Influência da composição química e da microestrutura na usinabilidade do aço de corte fácil com adição de chumbo (SAE12L14)

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Experimental and theoretical studies on the enhanced photoluminescence activity of zinc sulfide with a capping agent

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

Bacteria-derived hydrogen sulfide promotes IL-8 production from epithelial cells

Hydrogen Sulfide (H(2)S) a volatile Sulfur compound, is implicated as a cause of inflammation. especially when it is produced by bacteria colonizing gastrointestinal organs However, It IS Unclear if H(2)S produced by periodontal pathogens affects the inflammatory responses mediated by oral/gingival epithelial cells Therefore. the aims of this Study were (1) to compare the in vitro production of H(2)S among. 14 strains of Oral bacteria and (2) to evaluate the effects of H(2)S on inflammatory response induced in host oral/gingival epithelial cells Porphyromonas gingivalis (Pg) produced the most H(2)S in Culture, Which, in turn resulted in the promotion of proinflammatory cytokine IL-8 from both gingival and Oral epithelial cells The up-regulation of IL-8 expression was reproduced by the exogenously applied H(2)S Furthermore. the Mutant Strains of Pg that do not produce major Soluble Virulent factors. ie gingival, still showed the Production of H(2)S. as well as the promotion of epithelial IL-8 production. which was abrogated by H(2)S scavenging reagents These results demonstrated that Pg produces a concentration of H(2)S capable of Up-regulating-IL-8 expression induced in gingival and oral epithelial cells, revealing a possible mechanism that may promote the inflammation in periodontal disease (C) 2009 Elsevier B.V. All rights reserved

Electrooxidation of sulfide by cobalt pentacyanonitrosylferrate film on glassy carbon electrode by cyclic voltammetry

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

Fluorometric fiber optic drop sensor for atmospheric hydrogen sulfide

A fluorometric technique based on a liquid drop excited from its interior by an optical fiber is described for the measurement of low concentrations of atmospheric hydrogen sulfide (H2S). A drop of alkaline fluorescein mercuric acetate (FMA) solution is suspended in a flowing air sample stream and serves as a renewable sensor. An optical fiber contained within the conduit that forms the drop, brings in the excitation beam; the fluorescence emission is measured by an inexpensive photodiode positioned close to the drop. As H2S in the sample is collected by the alkaline drop, it reacts rapidly with FMA resulting in a significant decrease in fluorescence intensity, proportional to the concentration of H2S sampled. The chemistry of this uniquely selective reaction has been well established for many years, the present technique permits a simple fast inexpensive near real-time measurement with very little reagent consumption. Even without prolonged sampling/preconcentration steps, limits of detection (LODs) in the double digit ppbv range is readily attainable. (C) 1997 Elsevier B.V. B.V.

The Ni-Cu-PGE sulfide ores of the komatiite-hosted Fortaleza de Minas deposit, Brazil: Evidence of hydrothermal remobilization

The Fortaleza de Minas Ni-Cu-PGE sulfide deposit is hosted by Archean komatiitic rocks of the Morro do Ferro greenstone belt, near the southwestern margin of the Sa (aFrancisco) over tildeo Francisco craton, Minas Gerais state, Brazil. The deposit contains 6 million tonnes of ore with an average grade of 2.2 wt% Ni, 0.4% Cu, 0.05% Co and 1.2 ppm PGE+Au, and comprises (i) a main orebody, which is metamorphosed, deformed and transposed along a regional shear zone, consisting mainly of disseminated, brecciated and stringer sulfide ores that are interpreted to be of early magmatic origin, and (ii) PGE-rich discordant veins that are hosted in N-S- and NE-SW-trending late faults that cross-cut the main orebody. The discordant PGE-rich ore (up to 4 ppm total PGE) is characterized by thin, discontinuous and irregular veins and lenses of massive sulfides hosted by serpentinite and talc schist, and is relatively undeformed if compared with the early types of ore. It is composed mainly of pyrrhotite, pentlandite, chalcopyrite, magnetite, carbonates, and amphiboles, with minor cobaltite-gersdorffite, sphalerite, ilmenite, and quartz, and rarely maucherite (Ni11Asg), tellurides and platinum-group minerals (PGM). Omeeite, irarsite, sperrylite, and Ni-bearing merenskyite are the main PGM, followed by minor amounts of testibiopalladite and an unknown phase containing Ru, Te, and As. The PGM occur either included in, or at the margins of, sulfides, sulfarsenides, silicates and oxides, or filling fractures in pyrrhotite, pentlandite, and chalcopyrite, suggesting that they started to precipitate with these minerals and continued to precipitate after the sulfides were formed. The mantle-normalized metal distribution of the two samples of discordant veins shows distinct patterns: one richer in Ni-Pd-Ir-Rh-Ru-Os and another with higher amounts of Cu-Pt-Bi. Both are strongly depleted in Cr if compared with the metamorphosed magmatic ore of this deposit, which follows the general Kambalda-type magmatic trend. on the basis of structural, mineralogical and geochemical evidence, we propose that the PGE-rich discordant ore may have formed by remobilization of metals from the deformed, metamorphosed magmatic orebody (which shows a depleted pattern in these elements) by reduced (pyrrhotite - pentlandite - pyrite are stable), neutral to alkaline and carbonic fluids (carbonate-stable). The PGE may have been transported as bisulfide complexes, and precipitated as tellurides (mainly Pd) and arsenides (Pt, Rh, Ru, Os, Ir) in the late N-S and NE-SW-trending faults owing to a decrease in the activity of S caused by the precipitation of sulfides in the veins.

Poole-Frenkel effect in amorphous poly(p-phenylene sulfide)

The conductivity of poly(p-phenylene sulfide) (PPS) amorphous samples sandwiched between metallic electrodes has been studied as a function of applied voltage, temperature, and electrode material. The voltage (U) dependence of the currents for electric fields within the range 10(3)-10(6) V/cm exhibits exp beta U-1/2 behavior with beta = beta(Schottky) below the glass transition temperature (T-g congruent to 90 degrees C), and beta = beta(Poole-Frenkel) above T-g. Coordinated temperature measurements of de currents with different metallic contacts and thermally stimulated currents (TSC) indicate, however, that the conductivity at T < T-g is consistent with the so-called ''anomalous'' Poole-Frenkel effect rather than the Schottky effect. Consequently, the p-type conductivity in amorphous PPS is proposed to be a bulk-limited process due to ionization of two different types of acceptor centers in the presence of neutral hole traps. (C) 1996 John Wiley & Sons, Inc.

Nonlinear refractive index measurements in antimony-sulfide glass films using a single beam nonlinear image technique

The nonlinear refractive index, n(2), of films based on the new glass system Sb(2)O(3)-Sb(2)S(3) was measured at 1064 nm with laser pulses of 15 ps, using a single-beam nonlinear image technique in presence of a phase object. The films were prepared from bulk glasses by RF-sputtering. A large value of n(2) = 3 x 10-(15) m(2)/W, which is three orders of magnitude larger than for CS(2), was determined. The result shows the strong potential of antimony-sulfide glass films for integrated nonlinear optics. (c) 2005 Elsevier B.V. All rights reserved.

Metamorphism and PGE-Au content of chromitite from the Ipanema mafic/ultramafic Complex, Minas Gerais, Brazil

The Santa Cruz massif, which forms part of the Ipanema mafic/ultramafic Complex, Minas Gerais, Brazil, has an exposed upward sequence of metadunite, metaharzburgite (including three separate chromitite layers), metapyroxenite, metagabbro, and metaanorthosite. Primary igneous chromite grains in the main chromitite layer are poikiloblastic and tectonically fragmented, and have a narrow (10-20 mum) margin of chromian spinel. Cataclased chromite fragments are extensively replaced and mantled by chromian spinel; they have a composite margin comprised of an inner zone of more aluminous spinel and an euhedral outer zone of more Cr-rich spinel, representing granulite and amphibolite facies metamorphic events, respectively. The contents of platinum-group elements (PGE) and Au in chromite separates are relatively high (Os 45, Ir 23, Ru 136, Rh 19, Pt 98, Pd 63, and Au 83 ppb), and significantly enriched (similar to 4x) over whole rock values. Platinum-group minerals are not observed and micrometre-sized inclusions of sulfide minerals (chalcopyrite and pentlandite) in relict chromite are rare. However, comparison of mineral proportions in the separated chromite and whole rock shows that the precious metals are hosted predominantly in the relict igneous chromite grains, rather than the secondary chromian spinel and primary and secondary Mg-rich silicates. The major element composition and average chondrite-normalized PGE pattern of the separated chromite correspond to S-poor stratiform chromitite. We suggest that the precious metals accumulated with chromite during crystallization of a S-poor magma, and were not remobilized in the relict chromite during the subsequent high grade metamorphism.

Renewable drops electrochemical sensor for sulfide ions detection

The design and characteristics of a novel electrochemical system, which uses a drop as a renewable electroanalytical sensor, are described. This article describes the performance of the electrochemical system, the coupling of the experimental arrangement with flow injection technique and a demonstration of its applicability for the measurement of sulfide. The method is based on renewable drops of ferricyanide ions, buffered by borate. The ferrocyanide ions, product of the reaction between ferricyanide and sulfide ions, are oxidized on a platinum microelectrode and the current measured is related to sulfide concentration. The measurements can be done in continuous or static flow mode. In continuous mode, the detection limit is 5.0 x 10(-5) mol L-1.

Sn-polymetallic greisen-type deposits associated with late-stage rapakivi granites, Brazil: fluid inclusion and stable isotope characteristics

Tin-polymetallic greisen-type deposits in the Itu Rapakivi Province and Rondonia Tin Province, Brazil are associated with late-stage rapakivi fluorine-rich peraluminous alkali-feldspar granites. These granites contain topaz and/or muscovite or zinnwaldite and have geochemical characteristics comparable to the low-P sub-type topaz-bearing granites. Stockworks and veins are common in Oriente Novo (Rondonia Tin Province) and Correas (Itu Rapakivi Province) deposits, but in the Santa Barbara deposit (Rondonia Tin Province) a preserved cupola with associated bed-like greisen is predominant. The contrasting mineralization styles reflect different depths of formation, spatial relationship to tin granites, and different wall rock/fluid proportions. The deposits contain a similar rare-metal suite that includes Sri (+/-W, +/-Ta, +/-Nb), and base-metal suite (Zn-Cu-Pb) is present only in Correas deposit. The early fluid inclusions of the Correas and Oriente Novo deposits are (1) low to moderate-salinity (0-19 wt.% NaCl eq.) CO2-bearing aqueous fluids homogenizing at 245-450 degreesC, and (2) aqueous solutions with low CO2, low to moderate salinity (0-14 wt.% NaCl eq.), which homogenize between 100 and 340 T. In the Santa Barbara deposit, the early inclusions are represented by (1) low-salinity (5-12 wt.% NaCl eq.) aqueous fluids with variable CO2 contents, homogenizing at 340 to 390 T, and (2) low-salinity (0-3 wt.% NaCl eq.) aqueous fluid inclusions, which homogenize at 320380 degreesC. Cassiterite, wolframite, columbite-tantalite, scheelite, and sulfide assemblages accompany these fluids. The late fluid in the Oriente Novo and Correas deposit was a low-salinity (0-6 wt.% NaCl eq.) CO2-free aqueous solution, which homogenizes at (100-260 degreesC) and characterizes the sulfide fluorite-sericite association in the Correas deposit. The late fluid in the Santa Barbara deposit has lower salinity (0-3 wt.% NaCl eq.) and characterizes the late-barren-quartz, muscovite and kaolinite veins. Oxygen isotope thermometry coupled with fluid inclusion data suggest hydrothermal activity at 240-450 degreesC, and 1,0-2.6 kbar fluid pressure at Correas and Oriente Novo. The hydrogen isotope composition of breccia-greisen, stockwork, and vein fluids (delta(18)O quartz from 9.9parts per thousand to 10.9parts per thousand, deltaDH(2)O from 4.13parts per thousand to 6.95parts per thousand) is consistent with a fluid that was in equilibrium with granite at temperatures from 450 to 240 degreesC. In the Santa Barbara deposit, the inferred temperatures for quartz-pods and bed-like greisens are much higher (570 and 500 degreesC, respectively), and that for the cassiterite-quartz-veins is 415 degreesC. The oxygen and hydrogen isotope composition of greisen and quartz-pods fluids (delta(18)O(qtz-H2O)=5.5-6.1parts per thousand) indicate that the fluid equilibrated with the albite granite, consistent with a magmatic origin. The values for mica (delta(18)O(mica-H2O)=33-9.8parts per thousand) suggest mixing with meteoric water. Late muscovite veins (delta(18)O(qtz-H2O)=-6.4parts per thousand) and late quartz (delta(18)O(mica-H2O)=-3.8parts per thousand) indicate involvement of a meteoric fluid. Overall, the stable isotope and fluid inclusion data imply three fluid types: (1) an early orthomagmatic fluid, which equilibrated with granite; (2) a mixed orthomagmatic-meteoric fluid; and (3) a late hydrothermal meteoric fluid. The first two were responsible for cassiterite, wolframite, and minor coluChange in the redox conditions related to mixing-of magmatic and meteoric fluids favored important sulfide mineralization in the Correas deposit. (C) 2004 Elsevier B.V. All rights reserved.

Influence of Environmental Conditioning on the Shear Behavior of Poly(phenylene sulfide)/Glass Fiber Composites

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Oriented enstatite inclusions in natural diamond.

Six crystal inclusions in a twinned diamond from the Tibagi River deposits near Telemaco Borba, Parana State, Brazil, were identified as forsterite (prismatic crystals) and enstatite (tabular crystals, with a 18.17, b 8.81, c 5.17 A). The prismatic forsterite inclusions are oriented along the <110> directions of the host diamond; the main direction of the tabular enstatite crystals is in the same orientation. The identity and orientation of the inclusions were obtained by X-ray precession camera. Enstatite (210) is nearly parallel with the (111) octahedral layer of diamond; a possible epitaxial relationship is discussed.-R.A.H.

The application of thermally stimulated processes to the study of poly p-phenylene sulfide

The electrical properties of poly p-phenylene sulfide (PPS) samples sandwiched between metallic electrodes are studied as a function of the applied voltage, temperature, time, electrode materials, and sample thickness. Superlinear current-voltage characteristics are observed, which are explained in terms of Schottky effect and space-charge limited currents (SCLC). The conductivity data for variable-range hopping have also been studied, but the calculated values of density of states are approximately one order of magnitude higher than those obtained by SCLC measurements. From thermally stimulated polarization currents we observed a current peak around 80°C that was related with the glass transition temperature of PPS. © 1993.