In this study, a flat-type photocatalytic reactor is applied under solar irradiation for simultaneous treatment of target pollutants: reduction of Cr(VI) to Cr(III) and oxidation of EDCs (BPA, EE2, E2). An immobilized type of photocatalyst was fabricated to have self-grown nanotubes on its surface in order to overcome limitations of powdery photocatalyst. Moreover, Ti mesh form was chosen as substrate and modified to have both larger surface area and photocatalyst content. Ti mesh was anodized at 50V and 25°C for 30min in the mixed electrolytes (NH4F-H2O-C2H6O2) and annealed at 450°C for 2 hours in ambient oxygen to have anatase structure. Surface characterization was done with SEM and XRD methodologies. Fabricated NTT was applied to water treatment, and coexisting Cr(VI) and organics (EDCs) enhanced each other's reactions by scavenging holes and electrons and thus impeding recombination. Also, several experiments were conducted outdoor under direct sunlight and it was observed that both solar-tracking and applying modified photocatalyst were proven to enhance reaction efficiency.

Toxicity assessment of heavy metals (As, Cr and Pb) has been investigated by using the rate of survival and population growth(r) of marine rotifer, Brachionus plicatilis. The survival rate was determined after 24 hours of exposure to As, Cr and Pb. As and Cr reduced survival rate in dose-dependent manner and a significant reduction were occurred at concentration of greater than 30 and 150 mg L-1, but Pb had no effect on survival rate. The r was determined after 72 hours of exposure to As, Cr and Pb. As, Cr and Pb reduced r in dose-dependent manner and a significant reduction were occurred at concentration of greater than 5, 25 and 50 mg L-1. The toxicity of heavy metals were ranked As>Cr>Pb, with EC50 values of 12.98, 82.34 and 110.14 mg L-1, respectively. The no-observed-effect-concentration (NOEC) of r in As, Cr and Pb exposure were 1, 12.5 and 50 mg L-1, respectively. The lowest-observed-effect-concentration (LOEC) of r in As, Cr and Pb exposure were 5, 25, and 50 mg L-1, respectively. From the results, the concentration of As, Cr and Pb (greater than 5, 25 and 50 mg L-1, respectively) have toxic effect on the r of B. plicatilis in natural ecosystems. These results (including NOEC and EC50) might be useful for the mixing toxicity assessment and toxic guide line of heavy metals in marine ecosystems.

In the present study, the tensile properties and dynamic strain aging of an Fe-24.5Mn-4Cr-0.45C alloy were investigated in terms of strain rate. During tensile testing at room temperature, all the stress-strain curves exhibited serrated plastic flows related to dynamic strain aging, regardless of the strain rate. Serration appeared right after yield stress at lower strain rates, while it was hardly observed at high strain rates. On the other hand, strain-rate sensitivity, indicating a general relationship between flow stress and strain rate at constant strain and temperature, changed from positive to negative as the strain increased. The negative strain-rate sensitivity can be explained by the Portevin Le Chatelier effect, which is associated with dynamic strain aging and is dependent on the strain rate because it is very likely that the dynamic strain aging phenomenon in high-manganese steels is involved in the interaction between moving dislocations and point-defect complexes.

Ni and Ni-Cr reinforced Al alloy (AC8A) composites were fabricated by low pressure infiltration process. Porous Ni was applied as preform. Ni reinforced AC8A composites were fabricated under 0.3 MPa at 650, 700 and 750 degrees centigrade, respectively, while Ni-Cr reinforced AC8A composites were fabricated under low pressure limited to the maximum of 0.5 Mpa at 750, 800 and 850 degrees centigrade, respectively. Microstructure and phase composition of the composites were evaluated by optical microscope, X-Ray diffraction (XRD), electro-probe micro analyzer (EMPA). Intermetallic compounds Al3Ni and CrSi were observed in the composites. The results indicate that the grain size has been increasing with the increase of the infiltration temperatures. However, the wear resistance of Ni/AC8A and Ni-Cr AC8A peaked at 650 degree centigrade and 800 degrees centigrade, respectively. In addition, based on the wear characteristics and wear surfaces, Ni-Cr/AC8A composites have a better wear resistance than Ni/AC8A composites and AC8A.

This study attempts to manufacture a Ni-Cr-Al-Y coating layer using a kinetic spray process and investigates the microstructure and physical properties of the manufactured layer. The Ni-22Cr-10Al-1Y (wt.%) composition powder is used, and it has a spherical shape with an average diameter of 23.7 μm. Cu plate is used as the substrate. Optical microscope, X-ray diffraction, scanning electron microscope and Vickers hardness test are carried out to characterize the macroscopic properties of the coating layer. Furthermore, the coating layer underwent vacuum heat treatment at temperatures of 400˚C and 600˚C for 1 hour to check the effect of heat treatment temperature on the properties. The manufactured coating layer is 1.5 mm thick, and featured identical phases to those found in the powder. The porosity of the coating layer is measured at 2.99%, and the hardness is obtained at 490.57 Hv. The layer shows reduced porosity as heat treatment temperature increased, and hardness is reduced at 400˚C but shows a slight increase at 600˚C. Based on the findings described above, this study also discusses possible manufacturing methods for a Ni-Cr-Al-Y coating layer using the kinetic spray process.

본 논문에서는 구조물에 작용하는 하중의 크기와 진동수에 따른 거동의 비선형성을 확인하고 정확한 예측을 위한 방법을 모색하기 위하여 외팔보의 정적 및 동적해석의 수행에서 선형, 비선형 해석의 결과를 비교하는 연구를 진행하였다. 우선 보의 자유단에 수직방향의 정적 및 동적 하중을 가한 상황을 예측하였다. 선형 해석방법으로 고전 외팔보 이론을 적용하였고, co-rotational dynamic 유한요소해석 기법을 개발하여 비선형 해석방법으로 사용하였다. 먼저 정적해석에서 외력의 크기가 달라질 때 선형 및 비선형 해석 예측이 어떠한 차이를 보이는지 비교하였다. 그리고 동적해석을 통해 가진 진동수의 변화에 따른 보 끝단의 무차원화된 변위의 양상을 연구하였고, 공진진동수 근방에서의 상당한 변위가 발생함을 보였다. 마지막으로 주파수 지연현상을 조사하기 위해 특정 진동수에서의 시간 경과에 따른 보의 변위를 확인하였다.

The ductile-brittle transition behavior of two austenitic Fe-18Cr-10Mn-N-C alloys with different grain sizes was investigated in this study. The alloys exhibited a ductile-brittle transition behavior because of an unusual brittle fracture at low temperatures unlike conventional austenitic alloys. The alloy specimens with a smaller grain size had a higher yield and tensile strengths than those with a larger grain size due to grain refinement strengthening. However, a decrease in the grain size deteriorated the low-temperature toughness by increasing the ductile-brittle transition temperature because nitrogen or carbon could enhance the effectiveness of the grain boundaries to overcome the thermal energy. It could be explained by the temperature dependence of the yield stress based on low-temperature tensile tests. In order to improve both the strength and toughness of austenitic Fe-Cr-Mn-N-C alloys with different chemical compositions and grain sizes, more systematic studies are required to understand the effect of the grain size on the mechanical properties in relation to the temperature sensitivity of yield and fracture stresses.

The effects of Nb and Cr addition on the microstructure, corrosion and oxide characteristics of Zr based alloys wereinvestigated. The corrosion tests were performed in a pressurized water reactor simulated-loop system at 360oC. Themicrostructures were examined using OM and TEM, and the oxide properties were characterized by low-angle X-ray diffractionand TEM. The corrosion test results up to 360 days revealed that the corrosion rates were considerably affected by Cr contentbut not Nb content. The corrosion resistance of the Zr-xNb-0.1Sn-yCr quaternary alloys was improved by an increasing Nb/Cr ratio. The crystal structure of the precipitates was affected by a variation of the Nb/Cr ratio. The Zr-Nb beta-enrichedprecipitates were mainly formed in the high Nb/Cr ratio alloy while Zr(NbCr)2 precipitates were frequently observed in the lowNb/Cr ratio alloy. The studies of oxide characteristics revealed that the corrosion resistance was related to the crystal structureof the precipitate.

The porous metals are known as relatively excellent characteristic such as large surface area, light, lower heat capacity, high toughness and permeability. The Fe-Cr-Al alloys have high corrosion resistance, heat resistance and chemical stability for high temperature applications. And then many researches are developed the Fe-Cr-Al porous metals for exhaust gas filter, hydrogen reformer catalyst support and chemical filter. In this study, the Fe-Cr-Al porous metals are developed with Fe-22Cr-6Al(wt) powder using powder compaction method. The mean size of Fe-22Cr-6Al(wt) powders is about 42.69 μm. In order to control pore size and porosity, Fe-Cr-Al powders are sintered at 1200~1450oC and different sintering maintenance as 1~4 hours. The powders are pressed on disk shapes of 3 mm thickness using uniaxial press machine and sintered in high vacuum condition. The pore properties are evaluated using capillary flow porometer. As sintering temperature increased, relative density is increased from 73% to 96% and porosity, pore size are decreased from 27 to 3.3%, from 3.1 to 1.8 μm respectively. When the sintering time is increased, the relative density is also increased from 76.5% to 84.7% and porosity, pore size are decreased from 23.5% to 15.3%, from 2.7 to 2.08 μm respectively.

This study investigated the microstructure and tensile properties of a recently made block-type Ni-Cr-Al powder porous material. The block-type powder porous material was made by stacking multiple layers of powder porous thin plates with post-processing such as additional compression and sintering. This study used block-type powder porous materials with two different cell sizes: one with an average cell size of 1,200 μm (1200 foam) and the other with an average cell size of 3,000 μm (3000 foam). The γ-Ni and γ’-Ni3Al were identified as the main phases of both materials. However, in the case of the 1,200 foam, a β-NiAl phase was additionally observed. The relative density of each block-type powder porous material, with 1200 foam and 3000 foam, was measured to be 5.78% and 2.93%, respectively. Tensile tests were conducted with strain rates of 10−2~10−4 sec−1. The test result showed that the tensile strength of the 1,200 foam was 6.0~7.1 MPa, and that of 3,000 foam was 3.0~3.3 MPa. The elongation of the 3,000 foam was higher (~9%) than that (~2%) of the 1,200 foam. This study also discussed the deformation behavior of block-type powder porous material through observations of the fracture surface, with the results above.

We evaluated the developed microstructures and mechanical properties of a severely plastically deformed Ni-30Cr alloy. Normal rolling and differential speed rolling were used as deformation processes, and the thicknesses of the specimens were reduced to 68 % of the original thickness after holding at 700 oC for 10 min and annealing at 700 oC for 40 min to obtain a fully recrystallized microstructure. Electron backscattering diffraction was used to analyze the characteristic distribution of the grain boundaries on the deformed and annealed specimens. Differential speed rolling was more effective for refining grains in comparison with normal rolling. The grain size was refined from 33 mm in the initial material to 8.1 mm with normal rolling and 5.5 mm with differential speed rolling. The more refined grain in the differential-speed-rolled material directly resulted in increases in the yield and tensile strengths by 68 % and 9.0%, respectively, compared to normal rolling. We systematically explain the relationship between the grain refinement and mechanical properties through a plastically deformed Ni-30Cr alloy based on the development of a deformation texture. The results of our study show that the DSR process is very effective when used to enhance the mechanical properties of a material through grain refinement.

In this study, flat-type photocatalytic reaction system is applied to reduce toxic hexavalent chromium (Cr(VI)) to trivalent chromium (Cr(III)) in aqueous solution under UV irradiation. To overcome the limitation of conventional photocatalysis, a novel approach toward photocatalytic system for reduction of hexavalent chromium including nanotubular TiO2 (NTT) on two kinds of titanium substrates (foil and mesh) were established. In addition, modified Ti substrates were prepared by bending treatment to increase reaction efficiency of Cr(VI) in the flat-type photocatalytic reactor. For the fabrication of NTT on Ti substrates, Ti foil and mesh was anodized with mixed electrolytes (NH4F-H2O-C2H6O2) and then annealed in ambient oxygen. The prepared NTT arrays were uniformly grown on two Ti substrates and surface property measurements were performed through SEM and XRD. Hydraulic retention time(HRT) and substrate type were significantly affected the Cr(VI) reduction. Hence, the photocatalytic Cr(VI) reduction was observed to be highest up to 95% at bended(modified) Ti mesh and lowest HRT. Especially, Ti mesh was more effective as NTT substrate in this research.

Glancing angle deposition (GLAD) is a powerful technique to control the morphology and microstructure of thin film prepared by physical vapor deposition. Chromium (Cr) thin films were deposited on a polymer substrate by a sputtering technique using GLAD. The change in thickness and Vickers microhardness for the samples was observed with a change in the glancing angle. The adhesion properties of the critical load (Lc) by a scratch tester for the samples were also measured with varying the glancing angle. The critical load, thickness and Vickers microhardness for the samples decreased with an increase in the glancing angle. However, the thickness of the Cr thin film prepared at a 90o glancing angle showed a relatively large value of 50 % compared to that of the sample prepared at 0o. The results of X-ray diffraction and scanning electron microscopy demonstrated that the effect of GLAD on the microstructure of samples prepared by sputter technique was not as remarkable as the samples prepared by evaporation technique. The relatively small change in thickness and microstructure of the Cr thin film is due to the superior step-coverage properties of the sputter technique.

Despite having many attractive properties, ZrO2 ceramic has a low fracture toughness which limits its wide application. One of the most obvious tactics to improve its mechanical properties has been to add a reinforcing agent to formulate a nanostructured composite material. Nanopowders of ZrO2 and Cr were synthesized from CrO3 and Zr powder by high energy ball milling for 10 h. Dense nanocrystalline 2/3Cr-ZrO2 composite was consolidated by a high-frequency induction heated sintering method within 5 min at 600˚C from mechanically synthesized powder. The method was found to enable not only rapid densification but also the inhibition of grain growth, preserving the nano-scale microstructure. Highly dense 2/3Cr-ZrO2 composite with relative density of up to 99.5% was produced under simultaneous application of a 1 GPa pressure and the induced current. The hardness and fracture toughness of the composite were 534 kg/mm2 and 7MPa·m1/2, respectively. The composite was determined to have good biocompatibility.

Cr3+ 및 Se을 첨가하여 수경 재배한 치커리 3종의 에탄 올 추출물을 각각 제조하여 추출물별 항산화 활성을 비교 검토하였다. 그 결과 양액만으로 재배한 치커리보다 양액에 Se이나 Cr3+을 첨가한 치커리 추출물에서 총 폴리페놀 함량, 총 플라보노이드 함량 및 FRAP 환원능이 증가하였으며, DPPH 라디칼 소거능 및 ABTS 라디칼 소거능도 증가하였다. 특히 Se을 첨가한 치커리보다 Cr3+을 첨가한 치커리에서 더 우수한 항산화 활성을 나타내었다. 또한 Cr3+ 을 첨가한 CLER 및 CLE의 경우 α-glucosidase 저해활성이 있음을 알 수 있었다. 따라서 치커리 추출물의 수경재배 과정에서 양액에 Cr3+, Se의 첨가는 치커리의 항산화 활성 및 α-glucosidase 저해활성 증진에 영향을 주는 것으로 확인되었다.

After the content items of the secondary French curriculum changed to an achievement standards format, the new format appeared to be inconsistent with French education’s current content structure—language skills, language materials, and culture. This study aims to enhance the validity of the creation of the achievement standards by reshaping the curriculum to be more in line with the newly developed standards. This study provides a historical analysis of French curriculum structure and a review of existing literature on the second language education. And it also analyzes the foreign language curriculum structures in several foreign countries. Based on the discussion of preceding chapters, a restructuralization of French curriculum is suggested. The essence of the restructuralization is to divide the achievement standards into language achievement and cultural achievement, as well as to present language skills and materials—subcategories of language achievement in achievement standards formats. Also needed are standards for comprehensive skills including listening, speaking, reading, and writing. To be consistent with the purpose of the achievement standards format, the objectives, teaching and learning methods, and evaluation in French curriculum need to be modified. Finally, I suggest to the entities who are involved in the 2015 curriculum revision the need for scrutiny of the current curriculum format, as well as a change to the format in future development. Après le changement des éléments de contenu faisant partie du curriculum de l’enseignement du français au niveau secondaire pour un nouveau format basé sur les critères d’accomplissement, la structure actuelle de l’enseignement, composée de compétences langagières, de matières langagières et de contenus culturels, n’est plus conforme avec celle modifiée. Par conséquent, cette thèse vise à restucturer le cadre des contenus du curriculum, compte tenu des critères d’accomplissement développés, afin de réhausser la pertinence de l’établissement de ces critères. Cette étude explique l’analyse de la structure des contenus de tous les anciens curriculums et les résultats issus des études et de l’analyse précédentes portant sur les contenus de l’enseignement des langues vivantes. Elle présente ensuite les résultats de l’analyse des contenus des programmes en vigueur à l’étranger, ce qui nous conduit au dernier chapitre qui propose un programme restructuré. Pour résumer ce dernier, les points essentiels consistent à décliner les critères d’accompplissement en deux - critères langagiers et culturels ; proposer les compétences et les matières langagières, sous-catégorie des critères langagiers, sous forme du nouveau format des critères d’accomplissement ; présenter les critères d’accomplissement pour les compétences intégrales comprenant la compréhension et la production orales et écrites ; enfin, faire adapter d’autres points sous ce nouveau format des critères, tels que les objectifs d’enseignement, les méthodes didactiques et celles d’apprentissage, les critères d’évaluation dans le cadre du curriculum de l’enseignement du français. Avec cette proposition, cette thèse invite les chercheurs étudiant le nouveau curriculum 2015 à examiner avec prudence la stucture des contenus actuelle et à réfléchir à la nécessité de la restructuration des contenus à réaliser dans l’avenir.