Microstructural stability and creep properties of die casting Mg–4Al–4RE magnesium alloy

The AE44 (Mg–4Al–4RE) alloy was prepared by a hot-chamber die casting method. The microstructure, microstructural stability and creep properties at 175 °C were investigated. The microstructure was analyzed by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and the Rietveld method. The results show that die cast AE44 magnesium alloy consists of α-Mg, Al₁₁RE₃, Al₂RE and Al_2.12RE_0.88 phases. The Al₁₁RE₃ phase is thermally stable at 175 °C whereas the metastable Al_2.12RE_0.88 phase undergoes a transition into the equilibrium Al₂RE phase. The alloy investigated is characterized by good creep properties at temperatures of 175 °C and 200 °C.     

Mechanical and thermal properties of RE4Hf3O12 (RE=Ho,Er, Tm) ceramics with defect fluorite structure

The thermal and environmental barrier coatings (T/EBC) are technologically important for advanced propulsion engine system. In this study, RE₄Hf₃O₁₂ (RE=Ho, Er, Tm) with defect fluorite structure was investigated for potential use as top TBC layer. Dense pellets were fabricated via a hot pressing method and the mechanical and thermal properties were characterized. RE₄Hf₃O₁₂ (RE=Ho, Er, Tm) possessed a high Vickers hardness of 11 GPa. The material retained high elastic modulus at elevated temperatures up to 1773 K, which made it attractive for high temperature application. The coefficient of thermal expansion (CTE) of RE₄Hf₃O₁₂ (RE = Ho, Er, Tm) laid in the range between 7 × 10⁻⁶ K⁻¹ to 10 × 10⁻⁶ K⁻¹ from 473 K to 1673 K. In addition, the rare earth hafnates exhibited lower thermal conductivity which rendered it a good candidate material for thermal barrier applications.     

Superconducting and magnetic properties of ternary silicides in some rare earth-noble metal (Rh or Ir)-silicon systems

New families of ternary silicides have been prepared in the RE - Rh or Ir -Si systems and the crystal structures have been determined: RERh₃Si₂, RE₂Rh₃Si₅, RE₂RhSi₃ (RE = Y, La → Er), RERhSi (Y, La, Gd → Er), REIrSi (RE = La, Ce, Nd), RERhSi₂ and REIrSi₂ (RE = La → Gd). The RE₂RhSi₃ compounds crystallize with a new structural type, the other ones are isostructural with already known silicides or borides. Some of the silicides studied whose rare earths are diamagnetic (Y, La) show superconducting transitions above 1.6 K. They have been compared with other superconducting ternary borides, silicides, germanides and phosphides containing rare earths and noble metals. Except the phases with Y and La which are diamagnetic or show Pauli paramagnetism, the other materials order magnetically at low temperature. The onset of magnetic transitions vs. field has been observed for some compounds below 20 kOe at 4.2 K.     

Synthesis of New Pb-based 1222 Layered Cuprates in the (Pb,S)Sr2(RE,Ce)2Cu2O z (RE=Pr, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, and Y) System

A new family of the Pb-based layered cuprate with the 1222 structure has been synthesized in the (Pb,S)Sr₂(RE,Ce)₂Cu₂O _z (RE=Pr, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, and Y) system. The almost-single phase samples are obtained for x=0.25 and y=1.0 in the composition of (Pb_1?x S _x )Sr₂(RE_2?y Ce _y )Cu₂O _z . Each of the samples has the crystal structure with a tetragonal symmetry. Both of the lattice parameters a and c are decreasing with the decrease of the ionic radius of RE element. Among these samples, the sample with RE=Er has the smallest resistivity in the whole temperature range and the slope of the resistivity versus temperature is the most gentle. Despite annealing under O₂ atmosphere at high-pressure of 121 atm, this sample is a semiconductor with the transport process characteristics of three-dimensional variable range hopping conduction. Then the samples of RE=Er with smaller y are investigated for the composition of (Pb_0.75S_0.25)Sr₂(RE_2?y Ce _y )Cu₂O _z , the sample with y=0.4 is found to show an onset of resistivity drop phenomenon at about 11 K with the decrease of temperature. Moreover, we also discover that the samples of RE=Ho with y=0.4 show an onset of the resistivity dropping at over 20 K and zero resistivity at 13 K. From these results, the present (Pb_0.75S_0.25)Sr₂(RE_2?y Ce _y )Cu₂O _z system is considered to be a new family of the Pb-based superconducting cuprates with the 1222 structure.     

Characterization and magnetic properties of Sm- and Gd-substituted CoFe2O4 nanoparticles prepared by forced hydrolysis in polyol

Pure nanoparticles of the CoFe_2−xRE_xO₄ (RE = Gd, Sm; x = 0.0, 0.1) system have been prepared by forced hydrolysis in polyol. The insertion of Sm³⁺ and Gd³⁺ cations into the cobalt ferrite structure has been investigated. X-ray micro-analysis (EDX) shows that the RE contents are close to the nominal ones. X-ray diffraction (XRD) evidences a cell size increase with slight distortions in the spinel-like lattice indicating the entrance of RE³⁺ ions. Micro-Raman spectroscopy confirms the cubic inverse-spinel structure and rules out the existence of impurities like hematite. Magnetic measurements (SQUID) show important differences in the magnetic properties of the unsubstituted and substituted particles. All the particles are superparamagnetic at room temperature and ferrimagnetic at low temperature. However, their main magnetic characteristics appear to be directly dependent on the RE content.     

Simultaneous removals of NOx, HC and PM from diesel exhaust emissions by dielectric barrier discharges

The main target of this work is to characterize the abatements of particulate matter (PM), hydrocarbons (HC) and nitrogen oxides (NO_x) from an actual diesel exhaust using dielectric barrier discharge technology (DBD). The effects of several parameters, such as peak voltage, frequency and engine load, on the contaminant removals have been investigated intensively. The present study shows that for a given frequency, the removals of PM and HC are enhanced with the increase of peak voltage and level off at higher voltage, while in the range of higher voltages a decline of NO_x removal efficiency is observed. For a given voltage, the maximums of specific energy density (SED) and removal efficiency are attained at resonance point. The increase of peak voltage will result in a significant decrease of energy utilization efficiency of DBD at most engine loads. Alkanes in soluble organic fraction (SOF) are more readily subjected to removals than polycyclic aromatic hydrocarbons (PAHs).     

Sol-Gel Synthesis and Photoluminescence of RE<Subscript>x</Subscript>Lu<Subscript>2-<Emphasis Type="Italic">x</Emphasis></Subscript>O<Subscript>3</Subscript>:Eu<Superscript>3+</Superscript> (RE = Y,Gd) Nanophosphors

RE_xLu_2-x O₃:Eu³⁺ (RE = Y, Gd) nanophosphors with x = 0.4, 1.0, and 1.6 were synthesized using rare-earth salicylate coordination polymers as precursors for the luminescent species RE_xLu_2-x O₃:Eu³⁺ (RE = Y, Gd) composed of polyethylene glycol both as a dispersing medium and fuel. Their particle sizes were around 100 nm as determined by scanning electron microscopy and x-ray diffraction.__________From Neorganicheskie Materialy, Vol. 41, No. 6, 2005, pp. 706–710.Original English Text Copyright © 2005 by Zhou, Yan.This article was submitted by the authors in English.     

An analysis of the ammonium chloride route to anhydrous rare-earth metal chlorides

The ammonium chloride route to anhydrous rare-earth metal trichlorides, RECl₃, is a two-step procedure consisting in, firstly, the (dry or wet) synthesis of a complex chloride, (NH₄)₃ RECl₆ (t≈ 220°C) and, secondly, its decomposition either directly (small RE, t≈ 425°C) or via the intermediates (NH₄)₂ RECl₅ (large RE, t≈ 385°C) and NH₄RE₂Cl₇ (medium-size RE), respectively.     

Role of some rare earth (RE) ions (RE = La, Pr, Nd, Sm, Gd and Dy) in crystal and mechanical behaviours of sol-gel derived ZrO2-2 mol% REO2O3 spun fibres calcined at 1300°C

Crystal behaviours such as crystallization temperature (amorphous to tetragonal (t) zirconia), tendency of phase transformation (tetragonal to monoclinic (m) zirconia) and lattice strain were studied with mechanical property e.g. tensile strength of sol-gel derived ZrO₂-2 mol% RE₂O₃ (RE = La, Pr, Nd, Sm, Gd and Dy) spun fibres. Rare earth cations of varying sizes played a significant role in changing the above mentioned properties of ZrO₂-2 mol% RE₂O₃ fibres. It was found that with decreasing the ionic size difference between the zirconium and RE ions, crystallization temperature (amorphous →)t-ZrO₂) decreased, the probability of phase transformation (t→m) decreased, lattice strain which is related to lattice distortion decreased and tensile strength increased.     

Butane extraction of model organic pollutants from water

In this study, n-butane (n-C(4)H(10)), a by-product of the oil refining process, was used as the extractant to remove various model organic pollutants including halogenated hydrocarbons, phenols and aromatic compounds from aqueous matrices. The presence of salt, inorganic acid and dissolved organic materials in the aqueous matrix were found to have little influence on the removal efficiency. High removal efficiencies are readily achievable for a great number of organic pollutants. The removal efficiencies for hydrophobic pollutants were greater than 90% for a single stripping stage for pollutants with a distribution constants (K(D)) greater than 45 and for a n-butane to aqueous phase ratio of 1-5. Results were also reported for the removal of residual butane in treated effluent by combinations of depressurization, air stripping and elevating operating temperature.     

Effect of Ca, RE elements and semi-solid processing on the microstructure and creep properties of AZ91 alloy

The effects of calcium and rare earth elements (RE) on the microstructure and creep properties of as-cast and thixoformed AZ91 magnesium alloy have been investigated. It has been shown that the amount of β(Mg₁₇Al₁₂) intermetallic compound decreases by adding Ca and RE elements into AZ91 alloy and new Al₁₁RE₃ and Al₂Ca intermetallic compounds form in the microstructure. The coarsening of primary α(Mg) particles in AZ91 alloy and in the Ca and RE containing (AZRC91) alloy takes place by Ostwald ripening mechanism. Adding Ca and RE elements into AZ91 alloy results in a decrease in the coarsening rate of solid particles in semi-solid slurry, whereas it has no visible effect on the shape factor of the solid-particles. The creep properties of AZ91 alloy are improved by adding Ca and RE elements particularly, in the thixoformed condition.     

The Effect of Linker-to-Metal Energy Transfer on the Photooxidation Performance of an Isostructural Series of Pyrene-Based Rare-Earth Metal–Organic Frameworks

The tetratopic linker, 1,3,6,8-tetrakis(p-benzoic acid)pyrene (H₄TBAPy) along with rare-earth (RE) ions is used for the synthesis of 9 isostructures of a metal–organic framework (MOF) with shp topology, named RE-CU-10 (RE = Y(III), Gd(III), Tb(III), Dy(III), Ho(III), Er(III), Tm(III), Yb(III), and Lu(III)). The synthesis of each RE-CU-10 analogue requires different reaction conditions to achieve phase pure products. Single crystal X-ray diffraction indicates the presence of a RE₉-cluster in Y- to Tm-CU-10, while a RE₁₁-cluster is observed for Yb- and Lu-CU-10. The photooxidation performance of RE-CU-10 analogues is evaluated, observing competition between linker-to-metal energy transfer versus the generation of singlet oxygen. The singlet oxygen produced is used to detoxify a mustard gas simulant 2-chloroethylethyl sulfide, with half-lives ranging from 4.0 to 5.8 min, some of the fastest reported to date using UV-irradiation and < 1 mol% catalyst, in methanol under O₂ saturation.     

Electrical and Structural Properties of RE<Subscript>3</Subscript>Ba<Subscript>5</Subscript>Cu<Subscript>8</Subscript>O<Subscript>18</Subscript> (RE=Y,Sm and Nd) Superconductors

This paper presents the synthesis and characterization of the new superconducting compounds with nominal composition, RE₃Ba₅Cu₈O₁₈, RE=Y, Sm and Nd. The onset critical temperatures of the present samples are 97.5, 97 and 95 K for the RE=Y, Sm and Nd, respectively. The first two values are the highest for the RE–Ba–Cu–O superconductors recorded to date. The RE₃Ba₅Cu₈O₁₈ samples crystallize in the orthorhombic system, with increased unit cell volume as Sm and Nd replace the element Y.     

Direct photolysis of polycyclic aromatic hydrocarbons in drinking water sources

The widely used low pressure lamps were tested in terms of their efficiency to degrade polycyclic aromatic hydrocarbons listed as priority pollutants by the European Water Framework Directive and the U.S. Environmental Protection Agency, in water matrices with very different compositions (laboratory grade water, groundwater, and surface water). Using a UV fluence of 1500 mJ/cm², anthracene and benzo(a)pyrene were efficiently degraded, with much higher percent removals obtained when present in groundwater (83-93%) compared to surface water (36-48%). The removal percentages obtained for fluoranthene were lower and ranged from 13 to 54% in the different water matrices tested. Several parameters that influence the direct photolysis of polycyclic aromatic hydrocarbons were determined and their photolysis by-products were identified by mass spectrometry. The formation of photolysis by-products was found to be highly dependent on the source waters tested.     

Substitution Effects on Rare-Earth Ions-Doped Nickel-Zinc Ferrite Nanoparticles

Rare-earth ions (RE³⁺)-doped Ni-Zn ferrite nanoparticles with a structural formula of Ni_0.5Zn_0.5Fe_1.8RE_0.2O₄ (RE³⁺ = Nd, Ce, La and Pr) were synthesized at room temperature by a sol-gel auto-combustion method. The structural and magnetic properties of Ni-Zn ferrite samples were carried out by XRD, vibrating sample magnetometer (VSM), field emission scanning electron microscopy (FE-SEM) and FT-IR spectroscopy. XRD pattern of Ni-Zn ferrite revealed that all the diffraction planes are in agreement with cubic spinel phase and the addition of Fe₂O₃ phase was also observed. In the case of RE ions-doped Ni-Zn ferrite in addition to the Fe₂O₃ phase, very low intensity peaks corresponding to some secondary phase are also present. The average crystallite sizes were found to be from 42 to 56 nm using the Scherer formula. The lattice constant (a) values are gradually decreased from 8.378 to 8.349 Å with different substitutions of RE³⁺ ions in the Ni-Zn ferrite samples. VSM analysis revealed that saturation magnetization values are decreased and coercivity values are increased with substitution of different RE³⁺ ions. FE-SEM images exhibits that particles are spherical in shape. FT-IR interpretation revealed that two main metal oxygen bands (564 and 411 cm^?1) are observed in all the substituted Ni-Zn ferrite samples.     

Book review

Abstract

Magnesium based Mg–9Al–1Zn–5RE (RE=Y, La, Nd, Ce, or Pr) alloys with or without an addition of 1%Si were rapidly solidified by chill block melt spinning and splat quenching. The base alloy AZ91 (Mg–9Al–1Zn) was also rapidly solidified. Isochronal heat treatment for 1 h at 100–400°C showed that the microhardness of the ribbon maintained a similar level to that of the as spun alloy up to 300°C but decreased when heat treated at 400°C. Isothermal heat treatment for up to 24 h at 250–350°C showed that there were aging responses for the sample treated at 250°C while above this temperature, the microhardness decreased as the treatment time increased. The addition of 5% of RE elements to AZ91 displaced the Mg₁₇Al₁₂ phase in AZ91 with fine dispersoids of Al₂RE (RE=Y or Nd) or Al₁₁RE₃ (RE=La, Nd, Ce, or Pr) in Mg–9Al–1Zn–5RE alloys. These Al–RE intermetallics remained fine and precipitated at the grain boundaries so restraining grain growth during heat treatment at up to 400°C. Although Mg₂Si precipitates were found to be present in the silicon containing alloys after heat treatment at 400°C, their size was greater than those of Al–RE intermetallics, indicating that Mg₂Si has a lower thermal stability than these Al–RE intermetallics. The relationship between microhardness and grain size is discussed.

MST/3400     

Structural,electronic, elastic and thermodynamic properties of AlSi2RE (RE = La,Ce, Pr and Nd) from first-principle calculations

It is of academic interest to study the ternary intermetallic compounds of the Al–Si–RE system for the development of both structural and functional materials. In this work, the structural, electronic, elastic and thermodynamic properties of the AlSi₂RE (RE = La, Ce, Pr and Nd) compounds was investigated using first-principle calculations based on density functional theory. The calculated structural parameters of AlSi₂RE compounds are consistent with the experimental data. Due to the fact that there is strong Coulomb correlation among the partially filled 4f electron for RE atoms, we present a combination of the GGA and the LSDA + U approaches to investigate the electronic structures of Al₃RE compounds in order to obtain the appropriate results. The elastic constants were determined from a linear fit of the calculated stress–strain function according to Hooke’s law. The bulk modulus B, shear modulus G, Young’s modulus E, and Poisson’s ratio ν of polycrystalline AlSi₂RE compounds were determined using the Voigt–Reuss–Hill (VRH) averaging scheme. The Debye temperature of AlSi₂RE compounds can be obtained from elastic constants. The temperature dependence of the internal energy, free energy, entropy and heat capacity for AlSi₂RE compounds were also calculated by using the quasi-harmonic approximation.     

Enneahalodimetallates(III) of rare earth elements with the hexagonal Cs3Tl2Cl9-(h)6-type structure

Enneachloro- and bromodimetallates(III) of rare earth elements Cs₃RE₂X₉, of which only a few have been observed in a phase diagram, were prepared and investigated by Guinier-Simon X-ray technique. Except for Cs₃Sc₂Br₉ (isotypic with Cs₃Cr₂Cl₉) they - for RE = Sc, Y,Ho-Lu, X = Cl as well as RE = Sc, Sm-Lu, X = Br - crystallize with the Cs₃Tl₂Cl₉-type structure.     

Magnetic properties of RE2Mo2O7 pyrochlores

The magnetic properties of RE₂Mo₂O₇ (RE=Gd³⁺, Tb³⁺, Dy³⁺, Ho³⁺, Er³⁺, Tm³⁺, and Yb³⁺) and of solid solutions of the type (Nd_1?x A _x )₂Mo₂O₇ (A=Yb or Er; 0.05≤x≤0.4) have been studied using an ac mutual inductance bridge. All the compounds were found to exhibit magnetic ordering in the neighborhood of or below 77 K. The data have been analyzed using (i) the available susceptibility data on Y₂Mo₂O₇, (ii) a ferromagnetic coupling among the Mo⁴⁺ ions to obtain the contribution from the RE³⁺ ion, and (iii) the available susceptibility data on RE₂Ti₂O₇ to obtain the contribution from the Mo⁴⁺ ions. It was found that procedure (iii) gave the most satisfactory explanation of the magnetic ordering. The results indicated that (1) the Mo⁴⁺ ions become ordered magnetically, (2) the behavior of the RE³⁺ ions is almost the same as in the isostructural RE₂Ti₂O₇ and RE₂V₂O₇ compounds, and (3) the susceptibility values differ appreciably as we go from Nd³⁺ to Yb³⁺, possibly due to narrowing of the π* Mo-O conduction band.     

Molecular assembly and photoluminescence of novel rare earth/inorganic/polymeric hybrid materials with functional covalent linkages

In the context, organic polymeric precursor, polyethylene glycol (PEG) was firstly modified by inorganic component of 3-(triethoxysilyl)-propyl isocyanate (TEPIC) to form the inorganic/organic polymeric functional bridge precursor. Subsequently, the corresponding organic/inorganic molecular-based hybrids were assembled to behave the structural polymeric ligands with the two components equipped with covalent bonds. The coupling reagent part is a functional ureasils –NHC(=O)–O–group which is applied to coordinate to RE³⁺ and further formed Si–O backbones after hydrolysis and polycondensation processes. Furthermore, aromatic carboxylic acids (picolinic acid (HPIC), 2-chlorobenzoic acid (HCBA) and salicylic acid (HSAL)) were used as functional sensitized ligands to coordinate with RE³⁺(Eu³⁺, Tb³⁺ and Dy³⁺) and resulting in the quaternary rare earth/inorganic/organic polymeric hybrid materials with chemical bond (covalent bonds of –CO–NH– and Si–O, coordination bond of RE–O–C). Luminescence spectra were utilized to characterize the photophysical properties of the obtained hybrid material and the intramolecular energy transfer process took place within these molecular-based hybrids and characteristic emissions of RE³⁺ have been achieved.