Papers by Keyword: Rare Earth Element (REE)

Abstract: Cubic oxides with pyrochlore and garnet structures are promising matrices for long-lived actinides immobilization. Their isomorphic capacity with respect to An and REE was determined. To predict the long-term behavior of these matrices under their underground disposal radiation stability of synthetic pyrochlores and garnets was studied. Most of titanate phases have the critical (amorphization) doses close to 0.2 displacements per atom at 298 K. This value is significantly higher for Sn- and Zr-rich pyrochlores. Corrosion behavior of the pyrochlore- and garnet-composed matrices was investigated. The lowest actinides leach rates were observed in water and alkaline solutions most typical for underground waste repositories. Amorphization of the phases has a low influence on their corrosion behavior in solutions. Possibility for joint incorporation of actinides and Tc into zirconate- and titanate-based matrices with the pyrochlore structure is discussed.

Abstract: Microstructure and mechanical properties of Si3N4 and Si3N4 + SiC nanocomposites sintered with rare-earth oxide additives (La2O3, Y2O3, Yb2O3 and Lu2O3) have been investigated. The composites exhibited smaller grain diameter compared to that of monolithic materials. The aspect ratio of β-Si3N4 grains increased with a decreasing ionic radius of rare-earth elements in the Si3N4 monoliths as well as in the Si3N4-SiC nanocomposites. The hardness of both systems increased with a decreasing ionic radius of rare-earth element. The fracture toughness of the materials with coarser microstructure and higher aspect ratio was higher due to the more frequent toughening mechanisms. No significant difference between strength values of monoliths and composites was observed and the strength in the composites was determined mainly by the present processing flaws. Significantly improved creep resistance was observed in the case of composites and for materials with smaller ionic radius of RE3+.

Abstract: The formation and the growth of Cu-Sn intermetallic compound (IMC) layer at the interface between Sn-3.0Ag-0.5Cu-xEr(x=0, 0.1) solder and Cu substrate during soldering and aging were studied. The results show that Cu6Sn5 IMC is observed at the interface between solder and Cu substrate in all conditions. After aging for 120 h, the Cu3Sn IMC is then obtained. With increasing aging time, the scalloped Cu6Sn5 structure changes to a plate structure. The Cu3Sn film always forms with a relatively planar interface. By adding a small amount of the rare earth element Er (only 0.1%, mass fraction) into the Sn-3.0Ag-0.5Cu solder alloy, the growth rate of the Cu-Sn IMC at the interface of solder alloy system is decreased. When the time exponent is approximately 0.5, the growth of the IMC layer is mainly controlled by a diffusion over the studied time range.

Abstract: Commercial magnesium alloys such as AZ31 exhibit strong crystallographic textures during massive deformation such as rolling. A randomisation of the texture, however, was found in alloys with rare earth (RE) elements in solid solution. This paper describes the development of microstructure and texture during rolling of the Al-free RE-containing wrought magnesium alloy ZEK100 during hot rolling. This alloy develops a strong texture with a pronounced component towards the transverse direction (TD) of the sheets. This TD component forms already after the first rolling pass, persists through all following passes and is further enhanced by subsequent heat treatment. These results are contrasted with results from a study on texture development of binary RE containing Mg-alloys, which show that the presence of RE elements alone is not responsible for the tilt of basal planes towards the TD. There is, however, a threshold concentration at which the texture begins to weaken.

Abstract: Unique properties of biogenic Mn oxides were applied to a fundamental study of separation and recovery of rare earth elements. Selective sorption of Ce3+ over La3+ ions was achieved at neutral pH values using biogenic Mn oxides produced by Paraconiothyrium sp. WL-2 strain. The selective coefficient for Ce3+ (αCe) was much greater with biogenic and synthetic Mn oxides than those for La3+ (αLa). Ce3+ ions were oxidized to CeO2 by Mn(III, IV) in Mn oxides under anaerobic conditions resulting in the release of Mn2+ ions, while La3+ ions were sorbed without a redox reaction. With an increase in coexisting La3+ ions, sorption of Ce3+ on both Mn oxides was significantly suppressed, especially with synthetic Mn oxides. The edges of the structure are competitive sites because of fewer numbers of vacant sites in synthetic Mn oxide layers. The preferential sorption on the edge sites of Mn oxides is in the order of La3+ > Ce3+. These phenomena can be expanded to separation and recovery of other rare earth elements from natural and anthropogenic sources.

Abstract: Recently, biological system has revealed astonishing complex photonic structures. Freshwater pearls shows striking optical effects, such as reflection and interference, which closely related to its nanometer-scale multiplayer structure. In this paper, we tried to fabricate idea biological two-dimensional (2D) photonic crystals by growing freshwater pearls induced by Rare Earth Elements (REE) Cerium at a concentration of 1.2 mg•L-1. Comparing with the reference pearls cultured in nature freshwater, the superficial microstructure of REE pearls and their glossiness have taken large changes. The nacre of the REE pearls is structured 2D periodic photonic crystals layered structure, and each layer is composed by regular aragonite sheets, while the nature pearls has a mesa structure made of the spindly blocks, which were investigated by means of scanning electron microscopy (SEM). The glossiness of the pearls corresponds with the microstructure, the REE pearls possessing idea photonic crystals have higher glossiness than that of the nature pearls, which attribute to the strong interference effect of light on the photonic structure of REE pearls. It also provides an opportunity to grow perfect photonic crystals by culturing water pearls.

Abstract: The microstructures, mechanical properties, and formability of an Mg-1.5Zn-0.1Zr alloy with rare earth element of Erbium addition have been examined by using optical microscopy, scanning electron microscopy/energy dispersive X-ray spectroscopy, and thermal mechanical testing. The results showed that Erbium combined with Mg and impurity elements forming small particles dispersed on the matrix. Therm-mechanical simulation in the temperature range from 250°C to 400°C and strain rate from 0.1 to 1.0 indicated that the flow stress decreases with the increase of the temperature and the decrease of the strain rate. Sheet samples were prepared through ingot casting, hot rolling, cold rolling, and intermediate annealing. Remarkable grain size refinement was realized through recrystallization during the rolling process. Good combination of strength and ductility was achieved by applying intermediate annealing before the very last cold rolling. Further improvement of ductility and formability could be obtained by conducting proper heat treatment on the finishing cold-rolled sheets.

Abstract: The latest research results on new types of magnesium alloys containing strontium or rare earth elements are reviewed. Special attentions are paid to the alloying design, microstructure and properties controlling, the influence of minor addition of Sr and RE on the microstructure and properties of existing magnesium alloys. Some new types of magnesium alloys containing Sr or RE are introduced and discussed.

Abstract: The aims of this study are to investigate the effect of Y (yttrium) addition in the Mg-Al- Ca alloys on microstructure and mechanical properties. In additions, the alloys were solution treated in order to achieve a better understanding of the precipitation mechanisms. The as-cast microstructure of Mg-5Al-3Ca alloy and Mg-5Al-3Ca-xY alloys contains dendritic α-Mg matrix and eutectic intermetallic compound at grain boundary. The hardness values of Mg-Al-Ca alloy with Y additions were slightly increased than that of Mg-Al-Ca with no Y addition. It is because of reduction of α-Mg phase and presence of (Mg,Al)2Ca and Al-Y rich intermetallic phase at grain boundary and α-Mg matrix grains. Also, hardness value of yttrium (Y) containing alloys was increased with increasing Y contents. Compared to Mg-5Al-3Ca alloy, maximum strength and yield strength of the alloys with Y additions have slightly increased with increasing Y additions in the case of as-cast samples.

Abstract: Rare-earth modified coatings on 2024 aluminum alloy were prepared by sol-gel methods, aiming at improving the corrosion resistance with the environmental friendly features. The investigation put emphases on the effects of rare-earth additives on corrosion resistance and microstructure of sol-gel coatings. The results revealed that coated samples containing 2g·L-1 rare-earth not only delayed the incubation period of corrosion, but also hindered the development of it, and their corrosion rate decreased 80.3% compared with the bare ones and was 15.9% than the rare-earth free coated ones. The action of rare-earth on morphology and microstructure of sol-gel coatings for 2024 Al alloy was studied by SEM. High density good cohesion, and intact coverage were showed clearly ,which provided a reliable proof of the reformative effects of rare-earth additives.