Internal stresses and textures of nanostructured alumina scales growing on polycrystalline Fe(3)Al alloy

The evolution of internal stresses in oxide scales growing on polycrystalline Fe(3)Al alloy in atmospheric air at 700 degrees C was determined using in situ energy-dispersive synchrotron X-ray diffraction. Ex situ texture analyses were performed after 5 h of oxidation at 700 degrees C. Under these conditions, the oxide-scale thickness, as determined by X-ray photoelectron spectroscopy, lies between 80 and 100 nm. The main phase present in the oxide scales is alpha-Al(2)O(3), with minor quantities of metastable theta-Al(2)O(3) detected in the first minutes of oxidation, as well as alpha-Fe(2)O(3). alpha-Al(2)O(3) grows with a weak (0001) fiber texture in the normal direction. During the initial stages of oxidation the scale develops, increasing levels of compressive stresses which later evolve to a steady state condition situated around -300 MPa. (C) 2010 International Centre for Diffraction Data. [DOI: 10.1154/1.3402764]

Oxidation and abrasive wear of Fe-Si and Fe-Al intermetallic alloys

In the present work, intermetallic alloys Fe-Si and Fe-Al (Fe(3)Si-C-Cr and Fe(3)Al-C), produced by induction melting, were evaluated regarding their oxidation and abrasive resistance. The tests performed were quasi-isothermal oxidation, cyclic oxidation, and dry sand/rubber wheel abrasion. As reference, the ASTM A297-HH grade stainless steel was tested in the same conditions. In the oxidation tests, the Fe-Al based alloy presented the lowest oxidation rate, and the Fe-Si based alloy achieved the best results in the abrasion test, showing better performance than the HH type stainless steel.

Ab initio calculation of the BCC Fe-Al-Mo (Iron-Aluminum-Molybdenum) phase diagram: Implications for the nature of the tau(2) phase

The metastable phase diagram of the BCC-based ordering equilibria in the Fe-Al-Mo system has been calculated via a truncated cluster expansion, through the combination of Full-Potential-Linear augmented Plane Wave (FP-LAPW) electronic structure calculations and of Cluster Variation Method (CVM) thermodynamic calculations in the irregular tetrahedron approximation. Four isothermal sections at 1750 K, 2000 K, 2250 K and 2500 K are calculated and correlated with recently published experimental data on the system. The results confirm that the critical temperature for the order-disorder equilibrium between Fe(3)Al-D0(3) and FeAl-B2 is increased by Mo additions, while the critical temperature for the FeAl-B2/A2 equilibrium is kept approximately invariant with increasing Mo contents. The stabilization of the Al-rich A2 phase in equilibrium with overstoichiometric B2-(Fe,Mo)Al is also consistent with the attribution of the A2 structure to the tau(2) phase, stable at high temperatures in overstoichiometric B2-FeAl. (C) 2009 Elsevier Ltd. All rights reserved.

Synthesis of Fe/Ti oxides from a single source alkoxide precursor under inert atmosphere

The heterometal alkoxide [FeCl{Ti2(OPr i)9}] (1) was employed as a single source precursor for the preparation of Fe/Ti oxides under inert atmosphere. Three different synthetic procedures were adopted in the processing of 1, either employing aqueous HNO3 or HCl solutions, or in the absence of mineral acids. Products were characterised by powder X-ray diffractometry, scanning electron microscopy combined with energy dispersive X-ray spectroscopy (SEM/EDS) and Raman, electron paramagnetic resonance (EPR) and Mössbauer spectroscopies. Oxide products contained titanium(IV) and either iron(III) or iron(II), depending on reaction conditions and thermal treatment temperatures. An interesting iron(III)→iron(II) reduction was observed at 1000 ºC in the HNO3-containing system, leading to the detection of ilmenite (FeTiO3). SEM/EDS studies revealed a highly heterogeneous metal distribution in all products, possibly related to the presence of a significant content of carbon and of structural defects (oxygen vacancies) in the solids.

Podzolization as a deferralitization process: dynamics and chemistry of ground and surface waters in an Acrisol-Podzol sequence of the upper Amazon Basin

Hydrochemical processes involved in the development of hydromorphic Podzols are a major concern for the upper Amazon Basin because of the extent of the areas affected by such processes and the large amounts of organic carbon and associated metals exported to the rivers. The dynamics and chemical composition of ground and surface waters were studied along an Acrisol-Podzol sequence lying in an open depression of a plateau. Water levels were monitored along the sequence over a period of 2 years by means of piezometers. Water was sampled in zero-tension lysimeters for groundwater and for surface water in the drainage network of the depression. The pH and concentrations of organic carbon and major elements (Si, Fe and Al) were determined. The contrasted changes reported for concentrations of Si, organic carbon and metals (Fe, Al) mainly reflect the dynamics of the groundwater and the weathering conditions that prevail in the soils. Iron is released by the reductive dissolution of Fe oxides, mostly in the Bg horizons of the upslope Acrisols. It moves laterally under the control of hydraulic gradients and migrates through the iron-depleted Podzols where it is exported to the river network. Aluminium is released from the dissolution of Al-bearing minerals (gibbsite and kaolinite) at the margin of the podzolic area but is immobilized as organo-Al complexes in spodic horizons. In downslope positions, the quick recharge of the groundwater and large release of organic compounds lead to acidification and a loss of metals (mainly Al), previously stored in the Podzols.

Runoff and leachate losses of phosphorus in a sandy spodosol amended with biosolids

Florida Spodosols axe sandy, inherently low in Fe- and Al-based minerals, and sorb phosphorus (P) poorly. We evaluated runoff and leachate P losses from a typical Florida Spodosol amended with biosolids and triple superphosphate (TSP). Phosphorus losses were evaluated with traditional indoor rainfall simulations but used a double-deck box arrangement that allowed leaching and runoff to be determined simultaneously. Biosolids (Lakeland, OCUD, Milorganite, and Disney) represented contrasting values of total P, percent water-extractable p (PWEP), and percentage of solids. All P sources were surface applied at 224 kg P ha(-1), representing a soil P rate typical of N-based biosolids application. All biosolids-P sources lost less P than TSp, and leachate-P losses generally dominated. For Lakeland-amended I soil, bioavailable P (BAP) was mainly lost by runoff (81% of total BAP losses). This behavior was due to surface scaling and 1 drying after application of the slurry (31 g kg(-1) solids), material. For all other P sources, BAP losses in leachate were much,greater than in runoff, representing 94% of total BAP losses for TSP, 80% for Milorganite, 72% for Disney, and 69% for OCUD treatments. Phosphorus leaching can be extreme and represents a great concern in many coarse-textured Florida Spodosols, and other coastal plain soils with low P-sorption,capacities. The PWEP values of P sources were significantly correlared with total P and BAP losses in runoff and leachate. The PWEP of a source can serve as a good indicator of potential P loss when amended to sandy soils with low P-retention capacities.

Contribution of soil organic carbon to the ion exchange capacity of tropical soils

Highly weathered soils represent about 3 billion ha of the tropical region. Oxisols represent about 60% of the Brazilian territory (more than 5 million km 2), in areas of great agricultural importance. Soil organic carbon (SOC) can be responsible for more than 80% of the cation exchange capacity (CEC) of highly weathered soils, such as Oxisols and Ultisols. The objective of this study was to estimate the contribution of the SOC to the CEC of Brazilian soils from different orders. Surface samples (0.0 to 0.2 m) of 30 uncultivated soils (13 Oxisols, 6 Ultisols, 5 Alfisols, 3 Entisols, I Histosol, 1 Inceptisol. and I Molisol), under native forests and from reforestation sites from Sao Paulo State, Brazil, were collected in order to obtain a large variation of (electro)chemical, physical, and mineralogical soil attributes. Total content of SOC was quantified by titulometric and colorimetric methods. Effective cation exchange capacity (ECEC) was obtained by two methods: the indirect method-summation-estimated the ECECi from the sum of basic cations (Ca+ Mg+ K+ Na) and exchangeable Al; and the direct ECECd obtained by the compulsive exchange method, using unbuffered BaCl2 solution. The contribution of SOC to the soil CEC was estimated by the Bennema statistical method. The amount of SOC var ied from 6.6 g kg(-1) to 213.4 g kg(-1). while clay contents varied from 40 g kg(-1) to 716 g kg(-1). Soil organic carbon contents were strongly associated to the clay contents, suggesting that clay content was the primary variable in controling the variability of SOC contents in the samples. Cation exchange capacity varied from 7.0 mmol(c) kg(-1) to 137.8 mmol(c) kg(-1) and had a positive Correlation with SOC. The mean contribution (per grain) of the SOC (1.64 mmol(c)) for the soil CEC was more than 44 times higher than the contribution of the clay fraction (0.04 mmol(c),). A regression model that considered the SOC content as the only significant variable explained 60% of the variation in the soil total CEC. The importance of SOC was related to soil pedogenetic process, since its contribution to the soil CEC was more evident in Oxisols with predominance of Fe and Al (oxihydr)oxides in the mineral fraction or in Ultisols, that presented illuviated clay. The influence of SOC in the sign and in the magnitude of the net charge of soils reinforce the importance of agricultural management systems that preserve high levels of SOC, in order to improve their sustainability.

Deciphering the weathering processes using environmental mineralogy and geochemistry: Towards an integrated model of laterite and podzol genesis in the Upper Amazon Basin

This article reports major results from collaborative research between France and Brazil on soil and water systems, carried out in the Upper Amazon Basin. It reveals the weathering processes acting in the partly inundated, low elevation plateaus of the Basin, mostly covered by evergreen forest. Our findings are based on geochemical data and mineral spectroscopy that probe the crystal chemistry of Fe and Al in mineral phases (mainly kaolinite, Al- and Fe-(hydr)oxides) of tropical soils (laterites). These techniques reveal crystal alterations in mineral populations of different ages and changes of metal speciation associated with mineral or organic phases. These results provide an integrated model of soil formation and changes (from laterites to podzols) in distinct hydrological compartments of the Amazon landscapes and under altered water regimes. (C) 2010 Academie des sciences. Published by Elsevier Masson SAS. All rights reserved.

Microstructure and texture assessment of Al-Mn-Fe-Si (3003) aluminum alloy produced by continuous and semicontinuous casting processes

Aluminum sheets are currently produced by the direct-chill process (DC). The need for low-cost aluminum sheets is a challenge for the development of new materials produced by the twin roll caster (TRC) process. It is expected that sheets produced from these different casting procedures will differ in their microstructure. These differences in microstructure and in the crystallographic texture have great impact on sheet mechanical properties and formability. The present study investigated microstructure and evaluated texture of two strips of Al-Mn-Fe-Si (3003) aluminum alloy produced by TRC and by hot-rolling processes. It was possible to notice that the microstructure, morphology, and grain size of the TRC sample were more homogenous than those found in hot-rolled samples. Both strips, obtained by the two processes, showed strong texture gradient across the thickness.

Thermodynamic Assessment of the Aluminum Corner of the Al-Fe-Mn-Si System

A new assessment of the aluminum corner of the quaternary Al-Fe-Mn-Si system has been made that extends beyond the COST-507 database. This assessment makes use of a recent, improved description of the ternary Al-Fe-Si system. In the present work, modeling of the Al-rich corner of the quaternary Al-Fe-Mn-Si system has been carried out by introducing Fe solubility into the so-called alpha-AlMnSi and beta-AlMnSi phases of the Al-Mn-Si system. A critical review of the data available on the quaternary system is presented and used for the extension of the description of these ternary phases into the quaternary Al-Fe-Mn-Si.

Chemical similarities between Galactic bulge and local thick disk red giants: O, Na, Mg, Al, Si, Ca, and Ti

Context. The formation and evolution of the Galactic bulge and its relationship with the other Galactic populations is still poorly understood. Aims. To establish the chemical differences and similarities between the bulge and other stellar populations, we performed an elemental abundance analysis of alpha- (O, Mg, Si, Ca, and Ti) and Z-odd (Na and Al) elements of red giant stars in the bulge as well as of local thin disk, thick disk and halo giants. Methods. We use high-resolution optical spectra of 25 bulge giants in Baade's window and 55 comparison giants (4 halo, 29 thin disk and 22 thick disk giants) in the solar neighborhood. All stars have similar stellar parameters but cover a broad range in metallicity (-1.5 < [Fe/H] < +0.5). A standard 1D local thermodynamic equilibrium analysis using both Kurucz and MARCS models yielded the abundances of O, Na, Mg, Al, Si, Ca, Ti and Fe. Our homogeneous and differential analysis of the Galactic stellar populations ensured that systematic errors were minimized. Results. We confirm the well-established differences for [alpha/Fe] at a given metallicity between the local thin and thick disks. For all the elements investigated, we find no chemical distinction between the bulge and the local thick disk, in agreement with our previous study of C, N and O but in contrast to other groups relying on literature values for nearby disk dwarf stars. For -1.5 < [Fe/H] < -0.3 exactly the same trend is followed by both the bulge and thick disk stars, with a star-to-star scatter of only 0.03 dex. Furthermore, both populations share the location of the knee in the [alpha/Fe] vs. [Fe/H] diagram. It still remains to be confirmed that the local thick disk extends to super-solar metallicities as is the case for the bulge. These are the most stringent constraints to date on the chemical similarity of these stellar populations. Conclusions. Our findings suggest that the bulge and local thick disk stars experienced similar formation timescales, star formation rates and initial mass functions, confirming thus the main outcomes of our previous homogeneous analysis of [O/Fe] from infrared spectra for nearly the same sample. The identical a-enhancements of thick disk and bulge stars may reflect a rapid chemical evolution taking place before the bulge and thick disk structures we see today were formed, or it may reflect Galactic orbital migration of inner disk/bulge stars resulting in stars in the solar neighborhood with thick-disk kinematics.

Thermodynamic self-consistency issues related to the Cluster Variation Method: The case of the BCC Cr-Fe (Chromium-Iron) system

The Cluster Variation Method (CVM), introduced over 50 years ago by Prof. Dr. Ryoichi Kikuchi, is applied to the thermodynamic modeling of the BCC Cr-Fe system in the irregular tetrahedron approximation, using experimental thermochemical data as initial input for accessing the model parameters. The results are checked against independent data on the low-temperature miscibility gap, using increasingly accurate thermodynamic models, first by the inclusion of the magnetic degrees of freedom of iron and then also by the inclusion of the magnetic degrees of freedom of chromium. It is shown that a reasonably accurate description of the phase diagram at the iron-rich side (i.e. the miscibility gap borders and the Curie line) is obtained, but only at expense of the agreement with the above mentioned thermochemical data. Reasons for these inconsistencies are discussed, especially with regard to the need of introducing vibrational degrees of freedom in the CVM model. (C) 2008 Elsevier Ltd. All rights reserved.

Electronic Structure and Spectro-Structural Correlations of Fe(III)Zn(II) Biomimetics for Purple Acid Phosphatases: Relevance to DNA Cleavage and Cytotoxic Activity

Purple acid phosphatases (PAPs) are a group of metallohydrolases that contain a dinuclear Fe(II)M(II) center (M(II) = Fe, Mn, Zn) in the active site and are able to catalyze the hydrolysis of a variety of phosphoric acid esters. The dinuclear complex [(H(2)O)Fe(III)(mu-OH)Zn(II)(L-H)](CIO(4))(2) (2) with the ligand 2-[N-bis(2-pyridylmethyl)aminomethyl]-4-methyl-6-[N-(2-pyridylmethyl)(2-hydroxybenzyl) aminomethyl]phenol (H(2)L-H) has recently been prepared and is found to closely mimic the coordination environment of the Fe(III)Zn(II) active site found in red kidney bean PAP (Neves et al. J. Am. Chem. Soc. 2007, 129, 7486). The biomimetic shows significant catalytic activity in hydrolytic reactions. By using a variety of structural, spectroscopic, and computational techniques the electronic structure of the Fe(III) center of this biomimetic complex was determined. In the solid state the electronic ground state reflects the rhombically distorted Fe(III)N(2)O(4) octahedron with a dominant tetragonal compression align ad along the mu-OH-Fe-O(phenolate) direction. To probe the role of the Fe-O(phenolate) bond, the phenolate moiety was modified to contain electron-donating or -withdrawing groups (-CH(3), -H, -Br, -NO(2)) in the 5-position. Tie effects of the substituents on the electronic properties of the biomimetic complexes were studied with a range of experimental and computational techniques. This study establishes benchmarks against accurate crystallographic struck ral information using spectroscopic techniques that are not restricted to single crystals. Kinetic studies on the hydrolysis reaction revealed that the phosphodiesterase activity increases in the order -NO(2)<- Br <- H <- CH(3) when 2,4-bis(dinitrophenyl)phosphate (2,4-bdnpp) was used as substrate, and a linear free energy relationship is found when log(k(cat)/k(0)) is plotted against the Hammett parameter a. However, nuclease activity measurements in the cleavage of double stranded DNA showed that the complexes containing the electron-withdrawing -NO(2) and electron-donating CH3 groups are the most active while the cytotoxic activity of the biomimetics on leukemia and lung tumoral cells is highest for complexes with electron-donating groups.

A method for Ca, Fe, Ga, Na, Si and Zn determination in alumina by inductively coupled plasma optical emission spectrometry after aluminum precipitation

In this present work a method for the determination of Ca, Fe, Ga, Na, Si and Zn in alumina (Al(2)O(3)) by inductively coupled plasma optical emission spectrometry (ICP OES) with axial viewing is presented. Preliminary studies revealed intense aluminum spectral interference over the majority of elements and reaction between aluminum and quartz to form aluminosilicate, reducing drastically the lifetime of the torch. To overcome these problems alumina samples (250 mg) were dissolved with 5 mL HCl + 1.5 mLH(2)SO(4) + 1.5 mL H(2)O in a microwave oven. After complete dissolution the volume was completed to 20 mL and aluminum was precipitated as Al(OH)(3) with NH(3) (by bubbling NH(3) into the solution up to a pH similar to 8, for 10 min). The use of internal standards (Fe/Be, Ga/Dy, Zn/In and Na/Sc) was essential to obtain precise and accurate results. The reliability of the proposed method was checked by analysis of alumina certified reference material (Alumina Reduction Grade-699, NIST). The found concentrations (0.037%w(-1) CaO, 0.013% w w(-1) Fe(2)O(3), 0.012%w w(-1)Ga(2)O(3), 0.49% w w(-1) Na(2)O, 0.014% w w(-1) SiO(2) and 0.013% w w(-1) ZnO) presented no statistical differences compared to the certified values at a 95% confidence level. (C) 2011 Elsevier B.V. All rights reserved.

Isolation and characterization of Flavobacterium columnare (Bernardet et al. 2002) from four tropical fish species in Brazil

Flavobacterium columnare is the causative agent of columnaris disease in freshwater fish, implicated in skin and gill disease, often causing high mortality. The aim of this study was the isolation and characterization of Flavobacterium columnare in tropical fish in Brazil. Piracanjuba (Brycon orbignyanus), pacu (Piaractus mesopotamicus), tambaqui (Colossoma macropomum) and cascudo (Hypostomus plecostomus) were examined for external lesions showing signs of colunmaris disease such as greyish white spots, especially on the head, dorsal part and caudal fin of the fish. The sampling comprised 50 samples representing four different fish species selected for study. Samples for culture were obtained by skin and kidney scrapes with a sterile cotton swabs of columnaris disease fish and streaked onto Carlson and Pacha (1968) artificial culture medium (broth and solid) which were used for isolation. The strains in the liquid medium were Gram negative, long, filamentous, exhibited flexing movements (gliding motility), contained a large number of long slender bacteria and gathered into ‘columns'. Strains on the agar produced yellow-pale colonies, rather small, flat that had rhizoid edges. A total of four Flavobacterium columnare were isolated: 01 Brycon orbignyanus strain, 01 Piaractus mesopotamicus strain, 01 Colossoma macropomum strain, and 01 Hypostomus plecostomus strain. Biochemical characterization, with its absorption of Congo red dye, production of flexirubin-type pigments, H2S production and reduction of nitrates proved that the isolate could be classified as Flavobacterium columnare.