Filmes finos de Titanato de Chumbo e Lantânio - PLT: influência do pH

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

Crystal nucleation kinetics of a metastable phase on cordierite glass surfaces

The crystal nucleation rates of a metastable phase (chi) on the surface of a near stoichiometric cordierite glass were determined for temperatures between 839 and 910 degrees C (T-g similar to 800 degrees C). The surface nucleation kinetics of that phase on our glass, as well as on a stoichiometric glass (2 MgO-2Al(2)O(3)-5SiO(2)) studied by other authors, were analysed in terms of the classical nucleation theory; for the first time. It was shown that the effective interfacial energy for surface nucleation is substantially lower than that for homogeneous volume nucleation in silicate glasses, vindicating the assumption of heterogeneous nucleation on free glass surfaces. The average wetting angle between the nucleating crystals and the active solid particles was estimated to be around 46 degrees C. The pre-exponential constant was several orders of magnitude higher than the theoretical values as found for volume homogeneous nucleation in oxide glasses.

Optical properties of potassium niobate thin films prepared by the polymeric precursor method

Thin films of potassium niobate were deposited on MgO (100) substrates by the polymeric precursor method and annealing in static air at 600 degreesC for 20 h. The obtained films were characterized by X-ray diffraction, atomic force microscopy (AFM) and the prism coupling method. The phi-scan diffraction evidenced the growth of the films with fourfold symmetry. AFM study shows that the films are homogeneous, dense and present a smooth surface. The refractive index and optical losses were strongly influenced by the degree of crystallinity. (C) 2004 Elsevier B.V. All rights reserved.

Magnesium supplementation alleviates premenstrual symptoms of fluid retention

We investigated the effect of a daily supplement of 200 mg of magnesium (as MgO) for two menstrual cycles on the severity of premenstrual symptoms in a randomized, double-blind, placebo-controlled, crossover study. A daily supplement of 200 mg of Mg (as MgO) or placebo was administered for two menstrual cycles to each volunteer, who kept a daily record of her symptoms, using a 4-point scale in a menstrual diary of 22 items. Symptoms were grouped into six categories: PMS-A (anxiety), PMS-C (craving), PMS-D (depression), PMS-H (hydration), PMS-O (other), and PMS-T (total overall symptoms). Urinary Mg output/24 hours was estimated from spot samples using the Mg/creatinine ratio. Analysis of variance for 38 women showed no effect of Mg supplementation compared with placebo in any category in the first month of supplementation. In the second month there was a greater reduction (p = 0.009) of symptoms of PMS-H (weight gain, swelling of extremities, breast tenderness, abdominal bloating) with Mg supplementation compared with placebo. Compliance to supplementation was confirmed by the greater mean estimated 24-hour urinary output of Mg (p = 0.013) during Mg supplementation (100.8 mg) compared with placebo (74.1 mg). A daily supplement of 200 mg of Mg (as MgO) reduced mild premenstrual symptoms of fluid retention in the second cycle of administration.

Synthesis and thermal study of magnesium complexes with 8-hydroxyquinolinate derivatives

Magnesium ion was reacted with 5,7-dibromo-, 5,7-dichloro-, 7-iodo- and 5-chloro-7-iodo-8-hydroxyquinoline, in acetone/ammonium hydroxide medium under constant stirring to obtain (I) Mg[(C9H4ONBr2)(2)].2H(2)O; (II) Mg[(C9H4ONCl2)(2)].3H(2)O; (III) Mg[(C9H5ONI)(2)].2H(2)O and (IV) Mg[(C9H4ONICl)(2)].2.5H(2)O complexes. The compounds were characterized by elemental analysis, IR spectra, ICP, TG-DTA and DSC.Through thermal decomposition residues were obtained and characterized, by X-ray diffractometry, as a mixture of hexagonal MgBr2 and cubic MgO to the (I) compound at 850degreesC; cubic MgO to the (II), (III) and (IV) compounds at 750, 800 and 700degreesC, respectively.

Pb-210-derived chronology in sediment cores evidencing the anthropogenic occupation history at Corumbata River basin, Brazil

Activity profiles of excess Pb-210 combined with chemical data determined in two sediment cores from Corumbatai River basin, São Paulo State, Brazil, provided new insights into the reconstruction of historical inputs of anthropogenic constituents, contributing to improving management strategies of the hydrological resources in the basin since most of the municipalities extensively utilize the waters of Corumbatai River and tributaries for drinking purposes, among other uses. Excellent significant relationships between loss on ignition (LOI) and organic matter were found for sediments of both analyzed profiles. Silica was found to be inversely related to organic matter at both analyzed profiles: its decrease accompanied an increase in the specific surface of the sediments. This relationship was confirmed by a great number of inverse significant correlations among silica and oxides Na2O, K2O, CaO, MgO, Al2O3, P2O5, Fe2O3, MnO, and TiO2. It was possible to identify the role of organic matter on adsorption of several oxides/elements in the core sediments profiles. Apparent sediment mass accumulation rates corresponding to 224 and 802 mg cm(-2) year(-1) were obtained, and are compatible with field evidence, indicating a higher value associated with sand mining activities interfering with the natural/normal sedimentation process, due to modifications of the channel drainage.

Mechanochemical synthesis of lead magnesium niobate ceramics in iron media

The possibility of mechanochemical synthesis of the lead magnesium niobate (PMN) powders of the composition Pb(Mg(1/3)Nb(2/3))O(3) in iron vials was investigated. According to X-ray and energy-dispersive spectroscopy (EDS) analysis of the obtained powder mixtures, milling in iron vials resulted in incorporation of Fe and formation of PFN of composition Pb(Fe(1/2)Nb(1/2))O(3) simultaneously with formation of PMN. Relative amounts of PMN and PFN were determined based on values of Curie temperature and lattice constant of perovskite phase. Although only 1 wt pct of Fe was incorporated, a stoichiometry of the system was significantly changed, resulting in formation of pyrochlore phase and excess MgO. Single-phase perovskite was obtained when the excess of PbO and Nb(2)O(5) was added during mechanochemical synthesis. Because the dielectric properties were worse than expected, the alternative ways for improvement of dielectric properties were tried and discussed.

Pore size evolution during sintering of ceramic oxides

This paper reviews the influence of particle size distribution, agglomerates, rearrangement, sintering atmospheres and impurities on the pore evolution of some commonly studied oxides. These factors largely affect sintering mechanisms due to modifications of diffusion coefficients or evaporation-condensation. Very broad particle size distribution leads to grain growth and agglomerates densify first. Rearrangement of particles due to neck asymmetry mainly in the early stage of sintering is responsible for a high rate of densification in the first minutes of sintering by collapse of large pores. Sintering atmospheres play an important role in both densification and pore evolution. The chemical interaction of water molecules with several oxides like MgO, ZnO and SnO2 largely affects surface diffusion. As a consequence, there is an increase in the rates of pore growth and densification for MgO and ZnO and in the rate of pore growth for SnO2. Carbon dioxide does not affect the rate of sintering of MgO but greatly affects both rates of pore growth and densification of ZnO. Oxygen concentration in the atmosphere can especially affect semiconductor oxides but significantly affects the rate of pore growth of SnO2. Impurities like chlorine ions increase the rate of pore growth in MgO due to evaporation of HCl and Mg(OH)Cl, increasing the rate of densification and particle cuboidization. CuO promotes densification in SnO2, and is more effective in dry air. The rate of densification decrease and pore widening are promoted in argon. An inert atmosphere favors SnO2 evaporation due to reduction of CuO. © 1990.

Crystal morphologies on a cordierite glass surface

With suitable thermal treatments, a nearly stoichiometric cordierite glass (2 MgO.2 Al2O3. 5 SiO2) shows a variety of crystal morphologies on the external surfaces: lozenges, regular and elongated hexagons, spherical and square shaped particles. We initially identified these morphologies through optical and scanning electron microscopy techniques. Their structural features were distinguished by x-ray diffraction patterns, infrared and Roman microprobe spectra. We concluded that there are close structural similarities for: lozenges and glass matrix; regular and elongated hexagons; spherical and square particles. The ordering degree increases in the following sequence: glass matrix, lozenges, hexagons, squares and spheres. The lozenge crystals are known as X-phase. The hexagons belong to the μ-cordierite (high quartz solid solution) metastable phase and the squares and spheres to the α-cordierite stable phase.

Chemistry of Biotites and Whole Rocks from the Rapakivi Itu Complex (Late Precambrian), State of São Paulo, SE Brazil

Chemical analyses for biotites and their host rocks from the Cabreúva (three facies) and Salto (five facies) intrusions from the multiple-centered rapakivi Itu Complex, State of São Paulo, Brazil, are presented and compared. The Cabreúva intrusion comprises different kinds of mainly even-grained biotite and hornblende-bearing syenogranites, monzogranites and quartz syenites and the Salto intrusion several types of mainly porphyritic biotite syenogranites, some of them hornblende-bearing. The biotites from the Salto intrusion (S-micas) show a more restricted composition than those from the Cabreúva intrusion (C-micas). This reflects the chemical variability of the two bodies which is smaller in the Salto intrusion and larger in the Cabreúva pluton. In the AlIV x Fet/(Fet+Mg) diagram the S- and C-micas show similar AlIV contents, around 2.2-2.3, but C-micas have higher Fet/(Fet+Mg) ratios (0.7-0.9) compared to those of S-micas (0.5-0.6). In the Mg:(Al+Fe+3+Ti):(Fe+2+Mn) diagram the S-micas are defined as Fe+2-biotites and the C-micas occupy the area between the Fe+2-biotites and the siderophyllite/lepidomelane fields, slightly overlapping the latter. In the Al2O3 × FeOt, MgO × FeOt, Al2O3 x MgO and Alt x Mg diagrams, the S-micas always lie on the calc-alkaline/alkaline boundary (or in the subalkaline field) whereas the C-micas systematically plot in the alkaline field, reflecting the higher alkalis content of the Cabreúva intrusion. In the Fet/(Fet+Mg) x SiO2 diagram, the S-micas lie on a smooth line whereas the C-micas from the different facies are separated by distinct chemical gaps reflecting the major or minor chemical overlapping of the facies from the Salto and Cabreúva intrusions.

Geochemical Variability of the Rapakivi Itu Province, State of São Paulo, SE Brazil

This paper describes the chemical variability of the Late Precambrian Itu Rapakivi Province (IRP), State of São Paulo, SE Brazil, based on 187 selected analyses from the Itu, São Francisco, Sorocaba, Campina do Veado and Sguario/ Correa granites. The IRP has an almost uniform petrographic character conferred by the overall dominance of subalkaline biotite granites. Monzogranites (adamellites), granodiorites, quartz syenites, quartz monzonites are rare to very rare rock types and tonalites and quartz diorites are almost restricted to enclaves. Typical chemical features are the high FeO*/MgO ratio, a clustering of the K2O values between 4.5 and 6.0 wt.% and K2O/Na2O ratios which define the IRP as mildly potassic although more potassic rocks also occur. The overal Peacock Alkalinity Index is 54 defining the Province as alkali-calcic. In the Shand diagram the data cluster near the metaluminous/peraluminous boundary. Relationships between Nb, Rb and Y stress the within plate character of the IRP and the relationships between Rb, Ba and Sr reveal the importance of feldspar fractionation in magma evolution. The data also show an interbody and an intrabody chemical variability due to the variation in the composition of the crustal magma protoliths, as assigned by K/Rb relations. The presence of several magmatic cycles which built up the major intrusions reflects a magma ascent from collecting chambers successively drained and recharged, a feature in agreement with the clear link between the bodies and long lived, successively reactivated, transcurrent faults. Most of the chemical features of the IRP correspond to those of the classical Finnish rapakivi granites.

Key features of alumina/magnesia/graphite refractories for steel ladle lining

The corrosion resistance of resin bonded alumina/magnesia/graphite refractories containing different kinds of aggregates were investigated when submitted to the action of slags of several CaO/SiO2 ratios. The laboratory testing was performed by means of the rotary slag attack test. Specifically evaluated was the influence of alumina/carbon ratio and magnesia and silica contents on the refractories corrosion resistance. It was found that this property could be improved by increasing the refractory Al2O3/SiO2 ratio as well as by choosing the appropriate Al2O3/C ratio. © 2000 Elsevier Science Ltd.

Effects of superficial liming and silicate application on soil fertility and crop yield under rotation

Soil acidity and low natural fertility are the main problems for grain production in Brazilian 'cerrado'. Although lime has been the most applied source for soil correction, silicate may be an alternative material due to its lower solubility and Si supply, which is beneficial to several crops. This work aimed to evaluate the efficiency of superficial liming and calcium/magnesium silicate application on soil chemical attributes, plant nutrition, yield components and final yield of a soybean/white oat/maize/bean rotation under no-tillage system in a dry-winter region. The experiment was conducted under no tillage system in a deep acid clayey Rhodic Hapludox, Botucatu-SP, Brazil. The design was the completely randomized block with sixteen replications. Treatments consisted of two sources for soil acidity correction (dolomitic lime: ECC=90%, CaO=36% and MgO=12%; calcium/magnesium silicate: ECC=80%, CaO=34%, MgO=10% and SiO2=22%) applied in October 2006 to raise base saturation up to 70% and a control, with no soil correction. Soybean and white oat were sown in 2006/2007 as the main crop and off-season, respectively. Maize and bean were cropped in the next year (2007/2008). Products from silicate dissociation reach deeper soil layers after 18months from the application, compared to liming. Additionally, silicate is more efficient than lime to increasing phosphorus availability and reducing toxic aluminum. Such benefits in soil chemical attributes were only evidenced during bean cropping, when grain yield was higher after silicate application comparatively to liming. Both correction sources were improved mineral nutrition of all the other crops, mainly Ca and Mg levels and agronomical characteristics, reflecting in higher yield. © 2012 Elsevier B.V.

Geochemical and radioactivity characterization of rocks from the Rio Preto (Go) Project

The Rio Preto Project, developed by the extinct Brazilian nuclear state company, Nuclebrás, during the late 70s and early 80s, consisted of basic geological mapping and radiometric characterization by aerogeophysical gamma-ray spectrometry, without channel discrimination, of a surface area of 650 km2 located to the west of the Chapada dos Veadeiros National Park on the northeastern of Goiás State, Brazil, including the confluence area of Claro and Preto Rivers. Additionally, the natural radioelements U, Th and 40K were determined by gamma-ray spectrometry in 300 rock samples from cores of the Rio Preto Project area. The tests were conducted at LABIDRO-Isotopes and Hydrochemistry Laboratory of the Departament of Petrology and Metallogeny (DPM) of the Institute of Geosciences and Exact Sciences, UNESP, in Rio Claro, SP, Brazil. This paper reports the results of petrographic characterization and chemical analyses of major oxides (SiO2, TiO2, Al2O3, Fe2O3, MgO, MnO, K2O, Na2O, CaO and P2O5) for all samples used to determine the natural radioelements present in the region. The organic matter content results obtained by colorimetry are also reported for selected cores of different lithotypes in order to investigate the possible relationship between graphite and the radioelements uranium and thorium. Finally, uranium content and 234U/238U activity ratio data for selected samples of schists and gneisses of the Lower Member of the Ticunzal Formation suggest the influence of weathering processes in the area. © 2012 Sociedade Brasileira de Geofísica.

Caracterização de filmes finos de YBa2Cu3O7-x e La0.7Ca0.3MnO3 produzidos via síntese química

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