Rare Earth Mixtures Research Articles

Primary Creep of Die-Cast Magnesium–Rare Earth Based Alloys

The creep response of die-cast Mg-2.5RE-0.6Zn (wt pct) alloys with different rare earth (RE) mixtures has been investigated at 177 °C. The Nd-rich alloy displayed significantly lower primary creep than its La-rich counterpart. Microstructural analyses revealed the formation of additional Nd-containing precipitates on dislocations in the Nd-rich alloy during creep. The degree of supersaturation of RE solutes in the α-Mg matrix after die casting is suggested to be the key factor in influencing primary creep.

On the Creep Resistance of HPDC Mg-RE Based Alloys

This paper presents an analysis, based on microstructural observations by transmission electron microscopy, of the influence of chemical composition on creep resistance of high pressure die casting (HPDC) Mg-4RE-0.6Zn alloys. The improved creep resistance, by increasing the Nd/La ratio of the rare earth (RE) mixture, is shown to be associated with the supersaturation of Nd solute in the -Mg matrix, evidenced by the formation of Nd-rich precipitates on dislocations after a thermal ageing treatment. The result indicates that solid solution/precipitation strengthening of the -Mg matrix is important to the creep resistance of HPDC Mg-RE based alloys.

Synergistic separation of yttrium ions in lanthanide series from rare earths mixture via hollow fiber supported liquid membrane

Separation of yttrium ions from the mixture of rare earths in lanthanide series has been examined by a microporous hydrophobic hollow fiber supported liquid membrane. Cyanex 272 and TBP in kerosene are used separately as an extractant. Nitric acid solution is used as a stripping solution. Increasing the concentration of Cyanex 272 increases the percentages of extraction and stripping of yttrium from rare earths but slightly percentages are obtained by TBP. Interestingly, when TBP is added with Cyanex 272, the percentages of extraction and stripping increases. This is due to the synergistic effect of the extractants. Moreover, yttrium can be selectively extracted and stripped more than other lanthanide ions because the equilibrium constant decreases with an increase in atomic number or decreases with the ionic radius of the lanthanides. In other words, yttrium is separated selectively due to the smallest ionic radius while other lanthanides are separated with a decrease in ionic radius or an increase in atomic number.

Preparation of ceria nanoparticles

Ceria nanoparticles (D = 2.4−6.9 nm) with the fluorite structure have been prepared via oxidative precipitation of cerium from a solution of a rare-earth chloride mixture, followed by acid washing.

Effect of rare earth elements on in vitro rumen microbial fermentation and feed digestion

The objectives of this study were to investigate the effects of rare earth elements (REEs) on in vitro rumen fermentation, gas production, microbial protein synthesis and nutrient digestion using in vitro batch culture and continuous culture technique. A mixture of REE containing (g/kg) 380 g of LaCI 3·6H 2O, 521 g of CeCI 3·6H 2O, 30 g of PrCI 3·6H 2O and 69 g chlorides of other light REEs. The experimental diet consisted of 885 g/kg barley grain, 84 g/kg barley silage and 31 g/kg supplement (dry matter (DM) basis). Diet supplemented with different dosages of REE (control, no additional REE; low, 400 mg/kg REE; and high, 800 mg/kg REE, DM basis) were incubated for 4, 8, 14 and 24 h in diluted rumen fluid. At the end of 24 h of incubation, gas production and concentration of volatile fatty acid (VFA) linearly increased with increasing REE supplementation; whereas, influence of REE supplementation on VFA profile was marginal. Dry matter disappearance was not affected (P>0.10). Six dual-flow continuous culture fermenters were used in a replicated 3 × 3 Latin square with same treatments and same diet used in the batch culture. Mean ruminal pH (5.71) and total VFA (93.6 mM) concentration were not affected by supplementation of REE. The molar proportion (mol/100 mol) of acetate (39.1) and propionate (50.5) was similar among the treatments. However, the proportion (mol/100 mol) of butyrate was higher with the high REE (6.6) than with low REE (5.3) or the control (5.8). Ruminal true digestibilities of organic matter (OM) (0.785, 0.811 and 0.828), acid detergent fibre (0.360, 0.431 and 0.432) and crude protein (0.496, 0.590 and 0.589) for control, low and high REE, respectively, linearly increased with increasing REE supplementation, whereas, the increase in ruminal digestibility from low to high dosage of REE was minimal. Microbial nitrogen (N) production (g/day) and microbial efficiency (g N/kg of truly fermented OM) were not affected by treatments. Improvement of ruminal digestibility of OM due to REE supplementation was attributed to the increase in digestibility of fibre and degradability of protein. The results suggest that REE supplementation improved ruminal fibrolytic and proteolytic activities.

Retention, Thermodynamics and Adsorption Profile of Th(IV) Ions onto 1‐(2‐Pyridylazo)‐2‐Naphthol (PAN) Loaded Polyurethane Foam from Acetate Media and its Separation from Rare Earths

The sorption behavior of 2.7×10−5 M solution of Th(IV) ions on 1‐(2‐pyridylazo)‐2‐naphthol (PAN) loaded polyurethane foam (PUF) has been investigated. The quantitative sorption was occurred from pH 6 to 9 from acetate buffer solutions. The sorption conditions were optimized with respect to pH, shaking time, and weight of sorbent. The sorption data followed the Freundlich, Langmuir, and Dubinin‐Radushkevich (D‐R) isotherms very successfully at low metal ions concentration. The Freundlich isotherm constant (1/n) is estimated to be 0.22±0.01, and reflects the surface heterogeneity of the sorbent. The Langmuir isotherm gives the maximum monolayer coverage is to be 8.61×10−6 mol g−1. The sorption free energy of the D‐R isotherm was 17.85±0.33 kJ mol−1, suggesting chemisorption involving chemical bonding was responsible for the adsorption process. The numerical values of thermodynamic parameters such as enthalpy (ΔH), entropy (ΔS), and Gibbs free energy (ΔG) indicate that sorption is endothermic, entropy driven, and spontaneous in nature. The adsorption free energy (ΔGads) and effective free energy (ΔGeff) are also evaluated and discussed. The effect of different anions on the sorption of Th(IV) ions onto PAN loaded PUF was studied. The possible sorption mechanism on the basis of experimental finding was discussed. A new separation procedure of Th(IV) from synthetic rare earth mixture using batch, column chromatography, and squeezing techniques were reported.

Study and characterization of a metal hydride container

Sorption performance tests were conducted on a small metal hydride hydrogen-storage prototype container. The relevant aspects considered are mainly the activation behavior, desorption capacity, desorption flow rates and heat transfer. The alloy employed to fill the container is of the AB 5 intermetallic type, its chemical composition is MmNi 4.7 Al 0.3 (Mm stands for “mischmetal,” a mixture of rare earths) and its equilibrium pressure at room temperature is about 300 kPa, which is adequate for the required operating conditions. Pressure evolution was monitored during discharge tests at constant temperature for different flow rates and initial charge pressures. A decrease in the dynamic pressure measured during the discharge was observed as a function of time, in agreement with the alloy plateau pressure slope. Also, a decrease in the dynamic discharge pressure with increasing discharge flow rates was found, associated with the hydride decomposition kinetics and heat transfer conditions.

The effects of mischmetal, cooling rate and heat treatment on the eutectic Si particle characteristics of A319.1, A356.2 and A413.1 Al–Si casting alloys

The effects of mischmetal, cooling rate and heat treatment on the eutectic Si particle characteristics of A319.1, A356.2 and A413.1 Al–Si casting alloys were investigated and recorded for this study. Mischmetal was added to the alloys in the form of Al–20% mischmetal master alloy to produce four levels of mischmetal addition (0, 2, 4 and 6 wt%). The alloys were also modified with strontium (∼250 ppm) to study the combined modification effect of Sr and mischmetal at both high and low cooling rates corresponding to dendrite arm spacings of ∼40 and 120 μm, respectively. The alloys were subjected to solution heat treatment (495 °C/8 h for A319.1 and A413.1 alloys, and 540 °C/8 h for A356.2 alloy) to investigate its effect on the eutectic Si particle morphology. An optical microscope-image analyzer system was used to measure the characteristics of eutectic Si particles such as area, length, roundness ratio and aspect ratio, in order to monitor the modifying effect of mischmetal, as well as the combined modification effect of mischmetal and Sr. For each alloy sample examined, the Si particle characteristics were measured over an area of 50 fields and the average particle characteristics were thus determined. The eutectic Si particle measurements revealed that partial modification was obtained with the addition of mischmetal while full modification was achieved with the addition of Sr in the as-cast condition, at both high and low cooling rates. The interaction between Sr and mischmetal was observed to weaken the effectiveness of Sr as a Si particle-modifying agent. This effect was particularly evident at the low cooling rate. During solution heat treatment, the eutectic Si particles in the non-modified alloys underwent rapid coarsening, otherwise known as Ostwald ripening, whereas those in the Sr-modified alloys exhibited a high spheroidization rate. The coarsening was evidenced by an increase in the thickness of the Si particles, clearly observed in the A356.2 alloy at both cooling rates. In the alloys containing mischmetal, the presence of this mixture of rare earth elements reduced the coarsening of the Si particles slightly.

High pressure sintered ZrO2-6%wt REO

The sintering conditions employed in this work are innovative, due to the use of an alternative technology to process ZrO2-REO (rare earth oxide mixture), so called high temperature - high pressure (HPHT). A pressure of 5GPa was used, temperatures of 1100, 1200, and 1300 o C, for times of 2 and 5 minutes. The best results were obtained for samples sintered at 5GPa/1300 o C/5min., where a micro-hardness of 4.8GPa, fracture toughness of 5.3MPa.m ?, density of 97.9%, and 88% in volume of a tetragonal phase retained at room temperature were achieved.

Tribological properties of polytetrafluoroethylene composites filled with rare earths modified glass fibers

Rare earths were used to modify the surface of glass fiber in order to enhance the interfacial adhesion and improve the tribological properties of GF/PTFE composites. Three surface modifiers, a coupling agent, rare earths, and a mixture of coupling agent and rare earths, were investigated. It is found that the tensile properties of rare earths modified GF/PTFE composites were improved considerably under the same experimental conditions. The PTFE composites, filled with rare earths modified glass fibers, exhibited the lowest friction coefficient and the highest wear resistance under both dry friction and oil-dropped lubrication conditions. In addition, rare earths modified GF/PTFE composites showed the highest wear resistance under reciprocating impact load. The worn surfaces observation shows that rare earth elements modifier are superior to coupling agent modifier and the mixture of coupling agent and rare earths in promoting interfacial adhesion between the glass fiber and PTFE, accordingly improve tribological properties of GF/TFE composites due to their outstanding chemical activity.

The Impact of the Addition of Rare Earth Elements to Si1 − xSnx Negative Electrode Materials for Li-Ion Batteries

The impact of the addition of cerium and lanthanum-rich misch metal (MM, a mixture of rare earth elements) to silicon-tin alloys was studied using combinatorial and high-throughput materials science methods. Combinatorial libraries of , , and were prepared using the Dalhousie University combinatorial sputtering systems. The addition of MM increases the crystallization temperature of amorphous alloys, which makes their preparation in the amorphous state more likely by rapid solidification techniques like melt-spinning. Increasing the atomic fraction of MM in both and amorphous alloys decreases the reversible specific capacity of the alloys for lithium, but does not negatively impact capacity retention. Attractive compositions were identified in pseudoternary system that: (1) remain amorphous during charge-discharge cycling between 0.005 and vs ; (2) show excellent capacity retention; (3) have specific capacities as large as ; and (4) may be compatible with rapid solidification techniques for the production of amorphous materials. In particular, amorphous alloys containing tin and MM exhibited excellent capacity retention and reversible specific capacities near .

Effects of Rare Earth Elements on the Growth of Arnebia euchroma Cells and the Biosynthesis of Shikonin

Nd3+, La3+ and Ce3+ at proper concentrations had positive effects on the cell growth of Arnebia euchroma and production of shikonin derivatives. A mixture of rare earth elements (MRE, La2O3:CeO2:Pr6O11: Sm2O3 = 255:175:3:1, mol/mol) behaved the most remarkable effects. Two-stage culture was used for the cell proliferation and the biosynthesis of shikonin derivatives. After 20 days culture, 0.05 mM MRE gave the highest cell biomass (24.8 g dry weight l(-1)), which was 98.0% higher than that without rare earth elements. Similarly, when 0.05 mM MRE was added to the biosynthesis medium, the highest content (8.9% dry weight) and production (571.1 mg l(-1)) of shikonin derivatives were obtained, which were 89.4% and 165.3% higher than those without rare earth elements, respectively. The increase of the cell biomass and shikonin derivatives may due to increasing the activities of peroxidase and phenylalanine ammonia lyase caused by the addition of the rare earth elements.

Influence of Different Subsistence States of CeO 2-ZrO 2 Mixed Oxides in Catalyst Coating on Catalytic Properties

The metallic substrate-catalysts with different subsistence states of CeO 2-ZrO 2 mixed oxides were prepared and the catalytic properties were investigated. The studies on CeO 2-ZrO 2-V 2O 5-CuO mixed oxides which were prepared by coprecipitation, show that the doping of V 5+ and Cu 2+ in CeO 2-ZrO 2 mixed oxides can enhance the catalytic activity and thermal stability of coating materials. Moreover, different additives were doped in slurries of γ-Al 2O 3 to investigate the influence of additives on oxidation activity of catalysts. The mixture of ceria-zirconia, alkali metals and other rare earths acting as additives exhibits promotion effect on oxidation activity by optimizing the distribution of oxygen on the surface and in the bulk of ceria species. This mentioned mixture was mixed with γ-Al 2O 3 and a newly proposed active component to prepare a new catalyst. Afterward, the influence of thermal treatment on the new catalyst were investigated by calcinations at 500, 650, 750, 800, 850 and 900 °C for 2 h. The light-off curves of CO and HC show that after being treated at 650 ∼ 750 °C, catalysts present the best activity. XRD patterns show that ceria and zirconia species in the newly proposed active component form a phase of extra CeO 2-ZrO 2 mixed oxides on the surface of catalysts after the thermal treatment at 750 °C, which has practical value for improving the preparation process and promoting the catalytic properties. Moreover, XPS results imply the existence of Ce 1- x Pd x O 2-σ and Ce 1- x Pt x O 2-σ on the surface of these treated samples, which may show influence on the catalytic activities.

Eutectic Modification in a Low-Chromium White Cast Iron by a Mixture of Titanium, Rare Earths, and Bismuth: Part II. Effect on the Wear Behavior

In this work, we studied the wear behavior of a low-Cr white cast iron (WCI) modified with ferrotitanium-rare earths-bismuth (Fe-Ti-RE-Bi) up to 2%. These additions modified the eutectic carbide structure of the alloy from continuous ledeburite into a blocky, less interconnected carbide network. The modified structure was wear tested under pure sliding conditions against a hardened M2 steel counter-face using a load of 250 N. It was observed that wear resistance increased as the modifier admixture increased. The modified structure had smaller more isolated carbides than the WCI with no Fe-Ti-RE-Bi additions. It was observed that large carbides fracture during sliding, which destabilizes the structure and causes degradation in the wear behavior. A transition from abrasive to oxidative wear after 20 km sliding occurred for all alloys. In addition, the modified alloys exhibited higher values of hardness and fracture toughness. These results are discussed in terms of the modified eutectic carbide microstructure.

Eutectic Modification in a Low-Chromium White Cast Iron by a Mixture of Titanium, Rare Earths, and Bismuth: I. Effect on Microstructure

The present work studies the effect of small additions of a mixture of Ti, rare earths (RE), and Bi on the eutectic solidification of a low-Cr white cast iron (WCI) commercially designed as Ni-Hard Class I Type B according to the ASTM A532. For this purpose, systematic additions of a mixture of ferrotitanium-rare earths-bismuth (Fe-Ti-RE-Bi) up to 2% were made to a low-Cr WCI. By means of these additions, a modified carbide structure was obtained. Eutectic carbides changed from a highly interconnected ledeburite structure to more isolated, finer blocky structure. This microstructural change caused variations in the mechanical behavior of the WCI. The decrease in size and reduced connectivity of the eutectic carbides increased fracture toughness as well as wear resistance under dry sliding conditions. The effect of the admixture on the microstructure and mechanical properties is discussed in terms of the segregation and refining effects of the elements that comprise the mixture.

Rare Earth Elements in Forest-Floor Herbs as Related to Soil Conditions and Mineral Nutrition

Mixtures of rare earth elements (REEs) in fertilizers are widely used in Chinese agriculture to improve crop nutrition. REE concentrations in wild-growing plants, especially herbs, are little known. This study describes differences in the concentrations and proportions of REEs in eight forest-floor herbaceous plants and relates these differences to soil and mineral nutrient conditions. REEs studied were yttrium (Y), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu). Leaf concentrations of sum REEs differed more than one order of magnitude between species, being highest in Anemone nemorosa (10.1 nmol/g dry mass) and lowest in Convallaria majalis (0.66 nmol/g) from the same site. Leaf concentrations of all REEs correlated positively (p < 0.001), as did sum REE with calcium (Ca) and strontium (Sr) concentrations (p < 0.001). A negative relationship (r = -0.83, (p < 0.001) was measured between phosphorus (P) concentrations and sum REE concentrations in leaves. However, the proportions of the single REEs in the REE sum differed among species. In A. nemorosa, 57% of the molar REE sum was taken by Y + La, and only 21% by Ce. The other extreme was Maianthemum bifolium, with 37% La + Y and 41% Ce. These two species had 2.7-3.0% of the REE sum as heavier lanthanides, compared to 4.1-5.2% in the six other species. No clear relationship between soil properties or REE contents and leaf REE concentrations was detected. For La, however, an overrepresentation in leaves prevailed throughout all species compared to soils, whereas particularly Nd, Sm, and Tb had a lower proportion in the leaves of all species than in their soils. Possible uptake mechanisms of REEs in plants are discussed.

Chemical ripening of sugarcane: global progress and recent developments in China

Chemical ripening of sugarcane is a well established practice to enhance sucrose content in many sugarcane growing countries. Chemical ripeners such as Ethephon, Glyphosate analogues, Fusilade Super, Gallant Super are being used in large scale sugarcane plantations. The gains in sucrose content in sugarcane have been reported from 0.5-2.0 units, depending upon variety-weather-ripener interaction. In mainland China, many chemicals with ripeners like properties such as Lanthanium rich rare earth mixture, lime water, potassium di hydrogen phosphate etc. have been tried. Duoxiaohao- a product consisted of multiple nutrient elements also showed good results in improving plant growth and sugar accumulation in sugarcane. However, the best results have been obtained with glyphosate-borate complex which was effective even under water deficit stress and did not affect sprouting of subsequent ratoon crop. The average improvement in pol% cane was over 1.0 unit. Due to its commercial benefits, it has been popularized in large scale of sugarcane plantations in Guangxi Province and at present about 20,000 hectares have been brought under chemical ripening using glyphosate-borate aerial spray.

On-line and off-line preconcentration of trace and ultratrace amounts of lanthanides

The need for preconcentration of trace and ultratrace amounts of lanthanides from environmental, geological and biological samples is brought out in introductory part. Both on-line and off-line preconcentration procedures developed for lanthanides since 1980 are reviewed. The preconcentration techniques covered in this review include liquid–liquid extraction (LLE), ion-exchange, co-precipitation, and solid phase or solid–liquid extraction. Separate sections are devoted to each of the preconcentration techniques employed for enrichment of individual or mixtures of lanthanides. Future trends in singular or multielement preconcentration of lanthanides are also discussed.

On-line and off-line preconcentration of trace and ultratrace amounts of lanthanides

The need for preconcentration of trace and ultratrace amounts of lanthanides from environmental, geological and biological samples is brought out in introductory part. Both on-line and off-line preconcentration procedures developed for lanthanides since 1980 are reviewed. The preconcentration techniques covered in this review include liquid–liquid extraction (LLE), ion-exchange, co-precipitation, and solid phase or solid–liquid extraction. Separate sections are devoted to each of the preconcentration techniques employed for enrichment of individual or mixtures of lanthanides. Future trends in singular or multielement preconcentration of lanthanides are also discussed.

Fluctuation conductivity in melt-textured REBa2Cu3O7−δ superconductors

Abstract We have studied fluctuations on the electrical conductivity in melt-textured REBa 2 Cu 3 O 7− δ superconductors, where RE corresponds to a natural mixture of rare earth elements extracted from xenotime mineral. For this study, melt processed samples were prepared using the top seeding growth technique. To identify power-law divergences of the conductivity, the results were analyzed in terms of the temperature derivative of the resistivity and of the logarithmic temperature derivative of the conductivity. The data revealed the occurrence of a two-stage intragranular–intergranular transition. In the normal phase, different Gaussian and critical regimes were clearly observed to each current direction. Such an observation reveals that there is an evidence for anisotropies effects in studied conductivity regimes. Finally, the results obtained showed that the fluctuation conductivity in melt-textured samples of REBa 2 Cu 3 O 7− δ is very similar to those observed in YBa 2 Cu 3 O 7− δ .