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

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

Desenvolvimento de uma rota química alternativa de síntese de SrCo0,8Fe0,2O3- e LaNi0,3Co0,7O3- para aplicação na reação de oxidação do CO

This thesis focuses on the coprecipitation synthesis method for preparation of ceramic materials with perovskite structure, their characterization and application as catalytic material in the reaction of converting CO to CO2 developing a methodological alternative route of synthesis from the middle via oxalate coprecipitation material SrCo0,8Fe0,2O3-d. In order to check the influence of this method, it was also synthesized using a combined citrate - EDTA complexing method. The material was characterized by: X-ray diffraction (XRD), Rietveld refinement method, thermogravimetry and differential thermo analysis (TG / DTA), scanning (SEM) and transmission (TEM) electron microscopy, particle size distribution and surface analysis method BET. Both methods led to post-phase synthesis, with pH as a relevant parameter. The synthesis based on the method via oxalate coprecipitation among particles led to the crystalline phase as those obtained using a combined citrate - EDTA complexing method under the same conditions of heat treatment. The nature of the reagent used via oxalate coprecipitation method produced a material with approximately 80 % lower than the average size of crystallites. Moreover, the via oxalate coprecipitation method precursors obtained in the solid state at low temperature (~ 26 oC), shorter synthesis, greater thermal stability and a higher yield of around 90-95 %, maintaining the same order of magnitude the crystallite size that the combined citrate - EDTA complexing method. For purposes of comparing the catalytic properties of the material was also synthesized by the using a combined citrate - EDTA complexing method. The evaluation of catalytic materials SrCo0,8Fe0,2O3-d LaNi0,3Co0,7O3-d was accompanied on the oxidation of CO to CO2 using a stainless steel tubular reactor in the temperature range of 75-300 oC. The conversion CO gas was evaluated in both materials on the results shaved that the firm conversion was loves for the material LaNi0,3Co0,7O3-d

Materiais cerâmicos de inserção aplicados a baterias de íons lítio

Esta revisão visa ser uma introdução à aplicação de materiais cerâmicos em dispositivos de armazenamento de energia, em especial baterias secundárias de íons lítio, dispositivos nos quais os materiais cerâmicos, especialmente óxidos, são muito importantes em todas as partes do dispositivo. A revisão está focada nos materiais cerâmicos para catodos e anodos, partes chaves destes dispositivos. Ela tem por principal finalidade ser uma fonte de informação para aqueles que desejem trabalhar com o desenvolvimento de materiais cerâmicos para tais tipos de dispositivos. Aspectos relacionados à nanotecnologia e materiais óxidos nanoestruturados para esta área são discutidos ao final do artigo.

The Influence of Cutting Speed and Cutting Initiation Location in Specimen Preparation for the Microtensile Bond Strength Test

Purpose: This study evaluated the effect of cutting initiation location and cutting speed on the bond strength between resin cement and feldspathic ceramic.Materials and Methods: Thirty-six blocks (6.4 x 6.4 x 4.8 mm) of ceramic (Vita VM7) were produced. The ceramic surfaces were etched with 10% hydrofluoric acid gel for 60 s and then silanized. Each ceramic block was placed in a silicon mold with the treated surface exposed. A resin cement (Variolink II) was injected into the mold over the treated surface and polymerized. The resin cement-ceramic blocks were divided into two groups according to experimental conditions: a) cutting initiation location - resin cement, ceramic and interface; and b) cutting speed - 10,000, 15,000, and 20,000 rpm. The blocks were sectioned to achieve non-trimmed bar specimens. The microtensile test was performed in a universal testing machine (1 mm/min). The failure modes were examined using an optical light microscope and SEM. Bond strength results were analyzed using one-way ANOVA and Tukey's test (alpha = 0.05).Results: Significant influences of cutting speed and initiation location on bond strength (p < 0.05) were observed. The highest mean was achieved for specimens cut at 15,000 rpm at the interface (15.12 +/- 5.36 MPa). The lowest means were obtained for specimens cut at the highest cutting speed in resin cement (8.50 +/- 3.27 MPa), and cut at the lowest cutting speed in ceramic (8.60 +/- 2.65MPa). All groups showed mainly mixed failure (75% to 100%).Conclusion: The cutting speed and initiation location are important factors that should be considered during specimen preparation for microtensile bond strength testing, as both may influence the bond strength results.

Flexural Strength of Glass-Infiltrated Zirconia/Alumina-Based Ceramics and Feldspathic Veneering Porcelains

Purpose: To compare the flexural strength of two glass-infiltrated high-strength ceramics and two veneering glass-ceramics.Materials and Methods: Four ceramic materials were tested: two glass-infiltrated high-strength ceramics used as framework in metal-free restorations [In-Ceram Zirconia IZ (Gr1) and In-Ceram Alumina IA (Gr2)], and two glass-ceramics used as veneering material in metal-free restorations [Vita VM7 (Gr3) and Vitadur-alpha (Gr4)]. Bar specimens (25 x 5 x 2 mm(3)) made from core ceramics, alumina, and zirconia/alumina composites were prepared and applied to a silicone mold, which rested on a base from a gypsum die material. The IZ and IA specimens were partially sintered in an In-Ceram furnace according to the firing cycle of each material, and then were infiltrated with a low-viscosity glass to yield bar specimens of high density and strength. The Vita VM7 and Vitadur-alpha specimens were made from veneering materials, by vibration of slurry porcelain powder and condensation into a two-part brass Teflon matrix (25 x 5 x 2 mm(3)). Excess water was removed with absorbent paper. The veneering ceramic specimens were then removed from the matrix and were fired as recommended by the manufacturer. Another ceramic application and sintering were performed to compensate the contraction of the feldspar ceramic. The bar specimens were then tested in a three-point bending test.Results: The core materials (Gr1: 436.1 +/- 54.8; Gr2: 419.4 +/- 83.8) presented significantly higher flexural strength (MPa) than the veneer ceramics (Gr3: 63.5 +/- 9.9; Gr4: 57.8 +/- 12.7).Conclusion: In-Ceram Alumina and Zirconia were similar statistically and more resistant than VM7 and Vitadur-alpha.

Surface degradation of glass ceramics after exposure to acidulated phosphate fluoride

Objective: This study evaluated the surface degradation effect of acidulated phosphate fluoride (APF) gel exposure on the glassy matrix ceramics as a function of time. Material and methods: Disc-shaped ceramic specimens (N = 120, 10/per ceramic material) were prepared in stainless steel molds (inner diameter: 5 mm, height: 2 mm) using 6 dental ceramics: 3 indicated for ceramic-fused-to-metal (Vita Omega 900, Carmen and Vita Titankeramik), 2 for all-ceramic (Vitadur Alpha and Finesse (R) Low Fusing) and 1 for both types of restorations (IPS d. SIGN). The specimens were wet ground finished, ultrasonically cleaned and auto-glazed. All specimens were subjected to calculation of percentage of mass loss, surface roughness analysis and topographical description by scanning electron microscopy (SEM) before (0 min) and after exposure to 1.23 % APF gel for 4 min and 60 min representing short-and long-term etching effect, respectively. The data were analyzed using two-way ANOVA with repeated measures and Tukey` s test (alpha=0.05). Results: Significant effect of the type of the ceramics (p=0.0000, p=0.0031) and exposure time (p=0.0000) was observed in both surface roughness and percentage of mass loss values, respectively. The interaction factor between both parameters was also significant for both parameters (p=0.0904, p=0.0258). Both 4 min (0.44 +/- 0.1-0.81 +/- 0.2 mu m) and 60 min (0.66 +/- 0.1 - 1.04 +/- 0.3 mu m) APF gel exposure created significantly more surface roughness for all groups when compared to the control groups (0.33 +/- 0.2-0.68 +/- 0.2 mu m) (p<0.05). There were no significant differences in percentage of mass loss between the ceramics at 4 min (p>0.05) but at 60 min exposure, IPS d. SIGN showed the highest percentage of mass loss (0.1151 +/- 0.11). The mean surface roughness for Vita Titankeramik (0.84 +/- 0.2 mu m) and Finesse (R) Low Fusing (0.74.+/- 0.2 mu m) was significantly higher than those of the other ceramics (0.59 +/- 0.1 mu m - 0.49 +/- 0.1 mu m) and Vita Titankeramik (p<0.05) regardless of the exposure time. A positive correlation was found between surface roughness and percentage of mass loss for all ceramic materials [(r=0.518 (Vitadur Alpha), r=0.405 (Vita Omega 900), r=0.580 (Carmen), r=0.687 (IPS d. SIGN), r=0.442 (Finesse (R) Low Fusing), r=0.572 (Vita Titankeramik), Pearson's correlation coefficient)]. The qualitative SEM analysis showed evidence of corrosive attack on all of ceramics at varying degrees. Conclusions: The ceramics indicated for either metal-ceramic or all-ceramic restorations were all vulnerable to surface texture changes and mass loss after short-term and long-term APF gel exposure.

Surface equilibrium angle for anisotropic grain growth in SnO2 systems

Usually, the kinetic models used in the study of sintered ceramic are performed by means of indirect physical tests, such as, results obtained from data of linear shrinkage and mass loss. This fact is justified by the difficulty in the determinations of intrinsic parameters of ceramic materials along every sintering process. In this way, the technique of atomic force microscopy (AFM) was used in order to determine the importance and the evolution of the dihedral angle in the sintering of 0.5 mol% MnO2-doped tin dioxide obtained by the polymeric precursor method.

Addition of sedimentary rock to kaolinitic clays: influence on sintering process

Foram avaliadas, durante o processo de sinterização, as propriedades mecânicas de peças cerâmicas a base de argila com adição de rocha sedimentar. Foram preparados corpos de prova com 0, 20, 40, 60 e 80% em peso de rocha adicionada ao material argiloso. As peças foram sinterizadas nas temperaturas de 500, 800, 900, 1000, 1100 e 1200 °C e, posteriormente, submetidas à análise de difração de raios X e a ensaios tecnológicos Os resultados de difração de raios X mostram que a rocha sedimentar apresenta argilominerais micáceos enquanto o material argiloso possui a caulinita como fase principal. Técnicas de análises térmicas e difração de raios X das diferentes misturas mostram reações que indicam transformação (inversão do quartzo), decomposição (perda de hidróxidos) e formação de fase (mulita) durante o aquecimento das amostras. Os ensaios tecnológicos mostram que a adição da rocha sedimentar melhora algumas propriedades do material sinterizado, auxiliada pela presença de fundentes. Entretanto, a presença de quartzo na rocha dificulta a formação da fase mulita. A formação de novas fases e as transformações ocorridas no aquecimento e resfriamento das amostras ajuda explicar as propriedades tecnológicas dos materiais cerâmicos.

Programa de apoio à legalização mineral de olarias da região de Rio Claro (SP)

Esse artigo apresenta os resultados de um projeto denominado de Projeto Parceria, desenvolvido no período de 2007 a 2010, com objetivo de orientar, tecnicamente, os oleiros associados da ASCER, para a correta condução das atividades de extração de matéria-prima das jazidas utilizadas pela indústria oleira. As atividades desenvolvidas, nesse projeto, contemplam a legalização da situação minerária das atuais áreas de extração, orientação em relação à recuperação das áreas degradadas pela mineração e caracterização cerâmica dos materiais argilosos utilizados na produção de tijolos. Fizeram parte desse estudo quatorze Olarias situadas na região de Rio Claro (SP). A legalização das atividades de extração mineral, na área da jazida de cada olaria, conduziu, automaticamente, à legalização ambiental, que está sendo atualmente executada. Duas olarias não puderam regularizar as suas extrações, pois as áreas de suas propriedades estavam oneradas no DNPM. Outras duas olarias não possuíam documentações referentes à parte jurídica das empresas, necessárias para legalização de suas áreas. Os materiais argilosos utilizados pelos oleiros foram caracterizados quanto às suas aplicações cerâmicas como material nobre para a fabricação de telhas e tijolos, gerando produtos de alta qualidade.

Comparison of two bond strength testing methodologies for bilayered all-ceramics

Objectives. This study compared the shear bond strength (SBS) and microtensile (MTBS) testing methodologies for core and veneering ceramics in four types of all-ceramic systems.Methods. Four different ceramic veneer/core combinations, three of which were feldspathic and the other a fluor-apatite to their respectively corresponding cores, namely leucitereinforced ceramic ((IPS)Empress, Ivoclar), low leucite-reinforced ceramic (Finesse, Ceramco), glass-infiltrated alumina (In-Ceram Alumina, Vita) and lithium disilicate ((IPS)Empress 2, Ivoclar) were used for SBS and MTBS tests. Ceramic cores (N = 40, n = 10/group for SBS test method, N=5blocks/group for MTBS test method) were fabricated according to the manufacturers' instructions (for SBS: thickness, 3 mm; diameter, 5 mm and for MTBS: 10 mm x 10 mm x 2 mm) and ultrasonically cleaned. The veneering ceramics (thickness: 2 mm) were vibrated and condensed in stainless steel moulds and fired onto the core ceramic materials. After trying the specimens in the mould for minor adjustments, they were again ultrasonically cleaned and embedded in PMMA. The specimens were stored in distilled water at 37 degrees C for 1 week and bond strength tests were performed in universal testing machines (cross-head speed: 1mm/min). The bond strengths (MPa +/- S.D.) and modes of failures were recorded.Results. Significant difference between the two test methods and all-ceramic types were observed (P < 0.05) (2-way ANOVA, Tukey's test and Bonferroni). The mean SBS values for veneering ceramic to lithium disilicate was significantly higher (41 +/- 8 MPa) than those to low leucite (28 +/- 4 MPa), glass-infiltrated (26 +/- 4 MPa) and leucite-reinforced (23 +/- 3 MPa) ceramics, while the mean MTBS for low leucite ceramic was significantly higher (15 +/- 2 MPa) than those of leucite (12 +/- 2 MPa), glass-infiltrated (9 +/- 1 MPa) and lithium disilicate ceramic (9 +/- 1 MPa) (ANOVA, P < 0.05).Significance. Both the testing methodology and the differences in chemical compositions of the core and veneering ceramics influenced the bond strength between the core and veneering ceramic in bilayered all-ceramic systems. (c) 2006 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

Effect of mechanical cycling on the flexural strength of densely sintered ceramics

Objectives. The aim of this study was to evaluate the effect of mechanical cycling on the biaxial flexural strength of two densely sintered ceramic materials.Methods. Disc shaped zirconia (In-Ceram Zirconia) and high alumina (Procera AllCeram) ceramic specimens (diameter: 15 min and thickness: 1.2 mm) were fabricated according to the manufacturers' instructions. The specimens from each ceramic material (N = 40, n = 10/per group) were tested for flexural strength either with or without being subjected to mechanical cycling (20,000 cycles under 50 N load, immersion in distilled water at 37 degrees C) in a universal testing machine (1 mm/min). Data were statistically analyzed using two-way ANOVA and Tukey's test (alpha = 0.05).Results. High alumina ceramic specimens revealed significantly higher flexural strength values without and with mechanical cycling (647 +/- 48 and 630 +/- 143 MPa, respectively) than those of zirconia ceramic (497 +/- 35 and 458 +/- 53 MPa, respectively) (p < 0.05). Mechanical cycling for 20,000 times under 50 N decreased the flexural strength values for both high alumina andSignificance. High alumina ceramic revealed significantly higher mean flexural strength values than that of zirconia ceramic tested in this study either with or without mechanical cycling conditions. (C) 2005 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

Microstructural development of ZnO varistor during reactive liquid phase sintering

The microstructural evolution, grain growth and densification for the varistor systems ZnO-Bi2O3 (ZB), ZnO-Bi2O3-Sb2O3 (ZBS), ZnO-Bi2O3-Sb2O3-MnO-Cr 2O3-CoO (ZBSCCM) were studied using constant heating rate sintering, scanning electron microscopy (SEM) and in situ phase formation measurement by high temperature X-ray diffraction (HT-XRD). The results showed that the densifying process is controlled by the formation and decomposition of the Zn2Bi3Sb3O14 pyrochlore (PY) phase for the ZBS and ZBSCCM systems. The addition of transition metals (ZBSCCM system) alters the formation and decomposition reaction temperatures of the pyrochlore phase and the morphology of the Zn7Sb2O12 spinel phase. Thus, the spinel grains act as inclusions and decrease the ZnO grain growth rate. Spinel grain growth kinetics in the ZBSCCM system showed an n value of 2.6, and SEM and HT-XRD results indicate two grain growth mechanisms based on coalescence and Ostwald ripening. © 1996 Chapman & Hall.

Microstructure and phase evolution of SrTiO3 thin films on Si prepared by the use of polymeric precursors

The use of polymeric precursors was employed in preparing SrTiO3 thin films by dip coating using Si (111) as substrate. Crack free films were obtained after sintering at temperatures ranging from 550 to 1000°C. The microstructure, characterized by SEM, shows the development of dense polycrystalline films with smooth surface and mean grain size of 52 nm, for films sintered at 1000°C. Grazing incident angle XRD characterization of these films shows that the SrTiO3 phase crystallizes from an inorganic amorphous matrix. No intermediate crystalline phase was identified.