Addition Of Gd Research Articles

Solute atom mediated Hall-Petch relations for magnesium binary alloys

The solute atom mediated Hall-Petch relations for Mg-Y, Mg-Al, Mg-Gd and Mg-Zn alloys were reported at an equivalent nominal solute content of 0.35 at.%, namely, the obviously lower Hall-Petch slope k for Mg-Y (220 MPa μm1/2) and Mg-Gd (285 MPa μm1/2) than that for Mg-Al (324 MPa μm1/2) and Mg-Zn (322 MPa μm1/2) under compression along the extrusion direction (ED). The addition of Zn or Al forms a strong basal texture, which will lead to a {101¯2} twinning predominant deformation under compression along the extrusion direction (ED). In contrast, the addition of Gd or Y develops a weakened texture, and thus both {101¯2} twinning and basal slip are extensively activated. The lower k for basal slip and the favorable effect on activating {101¯2} twinning by the basal slip result in a lower k in Mg-Y and Mg-Gd.

Effect of Gd addition on non-isothermal and isothermal crystallisation of Cu–Zr–Al bulk metallic glass

Abstract The crystallisation kinetics of (Cu46Zr46Al8)100–xGdx (x = 0, 2 and 4 at.%) bulk metallic glasses in non-isothermal and isothermal conditions were studied by differential scanning calorimetry and X-ray diffraction. X-ray diffraction analysis shows that the crystallisation product Cu10Zr7 changes to Cu10Zr7 and Cu2Gd in the presence of Gd in non-isothermal and isothermal conditions. Crystallisation activation energy was calculated using the Kissinger and Ozawa methods in non-isothermal conditions and using the Arrhenius model in isothermal conditions. The results show that Gd addition triggers an increase in the energy barrier during crystallisation. The Johnson–Mehl–Avrami model was employed to analyse the crystallisation kinetics in the isothermal condition. The Avrami exponent, n, for Cu46Zr46Al8 is more than 2.5, which demonstrates that the crystallisation is mainly governed by diffusion-controlled three-dimensional growth with increasing nucleation rate. Comparably, n for (Cu46Zr46Al8)98Gd2 and (Cu46Zr46Al8)96Gd4 is 1.5 < n < 2.5, which suggests that the crystallisation is mainly determined by diffusion-controlled three-dimensional growth with decreasing nucleation rate.

Influence of Solution Heat Treatment on Microstructure and Tensile Properties of Gd-Treated Al-15% Mg2Si In-Situ Composites

ABSTRACT Microstructural alteration and tensile properties of Al-15% Mg2Si composite specimens was examined after addition of gadolinium (Gd) and conducting solution heat treatment. Various percentages of gadolinium (0.5, 1.0, 2.0 and 5.0 wt. % Gd) were added to the composite Al-15% Mg2Si composite. The specimens then solutionized at 500 °C for 4h followed by quenching. The results showed that regular morphology and small size of primary Mg2Si particles is achieved after addition of 1.0 wt.% Gd compared to untreated composite. Due to solutionizing effect, Mg2Si dissolution occurred which led to alter the morphology of primary Mg2Si particles to round shape. Tensile testing results revealed that enhancement in UTS and El% values owns to influence of both Gd addition and solution heat treatment on the Al-15% Mg2Si composite. The fracture surface of untreated composite depicted a cellular fracture, while the fracture surface of Gd treated and heat treated composite showed a ductile surface containing fine dimples, in which alteration of fracture mode is due to the role of Gd and heat treatment on microstructural modification, which results in reduction of potential sites for stress concentration and crack initiation areas.

The effects of in-situ ZrB2 particles and Gd on the solidification behavior and mechanical properties of AA6111 matrix composites

In this research work, the new AA6111 matrix composites reinforced by the cooperation of nano ZrB2 particles and Gd had been designed and fabricated via in situ reaction. The addition of Gd made the nano ZrB2 particles uniformly dispersed due to the reduction of solid-particle interfacial energy (σsp) by keeping the low-energy orientation relationship. Meanwhile, it promotes the formation of equiaxed grains whose formation is also based on the nano-sized reinforcing phases as the hindering of dendrite coherency points are related to the growth restriction factor (GRF) and as the pinning effect to the grain boundaries. The fluidity was improved because of uniform viscosity and dendrites avoided meeting with the neighboring ones by the entrapment of nano-sized reinforcing phases like AlGd and ZrB2. The results indicated that AA6111–0.5 wt. % Gd-2 vol. % ZrB2 composites possessed the longest fluidity length of 70 mm. Meanwhile, the composites displayed increases of 32.7 %, 47.3 % and 52.8 % in YS, UTS and elongation, respectively, compared to the matrix alloy. A notable lattice distortion of the matrix near the ZrB2 particles and AlGd phases was proclaimed via Geometric Phase Analysis (GPA) analysis. Strengthening mechanism comprehending yield strength, containing Orowan strengthening, grain refinement strengthening, was integrally elaborated.

Effects of Sn, Gd, and Mn additions on the surface chemistry and electrochemical behavior of CuAl-based alloys in sodium chloride solution

In the present work, the effects of Gd, Mn, and Sn additions on the surface chemistry and the electrochemical behavior of CuAl-based shape memory alloys were studied. Alloys were produced by arc furnace melting. The corrosion behavior was evaluated by electrochemical impedance spectroscopy (EIS) in 3.5 wt% NaCl solution up to 24 h of immersion. The surface chemical states were assessed by X-ray photoelectron spectroscopy (XPS). Correlation between the corrosion behavior and the surface chemistry is discussed. Gd addition increased the corrosion resistance of the CuAl-base alloy. Mn and Sn additions led to the formation of non-protective oxide films.

Microstructures and mechanical properties of as-cast Mg-Sm-Zn-Zr alloys with varying Gd contents

The effect of Gd content on the microstructure and tensile properties of as-cast Mg-Sm-Zn-Zr alloy has been systematically investigated. In the Mg-3Sm-0.5Zn-0.5Zr alloy, the intermetallic compounds with multiple morphologies are identified as Mg3Sm phase. In addition to Mg3RE phase, Mg5RE phase originated from Gd addition is observed in Gd-modified alloys. It should be noted that the lattice parameters of all the observed intermetallic compounds are significantly reduced by Zn segregation. The segregation behavior of Zn in Mg3Sm phase is inhibited to some extent by Gd addition due to the electronegativity difference between Sm/Gd and Zn elements. In addition, the increased Gd content effectively leads to much more accumulation of solute atoms in front of the liquid-solid interface during solidification, which can prominently promote nucleation in liquid region and then refine grains. The tensile yield stress of the present alloys is thus improved with increasing Gd addition. Finally, Gd-modified alloys exhibit significantly age-hardening effect, which can be mainly attributed to the high-volume fraction and high density nano-scale precipitates.

Noninvasive evaluation of elastic properties for magnesium-calcium biodegradable alloys

Bone injuries can be fixed and stabilized using degradable implants from magnesium - calcium alloys. Mg and Ca being natural elements in human body, they are easiest to be absorbed without causing toxicity problems. The aim of the paper is to present the effect of Gd and Mn addition in 0.5wt.% in order to improve elastic properties of Mg-Ca0.5-[E]x (E = Mn or Gd) and possibility to be used as biodegradable materials. The addition of Mn / Gd in the binary MgCa alloy modify the structural properties of the alloy (analyzed as elastic properties, respectively crystallographic structure). The measurements and the results calculus were carried out using the ultrasound methods and the Resonant Ultrasound Spectroscopy.

Photocatalytic degradation of atrazine under visible light using Gd-doped ZnO prepared by supercritical antisolvent precipitation route

Supercritical antisolvent precipitation route was employed for the first time to prepare Gd-doped ZnO photocatalysts to be tested in the photocatalytic degradation of atrazine under visible light. Physical-chemical characterization data show that the addition of Gd does not change the crystalline structure of ZnO and that Gd3+ ions are successfully introduced into the semiconductor lattice, leading to a decrease of band gap energy value and inducing the formation of oxygen vacancies inside the ZnO framework. The photocatalytic performances of the as-prepared samples are determined by analyzing the degradation of atrazine under visible light irradiation. The doped photocatalyst with a Gd loading of 0.7 mol% exhibits the highest photocatalytic activity under visible light irradiation compared to the other prepared photocatalysts. The possible reaction mechanism of the optimized photocatalyst is also discussed.

Strong Structural Modification of Gd to Co3O4 for Catalyzing N2O Decomposition under Simulated Real Tail Gases.

In this paper, Gd-promoted Co3O4 catalysts were prepared via a facile coprecipitation method for low-temperature catalytic N2O decomposition. Due to the addition of Gd, the crystallite size of Co3O4 in the Gd0.06Co catalyst surprisingly decreased to 4.9 nm, which is much smaller than most additive-modified Co3O4 catalysts. This huge change in the catalyst's textural structure endows the Gd0.06Co catalyst with a large specific surface area, plentiful active sites, and a weak Co-O bond. Hence, Gd0.06Co exhibited superior activity for catalyzing 2000 ppmv N2O decomposition, and the temperature for the complete catalytic elimination of N2O was as low as 350 °C. Meanwhile, compared with pure Co3O4, Ea decreased from 77.4 to 46.8 kJ·mol-1 and TOF of the reaction increased from 1.16 × 10-3 s-1 to 5.13 × 10-3 s-1 at 300 °C. Moreover, Gd0.06Co displayed a quite stable catalytic performance in the presence of 100 ppmv NO, 5 vol % O2, and 2 vol % H2O.

Grain Refinement and Enhancement of Critical Current Density in the V0.60Ti0.40 Alloy Superconductor With Gd Addition

The V-Ti alloys are promising materials as alternate to the commercial Nb-based superconductors for high current-high magnetic field applications. However, the critical current density (Jc) of these alloys are somewhat low due to their low grain-boundary density. We show here that grain refinement of the V-Ti alloys and enhancement of the Jc can be achieved by the addition of Gd into the system, which precipitates as clusters along the grain boundaries. Both the Jc and the pinning force density (FP) increase with the increasing Gd content up to 1 at. % Gd, where they are more than 20 times higher than those of the parent V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.60</sub> Ti <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.40</sub> alloy. Introduction of Gd into the system also leads to ferromagnetic (FM) correlations, and the alloys containing more than 0.5 at. % Gd exhibit spontaneous magnetization. In spite of the FM correlations, the superconducting transition temperature increases slightly with Gd-addition.

Effects of Gd Addition on the Microstructure and Tensile Properties of Mg–4Al–5RE Alloy Produced by Three Different Casting Methods

Effects of Gd Addition on the Microstructure and Tensile Properties of Mg–4Al–5RE Alloy Produced by Three Different Casting Methods

Artificial neural network modified constitutive descriptions for hot deformation and kinetic models for dynamic recrystallization of novel AZE311 and AZX311 alloys

Two novel alloys of AZE311 and AZX311 were designed through adding 1 wt% Gd and Ca to the AZ31 alloy, respectively. To study the hot deformation behavior, compression tests were conducted at temperatures of 200–350 °C and the strain rates of 0.001–0.1/s. The conventional strain-related Arrhenius-type constitutive equations were developed based on the true stress-strain curves. The activation energy for hot deformation of AZE311 and AZX311 were determined about 137.04 kJ/mol and 155.57 kJ/mol, respectively. Remarkable deviations existed between the predicted and the experimental results for the flow curves with obvious stress peaks. A dimensionless correction factor λ was introduced to the conventional constitutive model based on the artificial neural network (ANN) method. After the modification, the average absolute relative error (AARE) of the models decreased significantly from 10.331% to 1.428% for AZE311 and from 8.555% to 0.703% for AZX311. Kinetic models for the dynamic recrystallization (DRX) process were established. The average values of εc/εp of AZE311 and AZX311 were 0.54 and 0.58, respectively. The addition of Gd and Ca promoted the initiation and process of DRX and Gd had a larger effect. DRX occurred at the grain boundaries of AZX311 while more uniformly in AZE311. The actual DRX fraction at large strain was slightly lower than the predicted results. This was because the grain orientation factor on the deformation and the DRX process was not considered in the establishment of the Avrami-type DRX kinetic models. The effect of grain orientations on the DRX process was also discussed.

Crystal phase, electrical properties, and solid oxide fuel cell electrolyte application of scandia-stabilized zirconia doped with rare earth elements

ZrO2–10 ​mol% Sc2O3 (10ScSZ) has attracted attention as an electrolyte material for solid oxide fuel cells owing to its high conductivity. However, the phase transition between cubic and rhombohedral occurs in the range 500–600 ​°C, resulting in its rapid decrease in conductivity below 500 ​°C. In this study, we determined the elements that can eliminate phase transition in the range 500–600 ​°C for 10ScSZ to realize high conductivity for all temperature regions. Rare elements were incorporated to 10ScSZ. X-ray diffraction and conductivity measurements were used to confirm the occurrence of phase transition. The results noted that the addition of La, Ce, Pr, Nd, Sm, Eu, Gd, and Tb improved the conductivity of 10ScSZ below 500 ​°C, unlike that with the addition of Dy, Y, Ho, Er, Tm, Yb, Lu, and Sc. Further, although the addition of Ce to 10ScSZ was considered a solution, Nd and Sm were also noted to be effective additives.

A comparative study of (Ce) and (Gd) doping influence on the superconducting properties of YBCO ceramics

This work is devoted to investigate the structural and electrical properties of the Ce, Gd-doped YBCO superconductors bulk ceramics. YBa2-xRExCu3O7−δ (x = 0, 0.01, 0.05, 0.1) (RE = Gd, Ce) samples were prepared by means of conventional solid-state reaction. X-ray diffraction analysis was carried out to identify the present phases in the as-prepared samples followed by the determination of their lattice parameters. Fourier Transform Infrared Spectroscopy (FTIR) was used to identify the functional groups. Furthermore, the morphology and the surface roughness of the studied samples were characterized using Scanning Electronic Microscopy (SEM) and Atomic Force Microscopy (AFM). Vickers Micro-hardness of the as-prepared samples was examined. Besides, the electrical resistivity measurements were achieved to determine the critical transition temperature TC and the critical current density JC.The effect of Ce and Gd additions is clearly noticed in the obtained results, where all the prepared samples are superconductors with the presence of Y123 as a major polycrystalline phase. From the XRD patterns, the intensities of the Y123 corresponding peaks decrease with further increasing the Ce and Gd contents. In addition, the variation of the cell parameters was significant after additions of both Ce and Gd, which affect the grain size and the oxygen content of the YBa2-xRExCu3O7−δ system. An improvement of the structure and surface roughness is observed on SEM and AFM images. Likewise, Vickers micro-hardness has increased after the Ce and Gd additions. Although, the critical transition temperature TC was not further increased upon Ce or Gd additions compared to the undoped YBCO samples. Nevertheless, an exception has been recorded with an increase of TC for YBa2-xRExCu3O7−δ with (RE = Gd, x=0.01) to reach 88 K. In contrary, an improvement of the deduced critical current density JC was achieved for all Ce-doped YBCO samples unlike those of Gd-doped samples.

Investigation of the Wear Behavior of Surface Welding AZ91 and AZ91+Gd Alloys under Variable Loading Conditions

Adding rare earth elements to magnesium alloys is an effective way to improve their wear resistance. However, the effect achieved is closely related to the friction condition. In this paper, two different types of welding wires, AZ91 magnesium alloy and AZ91 + gadolinium (Gd), were used for surface welding. Dry sliding friction and wear experiments were performed on the surfacing alloys using the pin-on-disc test. The effects of Gd addition on the wear resistance and wear mechanism of the alloy were systematically studied under low to high loads. The results show that as the load increases, the friction coefficient of the surfacing AZ91 alloy gradually decreases as the wear rate increases. A mild–severe wear transition occurred at 100 N. The addition of Gd only slightly increased the wear rate under a load of 15 N. The wear rate was significantly decreased with loads in the range of 30 to 100 N and mild–severe wear transition was avoided. The influence of both Gd addition and load on the wear mechanism were considered. The overall wear resistance of the surfacing magnesium alloy was determined.

Investigation of phase evolution and Gd occupation in (Lu1-xGdx)2SiO5 lattice by Rietveld refinement and DFT simulation

Cerium-doped lutetium oxyorthosilicate (LSO:Ce, Lu2SiO5:Ce) is considered to be a typical scintillator with comprehensive good scintillation properties. The doping of Gd3+ elements with different concentrations strongly influences the structure and luminescence performance of LSO. The full concentration range of LGSO ((Lu1-xGdx)2SiO5) powders were prepared using a sol-gel method. The influences of the doping Gd3+ ion concentration on the phase evolution and lattice parameters of LGSO were investigated via X-ray diffraction (XRD), Rietveld refinement and density functional theory (DFT) simulations. It was found that the monoclinic crystal structure of LGSO gradually transitioned from C2/c to P21/c under elevated temperatures and phase transition temperature varied from 975 to 1400 ​°C as Gd replaced Lu. The lattice constants (a, b, and c) of LGSO lattice increased with the addition of Gd. The Rietveld refinement results indicate that doping Gd3+ in LGSO was prone to occupy the RE1 site rather than the RE2 site and Gd dopants was easily to form GdRE1-GdRE1 defect complex. The formation energy results of Gd3+ replacing different Lu3+ sites calculated by using the first-principles pseudopotential approach further proved this occupation mode. The intensity of photoluminescence of Ce:(Lu1-xGdx)2SiO5 attained the peak value when the content of Gd doping reached 0.05.

The role of Gd on the microstructural evolution and mechanical properties of Mg-3Nd-0.2Zn-0.5Zr alloy

This work was undertaken to investigate the specific role of element Gd on the microstructural evolution and mechanical properties of Mg-3Nd-0.2Zn-0.5Zr alloy. It is noticeable that, as the Gd content increases, the average grain size of as-cast alloys is continuously reduced, accompanied by the main secondary phases changing from Mg12Nd to Mg3Gd. Tensile tests reveal that addition of Gd (1.5–4.5 wt%) could lead to substantial enhancements of alloy strength (25–70 MPa) and an excellent combination of strength and ductility is obtained in the alloy with 4.5 wt% Gd addition (YS = 200 MPa, UTS = 343 MPa, EL = 5.4%). Microstructure characterization indicates that the improved solid-solution strengthening effect originated from increasing Gd additions plays a key role in the significant strength improvements obtained in as-quenched alloys. HAADF-STEM observations suggest that Gd is highly enriched in the dominantly disc-like prismatic β″ phases, leading to the strongly enhanced precipitation kinetics and greatly augmented volume fraction of β″ phase. A quantitative microstructural comparison of peak-aged specimens indicates that the significant strength enhancements should be primarily derived from the denser dispersion of β″ phases with higher aspect radio arising from Gd addition.

Environmental effects on degradation behavior in YbGdSi ternary system at elevated temperatures

The degradation behavior of Yb- and Gd-based ternary silicides (YbGdSi) was evaluated in Ar, 50 vol%air-H2O (air-H2O), and 100 vol%H2O (steam) environment and compared with the results obtained in a previous study conducted in air environment. Heat exposure at 1200 °C for 1, 2, 4, and 8 h was carried out in addition to thermogravimetric analysis up to 1200 °C. The results of these studies demonstrated that YbGdSi formed complex oxides in the (Yb- and/or Gd)-Si-O system and Yb2O3 was commonly formed for each environment. In addition, the resultant weight gain for YbGdSi in air, air-H2O and steam decreases by 2–5% in comparison with it for Yb3Si5. These results clearly indicate that the addition of Gd was effective in preventing the degradation of Yb-silicides.

The exposure of gadolinium at environmental relevant levels induced genotoxic effects in Arabidopsis thaliana (L.)

Rare Earth Elements (REEs) are increasingly being used in agriculture and are also used to produce high end technological devices, thereby increasing their anthropogenic presence in the environment. However, the ecotoxicological mechanism of REEs on organisms is not fully understood. In this study, the effects of gadolinium (Gd) addition on Arabidopsis thaliana (L.) were investigated at both physiological and molecular levels. Four treatments (0, 10, 50 and 200 μmol·L−1 Gd) were used in the exposure tests. Biomass, root length and chlorophyll content in shoots/roots were measured to investigate the plant’s physiological response to Gd stress. Random amplified polymorphic (RAPD)-Polymerase Chain Reaction (PCR) and methylation sensitive arbitrarily primed (MSAP)-PCR were used to investigate changes in genetic variation and DNA methylation of A. thaliana when exposed to Gd. At the physiological level, it was found that low concentration of Gd (10 μmol·L−1) could significantly increase the plant biomass and root length, while the growth of A. thaliana was significantly inhibited when exposed to 200 μmol·L−1 of Gd, yet the total soluble protein content in aerial plant parts increased significantly by 24.2% when compared to the control group. Among the 12 primers considered in the RAPD assessment, at the molecular level, only four primers revealed different patterns in their genomic DNA. Compared to the control group, the treatment with 50 μmol·L−1 of Gd was associated with lower polymorphism, while the treatment with 200 μmol·L−1 of Gd was associated with higher polymorphism. The polymorphism frequencies for the 50 μmol·L−1 of Gd and the 200 μmol·L−1 of Gd were 4.67% and 20.33%, respectively. The MSAP analysis revealed that the demethylation (D) type of Arabidopsis genomic DNA increased significantly under 10 and 50 μmol·L−1 of Gd, while the methylation (M) type was also significantly increased under 200 μmol·L−1 of Gd. Generally, the total methylation polymorphism (D+M) increased with an increase of Gd concentration. It was found that high concentrations of Gd appeared to cause DNA damage, but low concentrations of Gd (as low as 10 μmol·L−1) were associated with DNA methylation change. Further, it was verified by Real time Reverse Transcription PCR (RT-PCR) on the bands detected by the MSAP analysis, that the genes relative to processes including cell cycle, oxidative stress and apoptosis, appeared to be regulated by methylation under Gd stress. These findings reveal new insight regarding ecotoxicity mechanisms of REEs on plants.

Surface Modification of Biomedical MgCa4.5 and MgCa4.5Gd0.5 Alloys by Micro-Arc Oxidation.

The aim of this work was to characterize the structure and corrosion properties of the MgCa4.5(Gd0.5) alloys surface treated by the micro-arc oxidation (MAO) process. The MgCa4.5 and MgCa4.5Gd0.5 alloy samples were processed by MAO in an electrolyte composed of NaOH (10 g/dm3), NaF (10 g/dm3), NaH2PO4 (5 g/dm3), Na2SiO2·5H2O (10 g/dm3) and water. Two different voltages (120 V and 140 V) were used in the MAO process. The alloys protected by an oxide layer formed in the MAO were then the subject of corrosion resistance tests in an environment simulating the human body (Ringer’s solution). After the experiments, the resulting samples were investigated using SEM, XPS and EDS techniques. The addition of Gd affected the fragmentation of the coating structure, thereby increasing the specific surface; higher voltages during the MAO process increased the number and size of surface pores. Corrosion tests showed that the MgCa4.5Gd0.5 alloys were characterized by low polarization resistances and high corrosion current densities. The studies indicated the disadvantageous influence of gadolinium on the corrosion resistance of MgCa4.5 alloys. The immersion tests confirmed lower corrosion resistance of MgCa4.5Gd0.5 alloys compared to the referenced MgCa4.5 ones. The MgCa4.5 alloy with the MAO coating established at voltage 140 V demonstrated the best anticorrosion properties.