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Tenan, South Korea

Lee D.J.,KAIST | Jang J.J.,KAIST | Park H.S.,KAIST | Kim Y.C.,Agency for Defense Development | And 3 more authors.
Ceramics International | Year: 2012

Biomorphic SiC composites were fabricated from wood, including high-density compressed cedar, high-density fiberboard (HDF) and low-density paulownia followed by the fabrication of a preform and liquid silicon infiltration (LSI) process. The degree of molten silicon infiltration was strongly dependent on the cell wall thickness and pore size of the carbon preform. The mechanical properties of the biomorphic SiC composites were characterized by compressive tests at room temperature, 1000 °C and 1200 °C, and the relationship between the mechanical properties and the microstructural characteristics was analyzed. The compressive strength of the biomorphic composites was found to be strongly dependent on their bulk density and decreased as the test temperature increased to 1200 °C. Strength reduction in the biomorphic SiC composites occurred due to the deformation of the remaining Si at elevated temperatures under ambient atmospheric conditions. © 2011 Elsevier Ltd and Techna Group S.r.l. Source

Lee D.,KAIST | Kim Y.C.,Agency for Defense Development | Adeel Umer M.,KAIST | Lim K.H.,DaeYang Co. | And 2 more authors.
Ceramics International | Year: 2013

Biomorphic SiC composites were fabricated by infiltration of liquid Si into a preform fabricated from medium-density fiberboard (MDF). The phase compositions, microstructures, oxidation behaviors, and ablation properties of the composites were investigated. The composites were oxidized at elevated temperatures (up to 1450° C) in air to study their oxidation behavior. Pores and cracks initially formed from the oxidation of residual carbon, followed by melting of residual Si. The ablation resistance of a composite was gauged using an oxy-acetylene torch. The formation of a SiO2 layer by the oxy-acetylene flame improved the ablation resistance because molten SiO 2 spread over the ablated surface and partially sealed the pores, thus acting as an effective barrier against the inward diffusion of oxygen. © 2013 Elsevier Ltd and Techna Group S.r.l. Source

Ham Y.-S.,DaeYang Co. | Kim J.-T.,e Design Center | Kwak S.-Y.,e Design Center | Choi J.-K.,e Design Center | Yoon W.-Y.,Korea University
China Foundry | Year: 2010

Critical cooling rate to avoid carbide precipitation during quenching of austenitic manganese steel was investigated by means of optical microscopy, image analyzer and numerical analysis. An efficient heat treatment analysis program including temperature-dependent material properties was developed for the prediction of cooling rate and probability of carbide precipitation during quenching by finite difference method. Time-dependent heat transfer coefficient was adopted to achieve more precise results. Area ratio of carbide precipitation was measured by image analyzer to determine the critical point of carbide precipitation, Temperature-dependent critical cooling rate at that point was calculated by the developed numerical program. Finally, the probability of carbide precipitation on the whole area of specimen can be predicted by the proposed numerical program and the numerical result of a specimen was compared with the experimental result. Source

Lim Y.S.,Pukyong National University | Lim Y.S.,DaeYang Co. | Park K.-H.,Korea Institute of Ceramic Engineering And Technology | Tak J.Y.,Korea Institute of Ceramic Engineering And Technology | And 7 more authors.
Journal of Applied Physics | Year: 2016

Among many kinds of thermoelectric materials, CoSb3 has received exceptional attention for automotive waste heat recovery. Its cage structure provides an ideal framework for the realization of phonon-glass electron-crystal strategy, and there have been numerous reports on the enhanced thermoelectric performance through the independent control of the thermal and electrical conductivity by introducing fillers into its cage sites. Herein, we report colligative thermoelectric transport properties in n-type CoSb3 from the viewpoint of "guest electrons in a host lattice." Both the Seebeck coefficient and the charge transport properties are fundamentally determined by the concentration of the guest electrons, which are mostly donated by the fillers, in the conduction band of the host CoSb3. Comparing this observation to our previous results, colligative relations for both the Seebeck coefficient and the mobility were deduced as functions of the carrier concentration, and thermoelectric transport constants were defined to predict the power factor in filled CoSb3. This discovery not only increases the degree of freedom for choosing a filler but also provides the predictability of power factor in designing and engineering the n-type filled CoSb3 materials. © 2016 AIP Publishing LLC. Source

Kwon H.-J.,Korea Research Institute of Standards and Science | Choi W.-C.,DaeYang Co.
Microsystem Technologies | Year: 2010

This paper describes the design and fabrication of a flexible three-axial tactile sensor array using advanced polyimide micromachining technologies. The tactile sensor array is comprised of sixteen micro force sensors and it measures 13 mm × 18 mm. Each micro force sensor has a square membrane and four strain gauges, and its force capacity is 0.6 N in the three-axial directions. The optimal positions of the strain gauges are determined by the strain distribution obtained form finite element analysis (FEA). The normal and shear forces are detected by combining responses from four thin-film metal strain gauges embedded in a polyimide membrane. In order to acquire force signals from individual micro force sensors, we fabricated a PCB based on a multiplexer, operational amplifier and microprocessor with CAN network function. The sensor array is tested from the evaluation system with a three-component load cell. The developed sensor array can be applied in robots' fingertips, as well as to other electronic applications with three-axial force measurement and flexibility keyword requirements. © 2010 Springer-Verlag. Source

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