Síntese e caracterização de óxidos de cério e cobalto obtidos por gel-combustão e Pechini aplicados às reações de oxidação de n-hexano

Oxide type spinel AB2O4 presents structure adjusted for application in the automobile industry. The spinel of cobalt has many practical applications had its excellent physical and chemical properties such as catalyst in hydrocarbon oxidation reaction. The CeO2 has been used in many of these processes because it assigns to a material with excellent thermal resistance and mechanics, high capacity of oxygen stockage (OSC) among others properties. This work deals with the synthesis, characterization and catalytic application of spinel of cobalt and CeO2 with fluorita structure, obtained for method of Pechini and method of Gel-Combustion. The process of Pechini, the puff was obtained at 300 ºC for 2 h in air. In the process of Gel-Combustion the approximately at 350 ºC material was prepared and burnt for Pyrolysis, both had been calcined at 500 ºC, 700 ºC, 900 ºC and 1050 ºC for 2 h in air. The materials of the calcinations had been characterized by TG/DTA, electronic microscopy of sweepings (MEV), spectroscopy of absorption in the infra-red ray (FTIR) and diffraction of X-rays (DRX). The obtained material reaches the phase oxide at 450 oC for Pechini method and 500 °C for combustion method. The samples were submitted catalytic reaction of n-hexane on superficies of materials. The reactor function in molar ration of 0, 85 mol.h-1.g-1 and temperature of system was 450 °C. The sample obtained for Pechini and support in alumine of superficial area of 178,63 m2.g-1 calcined at 700 ºC, give results of catalytic conversions of 39 % and the sample obtained for method of gel-combustion and support in alumina of 150 mesh calcined at 500 ºC result 13 % of conversion. Both method were selective specie C1

Síntese, estudo cinético e análise microestrutural do sistema cério-níquel obtido pelo método pechini

The cerium oxide has a high potential for use in removing pollutants after combustion, removal of organic matter in waste water and the fuel-cell technology. The nickel oxide is an attractive material due to its excellent chemical stability and their optical properties, electrical and magnetic. In this work, CeO2-NiO- systems on molars reasons 1:1(I), 1:2(II) e 1:3(III) metal-citric acid were synthesized using the Pechini method. We used techniques of TG / DTG and ATD to monitor the degradation process of organic matter to the formation of the oxide. By thermogravimetric analysis and applying the dynamic method proposed by Coats-Redfern, it was possible to study the reactions of thermal decomposition in order to propose the possible mechanism by which the reaction takes place, as well as the determination of kinetic parameters as activation energy, Ea, pre-exponential factor and parameters of activation. It was observed that both variables exert a significant influence on the formation of complex polymeric precursor. The model that best fitted the experimental data in the dynamic mode was R3, which consists of nuclear growth, which formed the nuclei grow to a continuous reaction interface, it proposes a spherical symmetry (order 2 / 3). The values of enthalpy of activation of the system showed that the reaction in the state of transition is exothermic. The variables of composition, together with the variable temperature of calcination were studied by different techniques such as XRD, IV and SEM. Also a study was conducted microstructure by the Rietveld method, the calculation routine was developed to run the package program FullProf Suite, and analyzed by pseudo-Voigt function. It was found that the molar ratio of variable metal-citric acid in the system CeO2-NiO (I), (II), (III) has strong influence on the microstructural properties, size of crystallites and microstrain network, and can be used to control these properties

Síntese pelo método pechini e caracterização da zircônia dopada com cério e neodímio

In this study five compositions were synthesized zirconia doped with cerium and neodymium ions in the system Ce10-xNdx Zr90O2 with 0,5 ≤ x ≤ 4,0 using the Pechini method. The powders were characterized by thermogravimetric analysis, differential thermal analysis, infrared spectroscopy and X-ray diffraction, with application of Rietveld refinement of the calcination temperatures of 350ºC/3h and 30 minutes at 900ºC/3h. All compositions stabilized with a mixture of cubic and tetragonal phase zirconia. The samples were pressed into bars and sintered at 1500°C/3h and 1500°C/6h, being characterized by Xray diffraction, with application of the Rietveld refinement, density and porosity using Archimedes method, scanning electron microscopy and resistance the three point bending. It has been observed the increase in strength with increasing sintering temperature for the compositions x = 2,0 and x = 4,0. For x = 2,0 the main phase was the cubic with 92,56% with crystallite size of 0,56 μm, density and porosity of 96,82% from 1,36%. For x = 4,0 was a mixture of cubic and tetragonal phase with 21% and 37,98%, respectively. The crystallite size was 54,21 nm and 49,64 nm with a density porosity of 97,45% and 1,32% respectively. In the analysis of the fracture surface was observed a greater amount of grain fracture intragranular type, which contribute to increase the mechanical strength of the ceramic. Increased addition of the neodymium ion in the crystal lattice of the zirconium showed a nearly linear behavior with increasing mechanical strength of the zirconia ceramic. Was obtained a bending resistance of 537 ± 38 MPa for the composition x = 2,0 predominantly attributed to cubic phase with 92,56%

Potassium niobate thin films prepared through polymeric precursor method

Thin films of potassium niobate were deposited on (100) Si substrates by the polymeric precursor method (Pechini method). Annealing in static air was performed at 600degrees C for 20 h. The obtained films were characterized by X-ray diffraction and atomic force microscopy (AFM). Electrical characterization of the films pointed to ferroelectricity via hysteresis loop. The dielectric constant, dissipation factor and resistance were measured in frequency region from 10 Hz to 10 MHz. At 1 MHz, the dielectric constant was 158 and the dissipation factor was 0.11. (C) 2004 Elsevier B.V. All rights reserved.

LiNbO3 thin films prepared through polymeric precursor method

Thin films of lithium niobate were deposited on (100) silicon by the polymeric precursor method (Pechini method). Annealing in static air was performed at 500degreesC for 3 h. The films obtained were characterized by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. Electrical characterization of the films pointed to ferroelectricity via hysteresis loop. The dielectric constant, dissipation factor and resistance were measured in the frequency region from 10 Hz to 10 MHz. At 1 MHz, the dielectric constant was 46 and the dissipation factor was 0.043. (C) 2002 Elsevier B.V. B.V. All rights reserved.

Óxido de zinco dopado com gálio preparado pelo método Pechini

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Influence of the precursor salts in the synthesis of CaSnO3 by the polymeric precursor method

CaSnO3 was synthesized by the polymeric precursor method, using different precursor salts as (CH3COO)(2)Ca. H2O, Ca(NO3)(2). 4H(2)O, CaCl2. 2H(2)O and CaCO3, leading to different results. Powder precursor was characterized using thermal analysis. Depending on the precursor different thermal behaviors were obtained. Results also indicate the formation of carbonates, confirmed by IR spectra. After calcination and characterization by XRD, the formation of perovskite as single phase was only identified when calcium acetate was used as precursor. For other precursors, tin oxide was observed as secondary phase.

Hot-pressed 9.5/65/35 PLZT prepared by the polymeric precursor method

A 9.5/65/35 PLZT ceramic with a Pb-0.905 La-0.095 (Zr-0.65 Ti-0.35)(0.976) O-3 + 35 w% PbO formula was prepared using the Pechini method for powder preparation and two-step sintering in an oxygen atmosphere. Thr first step consisted of sintering at 1200 degrees C for 4 h with slow heating and cooling rates. The second step consisted of hot pressing at 1200 degrees C for 3 h, with slow heating and cooling rates and pressing pressures of 20 MPa (initial pressure) and 40 MPa (at sintering temperature). Investigations were made of the powder phase formation and powder morphology, i.e. The structure of sintered and hot-pressed PLZT ceramics. SEM microstructural analyses were carried out on the sintering and hot-pressing processes. (C) 2000 Elsevier B.V. Ltd and Techna S.r.l. All rights reserved.

Thermal and structural investigation of SnO2/Sb2O3 obtained by the polymeric precursor method

SnO2-based materials are used as sensors, catalysts and in electro-optical devices. This work aims to synthesize and characterize the SnO2/Sb2O3-based inorganic pigments, obtained by the polymeric precursor method, also known as Pechini method (based on the metallic citrate polymerization by means of ethylene glycol). The precursors were characterized by thermogravimetry (TG) and differential thermal analysis (DTA). After characterization, the precursors were heat-treated at different temperatures and characterized by X-ray diffraction. According to the TG/DTA curves basically two-step mass loss process was observed: the first one is related to the dehydration of the system; and the second one is representative to the combustion of the organic matter. Increase of the heat treatment temperature from 500 to 600 degrees C and 700 degrees C resulted higher crystallinity of the formed product.

Development of metal oxide nanoparticles by soft chemical method

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Nanometric Pb1-xLaxTiO3 (x=0, 0.13 and 0.27) powders obtained by the polymeric precursor method

PLT (Pb1-xLaxTiO3, in which x = 0, 0.13 and 0.27) powders were successfully synthesized using the polymeric precursor method, based on the Pechini method. The polymeric precursors were calcined at temperatures ranging from 350 to 500 degrees C for 4 h. X-ray diffraction (XRD) showed the evolution of the crystalline phase starting from the amorphous precursor. Thermogravimetric analyses (TG) and differential thermal analyses (DTA) of the powder precursors showed the influence of the pH on the elimination of organic material. PLT powders have a tendency to form agglomerates, what can be verified by comparing the values of the average particle sizes obtained by Brunauer-Emmett-Teller method, BET (D-BET) with the values of the average crystallite sizes obtained by XRD (D-XRD). (C) 2007 Elsevier Ltd. All fights reserved.

Preparation and characterization of BaBi2Nb2O9(BBN) ceramics synthetized by polymeric precursors method

Pure BBN powders and with addition of 1 and 2 wt% in excess of bismuth were obtained by Pechini Method. The powders calcined at 300°C/4h were analyzed by TG/DTA to study the temperature of organic matter decomposition. A systematic study of calcination temperature and time to the formation of the BBN phase was performed and the phase formation was accompanied by XRD. The calcined powders at 800°C during 2h were analyzed by infrared spectroscopy and by BET. The powders were isostaticaly pressed and sintered at temperatures ranging from 900°C to 1000°C. The ceramics were characterized by XRD to control the crystalline phase and by SEM to analyze the microstructure.

Influence of barium and strontium addition on the ratio c/a of PZT obtained by the polymeric precursor method

Lead zirconate titanate powder, with Zr/Ti ratio of 50/50 was prepared by Pechini method after adding up to 10,0 mol% of Ba +2 and Sr +2 ions. Tetragonal phase is favored by the increase of barium and strontium concentration in the LiNbO 3 crystal lattice. The ratio c/a for tetragonal phase increases with the content of Ba +2 and Sr +2.

Influencia del TiO2 y Al2O3 sobre las propiedades eléctricas y microestructurales de cerámicas de SnO2 obtenidas por el método Pechini

Tin oxide has wakened up great scientific and technological interest for its potential use in varistors production and as gas sensor. In order to improve the microstructural and electrical properties in SnO varistor ceramics, the influence of differents dopants used, like TiO2 and Al2O3, is under research. The effect of TiO2 and Al2O3 on the properties of Sn-Co-Nb varistor Systems obtained by the Pechini method has been investigated in this work. Characterization of synthesized raw material was performed by X-Ray Diffraction (XRD) and Scanning Electronic Microscopy (SEM). The microstructural and electrical characterization of sintered samples show that the TiO2 favors the grain growth and the Al2O3, contributes to the decrease it, effect that is manifested in the Sn-Co-Nb varistor systems. Breakdown field increase up to 6300V/cm with increasing Al2O3 content and non-linear coefficients with α=22 were obtained.

Heating rate and temperature effects on the BaTiO3 formation by thermal decomposition of (Ba,Ti) organic precursors during the Pechini process

Different thermal treatments for the synthesis of BaTiO3 powder obtained through the Pechini method were studied. The synthesis of BaTiO3 starts at 150 °C by the thermal dehydration of organic precursors. The usual inevitable formation of barium carbonate during the thermal decomposition of the precursor could be retarded at lower calcination temperatures and optimized heating rates. The organic precursors were treated at temperatures between 200 and 400 °C. Then, the samples were calcined at 700 and 800 °C for 4 and 2 h, respectively. The resulting ceramic powders were characterized by gravimetric and differential thermal analyses, X-ray powder diffraction and infrared spectroscopy. It was found that depending on the heating rate and final temperature of the thermal treatment, high amounts of BaCO3 and TiO2 could be present due to the high concentration of organics in the final calcination step. © 2007 Elsevier B.V. All rights reserved.