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Content available remote Effective compressive strengths of corner and exterior concrete columns intersected by slabs with different compressive strengths
100%
Choi S. H. , Lee D. H. , Hwang J. H. , Oh J. Y. , Kim K. S. , Kim S. H.
Archives of Civil and Mechanical Engineering
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2018
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tom Vol. 18, no. 3
731--741
EN
In modern high-rise reinforced concrete buildings, high strength concrete (HSC) has been typically used for column members, while normal strength concrete (NSC) has been generally used for floor slabs. This study proposed a new analytic approach that can reasonably estimate the effective compressive strengths of corner and exterior column members intersected by lower strength concrete slabs. The proposed model was theoretically derived based on strain distributions and constraint conditions at an interface between column and slab members. In addition, the compressive strength test results of isolated, exterior, and corner columns intersected by lower strength concrete slabs reported in the existing literature were compared to the effective compressive strengths estimated by the proposed model. The proposed model provided good accuracy on the effective compressive strengths of the column members intersected by slabs cast with lower concrete compressive strengths. It was also shown that the proposed model successfully reflects the effects of the aspect ratio between the slab thickness and the column width on the effective compressive strengths of the test specimens and their failure modes that changed significantly according to the column–slab compressive strength ratio.
2
Content available remote A study of the gas specificity of porous silicon sensors for organic vapours
100%
Choi S. H. , Cheng H. , Park S. H. , Kim H. J. , Kim Y. Y. , Lee K. W.
Materials Science Poland
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2009
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tom Vol. 27, No. 2
603--610
EN
A porous silicon sensor was investigated as a means to determine the response specificity for organic vapours. Porous silicon layers were fabricated by electrochemical anodization of p-type crystalline silicon in an HF ethanol solution under various conditions. The porous silicon sensors were placed in a gas chamber with various organic vapours, and the changes in electrical resistance under constant voltage of each sensor were used as detection signals. The sensors recorded various changes in resistivity for various organic vapours.
3
Content available Carbon Co-Deposition During Gas Reduction of Water-Atomized Fe-Cr-Mo Powder
100%
Ali B. , Choi S. H. , Seo S. J. , Maeng D. Y. , Lee C. G. , Kim T. S. , Park K. T.
Archives of Metallurgy and Materials
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2017
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tom Vol. 62, iss. 2B
1119--1124
EN
The water atomization of iron powder with a composition of Fe-3Cr-0.5Mo (wt.%) at 1600°C and 150 bar creates an oxide layer, which in this study was reduced using a mixture of methane (CH4) and argon (Ar) gas. The lowest oxygen content was achieved with a 100 cc/min flow rate of CH4, but this also resulted in a co-deposition of carbon due to the cracking of CH4. This carbon can be used directly to create high-quality, sinter hardenable steel, thereby eliminating the need for an additional mixing step prior to sintering. An exponential relationship was found to exist between the CH4 gas flow rate and carbon content of the powder, meaning that its composition can be easily controlled to suit a variety of different applications.
4
Content available Fabrication of a Spherical Titanium Powder by Combined Combustion Synthesis and DC Plasma Treatment
84%
Choi S. H. , Ali B. , Hyun S. K. , Sim J. J. , Choi W. J. , Joo W. , Lim J. H. , Lee Y. J. , Kim T. S. , Park K. T.
Archives of Metallurgy and Materials
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2017
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tom Vol. 62, iss. 2B
1057--1062
EN
Combustion synthesis is capable of producing many types of refractory and ceramic materials, as well as metals, with a relatively lower cost and shorter time frame than other solid state synthetic techniques. TiO2 with Mg as reductant were dry mixed and hand compacted into a 60 mm diameter mold and then combusted under an Ar atmosphere. Depending on the reaction parameters (Mg concentration 2 ≤ α ≤ 4), the thermocouples registered temperatures between 1160°C and 1710°C . 3 mol of Mg gave the optimum results with combustion temperature (Tc) and combustion velocity (Uc) values of 1372°C and 0.26 cm/s respectively. Furthermore, this ratio also had the lowest oxygen concentration in this study (0.8 wt%). After combustion, DC plasma treatment was carried out to spheroidize the Ti powder for use in 3D printing. The characterization of the final product was performed using X-ray diffraction, scanning electron microscopy, energy dispersive spectroscopy, and N/O analysis.
5
Content available Reaction Kinetics and Morphological Study of TiNb2O7 Synthesized by Solid-State Reaction
67%
Choi S. H. , Kim T. S. , Ali B. , Choi K. S. , Hyun S. K. , Sim J. J. , Choi W. J. , Joo W. , Lim J. H. , Lee T. H. , Park K. T.
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6
Content available Reaction Kinetics and Morphological Study of TiNb2O7 Synthesized by Solid-State Reaction
67%
Choi S. H. , Ali B. , Choi K. S. , Hyun S. K. , Sim J. J. , Choi W. J. , Joo W. , Lim J. H. , Lee T. H. , Kim T. S. , Park K. T.
Archives of Metallurgy and Materials
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2017
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tom Vol. 62, iss. 2B
1051--1056
EN
Although TiNb2O7 is regarded as a material with high application potential in lithium-ion batteries (LIBs) and solid-oxide fuel cells (SOFCs), it has been difficult to find suitable cost-effective conditions for synthesizing it on a commercial scale. In this study, TiNb2O7 compounds were synthesized by a solid state synthesis process. For stoichiometrically precise synthesis of the TiNb2O7 phase, the starting materials, TiO2 and Nb2O5 were taken in a 1:1 molar ratio. Activation energy and reaction kinetics of the system were investigated at various synthesis temperatures (800,1000,1200, and 1400°C) and for various holding durations (1,5,10, and 20 h). Furthermore, change in the product morphology and particle size distribution were also evaluated as a function of synthesis temperature and duration. Additionally, quantitative phase analysis was conducted using the Rietveld refinement method. It was found that increases in the synthesis temperature and holding time lead to increase in the mean particle size from 1 to 4.5 μm. The reaction rate constant for the synthesis reaction was also calculated.
7
Content available Carbon Co-Deposition During Gas Reduction of Water-Atomized Fe-Cr-Mo Powder
67%
Ali B. , Kim T. S. , Choi S. H. , Seo S. J. , Maeng D. Y. , Lee C. G. , Park K. T.
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