Influence of preparation methods and thermal treatment in melt-solidified and cast films of poly(vinylidene fluoride-trifluorethylene) copolymers

This paper is aimed at addressing the differences observed in film properties when poly(vinylidene fluoride-trifluorethylene) P(VDF-TrFE) films are fabricated using distinct methods. Samples were obtained either from casting a solution or by compression molding from a molten phase and characterized by differential scanning calorimetry (DSC). It is shown that the main differences between melt-solidified and cast films arise from the thermal treatment inherent in the former samples.

An ultra stable glass system for optical fiber devices

In this paper a modified chalcogenide glass was studied by X-ray powder diffraction, differential thermal analysis, infrared and Raman scattering spectroscopies. The study of this new matrix opens new perspectives to fabricate Pr3+-doped fibers to operate as an optical amplifier in the 1.3 mum telecommunications window. The Pr3+-doped 70Ga(2)S(3)-30La(2)S(3) glass was modified through the substitution of La2S3 by La2O3, which improves the thermal stability of these glasses without any modification of phonon energy. The possibility to pull a fiber from this glass system without any devitrification is easily achieved.

XPS study on water corrosion of fluorzirconate glasses and their protection by a layer of surface modified tin dioxide nanoparticles

The surface corrosion process associated with the hydrolysis of fluorozirconate glass, Z-BLAN (53ZrF(4), 20BaF(2), 20NaF, 4LaF(2), 3AlF(3)), and the corrosion protection efficiency of a nanocrystalline transparent SnO2 layer were investigated by X-ray photoelectron spectroscopy. The tin oxide film was deposited by the sol-gel dip-coating process in the presence of Tiron(R) as particle surface modifier agent. The chemical bonding structure and composition of the surface region of coated and non-coated ZBLAN were studied before water contact and after different immersion periods (5-30 min). In contrast to the effects occurring for non-coated glass, where the surface undergoes a rapid selective dissolution of the most soluble species inducing the formation of a new surface phase consisting of stable zirconium oxyfluoride, barium fluoride and lanthanum fluoride species, the results for the SnO2-coated glass showed that the hydrolytic attack induces a filling of the film nanopores by dissolved glass material and the formation of tin oxylluoride and zirconium oxyfluoride species. This process results in a modified film, which acts as a hermetic diffusion barrier protecting efficiently the glass surface. (C) 2006 Elsevier B.V. All rights reserved.

Differential scanning calorimetry, x-ray diffraction and F-19 nuclear magnetic resonance investigations of the crystallization of InF3-based glasses

Results of differential scanning calometry (DSC), x-ray diffraction (XRD), and F-19 nuclear magnetic resonance (NMR) of InF3-based glasses, treated at different temperatures, ranging from glass transition temperature (T-g) to crystallization temperature (T-c), are reported. The main features of the experimental results are as follows. DSC analysis emphasizes several steps in the crystallization process. Heat treatment at temperatures above T-g enhances the nucleation of the first growing phases but has little influence on the following ones. XRD results show that several crystalline phases are formed, with solid state transitions when heated above 680 K, the F-19 NMR results show that the spin-lattice relaxation, for the glass samples heat treated above 638 K, is described by two time constants. For samples treated below this temperature a single time constant T-1 was observed. Measurements of the F-19 spin-lattice relaxation time (T-1), as a function of temperature,made possible the identification of the mobile fluoride ions. The activation energy, for the ionic motion, in samples treated at crystallization temperature was found to be 0.18 +/- 0.01 eV. (C) 1998 American Institute of Physics.

Preparation of new glass systems by the polymeric precursor method for dental applications

Glass ionomer cements (GICs) are largely employed in Dentistry for several applications, such as luting cements for the attachment of crowns, bridges, and orthodontic brackets as well as restorative materials. The development of new glass systems is very important in Dentistry to improve of the mechanical properties and chemical stability. The aim of this study is the preparation of two glass systems containing niobium in their compositions for use as GICs. Glass systems based on the composition SiO2,Al2O3-Nb2O5-CaO were prepared by chemical route at 700degreesC. The XRD and DTA results confirmed that the prepared materials are glasses. The structures of the obtained glasses were compared to commercial material using FTIR, Al-27 and Si-29 MAS-NMR. The analysis of FTIR and MAS-NMR spectra indicated that the systems developed and commercial material are formed by SiO4 and AlO4 linked tetrahedra. These structures are essential to get the set time control and to have cements. These results encourage further applications of the experimental glasses in the formation of GICs. (C) 2004 Elsevier B.V. All rights reserved.

New glasses in the system InF3-BaF2-ErPO4

New glasses have been obtained in the system InF3-BaF2-ErPO4. Glass compositions with up to 30% mol Er3+ were shown to exist and characterized by thermal analysis, x-ray: diffraction, IR absorption and electronic spectroscopy. The systems with high Er3+ content were studied recording IR and visible emission spectral characteristics. A specially elaborated technique allowed the preparation of a high purity phosphate precursor ErPO4. X-ray identification of the crystalline phases appearing during thermal treatment have been carried out and parameters of a mixed fluoride Ba4In3-nErnF17 calculated.

In vitro biocompatibility of poly(vinylidene fluoride-trifluoroethylene)/barium titanate composite using cultures of human periodontal ligament fibroblasts and keratinocytes

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

On-line preconcentration and speciation analysis of Cr(III) and Cr(VI) using baker's yeast cells immobilised on controlled pore glass

A study was undertaken to evaluate Saccharonzyces cerevisiae as a substrate for the biosorption of Cr(III) and Cr(VI) aiming to the selective determination of these species in aqueous solutions. The yeast cells were covalently immobilised on controlled pore glass (CPG), packed in a minicolumn and incorporated in an on-line flow injection system. The effect of chemical and physical variables affecting the biosorption process was tested in order to select the optimal analytical conditions for the Cr retention by S. cerevisiae. Cr(III) was retained by the immobilised cells and Cr(VI) were retained by CPG. The speciation was possible by selective and sequential elution of Cr(III) with 0.05 mol L-1 HCl and 2.0 mol L-1 HNO3 for Cr(VI). The influence of some concomitant ions up to 20 mg L-1 was also tested. Quantitative determinations of Cr were carried out by means of inductively coupled plasma optical emission spectrometry (ICP OES). Preconcentration factors of 12 were achieved for Cr(III) and 5 for Cr(VI) when 1.7 mL of sample were processed reaching detection limits of 0.45 for Cr(III) and 1.5 mu g L-1 for Cr(VI). The speciation of inorganic Cr in different kinds of natural waters was performed following the proposed method. Spiked water samples were also analysed and the recoveries were in all cases between 81 and 103%. (c) 2005 Elsevier B.V. All rights reserved.

Collapse and Color Changes in Grapefruit Juice Powder as Affected by Water Activity, Glass Transition, and Addition of Carbohydrate Polymers

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)