One step hydrothermal synthesis of LaFeO3 perovskite

This work describes the synthesis of LaFeO3 oxide, using a one-step hydrothermal synthesis route, to obtain a solid exhibiting superficial, morphological and textural properties useful for potential applications. The synthesis process starts from corresponding metal nitrates of lanthanum and iron in well-defined concentration and KOH as mineralizing agent. The reaction is developed in a Teflon-lined stainless steel autoclave at 300 °C for 14 days. The composition and surface area were determined with X-ray fluorescence (XRF) and nitrogen adsorption isotherms (BET), verifying the obtaining of a stoichiometric, high, and active phase of oxide. The crystalline structure was evaluated with X-ray diffraction analysis (XRD), showing a pure orthorhombic perovskite phase. TPR results show the development of three single steps at different temperatures, kinetically detectable and related with reduction of component oxides. Scanning and transmission electron microscopy (SEM-TEM) results showed a remarkable degree of crystallization, favouring a specific morphology as a result of the low consolidation temperature of the perovskite phase. Catalytic test by means of methane reaction, performed along 240 on stream, reveals a light deactivation rate, decreasing progressively 7.1% until 60% of methane conversion, indicating the improved morphological and surface characteristics for potential applications

Development and Characterization of Glass-Ceramics from Combinations of Slag, Fly Ash, and Glass Cullet without Adding Nucleating Agents

Developments in the field of materials science are contributing to providing solutions for the recycling of industrial residues to develop new materials. Such approaches generate new products and provide optimal alternatives to the final disposal of different types of industrial wastes. This research focused on identifying and characterizing slag, fly ash, and glass cullet from the Boyacá region in Colombia as raw materials for producing glass-ceramics, with the innovative aspect of the use of these three residues without the addition of nucleating agents to produce the glass-ceramics. To characterize the starting materials, X-ray diffraction (XRD), X-ray fluorescence (XRF), and Scanning Electron Microscopy (SEM) techniques were used. The results were used to evaluate the best conditions to produce mixtures of the three waste components and to determine the specific compositions of glass-ceramics to achieve products with attractive technical properties for potential industrial applications. The proposed mixtures were based on three compositions: Mixture 1, 2, and 3. The materials were obtained through thermal treatment at 1200 °C in a tubular furnace in accordance with the results of a comprehensive characterization using thermal analysis. The microstructure, thermal stability, and structural characteristics of the samples were examined through SEM, differential thermal analysis (DTA), and XRD analyses, which showed that the main crystalline phases were diopside and anorthite, with a small amount of enstatite and gehlenite. The obtained glass-ceramics showed properties of technical significance for structural applications

Síntesis de óxidos tipo perovskita, mediante polimerización con acido cítrico y combustión con glicina.

En este trabajo se describe la preparación de la perovskita La0.25 Sr 0.25 CO 0.5 Fe 0.5 O3 (LSCoF), mediante la polimerización con acido cítrico y combustión con glicina, con el propósito de obtener materiales para potenciales aplicaciones catalíticas, eléctricas y electroquímicas; para ellos los sólidos se caracterizaron mediante difracción de rayos X (DRX) y microscopia electrónica de barrido (SEM); obteniendo información acerca de la formación y pureza de fases, la morfología, la estructura y las propiedades superficiales del sistema; indicando que es posible obtener sólidos con una distribución de grano homogéneo, textura y relieve característicos

Synthesis and Characterization of a Simple La 0.8 Sr 0.2 CrO3 perovskite.

En este trabajo se explora la síntesis y caracterización de un óxido cerámico tipo La 0.8 Sr 0.2 CrO3, a través de intermediarios tipo citrato que propiciaron la obtención de una fase cristalina pura del material a 900 grados centígrados. En la etapa inicial del proceso se partió de disoluciones de nitratos y ácido cítrico, que se tratarom a una temperatura de 120 grados centígrados, hasta la consolidación de un gel que luego de ser tratado a 250 grados centígrados conformó un precursor metal orgánico que sirvió de base para la obtención del óxido cerámico. El precursor se caracterizó por espectroscopia infrarroja (FTIR) y análisis térmico (TGA-DTA), para evaluar la formación de los respectivos citratos e identificar la temperatura ideal de tratamiento térmico para evitar la potencial volatización de especies de cromo. El material calcinado se caracterizó por difracción de rayos X (XRF)y microscopía electrónica (SEM-TEM), los resultados permitieron identificar la morfología, la textura y las características superficiales del material, con tamaños promedio de cristalito de 45 nm y distancias interplanares de 0.29 nm para el principal plano de difracción (1 1 2). La composición química del sólido fue determinada mediante fluorecencia de rayos X (XRF), indicando la efectividad del método de síntesis propuesto

Combustion synthesis, structural and magnetic characterization of Ce1-xPrxO2 system

The current work describes the synthesis of Ce1−xPrxO2 (x = 0.0, 0.2, 0.4, 0.6, 0.8) and Pr6O11 systems by the combustion method, using citric acid as chelating agent. The obtained solids after combustion and calcination processes were characterized by thermal analysis (TGA-DTA) and infrared spectroscopy (FT-IR) to evaluate the chemical process during the combustion reaction. The surface area analysis using isotherms of nitrogen adsorption, reveal that all samples exhibit values between 70 and 135 m2 g−1, with a pore volume that allows its classification as mesoporous materials. The structural analysis by X-ray diffraction (XRD) and Rietveld refinement, revealed the obtention of a pure cubic structure Fm3m (225) along all cerium oxide modifications with nanocrystalline domain sizes, except for the praseodymium oxide that shows two crystalline phases in a monoclinic crystalline phase P121/c 1 (14) in the case of Pr6O11 and a cubic phase Fm3m (225) for PrO2 oxide. The oxygen storage capacity measurements performed in all samples, demonstrate that exchange of Ce ions by Pr increases the storage capacity of samples over the reference values in accordance with the synthesis method. The characterization by high-resolution transmission electron microscopy, confirmed that the solids are composed by nanometric aggregates with d spacing between 0.29 and 0.31 nm along main diffraction signals, in accordance with the experimental XRD results. Finally, the magnetic characterization in a ZFC configuration and a M-H mode, shows a strong paramagnetic behavior in all systems except in CeO2 oxide, which exhibited a prevalent diamagnetic behavior

Effect of Pr on the electrical and chemical properties of cerium oxide prepared by combustion method

Nanoparticles of Ce1−xPrxO2 (X: 0.6 and 0.8), were synthesized by the combustion method using citric acid as chelating and fuel agent. The X‐ray diffraction patterns and Rietveld refinements confirm that samples shown as a single phase in a cubic fluorite structure, with an increase in the lattice parameter as a function of Pr con-centration. The crystallite size domains obtained by the Scherrer formula, confirm values around 10 and 37 nm. The scanning electron microscopy images, show that the solids are composed of dense heterogeneous aggregates. The X‐ray photoelectron spectroscopy, reveals that oxides are composed of cerium and praseodymium cations in oxidation states 4+ and 3+ respectively. The TPR‐H2 profiles indicate that cerium and praseodymium cations present in the obtained systems are completely reduced to Ce3+ and Pr3+ at temperatures above 790°C. The impedance spectroscopy data at room temperature showed that the conduction processes for the two systems take place at the grain boundaries. The Ce0.2Pr0.8O2 system offer lower resistance, due to the high amount of Pr3+ ions inserted in the structure and the high amount of oxygen vacancies formed in the synthesis process