Structural Relaxation Dynamics and Annealing Effects of Sodium Silicate Glass (original) (raw)
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The Journal of Physical Chemistry C, 2015
Direct observation of structural relaxation at molecular scale in network glasses near the glass transition and in the melt is very challenging. Distribution of structural units forming the glass is commonly believed to depend uniquely on composition and temperature. In this paper, we evidence the dynamical structural changes of the silicate network upon structural relaxation by monitoring the temperature and time evolution of its vibrational signature. Just above T g , the silicate network presents an unexpected time dependence of its relaxation process characterized by two subsequent regimes leading to a disordered equilibrium state. When annealed at 925 K, the network evolves rapidly toward silica and sodium silicate crystalline phases. Evolution models to describe the temperature time dependences of the Q n distributions are reported and discussed. A general picture of the hierarchical character of structural relaxation in network glasses is drawn.
Surface and bulk structural relaxation kinetics of silica glass
Journal of Non-crystalline Solids, 1997
The structural relaxation kinetics of a silica glass were measured by following the IR structural band positions, which are directly correlated with the average Si-O-Si bond angle as well as with the fictive temperature of the glass, as a function of heat-treatment time, temperature and the water vapor pressure. Both surface relaxation and bulk relaxation kinetics were determined by measuring the IR reflection and absorption band positions, respectively. The surface relaxation was much faster than the bulk relaxation and had a smaller activation energy. Also, both relaxation kinetics were faster in the presence of water vapor. The apparent bulk relaxation time determined from the IR absorption band shift was a composite relaxation time consisting of both the relaxation time of the water-catalyzed near surface layer and the true bulk relaxation time of the glass interior which is unaffected by water vapor. The true bulk relaxation time was evaluated and found to have an activation energy consistent with that of the viscous flow. 0022-3093r97r$17.00 Copyright q 1997 Elsevier Science B.V. All rights reserved.
Influence of pressure on fast picosecond relaxation in glass-forming materials
Physical Review B, 2010
Understanding the microscopic mechanism of the fast dynamics ͑gigahertz-terahertz frequency range͒ in amorphous materials remains a challenge. Disordered systems usually exhibit two additional contributions in this frequency range in comparison to their crystalline counterparts: a low-frequency excess vibrations, the so-called boson peak, and the fast picosecond relaxation that appears as a quasielastic scattering ͑QES͒ in the light-and neutron-scattering spectra. The nature of both contributions remains a subject of active discussions. In particular, QES intensity varies significantly with temperature. These variations might be caused by pure thermal effect and/or by change in density. To separate these two contributions we performed detailed light ͑Raman and Brillouin͒ scattering studies of the fast dynamics at different experimental conditions: isothermal, isobaric, isokinetic, and isochoric. The analysis demonstrates that the volume contribution dominates the fast relaxation behavior in a liquid state while the thermal energy becomes more important in the glassy state. Moreover, the presented analysis of the light-scattering data reveals significant difference in sensitivity of the fast dynamics to pressure among seven glass-forming materials ͑van der Waals-bonding and hydrogen-bonding molecular systems and polymers͒ studied in this work. It appears that the fast dynamics in orthoterphenyl and glycerol depends on pressure ͑density͒ significantly weaker than in other materials. However, the earlier observed correlations between pressure-induced variations in the QES and boson peak intensities and between the boson peak frequency and intensity are confirmed for all the studied materials. The obtained experimental results are compared to predictions of different models.
Relaxation dynamics and aging in structural glasses
2013
We present a study of the atomic dynamics in a Mg 65 Cu 25 Y 10 metallic glass former both in the deep glassy state and in the supercooled liquid phase. Our results show that the glass transition is accompanied by a dynamical crossover between a faster than exponential shape of the intermediate scattering function in the glassy state and a slower than exponential shape in the supercooled liquid. While the crossover temperature is independent on the previous thermal history, both the relaxation rate and the shape of the relaxation process depend on the followed thermal path. Moreover, the temperature dependence of the the structural relaxation time displays a strong departure from the Arrhenius-like behavior of the corresponding supercooled liquid phase, and can be well described in the Narayanaswamy-Moynihan framework with a large non-linearity parameter.
Transient Nature of Fast Relaxation in Metallic Glass
2022
Metallic glasses exhibit fast mechanical relaxations at temperatures well below the glass transition, one of which shows little variation with temperature known as nearly constant loss (NCL). Despite the important implications of this phenomenon to in aging and deformation, the origin of the relaxation is unclear. Through molecular dynamics simulations of a model metallic glass, Cu_64.5Zr_35.5, we implement dynamic mechanical analysis with system stress decomposed into atomic-level stresses to identify the group of atoms responsible for NCL. This work demonstrates that NCL relaxation is due to fully transient groups of atoms that become normal over picosecond timescales. They are spatially distributed throughout the glass and have no outstanding features, rather than defect-like as previously reported.
Heating Rate Effect on the Activation of Viscoelastic Relaxation in Silicate Glasses
Physics Procedia, 2013
Here we present a direct investigation of the heating rate effect on structural relaxation of sodium silicate glass near the glass transition by means of differential scanning calorimetry, and show the sensitivity of Brillouin light spectroscopy to the dynamic of structural relaxation in the medium range order (~100 nm).
On relaxation nature of glass transition in amorphous materials
Physica B-condensed Matter, 2017
A short review on relaxation theories of glass transition is presented. The main attention is paid to modern aspects of the glass transition equation qτ g = C, suggested by Bartenev in 1951 (qcooling rate of the melt, τ gstructural relaxation time at the glass transition temperature T g). This equation represents a criterion of structural relaxation at transition from liquid to glass at T = T g (analogous to the condition of mechanical relaxation ωτ = 1, where the maximum of mechanical loss is observed). The empirical parameter С = δT g has the meaning of temperature range δT g that characterizes the liquid-glass transition. Different approaches of δT g calculation are reviewed. In the framework of the model of delocalized atoms a modified kinetic criterion of glass transition is proposed (q/T g)τ g = C g , where C g ≅ 7•10 −3 is a practically universal dimensionless constant. It depends on fraction of fluctuation volume f g , which is frozen at the glass transition temperature C g = f g /ln(1/f g). The value of f g is approximately constant f g ≅ 0.025. At T g the process of atom delocalization, i.e. its displacement from the equilibrium position, is frozen. In silicate glasses atom delocalization is reduced to critical displacement of bridge oxygen atom in Si-O-Si bridge necessary to switch a valence bond according to Muller and Nemilov. An equation is derived for the temperature dependence of viscosity of glass-forming liquids in the wide temperature range, including the liquid-glass transition and the region of higher temperatures. Notion of (bridge) atom delocalization is developed, which is related to necessity of local low activation deformation of structural network for realization of elementary act of viscous flowactivated switch of a valence (bridge) bond. Without atom delocalization ("trigger mechanism") a switch of the valence bond is impossible and, consequently, the viscous flow. Thus the freezing of atom delocalization process at low temperatures, around T g , leads to the cease of the viscous flow and transition of a melt to a glassy state. This occurs when the energy of disordered lattice thermal vibrations averaged to one atom becomes equal or less than the energy of atom delocalization. The Bartenev equation for cooling rate dependence of glass transition temperature T g = T g (q) is discussed. The value of f g calculated from the data on the T g (q) dependence coincides with result of the f g calculation using the data on viscosity near the glass transition. Derivation of the Bartenev equation with the account of temperature dependence of activation energy of glass transition process is considered. The obtained generalized relation describes the T g (q) dependence in a wider interval of the cooling rate compared Bartenev equation. Experimental data related to standard cooling rate q = 3 K/min were used in this work.
Journal of Non-crystalline Solids, 2007
Dielectric spectra of several typical molecular glass-formers, showing one or more secondary processes resolved in the glassy state, have been measured at different temperatures. We found that the genuine Johari-Goldstein b-relaxation is connected to the structural relaxation. In fact, a clear correlation was found between the structural relaxation time, the Johari-Goldstein relaxation time and the dispersion of the structural relaxation (i.e. its Kohlrausch parameter). Moreover, for a group of epoxide oligomers the steepness index is correlated to the broadness of the structural peak and to the time separation between the structural and the Johari-Goldstein relaxation. These results support the idea that the Johari-Goldstein relaxation acts as a precursor of the structural relaxation. A rationale for our results is provided by the coupling model.
Fast and slow relaxation processes in glasses
Journal of Physics: Condensed Matter, 1999
We present dielectric relaxation (DS) and light scattering (LS) data of several glass formers. Relaxational features are compiled which are not yet properly taken into account by current models. (i) We distinguish two types of glass formers. Type A systems do not show a slow β-process whereas type B systems do. A full line-shape analysis of ε(ω) is presented (10 −2 Hz < ν < 10 9 Hz). In type A systems the evolution of the high-frequency wing of the α-process is the most prominent spectral change while cooling and leads to an essentially constant loss at T < T g . The analysis of ε(ω) of type B systems is carried out within the Williams-Watts approach and we focus on the temperature dependence of the β-relaxation strength. (ii) Concerning fast relaxations below T g as revealed by LS (10 9 Hz < ν < 10 13 Hz) we identify relaxation with a low-frequency power-law behaviour. No indication of a crossover to a white noise spectrum as previously reported and discussed within MCT is found. Analysing this relaxation we recourse to the model of thermally activated transitions in asymmetric double well potentials. We show that the model works well in some cases and the distribution of barrier heights may be extracted, but in other systems pronounced deviations occur. † Corresponding author. 0953-8984/99/SA0147+10$19.50
The Journal of Physical Chemistry B, 2005
Upon decreasing temperature or increasing pressure, a noncrystallizing liquid will vitrify; that is, the structural relaxation time, τ R , becomes so long that the system cannot attain an equilibrium configuration in the available time. Theories, including the well-known free volume and configurational entropy models, explain the glass transition by invoking a single quantity that governs the structural relaxation time. The dispersion of the structural relaxation (i.e., the structural relaxation function) is either not addressed or is derived as a parallel consequence (or afterthought) and thus is independent of τ R. In these models the time dependence of the relaxation bears no fundamental relationship to the value of τ R or other dynamic properties. Such approaches appear to be incompatible with a general experimental fact recently discovered in glass-formers: for a given material at a fixed value of τ R , the dispersion is constant, independent of thermodynamic conditions (T and P); that is, the shape of the R-relaxation function depends only on the relaxation time. If derived independently of τ R , it is an unlikely result that the dispersion of the structural relaxation would be uniquely defined by τ R .