Deposição de filmes finos de SnO2 e GaAs, visando confecção de dispositivos baseados na heterojunção SnO2/GaAs

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

Estudo das propriedades estímulo responsivas dos polímeros escovas

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

New flexible and transparent solution-based germanium-sulfide polymeric materials

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Desenvolvimento de detector eletroquímico para cromatografia líquida de alta eficiência baseado em um eletrodo modificado com nanopartículas metálicas para determinação de ácidos carboxílicos em vinhaça de cana-de-açúcar

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

Oxygen reduction reaction catalyzed by epsilon-MnO2: Influence of the crystalline structure on the reaction mechanism

The oxygen reduction reaction (ORR) was studied in KOH electrolyte on carbon supported epsilon-manganese dioxide (epsilon-MnO2/C). The epsilon-MnO2/C catalyst was prepared via thermal decomposition of manganese nitrate and carbon powder (Vulcan XC-72) mixtures. X-ray powder diffraction (XRD) measurements were performed in order to determine the crystalline structure of the resulting composite, while energy dispersive X-ray analysis (EDX) was used to evaluate the chemical composition of the synthesized material. The electrochemical studies were conducted using cyclic voltammetry (CV) and quasi-steady state polarization measurements carried out with an ultra thin layer rotating ring/disk electrode (RRDE) configuration. The electrocatalytic results obtained for 20% (w/w) Pt/C (E-TEK Inc., USA) and alpha-MnO2/C for the ORR, considered as one of the most active manganese oxide based catalyst for the ORR in alkaline media, were included for comparison. The RRDE results revealed that the ORR on the MnO2 catalysts proceeds preferentially through the complete 4e(-) reduction pathway via a 2 plus 2e(-) reduction process involving hydrogen peroxide as an intermediate. A benchmark close to the performance of 20% (w/w) Pt/C (E-TEK Inc., USA) was observed for the epsilon-MnO2/C material in the kinetic control region, superior to the performance of alpha-MnO2/C, but a higher amount of HO2- was obtained when epsilon-MnO2/C was used as catalyst. The higher production of hydrogen peroxide on epsilon-MnO2/C was related to the presence of structural defects, typical of this oxide, while the better catalytic performance in the kinetic control region compared to alpha-MnO2/C was related with the higher electrochemical activity for the proton insertion kinetics, which is a structure sensitive process. (C) 2012 Elsevier Ltd. All rights reserved.

Preparação de vidros e vitrocerâmicas de óxidos de metais pesados contendo prata: propriedades ópticas, estruturais e eletroquímicas

Silver containing heavy metal oxide glasses and glass ceramics of the system WO3-SbPO4-PbO-AgCl with different AgCl contents have been prepared and their thermal, structural and optical properties characterized. Glass ceramics containing metallic silver nanoparticles have been prepared by annealing glass samples at temperatures above the glass transition and analyzed by transmission electron microscopy and energy dispersive X-ray microanalysis. The presence of the metallic clusters has been also confirmed by the observation of a surface plasmon resonimce band in the visible range. Cyclic voltammetric measurements indicated the presence of metallic silver into the glasses, even before to perform the thermal treatment.

Characterization of calcium oxide in root perforation sealer materials

Root perforation represents an undesirable complication that may lead to an unfavorable prognosis. The aims of this study were to characterize and to compare the presence of calcium oxide (CaO) on the chemical composition of materials used for root perforation therapy: gray and white mineral trioxide aggregate (MTA) and Portland cement (PC), gray MTA+5%CaO and gray MTA+10%CaO. The last two materials were analyzed to evaluate the increase of CaO in the final sample. CaO alone was used as a standard. Eighteen polyethylene tubes with an internal diameter of 3 mm and 3 mm in length were prepared, filled and then transferred to a chamber with 95% relative humidity and a temperature of 37ºC. The chemical compounds (particularly CaO) and the main components were analyzed by energy-dispersive X-ray microanalysis (EDX). EDX revealed the following concentrations of CaO: gray MTA: 59.28%, white MTA: 63.09%; PC: 72.51%; gray MTA+5%CaO: 63.48% and gray MTA+10%CaO: 67.55%. The tested materials presented different concentrations of CaO. Even with an increase of 5 and 10% CaO in gray MTA, the CaO levels found in the MTA samples were lower than those found in PC.

Spectroscopic investigations of functional bulk and thin film Heusler alloys

Functional and smart materials have gained large scientific and practical interest in current research and development. The Heusler alloys form an important class of functional materials used in spintronics, thermoelectrics, and for shape memory alloy applications. An important aspect of functional materials is the adaptability of their physical properties. In this work functional polycrystalline bulk and epitaxial thin film Heusler alloys are characterized by means of spectroscopic investigation methods, X-ray magnetic circular dichroism (XMCD) and energy dispersive X-ray analysis (EDX). With EDX the homogeneity of the samples is studied extensively. For some cases of quaternary compounds, for example Co2(MnxTi1−x)Sn and Co2(Mn0.5Dy0.5)Sn, an interesting phase separation in two nearly pure ternary Heusler phases occurs. For these samples the phase separation leads to an improvement of thermoelectric properties. XMCD as the main investigation method was used to study Co2TiZ (Z = Si, Sn, and Sb), Co2(MnxTi1−x)Si, Co2(MnxTi1−x)Ge, Co2Mn(Ga1−xGex), Co2FeAl, Mn2VAl, and Ni2MnGa Heusler compounds. The element-specific magnetic moments are calculated. Also, the spin-resolved unoccupied density of states is determined, for example giving hints for half-metallic ferromagnetism for some Co-based compounds. The systematic change of the magnetic moments and the shift of the Fermi energy is a proof that Heusler alloys are suitable for a controlled tailoring of physical properties. The comparison of the experimental results with theoretical predictions improves the understanding of complex materials needed to optimize functional Heusler alloys.

Structural characterization of intermediate and metastable phases by electron microscopy

Structure characterization of nanocrystalline intermediates and metastable phases is of primary importance for a deep understanding of synthetic processes undergoing solid-to-solid state phase transitions. Understanding the evolution from the first nucleation stage to the final synthetic product supports not only the optimization of existing processes, but might assist in tailoring new synthetic paths. A systematic investigation of intermediates and metastable phases is hampered because it is impossible to produce large crystals and only in few cases a pure synthetic product can be obtained. Structure investigation by X-ray powder diffraction methods is still challenging on nanoscale, especially when the sample is polyphasic. Electron diffraction has the advantage to collect data from single nanoscopic crystals, but is limited by data incompleteness, dynamical effects and fast deterioration of the sample under the electron beam. Automated diffraction tomography (ADT), a recently developed technique, making possible to collect more complete three-dimensional electron diffraction data and to reduce at the same time dynamical scattering and beam damage, thus allowing to investigate even beam sensitive materials (f.e. hydrated phases and organics). At present, ADT is the only technique able to deliver complete three-dimensional structural information from single nanoscopic grains, independently from other surrounding phases. Thus, ADT is an ideal technique for the study of on-going processes where different phases exist at the same time and undergo several structural transitions. In this study ADT was used as the main technique for structural characterization for three different systems and combined subsequently with other techniques, among which high-resolution transmission electron microscopy (HRTEM), cryo-TEM imaging, X-ray powder diffraction (XRPD) and energy disperse X-ray spectroscopy (EDX).rnAs possible laser host materials, i.e. materials with a broad band emission in the near-infrared region, two unknown phases were investigated in the ternary oxide system M2O-Al2O3-WO3 (M = K, Na). Both phases exhibit low purity as well as non-homogeneous size distribution and particle morphology. The structures solved by ADT are also affected by pseudo-symmetry. rnSodium titanate nanotubes and nanowires are both intermediate products in the synthesis of TiO2 nanorods which are used as additives to colloidal TiO2 film for improving efficiency of dye-sensitized solar cells (DSSC). The structural transition from nantubes to nanowires was investigated in a step by step time-resolved study. Nanowires were discovered to consist of a hitherto unknown phase of sodium titanate. This new phase, typically affected by pervasive defects like mutual layer shift, was structurally determined ab-initio on the basis of ADT data. rnThe third system is related with calcium carbonate nucleation and early crystallization. The first part of this study is dedicated to the extensive investigations of calcium carbonate formation in a step by step analysis, up to the appearance of crystalline individua. The second part is dedicated to the structure determination by ADT of the first-to-form anhydrated phase of CaCO3: vaterite. An exhaustive structure analysis of vaterite had previously been hampered by diffuse scattering, extra periodicities and fast deterioration of the material under electron irradiation. rn

Effects of carbonation on the mineral composition of cement kiln dust

Due to their relatively high calcium oxide content, industrial mineral oxide wastes are potential candidates for mineral sequestration of carbon dioxide (CO2). Cement kiln dust (CKD), a byproduct of cement manufacturing contains 20-60% CaO making it a possible candidate for CO2 sequestration. In this study, three types of CKD are characterized, before and after carbonation, using environmental scanning electron microscopy and energy dispersive x-ray microanalysis to determine the mineralogical and morphological changes occurring due to carbonation. The reactants, products, and precipitation mechanisms were investigated to enhance understanding of the governing processes and allow better utilization of CKD for CO2 sequestration. The results of multiple independent analyses confirmed the formation of CaCO3 during carbonation. Examinations of the reaction pathways found that CaO and calcium hydroxide (Ca(OH)2) were the major reactants. Three types of CaCO3 precipitation mechanisms were observed: (1) diffusion of CO2 into Ca(OH)2 particles causing precipitation in the pores of the particle and the growth of a CaCO3 ring from the outside inward, (2) precipitation onto existing particles, and (3) precipitation from aqueous solution. The growth of a CaCO3 ring on the outside of a particle may slow further diffusion of CO2 into a particle slowing iv the overall sequestration rate. Additionally, changes caused by carbonation in the solubility of trace metals were studied by mixing pre- and post-carbonated CKD with water and analyzing the solution using inductively coupled plasma mass spectrometry. Decreases in the leaching of chromium, lead, and copper were observed, and is an incentive for use of CKD for CO2 sequestration. Equilibrium modeling using PHREEQC confirmed that CaO and Ca(OH)2 would carbonate readily and form CaCO3.

Microstructural and mechanical characterization of contemporary lingual orthodontic brackets.

OBJECTIVES To investigate the composition and the microstructural and mechanical characterization of three different types of lingual brackets. MATERIALS AND METHODS Incognito™ (3M Unitek), In-Ovation L (DENTSPLY GAC) and STb™ (Light Lingual System, ORMCO) lingual brackets were studied under the scanning electron microscope employing backscattered electron imaging and their elemental composition was analysed by energy-dispersive X-ray microanalysis. Additionally, Vickers hardness was assessed using a universal hardness-testing machine, and the indentation modulus was measured according to instrumented indentation test. Two-way analysis of variance was conducted employing bracket type and location (base and wing) as discriminating variable. Significant differences among groups were allocated by post hoc Student-Newman-Keuls multiple comparison analysis at 95% level of significance. RESULTS Three different phases were identified for Incognito and In-Ovation L bracket based on mean atomic number contrast. On the contrary, STb did not show mean atomic contrast areas and thus it is recognized as a single phase. Incognito is a one-piece bracket with the same structure in wing and base regions. Incognito consists mainly of noble metals while In-Ovation L and STb show similar formulations of ferrous alloys in wing and base regions. No significant differences were found between ferrous brackets in hardness and modulus values, but there were significant differences between wing and base regions. Incognito illustrated intermediate values with significant differences from base and wing values of ferrous brackets. CONCLUSIONS/IMPLICATIONS Significant differences exist in microstructure, elemental composition, and mechanical properties among the brackets tested; these might have a series of clinical implications during mechanotherapy.

A QUANTITATIVE INVESTIGATION OF SOURCE AND ELEMENTAL COMPOSITION OF INDOOR AND OUTDOOR FINE PARTICULATE AIR POLLUTION IN HOUSTON (TEXAS)

An investigation was undertaken to determine the chemical characterization of inhalable particulate matter in the Houston area, with special emphasis on source identification and apportionment of outdoor and indoor atmospheric aerosols using multivariate statistical analyses.^ Fine (<2.5 (mu)m) particle aerosol samples were collected by means of dichotomous samplers at two fixed site (Clear Lake and Sunnyside) ambient monitoring stations and one mobile monitoring van in the Houston area during June-October 1981 as part of the Houston Asthma Study. The mobile van allowed particulate sampling to take place both inside and outside of twelve homes.^ The samples collected for 12-h sampling on a 7 AM-7 PM and 7 PM-7 AM (CDT) schedule were analyzed for mass, trace elements, and two anions. Mass was determined gravimetrically. An energy-dispersive X-ray fluorescence (XRF) spectrometer was used for determination of elemental composition. Ion chromatography (IC) was used to determine sulfate and nitrate.^ Average chemical compositions of fine aerosol at each site were presented. Sulfate was found to be the largest single component in the fine fraction mass, comprising approximately 30% of the fine mass outdoors and 12% indoors, respectively.^ Principal components analysis (PCA) was applied to identify sources of aerosols and to assess the role of meteorological factors on the variation in particulate samples. The results suggested that meteorological parameters were not associated with sources of aerosol samples collected at these Houston sites.^ Source factor contributions to fine mass were calculated using a combination of PCA and stepwise multivariate regression analysis. It was found that much of the total fine mass was apparently contributed by sulfate-related aerosols. The average contributions to the fine mass coming from the sulfate-related aerosols were 56% of the Houston outdoor ambient fine particulate matter and 26% of the indoor fine particulate matter.^ Characterization of indoor aerosol in residential environments was compared with the results for outdoor aerosols. It was suggested that much of the indoor aerosol may be due to outdoor sources, but there may be important contributions from common indoor sources in the home environment such as smoking and gas cooking. ^

Estudio microestructural y de los procesos de hidratación de cementos con adiciones

En los últimos años, las sociedades industrializadas han tomado una mayor conciencia sobre el problema que suponen las emisiones indiscriminadas de gases de efecto invernadero a la atmósfera. El hormigón, cuyo principal componente es el cemento, es probablemente el material más utilizado en construcción. En la actualidad, las emisiones globales de CO2 debidas a la combustión del CaCO3 del cemento Pórtland representan entre el 5% y el 10% respecto del total. Estos valores son de gran interés si se considera que el compromiso aceptado al firmar el Protocolo de Kioto es de una reducción del 5% antes del año 2020, sobre el total de gases producidos. El principal objetivo del presente trabajo es el estudio microestructural y de los procesos de hidratación de los cementos con adiciones. Para ello se propone contribuir a la investigación sobre nuevos productos cementicios basados en micropartículas esféricas vítreas que pueden adicionarse al cemento antes del proceso de amasado. Los resultados obtenidos se han contrastado con las adiciones convencionales de más uso en la actualidad. El nuevo material basa su composición en la química del aluminio y el silicio. Al disminuir la cantidad de CaCO3, se contribuye al desarrollo sostenible y a la reducción de emisiones de CO2. La patente creada por el Grupo Cementos Pórtland Valderrivas (GCPV), describe el proceso de producción de las cemesferas (WO 2009/007470, 2010). Los productos que forman la materia prima para la elaboración de las cemesferas son arcillas, calizas, margas o productos o subproductos industriales, que tras su molienda, son fundidos mediante un fluido gaseoso a elevada temperatura (entre 1250ºC y 1600ºC). Este proceso permite obtener un producto final en forma esférica maciza o microesfera, que tras estabilizarse mediante un enfriamiento rápido, consigue una alta vitrificación idónea para su reactividad química, con una mínima superficie específica en relación a su masa. El producto final obtenido presenta prácticamente la finura requerida y no precisa ser molido, lo que reduce las emisiones de CO2 por el ahorro de combustible durante el proceso de molienda. El proceso descrito permite obtener un amplio abanico de materiales cementantes que, no solo pueden dar respuesta a los problemas generados por las emisiones de CO2, sino también a la disponibilidad de materiales en países donde hasta el momento no se puede fabricar cemento debido a la falta de calizas. Complementariamente se ha optimizado el método de cálculo del grado de hidratación a partir de los resultados del ensayo de ATD-TG en base a los modelos de cálculo de Bhatty y Pane. El método propuesto permite interpretar el comportamiento futuro del material a partir de la interpolación numérica de la cantidad de agua químicamente enlazada. La evolución del grado de hidratación tiene una relación directa con el desarrollo de la resistencia mecánica del material. Con el fin de caracterizar los materiales de base cemento, se ha llevado a cabo una amplia campaña experimental en pasta de cemento, mortero y hormigón. La investigación abarca tres niveles: caracterización microestructural, macroestructural y caracterización del comportamiento a largo plazo, fundamentalmente durabilidad. En total se han evaluado ocho adiciones diferentes: cuatro adiciones convencionales y cuatro tipos de cemesferas con diferente composición química. Los ensayos a escala microscópica comprenden la caracterización química, granulométrica y de la superficie específica BET de los materiales anhidros, análisis térmico diferencial y termogravimétrico en pasta de cemento y mortero, resonancia magnética de silicio en pasta de cemento, difracción de rayos X de los materiales anhidros y de las probetas de pasta, microscopía electrónica de barrido con analizador de energía dispersiva por rayos X en pasta y mortero, y porosimetría por intrusión de mercurio en mortero. La caracterización macroscópica del material comprende ensayos de determinación del agua de consistencia normal y de los tiempos de inicio y fin de fraguado en pasta de cemento, ensayos de resistencia mecánica a flexión y compresión en probetas prismáticas de mortero, y ensayos de resistencia a compresión en probetas de hormigón. Para caracterizar la durabilidad se han desarrollado ensayos de determinación del coeficiente de migración de cloruros y ensayos de resistividad eléctrica en probetas de mortero. Todos los ensayos enumerados permiten clarificar el comportamiento de las cemesferas y compararlo con las distintas adiciones de uso convencional. Los resultados reflejan un buen comportamiento resistente y durable de los materiales con adición de cemesferas. La caracterización microscópica refleja su relación con las propiedades mesoscópicas y permite comprender mejor la evolución en los procesos de hidratación de las cemesferas. In recent years industrialised societies have become increasingly aware of the problem posed by indiscriminate emission of greenhouse gases into the atmosphere. Concrete, with a main component being cement, is arguably the most widely used construction material. At present, global emissions of CO2 due to the combustion of CaCO3 from Portland cement represent between 5% and 10% of the total. If the requirement of the Kyoto Protocol of a reduction of 5% of the total gas produced before 2020 is considered, then such values are of significant interest. The main objective of this work is the assessment of the microstructure and the hydration processes of cements with additions. Such an examination proposes research into new cementitious products based on vitreous spherical microparticles that may be added to the cement before the mixing process. The results are compared with the most commonly used conventional additions. The new material bases its composition on the chemistry of aluminium and silicates. By decreasing the amount of CaCO3, it is possible both to contribute to sustainable development and reduce CO2 emissions. The patent created by Grupo Cementos Portland Valderrivas (GCPV) describes the production process of microspheres (WO 2009/007470, 2010). The products that form the raw material for manufacture are clays, lime-stone, marl and industrial products or by-products that melt after being ground and fed into a gaseous fluid at high temperatures (1250°C and 1600°C). This process allows the obtaining of a product with a solid-spherical or micro-spherical shape and which, after being stabilised in a solid state by rapid cooling, obtains a high vitrification suitable for chemical reactivity, having a minimal surface in relation to its mass. Given that the final product has the fineness required, it prevents grinding that reduces CO2 emissions by saving fuel during this process. The process, which allows a wide range of cementitious materials to be obtained, not only addresses the problems caused by CO2 emissions but also enhances the availability of materials in countries that until the time of writing have not produced cement due to a lack of limestone. In addition, the calculation of the degree of hydration from the test results of DTA-TG is optimised and based on Bhatty and Pane calculation models. The proposed method allows prediction of the performance of the material from numerical interpolation of the amount of chemically bound water. The degree of hydration has a direct relationship with the development of material mechanical strength. In order to characterise the cement-based materials, an extensive experimental campaign in cement paste, concrete and mortar is conducted. The research comprises three levels: micro-structural characterisation, macro-structural and long-term behaviour (mainly durability). In total, eight additions are assessed: four conventional additions and four types of microspheres with different chemical compositions. The micro-scale tests include characterisation of chemical composition, particle size distribution and the BET specific surface area of anhydrous material, differential thermal and thermogravimetric analysis in cement paste and mortar, silicon-29 nuclear magnetic resonance in cement paste, X-ray diffraction of the anhydrous materials and paste specimens, scanning of electron microscopy with energy dispersive X-ray analyser in cement paste and mortar, and mercury intrusion porosimetry in mortar. The macroscopic material characterisation entails determination of water demand for normal consistency, and initial and final setting times of cement paste, flexural and compressive mechanical strength tests in prismatic mortar specimens, and compressive strength tests in concrete specimens. Tests for determining the chloride migration coefficient are performed to characterise durability, together with electrical resistivity tests in mortar specimens. All the tests listed allow clarification of the behaviour of the microspheres and comparison with the various additions of conventional use. The results show good resistance and durable behaviour of materials with a microsphere addition. Microscopic characterisation reflects their relationship with mesoscopic properties and provides insights into the hydration processes of the microspheres.

Silver-based crystalline nanoparticles, microbially fabricated

One mechanism of silver resistance in microorganisms is accumulation of the metal ions in the cell. Here, we report on the phenomenon of biosynthesis of silver-based single crystals with well-defined compositions and shapes, such as equilateral triangles and hexagons, in Pseudomonas stutzeri AG259. The crystals were up to 200 nm in size and were often located at the cell poles. Transmission electron microscopy, quantitative energy-dispersive x-ray analysis, and electron diffraction established that the crystals comprise at least three different types, found both in whole cells and thin sections. These Ag-containing crystals are embedded in the organic matrix of the bacteria. Their possible potential as organic-metal composites in thin film and surface coating technology is discussed.

Change in Apoplastic Aluminum during the Initial Growth Response to Aluminum by Roots of a Tolerant Maize Variety1

Root elongation, hematoxylin staining, and changes in the ultrastructure of root-tip cells of an Al-tolerant maize variety (Zea mays L. C 525 M) exposed to nutrient solutions with 20 μm Al (2.1 μm Al3+ activity) for 0, 4, and 24 h were investigated in relation to the subcellular distribution of Al using scanning transmission electron microscopy and energy-dispersive x-ray microanalysis on samples fixed by different methods. Inhibition of root-elongation rates, hematoxylin staining, cell wall thickening, and disturbance of the distribution of pyroantimoniate-stainable cations, mainly Ca, was observed only after 4 and not after 24 h of exposure to Al. The occurrence of these transient, toxic Al effects on root elongation and in cell walls was accompanied by the presence of solid Al-P deposits in the walls. Whereas no Al was detectable in cell walls after 24 h, an increase of vacuolar Al was observed after 4 h of exposure. After 24 h, a higher amount of electron-dense deposits containing Al and P or Si was observed in the vacuoles. These results indicate that in this tropical maize variety, tolerance mechanisms that cause a change in apoplastic Al must be active. Our data support the hypothesis that in Al-tolerant plants, Al can rapidly cross the plasma membrane; these data clearly contradict the former conclusions that Al mainly accumulates in the apoplast and enters the symplast only after severe cell damage has occurred.