RESUMO
In situ micro-Raman spectroscopy was used to investigate the structural evolution of OH(-)-free calcium aluminosilicate glasses, under high pressure and at room temperature. Evaluation was made of the role of the SiO2 concentration in percalcic join systems, for Al/(Al + Si) in the approximate range from 0.9 to 0.2. Under high pressure, the intensity of the main band related to the bending mode of bridging oxygen ([Formula: see text][T-O-T], where T = Si or Al) decreased gradually, suggesting that the bonds were severely altered or even destroyed. In Si-rich glasses, compression induced a transformation of Q (n) species to Q (n-1). In the case of Al-rich glass, the Al in the smallest Q (n) units evolved from tetrahedral to higher-coordinated Al (([5])Al and ([6])Al). Permanent structural changes were observed in samples recovered from the highest pressure of around 15 GPa and, particularly for Si-rich samples, the recovered structure showed an increase of three-membered rings in the Si/Al tetrahedral network.
RESUMO
A dual-wavelength on/off-excitation thermal lens technique was used to identify and quantify a laser-induced chemical reaction in ionic aqueous solutions of Fe(II)-TPTZ. On/off modeling was used to fit the TL experimental data, which provided the primary effect generated during laser-excitation. The addition of HCl in the solutions reduced the activation barrier; this behavior followed the Arrhenius correlation. The nature of the photo-oxidation of Fe(II)-TPTZ complex is discussed. The results suggest that this technique may contribute to the understanding of the dynamics of complex reactions, which may lead to a more precise determination of the physicochemical properties involved in a photochemical reaction.
RESUMO
The optical, magnetic and structural properties of Eu doped low silica calcium aluminosilicate glasses were investigated. The optical absorption coefficient presented two bands at 39,246 and 29,416 cm(-1), which were assigned respectively to the [Formula in text], and [Formula in text] transitions of Eu(2+). The fluorescence measured at 300 K on a sample doped with 0.5 wt% of Eu(2)O(3) exhibited a broad band centered at 17,350 cm(-1), which is attributed to the [Formula in text] transition of Eu(2+), whereas the additional peaks are due to the [Formula in text] transitions of Eu(3+). From magnetization and XANES data it was possible to evaluate the fractions of Eu(2+) and Eu(3+) for the sample doped with 0.5 and 5.0 wt% of Eu(2)O(3), the values of which were approximately 30 and 70%, respectively.
RESUMO
In this work the time resolved thermal lens method is combined with interferometric technique, the thermal relaxation calorimetry, photoluminescence and lifetime measurements to determine the thermo physical properties of Nd(2)O(3) doped sodium zincborate glass as a function of temperature up to the glass transition region. Thermal diffusivity, thermal conductivity, fluorescence quantum efficiency, linear thermal expansion coefficient and thermal coefficient of electronic polarizability were determined. In conclusion, the results showed the ability of thermal lens and interferometric methods to perform measurements very close to the phase transition region. These techniques provide absolute values for the measured physical quantities and are advantageous when low scan rates are required.
RESUMO
This paper describes the preparation and characterization of collagen films extracted from swim bladders of three species of tropical fishes: Arius parkeri (Gurijuba), Cynoscion acoupa (Pescada Amarela) and Cynoscion leiarchus (Pescada Branca). Collagen was extracted under acidic conditions (CH(3)COOH, 2.5 pH) and precipitated by the addition of NaCl up to 3.0 mol L(-1). The films were prepared in acrylic containers and dried in a vacuum atmosphere. The collagen films were characterized by hydroxyproline contents, thermal analysis, scanning electron microscopy and impedance spectroscopy. The determined values of 4-hydroxiproline and collagens in the films were: 105.23+/-4.48 and 873.2; 102.94+/-4.42 and 854.1; 100.65+/-4.80 and 835.8 mg g(-1) for A. parkeri, C. acoupa and C. leiarchus, respectively. Differential scanning calorimetry revealed high denaturation temperature peaks at temperatures ranging from 65.9 to 74.8 degrees C. The micrographs showed no fibrillar organization along the material, but spongy structure, with cavity diameters relatively uniform, at around 2 microm. The impedance spectroscopy presented a distributed relaxation process. A. parkeri's films showed piezoelectricity.