HYDROTHERMAL REE FLUOROCARBONATE MINERALIZATION AT BARRA DO ITAPIRAPUA, A MULTIPLE STOCKWORK CARBONATITE, SOUTHERN BRAZIL

The Barra do Itapirapua ( BIT) carbonatites in southern Brazil belong to the final stages of the Early Cretaceous alkaline rock - carbonatite magmatism of the Ponta Grossa Arch Province. The BIT complex is a dyke and vein stockwork in which four main carbonatitic phases are recognized, mainly magnesiocarbonatites and ferrocarbonatites. These carbonatites are generally overprinted by pervasive hydrothermal events. The C-O stable isotopic data indicate re-equilibration under hydrothermal conditions at temperatures between 375 and 80 degrees C. Significant amounts of REE fluorocarbonate minerals, relatively Sr- and Th-rich, were deposited. Syntaxy between synchysite-(Ce) and parisite-(Ce) is very common owing to the similarity in structures, with alternating (001) layers of (CeF), (CO3) and (Ca). However, bastnasite-(Ce) occurs as individual crystals, overgrown by the synchysite and parisite polycrystals. Textural and chemical reactions between the REE fluorocarbonates provide insights into the mobility of rare-earth elements during fluid-rock interaction. The BIT complex is considered to be of potential economic interest for production of the rare-earth concentrates.

Sr-Nd isotopic evidence for crustal contamination in the Niquelandia complex, Goias, Central Brazil

The Niquelandia complex is a Neoproterozoic mafic-ultramafic intrusion resulting from fractional crystallization of primary picritic basalt intrusions. It consists of two layered sequences: a lower and larger one (LS), where four stratigraphic units exhibit an upward decrease of ultramafic layers and increase of gabbroic layers; an upper, smaller sequence (US), separated from LS by a high-temperature shear zone and consisting of two stratigraphic units (gabbros + anorthosites and amphibolites). Nd and Sr isotopic analyses and rare earth element (REE) profiles provide evidence that the complex suffered important crustal contamination. The LS isotopic array trends from a DM region with positive epsilon Nd and moderately positive epsilon Sr towards a field occupied by crustal xenoliths, especially abundant in the upper LS (negative epsilon Nd and large, positive E:Sr). Each LS stratigraphic unit is distinct from the next underlying unit, showing lower epsilon Nd and higher epsilon Sr, suggesting inputs of fresh magma and mixing with the contaminated, residual magma. The US is characterised by a relatively high variation of epsilon Nd and constant epsilon Sr. REE patterns vary within each unit from LREE depleted to LREE enriched in the samples having lower epsilon Nd and higher epsilon Sr. The contamination process has been modelled by using the EC-AFC algorithms from [Spera, F.J., Bohrson, W.A., 2001. Energy-constrained open-system magmatic processes 1: general model and energy-constrained assimilation and fractional crystallization (EC-AFC) formulation. J. Petrology 42, 999-1018]. The differences between the LS and US isotopic arrays are consistent with contamination by the same crustal component, provided that its melting degree was higher in LS than in US. The different degrees of anatexis are explained by the heat budget released from the magma, higher in LS (because of its larger mass) than in US. Comparison of the correlations between isotopes and incompatible trace element ratios of the models and of the gabbros shows some differences, which are demonstrably related with the variable amount of cumulus phases and trapped melt in the gabbros. (c) 2007 Elsevier Ltd. All rights reserved.

Age and geochemistry of mantle peridotites and diorite dykes from the Baldissero body: Insights into the Paleozoic-Mesozoic evolution of the Southern Alps

Trace element and isotopic data obtained for mantle spinel Iherzolites and diorite dykes from the Baldissero massif (Ivrea-Verbano Zone, Western Italy) provide new, valuable constraints on the petrologic and geodynamic evolution of the Southern Alps in Paleozoic to Mesozoic times. Whole rock and mineral chemistry indicates that Baldissero Iherzolites can be regarded as refractory mantle residues following limited melt extraction. In particular, the Light Rare Earth Elements (LREE)-depleted and fractionated compositions of whole rock and clinopyroxene closely match modelling results for refractory residues after low degrees (similar to 4-5%) of near-fractional melting of depleted mantle, possibly under garnet-facies conditions. Following this, the peridotite sequence experienced subsolidus re-equilibration at lithospheric spinel-facies conditions and intrusion of several generations of dykes. However, Iherzolites far from dykes show very modest metasomatic changes, as evidenced by the crystallisation of accessory titanian pargasite and the occurrence of very slight enrichments in highly incompatible trace elements (e.g. Nb). The Re-Os data for Iherzolites far from the dykes yield a 376 Ma (Upper Devonian) model age that is considered to record a partial melting event related to the Variscan orogenic cycle s.l. Dioritic dykes cutting the mantle sequence have whole rock, clinopyroxene and plagioclase characterised by high radiogenic Nd and low radiogenic Sr, which point to a depleted to slightly enriched mantle source. Whole rock and mafic phases of diorites have high Mg# values that positively correlate with the incompatible trace element concentrations. The peridotite at the dyke contact is enriched in orthopyroxene, iron and incompatible trace elements with respect to the Iherzolites far from dykes. Numerical simulations indicate that the geochemical characteristics of the diorites can be explained by flow of a hydrous, silica-saturated melt accompanied by reaction with the ambient peridotite and fractional crystallisation. The composition of the more primitive melts calculated in equilibrium with the diorite minerals show tholeiitic to transitional affinity. Internal Sm-Nd, three-point isochrons obtained for two dykes suggest an Upper Triassic-Lower Jurassic emplacement age (from 204 31 to 198 29 Ma). Mesozoic igneous events are unknown in the southern Ivrea-Verbano Zone (IVZ), but the intrusion of hydrous melts, mostly silica-saturated, have been well documented in the Finero region, i.e. the northernmost part of IVZ and Triassic magmatism with calc-alkaline to shoshonitic affinity is abundant throughout the Central-Eastern Alps. The geochemical and chronological features of the Baldissero diorites shed new light on the geodynamic evolution of the Southern Alps before the opening of the Jurassic Tethys. (C) 2010 Elsevier B.V. All rights reserved.

Zr- AND Ba-RICH MINERALS FROM THE PONTE NOVA ALKALINE MAFIC-ULTRAMAFIC MASSIF, SOUTHEASTERN BRAZIL: INDICATION OF AN ENRICHED MANTLE SOURCE

Zirconium- and Ba-rich minerals are found in gabbroic rocks from the Ponte Nova alkaline mafic-ultramafic massif in southeastern Brazil. The unusual mineralogical assemblage includes zirconolite, baddeleyite, Ba-rich alkali feldspar, and Ba- and Ti-rich biotite. Zirconolite of the Ponte Nova massif has higher levels of Zr (up to 1.172 apfu) than those registered in other terrestrial rocks and a prominent enrichment in the light rare-earth elements. Baddeleyite contains small quantities of Hf, Ti, and Fe. The Ba-rich alkali feldspar and Ba- and Ti-rich biotite contain up to 9.25 and 7.35 wt% BaO, respectively, and the biotite contains up to 12.01 wt% TiO(2). In the different intrusions of the Ponte Nova massif, such an unusual assemblage typifies the residual magma after the crystallization of clinopyroxene and olivine from previously enriched basanitic parental magma. The different trends of enrichments in REE and Th + U found for zirconolite of the intrusions of the Ponte Nova massif provide a better understanding of the variable degrees of enrichment of incompatible elements of the distinct gabbroic bodies. A lithospheric mantle source enriched in incompatible elements by the metasomatic action of volatile-rich fluids and with the presence of phlogopite or amphibole (or both) and other minor accessory phases could explain the presence of the Zr- and Ba-rich minerals in this gabbroic massif.

Rhyacian (2.23-2.20 Ga) juvenile accretion in the southern Sao Francisco craton, Brazil: Geochemical and isotopic evidence from the Serrinha magmatic suite, Mineiro belt

The Serrinha magmatic suite (Mineiro belt) crops out in the southern edge of the Sao Francisco craton, comprising the Brito quartz-diorite, Brumado de Cima and Brumado de Baixo granodiorites, granophyres and felsic sub-volcanic and volcanic rocks, part of which intruded into the Nazareno greenstone belt. The suite rocks have petrographic features that are consistent with magma supercooling due to the low water content combined with volatile loss, leading to crystallization of quartz and alkaline feldspar at the rims of plagioclase phenocrysts (granophyric intergrowth). The investigated rocks are sub-alkaline, calc-alkaline and show low content in rare earth elements. The U-Pb zircon crystallization ages for the Brumado de Cima granodiorite [2227 +/- 22 (23) Ma] and a coeval granophyre [2211 +/- 22 (23) Ma], coupled with available single-zircon Pb evaporation ages for the Brito and Brumado de Baixo plutons, are significantly older than the ""Minas orogeny"" (ca. 2100-2050 Ga) of Quadrilatero Ferrifero area, eastward from the Serrinha suite. Our data establish an early Rhyacian event tectonically linked with the evolution of the Mineiro belt. The bulk Nd isotopic signature [low negative to positive epsilon(Nd(t)) values] of the Serrinha samples are consistent with the important role of Paleoproterozoic mantle components in the magma genesis. The integrated geologic, geochemical and isotopic information suggests that Paleoproterozoic evolution of the Mineiro belt initiated in a passive continental margin basin with deposition of the Minas Supergroup at ca. 2500 Ma. This stage was succeeded by outboard rupture of the oceanic lithosphere with development and coalescence of progressively younger magmatic arcs during Rhyacian time. One of the earliest arcs formed the Serrinha suite. The tectonic collage of the Serrinha and Ritapolis (2190-2120 Ma) arcs produced the NE-SW Lenheiro shear zone, resulting in mylonitization and recrystallization of both the granitoid intrusions and host rocks. As a matter of fact juxtaposition of distinct magmatic units in age and origin took place along the Lenheiros structure in this sector of the Mineiro belt. (C) 2009 Elsevier Ltd. All rights reserved.

Lacustrine sediments provide geochemical evidence of environmental change during the last millennium in southeastern Brazil

A 172 cm-long sediment core was collected from a small pristine lake situated within a centripetal drainage basin in a tropical karst environment (Ribeira River valley, southeastern Brazil) in order to investigate the paleoenvironmental record provided by the lacustrine geochemistry. Sediments derived from erosion of the surrounding cambisoils contain quartz, kaolinite, mica, chlorite and goethite. Accelerator mass spectroscopy (AMS) (14)C dating provided the geochronological framework. Three major sedimentary units were identified based on the structure and color of the sediments: Unit III from 170 to 140 cm (1030 +/- 60-730 +/- 60 yr BP), Unit II from 140 to 90 cm (730 +/- 60-360 +/- 60 yr BP) and Unit I from 90 to 0 cm (360 +/- 60-0 yr BP). Results of major and trace element concentrations were analysed through multivariate statistical techniques. Factor analysis provided three factors accounting for 72.4% of the total variance. F1 and F2 have high positive loadings from K, Ba, Cs, Rb, Sr, Sc, Th, light rare earth element (LREE), Fe, Cr, Ti, Zr, Hf and Ta, and high negative loadings from Mg, Co, Cu, Zn, Br and loss on ignition (LOI). F3, with positive loadings from V and non-metals As and Sb, accounts for a low percentage (9.7%) of the total variance, being therefore of little interpretative use. The profile distribution of F1 scores reveals negative values in Units I and III, and positive values in Unit II, meaning that K, Ba, Cs, Rb, Sr, Sc, Th, LREE, Fe, Cr, Ti, Zr, Hf and Ta are relatively more concentrated in Unit II, and Mg, Co, Cu, Zn and Br are relatively more abundant in Units I and III. The observed fluctuations in the geochemical composition of the sediments are consistent with slight variations of the erosion intensity in the catchment area as a possible response to variations of climatic conditions during the last millennium. (c) 2009 Elsevier GmbH. All rights reserved.

Tectono-sedimentary evolution of the Neoproterozoic BIF-bearing Jacadigo Group, SW-Brazil

The Jacadigo Group contains one of the largest sedimentary iron and associated manganese deposits of the Neoproterozoic. Despite its great relevance, no detailed sedimentological study concerning the unit has been carried out to date. Here we present detailed sedimentological data and interpretation on depositional systems, system tracts, external controls on basin evolution, basin configuration and regional tectonic setting of the Jacadigo Basin. Six depositional systems were recognized: (I) an alluvial fan system; (II) a siliciclastic lacustrine system; (III) a fan-delta system; (IV) a bedload-dominated river system; (V) an iron formation-dominated lacustrine or marine gulf system; and (VI) a rimmed carbonate platform system. The interpreted depositional systems are related to three tectonic system tracts. The first four depositional systems are mainly made of continental siliciclastics and refer to the rift initiation to early rift climax stage; the lake/gulf system corresponds to the mid to late rift climax stage and the carbonate platform represents the immediate to late post rift stage (Bocaina Formation deposits of the Ediacaran fossil-bearing Corumba Group). The spatial distribution of the depositional systems and associated paleocurrent patterns indicate a WNW-ESE orientation of the master fault zone related to the formation of the Jacadigo Basin. Thus, the iron formations of the Jacadigo Group were deposited in a starved waterbody related to maximum fault displacement and accommodation rates in a restricted continental rift basin. The Fe-Si-Mn source was probably related to hydrothermal plume activity that reached the basin through the fault system during maximum fault displacement phases. Our results also suggest a restricted tectono-sedimentary setting for the type section of the Puga Formation. The Jacadigo Group and the Puga Formation, usually interpreted as glacial deposits, are readdressed here as basin margin gravitational deposits with no necessary relation to glacial processes. (C) 2011 Elsevier B.V. All rights reserved.

Petrology and geochemistry of the banded iron formation in the Eastern Sierras Pampeanas of San Luis (Argentina): Implications for the evolution of the Nogoli Metamorphic Complex

The metamorphosed banded iron formation from the Nogoli Metamorphic Complex of western Sierra de San Luis, Eastern Sierras Pampeanas of Argentina (Nogoli area, 32 degrees 55`S-66 degrees 15`W) is classified as an oxide facies iron formation of Algoma Type, with a tectonic setting possibly associated with an island arc or back arc, on the basis of field mapping, mineral and textural arrangements and whole rock geochemical features. The origin of banded iron formation is mainly related to chemical precipitation of hydrogenous sediments from seawater in oceanic environments. The primary chemical precipitate is a result of solutions that represent mixtures of seawater and hydrothermal fluids, with significant dilution by maficultramafic volcanic and siliciclastic materials. Multi-stage T(DM) model ages of 1670, 1854 and 1939 Ma and positive, mantle-like xi Nd((1502)) values of +3.8, +1.5 and +0.5 from the banded iron formation are around the range of those mafic to ultramafic meta-volcanic rocks of Nogoli Metamorphic Complex, which are between 1679 and 1765 Ma and +2.64 and +3.68, respectively. This Sm and Nd isotopic connection suggests a close genetic relationship between ferruginous and mafic-ultramafic meta-volcanic rocks, as part of the same island arc or back arc setting. A previous Sm-Nd whole rock isochron of similar to 1.5 Ga performed on mafic-ultramafic meta-volcanic rocks led to the interpretation that chemical sedimentation as old as Mesoproterozoic is possible for the banded iron formation. A clockwise P-T path can be inferred for the regional metamorphic evolution of the banded iron formation, with three distinctive trajectories: (1) Relict prograde M(1)-M(3) segment with gradual P and T increase from greenschist facies at M(1) to amphibolite facies at M(3). (2) Peak P-T conditions at high amphibolite-low granulite facies during M(4). (3) Retrograde counterpart of M(4), that returns from amphibolite facies and stabilizes at greenschist facies during M(5). Each trajectory may be regarded as produced by different tectonic events related to the Pampean? (1) and the Famatinian (2 and 3) orogenies, during the Early to Middle Paleozoic. The Nogoli Metamorphic Complex is interpreted as part of a greenstone belt within the large Meso- to Neoproterozoic Pampean Terrane of the Eastern Sierras Pampeanas of Argentina. (C) 2009 Elsevier Ltd. All rights reserved.

Photoluminescence study of new lanthanide complexes with benzeneseleninic acids

New lanthanide complexes with benzeneseleninic (ABSe) and 4-chloro-benzeneseleninic (ABSeCl) acids have been synthesized and characterized by elemental analysis, infrared and UV-visible spectroscopies. The emission spectra of the trivalent europium complexes presented the typical electronic (5)D(0) -> (7)F(j) transitions of the ion (J = 0-4). The ground-state geometries of the europium complexes have been calculated by using the Sparkle/AM1 model. From these results, the 4f-4f intensity parameters and energies of the ligand singlet and triplet excited states have been obtained. The lower emission quantum yield for the [Eu(ABSe)(3)(H(2)O)(2)](H(2)O)(2) compound, as compared to the [Eu(Al(3)SeCl)(3)(H(2)O)(2)] one, can be associated to the higher numbers of water molecules, in the first and second coordination spheres, that contribute to the luminescence quenching. The [Eu(Al(3)Se)(3)(H(2)O)(2)](H(2)O)(2) complex presents an intermediate state whose energy difference with respect to the first excited singlet state is resonant with three phonons from the water molecules, favouring a multiphonon relaxation process from the singlet state followed by a fast internal conversion process; this effect is less pronounced in the complex with the ABSeCl ligand. The luminescence decay curves of the gadolinium complexes indicate that the level responsible for the intramolecular energy transfer process has a triplet character for both compounds. The nephelauxetic effect in these compounds was investigated under the light of a recently proposed covalency scale based on the concept of overlap polarizability of the chemical bond. (C) 2009 Elsevier B.V. All rights reserved.

Biolabeling with nanoparticles based on Y(2)O(3):Nd(3+) and luminescence detection in the near-infrared

Neodymium based fluorescence presents several advantages in comparison to conventional rare earth or enzyme-substrate based fluorescence emitting sources (e.g.Tb, HRP). Based on this fact we have herein explored a Nd-based fluoroimmunoassay. We efficiently detected the presence of an oxidized low-density lipoprotein (oxLDL) in human plasma a well-known marker for cardiovascular diseases, which causes around 30% of deaths worldwide. Conventional fluoroimmunoassay uses time-resolved luminescence techniques, with detection in the visible range, to eliminate the fluorescence background from the biological specimens. By using an immunoassay based on functionalized Y(2)O(3):Nd(3+) nanoparticles, where the excitation and emission processes in the Nd(3+) ion occur in the near-infrared (NIR) region, we have succeeded in eliminating the interferences from the biological fluorescence background, avoiding the use of time-resolved techniques. This yields higher emission intensity from the Nd(3+)-nanolabels and efficient detection of anti-oxidized low-density lipoproteins (anti-oxLDL) by Y(2)O(3):Nd(3+)-antibody-antigen conjugation, leading to a novel biolabeling method. (C) 2010 Elsevier B.V. All rights reserved.

An Experimental Study of Submerged Entry Nozzles (SEN) Focusing on Decarburization and Clogging

The submerged entry nozzle (SEN) is used to transport the molten steel from a tundish to a mould. The main purpose of its usage is to prevent oxygen and nitrogen pick-up by molten steel from the gas. Furthermore, to achieve the desired flow conditions in the mould. Therefore, the SEN can be considered as a vital factor for a stable casting process and the steel quality. In addition, the steelmaking processes occur at high temperatures around 1873 K, so the interaction between the refractory materials of the SEN and molten steel is unavoidable. Therefore, the knowledge of the SEN behaviors during preheating and casting processes is necessary for the design of the steelmaking processes  The internal surfaces of modern SENs are coated with a glass/silicon powder layer to prevent the SEN graphite oxidation during preheating. The effects of the interaction between the coating layer and the SEN base refractory materials on clogging were studied. A large number of accretion samples formed inside alumina-graphite clogged SENs were examined using FEG-SEM-EDS and Feature analysis. The internal coated SENs were used for continuous casting of stainless steel grades alloyed with Rare Earth Metals (REM). The post-mortem study results clearly revealed the formation of a multi-layer accretion. A harmful effect of the SENs decarburization on the accretion thickness was also indicated. In addition, the results indicated a penetration of the formed alkaline-rich glaze into the alumina-graphite base refractory. More specifically, the alkaline-rich glaze reacts with graphite to form a carbon monoxide gas. Thereafter, dissociation of CO at the interface between SEN and molten metal takes place. This leads to reoxidation of dissolved alloying elements such as REM (Rare Earth Metal). This reoxidation forms the “In Situ” REM oxides at the interface between the SEN and the REM alloyed molten steel. Also, the interaction of the penetrated glaze with alumina in the SEN base refractory materials leads to the formation of a high-viscous alumina-rich glaze during the SEN preheating process. This, in turn, creates a very uneven surface at the SEN internal surface. Furthermore, these uneven areas react with dissolved REM in molten steel to form REM aluminates, REM silicates and REM alumina-silicates. The formation of the large “in-situ” REM oxides and the reaction of the REM alloying elements with the previously mentioned SEN´s uneven areas may provide a large REM-rich surface in contact with the primary inclusions in molten steel. This may facilitate the attraction and agglomeration of the primary REM oxide inclusions on the SEN internal surface and thereafter the clogging. The study revealed the disadvantages of the glass/silicon powder coating applications and the SEN decarburization. The decarburization behaviors of Al2O3-C, ZrO2-C and MgO-C refractory materials from a commercial Submerged Entry Nozzle (SEN), were also investigated for different gas atmospheres consisting of CO2, O2 and Ar. The gas ratio values were kept the same as it is in a propane combustion flue gas at different Air-Fuel-Ratio (AFR) values for both Air-Fuel and Oxygen-Fuel combustion systems. Laboratory experiments were carried out under nonisothermal conditions followed by isothermal heating. The decarburization ratio (α) values of all three refractory types were determined by measuring the real time weight losses of the samples. The results showed the higher decarburization ratio (α) values increasing for MgO-C refractory when changing the Air-Fuel combustion to Oxygen-Fuel combustion at the same AFR value. It substantiates the SEN preheating advantage at higher temperatures for shorter holding times compared to heating at lower temperatures during longer holding times for Al2O3-C samples. Diffusion models were proposed for estimation of the decarburization rate of an Al2O3-C refractory in the SEN. Two different methods were studied to prevent the SEN decarburization during preheating: The effect of an ZrSi2 antioxidant and the coexistence of an antioxidant additive and a (4B2O3 ·BaO) glass powder on carbon oxidation for non-isothermal and isothermal heating conditions in a controlled atmosphere. The coexistence of 8 wt% ZrSi2 and 15 wt% (4B2O3 ·BaO) glass powder of the total alumina-graphite refractory base materials, presented the most effective resistance to carbon oxidation. The 121% volume expansion due to the Zircon formation during heating and filling up the open pores by a (4B2O3 ·BaO) glaze during the green body sintering led to an excellent carbon oxidation resistance. The effects of the plasma spray-PVD coating of the Yttria Stabilized Zirconia (YSZ) powder on the carbon oxidation of the Al2O3-C coated samples were investigated. Trials were performed at non-isothermal heating conditions in a controlled atmosphere. Also, the applied temperature profile for the laboratory trials were defined based on the industrial preheating trials. The controlled atmospheres consisted of CO2, O2 and Ar. The thicknesses of the decarburized layers were measured and examined using light optic microscopy, FEG-SEM and EDS. A 250-290 μm YSZ coating is suggested to be an appropriate coating, as it provides both an even surface as well as prevention of the decarburization even during heating in air. In addition, the interactions between the YSZ coated alumina-graphite refractory base materials in contact with a cerium alloyed molten stainless steel were surveyed. The YSZ coating provided a total prevention of the alumina reduction by cerium. Therefore, the prevention of the first clogging product formed on the surface of the SEN refractory base materials. Therefore, the YSZ plasma-PVD coating can be recommended for coating of the hot surface of the commercial SENs.

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 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

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

Nanostructured hybrid films containing nanophosphor: Fabrication and electronic spectral properties

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