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Busan, South Korea

Nam K.W.,Pukyong National University | Kim J.S.,NGE Technology Inc.
Materials Science and Engineering A

Crack-healing behavior of SiC ceramics with additive SiO2 has been studied as functions of heat-treatment temperature and crack size. Results showed that heat treatment in air could significantly increase the strength. The heat-treatment temperature has a profound influence on the extent of crack healing and the degree of strength recovery. The optimum heat-treatment temperature had 1h at an atmospheric level of 1373K. After heat treatment at the optimum temperature in air, the crack morphology almost entirely disappeared and the strength recovered to the value of the smooth specimens at room temperature for the investigated crack sizes up to 450μm. The long crack up to 1000μm with width 1.4μm could completely heal the surface crack. © 2010 Elsevier B.V. Source

Yang S.-B.,University of Ulsan | Yu M.-S.,University of Ulsan | Kim J.-S.,NGE Technology Inc. | Jo W.-K.,Kyungpook National University
Cuihua Xuebao/Chinese Journal of Catalysis

The applicability of ultraviolet-light emitting diodes (LEDs) as a light source for photocatalysis using granular activated charcoal (GAC) impregnated with transition metal-enhanced photocatalysts for the control of volatile organic compounds (VOCs) was investigated. Two target compounds (toluene and methyl mercaptan) were selected to evaluate the removal activities of the TiO 2/GAC composites. The photocatalysts were prepared by a sol-gel method. Methyl trimethoxy silane was added as a precursor sol solution to bind the photocatalyst with the GAC. Metal (Zn 2+, Fe 3+, Ag +, and Cu 2+) enhanced TiO 2/GAC composites were prepared and tested for their photocatalytic activities under 400 nm LED irradiation. The specific surface area (SSA) and the surface chemical composition of the prepared composites were investigated. The SSAs of all the impregnated composites were similar to those of pure GAC. Both field emission-scanning electron microscopy and energy dispersive spectroscopic analysis confirmed that titanium and the impregnated metals were deposited on the surface of the adsorbent. The breakthrough time for GAC toward toluene or methyl mercaptan gas increased upon photocatalytic impregnation and LED illumination. Using different binders affected the breakthrough time of the TiO 2/GAC composite and the addition of zinc oxide to TiO 2 increased the VOC removal capacity of the GAC composite. Source

Nam K.W.,Pukyong National University | Kim J.S.,NGE Technology Inc. | Park S.W.,Pukyong National University
Materials Science and Engineering A

This study was carried out on the crack-healing behavior of two types of SiC ceramics based on a SiO2 additive, and mainly on the high temperature strength of crack-healed specimens. The mean particle sizes of the SiC, Al2O3 and Y2O3 powders used in this study were 0.27μm, 0.1μm and 33nm, respectively. The SiO2 employed was a nano-colloidal (SiO2 12% solid solution). The SiC ceramics were prepared using a mixture of 85 or 90wt.%. SiC powder and sintering additives (Al2O3:Y2O3=6:4 and SiO2=0 or 3wt.%). The mixtures were subsequently hot-pressed in N2 gas for 1h via hot-pressing conducted under 35MPa at 2053K. In both specimens, the optimized crack-healing condition was 1373K for 1h in air. The crack-healing material of the crack part was the glassy phase of SiO2 by oxidation reaction of SiC and O2. The limiting temperatures for bending strength of smooth and crack-healed specimens of two types of specimens of SAY and SAYS were 1373K and 1273K, respectively. That is, the crack-healed specimens had good high temperature strength in spite of the fact that the crack-healing material is the glassy phase of SiO2. © 2010 Elsevier B.V. Source

Nam K.W.,Pukyong National University | Chung Y.K.,Pukyong National University | Hwang S.H.,Pukyong National University | Kim J.S.,NGE Technology Inc. | Moon C.K.,Pukyong National University
Transactions of the Korean Society of Mechanical Engineers, A

We analyzed the wear characterization of Si3N4 ceramics according to the amount of added SiO2 nanocolloid. The test specimen was prepared by hot-press sintering at 35 MPa and 2123 K in an N 2 gas atmosphere for 1 h. A wear test was performed with a block-on-ring tester, and the test conditions were as follows: (1) the ring with a diameter of 35 mm had a rotational speed of 50 rpm; (2) the load was 9.8 N; and (3) the temperature was 25°C. The test results show that Si 3N4 ceramics have a friction coefficient of about 1.0 and a wear loss of about 0.02 mm. Of the specimens used this study, the test specimen with 1.3 wt% of added SiO2 nanocolloid has the best wear resistance because it has the lowest friction coefficient and the smallest wear loss. This specimen also has the highest Vickers hardness and bending strength. In this study, the friction coefficient is inversely proportional to the hardness and bending strength. © 2011 The Korean Society of Mechanical Engineers. Source

Nam K.W.,Pukyong National University | Kim J.S.,NGE Technology Inc. | Park S.W.,Pukyong National University
International Journal of Modern Physics B

Silicon carbide (SiC) exhibits good strength at high temperatures and resistance to radioactivity. However, it has poor fracture toughness. The ability to heal cracks represents a very desirable means of overcoming this weakness. This study focuses on the crack-healing behavior and bending strength of SiC ceramics to which sintering additives have been added. Optimized crack-healing condition was found to be 1hr at an atmospheric level of 1100 °C. The maximum crack size that can be healed at the optimized condition was a semi-elliptical surface crack of 450 m in diameter. Si oxide was revealed to be the principle material involved in crack-healing. © 2010 World Scientific Publishing Company. Source

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