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Topological Constraint Theory and Rigidity of Glasses
Published in Klaus D. Sattler, st Century Nanoscience – A Handbook, 2019
A fundamental question in glass science is to understand what makes it possible for a substance to avoid crystallization upon cooling below its melting point, that is, to understand the origin of glass-forming ability. For oxide glasses, some useful insights can be gained by considering the chemical composition of the system. The cations A that form the network of oxide glasses can be classified based on the energy of the A–O bonds. Namely, the cations A are classified as network formers and network modifiers if the A–O bond energy is higher than 330 kJ/mol and lower than 250 kJ/mol, respectively (Varshneya, 1993). Other cations are classified as intermediate. Network-forming species comprise Si, B, Ge, Al, P, etc., whereas network-modifying species comprise Ca, Mg, Li, Na, K, etc. This classification is based on the idea that, to avoid crystallization during cooling, supercooled liquids must have a viscosity that is high enough to prevent the atoms from easily reorganizing. This requires the existence of strong interatomic bonds. As such, network formers form the backbone of glasses, whereas network modifiers tend to depolymerize them.
Heat Capacity, Heat Content, and Energy Storage
Published in Mary Anne White, Physical Properties of Materials, 2018
A glass can be defined as a rigid supercooled liquid formed by a liquid that has been cooled below its normal freezing point such that it is rigid but not crystalline. A glass is also said to be amorphous, which means without shape, showing its lack of periodicity on a molecular scale. A supercooled liquid (i.e., a liquid cooled below its normal freezing point) is metastable with respect to its corresponding crystalline solid. Metastability is defined as a local Gibbs energy minimum, whereas the global energy minimum is stable (see Figure 6.9). While a supercooled liquid is in an equilibrium state (the molecules obey the Boltzmann distribution), a glass, which is obtained by cooling a supercooled liquid, is not in equilibrium with itself. This is because, in glasses, molecular configurations (i.e., the relative orientations and packing of the molecules) change slowly (sometimes hardly at all) so that Boltzmann distributions cannot be achieved. Given sufficient time, a glass would eventually convert to a crystalline form because it is more stable than the glass; an example of such a conversion is shown in Figure 6.10.
Solid State Background
Published in P.J. Gellings, H.J.M. Bouwmeester, Electrochemistry, 2019
Isaac Abrahams, Peter G. Bruce
Unlike crystalline solids, noncrystalline or amorphous solids have no regular repeating structure, and X-ray or electron diffraction results in a broad diffuse pattern with no sharp peaks. Under certain cooling conditions from the melt, some compounds or mixtures of compounds form a supercooled liquid or glass. The atomic arrangement in glasses is truly amorphous with no regular repeating array of atoms, and the structure effectively represents a frozen liquid. Glasses can be synthesized with wide-ranging properties, including semiconductivity as in Te0.8Ge0.2 and superconductivity as in Pb0.9Cu0.1. Oxides such as SiO2 and P2O5 are known as network formers, which give rise to a covalent framework to which network modifiers such as Li2O and Ag2O can be added to introduce ionic bonds and hence ionic conduction. Ionic conductivity in glasses is well known; for example, Li+ ion conductivity in LiAlSiO4 glasses, and Ag+ ion conductivity in the AgI-Ag2SeO4 system.3 Silver ion conducting glasses are of particular interest because of their very high ionic conductivities at low temperature, for example, 6 × 10−2 Scm−1 in 75% AgI− 25% Ag2SeO4.4 Because there is no regular repeating structure, many of the properties of amorphous solids, for example, ionic conductivity, are not dependent on the orientation of the solid material and are hence said to be isotropic. The lack of long-range order means that pathways for ionic conduction are less well defined than in crystalline solids.
A four-parameter generalized van der Waals equation of state: theoretical determination of thermodynamic stability boundary and vapor–liquid equilibrium of vanadium, niobium and tantalum
Published in Phase Transitions, 2023
Ramesh Arumugam, Balasubramanian Ramasamy
In cooling below the melting point, under the conditions that eliminate the crystallization process, the supercooled liquid goes to the amorphous state. Therefore, in the low temperature region, the value of determines the tensile strength limit of the amorphous state. The amorphous state has the greatest limiting tensile strength i.e ideal tensile strength at a temperature of absolute zero. The ideal tensile strength can also be considered in terms of thermodynamic stability of a liquid phase. This approach is justified by the fact that the intermolecular attractive force insignificantly changes in the crystal(solid)-liquid phase transition. Hence, the ideal tensile strength of a liquid(or amorphous) phase is approximately equal to the strength of a crystal. The spinodal in the phase diagram intersects the pressure axis at the point which is the ideal tensile strength of the liquid phase. The value defines the theoretical rupture resistance of a condensed matter under all around tension at.
An analytical solution to the nonlinear evolutionary equations for nucleation and growth of particles
Published in Philosophical Magazine Letters, 2018
E. V. Makoveeva, D. V. Alexandrov
It is well-known that the phase transition processes in metastable systems occur in a large variety of natural phenomena, laboratory experiments, and industrial production. In the case of substantial metastability degrees (supercooling or supersaturation in cases of supercooled liquids or supersaturated solutions), these processes are frequently accompanied by nucleation of newly born solid particles, which evolve with time and thus release the latent heat of solidification (or absorb the dissolved impurities) and reduce the system metastability. Nucleation and growth of crystals in metastable melts, the evolution of ice crystals in supercooled water solutions and production of food and specialty chemicals in crystallizers may be mentioned as examples of such processes [1–5].
Prediction of viscosity behavior in oxide glass materials using cation fingerprints with artificial neural networks
Published in Science and Technology of Advanced Materials, 2020
Jaekyun Hwang, Yuta Tanaka, Seiichiro Ishino, Satoshi Watanabe
A glass is an amorphous solid-state material obtained from rapid cooling from the high-temperature liquid state to a temperature below the glass transition temperature (). The rapid cooling suppresses crystallization and causes a supercooled liquid state. The supercooled liquid becomes more viscous as the temperature is lowered. Understanding the behavior of its viscosity is important in the case of glass materials, and many studies have been conducted to obtain this [1–6].