Advanced Materials Research Vols. 39-40

Abstract: Multicomponent (Ti, Zr, Al, B) silicon oxycarbide glasses and nanocomposite materials were derived after pyrolysis of gel hybrid structures in N2 atmosphere. MTES (methyltriethoxysilane) and PDMS (polydimethylsiloxane) were used as precursors for introducing “organic” SiO2. Transformation of the hybrid structure into oxycarbide was followed by SEM, FTIR, 29Si CP MAS NMR, BET analysis. Silicon oxycarbide structure is strongly influenced from the concentration and nature of modifying metal atom.

Abstract: High temperature viscosity and density of glass melts, glass transition temperature, and thermal expansion coefficient of glasses from the system MgO-CaO-B2O3-Al2O3-SiO2 with composition close to the E-glass were measured and interpreted with respect to the effect of CaO and MgO content on their physical properties. The Andrade model was applied for description of the temperature dependence of the glass viscosity within studied temperature range. The regression formaulae describing the compositional dependence of the viscosity points T2 = T( η = 100 dPa.s), T3 = T( η = 1000 dPa.s), the glass transition temperature, Tg, thermal expansion coefficient of glass, αg , and of the viscous flow activation energy, Ea, were proposed.

Abstract: This work aims to explore possible applications of the ab initio molecular dynamics (MD) in modeling of the soda-lime-silica (NCS) glass and melt doped with admixtures. Preparation of the basic glass (15.8 wt.% Na2O, 10.5 wt.% CaO, and 73.7 wt.% SiO2) by the MD simulation from scratch is described. The structure analysis of the NCS glass is presented in the form of total and partial radial distribution functions (RDF), coordination numbers, and fractions of Qn units. The reasonable first neighbor distances were obtained, even if a rather small basis set of electronic wavefunctions and softer pseudopotentials for atomic core regions were applied. All major discrepancies in the first neighbor distances can be easily explained, and the results can be improved if needed. The Qn distribution shows higher disproportionation of Q3 than NMR and Raman experimental data, however, it is lower than previous classical MD simulations.

Abstract: We present numerical studies of possible modifications of SiOH groups in “wet” SiO2 glass with 193 nm laser irradiation. We focus on structural changes associated with two conformations: (i) two nearby hydrogen bonded SiOH groups, and (ii) oxygen triclusters, i.e. bridging oxygen forming a third covalent bond with a hydrogen atom. The energies of these two systems and the activation barrier of thermal relaxation between them identify the latter conformation as a candidate for a product formed under 193 nm laser exposure, when we consider the former conformation as an initial state. We investigate the effects of local volume changes associated with the changes in conformation and find it has non-negligible effect on the index of refraction. These conformational changes thus appear able to contribute to the permanent changes in index of refraction and absorption of the glass after UV irradiation.

Abstract: The ab-initio molecular dynamics (MD) calculations of the yttrium - aluminate binary system 23Y2O3·77Al2O3 were performed with help of the Vienna ab-initio simulation package VASP. The thermodynamic model (TD) of glasses of the studied binary system was constructed. Both the Y/O and Al/O coordination numbers calculated from the partial pair radial distribution function (PP RDF) obtained for MD simulated melt at the temperature of 2500 K were significantly lower than the corresponding coordination numbers obtained from the TD model. The published neutron diffraction and X-ray diffraction studies give the results close to the results of the present ab-initio MD simulation. The TD model resulted in higher Al/O and Y/O coordination when compared with experimental results.

Abstract: The glasses of the series (1-x)[0.5ZnO-0.1B2O3-0.4P2O5]-xMoO3 with 0 ≤ x ≤ 0.6 were prepared by slow cooling of the melt. These glasses were characterized by the measurements of density, molar volume, chemical durability, glass transition temperature and the thermal expansion coefficient. The density and molar volume of the glasses increase with increasing MoO3 content. All glasses crystallize on heating and their crystallization temperature decreases with increasing MoO3 content. An incorporation of MoO3 into the parent borophosphate glass results in a substantial decrease of their glass transition temperature and also of their chemical durability. The observed changes were ascribed to the gradual replacement of stronger P-O-P bonds by weaker Mo- O-P and Mo-O-Mo bonds. ESR spectra revealed the presence of Mo5+ ions responsible for the blue colour of the glasses and the relative ratio of Mo5+/Mototal decreases with increasing MoO3 content.

Abstract: 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.

Abstract: Dynamic processes in glassy materials with ionic conductivity are extremely important since the ion transport significantly affects their practical performance. Conductivity measurement and dielectric relaxation spectroscopy are powerful techniques that reflect the essential features of the transport and relaxational dynamics of the mobile ions that encounter different kinds of site and ionic hopping motion connected with charge mobility. Acoustic spectroscopy is another technique for the study of relaxations in glasses. In this contribution the acoustic and electrical relaxation processes are compared on identical ionic phosphate glasses of the systems CuI-CuBr-Cu2O-P2O5 and CuI-CuBr-Cu2O-P2O5-MoO3 containing Cu+ ions. The acoustic attenuation spectra indicate various relaxation processes and at least two conductivity regimes of transport mechanisms were observed. Both the acoustic and electrical measured data were analyzed using suitable model representations.

Abstract: A general condition of transformation of a liquid or a crystal into a glass according to results of measurements of specific heats and transition heats is the drop in the internal pressure to negative values.

Abstract: The new conception of the polymeric-polymorphoid structure of glass and glassforming liquid of individual chemical substances (ICS) is presented. The analysis of numerous data of X-ray diffractometry, DSC, Raman spectroscopy etc. shows that such glassforming ICS as SiO2, GeO2. H2O, Se, GeS2, GeSe2, As2S3, AsSe, BeCl2 and other are the copolymers of the structural fragments (polymorphoids) having no translation symmetry of two (or more) polymorphous modifications (PM) of these substances. The physicochemical essence of glass transition process is discussed.