Boris A. Shakhmatkin

The thermodynamic properties of oxide glasses and glass-forming liquids and their chemical structure

Abstract It is shown that the thermodynamic and other physical properties of oxide glasses and glass-forming liquids are adequately described on the basis of the model of ideal associated solutions using information on the corresponding properties of crystalline compounds which exist in the systems considered. The validity of the model used is illustrated by calculations performed for certain silicate and borate systems.

Thermodynamic modelling of the structure of glasses and melts: single-component, binary and ternary systems

Abstract This paper presents the results of modelling the distribution of the basic structural units, that characterise the short-range order in various glasses and melts, as a function of the composition and (fictive) temperature. The approach used is based on a purely thermodynamic model and applies equally to binary and ternary systems, formed from components with different chemical natures (borates, silicates, aluminosilicates, etc.), and to one-component glasses (e.g., B2O3). It is shown that the model results are in good agreement with the relevant structural data available in literature.

A thermodynamic, molecular dynamics and neutron diffraction investigation of the distribution of tetrahedral {;Si(n)} species and the network modifying cation environment in alkali silicate glasses

Abstract Previous molecular dynamics (MD) simulations of alkali silicate glasses are extended to keep a separate record of the bridging and non-bridging oxygen atoms and the SiO and NaO first neighbour distance distributions are compared with those extracted from neutron diffraction data. The model of ideal associated solutions is used to predict the distributions of Si ( n ) tetrahedral species for the glasses studied and these are in good agreement with nuclear magnetic resonance data. However, the corresponding distributions for the MD simulations indicate a much higher fictive temperature than for the real glasses. The spatial distribution of the Si (4) species for the MD simulations is more uniform than would pertain if the various Si ( n ) species were interconnected randomly, which has implications for the modified random network theory.

Vitreous borate networks containing superstructural units: a challenge to the random network theory?

Abstract Borate glasses are an enigma in that there is now increasing evidence that their structures are dominated by superstructural units. Crystallographic data for a wide range of crystalline borates are used as a basis to propose a set of criteria for the formation of vitreous borate networks, taking into account the topological degrees of freedom necessary for conventional glass formation and using the PbOB 2 O 3 system as an example. It is concluded that random network models of vitreous B 2 O 3 containing large numbers of boroxol groups can be built with the correct density if they contain locally independent interpenetrating networks.

Can thermodynamics relate the properties of melts and glasses to their structure

In this paper, it is shown that the thermodynamic concept, which considers the structure of glasses and melts in terms of a non-statistical distribution of their basic structural units, enables a large variety of the properties of glasses (melts) to be predicted with a high degree of reliability. The paper continues a series of works on the thermodynamic modelling of properties and presents the results obtained for the diffusion coefficient, the solubility of gases and redox equilibria in glasses and melts.

The thermodynamic modelling of glass properties: a practical proposition?

The model of associated solutions is used not only to calculate thermodynamic functions but also to predict physical properties and structural parameters for a range of binary borate, silicate and phosphate glasses. In each case, the model yields good agreement with the relevant experimental data.

The Chemical Structure of Oxide Glasses: A Concept Consistent with Neutron Scattering Studies?

An outline is presented of the conventional and chemical approaches to the structure of multicomponent glasses, together with a brief summary of the application of neutron scattering techniques to investigate the glass structure. The concept of the chemical structure of glasses, as developed by Shultz and co-workers, is then examined in the light of neutron scattering studies of oxide systems. It is concluded that, to date, thermodynamic predictions based on the model of associated solutions are entirely consistent with the results of neutron scattering studies.

The Structure-Property Relationship in Oxide Glasses: A Thermodynamic Approach

This paper considers a rigorous thermodynamic approach that can be used for calculating a variety of glass properties and the content of various structural units in glasses. Since both the properties and the structure are calculated on a unified basis, this approach enables the structureproperty relationship in glasses to be established quantitatively, and the structural units that characterise changes in glass properties to be determined.

Investigation of the Phase Diagram of the Na2O–B2O3–SiO2 System by the Small-Angle X-ray Scattering Technique

Sodium borosilicate melts containing 60 mol % SiO2 are investigated in the temperature range Tg–1100°C by the small-angle X-ray scattering (SAXS) technique. The temperature dependences of the SAXS intensity for the studied melts consist of two linear portions. A change in the slope of these portions is observed at temperatures that coincide, to within the accuracy of the SAXS experiment (±5–10 K), with the liquidus temperatures, which are usually determined to approximately identical accuracy. The change in the slope is associated with the change in the temperature coefficients of the isothermal compressibility upon transition from a liquid state to a supercooled liquid state. Similar results were obtained earlier for binary melts in the sodium borate system and a number of other systems. On this basis, it is assumed that the transition from a liquid state to a supercooled liquid state for melts in any glass-forming system can be revealed from the temperature dependences of the SAXS intensity, and the SAXS technique can be used to determine the liquidus temperatures, primarily for glass-forming melts with a low crystallization ability.

A crystallographic guide to the structure of borate glasses

Borate glasses are an enigma in that there is now increasing evidence that their structures are dominated by superstructural units, which comprise well defined arrangements of the basic BO{sub 3} and BO{sub 4} structural units, with no internal degrees of freedom in the form of variable bond or torsion angles. In the present paper, it is shown that considerable insight into the structure of borate glasses can be gained from a study of the corresponding crystalline polymorphs. A simple, model is proposed to predict the fraction, x{sub 4}, of 4-fold coordinated boron atoms in vitreous borate networks and the topological criteria for the formation of such networks are discussed, taking into account the degrees of freedom necessary for conventional glass formation.