• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.11 no.12
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• pp.1099-1107
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• 1998

In this study, the microstructure and electric conductivity of 5mol% $Gd_2O_3$-5mol% $Y_2O_3-ZrO_2$ system(5G5YZ) with a variation of sintering time at $1600^{\circ}C$ were investigated. By the result of TEM analysis of 5G5YZ sintered for 12h, a microcrack was observed near grain boundary. The change of the sintering time did not affect the lattice conductivity, but the grain boundary contribution was varied with the sintering time. The grain boundary conductivity of the sample sintered for 1h showed the highest value. Furthermore, the activation energy of the total conductivity was independent upon the sintering time and showed approximately 1.01eV. The highest conductivity measured at $1000^{\circ}C$ was 0.0197S/cm with the sample sintered for 1h. Comparing to 0h’s, the thickness ration of grain boundary as a function of sintering time were 0.88, 1.11 and 1.29 for 1h, 5h and 12h, respectively. In case of the sample sintered for 1h, the thickness of the grain boundary showed the lowest value. The increase of the sintering time over 1h made the decrease of the electric conductivity as well as the increase of the grain growth and the thickness of the grain boundary. As a result, it seemed that the proper sintering time for 5G5YZ composition was 1h.

• 한국신재생에너지학회:학술대회논문집
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• 2011.11a
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• pp.47.1-47.1
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• 2011

We report on a direct measurement of two-dimensional chemical and electrical distribution on the surface of photovoltaic Cu(In,Ga)$Se_2$ thin-films using a nano-scale spectroscopic and electrical characterization, respectively. The Raman measurement reveals non-uniformed surface phonon vibration which comes from different compositional distribution and defects in the nature of polycrystalline thin-films. On the other hand, potential analysis by scanning Kelvin probe force microscopy shows a higher surface potential or a small work function on grain boundaries of the thin-films than on the grain surfaces. This demonstrates the grain boundary is positively charged and local built-in potential exist on grain boundary, which improve electron-hole separation on grain boundary. Local electrical transport measurements with scanning probe microscopy on the thin-films indicates that as external bias is increases, local current is started to flow from grain boundary and saturated over 0.3 V external bias. This accounts for carrier behavior in the vicinity of grain boundary with regard to defect states. We suggest that electron-hole separation at the grain boundary as well as chemical and electrical distribution of polycrystalline Cu(In,Ga)$Se_2$ thin-films.

• Nuclear Engineering and Technology
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• v.26 no.3
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• pp.374-380
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• 1994

A method to simulate the extent of interlinkage of grain boundary gas bubbles to the free surfaces of fuel pellet was developed. With the shape of UO$_2$gain treated as tetrakaidecahedron (TKD)), the interlinked fraction of fission gas bubbles to free surfaces at grain comers was calculated as a function of the radius of grain corner bubbles by the Monte Carlo technique. In spite of two dimensional analysis, the present method shooed reasonable agreement between predicted and measured fuel swelling at the moment that complete bubble interlinkage was achieved. However, for more realistic simulation of interlinkage, grain comer bubbles should be treated three dimensionally.

• Nuclear Engineering and Technology
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• v.53 no.5
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• pp.1587-1592
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• 2021

The effects of the symmetrical tilt Σ5 (310) <001> grain boundary (GB) on the evolution of radiation-induced point defects in pure δ-plutonium (Pu) were studied by Molecular dynamics (MD) simulations. The evolution of radiation-induced point defects was obtained when primary knock-on atom (PKA) was respectively set as -15 Å and 15 Å far from the GB and the number of residual defects was obtained as the distance from PKA to GB was changed. According to the results, compared with vacancies, interstitial atoms were more easily absorbed by GB. In addition, the formation energy of point defects was also calculated. The results showed that there was almost no difference for the formation energy of vacancies in the all matrix. However, the formation energy of interstitial atoms close to the GB was lower than that in the other bulk regions.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09a
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• pp.348-349
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• 2006

The plastic deformation behavior of cemented carbides is related to the WC grain boundary strength. Ab initio calculations predict that Co and Mn segregate to WC/WC grain boundaries. To experimentally study the effect of Mn, a WC-Co-Mn material was manufactured and compared to a WC-Co material. The microstructure was studied using scanning electron microscopy (SEM), including electron backscatter diffraction (EBSD). Special attention was paid to the WC grain size and the frequency of special low-energy grain boundaries. Mn was found to have negligible effect on both the WC grain growth and the fraction of $\sum2$ WC/WC boundaries in the as-sintered material.

• Korean Journal of Materials Research
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• v.10 no.9
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• pp.612-618
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• 2000

The WC/WC grain boundary structure and intergranular segregation in WC-Co and WC-VC-Co cemented carbides were investigated by high-resolution transmission electron microscopy and energy dispersive X-ray spectroscopy in order to elucidate whether contiguous boundaries were present or not at the atomic level. Some grain boundaries were separated by liquid phase, while others were contiguous at the atomic level. Cobalt was found to be segregated to WC/WC grain boundaries in WC-Co. Cobalt and vanadium were co-segregated to grain boundaries in WC-VC-Co. The segregation width in both materials was about 6 nm. These results suggest that the vanadium present in contiguous boundaries acts as an effective barrier to the migration of boundaries during sintering and annealing. This could explain the grain growth inhibiting mechanism of VC added to WC-Co.

• Proceedings of the Korean Radioactive Waste Society Conference
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• 2004.02a
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• pp.238-244
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• 2004

The relationship between the leaching and gap inventory of spent fuel has been studied. When a specimen of J44H08 spent PWR fuel with 38 GWD/MTU has been leached in the synthetic granitic groundwater in Ar atmosphere, the released fraction of cesium was increased rapidly up to 0.7% at around 500 days and stayed below 0.8% until 3 years. This 0.7% of cesium might be released from the gap in this fuel. The measurement of gap inventory with C15I08 spent PWR fuel, having 35 GWD/MTU and 0.22% of fission gas release, was also determined near 0.6% for the cesium, which is a similar fraction of cesium released from the leaching experiment with J44H08 fuel. Its gap inventories of strontium and iodine were about 0.03 and less than 0.2% respectively. Respective fractions of cesium and strontium in grain boundary of C15I08 were 0.78, 0.09%.

• Nuclear Engineering and Technology
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• v.54 no.8
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• pp.2771-2782
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• 2022

When assessing the radiological consequences of postulated accident scenarios, it is of primary interest to determine the amount of radioactive fission gas accumulated in the fuel rod free volume. The state-of-the-art semi-empirical approach (ANS 5.4-2010) is reviewed and compared with a mechanistic approach to evaluate the release of radioactive fission gases. At the intra-granular level, the diffusion-decay equation is handled by a spectral diffusion algorithm. At the inter-granular level, a mechanistic description of the grain boundary is considered: bubble growth and coalescence are treated as interrelated phenomena, resulting in the grain-boundary venting as the onset for the release from the fuel pellets. The outcome is a kinetic description of the release of radioactive fission gases, of interest when assessing normal and off-normal conditions. We implement the model in SCIANTIX and reproduce the release of short-lived fission gases, during the CONTACT 1 experiments. The results show a satisfactory agreement with the measurement and with the state-of-the-art methodology, demonstrating the model soundness. A second work will follow, providing integral fuel rod analysis by coupling the code SCIANTIX with the thermo-mechanical code TRANSURANUS.

• Korean Journal of Materials Research
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• v.17 no.7
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• pp.366-370
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• 2007

Silicon nitride ($Si_3N_4$) ceramics have been considered for various components of nuclear power plants such as the mechanical seal of a reactor coolant pump (RCP), the guide roller for a control rod drive mechanism (CRDM), and a seal support, etc. Corrosion behavior of $Si_3N_4$ ceramics in a high-temperature and high-pressure water must be elucidated before they can be considered as components for nuclear power plants. In this study, the corrosion behaviors of $Si_3N_4$ ceramics containing MgO and $Al_2O_3$ as sintering aids were investigated at a hydrothermal condition ($300^{\circ}C$, 9.0 MPa) in pure water and 35 ppm LiOH solution. The corrosion reactions were controlled by a diffusion of the reactive species and/or products through the corroded layer. The grain-boundary phase was preferentially corroded in pure water whereas the $Si_3N_4$ grain seemed to be corroded at a similar rate to the grain-boundary phase in LiOH solution. Flexural strengths of the $Si_3N_4$ ceramics were significantly degraded due to the corrosion reaction. Results of this study imply that a variation of the sintering aids and/or a control (e.g., crystallization) of the grain-boundary phase are necessary to increase the corrosion resistance of $Si_3N_4$ ceramics in a high-temperature water.

• Journal of Powder Materials
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• v.29 no.6
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• pp.485-491
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• 2022

Lithium lanthanum titanium oxide (LLTO) is a promising ceramic electrolyte because of its high ionic conductivity at room temperature, low electrical conductivity, and outstanding physical properties. Several routes for the synthesis of bulk LLTO are known, in particular, solid-state synthesis and sol-gel method. However, the extremely low ionic conductivity of LLTO at grain boundaries is one of the major problems for practical applications. To diminish the grain boundary effect, the structure of LLTO is tuned to nanoscale morphology with structures of different dimensionalities (0D spheres, and 1D tubes and wires); this strategy has great potential to enhance the ion conduction by intensifying Li diffusion and minimizing the grain boundary resistance. Therefore, in this work, 0D spherical LLTO is synthesized using ultrasonic spray pyrolysis (USP). The USP method primarily yields spherical particles from the droplets generated by ultrasonic waves passed through several heating zones. LLTO is synthesized using USP, and the effects of each precursor and their mechanisms as well as synthesis parameters are analyzed and discussed to optimize the synthesis. The phase structure of the obtained materials is analyzed using X-ray diffraction, and their morphology and particle size are analyzed using field-emission scanning electron microscopy.