Novel uses of the thermo-microbalance in the determination of nonstoichiometry in complex oxide systems

1974 ◽  
Vol 11 (1) ◽  
pp. 434-439 ◽  
Author(s):  
Robert L. Holman
Keyword(s):  
Complex Oxide ◽  
Oxide Systems

A Potentiometric Study on Proton-Transfer Equilibria and Cationic Conjugation in Pyridine N-Oxide Systems in Acetone and Methanol

1996 ◽  
Vol 49 (9) ◽  
pp. 931 ◽  
Author(s):  
L Chmurzynski ◽  
E Kaczmarczyk ◽  
M Nesterowicz ◽  
G Wawrzyniak ◽  
Z Warnke
Keyword(s):  
Proton Transfer ◽  
Equilibrium Constants ◽  
Proton Donor ◽  
Heterocyclic Amines ◽  
Transfer Reactions ◽  
Oxide Systems ◽  
Experimental Systems ◽  
Proton Transfer Reactions ◽  
Potentiometric Titration Method

The potentiometric titration method has been used to study the equilibria of cationic in sytems formed by substituted pyridine N-oxides in the polar, non-aqueous solvents acetone and methanol. For comparison, the systems with trimethylamine N-oxide as a representative of aliphatic amine N-oxides and pyridine representing parent heterocyclic amines were also studied. The cationic heteroconjugation constants, i.e. the equilibrium constants for conjugation reactions between free and protonated N-bases leading to the formation of unsymmetric BHB'+ cations, were determined in experimental systems with and without proton transfer. It was found that there were significant differences in the values of the cationic heteroconjugation constants determined in these two acid-base systems. The proton-transfer reactions limit and even preclude the determination of the cationic heteroconjugation constants. On this basis it was concluded that the heteroconjugation constants should be determined in systems without proton transfer. In such systems, in the amphiprotic solvent methanol, cationic heteroconjugation was ascertained in all substituted pyridine N-oxide systems, the values of heteroconjugation constants being relatively low (logarithms of their values of the order of 2-2.5), and only negligible in systems involving trimethylamine N-oxide. A more pronounced tendency towards cationic heteroconjugation of the [OHO]+ type was observed in the aprotic protophobic acetone, where heteroconjugation constants were determined for all amine N-oxide systems studied including those containing protonated trimethylamine N-oxide as a proton donor. However, the values of the cationic heteroconjugation constants were found to be, in methanol likewise, relatively low (log KBHB'+ of the order of 2-3). On the contrary, a greater extent of cationic heteroconjugation equilibria was observed in methanol than in acetone in the case of systems containing pyridine, i.e. [NHO]+ type bridges formed by amine N-oxides and heterocyclic amines. In methanol the heteroconjugation constants turned out to be determinable for all such systems studied (logarithms of the equilibrium constants being of the same order as for N-oxide systems), whereas in acetone the hetero constants were indeterminable for all systems.

Synthesis of YFeO3-δ and LaFeO3-δ Perovskites with High Catalytic Activity in Carbon Oxidation Reactions

2021 ◽  
Vol 316 ◽  
pp. 105-109
Author(s):  
Evgeny A. Kirichenko ◽  
Pavel G. Chigrin ◽  
Anton A. Gnidenko
Keyword(s):  
Oxidation Mechanism ◽  
Soot Oxidation ◽  
Complex Oxide ◽  
Maximum Temperature ◽  
High Catalytic Activity ◽  
Carbon Oxidation ◽  
Oxidation Reactions ◽  
Oxide Systems ◽  
Reduction Of Metal Oxides ◽  
Catalytic Reaction Mechanism

YFeO3-δ (δ = 0.26) and LaFeO3-δ (δ = 0.5) perovskites with a high specific surface and oxygen non-stoichiometry was firstly synthesized by pyrolysis of polymer-salt compositions. It was shown that the catalytic oxidation of carbon in the presence of these complex oxide systems proceeds in the range of 400 - 700 °С, with a maximum temperature at 556 °С for YFeO3-δ; and 380 - 620 °С ,with a maximum temperature at 501 °С for LaFeO3-δ, in one-stage mode for both. By means of thermal analysis and diffractometry, it was shown that there is no contribution to the soot oxidation mechanism by cyclic perovskite surface transformations, due to the reduction of metal oxides by the soot and their subsequent reoxidation. It has been established that the basis of the catalytic reaction mechanism for both perovskites is the presence of oxygen vacancies on the surface of complex oxides.

scholarly journals FP-LAPW Study of the EFG at Impurity Sites in Oxides: Cd in Rutile TiO2

2000 ◽  
Vol 55 (1-2) ◽  
pp. 267-270 ◽  
Author(s):  
Leonardo A. Errico ◽  
Gabriel Fabricius ◽  
Mario Rentería
Keyword(s):  
Electric Field ◽  
Electric Field Gradient ◽  
First Principles ◽  
Asymmetry Parameter ◽  
Oxide Systems ◽  
Absolute Value ◽  
Nearest Neighbours ◽  
Impurity Sites ◽  
Cation Sites

We report here first-principles determination of the electric-field gradient (EFG) tensor at the Cd im-purity located at cation sites in rutile TiO2 . As far as we know, these represent the first ab initio calcu-lations at impurity sites with the FP-LAPW method in oxide systems. We used super-cells to simulate the diluted impurity in the crystal. The free-relaxation process performed in our study shows that the changes in distances of the oxygen nearest-neighbours to the impurity are not isotropic as was suppo-sed in a previous study within the muffin-tin approximation. Our prediction for the EFG component of major absolute value agrees well with the experiment and is opposite in sign and direction if isotropic relaxations are assumed. Our value of the asymmetry parameter η also compares very well with the ex-perimental value.

A Study of Evaporation of Complex Oxide Systems Based on Chromium(III) Oxide

2003 ◽  
Vol 76 (10) ◽  
pp. 1564-1567 ◽  
Author(s):  
V. A. Popov ◽  
S. I. Lopatin ◽  
L. Sh. Tsemekhman ◽  
L. A. Pavlinova ◽  
S. P. Kormilitsyn ◽  
...  
Keyword(s):  
Complex Oxide ◽  
Oxide Systems

Quantitative Determination of Chromium Valence in Environmental Samples Using Xafs Spectroscopy

1996 ◽  
Vol 432 ◽  
Author(s):  
M. L. Peterson ◽  
G. E. Brown ◽  
G. A. Parks
Keyword(s):  
Ab Initio ◽  
Sample Pretreatment ◽  
Complex Oxide ◽  
Quantitative Information ◽  
Model Compounds ◽  
Xafs Spectroscopy ◽  
Industrial Sites ◽  
X Ray Absorption ◽  
Exafs Spectra

AbstractSynchrotron x-ray absorption fine structure (XAFS) spectroscopy provides quantitative information on the speciation of Cr in complex oxide samples, including the Cr(VI):Cr(III) ratio, without any sample pretreatment. We discuss several XAFS methods that can be used for this purpose, including: (1) measurement of the height of the pre-edge peak of Cr K-edge spectra which is caused by ls→3d electronic transitions occurring predominately in the Cr(VI)O4 tetrahedron; (2) fitting observed XANES spectra using combinations of experimental spectra from Cr(III)- and Cr(VI)-containing model compounds; (3) fitting observed EXAFS spectra using combinations of experimental spectra from Cr(III)- and Cr(VI)-containing model compounds; and (4) ab-initio modeling of observed Cr K-EXAFS spectra using theoretical phase-shift and amplitude parameters for Cr(III)O6 and Cr(VI)O4 models. The first method is shown to be the simplest and most accurate. The samples examined using these methods include highly pure model compounds, Cr3+2O3 and Na2Cr6+O4·4H42O, as well as more complex soil samples taken from Cr-contaminated industrial sites and Cr waste disposal pits. We present XAFS evidence for the reduction of Cr(VI) to Cr(III) after reaction with the Fe(Il)-bearing oxide magnetite, Fe3O4, and show that Cr associated with magnetite in soils is reduced, whereas that associated with non-Fe(II)-bearing silicate minerals is not. Also presented are ab-initio multiplescattering calculations of XANES spectra of an Cr(VI)O4 tetrahedron, which help explain the XANES features of this Cr species in solids and aqueous solutions.

scholarly journals CHARACTERIZATION OF THE SOL-GEL PROCESS IN THE SYSTEM YxBax+nCu2x+nOδ (x = 1, n=1, x=2, n=3, x=3, n=2)

2017 ◽  
pp. 31-34
Author(s):  
A. Pilipenko ◽  
I. Fesych ◽  
S. Nedilko ◽  
A. Dzyazko
Keyword(s):  
Electron Microscopy ◽  
Heat Treatment ◽  
Solid Phase ◽  
Sol Gel ◽  
Complex Oxide ◽  
Present Calculation ◽  
Calculation Algorithm ◽  
Oxide Systems ◽  
Chemical Homogeneity ◽  
Lower Temperature

With the help of sol-gel technology was obtained superconducting compound number YxBax+nCu2x+nOδ (x=1, n=1; x=2, n=3; x=3, n=2) with submicron size particles. As a gel maker in these systems was used citric acid monohydrate. An extensive scheme fusion technology was shown. The process described synthesis using thermal, infrared spectroscopic analysis and scanning electron microscopy. There are some aggregations of microparticles mostly for the phases that are synthesized at higher temperatures. Due to Thermal Analysis of modes were optimized heat treatment samples. According to IR spectroscopy were controlled processes of decomposition of the charge and the formation of the superconducting phase. It was grounded the choice of analysis methods for the starting compounds and the present calculation algorithm for this synthesis. Studies have shown that even at the beginning of the synthesis batch contained no impurity compound allowing argued that the sol-gel synthesis is a promising method that provides high homogeneity of the material the early stages of the synthesis and enables lower temperature and a subsequent heat treatment. The results of electron microscopy showed that due to the relatively low temperature of synthesis occurs the formation of submicron sized particles, while solid-phase techniques facilitate rapid crystal growth due to the formation of liquid phases at high temperature. The principles and ideas described in this paper can be adapted to more complex oxide systems. Thus, in this paper describes how you can achieve chemical homogeneity at the molecular level in multicomponent systems YxBax+nCu2x+nOδ (x=1, n=1; x=2, n=3; x=3, n=2) using sol-gel technology.

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