Effect of temperature on glass-ceramic films prepared by impregnation of commercial float glass surfaces with oxide powders under pressure

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Calcium hydroxide root canal sealers: Evaluation of pH, calcium ion concentration and conductivity

The calcium hydroxide ionization of four root canal sealers (Sealapex, CRCS, Sealer 26, and Apexit) was studied by measuring conductivity and pH and by conducting atomic absorption spectrophotometry. Samples 6 mm in diameter and 15 mm long were prepared from these sealers. After setting and 48 h storage in a desiccator, five samples of each material were placed in 50 mL distilled water and analysed after 0,1,2,4, 6 and 24 h and 5, 15 and 30 days. The results showed that Sealapex was the root canal sealer showing the highest pH, ionic calcium and total calcium values (P<0.05) throughout the experimental period, followed by CRCS, Apexit and Sealer 26.

Photon-photon and pomeron-pomeron processes in peripheral heavy ion collisions

We estimate the cross sections for the production of resonances, pion pairs, and a central cluster of hadrons in peripheral heavy-ion collisions through two-photon and double-pomeron exchange, at energies that will be available at the Relativistic Heavy Ion Collider (RHIC) and the Large Hadron Collider (LHC). The effect of the impact parameter in the diffractive reactions is introduced, and by imposing the condition for realistic peripheral collisions we verify that in the case of very heavy ions the pomeron-pomeron contribution is indeed smaller than the electromagnetic one. However, they give a non-negligible background in the collision of light ions. This diffractive background will be more important at RHIC than at LHC.

Cation distribution and magnetic characterization of the multiferroic cobalt manganese Co2MnO4 spinel doped with bismuth

The structural and magnetic properties of the cubic spinel oxide Co 2MnO4 (Fd3m space group) doped with different concentrations of bismuth, were investigated by X-ray diffraction and SQUID magnetometry. The Bi3+ ions entering into the CoIII octahedral sites do not alter the effective moment, μeff ∼8.2 μB, whereas both the magnetization M50 kOe at the highest field (50 kOe) and the field-cooled MFC magnetizations increased when increasing the Bi content. The ferrimagnetic character of the parent compound, Co2MnO4, is maintained for all materials although the antiferromagnetic interactions Co2+-Co2+ are affected, resulting in higher values of the Curie-Weiss temperature. Due to the large ionic radius of Bi, octahedra distortions occur as well as valence fluctuations of the Mn ions, giving rise to Jahn-Teller effects and enhancing the exchange interactions. The off-center Bi3+ ion is responsible of non-centrosymmetric charge ordering and should lead to multiferroïsme conditions for the BixCo2-xMnO4 material. © 2012 Elsevier B.V.

Supplementation of soft drinks with metallic ions reduces dissolution of bovine enamel

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

Estudo da concentração e recuperação de íons lantânio e neodímio por biossorção em coluna com a biomassa Sargassum sp

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Structural refinement, optical and electrical properties of [Ba1-x Sm-2x/3](Zr0.05Ti0.95)O-3 ceramics

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Determination of mercury in river water by diffusive gradients in thin films using P81 membrane as binding layer

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

Effects of the addition of ions barium on the structural and electrical properties of PZT ceramic

Lead zirconate titanate, with Zr/Ti ratio of 53/47 was prepared by the polymeric precursor method. It was investigated the barium (II) modification at 0.0, 0.2, 0.4 and 0.6 mol% in substitution to the lead (II) cation in A site of perovskite structure. The powder samples were characterized by XRD and the diffraction patterns were used to Rietveld refinement. The percentages of tetragonal and rhombohedral phases and a systematic study of the effect of barium (II) on the morphology and the dielectric properties of PZT were carried out. The results showed that the tetragonal phase is favored and the ceramic density is improved with the barium (II) insertion. The Curie temperature (Tc) is increased besides the slight reduction of dielectric constant (Kc).

Frequency upconversion involving triads and quartets of ions in a Pr3+/Nd3+ codoped fluoroindate glass

Frequency upconversion (UC) processes involving energy transfer (ET) among Nd 3+ and Pr 3+ ions in a fluoroindate glass are reported. In a first experiment, the excitation of Pr 3+ [transition 3H 4→ 1D 2] and of Nd 3+ [transition 4I 9/2→( 2G 7/2+ 4G 5/2)] was achieved with a dye laser operating in the 575-590 nm range. In a second experiment, the Nd 3+ ions were excited with the second harmonic of a Nd: YAG laser at 532 nm. The ET processes leading to UC in both experiments were studied by monitoring the blue fluorescence decay at 480 nm due to the transition 3P 0→ 3H 4 in Pr 3+. In the more relevant UC process, quartets of ions (Nd-Nd-Pr-Pr) are excited due to absorption of three laser photons by two Nd 3+ ions which transfer their energy to two Pr 3+ ions. Each Pr 3+ ion promoted to the 3P 0 level decays to the ground state emitting one photon in the blue region. This conclusion was achieved investigating the dependence of the UC fluorescence intensity as a function of laser intensity, samples concentrations, and temporal behavior of the UC signal. Other UC processes involving nonisoionic groups of three ions are also reported. © 2002 American Institute of Physics.

A comparative study of the electrochemical oxidation of the herbicide tebuthiuron using boron-doped diamond electrode

The thiadiazolylurea derivative tebuthiuron (TBH) is commonly used as an herbicide even though it is highly toxic to humans. While various processes have been proposed for the removal of organic contaminants of this type from wastewater, electrochemical degradation has shown particular promise. The aim of the present study was to investigate the electrochemical degradation of TBH using anodes comprising boron-doped (5000 and 30000 ppm) diamond (BDD) films deposited onto Ti substrates operated at current densities in the range 10-200 mA cm(-2). Both anodes removed TBH following a similar pseudo first-order reaction kinetics with k(ap)p close to 3.2 x 10(-2) min(-1). The maximum mineralization efficiency obtained was 80%. High-pressure liquid chromatography with UV-VIS detection established that both anodes degraded TBH via similar intermediates. Ion chromatography revealed that increasing concentrations of nitrate ions (up to 0.9 ppm) were formed with increasing current density, while the formation of nitrite ions was observed with both anodes at current densities >= 150 mA cm(-2). The BDD film prepared at the lower doping level (5000 ppm) was more efficient in degrading TBH than its more highly doped counterpart. This unexpected finding may be explained in terms of the quantity of impurities incorporated into the diamond lattice during chemical vapor deposition. (C) 2012 Elsevier Ltd. All rights reserved.

Paper-based diffusive gradients in thin films technique coupled to energy dispersive X-ray fluorescence spectrometry for the determination of labile Mn, Co, Ni, Cu, Zn and Pb in river water

The diffusive gradients in thin films (DGT) technique has shown enormous potential for labile metal monitoring in fresh water due to the preconcentration, time-integrated, matrix interference removal and speciation analytical features. In this work, the coupling of energy dispersive X-ray fluorescence (EDXRF) with paper-based DGT devices was evaluated for the direct determination of Mn, Co. Ni, Cu, Zn and Pb in fresh water. The DGT samplers were assembled with cellulose (Whatman 3 MM chromatography paper) as the diffusion layer and a cellulose phosphate ion exchange membrane (Whatman P 81 paper) as the binding agent. The diffusion coefficients of the analytes on 3 MM chromatography paper were calculated by deploying the DGT samplers in synthetic solutions containing 500 mu g L-1 of Mn. Co, Ni, Cu, Zn and Pb (4 L at pH 5.5 and ionic strength at 0.05 mol L-1). After retrieval, the DGT units were disassembled and the P81 papers were dried and analysed by EDXRF directly. The 3 MM chromatographic paper diffusion coefficients of the analytes ranged from 1.67 to 1.87 x 10(-6) cm(2) s(-1). The metal retention and phosphate group homogeneities on the P81 membrane was studied by a spot analysis with a diameter of 1 mm. The proposed approach (DGT-EDXRF coupling) was applied to determine the analytes at five sampling sites (48 h in situ deployment) on the Piracicaba river basin, and the results (labile fraction) were compared with 0.45 mu m dissolved fractions determined by synchrotron radiation-excited total reflection X-ray fluorescence (SR-TXRF). The limits of detection of DGT-EDXRF coupling for the analytes (from 7.5 to 26 mu g L-1) were similar to those obtained by the sensitive SR-TXRF technique (3.8 to 9.1 mu g L-1). (C) 2012 Elsevier B.V. All rights reserved.

Mechanistic Implications of Zinc(II) Ions on the Degradation of Phenol by the Fenton Reaction

A study of the interference of Zn2+ ions on phenol degradation by Fenton reaction (Fe2+/Fe3(+) + H2O2) is reported. One of the first intermediates formed in the reaction, catechol, can reduce Fe3+ to Fe2+ and, in the presence of H2O2 initiates an efficient catalytic redox cycle. In the initial stages of the reaction, this catechol-mediated cycle becomes the principal route of thermal degradation of phenol and its oxidation products. The Zn2+ ion addition enhances the persistence time of catechol, probably by stabilization of the corresponding semiquinone radical via complexation.

Exploring the intrinsic polar [4?+?2+] cycloaddition reactivity of gaseous carbosulfonium and carboxonium ions

Gas-phase reactions of model carbosulfonium ions (CH3-S+?=?CH2; CH3CH2-S+?=?CH2 and Ph-S+?=?CH2) and an O-analogue carboxonium ion (CH3-O+?=?CH2) with acyclic (isoprene, 1,3-butadiene, methyl vinyl ketone) and cyclic (1,3-cyclohexadiene, thiophene, furan) conjugated dienes were systematically investigated by pentaquadrupole mass spectrometry. As corroborated by B3LYP/6-311?G(d,p) calculations, the carbosulfonium ions first react at large extents with the dienes forming adducts via simple addition. The nascent adducts, depending on their stability and internal energy, react further via two competitive channels: (1) in reactions with acyclic dienes via cyclization that yields formally [4?+?2+] cycloadducts, or (2) in reactions with the cyclic dienes via dissociation by HSR loss that yields methylenation (net CH+ transfer) products. In great contrast to its S-analogues, CH3-O+?=?CH2 (as well as C2H5-O+?=?CH2 and Ph-O+?=?CH2 in reactions with isoprene) forms little or no adduct and proton transfer is the dominant reaction channel. Isomerization to more acidic protonated aldehydes in the course of reaction seems to be the most plausible cause of the contrasting reactivity of carboxonium ions. The CH2?=?CH-O+?=?CH2 ion forms an abundant [4?+?2+] cycloadduct with isoprene, but similar to the behavior of such alpha,beta-unsaturated carboxonium ions in solution, seems to occur across the C?=?C bond. Copyright (c) 2012 John Wiley & Sons, Ltd.

Mechanistic implications of zinc(II) ions on the degradation of phenol by the fenton reaction

A study of the interference of Zn2+ ions on phenol degradation by Fenton reaction (Fe2+/Fe3+ + H2O2) is reported. One of the first intermediates formed in the reaction, catechol, can reduce Fe3+ to Fe2+ and, in the presence of H2O2 initiates an efficient catalytic redox cycle. In the initial stages of the reaction, this catechol-mediated cycle becomes the principal route of thermal degradation of phenol and its oxidation products. The Zn2+ ion addition enhances the persistence time of catechol, probably by stabilization of the corresponding semiquinone radical via complexation.