Papers by Keyword: Rare Earth Element (REE)

Abstract: It is the important way to improve thermoelectric properties of skutterudite materials by doping with rare earth elements. The mechanisms of improving properties of bulk RE_xCo₄Sb₁₂ materials prepared by mechanical alloy and spark plasma sintering (MA-SPS) at 650°C were investigated by analyzing the composition, microstructure and atomic occupying locations. According the results it can be considered that the mechanism to improve the thermoelectric properties of rare earth elements is that rare earth element Ce in the samples mainly plays the doping role in reducing the resistivity of the sample and improving the conductivity, so that it makes the figure of merit ZT of samples increase significantly.

Abstract: In this paper, the impact deformation behavior of the as-rolled and annealed Mg-3%Li-1%Nd alloy was investigated by using the Hopkinson compressive bar. The effects of rolling and annealing on the high speed impact deformation behavior were analyzed. The relationship between microstructure evolution and impact fracture mechanism was discussed.

Abstract: Rare earth modified SO^2-₄/ZrO2 solid acid catalysts were prepared by coprecipitation and impregnation methods respectively. The properties of the samples were characterized by XRD (X-ray diffraction), FT-IR (Fourier transform infrared spectroscopy). And their catalytic performances were evaluated and investigated by transesterification of waste oil with methanol. The results showed that the catalyst containing 4% Ce and calcined at 550°C displayed the highest production rate and the better reuse ability than the others. 63.5% yield of fatty acid methyl ester was achieved. An analysis of XRD patterns reveal that the incorporation of rare earth into tetragonal zirconia stabilizes the compound, and the calcination at 550°C increases the reactivity of the catalyst by producing a greater fraction of active tetragonal zirconia. It can be seen from the FT-IR spectra that superacids structures are formed in the catalysts and the acidity is strengthened remarkably and the activated centre of the catalyst were increasesed.

Abstract: Polymetallic nodules/crusts are one of the most important mineral deposits in the ocean, in which iron, manganese, copper, cobalt, nickel and other metals are rich, and rare earth elements are rich, too. In this study, the contents of 11 rare earth samples in polymetallic nodules/crusts from the Pacific, Atlantic, Indian Ocean and north of the South China Sea are analyzed. The average content of rare earth in polymetallic nodules/crusts is 1265.57×10^-6, the average content of nodules is 1096.96×10^-6, and the average content of crust is 1623.88×10^-6. The enrichment of rare earth elements is controlled by iron and manganese oxides and clay minerals in nodules/crusts, which could absorb rare earth elements from seawater and sediment. Ce elements are highly enriched, making polymetallic nodules/crusts become the first used rare earth elements in mineral development.

Abstract: The rare earth elements (RE= Y, Sm, La, Ce) were used as alloying materials in Cu₅₀Zr₄₅Al₅ BMG, and their influences on the glass-forming ability and thermal stability were studied in this paper. All the samples remained in full metallic glass state with minor additions of Y, Sm and La. Increasing the amount of RE additions, the Cu₁₀Zr₇ and Zr₂Cu phases precipitated and glass transition temperature T_g and crystallization temperature T_x significantly decreased. The reduced glass transition temperature T_rg =T_g/T_l ranged from 0.592 to 0.611 and the γ parameter ranged from 0.393 to 0.409.

Abstract: The beautiful luster of freshwater pearls is closely related to its multiplayer microstructure. We present the improvement of their luster by refinement their superficial microstructure of pearls by rare earth cerium (REE) inducing grown. The pearls were cultured in freshwater containing 0 (control group), 0.5, and 1 mg·L^-1 REE Ce additive, respectively. As the concentration of Ce in the aqueous increasing, we find that their superficial microstructure take large change. The shape of the blocks that builds up the microstructure changes from anomalous to round discs, and finally to perfect regular square sheets. Correspondingly, the glossiness of the pearls changed with the microstructure, in which the pearls with the regular hexagonal blocks having the highest glossiness.

Abstract: By the way of adding rare earth element into the coating of electrode, this article has studied the effects of rare earth element erbium and cerium on the properties of welding surface. Experiment results show that adding rare earth element to the welding rod coating could make the grains fine, increase the content of acicular ferrite and improve the hardness and abrasion resistances of weld metal. After joining 0.3% Er and 0.3% Ce, the weld metal's macroscopic hardness achieves 39HRC, enhanced 23.8%. And the relative wear resistance enhanced 25.6%

Abstract: Influence of rare-earth oxide additives on the strength, fracture toughness and tribological behaviour of hot-pressed Si3N4 and Si3N4/SiC micro/nano-composites has been investigated. Four-point bending mode and ball on disc methods have been used for strength and wear tests and Single-Edge V-Notched Beam, Chevron Notched Beam, Indentation Strength and Indentation Fracture techniques for fracture toughness measurement. Fractography has been used to characterize strength limiting defects, fracture micromechanisms and damage mechanisms during the wear test. The strength values were strongly influenced by the present processing flaws. Wear behavior is significantly influenced by the chemical composition and by the microstructure of the materials.

Abstract: The strength and microstructure characteristics of the nugget in aluminum ally resistance spot welding were evaluated in this study with and without addition of rare earth elements Er, Ce. The strength was assessed using a small punch test mode and the microstructure was studied using an optical microscope, scanning electron microscope, and energy-dispersive spectroscope. Results indicated that the hardness and strength were increased about 10% after adding rare earth elements Er, Ce in the nugget. The grain of nugget zone was refined significantly. In the boundary and interior of the grain, a number of rare elements and its compounds were dispersed. This showed that parts of rare earth elements existed as solid solution in Al Matrix, part as the rare earth compounds. This improved that the elements not only can promote nucleation and refinement, but also can inhibit plastic deformation by hindering the dislocation movement. Thus they could play a strengthened role. The strengthening mechanism of the rare earth elements Er, Ce in the alloy nugget is mainly the second phase strengthening and fine grain strengthening.

Abstract: A new technique using slope vibration casting process during heating and isothermal holding period to prepare Al-7Si-2RE alloy has been studied. The small, near-spherical and non-dendritic microstructure with the semi-solid processing requirements has been obtained. Experiments show that the cooling method, pouring process and the convection of melt caused by slope vibration had significant effects on the formation of near-spherical primary gains. The water-cooled copper mold casting with slope vibration at the temperature near liquidus can obtain Al-7Si-2RE alloy with small homogeneous equiaxed grains, the average grain diameter is 48.3μm, and the average grain roundness is 1.92.