Combustion synthesis and properties of Ln3Fe5O12 and yttrium aluminium garnets

The rare earth iron garnets Ln3Fe5O12 and Y3AlxFe5-xO12, where x=1.0-5.0, and Y1.5Gd1.5Al0.2Fe4.8O12 have been prepared by the combustion of redox mixtures containing corresponding metal nitrates and oxalyl dihydrazide, i.e. C2H6N4O2 at 350-degrees-C. The solid combustion products are amorphous, submicrometre-sized powders which, on heating at 750-degrees-C for 3 h, yield crystalline single-phase garnets. The particle size of the garnets is below 1 mum and the surface area ranges from 16 to 90 m2 g-1. Yttrium iron garnet could be sintered to a density of more than 95% at 1200-degrees-C for 3 h, giving an average grain size of 3-5 mum.

The effect of mischmetal addition on the structure and mechanical properties of a cast Al-7Si-0.3Mg alloy containing excess iron (up to 0.6 Pct)

The effect of Fe content (0.2 to 0.6 pct) on the microstructure and mechanical properties of a cast Al-7Si-0.3Mg (LM 25/356) alloy has been investigated. Further, 1 pct mischmetal (MM) additions (a mixture of rare-earth (RE) elements) were made to these alloys, and their mechanical properties at room and at elevated temperatures (up to 200 degreesC) were evaluated. A structure-property correlation on this alloy was attempted using optical microstructure analysis, fractographs, X-ray diffraction, energy-dispersive analysis of X-rays (EDX), and quantitative metallography by image analysis. An increase in Fe content increased the volume percentage of Fe-bearing intermetallic compounds (beta and pi phases), contributing to the lower yield strength (YS), ultimate tensile strength (UTS), percentage elongation, and higher hardness. An addition of 1 pct MM to the alloys containing 0.2 and 0.6 pct Fe was found to refine the microstructure; modify the eutectic silicon and La, Ce, and Nd present in the MM; form different intermetallic compounds with Al, Si, Fe, and Mg; and improve the mechanical properties of the alloys both at room and elevated temperatures.

Thermodynamic properties of oxygen in RE-O (RE = Gd, Tb, Dy, Er) solid solutions

The oxygen potentials of four rare-earth metal – oxygen (RE–O: RE=Gd, Dy, Tb, Er) solid solutions have been measured by equilibration with yttrium – oxygen (Y–O) and titanium – oxygen (Ti–O) solid solutions. Rare-earth metal, yttrium and titanium samples were immersed in calcium-saturated CaCl2 melt at temperatures between 1093 and 1233 K. Homogeneous oxygen potential was established in the metallic samples through the fused salt, which contains some dissolved CaO. The metallic samples were analyzed for oxygen after quenching. The oxygen potentials of RE–O solid solutions were determined using either Y–O or Ti–O solid solution as the reference. This method enabled reliable measurement of extremely low oxygen potentials at high temperature (circa pO2=10−48 atm at 1173 K). It was found that the oxygen affinity of the metals decreases in the order: Y>Er>Dy>Tb>Gd>Ti. Values for the standard Gibbs energy of solution of oxygen in RE metals obtained in this study, permit assessment of the extent of deoxidation that can be achieved with various purification techniques. It may be possible to achieve an oxygen level of 10 mass ppm using an electrochemical deoxidation method.

Electrochemical deoxidation of RE–O (RE=Gd, Tb, Dy, Er) solid solutions

The removal of oxygen from rare-earth metals (RE, RE=Gd, Tb, Dy, Er) by an electrochemical deoxidation method was investigated. A titanium basket containing the rare-earth metal sample, submerged in molten CaCl2 electrolyte, formed the cathode of an electrolysis cell. A high-purity graphite anode was used. The calcium metal produced at the cathode effectively deoxidized the rare-earth metal. Carbon monoxide and dioxide were generated at the graphite anode. Rare-earth metals containing more than 2000 mass ppm oxygen were deoxidized to 10–50 mass ppm level by electrolysis at 1189 K for 36 ks (10 h). Cyclic voltammetry was used to characterize the molten salt at different stages of the process. The effectiveness of the process is discussed with the aid of a chemical potential diagram for RE–O solid solutions. The new electrochemical technique is compared with the conventional deoxidation methods reported in the literature. The possibility of nitrogen removal from the rare-earth metals by the electrochemical method is outlined.

System Gd-Rh-O: Thermodynamics and phase relations

Thermodynamic properties of GdRhO3 are investigated in the temperature range from 900 to 1300 K by employing a solid-state electrochemical cell, incorporating calcia-stabilized zirconia as the electrolyte. The standard Gibbs free energy of formation of GdRhO3 from component binary oxide Gd2O3 with C-rare earth structure and Rh2O3 with orthorhombic structure can be expressed as; Delta G(f(ox))(o)(+/- 60)/J mol(-1) = -56603 + 3.78(T/K) Based on the thermodynamic information on GdRhO3 from experiment and auxiliary data for binary oxides from the literature and estimated properties of Gd-Rh alloys, phase relations are computed for the system Gd-Rh-O at 1273 K. Gibbs free energies for intermetallic phases in the binary Gd-Rh are evaluated using calorimetric data available in the literature for two compositions and Miedema's model, consistent with the binary phase diagram. Isothermal section of the ternary phase diagram, oxygen potential-composition diagram and a 3-D chemical potential diagram for the system Gd-Rh-O at 1273 K are developed. Phase relations in the ternary Gd-Rh-O are also computed as a function of temperature at constant oxygen partial pressures. The ternary oxide, GdRhO3 decomposes to Gd2O3 with B-rare earth structure, metallic Rh and O-2 at 1759(+/- 2) K in pure O-2 and 1649(+/- 2) K in air at a total pressure P-0 -0.1 MPa. (c) 2012 Elsevier B.V. All rights reserved.

Structure and properties of amorphous thin film for optical data storage

In this paper the magnetic and magneto-optical properties of amorphous rare earth-transition metal (RE-TM) alloys as well as the magnetic coupling in the multi-layer thin films for high density optical data storage are presented. Using magnetic effect in scanning tunneling microscopy the clusters structure of amorphous RE-TM thin films has been observed and the perpendicular magnetic anisotropy in amorphous RE-TM thin films has been interpreted. Experimental results of quick phase transformation under short pulse laser irradiation of amorphous semiconductor and metallic alloy thin films for phase change optical recording are reported. A step-by-step phase transformation process through metastable states has been observed. The waveform of crystallization propagation in micro-size spot during laser recording in amorphous semiconductor thin films is characterized and quick recording and erasing mechanism for optical data storage with high performance are discussed. The nonlinear optical effects in amorphous alloy thin films have been studied. By photo-thermal effect or third order optical nonlinearity, the optical self-focusing is observed in amorphous mask thin films. The application of amorphous thin films with super-resolution near field structure for high-density optical data storage is performed. (c) 2007 Elsevier B.V. All rights reserved.

In-situ synthesis of AlN powders and composite AlN powders with yttrium addition

Using Al-Mg and Al-Mg-Y alloys as raw materials and nitrogen as gas reactants, AIN powders and composite AIN powders by in-situ synthesis method were prepared. AIN lumps prepared by the nitriding of Al-Mg and Al-Mg-Y alloys have porous microstructure, which is favorable for pulverization. They have high purity, containing 1.23 % (mass fraction) oxygen impurity, and consisted of AIN single phase . The average particle size of AIN powders is 6.78 mum. Composite AlN powders consist of AlN phases and rare, earth oxide Y2O3 phase. The distribution of particle size of AIN powders shows two peaks. In view, of packing factor, AIN powders with such size distribution can easily be sintered to high density.

Mossbauer spectroscopic study of R3Fe29-xCrx and R3Fe29-xCrxH,(y)(R = Y, Ce, Nd, Sm, Gd, Tb, and Dy)

Fe-57 Mossbauer spectra for the series of R3Fe29-xCrx (R = Y,Ce, Nd, Sm, Gd, Tb, and Dy) compounds and their hydrides have been measured at 4.2 K. The weighted average hyperfine field at the Fe sites was separated into a 3d-electron contribution, proportional to the average Fe moment, and a transferred contribution due to rare earth moments. The latter was found to increase with the rare earth effective spin (g(J) - 1) J. Hyperfine fields in the hydrides were only slightly larger than in the corresponding alloys.

Fe-57 Mossbauer spectroscopic and magnetic studies of R3Fe29-xVx (R = Y, Ce, Nd, Sm, Gd, Tb, and Dy)

Mossbauer spectra for Fe atoms in the series of R3Fe29-xVx (R = Y, Ce, Nd, Sm, Gd, Tb, and Dy) compounds were collected at 4.2 K. The ratio of 14.5 T/mu(B) between the average hyperfine field B-hf and the average Fe magnetic moment mu(Fe)(MS), obtained from our data, in Y3Fe29-xVx is in agreement with that deduced from the RxTy alloys by Gubbens et al. The average Fe magnetic moments mu(Fe)(MS) in these compounds at 4.2 K, deduced from our Mossbauer spectroscopic studies, are in accord with the results of magnetization measurement. The average hyperfine field of the Fe sites for R3Fe29-xVx at 4.2 K increases with increasing values of the rare earth effective spin (g(J) - 1) J, which indicates that there exists a transferred spin polarization induced by the neighboring rare earth atom.

Fe-57 Mossbauer spectroscopic and magnetic studies of R3Fe29-xVx (R = Y, Ce, Nd, Sm, Gd, Tb, and Dy)

Mossbauer spectra for Fe atoms in the series of R3Fe29-xVx (R = Y, Ce, Nd, Sm, Gd, Tb, and Dy) compounds were collected at 4.2 K. The ratio of 14.5 T/mu(B) between the average hyperfine field B-hf and the average Fe magnetic moment mu(Fe)(MS), obtained from our data, in Y3Fe29-xVx is in agreement with that deduced from the RxTy alloys by Gubbens et al. The average Fe magnetic moments mu(Fe)(MS) in these compounds at 4.2 K, deduced from our Mossbauer spectroscopic studies, are in accord with the results of magnetization measurement. The average hyperfine field of the Fe sites for R3Fe29-xVx at 4.2 K increases with increasing values of the rare earth effective spin (g(J) - 1) J, which indicates that there exists a transferred spin polarization induced by the neighboring rare earth atom.

The solid-liquid extraction of yttrium from rare earths by solvent (ionic liquid) impreganated resin coupled with complexing method

A kind of solvent (ionic liquid) impreganated resin (IL-SIR) was developed herein for ameliorating imidazolium-type IL-based liquid-liquid extraction of metal ions. In this study, [C(8)mim][PF6] containing Cyanex923 was immobilized on XAD-7 resin for solid-liquid extraction of rare earth (RE). The solid-liquid extraction contributed to ameliorating mass transfer efficiency, i.e. shortening equilibrium time from 40 min to 20 min, increasing extraction efficiency from 29% to 80%. In additional, the novel IL-SIR could separate Y(III) from Sc(III), Ho(III), Er(III), Yb(III) effectively by adding water-soluble complexing agent.

Effect of Nd on the microstructure, mechanical properties and corrosion behavior of die-cast Mg-4Al-based alloy

Die-cast Mg-4Al-0.4Mn-xNd(x = 0, 1, 2, 4 and 6 wt.%) magnesium alloys were prepared successfully and influences of Nd on the microstructure, mechanical properties and corrosion behavior of the Mg-4Al-0.4Mn alloy have been investigated. The results showed that with the addition of Nd binary Al2Nd phase and Al11Nd3 phase. which mainly aggregated along the grain boundaries, were formed, and the relative ratio of above two phases was in correlation with the Nd content in the alloy. Meanwhile, the grain sizes were greatly reduced with the increasing Nd content. It was found that due to the addition of Nd both the tensile properties and corrosion resistance were improved substantially.

Synergistic extraction of rare earths using acid-base coupling extractants of calix[4]arene carboxyl derivative and primary amine N1923

Synergistic effect in the extraction of rare earth (RE) metals by the acid-base coupling (ABC) extractants of calix[4]arene carboxyl derivative Bu-t[4]CH2COOH (H(4)A) and primary amine N1923 (RNH2) has been investigated. The extraction of RE was enhanced by the addition of sodium cations into the aqueous phase not only in the extraction system of Bu-t[4]CH2COOH alone but also in the mixture of Bu-t[4]CH2COOH and N1923. The separation factors (SFs) indicating the extraction selectivity of adjacent RE elements became higher in the mixture system.

Synthesis and fluorescent property of NH4Y1.9Eu0.1F7 nanoparticles with the temperature effect on the morphology

Sphere NH4Y1.9Eu0.1F7 nanoparticles were successfully synthesized by a hydrothermal method at 180 degrees C for 10 h. SEM and TEM images show the particles are spheres and have lots of hollows in them. The mean particle size is about 60 nm. The shape and size of the particles can be controlled by changing temperature and time of reactants. The luminescent property of the sample indicates that strong emission peaks of the Eu3+ ions are located at about 589 and 612 mm.

Electrochemical corrosion behavior of Mg-5Al-0.4Mn-xNd in NaCl solution

The electrochemical corrosion behavior of Mg-5Al-0.4Mn-xNd (x = 0, 1, 2 and 4 wt.%) alloys in 3.5% NaCl solution was investigated. The corrosion behavior of the alloys was assessed by open circuit potential measure, potentiodynamic polarization, and electrochemical impedance spectroscopy. The electrochemical results show the intermetallic precipitates with Nd behave as less noble cathodes in micro-galvanic corrosion and suppress the cathodic process. During corrosion, Al2O3 and Nd2O3, in proper ratio, is incorporated into the corrosion film, and enhances the corrosion resistance.