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Reaction Kinetics, Mechanisms and Catalysis
Authors: Z. Taheri, K. Nazari, N. Seyed-Matin, A. Safekordi, B. Ghanbari, S. Zarrinpashne, and R. Ahmadi

Abstract  

Three dense membranes of types SrCo0.8Fe0.2O3−δ (SCF(82)), La0.6Sr0.4Co0.8Fe0.2O3−δ (LSCF(6482)) and La0.8Sr0.2Co0.6Fe0.4O3−δ (LSCF(8264)) perovskites were prepared by complexation applying a chelating agent, ethylene diamine N,N,N′,N′-tetra-N-acetyl-diamine (EDTNAD). The oxygen permeation flux through the perovskite membranes was measured as a function of temperature within 1,073–1,223 K as well as the oxygen partial pressure of 0.1–1.0 bar. The oxygen permeation fluxes for the membranes, SCF(82), LSCF(6482), LSCF(8264) with the thickness of 0.85 mm were observed as 9.2 × 10−7 (mol/cm2 s), 1.7 × 10−7 (mol/cm2 s), and 1.0 × 10−7 (mol/cm2 s) in these cases at 1,153 K. The results indicated the oxygen permeation process was mainly controlled by the oxygen bulk diffusion through these membranes.

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Abstract  

Perovskite SrCo0.6Fe0.2Nb0.2O3-z attracts attention as a promising material with high oxygen conductivity. The sample was investigated by means of high-temperature X-ray powder diffraction and thermogravimetry. Phase transition was detected near 400 °C and accompanied with significant mass loss. The phase transition affects oxygen mobility, important for the synthesis of oxygen permeable membranes. The unit cell parameters are proved to change with temperature after two effects (1) reversible conventional thermal expansion and (2) irreversible contraction-expansion due to the changes in the oxygen content. In situ high-temperature X-ray diffraction experiments allowed us to separate the contributions and to measure them as a function of temperature.

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Abstract  

La0.8Cu0.2MnO3 and La0.8Sr0.2MnO3 perovskite catalysts were prepared by the co-precipitation method. The resistance of these catalysts to sulfur poisoning was tested via catalytic combustion of toluene. The results show that the perovskite catalysts were poisoned in the presence of SO2. In the presence of dodecyl mercaptan (C12H25SH), La0.8Sr0.2MnO3 exhibits better resistance to sulfur poisoning than La0.8Cu0.2MnO3. It was determined that the SO2 deactivation is due to the formation of CuSO4 on the catalyst surface.

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Abstract  

Perovskites belong to the great group of the inorganic pigments and thanks to their excellent properties they have been widely used in an industry. CaTiO3, BaTiO3 and SrTiO3 with the perovskite structure were prepared in this work. These compounds were synthesized with using the solid state reaction by calcination in temperature region 1000–1200°C. The thermal analysis was used for characterization of thermal behaviour and formation of tested perovskites. The main aim of this work was studied the influence of calcination temperature on colour properties of perovskites. Colour properties of powdered compounds and samples applied into ceramic transparent glaze P 07491 were also studied. The tested compounds can be described by different light colour hues and that depending on calcining temperature. The structures of the powdered compounds were studied by X-ray diffraction analysis.

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Journal of Thermal Analysis and Calorimetry
Authors: Márcia Silva, Mary Alves, S. Lima, L. Soledade, Elaine Paris, E. Longo, A. Souza, and Iêda Santos

Abstract  

Sr(Ti,Nd)O3 was synthesized in order to evaluate the influence of the amount of neodymium on the thermal and structural properties of SrTiO3. The synthesis was carried out using the polymeric precursor method. A small mass gain was observed for the SrTiO3 and SrTi0.98Nd0.02O3 samples accompanied by an exothermic peak in the DTA curves. Other steps at higher temperatures are assigned to the combustion of the organic material and carbonate. Elimination of defects by previous calcination of the precursors is responsible by the short and long range ordering of the perovskite. Cubic phase was obtained for undoped and doped SrTiO3.

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Journal of Radioanalytical and Nuclear Chemistry
Authors: Z. Németh, Z. Homonnay, F. Árva, Z. Klencsár, E. Kuzmann, J. Hakl, K. Vad, S. Mészáros, K. Kellner, G. Gritzner, and A. Vértes

Abstract  

In this paper we present 57Co emission Mössbauer and AC magnetic susceptibility studies of La0.8Sr0.2CoO3-δ perovskite. The observed coexistence of paramagnetic and magnetic subspectra in the 57Co emission Mössbauer spectra, as well as the difference of their isomer shifts support the existence of electronic phase separation in this perovskite, in good agreement with the double exchange based cluster model.

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Abstract  

Synthesis of perovskite-type oxides Ln1-xAxBO3 (Ln: lanthanoid; A: alkaline earth; B: transition metal) by heating at low temperature with large ratio of alkaline earth element, especially barium, easily involves impurity of alkaline earth carbonate. We succeeded to prepare the precursor without the formation of barium carbonate even at a large content of barium. The chemical state and structure of Ln1-xAxBO3- d (Ln: La, Eu; A: Ca, Sr, Ba: B: Fe, Mn) perovskite-type oxides prepared by using those precursors have been studied by Mössbauer spectroscopy and X-ray powder diffraction. The X-ray powder patterns showed many types of crystal system depending on x.

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Journal of Thermal Analysis and Calorimetry
Authors: V. Balek, H. Mitamura, T. Banba, M. Beneš, Z. Málek, I. N. Beckman, I. M. Bountseva, H. Haneda, and T. Mitsuhashi

Summary Emanation thermal analysis (ETA) was used to characterize thermal behaviour of the perovskite ceramics designed as a matrix for the encapsulation of high level radioactive waste. The perovskite ceramics (composition CaTiO3 where small admixtures of Nd and Ce simulated the radioactive elements Cm and Pu, respectively) was prepared from sol-gel precursors by hot pressing at 1250°C/29 MPa for 2 h. The chemical durability of the ceramics was tested by leaching in the solution with pH 2 at 90°C/2 months. ETA results of ‘as-leached’ and ‘as-prepared’ perovskite ceramics samples were compared and evaluated by means of a mathematical model. Three temperature ranges of the annealing of structure defects in the ‘as-prepared’ sample were determined from the decrease of radon release rate in the ranges 280-560, 800-960 and 960-1200°C, respectively. One annealing step was determined for the ‘as-leached’ sample from the decrease of radon release rate in the range of 800-950°C.

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Journal of Thermal Analysis and Calorimetry
Authors: Soraia de Souza, Mary Alves, A. de Oliveira, E. Longo, F. Ticiano Gomes Vieira, Rodinei Gomes, L. Soledade, A. de Souza, and Iêda Garcia dos Santos

Abstract  

In this work, the synthesis of Nd-doped SrSnO3 by the polymeric precursor method, with calcination between 250 and 700 °C is reported. The powder precursors were characterized by TG/DTA and high temperature X-ray diffraction (HTXRD). After heat treatment, the material was characterized by XRD and infrared spectroscopy. Ester and carbonate amounts were strictly related to Nd-doping. According to XRD patterns, the orthorhombic perovskite was obtained at 700 °C for SrSnO3 and SrSn0.99Nd0.01O3. For Sr0.99Nd0.01SnO3, the kinetics displayed an important hole in the crystallization process, as no peak was observed in HTXRD up to 700 °C, while a XRD patterns showed a crystalline material after calcination at 250 °C.

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Journal of Thermal Analysis and Calorimetry
Authors: Mary Alves, Soraia Souza, Márcia Silva, Elaine Paris, S. Lima, R. Gomes, E. Longo, A. de Souza, and Iêda Garcia dos Santos

Abstract  

SrSnO3 was synthesized by the polymeric precursor method with elimination of carbon in oxygen atmosphere at 250 °C for 24 h. The powder precursors were characterized by TG/DTA and high temperature X-ray diffraction (HTXRD). After calcination at 500, 600 and 700 °C for 2 h, samples were evaluated by X-ray diffraction (XRD), infrared spectroscopy (IR) and Rietveld refinement of the XRD patterns for samples calcined at 900, 1,000 and 1,100 °C. During thermal treatment of the powder precursor ester combustion was followed by carbonate decomposition and perovskite crystallization. No phase transition was observed as usually presented in literature for SrSnO3 that had only a rearrangement of SnO6 polyhedra.

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