Effects Of Rare Earth Elements Research Articles

Effect of RE elements on the microstructural evolution of as cast and SIMA processed Mg–4Al alloy

In the present article, the effect of Rare Earth elements on the microstructural development of as cast and semisolid Mg–4Al alloy produced by SIMA process is studied. Investigation conducted by metallographic observation, scanning electron microscope and quantitative metallographic methods. Results showed that alloy's dendrites turn into larger fully dendritic shape with sharp and narrow arms from equiaxed rosette type as the amount of RE elements increased from 0 through 4%. The effect of RE elements on the microstructure of the treated-alloys was detectable through elimination of vast number of intragranular liquid droplets as well as by decreasing kinetic of microstructural changes. It was shown that the trend of grain coarsening decreased drastically by addition of RE elements to the Mg–4Al alloy during partial remelting at 610 °C. Moreover, the effect of REs on the other parameters such as fraction of liquid, shape factor and particle size was studied.

Microstructure and creep behavior of the rare-earth doped Mg–6Zn–3Cu cast alloy

The effect of 1, 2 and 3wt.% rare earth (RE) additions on the microstructure and creep resistance of the Mg–6Zn–3Cu alloy (ZC63) was investigated by impression creep tests in the temperature range 423–498K and under punching stresses in the range 150–700MPa for dwell times up to 3600s. The results showed that the creep strength of the base alloy was remarkably improved by RE addition. This was attributed to the grain refinement effect of RE elements, and formation of thermally stable Mg12RE, MgRE, and Cu2RE compounds which strengthen both matrix and grain boundaries during creep deformation. The creep behavior can be divided into two stress regimes, with a change from the low-stress regime to the high-stress regime occurring, depending on the test temperature, around 0.017<σimp/G<0.037. Based on the steady-state power-law creep relationship, the stress exponents of about 4.4–6 and 7–12.7 were obtained at low and high stresses, respectively. The creep activation energies were found to be in the range 73–78 and 122–130kJ/mol, at low- and high-stress regimes, respectively. It is suggested that the operative creep mechanism is pipe-diffusion-controlled dislocation viscous glide in the low-stress regime, and dislocation climb with some sort of back stress, similar to those noted in dispersion strengthening alloys, in the high-stress regime.

Effects of Rare Earth Elements on the Quality of Nugget in Aluminum Alloy Spot Welding

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.

Effect of yttrium on the cyclic oxidation behaviour of HP40 heat-resistant steel at 1373 K

The effect of rare earth elements on cyclic oxidation behaviour of HP40 at 1373 K has been investigated. The results demonstrate that 0.06 wt.% addition of Y effectively improves the cyclic oxidation resistance of such Si-containing alloy. By observing the cross-section of the scale, it is found that Y facilitates the formation of Si-rich internal oxide, which improves the spalling resistance of the scale. As a result, compared with the sample without Y addition, on which the spinel layer is discontinuous, a continuous duplex scale of chromia overlaid by manganese-rich spinel is kept at the outmost of the Y-modified alloy.

Effects of rare-earth elements on the glass-forming ability and mechanical properties of Cu46Zr47−x Al7M x (M = Ce, Pr, Tb, and Gd) bulk metallic glasses

Cu46Zr47−x Al7M x (M = Ce, Pr, Tb, and Gd) bulk metallic glassy (BMG) alloys were prepared by copper-mold vacuum suction casting. The effects of rare-earth elements on the glass-forming ability (GFA), thermal stability, and mechanical properties of Cu46Zr47−x Al7M x were investigated. The GFA of Cu46Zr47−x Al7M x (M = Ce, Pr) alloys is dependent on the content of Ce and Pr, and the optimal content is 4 at.%. Cu46Zr47−x Al7Tb x (x = 2, 4, and 5) amorphous alloys with a diameter of 5 mm can be prepared. The GFA of Cu46Zr47−x Al7Gd x (x = 2, 4, and 5) increases with increasing Gd. T x and T p of all decrease. T g is dependent on the rare-earth element and its content. ΔT x for most of these alloys decreases except the Cu46Zr42Al7Gd5 alloy. The activation energies ΔE g, ΔE x, and ΔE p for the Cu46Zr42Al7Gd5 BMG alloy with Kissinger equations are 340.7, 211.3, and 211.3 kJ/mol, respectively. These values with Ozawa equations are 334.8, 210.3, and 210.3 kJ/mol, respectively. The Cu46Zr45Al7Tb2 alloy presents the highest microhardness, Hv 590, while the Cu46Zr43Al7Pr4 alloy presents the least, Hv 479. The compressive strength (σ c.f.) of the Cu46Zr43Al7Gd4 BMG alloy is higher than that of the Cu46Zr43Al7Tb4 BMG alloy.

Effect of rare earth elements on the microstructure and texture development in magnesium–manganese alloys during extrusion

Single additions of the rare earth (RE) elements cerium, yttrium or neodymium have been made to magnesium–manganese alloys in order to investigate their influence on the microstructure and texture formed during indirect extrusion and the resulting mechanical properties. Whereas the binary Mg–Mn alloy M1 exhibits a 〈10.0〉 or 〈10.0〉–〈11.0〉 fibre texture depending on the extrusion rate, the RE-containing alloys exhibit weaker recrystallisation textures and the formation of a new texture component. The preferential growth of grains having 〈11.0〉 parallel to the extrusion direction was hindered in these alloys. For the rare earth elements used in this work it appears that Nd is a much stronger texture modifier compared to Ce or Y in Mg–Mn alloys. The weaker texture leads to increased ductility, lower yield and ultimate stresses, but a decrease in the asymmetric yield behaviour of the extruded bars.

Viscosity and thermal expansion of rare earth containing soda–lime–silicate glass

Viscosity, coefficient of thermal expansion, glass transition temperature and dilatometric softening temperature of soda–lime–silicate glass doped with rare earth oxides (La 2O 3, CeO 2, Nd 2O 3) were investigated by the rotating crucible viscometer and dilatometry, the melting temperature and activation energy for viscous flow of the studied melt were derived on the basis of Arrhenius equation, in order to reveal the effects of rare earth elements on the behavior of soda–lime–silicate glass. The results show that introduction of rare earth oxides increases the coefficient of thermal expansion, decreases viscosity of soda–lime–silicate glass, and Nd 2O 3 is an exception in viscosity. The glass transition temperature, dilatometric softening temperature, melting temperature and activation energy for viscous flow of soda–lime–silicate glass doped with rare earth oxides increase with increasing cationic field strength of corresponding rare earth ions.

Effects of rare earth elements and Ca additions on high temperature mechanical properties of AZ31 magnesium alloy processed by ECAP

High temperature mechanical properties of equal channel angularly pressed (ECAPed) AZ31 magnesium alloy with 0.6%RE, 0.6%Ca and 0.3%RE–0.3%Ca additions were investigated. After extruding, the materials were ECAPed for 4 passes using route B C. Due to the textural effects induced by ECAP, the flow stress of the ECAPed AZ31 was lower than that of the extruded alloy at 523 K while tensile ductility was not changed. Thermal stability of the grain structure was achieved by RE-and Ca-containing particles, mainly due to the suppression of grain growth. Addition of the RE elements and calcium increased tensile strength mainly by dispersive strengthening effects of particles. The improved tensile ductility of the extruded material, however, was achieved by the presence of stable fine grains. Among all tested materials, AZ31-0.6%RE showed the maximum ductility of 198% at 523 K and a strain rate of 10 −4 s −1.

Effect of Rare Earth Element on Microstructure and Mechanical Properties of Mg-Sn-Ca Alloys

In the present work, the effect of Nd addition on microstructure change, precipitation behaviours and mechanical properties, of Mg-5Sn-3Ca based alloys were investigated. With increasing of Nd addition, size of the Mg-Sn-Ca ternary phases with fine needle shape (A-type) was decreased and volume fraction of these phase were increased. As Nd was increase from 0.5, 1.0 and 3.0 wt.%, size and volume fraction of Mg2Sn with coarse needle shape phase (B-type) was decreased. However, in 3.0 wt.% Nd containing alloy, size of these Mg2Sn phase was smaller than that of 0.5 and 1.0 wt% Nd addition alloy and volume fraction of these phase was decreased.

Effect of Rare Earth Elements on the Valence Electron Structure and Properties of ZrB&lt;SUB&gt;2&lt;/SUB&gt; Ceramics

Effect of Rare Earth Elements on the Valence Electron Structure and Properties of ZrB&lt;SUB&gt;2&lt;/SUB&gt; Ceramics

Effects of La3+ and Eu3+ on outward potassium channels in Vicia guard cells

Effects of La3+ and Eu3+ on outward potassium channels (Kout+) in Vicia guard cells have been studied by patch clamping technique. Extracellular La3+ inhibited Kout+ currents with a half-inhibition concentration (IC50) of 81 µmol·L−1. Interestingly, intracellular La3+ activated Kout+ currents at a free concentration of 1.13 × 10−14 mol·L−1, and inhibited Kout+ currents at a free concentration of 5.86 × 10−14 mol·L−1. Extracellular Eu3+ also activated Kout+ currents at concentrations of 10 µmol·L−1 and 50 µmol·L−1, and inhibited Kout+ currents at concentrations of more than 1 mmol·L−1. The effects of La3+ and Eu3+ on Kout+ currents may contribute to regulation of the plant water status, which may be one of the mechanisms of the biological effect of rare earth elements.

Effects of Ce and La Additions on the Microstructure and Mechanical Properties of Sn-9Zn Solder Joints

The effects of rare-earth elements on the microstructure and mechanical properties of Sn-9Zn alloys and solder joints in ball grid array packages with Ni/Au(ENIG) surface finishes have been investigated. Metallographic observations showed that (Ce0.8Zn0.2)Sn3 and (La0.9Zn0.1)Sn3 intermetallic compounds appeared in the solder matrix of Sn-9Zn-0.5Ce and Sn-9Zn-0.5La alloys, respectively. Both fiber- and hillock-shaped tin whiskers were inhibited in the Sn-9Zn-0.5Ce solder, while tin fibers were still observed on the surface of oxidized (La0.9Zn0.1)Sn3 intermetallics in Sn-9Zn-0.5La after air exposure at room temperature. Mechanical testing indicated that the tensile strength of Sn-9Zn alloys doped with Ce and La increased significantly, and the elongation decreased, in comparison with the undoped Sn-9Zn. The bonding strengths of the as-reflowed Sn-9Zn-0.5Ce and Sn-9Zn-0.5La solder joints were also improved. However, aging treatment at 100°C and 150°C caused degradation of ball shear strength in all specimens. During the reflowing and aging processes, AuZn8 intermetallic phases appeared at the interfaces of all solder joints. In addition, Zn-rich phases were observed to migrate from the solder matrix to the solder/pad interfaces of the aged specimens.

The effect of rare earth elements on the kinetics of the isothermal coarsening of the globular solid phase in semisolid AZ91 alloy produced via SIMA process

In the present study, the effects of rare earth (RE) elements on the microstructure and coarsening kinetics of the solid globular particle in the semisolid slurry of AZ91 magnesium alloy have been studied at 570 °C and 580 °C. The results showed that the coarsening kinetics of the solid globular particles in semisolid slurry of AZ91 alloy satisfies the Ostwald ripening theory. It was shown that the coarsening rate of the solid particles decreases by adding RE elements into AZ91 alloy, specially at 580 °C, which results in the smaller particles size. It was attributed to the solid–liquid interfacial energy reduction due to the addition of RE elements.

Solvent extraction study of rare earth elements from chloride medium by mixtures of sec-nonylphenoxy acetic acid with Cyanex301 or Cyanex302

The extraction of rare earth elements from chloride medium by mixtures of sec-nonylphenoxy acetic acid (CA100) with bis(2,4,4-trimethylpentyl) dithiophosphinic acid (Cyanex301) or bis(2,4,4-trimethylpentyl) monothiophosphinic acid (Cyanex302) in n-heptane has been studied. The synergistic enhancement of the extraction of lanthanum (III) by mixtures of CA100 with Cyanex301 has been investigated using the methods of slope analysis and constant mole. The extracted complex of lanthanum (III) is determined. The logarithm of the equilibrium constant is calculated as – 1.41. The formation constants and the thermodynamic functions, Δ H, Δ G, and Δ S have also been determined. Moreover, the different extraction effects of rare earth elements in the mixing systems of CA100 with Cyanex301 or Cyanex302 have been employed to consider the possibility of separating rare earth elements according to their separation factors.

Effects of rare-earth elements and Ca additions on the microstructure and mechanical properties of AZ31 magnesium alloy processed by ECAP

The effects of 0.6wt.%RE, 0.6wt.%Ca and 0.3wt.%RE+0.3wt.%Ca additions on the microstructure and mechanical properties of equal channel angularly pressed (ECAPed) AZ31 magnesium alloy were investigated. After extruding, the materials were ECAPed for 1, 2, and 4 passes using route BC. After 4 passes of ECAP, AZ31 showed lower yield stress and higher ductility respect to the as-extruded condition, indicating that texture softening has overcome the strengthening effects of grain refinement. The introduction of RE elements and calcium in the AZ31 resulted in further refinement of the grain structure, mainly due to the suppression of the dynamic recrystallization by RE- and Ca-containing particles during the hot deformation process. Addition of the RE elements and calcium increased tensile strength mainly by dispersive strengthening effects of particles, and improved tensile ductility of the extruded material by texture modification.

Effect of La 2O 3 addition on the microstructure, hardness and abrasive wear behavior of flame sprayed Ni based coatings

This paper describes the effect of rare earth elements (La 2O 3) on the microstructure; hardness and abrasive wear behavior of Ni based flame sprayed coatings. The mechanical and tribological properties of the coatings can be significantly improved by refinement of grain structure of the coatings. A commercially available Ni based powder was modified with the addition of La 2O 3 (0.4–2 wt.%) to refine the grain structure of coatings. Unmodified and La-modified coatings were investigated in respect of microstructure, hardness and abrasive wear behavior. It has been observed that an optimal addition of La 2O 3 (1.2 wt.%) refines the grain size, improves hardness and abrasive wear resistance of the coatings. The XRD of the unmodified and La-modified coating with optimum addition of La 2O 3 (1.2 wt.%) was also carried out to identify the various phases present in the coating.

Effect of rare earth elements on electrochemical properties of La–Mg–Ni-based hydrogen storage alloys

La 0.60R 0.20Mg 0.20(NiCoMnAl) 3.5 (R = La, Ce, Pr, Nd) alloys were prepared by inductive melting. Variations in phase structure and electrochemical properties due to partial replacement of La by Ce, Pr and Nd, were investigated. The alloys consist mainly of LaNi 5 phase, La 2Ni 7 phase and LaNi 3 phase as explored by XRD and SEM. The maximum discharge capacity decreases with Ce, Pr and Nd substitution for La. However, the cycling stability is improved by substituting Pr and Nd at La sites, capacity retention rate at the 100th cycle increases by 13.4% for the Nd-substituted alloy. The electrochemical kinetics measurements show that Ce and Pr substitution improves kinetics and thus ameliorates the high rate dischargeability (HRD) and low temperature dischargeability. The HRD at 1200 mA g −1 increases from 22.1% to 61.3% and the capacity at 233 K mounts up from 90 mAh g −1 to 220 mAh g −1 for the Ce-substituted alloy.

Effects of erbium on microstructure and mechanical properties of as-cast Mg-7Zn-3Al alloy

Mg-7Zn-3Al- xEr ( x=0.1, 0.4, 0.7) magnesium alloys were prepared by permanent mould casting. The effects of rare earth element of erbium on the microstructure and mechanical properties of as-cast Mg-7Zn-3Al alloy at both room temperature and elevated temperatures were investigated with optical microscopy, scanning electron microscopy/energy dispersive X-ray spectroscopy, differential scanning calorimetry, and tensile testing. The results show that the quasi-continuous grain boundary networked τ(Mg 32(Al, Zn) 49) phases are changed into discontinuous globular particles due to the addition of Er. Spherical Al-Er compounds are also identified in the matrix. The mechanical testing reveals that, with Er addition, the elevated temperature tensile properties can be remarkably improved. The microstructure evolution during tensile deformation under both temperature and stress and its effects on the mechanical properties were further discussed.

Review on the effects of rare earth elements on seed germination

稀土元素在农业上得到了广泛应用，产生了显著的经济效益。适量稀土浓度可促进植物生长，提高种子萌发能力，还可增强植物的抗逆性并对一些植物病害具有一定的防治作用。本文从稀土元素对植物种子萌发的影响和影响萌发的机理两方面分析了稀土元素对植物萌发阶段影响的最新研究成果，重点介绍了稀土元素对植物发芽率（势）、发芽指数和活力指数的影响，以及稀土元素对酶合成、呼吸作用、吸水、物质分解和激素变化的影响机理，为稀土农用技术的研究提供新思路。

Observation on Probability Function by Measuring Time Series of Electric Property in Gadolinium Nitrate Crystal at Low Temperature

The observation of the dynamics of fluctuation in a nonlinear nonequilibrium material system in a low-temperature region gives valuable information for developments in the physics of both nonlinear quantum dynamics and nonequilibrium thermodynamics. Rare-earth nitrate crystals have the same crystal habit and triclinic space group. The crystal structure is independent of temperature above 80K. Nonlinear and nonequilibrium phenomena have been observed in rare-earth nitrate crystals. Distinct intermittent nonperiodic oscillations (bursts) were observed in the measurement of the time series data for conductivity. The phenomena could be classified into a macroscopic chaos in a dissipative dynamical system. The effect of rare-earth elements on the fluctuation was found in the electric properties of the crystals. The characteristic properties of rare-earth nitrate crystals were observed in the electric measurement of the crystals in the lower-temperature region below 200K. We have measured the time series of ac conductivity, and clarified unknown properties of rare-earth nitrate crystals in the low-temperature region below 200K. A singularity in the probability distribution function was observed by measuring the time series of ac conductivity in the direction perpendicular to the c-axis of the gadolinium nitrate crystal at 11K. The result was given in the present note. A single crystal was grown in a gadolinium nitrate aqueous solution by evaporation at temperatures from 312 to 309K for 1994 h. The sample was 0:040 0:005 cm in thickness and 0:276 0:005 cm in area. The time series data of ac conductivity at 2 kHz were measured using a twophase digital lock-in amplifier (EG&G Princeton Applied Research 5210) and an analog memory recorder (Yokogawa AR1100). The experimental apparatus was controlled by a computer with a general-purpose interface bus (GPIB). The time series data of ac conductivity perpendicular to the c-axis (c2-axis) were measured at a sensitivity within 10 11 1 cm . The measurement was performed under isothermal condition controlled within 0:1K using a closed-cycle refrigerator system (Janis Research CCS-300). At 11K, with a sampling time of 50ms, 5000 data points were collected for the time series data. Figure 1 shows the time series of the fluctuation 0 for the real part 0 of the complex conductivity at 2 kHz for the electric field E applied in the direction perpendicular to the c-axis at 11K in a cooling cycle. The fluctuation 0 is defined by the relation 0 1⁄4 0 0, where 0 is the average derived from the data of the conductivity 0, given by 0 2:0298 10 6 1 cm 1 at 11K. Bursts occur randomly as nonperiodic unstable oscillations in the time series of 0 at the temperature. The probability distribution function of the time series data { 0} on the semilogarithm scale is given in Fig. 2. The probability function could not be classified into both standard Gaussian and Lorentzian line shapes. The functional form of the probability function is symmetrical and has a sharp peak as seen from Fig. 2. Figure 3 shows a log– log plot of the probability distribution function versus the fluctuation 0. The result indicates that the singularity of the probability function is proportional to ð 0Þ , where the exponent s of the power law is given by s 1⁄4 1:43 0:2. The temperature variation in the probability functions was observed in other rare-earth nitrate crystals, which were classified into the Gaussian one. 0 50 100 150 200 250 -10 -5 0 5 10