Papers by Keyword: Gadolinium

Abstract: Mg-5Y-3Nd-Zr-xGd (x=0 and 4 wt.%) alloys were prepared by metal mould casting, and aging behavior, mechanical properties and fracture morphology were investigated. The result shows that after T6 treatment, the massive eutectic phase in as-cast alloys dissolved and finer Mg5RE phase precipitated dispersively in the matrix, and mechanical properties were improved simultaneously. Mg-5Y-3Nd-4Gd-Zr alloy exhibits good age hardening behavior and the peak hardness is about 20% higher than the Gd-free alloy. Gd addition can significantly improve mechanical properties of the alloy especially at the elevated temperature. The ultimate tensile strength and yield strength of Mg-5Y-3Nd-4Gd-Zr alloy at 250°C, with the value of 276 and 168 MPa, respectively, are over 20% higher than those of the Gd-free alloy. It is mainly attributed to the increase and homogeneous distribution of the fine heat-resistant Mg5RE precipitate in the matrix.

Abstract: For uses at high temperatures, magnesium alloys containing rare earths have proven to be very suitable. High proportions of melting precipitates contribute to strengthening, even at temperatures above 200°C. If these alloys are extruded, their creep resistance rises even further due to the resulting fine-grained structure. In this paper, magnesium alloys with 10% Gd and additional small amounts of La and Nd are compared with WE43 for compression creep at temperatures of 240°C and stresses between 80 and 150 MPa. The minimum creep rates are determined and the stress exponent evaluated in accordance with the Norton equation. By calculating the threshold stress, the true stress exponents are determined.

Abstract: Pure TiO₂, Sm³⁺ and Gd³⁺ co-doping TiO₂ have been prepared by sol-gel method and characterized by the techniques such as XRD and SEM. The photocatalytic degradation of methylene blue (MB) in aqueous solution was used as a probe reaction to evaluate Pure TiO₂, Sm³⁺ and Gd³⁺ co-doping TiO₂ photocatalytic activity. The matrix distortion of TiO₂ increases after co-doping of Sm³⁺ and Gd³⁺ are clearly observed. The results show that co-doping of Sm³⁺ and Gd³⁺ inhibits the phase transformation of TiO₂ from anatase to rutile, decreases the diameter of TiO₂ nano-particles and significantly enhance the photocatalytic activity of TiO₂. When the co-doped amounts for Sm³⁺ and Gd³⁺ are 0.1% and 0.2%, its degradation rate reaches 99%.

Abstract: According to the low current efficiency of magnesium sacrificial anode, magnesium sacrificial anode material with gadolinium addition was investigated. The electrochemical properties of the material were measured by constant current method. The microstructure and composition of the anode material were characterized by metallurgical microscope and energy spectrum analysis. The results show that addition of gadolinium in magnesium sacrificial anode can refine grain size, change second-phase distribution, maximize current efficiency, and minimize potential of magnesium sacrificial anode. When the addition of gadolinium reaches 0.1%, the highest current efficiency is reached as much as 65.32%, which increases by 10%, compared with magnesium anode without gadolinium addition.

Abstract: Structure and magnetic properties of nanoscale [Gd/Ti]n multilayers prepared by rf-sputtering are studied. It is found that the decrease in the Gd layer thickness LGd leads to beginning of the structure transformation in Gd layers from the fine-crystalline to amorphous state when LGd becomes less than 2 nm. The Curie temperature TC decreases as a function of the Gd layer thickness in the same way as in early studied epitaxially grown Gd films, i.e. in case for which the finite-size effect plays most important role. A deviation of the TC(LGd) behaviour at very low LGd from the fit according to the finite-size law is probably caused by the island-like structure of the Gd layers.

Abstract: The rheo-diecasting (RDC) process, a novel semi-solid processing technology, was used to produce cast components with high integrity, fine and uniform microstructure, and therefore enhanced performance. AZ91D samples with 1-3 mass%Gd were solidified by RDC process. It was found that under intensive forced convection, the primary α-Mg phase produced inside the twin-screw slurry maker had fine particle size, spherical morphology and uniform distribution throughout the samples. Microstructure observations showed that Gd addition resulted in the formation of Al2Gd which dispersed in the α-Mg matrix. The size and amount of β-Mg17Al12 phase was reduced and its continuity was broken, which was the main reason for improving mechanical properties of the AZ91D alloy at high temperatures. The amount of Al2Gd particles increased with increasing Gd addition. From EPMA quantitative analysis, almost all Gd reacted with Al, leading to the low concentration of Gd in the α-Mg matrix. The Vickers hardness increased monotonously from HV=50.4 to HV=67.3 with increasing amount of Gd. This improvement was attributed to the consummation of aluminum in melt by precipitation of the Al2Gd phases.

Abstract: A visible-light-active nitrogen and gadolinium codoped TiO2 catalyst was synthesized by the sol-gel route. For comparison, Gd-doped sample, N-doped sample, and pure titania were prepared through the same method, without adding the corresponding dopants. The as-prepared photocatalysts were characterized by X-ray diffraction (XRD) and Uv-vis spectra. The results showed that the codoped photocatalyst exhibited a smaller size than the undoped titania. The transformation from anatase to rutile was suppressed by doping with N and Gd atoms. Furthermore, the absorbance spectra of N, Gd-codoped TiO2 exhibited a significant red shift to the visible region. The photocatalytic activity of N, Gd-codoped TiO2 was evaluated by photodegradation of methyl orange under visible light irradiation. This codoped sample exhibited enhanced photocatalytic activity compared to N-doped TiO2, Gd-doped TiO2, and pure TiO2. The improvement of the photocatalytic activity was ascribed to the synergistic effects of the N and Gd co-doping.

Abstract: New gadolinium-yttrium zirconate thermal barrier coating(TBC) material is deposited by electron beam PVD method, as an alternative to YSZ TBC layer for gas turbine blade applications. XRD analysis reveals that the new TBC material consists of thermally stable pyrochlore structure. Hertzian and nanoindentation evaluations reveal that gadolinium zirconate materials show superior properties as a TBC candidate material with high mechanical properties. The Y2O3 doping improved hardness and elastic modulus of TBC layers. The indentation stress-strain curves by Hertzian indentation and the load-penetration depth curves by nanoindentation indicate that the new TBC layer has higher damage resistance combined with superior thermal insulation properties rather than commercial YSZ coatings.

Abstract: The increase of the efficiency for gas turbines leads to the increasing combustion-chambertemperatures. Rapid degradation of the conventional yttria-stabilized zirconia coatings does not fulfill therequirements at these temperatures for a reliable thermal barrier coatings (TBCs) due to the phasetransformation of zirconia and the sintering behaviour. Therefore, it is very important to develop novel ceramic materials for TBCs with low thermal conductivity and long-term stability at high temperatures.In this paper, the developments of potential novel ceramic materials for TBCs with low thermalconductivity are reviewed.

Abstract: Yttria-stabilized zirconia (YSZ) ceramic is considered as an attractive matrix for nuclear applications, such as inert matrix for the destruction of excess plutonium or good host material for nuclear waste storage. Some actinide elements in high-level radioactive wastes can be simulated by cerium as tetravalent actinide, and gadolinium as trivalent actinide or neutron absorber. The present work is focused on the diffusion study of Ce and Gd in YSZ single crystal and high density polycrystals. A thin film of Ce or Gd was deposited either by spin-coating method or by physical vapour deposition on the surface of polished samples. The diffusion experiments were performed from 1173 to 1673 K under air. The Ce or Gd diffusion profiles were determined by secondary ion mass spectrometry. The experiments led to the determination of effective diffusion coefficient, Deff, bulk and grain boundary diffusion coefficients, DB and DGB. The dependence of these diffusion coefficients on temperature is described by means of Arrhenius equations and the diffusivity is compared with literature.