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Item Impact of microaeration bioreactor on dissolved sulfide and methane removal from real UASB effluent for sewage treatment.(202) Souza, Cássia Cabral e; Sanson, Ananda Lima; Afonso, Robson José de Cássia Franco; Chernicharo, Carlos Augusto de Lemos; Araújo, Juliana Calábria deTwo bioreactors were investigated as an alternative for the post-treatment of effluent from an upflow anaerobic sludge blanket (UASB) reactor treating domestic sewage, aiming at dissolved sulfide and methane removal. The bioreactors (R-control and R-air) were operated at different hydraulic retention times (HRT; 6 and 3 h) with or without aeration. Large sulfide and methane removal efficiencies were achieved by the microaerated reactor at HRT of 6 h. At this HRT, sulfide removal efficiencies were equal to 61% and 79%, and methane removal efficiencies were 31% and 55% for R-control and R-air, respectively. At an HRT of 3 h, sulfide removal efficiencies were 22% (R-control) and 33% (R-air) and methane removal did not occur. The complete oxidation of sulfide, with sulfate formation, prevailed in both phases and bioreactors. However, elemental sulfur formation was more predominant at an HRT of 6 h than at an HRT of 3 h. Taken together, the results show that post-treatment improved the anaerobic effluent quality in terms of chemical oxygen demand and solids removal. However, ammoniacal nitrogen was not removed due to either the low concentration of air provided or the absence of microorganisms involved in the nitrogen cycle.Item Xanthones from Kielmeyera rubriflora.(1971) Gottlieb, Otto Richard; Mesquita, Antônio Augusto Lins; Nagem, Tanus JorgeKielmeyera rubriflora Camb. contains 2_hydroxyxanthone, 2,4-dimethoxy-3-hydroxyxanthone, 2,3-dimethoxy-4_hydroxyxanthone, 4-hydroxy-2,3-methylenedioxyxanthone, 4-methoxy-2,3-methylenedioxyxanthone and 1,7-dimethoxy-2,3,&trihydroxyxanthone (Ia).Item Mössbauer and X-ray diffraction studies of the Morin transition in tabular hematites.(1991) Costa, Geraldo Magela da; Silva, E. Galvão da; Jesus Filho, M. F. deSeveral synthetic hematites have been analysed by X-ray diffraction and M~Sssbauer spectroscopy. They have tabular shape and their Morin transition at 85 K show a dependence on the ratio (R) of the sizes in c and a directions. The Morin transition has been observed for samples with R = 0.43 _+ 0.05.Item Mössbauer study of rock paintings from Minas Gerais, Brazil.(1991) Costa, Geraldo Magela da; Souza, Luiz Antonio Cruz; Jesus Filho, M. F. deFour samples of a wall containing rock paintings have been studied by M(:,ssbauer spectroscopy in combination with optical microscopy analysis and X-ray diffraction. Hematite and goethite were identified as the pigments responsible for the colors and the mineral tinsleyite, as the principal component of a light pink layer that is present in some parts of the wall.Item X-ray differential line broadening on tabular haematites.(1992) Costa, Geraldo Magela da; Jesus Filho, M. F. deThe haematites obtained by dehydration of three synthetic goethites of different sizes have been characterized by X-ray diffraction, M6ssbauer spectroscopy and transmission electron microscopy. The transformation itself has been studied by thermogravimetric analysis and differential scanning calorimetry. Samples (24) obtained by annealing the goethites for 30 min at several temperatures up to 900 ~ were analysed. All samples had a tabular shape. The variation of the internal magnetic field, as well as of the line widths of the spectra at room temperature, indicate growth of the particle size. The constant value for the quadrupole splitting and the absence of a distribution of hyperfine interactions of the spectra at 80 K excluded the presence of iron ions out of their normal positions. No strain was detected by Xray diffraction. The results also showed a differential line broadening in the haematite pattern, but there was no shift in the position of the lines. This broadening was present in all lines, including those wih /= 3n (n = 0,1,2 .... ). Increasing the treatment temperature made all lines sharp. The relative integrated intensities, /(1 1 0)//(1 04), of each series remained unaltered, but the relative intensities did not. The above results lead to the conclusion that the differential Xray line broadening of haematites derived from goethite occurs only in tabular (or acicular) haematites with small size. For small spherical particles, the broadening should be uniform for all lines.Item Synthesis and characterization of lanthanide trifluoroacetate complexes with 3-picoline-N-oxide.(1992) Zinner, Léa Barbieri; Carvalho, Carlos Alberto Alves de; Zinner, KlausComplexes with composition Ln(F3C-COO)3•2(3-picNO)•ξH2O were synthesized. According to X-ray powder patterns and IR data five series of isomorphous compounds were detected: LaNd; SmEu; Gd>Tm, Y; Ho, Er, Tb; Dy, Yb, Lu. They behave as nonelectrolytes in methanol. IR spectra show a shift of νNO to lower frequencies, as compared with the free ligand, as a result of coordination through the oxygen. The bands attributed to the anions indicate two modes of coordination. The neodymium spectrum at 77 K shows that the central ion is not involved in a cubic site. Electrostatic bonds between Nd3+ and ligands were evidenced by the nephelauxetic, Sinha's parameters and covalent factor from the room temperature spectrum. Using the electronic emission spectrum, at 77 K, it was possible to conclude that europium ions present two different symmetry sites, since a splitting of the 5D0 → 7F9 band was observed. The complex species are probably polymeric or at least dimeric, and europium ions are involved in two different sites, but with the same C3ν symmetry.Item Positronium formation and inhibition in binary solid solutions on Al (III) and Co (III) tris (acetylacetonates).(1993) Machado, José Caetano; Carvalho, Cornélio de Freitas; Magalhães, Welington Ferreira de; Netto, Antonio Marques; Abbé, J. Ch.; Duplâtre, G.Positron annihilation lifetime spectroscopy has been applied in mixtures and in solutions of solid Al(W), Al(acac),, and Co(III), Co(acac)g, tris(acetylacetonates). For the solid solutions of Co(acac), in Al(a~+c)~, a strong inhibition of positronium formation is observed with increasing cobalt complex concentration, while there is no quenching of the positronium lifetime. In the solid mixtures the positronium formation probability decreases linearly with Co(acac)g concentration, while the positronium lifetime remains constant. The free volume model appears inadequate to explain the experimental results which are satisfactorily understood on the basis of the spur model.Item Positron annihilation studies in binary solid solutions of metal betadiketonates, using lifetime and doppler broadening spectroscopies.(1993) Machado, José Caetano; Porto, Arilza de Oliveira; Carvalho, Cornélio de Freitas; Magalhães, Welington Ferreira de; Netto, Antônio MarquesPositron annihilation lifetime (LS) and Doppler broadening annihilation kadiation lineshape (DBARL) spectroscopies measurements were performed in several binary solid solutions of the general formula M(l-x,Gfx,L,3 where M = Al(II1) , Ga(II1) , or In(II1) , as matrix; G = Cr (111) , Mn (111) , Fe (111) , co (111) , Ru (111) , Rh(III), and Ir(III), as guest molecules, L = acetylacetone (acac) or dipivaloylmethane (dpm), and X = guest molecule mole fraction. The studied systems can be classified in two groups: the first one presenting only inhibition of positronium formation and the second one presenting inhibition and quenching effects. The inhibition and quenching constants were determined.Item The center shift in the Mössbauer spectra of maghemite and aluminum maghemites.(1994) Costa, Geraldo Magela da; Grave, Eddy De; Bowen, L. H.; Vandenberghe, Robert Emile; Bakker, P. M. A. deSynthetic, relatively well-crystallized aluminum-substituted maghemite samples, y-(Aly. Fe~_y)203, with y = 0, 0.032, 0.058, 0.084, 0.106 and 0.151 have been studied by X-ray diffraction and zero-field Mrssbauer spectroscopy in the range 8 K to 475 K, and also with an external field of 60 kOe at 4.2 K and 275 K. It was found that there are two different converging models for fitting the zero-field spectra of the maghemites with a superposition of two Lorentzian-shaped sextets, both resulting in inconsistent values for the hyperfine fields (Hhf) and/or the center shifts (6) of the tetrahedral (A) and octahedral (B) ferric ions. From the applied-field measurements it is concluded that there is a constant difference of 0.12 _+ 0.01 mm/s between 6B and 6A, regardless of the A1 content. For the Al-free sample the center shifts are found as: 64 = 0.370 mm/s and 6a = 0.491 mm/s at 4.2 K and 6n = 0.233 mm/s and fib = 0.357 mm/s at 275 K (relative to metallic iron), with an estimated error of 0.005 mm/s. Both 6A and fib are observed to decrease with increasing AI concentration. The effective hyperfine fields for the non-substituted maghemite sample are: Hefr.A = 575 kOe and Hofr.B = 471 kOe at 4.2 K and He~,A = 562 kOe and H~er.B = 449 kOe at 275 K, with an error of 1 kOe. The B-site hyperfine field remains approximately constant with A1 substitution, while for the A site a slight decrease with increasing A1 content was observed.Item Synthesis and characterisation of some iron oxides by Sol-gel method.(1994) Costa, Geraldo Magela da; Grave, Eddy De; Bakker, P. M. A. de; Vandenberghe, Robert EmileItem Mössbauer studies of nano-sized aluminum-substituted maghemites.(1994) Costa, Geraldo Magela da; Grave, Eddy De; Bryan, A. M.; Bowen, L. H.Several Al-maghemites prepared from Al-lepidocrocites have been studied by M6ssbauer spectroscopy from 6 to 300 K, and also at 4.2 K with an applied field of 6 T. A linear decrease in the A and B site fields at 4.2 K for samples containing up to 10% of aluminum suggests a limit for the substitution. The importance of applied-field measurements for a correct characterization of small-particle maghemite is also shown.Item Formation and annealing of micropores in hematite.(1995) Dauwe, C.; Costa, Geraldo Magela da; Van Hoecke, T.; Segers, D.In iron oxide powders positrons are trapped in the surface layers and the value of the S-parameter is an indicator of the total specific surface, including external surface and internal surfaces of micropores. The evolution of micropores is followed when α-FeOOH is thermally decomposed into α-Fe2O3 . It is shown that the micropore formation is not linked to the decomposition process, but that they also form in hematite synthesized from a ferrihydrite precursor in aqueous solution.Item Analytical application of positron lifetime spectroscopy in the characterization of binary solid solutions.(1995) Porto, Arilza de Oliveira; Magalhães, Welington Ferreira de; Carvalho, Cornélio de Freitas; Machado, José CaetanoPositron Lifetime Spectroscopy (LS) measurements were performed in a series of binary molecular solid solutions of the general formula M1−xGxL3, where L(ligand)=acetylacetone, dipivaloylmethane, or N-benzoyl-N-phenylhydroxylamine, M=Al(III), Ga(III) or In(III), as matrix, and G=Cr(III), Mn(III), Fe(III), Co(III), Ru(III), Rh(III) and Ir(III), as guest molecules, and the corresponding mechanical mixtures. For the solid solutions, the o-Ps yield values (I3) decrease very rapidly with the increase of the guest mole fraction, showing a high efficient Ps inhibition process, while for the corresponding mechanical mixtures, these values decrease linearly with the increase of the “guest” molecule concentration, indicating the presence of two distinct phases. These results confirm our previous proposal that the LS technique is able to characterize solid solutions formed by one matrix, in whichI3 values are high, and one guest, in which theI3 values are very low.Item Variable-temperature Mössbauer spectroscopic study of nano-sized maghemite and Al-substituted maghemites.(1995) Costa, Geraldo Magela da; Grave, Eddy De; Bowen, L. H.; Bakker, P. M. A. de; Vandenberghe, Robert EmileSynthetic aluminum-substituted maghemite samples, "g-(Fe~ _xAlx)203, have been prepared by thermal decomposition of Al-lepidocrocite (3,-Fe~_xAlxOOH), with x = 0, 0.04, 0.06, 0.14 and 0.18. The particles are needle-shaped and the mean crystallite diameter along the [311] crystallographic direction was found to be between 2.0 and 5.0 nm. MSssbauer spectra were collected at 6 K and from 80 K up to 475 K at steps of 25 K. In a wide range of temperatures the spectra of the non-substituted sample consist of a superposition of a broad sextet and a superparamagnetic doublet, whereas for the Al-maghemites this range is much smaller. From the temperature variation of the fractional doublet area two different parameters were defined: the temperature corresponding to a 50/50 doublet-sextet spectrum (T1/2), and the temperature below which the doublet ceases to exist (To). These two parameters (T1/2 and To) decrease from 390 K and 92 K (Al-free sample), to 118 K and 64 K (4 mole % AI) and to 100 K and 48 K (18 mole % A1), respectively. The average hyperfine fields at 6 K undergo a steep drop in going from the AIfree sample (I:I~f = 506 kOe) to the sample with 4 mole % A1 (I:Ihr = 498 kOe), but for higher substitutions the effect is much smaller. The A- and B-site quadrupole splittings, obtained from the data between 220 K and 475 K, were found as: AEQ.A = 0.86 --+ 0.04 mm/s and AEo.B = 0.65 _+ 0.04 mm/s for the 4 mole % A1 sample. The characteristic MiJssbauer temperature, determined from the temperature dependence of the average isomer shift, was found to be in the range of 500-600 K.Item Temperature dependence of the hyperfine parameters of maghemite and Al-substituted maghemites.(1995) Costa, Geraldo Magela da; Grave, Eddy De; Bowen, L. H.; Bakker, P. M. A. de; Vandenberghe, Robert EmileSynthetic aluminum-substituted maghemite samples, 7-(AlyFel_y)203, with y = 0, 0.032, 0.058, 0.084, 0.106 and 0.151 have been studied by M6ssbauer spectroscopy at 8 K and in the range 80 K to 475 K at steps of 25 K. The spectra have been analysed as a superposition of two sextets composed of asymmetrical Lorentzians. The A- and B-site isomer shifts were constrained as: 6A---- 6B-- 0.12 mm/s. From the temperature dependence of 6B it was possible to determine the characteristic M6ssbauer temperature and the intrinsic shift. Both quantities clearly increase with increasing A1 content, at least up to 10 mole%. The temperature dependence of the Aand B-sites hyperfine fields could be satisfactorily reproduced using the molecular-field theory assuming an antiparallel spin configuration. The exchange integrals were found as: JAB = --25 K; JAA = --18 K and JBB= --3 K. The hyperfine fields show a crossing in the vicinity of 300 K as a result of the relatively strong A-A interaction. The Curie temperature for the non-substituted sample was calculated to be 930 K and decreases to 765 K for the sample with 15 mol% A1. The gradual decrease of the saturation value of the A-site hyperfine field with increasing A1 substitution and the constancy of this quantity for the B sites, suggest that the A1 cations occupy the B sites.Item Influence of nonstoichiometry and the presence of maghemite on the Mössbauer spectrum of magnetite.(1995) Costa, Geraldo Magela da; Grave, Eddy De; Bakker, P. M. A. de; Vandenberghe, Robert EmileSeveral samples of large- and small-particle magnetite (Fe304), as well as its thermal decomposition products formed at different temperatures and atmospheres, have been studied extensively by Mrssbauer spectroscopy (MS), both with and without an applied field of 6T. Synthetic mixtures of magnetite and poorly- or well-crystallized maghemite have also been studied. Large-particle magnetite (MCD > 200 nm), when heated in air for 12 hours at T < 400*(2, transforms to a mixture of wellcrystallized hematite and magnetite, the latter one remaining stoichiometric, according to the relative area-ratios obtained from MS. Thermal treatment at 1300"C in a controlled 02 partial pressure, produced a mixture of stoichiometric and nonstoichiometric magnetite, but the latter component seems to be composed of particles with different degrees of nonstoichiometry. The Mrssbauer spectra of the decomposition products at T < 200"C in air of small-particle magnetite (MCD ~ 80 nm) could be successfully interpreted as a mixture of magnetite and maghemite, rather than nonstoichiometric magnetite. This suggestion is further supported by the experiments with the synthetic mixtures. It is clearly demonstrated that is not possible, even by applying a strong external field, to separate the contribution of the A-site of magnetite from that of maghemite.Item Naturally occurring pentaoxygenated, hexaoxygenated and dimeric xanthones : a literature survey.(1996) Peres, Valdir; Nagem, Tanus JorgeThis review gives information on the chemical study of 71 pentaoxygenated, 11 hexaoxygenated and 9 dimeric and more complex xanthones naturally occurring in 7 families, 29 genus and 62 species of higher plants, and 11 described as fern and fungal metabolites. The value of these groups of substances in the connection with the pharmacological activity and the therapeutic use of some species is shown. The structural formulas of 23 isolated compounds and their distribution in the species studied are given.Item 57Fe Mössbauer effect study of Al-substituted lepidocrocites.(1996) Grave, Eddy De; Costa, Geraldo Magela da; Bowen, L. H.; Schwertmann, U.; Vandenberghe, Robert EmileSeven A|-containing lepidocrocite samples, ~/-Fe,_xAlxOOH, prepared from FeC12/AI(NO3)3 solutions with initial A1/(A1 + Fe) mole ratios C~ of 0.0025, 0.01, 0.025, 0.05, 0.075, 0.10 and 0.15 tool/ mol, were examined by means of M6ssbauer spectroscopy at room temperature (RT) and at various temperatures in the range of 8 to 80 K. The spectra at RT and 80~ consist of broadened quadrupole doublets and were analyzed in terms of a single doublet and of a model-independent quadrupole-splitting distribution, the latter yielding the best fit. The observed variations of the quadrupole-splitting parameters with increasing C i are inconclusive as to whether the A1 cations are substituting into the structure. The temperature at which the onset of magnetic ordering is reflected in the spectra, was measured by the therrnoscan method with zero source velocity. A gradual shift from 50 K for Ci = 0.0025 mol/mol to 44 K for Ci = 0.10 mol/mol was observed for that temperature. As compared to earlier studies of Al-free ~-FeOOH samples with similar morphological characteristics, the fractional doublet area in the mixed sextet-doublet spectra at 35 K is significantly higher for the present lepidocrocites. This observation is ascribed to the substitution of A1 cations into the lepidocrocite structure. A similar conclusion is inferred from the variation with C~ of the maximum-probability hyperfine field derived from the spectra recorded at 8 K and fitted with a model-independent hyperfine-field distribution. The magnetic results suggest that for the sample corresponding to Ci = 0.15 mol/mol, not all of the initially present A1 has been incorporated into the structure.Item Xanthones and other constituents of Vismia parviflora.(1997) Nagem, Tanus Jorge; Oliveira, Fernando Faustino deVismia parviflora, planta da família Guttiferae, é uma espécie da tribo Vismeae encontrada na região de Ouro Preto MG. Dos extratos benzênico e etanólico dos galhos e etanólico dos frutos de um especimen desta planta, cromatografados em sílica gel, foram isolados sitosterol, ácido betulínico, lupeol, friedelina, β-friedelinol, ácido chiquímico, ácido 3,4-diidroxibenzóico, uercet-ina e as antraquinonas madagascina, ácido crisofânico, vismiaquinona-A e vismiaquinona-C, além das xantonas 1,7-diidroxixantona e 1,5-diidroxi-8-metoxixantona. Estas substâncias tiveram suas estruturas elucidadas com base nos seus dados espectrométricos de IV, UV, EM e RMN de 1H e 13 C uni-(1D) e bidimensional-(2D).Item Sintering studies of hydrothermal NiZn ferrites.(1997) Dias, Anderson; Moreira, Roberto Luiz; Mohallem, Nelcy Della SantinaThe isothermal sintering behavior of submicrometer-sized (< 50 nm) powders of Ni0.38Zn0.53Fe2.09O4, prepared by hydrothermal process, was investigated under different sintering conditions. The powders were characterized by chemical analysis, energy-dispersive spectrometry (EDS), X-ray powder diffraction and scanning electron microscopy. The powders were compacted uniaxially with polyvinylalcohol and sintered at different times and temperatures, under constant heating and cooling rates. The characterization of the ceramic bodies was conducted by X-ray diffraction, optical and scanning electron microscopy, helium picnometry and EDS. The investigations showed high density ferrites with different porosity and microstructures depending on the sintering conditions. The results have been explained in terms of a qualitative model, which indicates the relative influence of the densification and grain growth rates.