Synthesis and characterization of lanthanum- and yttrium-doped Fe2O3 pigments

MELO, D. M. A. et al. Synthesis and charactezarion of lanthanum and yttrium doped Fe2O3 pigments. Cerâmica, São Paulo, v. 53, p. 79-82, 2007.

Síntese, caracterização e cinética da decomposição térmica dos materiais cerâmicos PrMO3 (M = Ni ou Co)

In this work have been studied the preparation, characterization and kinetic study of decomposition of the polymerizing agent used in the synthesis under non-isothermal condition ceramics PrMO3 of general formula (M = Co and Ni). These materials were obtained starting from the respective metal nitrates, as a cations source, and making use of gelatin as polymerizing agent. The powders were calcined at temperatures of 500°C, 700°C and 900°C and characterized by X-ray Diffraction (XRD), Thermogravimetric Analysis (TG / DTG/ DTA), Infrared Spectroscopy (FTIR), Temperature Programmed Reduction (TPR) and Scanning Electron Microscopy (SEM). The perovskite phase was detected in all the X-rays patterns. In the infrared spectroscopy observed the oxide formation as the calcination temperature increases with the appearance of the band metal - oxygen. The images of SEM revealed uniform distribution for the PrCoO3 and particles agglomerated as consequence of particle size for PrNiO3. From the data of thermal analysis, the kinetics of decomposition of organic matter was employed using the kinetics methods called Model Free Kinetics and Flynn and Wall, in the heating ratios 10, 20 and 30° C.min-1 between room temperature and 700°C. Finally, been obtained the values of activation energy for the region of greatest decomposition of organic matter in samples that were determined by the degree of conversion (α)

Síntese e caracterização de catalisadores nanométricos de LaSrNiO4 para aplicação em dessulfurização de tiofeno

The mixed metal oxides constitute an important class of catalytic materials widely investigated in different fields of applications. Studies of rare earth nickelates have been carried by several researchers in order to investigate the structural stability afforded by oxide formed and the existence of catalytic properties at room temperature. So, this study aims synthesize the nanosized catalyst of nickelate of lanthanum doped with strontium (La(1-x)SrxNiO4-d; x = 0,2 and 0,3), through the Pechini method and your characterization for subsequent application in the desulfurization of thiophene reaction. The precursor solutions were calcined at 300ºC/2h for pyrolysis of polyester and later calcinations occurred at temperatures of 500 - 1000°C. The resulting powders were characterized by thermogravimetric analysis (TG / DTG), surface area for adsorption of N2 by BET method, X-ray diffraction (XRD), scanning electron microscopy (HR_SEM) and spectrometry dispersive energy (EDS). The results of XRD had show that the perovskites obtained consist of two phases (LSN and NiO) and from 700ºC have crystalline structure. The results of SEM evidenced the obtainment of nanometric powders. The results of BET show that the powders have surface area within the range used in catalysis (5-50m2/g). The characterization of active sites was performed by reaction of desulfurization of thiophene at room temperature and 200ºC, the relation F/W equal to 0,7 mol h-1mcat -1. The products of the reaction were separated by gas chromatography and identified by the selective detection PFPD sulfur. All samples had presented conversion above 95%

Síntese e caracterização de cerâmicas nanométricas para produção de gás de síntese

In this work, ceramic powders belonging to the system Nd2-xSrxNiO4 (x = 0, 0.4, 0.8, 1.2 and 1.6) were synthesized for their use as catalysts to syngas production partial. It was used a synthesis route, relatively new, which makes use of gelatin as organic precursor. The powders were analyzed at several temperatures in order to obtain the perovskite phase and characterized by several techniques such as thermal analysis, X-rays diffraction, Rietveld refinement method, specific surface area, scanning electron microscopy, energy dispersive spectroscopy of X-rays and temperature programmed reduction. The results obtained using these techniques confirmed the feasibility of the synthesis method employed to obtain nanosized particles. The powders were tested in differential catalytic conditions for dry reforming of methane (DRM) and partial oxidation of methane (POM), then, some systems were chosen for catalytic integrals test for (POM) indicating that the system Nd2-xSrxNiO4 for x = 0, 0.4 and 1.2 calcined at 900 °C exhibit catalytic activity on the investigated experimental conditions in this work without showing signs of deactivation

Caracterização microestrutural e elétrica de La(FexNi1-x)O3 sintetizado pelo método da gelatina

The present work deals with the synthesis of materials with perovskite structure with the intention of using them as cathodes in fuel cells SOFC type. The perovskite type materials were obtained by chemical synthesis method, using gelatin as the substituent of citric acid and ethylene glycol, and polymerizing acting as chelating agent. The materials were characterized by X-ray diffraction, thermal analysis, spectroscopy Fourier transform infrared, scanning electron microscopy with EDS, surface area determination by the BET method and Term Reduction Program, TPR. The compounds were also characterized by electrical conductivity for the purpose of observing the possible application of this material as a cathode for fuel cells, solid oxide SOFC. The method using gelatin and polymerizing chelating agent for the preparation of materials with the perovskite structure allows the synthesis of crystalline materials and homogeneous. The results demonstrate that the route adopted to obtain materials were effective. The distorted perovskite structure have obtained the type orthorhombic and rhombohedral; important for fuel cell cathodes. The presentation material properties required of a candidate cathode materials for fuel cells. XRD analysis contacted by the distortion of the structures of the synthesized materials. The analyzes show that the electrical conductivity obtained materials have the potential to act as a cell to the cathode of solid oxide fuel, allowing to infer an order of values for the electrical conductivities of perovskites where LaFeO3 < LaNiO3 < LaNi0,5Fe0,5O3. It can be concluded that the activity of these perovskites is due to the presence of structural defects generated that depend on the method of synthesis and the subsequent heat treatment

Preparação e caracterização de filmes cerâmicos para cátodos de células a combustível de óxido sólido

Alternative and clean energy generation research has been intensified in last decades. Among the alternatives, fuel cells are one of the most important. There are different types of fuel cells, among which stands out intermediate temperature solid oxide fuel cell (IT-SOFC) matter of the present work. For application as cathode on this type of devices, the ceramic Ba0.5Sr0.5C0.8Fe0.2O3-δ doped with rare earth ions (Nd, Sm) have been quite promising because they show good ionic conductivity and operate at relatively low temperatures (500 - 800°C). In this work, Ba0.5Sr0.5Co0.8Fe0.2O3-δ, (BaSr)0.5Sm0.5Co0.8Fe0.2O3-δ and (BaSr)0.5Nd0.5C0.8Fe0.2O3-δ were obtained by modified Pechini method, making use of gelatin as polymerizing agent. The powders were characterized by X-Ray Diffraction (XRD), Temperature Programmed Reduction (TPR) and Scanning Electron Microscopy (SEM). The perovskite phase was observed in all X-ray patterns for the materials Ba0.5Sr0.5C0.8Fe0.2O3-δ doped with rare earth ions (Nd, Sm). The SEM images showed that the materials have a characteristics porous, with very uniform pore distribution, which are favorable for application as cathodes. Subsequently, screen-printed assymmetrical cells were studied by impedance spectroscopy, to assess the kinetics of the cathode for the reduction reaction of oxygen. The best resistance to the specific area was found for the cathode BSSCF sintered at 1050 °C for 4 hours with around 0.15 Ω.cm2 at 750 °C as well as cathodes BSNCF and BSCF obtained resistances specific area of 0.2 and 0.73 Ω.cm2, respectively, for the same conditions. The polarization curves showed similar behavior to the best cathodes BSSCF and BSNCF, such combination of properties indicates that the film potentially depict good performance as IT-SOFC cathodes

Síntese e caracterização de catalisadores de LaNiO3 não suportados e suportados em Al2O3 e ZrO2 para a reforma a vapor do metano

Ionic oxides with ABO3 structure, where A represents a rare earth element or an alkaline metal and B is a transition metal from group VIII of the periodic table are potential catalysts for oxidation and good candidates for steam reforming reaction. Different methods have been considered for the synthesis of the oxide materials with perovskite structure to produce a high homogeneous material with low amount of impurities and low calcination temperatures. In the current work, oxides with the LaNiO3 formula had been synthesized using the method of the polymeric precursors. The thermal treatment of the materials took place at 300 ºC for 2h. The material supported in alumina and/or zirconia was calcined at 800 ºC temperature for 4h. The samples had been characterized by the following techniques: thermogravimetry; infrared spectroscopy; X-ray diffraction; specific surface area; distribution of particle size; scanning electron microscopy and thermo-programmed reduction. The steam reforming reaction was carried out in a pilot plant using reducing atmosphere in the reactor with a mixture of 10% H2-Argon, a mass about 5g of catalyst, flowing at 50 mL.min-1. The temperature range used was 50 - 1000 oC with a heating rate of 10 oC.min-1. A thermal conductivity detector was used to analyze the gas after the water trapping, in order to permit to quantify the consumption of hydrogen for the lanthanum nickelates (LaNiO3). The results showed that lanthanum nickelate were more efficient when supported in alumina than when supported in zirconia. It was observed that the methane conversion was approximately 100% and the selectivity to hydrogen was about 70%. In all cases were verified low selectivity to CO and CO2

Caracterização morfológica e microestrutural da perovskita BaCexPr1-xO3 sintetizada a partir do método de complexação combinando EDTA/Citrato

In this study, binary perovskite (BaCexO3) were doped with praseodymium (Pr) to obtainment of the ternary material BaCexPr1-xO3. This material was synthesized by the complexation method combining EDTA/Citrate with the stoichiometric ratio of the element Praseodymium ranging from x = 0.1 to x = 0.9 in order to determine the influence of this rare earth element on the morphology and microstructure of the final powder. At first the material was synthesized based on the route proposed by literature (Santos, 2010), and then characterized by SEM and XRD, besides being refined by the Rietveld method. In the material that had lowest residual parameter, S, and lowest average size of crystal, pH variation of synthesis solution was made in order to identify the influence of this parameter on the morphology and microscopy of the final powder. The results show that addition of praseodymium did not directly influence the crystallographic and lattice parameters, keeping even the same orthorhombic structure of the binary material BaCexO3, according to Yamanaka et al (2003). Material type BaCe0,2Pr0,8O3 had lowest residual parameter (S=1.4) and lowest average size of crystallite (26.4 nm), being used as reference in the pH variation of synthesis solution for 9, 7, 5 and 3, respectively. Variation of this parameter showed that when the synthesis solution pH was decreased to below 11, there was an increase in the average size of crystals, for pH 9, about 58.3%, for pH 7 (30.3 %), for pH 2 (2.3%) and for pH 3 (42%), indicating that the value initially used and quoted by Santos (2010) was the most coherent

Síntese de Fischer-Tropsch sobre perovskitas LayCu0,4Fe0,6O3

The current natural gas production of 52 Mm3d-1 and the large projects for its expansion has been setting new boundaries for the Brazilian industry of oil and gas. So far, one of the biggest challenges regards to the logistics for gas transportation from offshore fields. Therefore, the transformation of natural gas into gasoline, diesel and/or olefins via Fischer-Tropsch synthesis would be an alternative to this matter. In this work, the production of hydrocarbons by Fischer-Tropsch synthesis in a slurry reactor was investigated and a perovskite-type catalyst (LayCu0,4Fe0,6O3 ± d) was used with y varying from 0 to 1 on a molar basis. In addition, Nb2O5 support was also applied in order to observe the selectivity of the produced hydrocarbons by the Fischer-Tropsch process. It is shown that the hydrogen conversion was influenced by the support as well as the different phases of the samples. The kinetic results for the CO2 production suffered great influence with the introduction of the Nb2O5 support throughout the series of samples studied. The catalysts allowed obtaining welldefined cuts of hydrocarbons in the range of C1-C6 and C17-C28, and these results were clearly influenced by the support and the lanthanum content. The higher olefin/paraffin ratio obtained was 1.8 when using a non-supported perovskite with y equal to 0.8. This would indicate the suitability of using this material for the production of olefins

Estudo dos óxidos A2B2O7 e ABO3 a base de terras raras, para aplicações térmicas e catalíticas a altas temperaturas

Rare earth elements have recently been involved in a range of advanced technologies like microelectronics, membranes for catalytic conversion and applications in gas sensors. In the family of rare earth elements like cerium can play a key role in such industrial applications. However, the high cost of these materials and the control and efficiencies associated processes required for its use in advanced technologies, are a permanent obstacle to its industrial development. In present study was proposed the creation of phases based on rare earth elements that can be used because of its thermal behavior, ionic conduction and catalytic properties. This way were studied two types of structure (ABO3 and A2B2O7), the basis of rare earths, observing their transport properties of ionic and electronic, as well as their catalytic applications in the treatment of methane. For the process of obtaining the first structure, a new synthesis method based on the use of EDTA citrate mixture was used to develop a precursor, which undergone heat treatment at 950 ° C resulted in the development of submicron phase BaCeO3 powders. The catalytic activity of perovskite begins at 450 ° C to achieve complete conversion at 675 ° C, where at this temperature, the catalytic efficiency of the phase is maximum. The evolution of conductivity with temperature for the perovskite phase revealed a series of electrical changes strongly correlated with structural transitions known in the literature. Finally, we can establish a real correlation between the high catalytic activity observed around the temperature of 650 ° C and increasing the oxygen ionic conductivity. For the second structure, showed clearly that it is possible, through chemical processes optimized to separate the rare earth elements and synthesize a pyrochlore phase TR2Ce2O7 particular formula. This "extracted phase" can be obtained directly at low cost, based on complex systems made of natural minerals and tailings, such as monazite. Moreover, this method is applied to matters of "no cost", which is the case of waste, making a preparation method of phases useful for high technology applications

Cálculos AB initio de propriedades estruturais, eletrônicas e ópticas de colmpostos CaXo3 (X=Si, Ge, Sn)

In this work we present a study of structural, electronic and optical properties, at ambient conditions, of CaSiO3, CaGeO3 and CaSnO3 crystals, all of them a member of Ca-perovskite class. To each one, we have performed density functional theory ab initio calculations within LDA and GGA approximations of the structural parameters, geometry optimization, unit cell volume, density, angles and interatomic length, band structure, carriers effective masses, total and partial density of states, dielectric function, refractive index, optical absorption, reflectivity, optical conductivity and loss function. A result comparative procedure was done between LDA and GGA calculations, a exception to CaSiO3 where only LDA calculation was performed, due high computational cost that its low symmetry crystalline structure imposed. The Ca-perovskite bibliography have shown the absence of electronic structure calculations about this materials, justifying the present work

Síntese e caracterização de componentes nanoestruturados de células a combustível de óxidos sólidos

Perovskite-like ceramic materials present the general formula ABO3, where A is a rare earth element or an alkaline metal element, and B is a transition metal. These materials are strong candidates to assume the position of cathode in Solid Oxide Fuel Cells (SOFC), because they present thermal stability at elevated temperatures and interesting chemical and physical properties, such as superconductivity, dieletricity, magnetic resistivity, piezoelectricity, catalytic activity and electrocatalytic and optical properties. In this work the cathodes of Solid Oxide Fuel Cells with the perovskite structure of La1-xSrxMnO3 (x = 0.15, 0.22, 0.30) and the electrolyte composed of zirconia-stabilized-yttria were synthesized by the Pechini method. The obtained resins were thermal treatment at 300 ºC for 2h and the obtained precursors were characterized by thermal analysis by DTA and TG / DTG. The powder precursors were calcined at temperatures from 450 to 1350ºC and were analyzed using XRD, FTIR, laser granulometry, XRF, surface area measurement by BET and SEM methods. The pellets were sintered from the powder to the study of bulk density and thermal expansion

Síntese e caracterização de carreadores de oxigênio para combustão com recirculação química obtidos via reação de combustão assistida por microondas

Perovskites oxides win importance by its properties and commercials applications, they have a high thermal stability, have conductive properties, electrical, catalytic, electro catalytic, optical and magnetic, and are thermally stable. Because of these properties, are being widely studied as carriers of oxygen in the process of power generation with CO2 capture. In this work, the base carrier system La1-xMexNiO3 (Me = Ca and Sr) were synthesized by the method via the combustion reaction assisted by microwave. were synthesized from the combustion reaction method by microwave process. This method control the synthesi`s conditions to obtain materials with specific characteristics. The carriers calcined at 800 ° C/2h were analyzed by thermal analysis (TG-DTA), to verify its thermal stability, X-ray diffraction (XRD) to verify the phase formation, with subsequent refinement by the Rietveld method, to quantify the percentage of phases formed, the surface area by BET method was determined, scanning electron microscopy (SEM) was obtained to evaluate the material morphology and temperature programmed reduction (TPR) was done to observe the metallic phase of the nickel. After all proposed characterization and analysis of their results can be inferred to these oxides, key features so that they can be applied as carriers for combustion reactions in chemical cycles. The final products showed perovskite-type structures K2NiF4 (main) and ABO3.

Caracterização dos eletrocatalisadores LaMnO3, LaFeO3, LaFe0,2Mn0,8O3 E La0,5Fe0,5MnO3 preparados por autocombustão assistida por microondas para cátodos de células a combustível do tipo SOFC

Materials consisting of perovskite-type oxides (ABO3) have been developed in this work for applications in fuel cell cathodes of solid oxide type (SOFC). These ceramic materials are widely studied for this type of application because they have excellent electrical properties, conductivity and electrocatalytic. The oxides LaMnO3, LaFeO3, LaFe0.2Mn0.8O3 e La0.5Fe0.5MnO3 were synthesized by the method of microwave assisted combustion and after sintering at 800°C in order to obtain the desired phases. The powders were characterized by thermogravimetry (TG), X-ray diffraction (XRD), X-ray fluorescence (XRF), scanning electron microscopy (SEM) and voltammetric analysis (cyclic voltammetry and polarization curves). The results obtained by XRF technique showed that the microwave synthesis method was effective in obtaining doping oxides with values near stoichiometric. In general, powders were obtained with particle size less than 0.5 μm, having a porous structure and uniform particle size distribution. The particles showed spherical form, irregular and crowded of varying sizes, according to the analysis of SEM. The behavior of the oxides opposite the thermal stability was monitored by thermogravimetric curves (TG), which showed low weight loss values for all samples, especially those of manganese had its structure. By means of Xray diffraction of the samples sintered at 800°C was possible to observe the formation of powders having high levels of crystallinity. Furthermore, undesirable phases such as La2O3 and MnOx were not identified in the diffractograms. These phases block the transport of oxygen ions in the electrode/electrolyte interface, affecting the electrochemical activity of the system. The voltammetric analysis of the electrocatalysts LF-800, LM-800, LF2M8-800 e L5F5M-800 revealed that these materials are excellent electrical conductors, because it increased the passage of electrical current of the working electrode significantly. Best performance for the oxygen reduction reaction was observed with iron-rich structures, considering that the materials obtained have characteristics suitable for use in fuel cell cathodes of solid oxide type

Síntese, caracterização e estudo das propriedades magnéticas de ortoferritas de lantânio dopadas com manganês

Orthoferrites AFeO3 (A = rare earth) are an important class of perovskite oxides that exhibit weak ferromagnetism. These materials find numerous applications as chemical sensors, cathodes for fuel cells and catalysis, which make them interesting from the standpoint of science and technology. Their structural, electrical and magnetic properties are dependent on many factors such as the preparation method, heat treatment conditions, chemical composition and replacement of cations in sites A and/or B. In this paper, LaFe1-xMnxO3 (0 ≤ x ≤ 1) orthoferrites-type was prepared by Pechini method and Microwave-assisted combustion reaction in order to evaluate the influence of synthesis route on the formation of oxide, as well as the effect of parcial replacement of iron by manganese and heat treatment on the magnetic properties. The precursor powders were calcined at 700°C, 900°C, 1100°C and 1300°C for 4 hours and they were characterized by the techniques: Thermogravimetric analysis (TGA), X ray diffraction (XRD), Refinement by Rietveld method, Scanning electron microscopy (SEM), Reduction temperature programmed (RTP) and Magnetic hysteresis measurements performed at room temperature. According to the XRD patterns, the formation of perovskite phase with orthorhombic structure was observed for the systems where 0 ≤ x ≤ 0.5 and rhombohedral for x = 1. The results also showed a decrease of lattice parameters with the parcial replacement of iron by manganese and consequently a reduction in cell volume. The hysteresis curves exhibited weak ferromagnetism for the systems prepared by both synthesis methods. However, a dependence of magnetization as a function of dopant content was observed for samples produced by Pechini method. As for the systems prepared by combustion reaction, it was found that the secondary phases exert a strong influence on the magnetic behavior