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Kim, Daejong,Jeong, Sang Min,Yoon, Soon Gil,Woo, Chang Hyun,Kim, Joung Il,Lee, Hyun-Geun,Park, Ji Yeon,Kim, Weon-Ju The Korean Ceramic Society 2016 한국세라믹학회지 Vol.53 No.6
Tantalum carbide, which is one of the ultra-high temperature ceramics, was deposited on graphite by low pressure chemical vapor deposition from a $TaCl_5-C_3H_6-Ar-H_2$ mixture. To maintain a constant $TaCl_5/C_3H_6$ ratio during the deposition process, $TaCl_5$ powders were continuously fed into the sublimation chamber using a screw-driven feeder. Sublimation behavior of $TaCl_5$ powder was measured by thermogravimetric analysis. TaC coatings have various phases such as $Ta+{\alpha}-Ta_2C$, ${\alpha}-Ta_2C+TaC_{1-x}$, and $TaC_{1-x}$ depending on the powder feeding methods, the $C_3H_6/TaCl_5$ ratio, and the deposition temperatures. Near-stoichiometric TaC was obtained by optimizing the deposition parameters. Phase compositions were analyzed by XRD, XPS, and Raman analysis.
김대종(Daejong Kim),오승진(Seung Jin Oh),장창희(Changheui Jang),김인섭(In Sup Kim),김응선(Eeung Sun Kim),지세환(Se Hwan Chi) 대한기계학회 2005 대한기계학회 춘추학술대회 Vol.2005 No.8
Fracture toughness of the fine grain isotropic graphite IG-11 was evaluated. Fracture toughness value, K<SUB>IC</SUB> was obtained by 3-point bending test using SENB specimen. To determine the optimum loading rate, the effects of loading rate on fracture toughness were investigated. The crack initiation point was determined by DCPD method. Weibull modulus of IG-11 graphite was determined by two parameter Weibull equation using test results of 30 SENE specimens. Crack lengths estimated by DCPD method were lower than real crack length because of leakage of current through contacting and non-broken regions within the specimens. Fraction of those area on the cracked surfaces can be inferred from the difference between the crack lengths measured by DCPD and dye penetration method. Contacting and non-broken regions which are mainly induced by shear cracking and crack bridging increase fracture toughness of graphite.
Microstructure evolution of a ZrC coating layer in TRISO particles during high-temperature annealing
Kim, Daejong,Chun, Young Bum,Ko, Myeong Jin,Lee, Hyeon-Geun,Cho, Moon-Sung,Park, Ji Yeon,Kim, Weon-Ju ELSEVIER 2016 JOURNAL OF NUCLEAR MATERIALS Vol.479 No.-
<P><B>Abstract</B></P> <P>The influence of high-temperature annealing on the microstructure of zirconium carbide (ZrC) was investigated in relation to its application as a coating layer of a nuclear fuel in a very high temperature gas cooled reactor. ZrC was deposited as a constituent coating layer of TRISO coated particles by a fluidized bed chemical vapor deposition method using a ZrCl<SUB>4</SUB>-CH<SUB>4</SUB>-Ar-H<SUB>2</SUB> system. The grain growth of ZrC during high-temperature annealing was strongly influenced by the co-deposition of free carbon. Sub-stoichiometric ZrC coatings have experienced a significant grain growth during high-temperature annealing at 1800 °C and 1900 °C for 1 h. On the other hand, a dual phase of stoichiometric ZrC and free carbon experienced little grain growth. It was revealed that the free carbon of the as-deposited ZrC was primarily distributed within the ZrC grains but was redistributed to the grain boundaries after annealing. Consequently, carbon at the grain boundary retarded the grain growth of ZrC. Electron backscatter diffraction (EBSD) results showed that as-deposited ZrC had (001) a preferred orientation that kept its favored direction after significant grain growth during annealing. The hardness slightly decreased as the grain growth progressed.</P>
Kim, Daejong,Lee, Hyun-Geun,Park, Ji Yeon,Kim, Weon-Ju Elsevier 2015 JOURNAL OF NUCLEAR MATERIALS Vol.458 No.-
<P><B>Abstract</B></P> <P>The SiC ceramics are under investigation for the fuel cladding in the light water nuclear reactors because of its excellent high temperature strength and corrosion resistance against hot steam under the severe accident conditions. In this study, the SiC triplex tubes consisting of a SiC inner layer, a SiC/PyC/SiC intermediate layer, and a SiC outer layer were fabricated by the chemical vapor processes. The hoop strength and fracture behaviors of the SiC triplex tube were investigated. The SiC triplex tubes fabricated at the high ratio of H<SUB>2</SUB>/MTS had a quite high average strength with a relatively small standard deviation. The hoop strength of the composite tubes tends to increase with the volume fraction of the reinforced fibers. The highest fiber volume fraction was obtained using Tyranno SA3-0.8k with the dense winding patterns such as bamboo-like mosaic pattern, which resulted in the high hoop strength compared to other fibers of Tyranno SA3-1.6k and Hi-Nicalon Type S. Hoop strength also increased slightly as the winding angle increased from 45° to 65°. Fracture behaviors of the SiC triplex tube were investigated via the observation of microstructure of the failed samples.</P>
Kim, Weon-Ju,Kim, Daejong,Jung, Choong Hwan,Park, Ji Yeon,Snead, Lance L. The Korean Ceramic Society 2013 한국세라믹학회지 Vol.50 No.6
Continuous fiber-reinforced ceramic matrix composites (CFCCs) have a complex distribution of porosity, consisting of interfiber micro pores and interbundle/interply macro pores. Owing to the complex geometry of the pores and fiber architecture, it is difficult to obtain representative microstructural features throughout the specimen volume with conventional, destructive ceramographic approaches. In this study, we introduce X-ray computed microtomography (X-ray ${\mu}CT$) to nondestructively analyze the microstructures of disk shaped and tubular $SiC_f$/SiC composites fabricated by the chemical vapor infiltration (CVI) method. The disk specimen made by stacking plain-woven SiC fabrics exhibited periodic, large fluctuation of porosity in the stacking direction but much less variation of porosity perpendicular to the fabric planes. The X-ray ${\mu}CT$ evaluation of the microstructure was also effectively utilized to improve the fabrication process of the triple-layered tubular SiC composite.
Deletion of N-type Ca(2+) channel Ca(v)2.2 results in hyperaggressive behaviors in mice.
Kim, Chanki,Jeon, Daejong,Kim, Young-Hoon,Lee, C Justin,Kim, Hyun,Shin, Hee-Sup American Society for Biochemistry and Molecular Bi 2009 The Journal of biological chemistry Vol.284 No.5
<P>Voltage-dependent N-type Ca(2+) channels play important roles in the regulation of diverse neuronal functions in the brain, but little is known about its role in social aggressive behaviors. Mice lacking the alpha1B subunit (Ca(v)2.2) of N-type Ca(2+) channels showed markedly enhanced aggressive behaviors to an intruder mouse in the resident-intruder test. The dorsal raphe nucleus (DRN), which contains serotonin neurons, is known to be involved in aggression in animals. We thus examined the DRN neurons in the Ca(v)2.2-deficient (Ca(v)2.2(-/-)) mice. Microinjection of omega-conotoxin GVIA, an N-type Ca(2+) channel-specific blocker, into the DRN of wild type mice resulted in escalated aggression, mimicking the phenotypes of Ca(v)2.2(-/-). Electrophysiological analysis showed increased firing activity of serotonin neurons with a reduced inhibitory neurotransmission in the Ca(v)2.2(-/-) DRN. Ca(v)2.2(-/-) mice showed an elevated level of arginine vasopressin, an aggression-related hormone, in the cerebrospinal fluid. In addition, Ca(v)2.2(-/-) mice showed an increase of serotonin in the hypothalamus. These results suggest that N-type Ca(2+) channels at the DRN have a key role in the control of aggression.</P>