Deformation–activation model of viscous flow of glass-forming liquids

Сандитов, Д. С.

doi:10.1016/j.jnoncrysol.2014.04.011

Cited by 9 publications

(3 citation statements)

References 28 publications

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“…Interest in the physics of disordered state of matter and in particular to study the rheology is high, and in recent years a number of results have shed light on the nature of the changes occurring at the glass transition [1][2][3][4][5][6][7]. Vitrification according to the IUPAC definition is considered as a quasi-second order transition in which a supercooled melt yields, on cooling, a glassy structure so that below the glass-transition temperature the physical properties of glasses vary in a manner similar to those of the crystalline phases.…”

Section: Introductionmentioning

confidence: 99%

“…Note that for some materials this value belongs to the glasstransition region defined by specific heat capacity measurement, but it is not the case for other materials [9]. A significant interest is also seen to study the viscous flow [1,[7][8][9][10][11][12][13][14]. The activation energy of viscous flow of amorphous materials Q (T) is nearly constant in the two asymptotic cases -at low temperatures when the material is in the glassy state, and at high temperatures, when the material is in a state of true melt.…”

Section: Introductionmentioning

confidence: 99%

“…The activation energy of viscous flow of amorphous materials Q (T) is nearly constant in the two asymptotic cases -at low temperatures when the material is in the glassy state, and at high temperatures, when the material is in a state of true melt. At intermediate temperatures the activation energy is changed from a high value at low temperatures, to low values at high temperatures [1,[10][11][12][13][14]. These changes are universal, regardless of the nature of the amorphous material, moreover, they are the basis for the Angel classification scheme of melts into two types: strong fragile [15,16].…”

Section: Introductionmentioning

confidence: 99%

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About activation energy of viscous flow of glasses and melts

Ojovan

2015

MRS Proc.

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Data on a viscous flow model based on network defects -broken bonds termed configurons -were analysed. An universal equation has been derived for the variable activation energy of viscous flow Q(T) of the generic Frenkel equation of viscosity η(T)=A·exp(Q/RT) which is known to have two constant asymptotes -high Q H at low temperatures and low Q L at high temperatures. The defect model of flow used by e.g. Doremus, Mott, Nemilov, Sanditov states that higher the concentration of defects (e.g. configurons) the lower the viscosity. We have used the configuron percolation theory (CPT) which treats glass-liquid transition as a percolation-type phase transition. Additionally the CPT results in a continuous temperature relationship for viscosity valid for both glassy and liquid amorphous materials. We show that a particular result of CPT is the universal temperature relationship for the activation energy of viscous flow: Q(T)=Q L +RT·ln[1+exp(-S d /R) exp((Q H -Q L )/RT)] which depends on asymptotic energies Q L (for the liquid phase) and Q H (for the glassy phase), and on entropy of configurons S d . This equation has two asymptotes, namely Q(T<>T g ) = Q L . Moreover we demonstrate that the equation for Q(T) practically coincides in the transition range of temperatures with known Sanditov equation.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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About activation energy of viscous flow of glasses and melts

Ojovan

2015

MRS Proc.

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Correlative activation free energy (CAFE) model: Application to viscous processes in inorganic oxide glass-formers

Beg,

Byeon,

Berman

et al. 2025

Acta Materialia

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On relaxation nature of glass transition in amorphous materials

Сандитов

Ojovan

2017

Physica B: Condensed Matter

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A short review on relaxation theories of glass transition is presented. The main attention is paid to modern aspects of the glass transition equation qτg = C, suggested by Bartenev in 1951 (q – cooling rate of the melt, τg – structural relaxation time at the glass transition temperature Tg). This equation represents a criterion of structural relaxation at transition from liquid to glass at T = Tg (analogous to the condition of mechanical relaxation ωτ = 1, where the maximum of mechanical loss is observed). The empirical parameter С = δTg has the meaning of temperature range δTg that characterizes the liquid-glass transition. Different approaches of δTg calculation are reviewed. In the framework of the model of delocalized atoms a modified kinetic criterion of glass transition is proposed (q/Tg)τg = Cg, where Cg ≅ 7·10−3 is a practically universal dimensionless constant. It depends on fraction of fluctuation volume fg, which is frozen at the glass transition temperature Cg = fg/ln(1/fg). The value of fg is approximately constant fg ≅ 0.025. At Tg 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 flow – activated 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 Tg, 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 Tg = Tg(q) is discussed. The value of fg calculated from the data on the Tg(q) dependence coincides with result of the fg 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 Tg(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

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Deformation–activation model of viscous flow of glass-forming liquids

Cited by 9 publications

References 28 publications

About activation energy of viscous flow of glasses and melts

About activation energy of viscous flow of glasses and melts

Correlative activation free energy (CAFE) model: Application to viscous processes in inorganic oxide glass-formers

On relaxation nature of glass transition in amorphous materials

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