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Abstract
Catalytic activity of rare earth oxides (REO); La2O3, Sm2O3, Gd2O3 and Ce2O3 on the isothermal decomposition of barium oxalate has been studied at 723 K. The α−t plots for pure salt as well as mixtures indicate that the process follows: initial gas evolution, a short acceleratory and a long decay stages. The results of the kinetic analysis show that Prout-Tompkins relationship and two-dimensional phase boundary reaction give best fit of the data for both pure salt as well as mixtures. The rate constants of acceleratory and decay periods are enhanced remarkably by adding REO admixtures and their catalytical activity is in the order La2O3>Sm2O3>Gd2O3 >Ce2O3. The plausible mechanism of decomposition and the role of admixture there on has been discussed in the light of electron transfer process.
The kinetics of the decomposition of ammonium perchlorate (AP) in the presence of rare earth oxides, yttrium oxide (Y2O3) and lanthanum oxide (La2O3) as catalysts have been investigated. The Prout-Tompkins and contracting-cube equations have been found to fit the isothermal thermogravimetry data of catalysed AP decomposition. Gases evolved during catalytic decomposition of AP were analysed by infrared spectroscopy by matrix isolation technique. The mechanism of the catalysed thermal decomposition of AP has also been discussed in terms of an electron transfer process.
improve physical, mechanical, and electrical properties such as enhanced solubility, conductivity, magnetic, optoelectronic properties, etc. In recent years, rare earth oxides are gradually introduced to the area of PANI composites because of their
Abstract
The oxidation-reduction behaviour of transition metal and rare earth oxide systems in oxygen potential controlled atmospheres was investigated by means of a solid electrolyte-based coulometric technique (SEC) in carrier gas mode to obtain information concerning the extent of oxygen stoichiometry, thep-T-x diagram of any mixed oxide phase, the kinetics of the oxygen exchange and the phase transitions.
The direct coupling of SEC and electrical conductivity measurements provides further information about the relationship between oxygen deficiency and conductivity, especially as concerns the oxygen mobility and the transition from ionic to mixed ionic/electronic conductivity in any system.
In the fluorite-type phases PrO2−x, Ce0.8Pr0.2Oy−x and Ce0.8Sr0.08Pr0.12Oy−x, the higher oxidation state of Pr is stabilized and the electrical conductivity increases in this sequence. The perovskite-type phase Sr1−yCeyFeO3−x, shows transitions and a second phase reflected in the temperature-programmed spectrum of this substance. The electrical conductivity of Sr0.9Ce0.1FeO3−x changes fromn-type top-type with increasing oxygen pressure.
Al 2 O 3 , respectively on the specimen surfaces and these oxides did not spall [ 3 , 4 ]. All the specimens revealed parabolic oxidation behavior. The effect of rare earth oxide addition to the surface of the Fe20Cr alloy was clearly evident upon
The binary rare earth oxides KA Gschneidner Jr L Eyring eds. Handbook on the physics and chemistry of rare earths North Holland
Synthesis and dehydration of double oxalates of rare earths(III) with some monovalent metals
I. Synthesis and thermal behaviour of KLn(C2O4)2·nH2O
The synthesis of double oxalates of rare earths(III) and potassium with empirical formulae K4Ln2(C2O4)5·10H2O (Ln=La, Ce) and KLn(C2O4)2· nH2O (wheren=4 for Pr-Dy andn=4.5 for Ho-Lu, Y) is described. The compounds obtained were studied by TG, DTG and DTA over the temperature interval 25–500‡C and by X-ray powder diffraction and chemical analysis. Three structurally different groups were recognized. It was found that either rare earth oxide or basic carbonate (Ln2O2·CO3) and potassium carbonate were obtained as final product at 500‡C, depending on the rare earth element. The thermal decomposition takes place in two well-resolved stages.
Abstract
Rare earth picrate complexes with L-leucine (Leu) were synthesized and characterized. Elemental analysis (CHN), EDTA titrations and thermogravimetric data suggest a general formula RE(pic)32Leu⋅5H2O (RE=La–Lu, Y and pic=picrate). IR spectra indicate the presence of water and suggest that L-leucine is coordinated to the central ion through the nitrogen of the aminogroup. The absorption spectrum of the solid Nd compound indicates that the metal-ligand bonds show a weak covalent character. Emission spectra and biexponential behavior of the luminescence decay of the Eu compound suggest the existence of polymeric species. Thermal analysis results indicate that all the compounds present a similar behavior, with five major thermal decomposition steps. The final products are rare earth oxides. A slow heating rate is necessary to observe all decomposition steps.
