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Magnesium alloys are emerging materials for green cars because they have the lowest density among structural metallic materials. With the increased use of magnesium the development of more effective magnesium recycling technology for all scrap types becomes more important. This paper extensively reviews the recycling technology of end-of-life magnesium scrap. Firstly, it describes the typical refining processes for sorted clean scrap such as flux and fluxless remelting. And it describes the several processes which are feasible to separate magnesium lloys from a light metal shredder fraction containing aluminum and other light matters or to remove surface contaminants and coated layers containing organic matters such as hydrocarbon compounds or harmful metallic elements such as nickel, copper, iron, and chromium. It also introduces the existing purification techniques for a seriously contaminated magnesium melt due to the incomplete removal of impurities.Finally, it discusses the cleanliness assessment techniques of magnesium alloy.

keyword : metals, recycling, melting, magnesium alloy

The effect of high temperature oxidation on the mechanical properties of Zr-1Nb-1Sn-0.1Fe alloy cladding tubes were studied. The oxidation rate was far greater at 700℃than at600℃, reflecting the increasing volume fraction of porous monoclinic ZrO2. The ductility increased and strength decreased after oxidation at 600℃, suggesting softening due to recovery, and recrystallization was predominant over the ductility loss caused by oxidation. In the temperature range between 200℃and 450℃, the flow stress is greater in the oxidized Zr alloy than that annealed at 600℃in a vacuum, suggesting the increased contribution of dynamic strain aging associated with the diffusion of oxygen atoms into a Zr matrix. At 700℃, the ductility decreased significantly after oxidation due to crack propagation into the Zr alloy matrix from the brittle oxide. A stress plateau and a decrease in ductility were observed even in Zr-1Nb-1Sn-0.1Fe with thick brittle oxide after oxidation at 700℃ for 24 hrs in air, suggesting the deformation mechanism was not greatly affected by oxidation.

keyword : alloys, annealing, oxidation, tensile test, fuel cladding

As part of developing a fuel cladding tube for the Sodium-cooled Fast Reactor (SFR), KAERI has manufactured a ferritic-martensitic cladding tube (12Cr1MoWV, HT9) in cooperation with a domestic steelmaking company. After making a steel ingot, followed by multiple processes of tube reduction and subsequent heat treatment, a seamless HT9 tube with a 7.4 mm outer diameter, 0.56 mm thickness and 3000 mm length was manufactured. The objective of this study is to evaluate the out-of pile mechanical properties of the HT9 tube for an assessment of quality inspection as well as validation of its performance. An axial tensile test, a biaxial burst test, and a pressurized creep test of the fuel cladding were carried out at various test temperatures. Finally, the long-term mechanical properties were evaluated, along with the mechanical properties and the mid-term aging data, which showed that microstructural change characterized by the aging mechanism can mainly affect the mechanical roperties of the HT9 cladding tube.

keyword : alloys, deformation, mechanical properties, tensile test, HT9

The mechanical properties and corrosion behavior in welded EH36 TMCP steel were investigated with different Ni content and heat input. Weldments were produced by adjusting the heat input and Ni content of 0, 1.3 wt%. The acicular ferrite fraction increased as the Ni content increased. In contrast, the grainboundary ferrite and Widmanstatten ferrite decreased. The impact energy absorption increased with the addition of the Ni content and decreased as the test temperature decreased. Both tensile and yield strengths increased with either the addition of Ni or reduced heat input. As a result of the polarisation test conducted in a salt solution, the corrosion potential of the 1.3 wt% Ni added specimens was higher than the free Ni specimens.

keyword : metals, welding, mechanical properties, scanning electron microscopy, SEM, impact test

Finite element analysis (FEA) was conducted to find an optimum friction condition for cold-roll cladding of Al/Al-Mg/Al composite sheets. X-ray diffraction was used to analyze the initial macrotexture in each component layer of Al/Al-Mg/Al composite sheets. Electron back-scatter diffraction (EBSD) was used to analyze the heterogeneity of the deformation texture in each component layer through the thickness direction after cold-roll cladding. The velocity gradient tensors determined by the FEA were used in a rate sensitive polycrystal model to simulate the evolution of deformation texture through the thickness direction of Al/Al-Mg/Al composite sheets during cold-roll cladding. The theoretical simulation provided an optimum friction condition for cold-roll cladding analysis of the Al/Al-Mg/Al composite sheets.

keyword : deformation texture, finite element analysis, friction coefficient, polycrystal model

A sample with a composition of 80 wt% Mg-14 wt% Ni-6 wt% TaF5 was prepared by reactive mechanical grinding. Its hydriding and dehydriding properties were then examined. The hydriding rate in the beginning was very high from the first cycle, even at a relatively low temperature of 553 K. At n = 1, the sample absorbed 4.53 wt% H for 5 min, 4.78 wt% H for 10 min, 5.15 wt% H for 30 min, and 5.26 wt% H for 60 min at 553 K under 12 bar H2. At n = 1, the sample desorbed 1.32 wt% H for 5 min, 2.32 wt% H for 10 min, 4.53 wt% H for 30 min, and 5.00 wt% H for 60 min at 593 K under 1.0 bar H2. Activations of the samples were completed after two hydriding (under 12 bar H2)-dehydriding (in vacuum) cycles at 573 K. The activated 80 wt% Mg-14 wt% Ni-6 wt% TaF5 had an effective hydrogen-storage capacity near 6 wt%, absorbing 5.78 wt% H under 12 bar H2 and desorbing 5.16 wt% H under 1.0 bar H2 at 593 K for 60 min.

keyword : hydrogen absorbing materials, mechanical alloying/milling, scanning electron microscopy (SEM), X-ray diffraction, Ni and TaF5 addition

CeO2/TiO2 nano powders for the low-temperature selective catalytic reduction (SCR) of NOx prepared by the sol-gel method were characterized by structural, morphological, and physico-chemical techniques. The catalysts based on 10 wt%-CeO2/TiO2 were synthesized using a sol-gel method and their characteristics were compared with the catalyst prepared by the impregnation method. The XRD peaks of all the samples were assigned to a TiO2 phase (anatase). The sample synthesized by the sol-gel method had a very fine particle size and a higher specific surface area than the CeO2/TiO2 catalyst prepared by the impregnation method, 123.4 m2/g and 47.9 m2/g, respectively. The CeO2/TiO2 catalyst made by sol-gel method had stronger catalytic acid sites according to Fourier transform infrared spectroscopy, showing NOx conversion of 80% at 250℃ and 98% at 300℃. The CeO2/TiO2 catalyst prepared by the sol-gel method showed excellent SCR activities and resistance to SO2, even with a relatively small ceria (CeO2) content.

keyword : nanostructured materials, sol-gel, surface, activation analysis, De-NOx SCR catalyst

Nano-fibrous ZnO thin films were grown on porous silicon (PS) by sol-gel spin-coating method. Atomic force microscopy, X-ray diffraction, Raman, and photoluminescence were carried out to investigate the structural and optical properties of the nano-fibrous ZnO thin films. When the nano-fibrous thin films were grown on PS, their residual stress could be reduced, and the full width at half maximum (FWHM) of the ZnO (002) diffraction peak and near-band-edge emission (NBE) peak were decreased, indicating that the optical as well as the structural properties were enhanced. Furthemore, white light emission was observed from nano-fibrous ZnO thin films grown on PS.

keyword : ZnO, porous Si, nano pore, sol-gel, optical properties, atomic force microscopy, photoluminescence

Palladium (Pd) nano films were deposited at different thicknesses of 34, 46, and 90 nm by sputtering for use as the counter electrode (CE) in dye sensitized solar cell (DSSC). Conventional Pt layers were also prepared using the same process for comparison. Finally 0.45 cm2 DSSCs employing the Pd or Pt CE were prepared, and their photovoltaic properties and microstructure were examined by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), current-voltage (I-V), and transmission electron microscopy (TEM) characterization. CV showed that the catalytic activity of Pd was lower than that of Pt. Moreover, the catalytic activity of Pd increased with increasing thickness. Impedance analysis revealed huge charge transfer resistance at the Pd interface that decreased with increasing Pd thickness. Pt showed low resistance without a thickness dependence. The I-V result of the DSSC device employing Pd and Pt revealed a mean energy conversion efficiency of 4.32% and 6.57%, respectively. TEM showed that the Pd films were not deposited conformally compared to Pt films. The uneven microstructure of the Pd film can lead huge interface resistance and low efficiency. These results suggest that Pd can be used as the counter electrode in DSSCs instead of conventional Pt but the Pd film uniformity needs to be improved.

keyword : Pd, solar cells, sputter, nano electrode

We investigated a method in which magnesium hydroxide nanoparticles were synthesized by irradiation of microwaves with a hydrothermal method. The precursor was prepared with different molar ratios of magnesium sulfate and sodium hydroxide in an aqueous solution. In this experiment, the influences of the concentration of the precursor, pH, reaction watt and irradiation of microwaves on the magnesium hydroxide crystals were examined by the morphology and particle sizes of the products. We found that the average particle sizes of the magnesium hydroxide nanoparticles were 100-300 nm and they could be varied by a reaction pH of 10-13. Mg(OH)₂decomposed into MgO at a temperature range from 358 to 383℃.The magnesium hydroxide was synthesized within 15 minutes and showed a flake-shape morphology with a hexagonal phase. The nano particles were characterized by x-ray diffractometer (XRD), fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), scanning electron microscope (SEM) and particle size analysis (PSA).

keyword : nanostructured materials, chemical synthesis, decomposition, thermal analysis, microwave