• Journal of Powder Materials
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• v.23 no.3
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• pp.240-246
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• 2016

In order to improve the high-temperature oxidation stability, sintered 434L stainless steel is studied, focusing on the effect of the addition of metallic oxides to form stable oxide films on the inner particle surface. The green compacts of Fecralloy powder or amorphous silica are added on STS434L and oxidized at $950^{\circ}C$ up to 210 h. The weight change ratio of 434L with amorphous silica is higher than that of 434L mixed with Fecralloy, and the weight increase follows a parabolic law, which implies that the oxide film grows according to oxide diffusion through the densely formed oxide film. In the case of 434L mixed with Fecralloy, the elements in the matrix diffuse through the grain boundaries and form $Al_2O_3$ and Fe-Cr oxides. Stable high temperature corrosion resistance and electrical resistivity are obtained for STS434L mixed with Fecralloy.

• Journal of Korea Technology Innovation Society
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• v.11 no.4
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• pp.613-638
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• 2008

The Korean government established 'the Act on Performance Evaluation and Management for National Research & Development (R&D) Programs' in 2005, and one year later constructed a master plan, 'A Basic Plan for the Management and Utilization of R&D performance' that focused on better diffusing the public R&D outcomes. In this study we propose a model of performance monitoring, evaluation, and management system for national R&D, which is based on a systematic approach and the logic model that has been prevalently used in planning and evaluating the public programs, to meet the purpose of the law and the master plan as well as to facilitate the diffusion of national R&D outcomes focused mainly on the industrial application technology. Furthermore, in order to use the model for the several applications, the model's specific measures which includes the quantitative methodologies such as analytic hierarchy process (AHP) and data envelopment analysis (DEA) are suggested in accordance with the existing system of the evaluation institution in Korea.

• Proceedings of the Korean Nuclear Society Conference
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• 1996.05c
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• pp.231-237
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• 1996

Defect equilibrium equations were modelled, and the relations of P $o_2$, venus x were derived using the mass action law. The dominant defect species active in a specified region were determined by fitting the curve of experimental data to the calculated curve of log P $o_2$, versus log x for each theoretical model. The calculated curve for (2:1:2) and (Er')$^{x}$ in the hyperstoichiometric $U_{1-y}$E $r_{y}$ $O_{2＋x}$ and that for (2Er'quot;)$^{x}$ $_{dec}$ in the hypostoichiometric $U_{1-y}$E $r_{y}$ $O_{2－x}$ are in good agreement with the present experimental results. The sintering behavior of Er-doped U $O_2$ is observed with erbium content in oxidizing and reducing atmospheres. For sintering in oxidizing atmosphere, sintered density decreases as increasing y in $U_{1-y}$E $r_{y}$ $O_{2＋x}$. However, in hydrogen atmosphere, sintered density decreases as increasing y at lower erbium content but the density increases again above y=0.10. In oxidizing sintering conditions, the formation of (Er'U')$^{x}$ clusters hinders the diffusion of cations, and hence the sinterability of Er-doped U $O_2$ decreases. In reducing atmosphere of Er-doped U $O_2$ for higher Er concent, the oxygen vacancies make (Er')$^{x}$ cluster decompose by charge compensation and the concentration of mobile cations increases, thereby improving the sinterability.ntration of mobile cations increases, thereby improving the sinterability.ability.

• Korean Journal of Optics and Photonics
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• v.21 no.6
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• pp.241-246
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• 2010

In this paper, we propose an electric field enhanced postexposure baking (EFE-PEB) method to obtain deep and high aspect ratio pattern profile in near-field recording. To describe the photoacid distribution under an external electric field during the PEB, we derived the governing equations based on Fick's second law of diffusion. From the results of the numerical calculations, it is found that the vertical movement of photoacid increases while the lateral movement is stationary as electric field varies from 0 to $8.0{\times}10^6\;V/m$. Also, it is proven that the profile of near-field recording is improved by using the EFE-PEB method with increased depth, higher aspect ratio and larger sidewall angle.

• Journal of the Korean Ceramic Society
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• v.47 no.2
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• pp.106-112
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• 2010

This paper presents some experimental results on incubation time for massive hydriding of Zr alloys with oxide thickness. Oxide effects experiments on massive hydriding reaction of commercial Zr alloy claddings and pre-oxidized Zr alloys with hydrogen gas were carried out in the temperature range from 300 to $400^{\circ}C$ with thermo-gravimetric apparatus. Experimental results for oxide effects on massive hydriding kinetics show that incubation time is not proportional to oxide thickness and that the massive hydriding kinetics of pre-filmed Zr alloys follows linear kinetic law and the hydriding rate are similar to that of oxide-free Zr alloys once massive hydriding is initiated. There was a difference in micro-structures between oxide during incubation time and oxide after incubation time. Physical defects such as micro-cracks and pores were observed in only oxide after incubation time. Therefore, the massive hydriding of Zr alloys seems to be ascribed to short circuit path, mechacical or physical defects, such as micro-cracks and pores in the oxide rather than hydrogen diffusion through the oxide resulting from the increase of oxygen vacancies in the hypostoichiometric oxide.

• Transactions of the Korean hydrogen and new energy society
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• v.14 no.1
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• pp.17-23
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• 2003

$H_2$ permeation flux though a $100{\mu}m-thick$ Pd-Ru (6wt%) membrane was measured at various temperatures and pressures. The permeation flux followed the Sievert's law and thus the rate-limiting step of the hydrogen permeation was the bulk atomic diffusion step. The activation energy of the permeation flux was obtained at 17.9 kJ/mol and this value is consistent with those published previously. While no degradation of the permeation flux wasfound in the membrane exposed to the $O_2$ and $CO_2$ environments for 100 hours, the membrane exposed to $N_2$ environment for 100 hours showed the degradation in the $H_2$ permeation flux. The $H_2$ permeation was decreased as the exposure temperature to $N_2$, environment was increased. The $H_2$ permeation flux was fully recovered after the membrane was kept in the $H_2$ environment for certain time. The permeation flux degradation might be caused by the formation of metal nitride on the membrane surface.

• Journal of the Korea Concrete Institute
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• v.15 no.4
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• pp.574-584
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• 2003

The most common deterioration cause of concrete structures in urban environment is carbonation. Recently, the $CO_2$ concentration and temperature at atmosphere is sharply increased with time due to global warming phenomena. In this study, the climate scenario IS92a, which was suggested by the IPCC, is used to consider temperature and atmospheric $CO_2$ concentration change in the model of service life prediction. The modified mathematical solution, which was based on the Fick's 1st law of diffusion, was used to reflect concrete materials properties such as the degree of hydration of concrete with elapsed time, and important parameters, which associated with deterioration rate. The techniques of service life prediction are developed introducing the method of reliability and stochastic concept to consider microclimatic condition in Seoul, South Korea. From the result of service life prediction, concrete containing high W/C ratio is shown fast carbonation rate due to $CO_2$ concentration increase. It is concluded that the deterioration of concrete structures due to carbonation is insignificant problem on the conditions that below W/C 55%, well curing concrete.

• Computers and Concrete
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• v.2 no.4
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• pp.325-343
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• 2005

Chloride ingress is a common cause of deterioration of reinforced concrete located in coastal zone. Modeling the chloride ingress is an important basis for designing reinforced concrete structures and for assessing the reliability of an existing structure. The modeling is also needed for predicting the deterioration of a reinforced structure. The existing deterministic solution for prediction model of corrosion initiation cannot reflect uncertainties which input variables have. This paper presents an approach to the fuzzy arithmetic based modeling of the chloride-induced corrosion of reinforcement in concrete structures that takes into account the uncertainties in the physical models of chloride penetration into concrete and corrosion of steel reinforcement, as well as the uncertainties in the governing parameters, including concrete diffusivity, concrete cover depth, surface chloride concentration and critical chloride level for corrosion initiation. There are a lot of prediction model for predicting the time of reinforcement corrosion of structures exposed to chloride-induced corrosion environment. In this work, RILEM model formula and Crank's solution of Fick's second law of diffusion is used. The parameters of the models are regarded as fuzzy numbers with proper membership function adapted to statistical data of the governing parameters instead of random variables of probabilistic modeling of Monte Carlo Simulation and the fuzziness of the time to corrosion initiation is determined by the fuzzy arithmetic of interval arithmetic and extension principle. An analysis is implemented by comparing deterministic calculation with fuzzy arithmetic for above two prediction models.

• Transactions of the Korean Society of Mechanical Engineers
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• v.9 no.4
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• pp.395-402
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• 1985

The apparent activation energy Q$_{c}$ and the applied stress exponent n have been determined during creep of Al 7075 alloy over the temperature range of 90.deg. C to 320.deg. C (0.4-0.65T$_{m}$) and stress range of 1.85 kgf/mm$^{2}$ to 21 kgf/mm$^{2}$, respectively in order to investigate the creep behavior. Constant load creep tests were carried out in the experiment. At round the temperature of 200.deg. C-240.deg. C and under the stress level 8.13-9.55kgf/mm$^{2}$ and again at around the temperature of 280.deg. C-320.deg. C and under the stress level of 1.85-2.55kgf/mm$^{2}$, the creep behavior obeyed for the creep deformation was nearly equal to that of the volume self diffusion of pure aluminum (34kcal/mole). But at around the temperature of 90.deg. C and under the stress level of 10-21kgf/mm$^{2}$, the creep behavior did not obey a simple power-law relation and the apparent activation enrgy, Q$_{c}$ was 26.01 kcal/mole. From the above facts, at around the temperature of 200.deg. C-240.deg. C and 280.deg. C-320.deg. C, the creep deformation for Al 7075 alloy seemed to be controlled by dislocation climb but at 90.deg. C, by cross slip over the range of experimental stress conditions.tions.

• Water for future
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• v.28 no.4
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• pp.185-194
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• 1995

The objective of this study is to explore scale problem and to analyze the relations between scale and geomorphologic parameters of the rainfall-runoff model. Generally, measurement and calculation of geomorphologic parameters rely on and are sensitive to the resolution of source information available. Therefore, rainfall-runoff models using geomorphologic parameters should take account of the effects of the map scale used in their development. The derived rainfall-runoff model considering scale problem in this research is the GIUH type model, that is a basin IUH consisting of the channel network response and hillslope response. The cannel network response is computed by means of the diffusion analogy transformed from linearized St. Venant equation and hillslope response is calculated by 2-parameter gamma distribution function. Representing geomorphologic structure of the channel network and initial distribution of its response is width function. This width function is derived by fractal theory and Melton's law to consider scale problems and is weighted by the source location function (SLF) proposed in this research to increase the applicability.