Article
Glass formation in amorphous SiO2 as a percolation phase transition in a system of network defects
JETP Letters (Impact Factor: 1.52). 01/2004; 79(12):632634. DOI: 10.1134/1.1790021

Article: Thermodynamic parameters of bonds in glassy materials from viscositytemperature relationships
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ABSTRACT: Doremus's model of viscosity assumes that viscous flow in amorphous materials is mediated by broken bonds (configurons). The resulting equation contains four coefficients, which are directly related to the entropies and enthalpies of formation and motion of the configurons. Thus by fitting this viscosity equation to experimental viscosity data these enthalpy and entropy terms can be obtained. The nonlinear nature of the equation obtained means that the fitting process is nontrivial. A genetic algorithm based approach has been developed to fit the equation to experimental viscosity data for a number of glassy materials, including SiO2, GeO2, B2O3, anorthite, diopside, xNa2O–(1x)SiO2, xPbO–(1x)SiO2, sodalimesilica glasses, salol, and αphenylocresol. Excellent fits of the equation to the viscosity data were obtained over the entire temperature range. The fitting parameters were used to quantitatively determine the enthalpies and entropies of formation and motion of configurons in the analysed systems and the activation energies for flow at high and low temperatures as well as fragility ratios using the Doremus criterion for fragility. A direct anticorrelation between fragility ratio and configuron percolation threshold, which determines the glass transition temperature in the analysed materials, was found.Journal of Physics Condensed Matter 01/2007; · 2.22 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: The paper presents an algorithm for calculating the threedimensional VoronoiDelaunay tessellation for an ensemble of spheres of different radii (additivelyweighted Voronoi diagram). Data structure and output of the algorithm is oriented toward the exploration of the voids between the spheres. The main geometric construct that we develop is the Voronoi Snetwork (the network of vertices and edges of the Voronoi regions determined in relation to the surfaces of the spheres). General scheme of the algorithm and the key points of its realization are discussed. The principle of the algorithm is that for each determined site of the network we find its neighbor sites. Thus, starting from a known site of the network, we sequentially find the whole network. The starting site of the network is easily determined based on certain considerations. Geometric properties of ensembles of spheres of different radii are discussed, the conditions of applicability and limitations of the algorithm are indicated. The algorithm is capable of working with a wide variety of physical models, which may be represented as sets of spheres, including computer models of complex molecular systems. Emphasis was placed on the issue of increasing the efficiency of algorithm to work with large models (tens of thousands of atoms). It was demonstrated that the experimental CPU time increases linearly with the number of atoms in the system, O(n).Journal of Computational Chemistry 12/2006; 27(14):167692. · 3.84 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: Glassy wasteforms currently being used for highlevel radioactive waste (HLW) as well as for low and intermediatelevel radioactive waste (LILW) immobilization are discussed and their most important parameters are examined, along with a brief description of waste vitrification technology currently used worldwide. Recent developments in advanced nuclear wasteforms are described such as polyphase glass composite materials (GCMs) with higher versatility and waste loading. Aqueous performance of glassy materials is analyzed with a detailed analysis of the role of ion exchange and hydrolysis, and performance of irradiated glasses.Metallurgical and Materials Transactions A 01/2011; 42(4):837851. · 1.73 Impact Factor
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