Alisson M. Rodrigues

Thermal analysis of Li2O TeO2 glass

The thermal properties of 0.30Li2O 0.70TeO2 glass are studied. Specific heat, Cp, is measured in the 170∞C < T < 270∞C interval. The Einstein temperature, hAa 840 K, is determined from the temperature course of Cp. In the glass transition interval, the heat capacity undergoes an S-shaped transition from the value, Cgl, of the glass to that of undercooled melt, Cp. It is found that Cgl=Cp 0:62. The activation energy, EOTfU, for structural relaxation depends on a fictive temperature, Tf . For the glass under study, it is demonstrated that: EOTfUa655a 300O 520 Tf ˇ 1U kJ/ mol. ” 2000 Elsevier Science B.V. All rights reserved.

Mixed former effect between TeO2 and SiO2 in the Li2O-TeO2-SiO2 system

Abstract Glass samples of the 0.30Li2O·0.70(xTeO2·(1−x)SiO2) system were synthesized. The difference between the melting points of silica and tellurium oxide, which melts at 733°C with further volatilization, makes this synthesis a complex one. However, transparent and homogeneous glasses were obtained in the SiO2-rich domain up to x=0.30 by mixing appropriate amounts of the two binary systems, 0.30Li2O·0.70SiO2 and 0.30Li2O·0.70TeO2, in an induction furnace. With the increase of the TeO2 content in the samples investigated a decrease of Tg and an increase in the samples’ densities were measured. The results of electrical measurements, carried out by impedance spectroscopy, show an increase in electrical conductivity when TeO2 is added to the Li2O·SiO2 glass, which we attribute to a mixed former effect between TeO2 and SiO2. Both the activation energy and the σ0 parameter of the Arrhenius equation increase with increased TeO2 content in the samples. A carbon replica analysis of the samples shows a phase separation in the ternary glasses.

Determination of crystallization kinetics parameters of a Li1.5Al0.5Ge1.5(PO4)3 (LAGP) glass by differential scanning calorimetry

Crystallization kinetics parameters of a stoichiometric glass with the composition Li 1.5 Al 0.5 Ge 1.5 (PO 4 ) 3 were investigated by subjecting parallelepipedonal samples (3 × 3 × 1.5 mm) to heat treatment in a differential scanning calorimeter at different heating rates (3, 5, 8 and 10 °C/min). The data were analyzed using Ligeros and Kissingers methods to determine the activation energy (E) of crystallization, which yielded, respectively, E = 415 ± 37 kJ/mol and 378 ± 19 kJ/mol. Ligeros method was also employed to calculate the Avrami coefficient ( n), which was found to be n = 3.0. A second set of samples were heat-treated in a tubular furnace at temperatures above the glass transition temperature, T g , to induce crystallization. The X-ray diffraction analysis of these samples indicated the presence of LiGe 2 (PO 4 ) 3 which displays a NASICON-type structure. An analysis by optical microscopy revealed the presence of spheric crystals located primarily in the volume, in agreement with the crystallization mechanism predicted by the Avrami coefficient.

Structural and dynamic properties of vitreous and crystalline barium disilicate: molecular dynamics simulation and Raman scattering experiments

In this paper, we use a molecular dynamics simulation and Raman scattering measurements to study the vibrational and structural characteristics of barium disilicate, BaSi2O5, in vitreous and crystalline states. Our proposed atomic interaction potential describes the structural and dynamic behaviour of this material very well and can also be used for further extended studies. In addition, Raman spectroscopy enabled validation of the predictions of the potential by comparing the simulated vibrational density of states with the spectrum of the material in its vitreous state. Furthermore, we characterized the kinetics of the crystallization process through in situ Raman measurements as a function of temperature.

Elemental and cooperative diffusion in a liquid, supercooled liquid and glass resolved

The diffusion mechanisms controlling viscous flow, structural relaxation, liquid-liquid phase separation, crystal nucleation, and crystal growth in multicomponent glass-forming liquids are of great interest and relevance in physics, chemistry, materials, and glass science. However, the diffusing entities that control each of these important dynamic processes are still unknown. The main objective of this work is to shed some light on this mystery, advancing the knowledge on this phenomenon. For that matter, we measured the crystal growth rates, the viscosity, and lead diffusivities in PbSiO3 liquid and glass in a wide temperature range. We compared our measured values with published data covering 16 orders of magnitude. We suggest that above a certain temperature range Td (1.2Tg-1.3Tg), crystal growth and viscous flow are controlled by the diffusion of silicon and lead. Below this temperature, crystal growth and viscous flow are more sluggish than the diffusion of silicon and lead. Therefore, Td marks the temperature where decoupling between the (measured) cationic diffusivity and the effective diffusivities calculated from viscosity and crystal growth rates occurs. We reasonably propose that the nature or size of the diffusional entities controlling viscous flow and crystal growth below Td is quite different; the slowest is the one controlling viscous flow, but both processes require cooperative movements of some larger structural units rather than jumps of only one or a few isolated atoms.

Macromolecular interactions and synergy in xanthan/HPAM aqueous solutions

It is known that the rheological properties of a polymer solution are strongly dependent on the polymer structure, composition, conformation and interactions between the polymer and the solvent. Indeed, the macromolecular interactions change the polymer conformation which can result in an improvement of rheological behavior. Herein, the synergy and interactions between hydrolyzed polyacrylamide (HPAM) and xanthan were explored by rheology experiments and dynamic light scattering. The results indicated that hydrogen bonding interactions occur between the HPAM and xanthan existing in saline solution. It was showed that negative or positive synergistic effects occurred when the proportions of partially hydrolyzed polyacrylamide and xanthan were changed and the maximum positive synergy occurred when the content of xanthan was ca. 80% for the present experimental conditions. In addition, the synergy of mixed solution was markedly influenced by temperature and the HPAM molecular weight and mineralization degree. The two types of synergistic effects tended to recede with increasing shear rate in the rheological experiments. It is noted the calculation of relaxation time (t) for the mixed solutions also demonstrated an interaction between the HPAM and xanthan in aqueous solutions.

Influence of molecular interplay on the HPAM/UR rheological properties in an aqueous solution

Herein, the interaction between partially hydrolyzed polyacrylamide (HPAM) and urea (UR) in an aqueous solution was characterized via differential scanning calorimetry (DSC) and two-dimension correlation spectra (2DCOS). The rheological properties of the HPAM solution (2000 and 2500 mg L−1) were studied as a function of the addition of the UR content (50, 100, 200, 300, and 400 mg L−1). The results indicate that the HPAM/UR solution exhibits higher intrinsic viscosity, apparent viscosity, first normal stress difference, and modulus than the HPAM solution due to the larger hydraulic size of HPAM in the aqueous solution. From the DSC and 2DCOS results, a stronger hydrogen bonding interaction between carbonyl and amino groups was observed in the vicinity of 45 °C. Dynamic light scattering (DLS) was employed to directly analyze the hydrodynamic diameter, and it further confirmed that a certain amount of UR enabled the blending solution to increase the hydraulic size. Moreover, an interplay model was put forward based on the rheology and dynamic light scattering data.