Search Results

You are looking at 1 - 10 of 120 items for :

  • "perovskites" x
  • All content x
Clear All

successful worldwide. Several reports have argued that the perovskite metal oxide has the ability to promote the conversion of soot into CO 2 in catalytic traps. The perovskite metal oxide is a general formula ABO 3 , in which the A site is generally

Open access

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.

Restricted access
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.

Restricted access

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.

Restricted access
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.

Restricted access

Abstract  

Perovskite oxides of composition (Sr1-xCax)(Fe0.5Co0.5)O3- were investigated for CO2 absorption properties and were proved to be useful as materials for CO2 absorption in the temperature range from 550 to 850 °C. The absorption rate of CO2 increased with Ca doping. The mechanical treatment of perovskite oxides for several minutes, especially for the oxides containing a small amount of Ca, was found to be effective for activating the oxides for CO2 absorption and for reducing the starting temperature of CO2 absorption by about 80 °C. However, it was not less effective to treat the oxides for a long time. The site distortion due to Sr and Ca ions at site A and the mixed valence states at site B were confirmed to be effective for CO2 absorption at high temperatures. During the absorption of CO2, a spinel compound was formed according to the following reaction: 2(Sr,Ca)(Fe,Co)O2.5 + CO2 (Sr,Ca)CO3 + (Sr,Ca)(Fe,Co)2O4.

Restricted access
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.

Restricted access

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.

Restricted access

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.

Restricted access

Abstract  

La0.8 A'0.2 MnO3+δ (A'=Sr, Ba, K, Cs) perovskites were studied by temperature-programmed reduction. The amount of non-stoichiometric oxygen was found to decrease from δ=0.16 for LaMnO3+δ to δ=0.07 (Sr-), 0.06 (Ba-), 0.07 (K-) and 0.03 (Cs-) substituted manganites. The reducibility at low and mean-temperatures (t<500C) increased in the sequence La<(La, Sr)≈(La, Ba)<(La, Cs)<(La, K).

Restricted access