Mineralogia e química dos sedimentos de fundo do médio e baixo Madeira e de seus principais tributários: Amazonas - Brasil

O objetivo deste trabalho foi investigar a variação composicional e mineralógica dos sedimentos de fundo transportados pelos grandes rios da Amazônia, com nascentes nos Andes provenientes de rochas cratônicas. O estudo foi realizado com base em análises granulométricas, mineralógicas e químicas, incluindo isótopos de Pb, no rio Madeira e seus tributários. O conjunto de dados mostra que os sedimentos de fundo do rio Madeira são granulométrica, mineralógica e quimicamente distintos de seus principais tributários. Os sedimentos do rio Madeira são mais arenosos; têm maior quantidade de quartzo; menor conteúdo de Al₂O₃, Fe₂O₃, K₂O, MgO, Na₂O, PF, Ti₂O, P₂O₅, MnO e elementos-traço; e a maturidade aumenta de montante para jusante. Dentre os sedimentos dos tributários, os rios Machado e secundariamente o rio Marmelos são os que mais se aproximam da composição dos sedimentos do rio Madeira, enquanto que o Jamari com sedimentos com maior proporção de TiO_2,, Zr, Y, Nb, Ga, Hf, U, Ta e ETR, é o mais distinto. Apesar do ambiente de intenso intemperismo e erosão, em condições tropicais úmidas, a que estão submetidas as rochas drenadas pela bacia do rio Madeira, os valores das razões Th/Co, Th/Pb, Th/Yb, Al/Pb, Zr/Co e a composição isotópica de Pb indicam fontes distintas para os sedimentos de fundo estudados. Os sedimentos do rio Madeira são provenientes, principalmente, de rochas máficas, enquanto que os sedimentos de seus tributários têm como fonte essencialmente rochas félsicas.

Mineralogia dos greisens da área Grota Rica, Plúton Água Boa, Pitinga, Amazonas

O topázio-álcali-feldspato-granito, fácies mais evoluída do plúton Água Boa, foi afetado por processos de alteração hidrotermal, que culminaram com a formação de greisens e veios de quartzo, principais hospedeiros de mineralizações de Sn e, subordinadamente, Zn. Os greisens foram classificados como quartzo-topázio-siderofilita-greisen, topázio-siderofilita-quartzo-greisen e topázio-quartzo-greisen. São compostos por quartzo, siderofilita e topázio, acompanhados por quantidades variáveis de fluorita, zinnwaldita, esfalerita, cassiterita, zircão, anatásio e, localmente, Ce-monazita, galena, pirita, calcopirita e bismuto nativo. Estudos de química mineral em microssonda eletrônica permitiram identificar três tipos de micas: (1) siderofilita marrom, presente no topázio-granito; (2) siderofilita verde, encontrada nos greisens; (3) zinnwaldita, fracamente colorida, encontrada como coroas finas e descontínuas em torno da siderofilita verde dos greisens, e encontrada também em veios de quartzo. A composição da siderofilita do granito varia com a proximidade dos greisens, mostrando uma evolução de siderofilita siderofilita litinífera, com aumento nos conteúdos de ^VIAl, Li e Si. A siderofilita do greisen foi, por sua vez, parcialmente substituída por zinnwaldita, também com aumento nos teores de ^VIAl, Li e Si. A cassiterita nos greisens forma cristais euédricos a subédricos em contato reto com siderofilita ou como agregados junto com topázio, quartzo e fluorita. Exibe cristais maclados, zonados e com forte pleocroísmo. As composições muito puras e baixos conteúdos de Nb e Ta, indicam formação em condições hidrotermais.

Luminescência e propriedades estruturais de 'LI''TA'O IND.3'nanoestruturado dopado com európio (III) e magnésio

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Estudo da redução fotocatalítica e fotoeletrocatalítica de 'CO IND. 2' em meio aquoso sobre 'CU'/'CU IND. 2 'O'', 'TI' 'O IND. 2'/'PT', 'CU''NB' 'O IND. 3' - 'CU''O' e 'CU IND. 0,85''ZN IND. 0,15''NB IND. 2''O IND.6' como catalisadores para formação de metanol

Pós-graduação em Química - IQ

Preparação e caracterização estrutural, mecânica e anelástica de ligas do sistema Ti-Ta contendo oxigênio intersticial, para uso biomédico

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Structure and photocatalytic properties of Nb-doped Bi12TiO20 prepared by the oxidant peroxide method (OPM)

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Corrosion properties of Fe-Cr-Nb-B amorphous alloys and coatings

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Desenvolvimento de uma nova liga quaternária Ti25Ta25Nb3Sn para aplicações odontológicas

Pós-graduação em Engenharia Mecânica - FEG

Electrophoretic deposition of (Zn, Nb)SnO2-films varistor superficially modified with Cr3+

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Interaction between recrystallization and strain-induced precipitation in a high Nb- and N-bearing austenitic stainless steel: influence of the interpass time

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Obtenção e caracterização óptica e elétrica de 'La''Ta'O IND.4' e LiTaO Ind.3 puros e dopados com Eu POT.3+

Eletronicalceramics are used in many applications such as: multilayer capacitor, transducer, pyroelectric sensors and electrooptic devices. In recent years there has been a growing demand for eletronicalceramics with better performance and functionality. This demand has accelerated the development of synthesis techniques to produce powders with well-defined particle size, shape and crystallinity. The eletronicalceramics in the form of bulk are determined by their performance characteristics of the powders used and the preparation process. So, physical and chemical properties of powders, such as chemical control of stoichiometry, purity, homogeneity, particle size and shape should be observed when choosing the methods of synthesis. Among the techniques used so far, the polymeric precursor method, also known as Pechini, has been considered ideal for the preparation of nanosized powders. Thus, this research project aims to use the polymeric precursor method to prepare powders of lithium tantalate and lanthanum tantalate, with good chemical stability. In this aspect is proposed to investigate the effects of variation of the concentration of europium about the properties of tantalate because doping with Eu3 + indicates that they may occupy different sites in the crystal structure, as in the case of LiTaO3. Effects of things like occupation sites, stability of phases and formation temperature have been previously investigated by the group, which motivated the formulation of this project. Our proposal aims to introduce the Eu3 + LaTaO4 and LiTaO3 and study the structural and optical properties of the powders obtained by Pechini method, as well as correlate these studies with the electrical properties of the material, mainly the Ironelectricty Hysteresis.

Diffusion of oxygen in some binary Ti-Based alloys used as biomaterials

Ti and its alloys are widely used as biomaterials. Their main properties are excellent corrosion resistance, relatively low elastic modulus, high specific strength, and good biocompatibility. The development of new Ti alloys with properties favorable for use in the human body is desired. To this end, Ti alloys with Mo, Nb, Zr, and Ta are being developed, because these elements do not cause cytotoxicity. The presence of interstitial elements (such as oxygen and nitrogen) induces strong changes in the elastic properties of the material, which leads to hardening or softening of the alloy. By means of anelastic spectroscopy, we are able to obtain information on the diffusion of these interstitial elements present in the crystalline lattice. In this paper, the effect of oxygen on the anelastic properties of some binary Ti-based alloys was analyzed with anelastic spectroscopy. The diffusion coefficients, pre-exponential factors, and activation energies were calculated for oxygen and nitrogen in these alloys.

Estudo da resistência à corrosão de ligas Ni-Cr-Mo-Ta E Ni-Cr-Mo-W em solução NaF 0,08 mol/L, pH 4,7 para aplicações odontológicas

A large number of metal alloys are used in Dentistry for the manufacture of fixed and removable dentures. In the oral cavity, these structures are exposed to a chemically aggressive medium, like saliva and mechanical efforts, like mastication. In addition, acidic solutions containing fluoride ions are also frequently used in dental treatments to prevent dental plates and decays development. In this context, it was considered important to investigate the influence that a fourth element could exert when added to the ternary alloy Ni-Cr-Mo, largely used in Brazil. Therefore, electrochemical tests were done to evaluate the resistance to corrosion of quaternary alloy 65Ni-25Cr-5Mo-5Ta and 65Ni-25Cr-5Mo-5W in NaF solution 0,08mol / L, pH = 4.7. For greater understanding the microstructure and morphology of alloys were studied, through metallographic analysis, using optics microscopy and electron microscopy scanning. For the electrochemical tests were applied techniques traditionally used in corrosion researches, such as: potential measures in open circuit (OCP) and cyclic polarization (CP). It was found that both quaternary alloys showed very similar results. Comparing these quaternary alloys with the ternary 65Ni-25Cr-10Mo, it was found that the quaternary alloys exhibit greater resistance to corrosion, in other words, less passivation current density than the ternary alloy, showing that it is advantageous to add a fourth element in the alloy

Estudo da resistência à corrosão de ligas Ni-Cr-Mo-Ta E Ni-Cr-Mo-W em solução NaF 0,08 mol/L, pH 4,7 para aplicações odontológicas

A large number of metal alloys are used in Dentistry for the manufacture of fixed and removable dentures. In the oral cavity, these structures are exposed to a chemically aggressive medium, like saliva and mechanical efforts, like mastication. In addition, acidic solutions containing fluoride ions are also frequently used in dental treatments to prevent dental plates and decays development. In this context, it was considered important to investigate the influence that a fourth element could exert when added to the ternary alloy Ni-Cr-Mo, largely used in Brazil. Therefore, electrochemical tests were done to evaluate the resistance to corrosion of quaternary alloy 65Ni-25Cr-5Mo-5Ta and 65Ni-25Cr-5Mo-5W in NaF solution 0,08mol / L, pH = 4.7. For greater understanding the microstructure and morphology of alloys were studied, through metallographic analysis, using optics microscopy and electron microscopy scanning. For the electrochemical tests were applied techniques traditionally used in corrosion researches, such as: potential measures in open circuit (OCP) and cyclic polarization (CP). It was found that both quaternary alloys showed very similar results. Comparing these quaternary alloys with the ternary 65Ni-25Cr-10Mo, it was found that the quaternary alloys exhibit greater resistance to corrosion, in other words, less passivation current density than the ternary alloy, showing that it is advantageous to add a fourth element in the alloy

TUNGSTEN ISOTOPIC COMPOSITIONS IN STARDUST SiC GRAINS FROM THE MURCHISON METEORITE: CONSTRAINTS ON THE s-PROCESS IN THE Hf-Ta-W-Re-Os REGION

We report the first tungsten isotopic measurements in stardust silicon carbide (SiC) grains recovered from the Murchison carbonaceous chondrite. The isotopes (182,183,184,186)Wand (179,180)Hf were measured on both an aggregate (KJB fraction) and single stardust SiC grains (LS+ LU fraction) believed to have condensed in the outflows of low-mass carbon-rich asymptotic giant branch (AGB) stars with close-to-solar metallicity. The SiC aggregate shows small deviations from terrestrial (= solar) composition in the (182)W/(184)Wand (183)W/(184)Wratios, with deficits in (182)W and (183)W with respect to (184)W. The (186)W/(184)W ratio, however, shows no apparent deviation from the solar value. Tungsten isotopic measurements in single mainstream stardust SiC grains revealed lower than solar (182)W/(184)W, (183)W/(184)W, and (186)W/(184)W ratios. We have compared the SiC data with theoretical predictions of the evolution of W isotopic ratios in the envelopes of AGB stars. These ratios are affected by the slow neutron-capture process and match the SiC data regarding their (182)W/(184)W, (183)W/(184)W, and (179)Hf/(180)Hf isotopic compositions, although a small adjustment in the s-process production of (183)W is needed in order to have a better agreement between the SiC data and model predictions. The models cannot explain the (186)W/(184)W ratios observed in the SiC grains, even when the current (185)W neutron-capture cross section is increased by a factor of two. Further study is required to better assess how model uncertainties (e. g., the formation of the (13)C neutron source, the mass-loss law, the modeling of the third dredge-up, and the efficiency of the (22)Ne neutron source) may affect current s-process predictions.