Síntese e caracterização de NiO-CGO para anodo e eletrólitos sólidos e base de Céria para SOFC

The direct use of natural gas makes the Solid Oxide Fuel Cell (SOFC) potentially more competitive with the current energy conversions technologies. The Intermediate Temperature SOFC (IT-SOFC) offer several advantages over the High Temperature SOFC (HT-SOFC), which includes better thermal compatibility among components, fast start with lower energy consumption, manufacture and operation cost reduction. The CeO2 based materials are alternatives to the Yttria Stabilized Zirconia (YSZ) to application in SOFC, as they have higher ionic conductivity and less ohmic losses comparing to YSZ, and they can operate at lower temperatures (500-800°C). Ceria has been doped with a variety of cations, although, the Gd3+ has the ionic radius closest to the ideal one to form solid solution. These electrolytes based in ceria require special electrodes with a higher performance and chemical and termomechanical compatibility. In this work compounds of gadolinia-doped ceria, Ce1-xGdxO2-δ (x = 0,1; 0,2 and 0,3), used as electrolytes, were synthesized by polymeric precursors method, Pechini, as well as the composite material NiO - Ce0,9Gd0,1O1,95, used as anode, also attained by oxide mixture method, mixturing the powders of the both phases calcinated already. The materials were characterized by X ray diffraction, dilatometry and scanning electronic microscopy. The refinement of the diffraction data indicated that all the Ce1-xGdxO2-δ powders were crystallized in a unique cubic phase with fluorite structure, and the composite synthesized by Pechini method produced smaller crystallite size in comparison with the same material attained by oxide mixture method. All the produced powders had nanometric characteristics. The composite produced by Pechini method has microstructural characteristics that can increase the triple phase boundaries (TPB) in the anode, improving the cell efficiency, as well as reducing the mass transport mechanism effect that provokes anode degradation

Estudos de Durabilidade Frente ao Ataque Ácido de Compósitos Portland-Polímero para Cimentação de Poços de Petróleo

Portland-polymers composites are promising candidates to be used as cementing material in Northeastern oil wells of Brazil containing heavy oils submitted to steam injection. In this way, it is necessary to evaluate its degradation in the commonly acidizind agents. In addition, to identify how aggressive are the different hostile environments it is an important contribution on the decision of the acidic systems to be used in. It was investigated the performance of the Portland-polymer composites using powdered polyurethane, aqueous polyurethane, rubber tire residues and a biopolymer, those were reinforced with polished carbon steel SAE 1045 to make the electrochemical measurements. HCl 15,0 %, HCl 6,0 % + HF 1,5 % (soft mud acid), HCl 12,0 % + HF 3,0 % (regular mud acid) and HAc 10 % + HF 1,5 % were used as degrading environment and electrolytes. The more aggressive acid solution to the plain Portland hardened cement paste was the regular mud acid, that showed loss of weight around 23.0 %, followed by the soft mud acid, the showed 11.0 %, 15.0 % HCl with 7,0 % and, at last the 10.0 % HAc plus HF 1.5 % with just 1.0 %. The powdered polyurethane-composite and the aqueous polyurethane one showed larger durability, with reduction around 87.0 % on the loss of weight in regular mud acid. The acid attack is superficial and it occurs as an action layer, where the degraded layer is responsible for the decrease on the kinetic of the degrading process. This behavior can be seen mainly on the Portland- aqueous polyurethane composite, because the degraded layer is impregnated with chemically modified polymer. The fact of the acid attack does not have influence on the compressive strength or fratography of the samples, in a general way, confirms that theory. The mechanism of the efficiency of the Portland-polymers composites subjected to acid attack is due to decreased porosity and permeability related with the plain Portland paste, minor quantity of Ca+2, element preferentially leached to the acidic solution, wave effect and to substitute part of the degrading bulk for the polymeric one. The electrolyte HAc 10 % + HF 1,5 % was the least aggressive one to the external corrosion of the casing, showing open circuit potentials around +250 mV compared to -130 mV to the simulated pore solution to the first 24 hours immersion. This behavior has been performed for two months at least. Similar corrosion rates were showed between both of the electrolytes, around 0.01 μA.cm-2. Total impedance values, insipient arcs and big polarization resistance capacitive arcs on the Nyquist plots, indicating passivity process, confirm its efficiency. In this way, Portlandpolymers composites are possible solutions to be succeed applied to oilwell cementing concomitant submitted to steam injection and acidizing operation and the HAc 10,0 % + HF 1,5 % is the less aggressive solution to the external corrosion of the casing

Sinterização de Ce1-XEuXO2-(X/2) para aplicação como eletrólito sólido em células a combustível de temperaturas intermediárias

Given the environmental concern over global warming that occurs mainly by emission of CO2 from the combustion of petroleum, coal and natural gas research focused on alternative and clean energy generation has been intensified. Among these, the highlight the solid oxide fuel cell intermediate temperature (IT-SOFC). For application as electrolyte of the devices doped based CeO2 with rare earth ions (TR+ 3) have been quite promising because they have good ionic conductivity and operate at relatively low temperatures (500-800 ° C). In this work, studied the Ce1-xEuxO2-δ (x = 0,1, 0,2 and 0,3), solid solutions synthesized by the polymeric precursor method to be used as solid electrolyte. It was also studied the processing steps of these powders (milling, compaction and two step sintering) in order to obtain dense sintered pellets with reduced grain size and homogeneous microstructure. For this, the powders were characterized by thermal analysis, X-ray diffraction, particle size distribution and scanning electrons microscopy, since the sintered samples were characterized by dilatometry, scanning electrons microscopy, density and grain size measurements. By x-ray diffraction, it was verified the formation of the solid solution for all compositions. Crystallites in the nanometric scale were found for both sintering routes but the two step sintering presented significant reduction in the average grain size

Estudo da viabilidade do sistema LZAS para uso como selante de PaCOS

Cells the solid oxide fuel are systems capable to directly convert energy of a chemical reaction into electric energy in clean, quiet way and if its components in the solid state differentiate of excessively the techniques for having all. Its more common geometric configurations are: the tubular one and to glide. Geometry to glide beyond the usual components (anode, cathode and electrolyte) needs interconnect and sealant. E the search for materials adjusted for these components is currently the biggest challenge found for the production of the cells. The sealants need to present chemical stability in high temperatures, to provoke electric isolation, to have coefficient of compatible thermal expansion with the excessively component ones. For presenting these characteristics the glass-ceramics materials are recommended for the application. In this work the study of the partial substitution of the ZrO2 for the Al2O3 in system LZS became it aiming at the formation of system LZAS, this with the addition of natural spodumene with 10, 20 and 30% in mass. The compositions had been casting to a temperature of 1500°C and later quickly cooled with the objective to continue amorphous. Each composition was worn out for attainment of a dust with average diameter of approximately 3μm and characterized by the techniques of DRX, FRX, MEV, dilatometric analysis and particle size analysis. Later the samples had been conformed and treated thermally with temperatures in the interval between 700-1000 °C, with platform of 10 minutes and 1 hour. The analyses for the treated samples had been: dilatometric analysis, DRX, FRX, electrical conductivity and tack. The results point with respect to the viability of the use of system LZAS for use as sealant a time that had presented good results as isolating electric, they had adhered to a material with similar α of the components of a SOFC and had presented steady crystalline phases

Utilização de matérias primas vegetais para aplicabilidade como inibidores de corrosão

In the search for products that act as corrosion inhibitors and do not cause environmental, impact the use of plant extracts as corrosion inhibitors is becoming a promising alternative. In this work the efficiency of polar extracts (ethanol extracts) obtained from the plants Anacardium occidentale Linn (AO) and Phyllantus amarus Schum. & Thonn (PA) as corrosion inhibitors were evaluated in different concentrations. For that AO and PA extracts were solubilized in the microemulsion systems (SME) containing saponified coconut oil as surfactant (SME -OCS and SME-OCS-1) in saline (NaCl 3,5 %) solution, which was also used as electrolyte. Both SME-OCS and SME-OCS-1 were characterized by surface tension and viscosity methods showing a Newtonian fluid behavior. The SME-OCS and SME-OCS-1 systems satisfactorily solubilized the polar extracts AO and PA with measurements carried out by ultraviolet spectroscopy. The measurements of corrosion inhibition efficiencies were performed by the electrochemical linear polarization resistance (LPR) technique as well as weight loss, on the surface of AISI 1020 carbon steel. The maximum corrosion inhibition efficiencies were determined by extrapolation of Tafel plots, showing the following values: 95,6 % for the system SME-OCS-AO, 98,9 % for the system SME-OCS-AO-1 and 93,4 % for the system SME-OCS-PA

Estudo da sinterização de eletrólito sólido de céria dopada com gadolínia

Fuel cells are electrochemical devices that convert chemical energy in electrical energy by a reaction directly. The solid oxide fuel cell (SOFC) works in temperature between 900ºC up to 1000ºC, Nowadays the most material for ceramic electrolytes is yttria stabilized zirconium. However, the high operation temperature can produce problems as instability and incompatibility of materials, thermal degradation and high cost of the surround materials. These problems can be reduced with the development of intermediate temperature solid oxide fuel cell (IT-SOFC) that works at temperature range of 600ºC to 800ºC. Ceria doped gadolinium is one of the most promising materials for electrolytes IT-SOFC due high ionic conductivity and good compatibility with electrodes. The inhibition of grain growth has been investigated during the sintering to improve properties of electrolytes. Two-step sintering (TSS) is an interesting technical to inhibit this grain growth and consist at submit the sample at two stages of temperature. The first one stage aims to achieve the critical density in the initiating the sintering process, then the sample is submitted at the second stage where the temperature sufficient to continue the sintering without accelerate grain growth until to reach total densification. The goal of this work is to produce electrolytes of ceria doped gadolinium by two-step sintering. In this context were produced samples from micrometric and nanometric powders by two routes of two-step sintering. The samples were obtained with elevate relative density, higher than 90% using low energy that some works at the same area. The average grain size are at the range 0,37 μm up to 0,51 μm. The overall ionic conductivity is 1,8x10-2 S.cm and the activation energy is 0,76 eV. Results shown that is possible to obtain ceria-doped gadolinium samples by two-step sintering technique using modified routes with characteristics and properties necessary to apply as electrolytes of solid oxide fuel cell

Efeito da Gália como aditivo de sinterização em eletrólitos cerâmicos à base de céria sintetizados pelo método de complexação de cátions

Fuel cells are considered one of the most promising ways of converting electrical energy due to its high yield and by using hydrogen (as fuel) which is considered one of the most important source of clean energy for the future. Rare earths doped ceria has been widely investigated as an alternative material for the electrolyte of solid oxide fuel cells (SOFCs) due to its high ionic conductivity at low operating temperatures compared with the traditional electrolytes based on stabilized zirconia. This work investigates the effect of gallium oxide (Gallia) as a sintering aid in Eu doped ceria ceramic electrolytes since this effect has already been investigated for Gd, Sm and Y doped ceria electrolytes. The desired goal with the use of a sintering aid is to reduce the sintering temperature aiming to produce dense ceramics. In this study we investigated the effects on densification, microstructure and ionic conduction caused by different molar fraction of the dopants europium (10, 15 and 20%) and gallium oxide (0.3, 0.6 and 0.9%) in samples sintered at 1300, 1350 and 1450 0 C. Samaria (10 and 20%) doped ceria samples sintered between 1350 and 1450 °C were used as reference. Samples were synthesized using the cation complexation method. The ceramics powders were characterized by XRF, XRD and SEM, while the sintered samples were investigated by its relative density, SEM and impedance spectroscopy. It was showed that gallia contents up to 0.6% act as excellent sintering aids in Eu doped ceria. Above this aid content, gallia addition does not promote significant increase in density of the ceramics. In Ga free samples the larger densification were accomplished with Eu 15% molar, effect expressed in the microstructure with higher grain growth although reduced and surrounded by many open pores. Relative densities greater than 95 % were obtained by sintering between 1300 and 1350 °C against the usual range 1500 - 1600 0 C. Samples containing 10% of Sm and 0.9% of Ga reached 96% of theoretical density by sintering at 1350 0 C for 3h, a gain compared to 97% achieved with 20% of Sm and 1% of Ga co-doped cerias sintered at 1450 0 C for 24 h as described in the literature. It is found that the addition of gallia in the Eu doped ceria has a positive effect on the grain conductivity and a negative one in the grain boundary conductivity resulting in a small decrease in the total conductivity which will not compromise its application as sintering aids in ceria based electrolytes. Typical total conductivity values at 600 and 700 °C, around 10 and 30 mS.cm -1 respectively were reached in this study. Samples with 15% of Eu and 0.9 % of Ga sintered at 1300 and 1350 °C showed relative densities greater than 96% and total conductivity (measured at 700 °C) between 20 and 33 mS.cm -1 . The simultaneous sintering of the electrolyte with the anode is one of the goals of research in materials for SOFCs. The results obtained in this study suggest that dense Eu and Ga co-doped ceria electrolytes with good ionic conductivity can be sintered simultaneously with the anode at temperatures below 1350 °C, the usual temperature for firing porous anode materials

Síntese e caracterização do líquido iônico tetrafluoroborato de 1-metil-3-(2,6-(S)-dimetiloct-2-eno)-imidazol como eletrólito para produção de hidrogênio via eletrólise da água

Ionic liquids (ILs) are organic compounds liquid at room temperature, good electrical conductors, with the potential to form as a means for electrolyte on electrolysis of water, in which the electrodes would not be subjected to such extreme conditions demanding chemistry [1]. This paper describes the synthesis, characterization and study of the feasibility of ionic liquid ionic liquid 1-methyl-3(2,6-(S)-dimethyloct-2-ene)-imidazole tetrafluoroborate (MDI-BF4) as electrolyte to produce hydrogen through electrolysis of water. The MDI-BF4 synthesized was characterized by thermal methods of analysis (Thermogravimetric Analysis - TG and Differential Scanning Calorimetry - DSC), mid-infrared spectroscopy with Fourier transform by method of attenuated total reflectance (FTIR-ATR), nuclear magnetic resonance spectroscopy of hydrogen (NMR 1H) and cyclic voltammetry (CV). Where thermal methods were used to calculate the yield of the synthesis of MDI-BF4 which was 88.84%, characterized infrared spectroscopy functional groups of the compound and the binding B-F 1053 cm-1; the NMR 1H analyzed and compared with literature data defines the structure of MDI-BF4 and the current density achieved by MDI-BF4 in the voltammogram shows that the LI can conduct electrical current indicating that the MDI-BF4 is a good electrolyte, and that their behavior does not change with the increasing concentration of water

Acurácia dos indicadores clínicos do diagnóstico de enfermagem volume de líquidos excessivo em pacientes submetidos à hemodiálise

Trasnversal study, with the objective of evaluating the accuracy of clinical indicators of nursing diagnosis excessive fluid volume in patients undergoing hemodialysis. The study occurred in two stages, the first consisted of the evaluation of the diagnostic indicators in study; and the second, the diagnostic inference conducted by nurse diagnosticians. The first stage occurred from december 2012 to april 2013, in a University Hospital and a Hemodialysis Clinic in Northeastern of Brazil, with a sample of 100 chronic renal failure patients on hemodialysis. The data were selected through an interview form and a physical examination, organized into spreadsheets and analyzed as to the presence or absence of the indicators of diagnosis excessive fluid volume. In the second step, the spreadsheets were sent to three nurses diagnosticians, who judged the presence or absence of diagnosis in the clientele searched. This step was conducted from july to september 2013. For analysis of the data, we used descriptive and inferential statistics. In the descriptive analysis, we used measures of central tendency and dispersion. In inferential analysis, we used the tests Chi- square, Fisher and prevalence ratios. The accuracy of the clinical indicators pertaining to the diagnosis were measured as to the specificity, sensitivity, predictive values, likelihood ratios and Diagnostic Odds Ratio. Also developed a logistic regression. The results were organized in tables and discussed with literature. This study was approved by the Ethics Committee in Research of the Federal University of Rio Grande do Norte, with Presentation Certificate for Ethics Appreciation nº 08696212.7.0000.5537. The results revealed that the diagnosis studied was present in 82% of patients. The characteristics with prevalence above 50 % that stood out were: azotemia, decreased hematocrit, electrolyte imbalance, intake exceeds output, anxiety, edema, decreased hemoglobin, oliguria and blood pressure changes. Eight defining characteristics were presented statistically significant association with the nursing diagnosis investigated: pulmonary congestion, intake exceeds output, electrolytes imbalance, jugular vein distension, edema, weight gain over short period of time, agitation and adventitious breath sounds. Among these, the 10 characteristics which showed higher prevalence ratios were: edema and weight gain over short period of time. The features with the highest sensitivity were edema, electrolytes imbalance and intake exceeds output and the standing out with greater specificity were: anasarca, weight gain over short period of time, change in respiratory pattern, adventitious breath sounds, pulmonary congestion, agitation and jugular vein distension. The indicators jugular vein distension, electrolytes imbalance, intake exceeds output, increased central venous pressure and edema, together, were identified in the logistic regression model as the most significant predictors. It is concluded that the identification of accurate clinical indicators allow a good prediction of the nursing diagnosis of excessive fluid volume in patients undergoing hemodialysis in order to assist the nurse in the inference process, which will contribute to the success of patient care. In addition, nurses will consider for diagnostic inference not only his clinical experience, but also scientific evidence of the occurrence of excessive fluid volume, contributing to the control of volemia in these patients

Anodização para obtenção de membranas cerâmicas

This a study on the achievement of alumina membranes by the method of anodizing. From this method got up a layer of aluminum oxide on the anodic metal, who presented the basic properties necessary for the application as a support for the production and acquisition of nanomaterials, such as porosity nano and resistance to high temperature, and other properties, as resistance to corrosion, and chemical, high ranking of the structure and pore size of the pores. The latter, ranging from 10 to 100nm depended on the electrolyte used, which in this study was the H2SO4. To remove all remaining aluminum, it is a bath of dissolution with HCl and CuCl where the residual aluminum has been withdrawn, and the deep pores were opened after chemical treatment with NaOH. After the dissolution, the membranes were calcined at temperatures of 300, 600 and 900° C, and sintered at temperatures of 1200 and 1300º C to win mechanical strength, porosity and observe the desired crystallization. Then went through analyses of composition through X-ray diffraction and morphology of the microstructure through a scanning electron microscope. The method was effective for obtaining alumine membranes applied in the processes of production of materials in nano

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

Desenvolvimento de componentes nanométricos para aplicação em células a combustível à base de sólidos estruturados e filmes finos

The present work aims the preparation of filmes of strontium-doped lanthanum manganite (perovskita) yttria-stabilized zirconia (LSM-SDC) films deposited on substrate of YSZ by means of spin coating technique having as principal objective their application to solid oxide fuel cells of intermediate temperature. La0,8Sr0,2MnO3 and Ce0,8Sm0,2O1,9 were obtained by modified Pechini method by use of gelatin which act as polymerization agent. The powders obtained were characterized by Xray fluorescence, X ray diffraction, electronic scanning microscopy and the superficial area by BET method. The results obtained by X-ray fluorescence showed that the route adopted for obtention of powders was effective in the obtention of the compositions with close values to the stoichiometrics. Ethyl cellulose was used as pore-forming agent and mixed with the LSM-SDC powders in weight proportions of 1:24, 2:23 and 1:9. The films were sintered at 1150 °C for 4 h and characterized by X-ray diffraction and scanning electron microscopy technique (SEM) and atomic force. The phases quantification of the precursory powders and of the obtained films was carried through Rietveld method. According with the analysis of SEM, as the content of ethyl cellulose was increased, the pore distribution in films become more uniform and the pore size reduced. The methodology used for the obtention of the films was very efficient, considering a material was obtained with characteristics that were proper to the application as electrolyte/cathode system to solid oxide fuel cells

Conciliação entre modelos de mecanismos avançados de oxidação eletroquímica

Many pollutants dumped in waterways, such as dyes and pesticides, have become so ubiquitous that they represent a serious threat to human health. The electrochemical oxidation is presented as an alternative clean, efficient and economic degradation of wastewater containing organic compounds and a number of advantages of this technique is to just not make use of chemical reagents, since only electrical energy is consumed during the removal of pollutants organic. However, despite being a promising alternative, still needs some tweaking in order to obtain better efficiency in the elimination of persistent pollutants. Thus, this study sought a relationship between a recently discovered phenomenon that reflects the participation of dissolved oxygen in solution in the electrochemical oxidation process, as an anomaly, present a kinetic model that shows instantaneous current efficiency (ICE) above 100% limited by theory, manifested for some experiments with phenolic compounds with H2SO4 or HClO4 as supporting electrolyte with electrodes under anodic oxidation on boron doped diamond (BDD). Therefore it was necessary to reproduce the data ICE exposes the fault model, and thus the 2-naphthol was used as phenolic compound to be oxidised at concentrations of 9, 12 and 15 mmol L-1, and H2SO4 and HClO4 to 1 mol L-1 as a supporting electrolyte under a current density of 30 mA cm-2 in an electrochemical reactor for continuous flow disk configuration, and equipped with anodes DDB at room temperature (25 oC). Experiments were performed using N2 like as purge gas for eliminate oxygen dissolved in solution so that its influence in the system was studied. After exposure of the anomaly of the ICE model and investigation of its relationship with dissolved O2, the data could be treated, making it possible for confirmation. But not only that, the data obtained from eletranálise and spectroscopic analysis suggest the involvement of other strongly oxidizing species (O3 (ozone) and O radicals and O2 -), since the dissolved O2 can be consumed during the formation of new strong oxidizing species, not considered until now, something that needs to be investigated by more accurate methods that we may know a little more of this system. Currently the performance of the electrocatalytic process is established by a complex interaction between different parameters that can be optimized, so it is necessary to the implementation of theoretical models, which are the conceptual lens with which researchers see

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