• Journal of the Korean Ceramic Society
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• v.12 no.3
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• pp.13-17
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• 1975

본 연구는 열분해반응에 의한 바리움 페라이트 합성반응 후기에 있어서의 반응기구를 규명코자 수행되었다. 실험은 등온하에 90$0^{\circ}C$부터 110$0^{\circ}C$까지 50도의 간격으로 행해졌으며, 반응량의 결정은 X-선의 회절분석법을 이용하여 기초실험에서 얻은 표준보정자료와 비교함으로서 이루어졌다. 연구실험결과 합성반응의 후기는 주로 확산기구에 의해 지배되며 실험적으로 구한 활성화에너지는 14$\pm$10Kcal/mole이었다. 그리고 반응초기는 표면반응이나 혹은 반응후기와는 다른 이온에 의한 확산에 의해 지배될 것이다.

• Journal of Electrochemical Science and Technology
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• v.15 no.1
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• pp.161-167
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• 2024

Despite the important role of manganese (Mn) in cobalt-free, Ni-rich cathode materials, existing reports on the effects of Mn as a substitute for cobalt are not consistent. In this work, we analyzed the performance of cathodes comprised of Li(Ni_1-xMn_x)O₂ (LNMO). Both beneficial and detrimental results occurred as a result of the Mn substitution. We found that a complex interplay of effects (Li/Ni mixing driven by magnetic frustration, grain growth suppression, and retarded lithium insertion/extraction kinetics) influenced the performance and was intimately related to calcination temperature. This indicates the importance of establishing an optimal reaction temperature for the development of high-performance LNMO.

• Korean Journal of Materials Research
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• v.9 no.9
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• pp.905-912
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• 1999

Tensile properties of powder metallurgy (PM) processed Cu-7.5Ni-5Sn alloys, either as-received or additionally solution heat treated, were examined as a function of aging time. It was found that the as-received Cu-7.5Ni-5Sn alloys showed an abrupt increase in tensile strength after aging at $350^{\circ}C$ for 20 minutes, due to the metastable ${\gamma}$\\` precipitation and a marginal Spinodal decomposition. The resolutionized PM Cu-7.5Ni-5Sn alloys, on the other hand, showed a gradual increase in tensile strength from the very early stage of aging. The overall tensile strength of resolutionized PM Cu-7.5Ni-5Sn alloys, however, was lower than that of the as-received and aged counterparts, due to the grain growth during resolutionization. Afterprolonged aging for the as-received PM Cu-7.5Ni-5Sn alloys, a considerable amount of discontinuous precipitates formed along the grain boundaries. The formation and growth kinetics of such discontinuous precipitates appeared to be dependent on the heat treatment conditions, and affect the mechanical properties greatly.

• Nuclear Engineering and Technology
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• v.15 no.3
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• pp.197-206
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• 1983

The slightly hyperstoichiometric uranium dioxide, i.e. U $O_{2.005}$ and U $O_{2.01}$ within a range of the requirement for the use of a nuclear fuel, were sintered directly in an atmosphere of $CO_2$/CO mixture without any succeeding reduction process. The kinetics of sintering in the late stage were investigated for various O/U ratios. A sintering diagram, which show the relation of Temperature-Time-Density-Grain size, was established for each O/U ratio. Only by controlling the oxygen partial pressure in the sintering atmosphere, U $O_2$ pellet could be sintered very easily at low temperature 1050$^{\circ}$～120$0^{\circ}C$ with a density above 95% T.D. and average grain size above 7${\mu}{\textrm}{m}$. It was found that the rate of grain growth follows D=(Kt)$^{1}$4/ in the late stage of sintering. And the activation energies for grain growth in the final sintering stage were found to be 75, 64 and 62kca1/mo1 for U $O_{2.005}$, U $O_{2.01}$ and U $O_{2.10}$, respectively. Although no significant differences are obtained between the activation energies for different O/U ratios, the sinterability is enhanced considerably with increasing the oxygen partial pressure in the sintering atmosphere.tmosphere.

• Journal of Powder Materials
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• v.28 no.3
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• pp.246-252
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• 2021

The effect of sintering conditions on the austenite stability and strain-induced martensitic transformation of nanocrystalline FeCrC alloy is investigated. Nanocrystalline FeCrC alloys are successfully fabricated by spark plasma sintering with an extremely short densification time to obtain the theoretical density value and prevent grain growth. The nanocrystallite size in the sintered alloys contributes to increased austenite stability. The phase fraction of the FeCrC sintered alloy before and after deformation according to the sintering holding time is measured using X-ray diffraction and electron backscatter diffraction analysis. During compressive deformation, the volume fraction of strain-induced martensite resulting from austenite decomposition is increased. The transformation kinetics of the strain-induced martensite is evaluated using an empirical equation considering the austenite stability factor. The hardness of the S0W and S10W samples increase to 62.4-67.5 and 58.9-63.4 HRC before and after deformation. The hardness results confirmed that the mechanical properties are improved owing to the effects of grain refinement and strain-induced martensitic transformation in the nanocrystalline FeCrC alloy.

• Journal of Magnetics
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• v.4 no.1
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• pp.5-9
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• 1999

Effect of sulfur segregation on tertiary recrystallization and magnetic induction during final annealing was investigated in a 3% Si-Fe electrical strip containing 6 ppm(LS) and 15 ppm(HS) sulfur. During final annealing, Auger peak height of segregated sulfur on the surface of the strips reached a maximum, and then decreased to low level with increasing annealing time, which is attributed to sulfur segregation and evaporation. The magnetic induction of the thin-gauged 3% Si strip was inversely proportional to the Auger peak height of segregated sulfur on the surface. The overall profile for surface segregation of sulfur and B10 was observed, irrespective of sulfur content in Si-Fe strips, but the peaks of LS strips appeared earlier than those of HS strips. The grain growth rate of the LS strips during final annealing was faster than that of the HS strips, which may be attributed to the pinning effects of segregated sulfur. With increasing final annealing temperature, B10 value increased rapidly and the saturation level in B10 increased.

• Nuclear Engineering and Technology
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• v.53 no.8
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• pp.2576-2581
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• 2021

The thermal stability and crystallization behaviors of La₂O₃ containing B₂O₃-CaO-Al₂O₃ glass waste forms were investigated to evaluate the stability of waste form during emergencies in deep geological disposal. For glasses containing 15% La₂O₃, LaBO₃ phases were observed as major crystals from 780 ℃ and exhibited needlelike structures. Al, Ca, and O were homogeneously distributed throughout the entire specimen, while some portions of B and La were concentrated in some parts. By differential thermal analysis at various heating rates, the activation energy for grain growth and the crystallization rate of LaBO₃ were calculated to be 12.6 kJ/mol and 199.5 kJ/mol, respectively. These values are comparable to other waste forms being developed for the same purpose.

• Nuclear Engineering and Technology
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• v.54 no.1
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• pp.226-233
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• 2022

In the present work, a phase-field model was developed to investigate the influence of recrystallization on bubble evolution during irradiation. Considering the interaction between bubbles and grain boundary (GB), a set of modified Cahn-Hilliard and Allen-Cahn equations, with field variables and order parameters evolving in space and time, was used in this model. Both the kinetics of recrystallization characterized in experiments and point defects generated during cascade were incorporated in the model. The bubble evolution in recrystallized polycrystalline of U-Mo alloy was also investigated. The simulation results showed that GB with a large area fraction generated by recrystallization accelerates the formation and growth of bubbles. With the formation of new grains, gas atoms are swept and collected by GBs. The simulation results of bubble size and distribution are consistent with the experimental results.

• Korean Journal of Materials Research
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• v.17 no.9
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• pp.453-457
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• 2007

Interest in use of ink-jet printing for pattern-on-demand fabrication of metal interconnects without complicated and wasteful etching process has been on rapid increase. However, ink-jet printing is a wet process and needs an additional thermal treatment such as an annealing process. Since a metal ink is a suspension containing metal nanoparticles and organic capping molecules to prevent aggregation of them, the microstructure of an ink-jet printed metal interconnect 'as dried' can be characterized as a stack of loosely packed nanoparticles. Therefore, during being treated thermally, an inkjet-printed interconnect is likely to evolve a characteristic microstructure, different from that of the conventionally vacuum-deposited metal films. Microstructure characteristics can significantly affect the corresponding electrical and mechanical properties. The characteristics of change in microstructure and electrical resistivity of inkjet-printed silver (Ag) films when annealed isothermally at a temperature between 170 and $240^{\circ}C$ were analyzed. The change in electrical resistivity was described using the first-order exponential decay kinetics. The corresponding activation energy of 0.44 eV was explained in terms of a thermally-activated mechanism, i.e., migration of point defects such as vacancy-oxygen pairs, rather than microstructure evolution such as grain growth or change in porosity.

• Journal of Ceramic Processing Research
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• v.19 no.5
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• pp.372-377
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• 2018

MgO or gadolinium-doped ceria (GDC, $Ce_{0.9}Gd_{0.1}O_{2-{\delta}}$) was added as a promoter to improve the oxygen transfer kinetics of $MgMnO_3$ oxygen carrier material for chemical looping combustion. Neither MgO nor GDC reacted with $MgMnO_3$, even at the high temperature of $1100^{\circ}C$. The average oxygen transfer capacities of $MgMnO_3$, 5 wt% $MgO-MgMnO_3$, and 5 wt% $GDC-MgMnO_3$ were 8.74, 8.35, and 8.13 wt%, respectively. Although the addition of MgO or GDC decreased the oxygen transfer capacity, no further degradation was observed during their use in 5 redox cycles. The addition of GDC significantly improved the conversion rate for the reduction reaction of $MgMnO_3$ compared to the use of MgO due to an increase in the surface adsorption process of $CH_4$ via oxygen vacancies formed on the surface of GDC. On the other hand, the conversion rates for the oxidation reaction followed the order 5 wt% $GDC-MgMnO_3$ > 5 wt% $MgO-MgMnO_3$ >> $MgMnO_3$ due to morphological change. MgO or GDC particles suppressed the grain growth of the reduced $MgMnO_3$ (i.e., (Mg,Mn)O) and increased the specific surface area, thereby increasing the number of active reaction sites.