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Volume 1992 (1992)
- Issue 155 Pages 282-
- Issue 154 Pages 213-
- Issue 153 Pages 149-
- Issue 152 Pages 67-
- Issue 151 Pages 2-
Volume 1992, Issue 152
Displaying 1-10 of 10 articles from this issue
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Shintarou Ishiyama, Motokuni Eto, Tatsuo Oku1992 Volume 1992 Issue 152 Pages 67-73
Published: April 30, 1992
Released on J-STAGE: March 01, 2011
JOURNAL FREE ACCESSEffect of oxidation on fracture toughness and crack extension resistance of HTGR (High Temperature Gas-cooled Reactor) graphites were examined. Oxidation tests were performed at 500°C in air for isotropic fine-grained graphite IG-110 and near-isotropic coarse-grained graphite PGX. Specimens of IG-110 and PGX were oxidized to a maximum off level of 13%. Fracture toughness test was carried out at room temperature in using CT (Compact Tension) specimen recommended by ASTM-E813. Crack onset and crack extension were detected by electrical potential method and following results were derived:
(1) Fracture toughness decreased as oxidation proceeds and the degradation of fracture toughness can be inferred considering density change due to oxidation.
(2) Crack extension resistance decreases as oxidation proceeds.
(3) Fracture of graphite can be stabilized as oxidation proceeds.View full abstractDownload PDF (2159K) -
Kiyoshi Azami, Shunichi Yamamoto, Yuzo Sanada1992 Volume 1992 Issue 152 Pages 74-78
Published: April 30, 1992
Released on J-STAGE: June 28, 2010
JOURNAL FREE ACCESSFour pristine and two oxidized Argonne Premium Coals have been investigated by in-situ high-temperature 13C-NMR. In-situ monitoring for changes of mobility and chemical structure for coals has been successfully accomplished. Characteristic temperatures for coals during the early stage of carbonization were determined from the series of spectra of in-situ high-temperature 13C-NMR. It was found that the temperature of minimum of half-width, Tm, and the temperature interval from softening to minimum of half-width, Tsm, correlate to the coal rank for the three lower rank coals tested. It was suggested that aliphatic carbons in coal have a large role for depolymerization and/or polymerization of coals oxidized during heating.View full abstractDownload PDF (605K) -
Low Stress Type Low Cycle Fatigue of an HTGR GraphiteShintarou Ishiyama, Motokuni Eto1992 Volume 1992 Issue 152 Pages 79-83
Published: April 30, 1992
Released on J-STAGE: June 28, 2010
JOURNAL FREE ACCESSHigh-low type two step fatigue tests were carried out at a stress ratio of-1.0 with a fine-grained isotropic nuclear graphite IG-110, for which the cumulative fatigue damage was evaluated. The following conclusions were derived:
(1) Cumulative fatigue damage was enhanced with decreasing the first cycle ratio and the stress level.
(2) The regeneration of stress history was observed at the first stress ratio of 0.1.
(3) Cumulative fatigue damage for first cycle ratios in excess of 0.3 can be described by the linear cumulative fatigue damage rule, whereas the ratios less than 0.3 result in a cosiderable deviation from the linear rule.View full abstractDownload PDF (490K) -
Masahiro Katsura, Masayuki Hirota, Masanobu Miyake, Kazuo Hamada1992 Volume 1992 Issue 152 Pages 84-90
Published: April 30, 1992
Released on J-STAGE: June 28, 2010
JOURNAL FREE ACCESSA mixture of uranium sesquinitride and carbon was prepared by the reaction of UC or UC2 with N2 in the temperature range from 700 to 1400°C. When the mixture of uranium sesquinitride and carbon is kept at temperatures above 1200°C in the atmosphere of N2 at low pressure, the state where uranium carbonitride (UC1-x, Nx) and carbon are present together in chemical equilibrium will be established. A thermodynamic analysis suggests that, in the equilibrium state, the composition of UC1-xNx is determined by the chemical activity of carbon, ac, which is related to the chemical potential of the carbon, μE c, by the equation, μc=μc°+RT 1n ac. Here μc° refers to graphite, which is usually taken as the standard state of carbon (ac=1). Mixtures of U2N3 and carbon with several degrees of graphitization were heat-treated at 1400°C, and the composition of UC1-xNx in the reaction product was determined. From these experimental results and the thermodynamic analysis, values of the activity of the carbon coexisting with UC1-xNx were estimated.View full abstractDownload PDF (2002K) -
Hitoshi Shinno, Masakazu Fujitsuka, Tatsuhiko Tanabe, Haruki Shiraishi1992 Volume 1992 Issue 152 Pages 91-97
Published: April 30, 1992
Released on J-STAGE: June 28, 2010
JOURNAL FREE ACCESSC-B-Ti composite ceramic materials have some preferable properties including high melting point as the inner wall materials of nuclear fusion devices, but their thermal shock resistances are not well known. In this experiment, those materials were fabricated by sintering carbon, boron and titanium powders, and then characterized by X-ray diffraction, X-ray micro-analysis, scanning electron microscopy and density measurement. Thermal shock tests of these samples were performed using a hollow-cathode type electronbeam apparatus.
Thermal-stress fracture was more infrequent in samples containing higher carbon and lower titanium contents. The investigation of relations between the microstructures and the atomic concentration ratios revealed that samples with high titanium and low carbon concentrations had polycrystals of TiC and TiB2, while those containing high carbon and low titanium consisted of TiC, TiB2 and graphite polycrystals, and exhibited complex microstructures of the ceramics and the graphite. Higher resistance to thermal-stress fracture of samples with high carbon and low titanium contents may be highly related to the constituent graphite for it has high thermal-shock resistance and complex microstructures with high crack-propagation resistances.View full abstractDownload PDF (1126K) -
Tadashi Maruyama, Yasushi Nishimura1992 Volume 1992 Issue 152 Pages 98-105
Published: April 30, 1992
Released on J-STAGE: June 28, 2010
JOURNAL FREE ACCESSInvestigations were made of effect of test environments on bend strength and fracture toughness of fine-grained isotropic graphites. Four-point bend tests were carried out in various atmospheres of air, helium and vacuum. When we measured the bend strength of fully outgassed specimens in a vacuum, we obtained values higher than those measured in air by up to 45%. When measurements were made in helium atmosphere containing 1 to 3 ppm of water vapor, the bend strength was higher by 20 to 30% than those measued in air. When the water content in helium increased to about 20 ppm, the strength decreased to the same value with that measured in air. The bend strength of graphite specimens which were fully outgassed at 1200°C decreased with increasing temperature up to 900°C, whereas that of specimens which were not subjected to the outgas treatments showed a positive temperature dependence. Furtheremore, the fracture toughness of fully out gassed specimens measured in a vacuum was about 20% higher than that measured in air. These experimental results were interpreted in terms of effect of adsorbed gases on strength of graphite materials.View full abstractDownload PDF (1006K) -
Takamasa Kawakubo, Yoshihisa Suda, Hiroko Kaneko, Akira Negishi, Masah ...1992 Volume 1992 Issue 152 Pages 106-114
Published: April 30, 1992
Released on J-STAGE: June 28, 2010
JOURNAL FREE ACCESSTwo types of new carbon ultramicroelectrodes for the use of electrochemical detector were developed by using graphite/carbon composite PFC (Plastic Formed Carbon), and their electrochemical behaviors were evaluated by cyclic voltammetry. One of the carbon samples used had a fiber shape with 30μm in diameter. The other had a rod shape with 300μm in diameter, which was formed to be a conical shape at an end of the rod by electrochemical oxidizing in KOH solution as an anode. The diameter of the tip of the conical electrode was 10μm. These samples were made into electrodes by silicon oil impregnation and by insulating on the surface. Both microelectrodes were found to have excellent properties in electrochemical behavior, as compared with a Pt electrode of the same type. In electrochemical behavior, a relationship between the microstructure of carbon electrode and heterogeneous electron transfer activity was found. Crystal edge plane of graphite was necessary for fast electron transfer, and electrochemical activation correlated with crystal edge plane density. By silicon oil impregnation reduced the blank current and enhanced the S/N ratio. The peakpotentials of the C-V curves of Fe (CN) 64-/3-were in good agreement between both electrodes. Reproducibility of the electrode reactions of the redox ions were good. The blank current was proportional to the potential sweep rates, υ, in the range between 0.1 and 2.0V (vs SCE). Relation between υ1/2 and the peak current were linear.View full abstractDownload PDF (1720K) -
Kazuro Kawamura1992 Volume 1992 Issue 152 Pages 115-119
Published: April 30, 1992
Released on J-STAGE: June 28, 2010
JOURNAL FREE ACCESSExplosive shock compression by RDX was given to the natural graphite powder packed in a mild steel bottle in a low density. The appearance of the shock-compressed graphite sample depended on the position in the bottle. At the top and middle of the bottle, the sample became pieces of mass but powder at the bottom. The massive sample looked to form a polycrystaline graphite. The powdered one contained several types of small crystallines which is totally different from the original graphite powder. The morphological feature seen in the bottom sample was almost the same as that of the carbon black in the previous report. These morphological features are brought by the high temperature induced from an adiabatic compression through explosion.View full abstractDownload PDF (890K) -
Toshiro Ando, Hideyuki Takatsu, Masahiro Yamamoto, Masatsugu Shimizu, ...1992 Volume 1992 Issue 152 Pages 120-127
Published: April 30, 1992
Released on J-STAGE: June 28, 2010
JOURNAL FREE ACCESSPhysical and mechanical properties of newly developed carbon/carbon (C/C) com-posites and isotropic graphites have been measured for application to the first wall and divertor plate of JAERI Tokamak-60 Upgrade (JT-60U). The divertor plate of JT-60U is subjected to high heat flux of up to 20 MW/m2 during normal operations and to large thermal shock during disruptions. The surface temperature of the divertor plate should be lowered enough to prevent unacceptable carbon influx due to sublimation. The evaluation of these plasma facing component materials has been made mainly from thermal conductivity, thermal shock resistance and mechanical strength points of view. Outgassing properties and erosion characteristics against high heat flux are also considered in selecting the materials. It is found from these tests that a few kinds of 2-D felt type C/C composites have large thermal shock resistances and superior thermal conductivity in the range of 300-400 W·m-1·K-1 at room temperature which satisfies the JT-60U design requirement of 300 W·m-1·K-1. In addition, the investigated isotropic graphites also exhibit; improved thermal conductivity in the range of 150-180 W·m-1·K-1 at room temperature. Con-sequently, 2-D felt type C/C composites with superior thermal conductivity have been selected for the divertor plate. As for the first wall, two grades of isotropic graphites with relatively high thermal conductivity have also been selected as well as one which was used in the JT-60 operation.View full abstractDownload PDF (970K) -
[in Japanese]1992 Volume 1992 Issue 152 Pages 129-134
Published: April 30, 1992
Released on J-STAGE: June 28, 2010
JOURNAL FREE ACCESSDownload PDF (1099K)
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