Processing math: 100%
  • Title/Summary/Keyword: relative density

Search Result 2,087, Processing Time 0.031 seconds

Fabrication of Nano Y2O3CeO2 Sintered Body Using Dispersion Stability (분산 안정성을 이용한 나노 Y2O3CeO2 소결체의 제조)

  • Kim, Eun-Jung;Lee, Sang-Hoon;Choi, Sung-Churl
    • Journal of the Korean Ceramic Society
    • /
    • v.38 no.9
    • /
    • pp.853-859
    • /
    • 2001
  • The dispersion stability of nano Y2O3CeO2 system was investigated using colloid surface chemistry. Green body of Y2O3 doped CeO2 was prepared by slip casting in and aqueous system. The dispersion stability of suspension between powders and organic additive was accomplished through electrokinetic behavior of suspension, which was done by ESA apparatus. The dynamic mobility of particles was enhanced when the anionic dispersant of the amount of 1wt% was added. The dissolution of Y3+ ion in suspension occurred in the acidic region so that pH value in slurries did not move to below 7.0. In the CeO2Y2O3 system, optimal preparation of suspension was made after adding the anionic dispersant as the amount of 1wt% and pH value of 11.0, and then slip-cast and sintered at 1400C, 2 hrs. It appeared relative density of >98% and homogeneous distribution of Y element in depth direction as well as in the microstructure of surface.

  • PDF

Sintering and Dielectric Properties of K2O-CaO-P2O5 Glasses-BNT(BaO-Nd2O3-TiO2) Ceramic Composites (K2O-CaO-P2O5계 유리-BNT(BaO-Nd2O3-TiO2)계 세라믹 복합체의 소결 및 유전특성)

  • 오영석;이용수;강원호;정병해;김형순
    • Journal of the Korean Ceramic Society
    • /
    • v.40 no.10
    • /
    • pp.954-960
    • /
    • 2003
  • To develop mobile phone antenna modules, glass-ceramics composites that are 20∼80 dielectric constant materials which has been fabricated. The glass-ceramics composites were based in the BNT (BaO-Nd2O3-TiO2), and properties-a sintering and dielectric property-were investigated in its composites according to the K2O-CaO-P2O5 system glass frits. The prepared ceramics were sintered at 900∼1200C with the glass frit contents ranging from 10 to 40 wt%. The shrinkage and relative density grew into increasing glass frits and sintering temperature. Sintered composites showed the tendency that the dielectric constant (εr) and quality factor (Q×f) decreased in increasing glass frits and sintering temperature.

Synthesis and Characterization of La0.75Sr0.25FeO3 Used as Cathode Materials for Solid Oxide Fuel Cell by GNP Method (GNP법을 이용한 고체산화물 연료전지의 공기극용 La0.75Sr0.25FeO3의 제조 및 특성)

  • Park, Ju-Hyun;Son, Hui-Jeong;Lim, Tak-Hyoung;Lee, Seung-Bok;Yun, Ki-Seok;Yoon, Soon-Gil;Shin, Dong-Ryul;Song, Rak-Hyun
    • Journal of the Korean Electrochemical Society
    • /
    • v.10 no.1
    • /
    • pp.7-13
    • /
    • 2007
  • We synthesized and investigated La0.75Sr0.25FeO3 by Glycine Nitrate Process(GNP) method used as cathode materials for SOFC(solid oxide fuel cell). Optimized amount of glycine is 3.17 mol. ICP elemental composition analysis indicated that the stoichiometry of the synthesized powders have nearly nominal values. SEM images and XRD patterns reveal that the synthesized powder has uniform size distribution and high degree of crystallinity. The sample powders were isostatically pressed to form a pellet. The green body was sintered at 1200C and the relative density of the sintered specimens were measured by Archimedes mettled. We measured electrochemical performance of LSF by AC impedance spectroscopy. Resistance of LSF shows lower value than that of LSM throughout all temperature region. The anode-supported solid oxide fuel cell showed a performance of 342mW/cm2(0.7V,488mA/cm2) at 750C. The electrochemical characteristics of the single cell were examined by at impedance method.

Comparison of Behaviour of Straight and Curved Mechanically Stabilized Earth Walls from Numerical Analysis Results (수치해석을 통한 보강토옹벽 직선부와 곡선부의 거동 특성)

  • Jung, Hyuk-Sang
    • Journal of the Korean Geosynthetics Society
    • /
    • v.16 no.4
    • /
    • pp.83-92
    • /
    • 2017
  • This paper deals with numerical analysis of behavior of curved mechanically stabilized earth(MSE) walls with geosynthetics reinforcement. Unlike typical concrete retaining walls, MSE wall enables securing stability of higher walls without being constrained by backfill height and is currently and widely used to create spaces for industrial and residential complexes. The design of MSE walls is carried out by checking external stability, similarly to the external checks of conventional retaining wall. In addition, internal stability check is mandatory. Typical stability check based on numerical analysis is done assuming 2-dimensional condition (plane strain condition). However, according to the former studies of 3-dimensional MSE wall, the most weakest part of a curved geosynthetic MSE wall is reported as the convex location, which is also identified from the studies of the laboratory model tests and field monitoring. In order to understand the behaviour of the convex location of the MSE wall, 2-dimensional analysis clearly reveals its limitation. Furthermore, laboratory model tests and field monitoring also have restriction in recognizing their behaviour and failure mechanism. In this study, 3-dimensional numerical analysis was performed to figure out the behaviour of the curved part of the geosynthetic reinforced wall, and the results of the straight-line and curved part in the numerical analysis were compared and analysed. In addition, the behaviour characteristics at each condition were compared by considering the overburden load and relative density of backfill.

Changes of Hysteresis Loop Characteristics of the Tendon Under Tensile Stress (Tendon의 인장응력에 따른 자기이력특성 변화의 측정)

  • Kang, Sunju;Son, Derac;Joh, Changbin;Lee, Jungwoo
    • Journal of the Korean Magnetics Society
    • /
    • v.25 no.4
    • /
    • pp.123-128
    • /
    • 2015
  • The iron is an element having a high yield strength, mechanical hardness, good electrical conductivity, and also it has been used in various fields because of ease machining. In bridges have been used tendon made of a steel wire for large loads and light weight. Tension measurement of tendon employed in PreStressed Concrete (PSC) bridge is very important for the bridge safety check. NDT (Non-Destructive Testing) is essential for the safety check, however, magnetic NDT is difficult to apply due to the non-linear magnetization curve and hysteresis loop in the magnetic properties. In this work, for basic study of magnetic NDT application, we have constructed a B-H loop measuring system for 7-strand tendon of which diameter is 15.5 mm, and which can apply tensile stress up to 2.0 GPa. We have measured hysteresis loops of two kinds of tendons under different tensile stress. Amplitude permeability and maximum magnetic induction near knee show the most sensitive and high linearity depends on tensile stress. Relative amplitude permeability was decreased from 500 to 200 and maximum magnetic flux density changed 0.6 T.

Annual Base Performance Evaluation on Cell Temperature and Power Generation of c-Si Transparent Spandrel BIPV Module depending on the Backside Insulation Level (스팬드럴용 투광형 결정계 BIPV창호의 후면단열 조건에 따른 연간 온도 및 발전성능 분석 연구)

  • Yoon, Jong-Ho;Oh, Myung-Hwan;Kang, Gi-Hwan;Lee, Jae-Bum
    • Journal of the Korean Solar Energy Society
    • /
    • v.32 no.4
    • /
    • pp.24-33
    • /
    • 2012
  • Recently, finishing materials at spandrel area, a part of curtain-wall system, are gradually forced to improve thermal insulation performance in order to enhance the building energy efficiency. Also, Building Integrated Photovoltaics(BIPV) systems have been installed in the exterior side of the spandrel area, which is generally composed of windows. Those BIPVs aim to achieve high building energy efficiency and supply the electricity to building. However, if transparent BIPV module is combined with high insulated spandrel, it would reduce the PV efficiency for two major reasons. First, temperature in the air space, located between window layer and finishing layer of the spandrel area, can significantly increase by solar heat gain, because the space has a few air density relative to other spaces in building. Secondly, PV has a characteristics of decreased Voltage(Voc and Vmp) with the increased temperature on the PV cell. For these reasons, this research analyzed a direct interrelation between PV Cell temperature and electricity generation performance under different insulation conditions in the spandrel area. The different insulation conditions under consideration are 1) high insulated spandrel(HIS) 2) low insulated spandrel(LIS) 3) PV stand alone on the ground(SAG). As a result, in case of 1) HIS, PV temperature was increased and thus electricity generation efficiency was decreased more than other cases. To be specific, each cases' maximum temperature indicated that 1) HIS is 83.8C, 2) LIS is 74.2C, and 3) SAG is 66.3C. Also, each cases yield electricity generation like that 1) HIS is 913.3kWh/kWp, 2) LIS is 942.8kWh/kWp, and 3) SAG is 981.3kWh/kWp. These result showed that it is needed for us to seek to the way how the PV Cell temperature would be decreased.

Improvement Method of Sand Ground Using an Environmental Friendly Bio-grouting Material (친환경 바이오그라우팅을 이용한 모래지반 개량 공법)

  • Kim, Dae-Hyeon;Sagong, Myung;Park, Kyung-Ho
    • Journal of the Korean Society for Railway
    • /
    • v.16 no.6
    • /
    • pp.473-481
    • /
    • 2013
  • The purpose of this research is to evaluate the improvements in the strength and injection range of loose ground after injecting CaCO3(created by microorganism reaction). For this purpose, three cases of single-layer (Sand, SP, SW) specimens were made in a 150mm D × 200mm H space and two cases of multi-layer specimens (SW/SP, SP/SW) were made in a 150mm D × 300mm H space. The specimens were made with a relative density of 30% of soft ground and an injection was given over a time of one day. The uniaxial compression strength was measured with a cone penetrometer and the injection range was observed by checking the bulb formation around the injection nozzle. Also, the compositions of the specimens were assessed through XRD analyses. Based on the test results, a compressive strength of 500kPa and 15cm thick cementation were noted due to the cementation of the soil. This implies that there are significant effects of the pore condition and size on bio-grouting technology.

Yield and Chemical Component of Grain as Affected by Transplanting Dates in the Colored Rice Varieties (이앙시기에 따른 유색미 품종의 수량 및 성분 변화)

  • 이순계;김현호;이재철;신철우;김창영;변종영;이종철
    • Korean Journal of Plant Resources
    • /
    • v.12 no.2
    • /
    • pp.145-151
    • /
    • 1999
  • This study was conducted to know the influence of transplanting dates on yield and chemical component of colored rice varieties at Taejon area in middle part in Korea. The late transplanting led to late heading in which the latest transplanting on June 18 headed on August 9 in Heugiinjubyeo and on August 24 in Heugnambyeo, respectively, which in the safe latest heading date at Taejon area. The highest yield was attained by middle of June transplanting in Heugjinjubyeo, while that for the Heugnambyeo was transplanting from end of May to beginning of June. The relative optical density(ROD) of the pigment measured at 530 nm was higher in Heugjinjubyeo than that of Heugnambyeo. The late transplanting increased the ROD in Heugnambyeo, while later than May 28 decreased the ROD in Heugjinjubyeo. There was a varietal difference in cation contents such as K, Ca, Mg and Fe. The Contents of the former three was not influenced by different transplanting dates, while the Fe content was increased by early transplanting.

  • PDF

The Reactivity and Regiochemical Effect of Nitrosonium Species in the Nitrosation of N-Methyl-N'-Substituted Phenylureas (N-메틸-N'-치환페닐우레아화합물들의 니트로소화 반응에 있어서 니트로소화 화학종의 반응성 및 위치화학적 영향)

  • Jack C. Kim;In-Seop Cho;Soon-Kyu Choi
    • Journal of the Korean Chemical Society
    • /
    • v.35 no.3
    • /
    • pp.240-248
    • /
    • 1991
  • The regioselectivity in the nitrosation of seven N-methyl-N'-substituted phenylureas (CH3NHCONHC6H4G; G = H, p-CH3, m-CH3, m-CH3O, p-F, m-F, m-Br) was examined using NaNO2 and 4 different acids (diluted HCl, HCOOH, CH3COOH, CF3COOH). In all cases, the two regioisomeric products, N-nitroso-N-methyl-N'-substituted phenylureas (A) and N'-nitroso-N-methyl-N'-substituted phenylureas (B) were observed to be formed as major products and product ratios were determined by the integration of their methyl peaks in 1H-NMR. Electron donating substitutent(G) on phenyl of the ureas generally led to increase the ratio of B to A. The data have revealed that the relative sensitivity of the nitrosonium species (HONO, HCOONO, CH3COONO, CF3COONO) toward the change of electron density on nitrogen with phenyl substitutents are 1.00 : 0.93 : 0.78 : > ∼ 0.7.

  • PDF

Theoretical Studies on the Structure and Aromaticity of 1H-Indene and Mono-sila-1H-Indene (1H-Indene과 Mono-sila-1H-Indene의 구조와 방향족성에 대한 이론적 연구)

  • Ghiasi, Reza;Monnajemi, Majid
    • Journal of the Korean Chemical Society
    • /
    • v.50 no.4
    • /
    • pp.281-290
    • /
    • 2006
  • The electronic structure and properties of the 1H-indene and mono-sila-1H-indene series have been investigated using basis set of 6-31G(d, p) and hybrid density functional theory. Basic measures of aromatic character derived from structure, molecular orbitals, a variety of magnetic criteria (magnetic isotropic and anisotropic susceptibilities) are considered. Energetic criteria suggest that In(Si7) enjoy conspicuous stabilization. However, by magnetic susceptibility isotropic this system are among the least aromatic of the family: Within their isomer series, In(Si4) is the most aromatic using this criteria. Natural bond orbital (NBO) analysis method was performed for the investigation of the relative stability and the nature of the 8-9 bonds in 1H-indene and mono-sila-1H-indene compounds. The results explained that how the p character of natural atomic hybrid orbital on X8 and X9 (central bond) is increased by the substitution of the C8 and C9 by Si. Actually, the results suggested that in these compounds, the X8-X9 bond lengths are closely controlled by the p character of these hybrid orbitals and also by the nature of C-Si bonds. The magnitude of the molecular stabilization energy associated to delocalization from X8-X9 and to * X8-X9 bond orbital were also quantitatively determined. Molecular orbital (MO) analysis further reveal that all structure has three delocalized MOs and two delocalized MOs and therefore exhibit the aromaticity.