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

Glass-Ceramic Materials Obtained by Sintering of Vitreous Powders from Industrial Waste: Production and Properties

Glass-ceramics are advanced inorganic silicate materials that can be obtained by sintering glass powders using a careful temperature control to result in the densification, nucleation, and crystallization of the material. In the current work, three different samples were obtained starting from amorphous silicate materials derived from mixtures of metallurgical slag, coal fly ash, and glass cullet, mixed in different proportions. The as-received waste samples were heat-treated to high temperatures to achieve complete melting at 1200, 1300, and 1400 °C for two hours, performing a rapid cooling in order to yield an amorphous material (glass). The obtained frit was ball-milled to a powder, which was then cold pressed to obtain compact pellets. The thermal treatment of pellets was carried out at 800–1100 °C for 2 h followed by a cooling rate of 10 °C/min to obtain the final glass-ceramics. The microstructure of samples was evaluated with scanning electron microscopy (SEM), which showed heterogeneous conglomerates and clusters of ~20 microns. The formation of crystalline phases was corroborated by means of X-ray diffraction (XRD) analysis, showing the presence of anorthite in all samples. Depending on the sample composition, other crystalline phases such as augite, enstatite, and diopside were detected. Using the Debye–Scherrer equation, it was possible to find the average size of the nano-crystalline domains. The quantification of the non-crystalline or amorphous fraction was also performed. Additionally, the density and porosity of the materials were calculated using the procedures defined in the ASTM C373 and ASTM C20 standards, measuring density values in the range 2.2–3.1 g·cm−3. The apparent porosity was approx. 33% in the three materials. Raman spectroscopy analysis showed characteristic signals associated with crystalline phases containing alumina, silica, iron, and calcium. Overall, the study confirmed the possibility of obtaining glass-ceramics with fine (nanometric) crystal sizes from a combination of silicate waste and the capability of modifying the crystalline composition by changing the proportions of the different wastes in the initial formulations

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