural and magnetic behavior. X-ray diffraction confirmed that the ceramics had tetragonal symmetry with less tetragonal strain (c/a) than BaTi$O_3$. The magnetic hysteresis measured at room temperature suggested that the magnetic nature deviates from that of the parent LaFe$O_3$, which has antiferromagentic with a G-type spin structure. Improved magnetic behavior of the solid solution compound might be due to the increase in the canting angle of the spin. The presence of oxygen vacancies and fluctuating Fe valence, arising from the substitution of $Ba^{2+}$ and $Ti^{4+}$ at the A- and B-sites of the lattice, might contribute to bulk magnetization. The temperature dependent magnetization indicated that magnetization was higher at low temperatures and showed a decreasing trend with increasing temperature to room temperature. The magnetic transition temperature of these samples was 665 K and 743 K for the mixed system and LaFe$O_3$, respectively.