Gd Oxides Research Articles

Effect of yttrium on the corrosion of AB 5-type alloys for nickel–metal hydride batteries

The influence of Y 2O 3 powder addition (as well as of rare earth oxides of Gd, Ho, Dy, Nd, Sm or Yb) to the metal hydride electrode on AB 5 alloy corrosion rates and on the chemical composition, morphology and density of the corrosion products was studied by X-ray, SEM, TEM and HRTEM. Adding Y 2O 3 reduces the corrosion rate. This is particularly observed in the long-term behavior of the batteries and is more pronounced at higher temperature. When yttrium is added as an oxide to the electrode or electrolyte, it is dissolved in the electrolyte and is further incorporated as hydroxide in the corrosion scale. The decrease in the global alloy corrosion rate can be explained by a decrease of the driving force for diffusion of Mm 3+ and OH −. Yb is the rare earth element which is expected to produce the largest decrease in corrosion rate, since its solubility in the electrolyte and its content in the corrosion scale are higher than for any other rare earth element.

Distribution of trivalent rare-earth additives between A and B sites in the ABO 3 PZT system

Lead zirconate titanate ceramics having composition at the morphotropic phase boundary have been modified with 2 mol % rare-earth oxides of Er, Gd, Eu, Nd and La. The samples have been prepared using the standard solid state reaction route. The ionic radius of the additives investigated vary from 0.088 to 0.106 nm. A theoretical model has been used which allows the additive cation distribution between A and B sites to be established from its ionic radius. It has been concluded that the additive goes increasingly to the A site with increasing ionic radius. The amounts of lead monoxide liberated during sintering due to incorporation of the additives have been studied. Using this PbO loss data the distribution of the additive between A and B sites has been calculated. It has been observed that the experimental results agree well with theoretical calculations.

Aqueous Durability of Titanate Ceramics Designed to Immobilise Excess Plutonium

Aqueous durability has been assessed for fourteen pyrochlore- and zirconolite-rich titanate waste forms designed for the immobilisation of excess Pu. The ceramics used in this study contained about 12 wt% Pu and about 15 wt% of Hf and Gd oxides as neutron absorbers and were fabricated by cold-pressing and sintering or hot isostatic pressing. Total release rates (i.e. unfiltered solution + vessel wall inventory) have been measured withthe MCC-1 test method at 90 °C in deionised water. For all samples, 7-day release rates of Pu are between 4 × 10−5 and about 10−3 g.m−2.d−1, reducing to between about 8 × 10−6 and 3 × 10−5 g.m−2.d−1after more than 300 days of leaching. Release rates of U from the baseline ceramic were found to decrease to values between 6 × 10−4 and 1 × 10−5 g.m−2.d−1after 200 days. Hf leach rates were generally < 5 × 10−6 g.m−2.d−l after more than 7 days. Further, the addition of several % of chemical impurities to the baseline sintered formulations was found to reduce U and Gd releases by about a factor of 10 after 200 days.

Oxidative coupling of methane over alkaline earth oxides deposited on commercial support precoated with rare earth oxides

A number of supported catalysts, prepared by depositing alkaline earth (viz. Mg, Ca, Sr and Ba) oxides on a commercial support (SA-5205) precoated with various rare earth (viz. La, Ce, Nd, Sm, Gd, Er and Yb) oxides have been evaluated for their surface properties and activity/selectivity in oxidative coupling of methane (OCM) at low contact time (GHSV=1.02×10 5 cm 3 g −1 h −1). The catalysts have been characterized for their basicity and acidity distributions by temperature programmed desorption (TPD) Of CO 2 and ammonia from 50°C to 950°C, respectively, and for their oxygen chemisorption sites by TPD of O 2. The OCM activity of the catalysts has been correlated with their basic sites measured in terms of the CO 2 desorbed between 500°C and 950°C. The catalysts with La 2O 3 and/or Nd 2O 3, showing good OCM activity, have been compared for their performance in the OCM process at different temperatures (750°C–850°C), and CH 4/O 2 ratios (4.0–20.0) in the feed. At 850°C, the catalyst with SrO deposited on the support precoated with mixed La 2O 3–Nd 2O 3 shows best performance in the OCM process.

Optical constants of nanocrystalline lanthanide-doped ceria thin films with the fluorite structure

The optical constants and structure of yttria-doped ceria and ceria doped with Nd, Sm, Gd, Dy, Er and Yb oxides are reported. These films were prepared using an inorganic sol-gel route and characterized for their refractive index, optical absorption edge, structure and crystallite size. All the films crystallized into the fluorite structure well below 450 °C, with cell constants altering as a function of ionic radius. The films were also nanocrystalline and continuous, with crystallite sizes in the range of 10–16nm after 600 °C. They have high transparency in the region 350 to 1500 nm and a reasonably high refractive index (1.7–1.79 at a wavelength of 800 nm) in the dispersion-free region. The dispersion behaviour in the refractive index has been fitted to the single oscillator model and is also shown to be dependent on the ionic size of the dopant material. It is therefore proposed that they should be suitable materials for application as transparent ion intercalation films and optoionic smart windows.

Corrosion of a Plutonium-Bearing Titanate Ceramic

Abstract A titanate-based ceramic waste form, rich in phases structurally related to zirconolite (CaZrTi2O7), is being developed as a possible candidate for immobilizing excess plutonium from dismantled nuclear weapons. The waste form is made by cold pressing and sintering of CaO, TiO2, ZrO2, A12O3, BaO, and Gd and Pu oxides. A prototype Pu-loaded ceramic that is being tested contains Pu,Gd-zirconolite-(3T), Pu-bearing brannerite, Gd-zirconolite-(4M), zirconolite-(2M) (see Figure 1), rutile (TiO2), Gd-bearing perovskites, various aluminotitanate phases, and undissolved plutonium oxide. Evidence from laboratory testing and natural analogues of titanates suggests that these phases are extremely corrosion resistant. Zirconolite-rich ceramics have also been considered for the disposal of actinide-bearing waste streams, because zirconolite and related polytypes are able to incorporate at least 20 wt% of actinides. However, since each phase in the multiphase ceramic corrodes at a different rate, the release of any one component or the corrosion of the bulk waste form is difficult to predict

Photoemission and inverse-photoemission study on Bi 2(Sr 2−xM x)CuO y (M [dbnd]Nd and Gd) oxides

Photoemission and inverse-photoemission studies of core-levels, valence-bands, and conduction bands of Bi 2Sr 2−xM xCuO y(M Nd) and Gd) are presented. It is found that density of states at the Fermi level is reduced with increasing trivalent ion contents at Sr sites. Photoemission spectra show that energy shifts of core levels and valence and conduction bands for the samples substituted by Gd, which are non-superconductors, are explained by the rigid band model. On the contrary, no energy shift of conduction bands was observed for Bi 2Sr 2−xNd xCuO y superconductors.

Physico-chemical Characterizations of Au(III) in Ln2Li 0.50Au 0.50O 4 ( Ln = La, Nd, Sm, Eu, Gd) Oxides

The Ln 2Li 0.50Au 0.50O 4 ( Ln = La, Nd, Sm, Eu, Gd) oxides have been prepared under oxygen pressure. The physical and chemical characterizations of the lanthanum phase confirm the stabilization of trivalent gold in a square-planar surrounding. Lithium is located in two similar crystallographic sites, in agreement with a layered structure with a 1/1 cationic order in the layers. The crystal structure is discussed, but the absence of single-crystal data does not allow a precise determination.

Fabrication and Secondary‐Phase Crystallization of Rare‐Earth Disilicate–Silicon Nitride Ceramics

The fabrication and intergranular‐phase devitrification of silicon nitride densified with rare‐earth (RE) oxide additives has been investigated. The additions of the oxides of Sm, Gd, Dy, Er, and Yb, having high melting points and behaving similarly to Y2O3, were compositionally controlled to tailor a microstructure with a crystalline secondary phase of RE2Si2O7. The lanthanide oxides were found to be as effective as Y2O3 in densifying Si3N4, resulting in identical microstructures and densities of 98–99% of theoretical density. The crystallization behavior of all six disilicates was similar, characterized by a limited nucleation and rapid growth mechanism resulting in large single crystals. Complete crystallization of the intergranular phase was obtained with the exception of a thin residual amorphous film which was observed at interfaces and believed to be rich in impurities, the cause of incomplete devitrification.

The selective oxidation of methane to ethane and ethylene over doped and un-doped rare earth oxides

A comparison has been made of the behaviour in the oxidative coupling of methane of the oxides of Sm, Dy, Gd, La and Tb with that of a Li/MgO material. All but the Tb 4O 7 (which gave total oxidation) were found to give higher yields than the Li/MgO material at temperatures up to approaching 750°C but the Li/MgO system gave better results at higher temperatures. The cubic structure of Sm 2O 3 was found to be responsible for its good performance while the monoclinic structure was relatively inactive and unselective. The addition of Na or Ca to cubic Sm 2O 3 gives a higher optimum C 2 yield than that of unpromoted Sm 2O 3. Sm 2O 3 and Ca/Sm 2O 3 catalysts are more stable than Li/MgO, Li/Sm 2O 3 or Na/Sm 2O 3. The addition of Li or Na to Sm 2O 3 causes the structure to change from cubic to monoclinic; the deactivation of the Na/Sm 2O 3 catalysts is caused by a loss of Na coupled with the formation of the monoclinic form of Sm 2O 3.

Magnetic proximity effect at a superconductor–rare-earth oxide interface

Using spin-polarized electron tunneling, we have observed an enhancement of an applied magnetic field in a thin superconducting Al film in contact with an oxide of a rare-earth metal. The Zeeman splitting of the superconducting density of states of this Al film is 2μ(B+B*), where B is the applied field and B* is of the order of the magnetization of the rare-earth oxide. The field is applied parallel to the plane of the film. Oxides of Eu, Gd, Tb, Dy, and Er have produced this effect. The enhancement can be quite large: an Al film in contact with Gd2O3 in an applied field of 1.5 T behaves as though it were in a field of over 4 T. Both S-I-S tunneling and critical field measurements provide quantitative confirmation of the enhancement. A proximity model by de Gennes accounts qualitatively for some but not all of the observations, and quantitative aspects of the experiment are not understood. This proximity effect may provide a method of studying the surface magnetism of insulating magnetic materials in an applied magnetic field.

Formation of Aluminosilicate Glasses Containing Rare-Earth Oxides

Formation of aluminosilicate glasses containing oxides of rare-earth elements, e.g. Sc, Ce, Pr, Nd, Eu, Gd, Tb, Dy, Ho, Er, and Yb, was studied by melting at 1550°C and air quenching. The upper limit of the amount of rare-earth oxide which can be incorporated into the aluminosilicate glasses decreases according to the lanthanide contraction.

ChemInform Abstract: TOPOCHEMICALLY CONTROLLED HYDROGEN REDUCTION OF SCHEELITE‐RELATED RARE EARTH METAL MOLYBDATES

AbstractDie Scheelit‐artigen Molybdate (I) werden mit zu den Mo(IV)‐ oxiden (III) reduziert, die in einer tetragonalen Struktur vom Scheelit‐Typ kristallisieren.

Topochemically controlled hydrogen reduction of scheelite-related rare-earth metal molybdates

Scheelite-related α-Ln2Mo3O12(Ln = La, Pr, Nd, Sm, Gd, Tb, or Dy) oxides are reduced by hydrogen at 780–870 K yielding molybdenum (IV) oxides of formula Ln2Mo3O9. The latter crystallize in a tetragonal scheelite (ABO4) type structure where one third of the A sites and a quarter of the anion sites are vacant: Ln2/3(□cat)1/3MoO3(□an). The reaction Ln2Mo3O12+ 3H2→ Ln2Mo3O9(□an)3+ 3H2O may be regarded as topochemically controlled, since both the parent and the product phases have scheelite-related structures. Infrared spectra and electrical and magnetic properties of these metastable defect scheelite phases are reported.

An Experimental Investigation of the Dielectric Properties of Thermally Evaporated Rare Earth Oxides for Use in Thin Film Capacitors

An experimental survey of rare earth oxides for use in thin film capacitors has been completed. Dielectric properties measured at 300°K are reported for thermally evaporated oxides 300 to 6000 Å in thickness of the metals, La, Ce, Pr, Nd, Sm, Gd, Dy, Ho, Er, Yb, Y, Sc, and also, V. Thin evaporated aluminum electrodes were utilized to impress voltages in the range zero to 75 V across the oxide layers. Dielectric breakdown strengths in excess of 5 × 106V/cm were observed. Relative dielectric constants measured for the oxides range from two to twenty, and measured capacitances were as high as 156 × 10−9F/cm2. The oxides of Ce, La, Nd, Gd, Pr, and Er show the most promise as potential materials for use in thin film capacitors.