Oxynitride Glasses

Oxynitride glasses are grain boundary phases within silicon nitride ceramics. The desire to understand their nature led to various investigations on oxynitride glass formation, structure, properties, and crystallization. This paper provides a review of oxynitride glasses and outlines the effect of glass chemistry, including nitrogen contents and cation ratios, on properties such as glass transition temperature, Young's modulus, and viscosity and relates this to structural features within the glass. A short outline of crystallization of oxynitride glasses to form glass–ceramics is presented.     

Effect of Nitriding on Electrolysis and Devitrification of High-Silica Glasses

Devitrification occurs near the cathode when reconstructed high-silica glasses and fused quartz undergo electrolysis at 900°C. The crystalline phase is cristobalite and results from a concentration of alkali ions. Subsequent and more superficial crystallization around the alkali-rich spot is caused by interaction of the glass with alkali vapors coming from the central spot. The degree of devitrification increases with the alkali content of the glass. Devitrification at constant alkali level can be reduced in reconstructed glasses by nitriding the porous glass with ammonia at a high temperature before consolidation. Devitrification decreases and viscosity and electrical resistivity increase as the nitriding temperature increases 500° to 1000°C. Nitrided glasses are more resistant to electrolytically induced devitrification than is fused quartz.     

Liquidus Prediction in Multicomponent Lithium Alumosilicate Glasses

An empirical nine-parameter linear mixing model was developed to estimate the liquidus temperature of zirconia-bearing technical lithium alumosilicate glasses that contain up to 12 major components. The model covers glasses that are suitable as precursor glasses for β-quartz or β-spodumene-type glass ceramics with low coefficients of thermal expansion. Molar coefficients of liquidus temperatures are provided for each component. A self-consistency test results in a standard deviation between predicted and measured liquidus temperatures of 7.5°C, within a range of approximately 200°C and for a typical experimental error of 10°C.     

The Role of Vibrations of Medium-Range Order Clusters in Thermal Conduction of Materials with a Disordered Structure

A microscopic model that provides a satisfactory explanation of the temperature dependence of the thermal conductivity coefficient for dielectric glasses in the temperature range above the plateau is proposed for the first time. According to this model, the transfer of thermal perturbations occurs through harmonic interaction of oscillators localized at medium-range order clusters with hinged bonds. It is demonstrated that the interaction coefficient of these clusters depends on the overlap integral of the spectral lines attributed to natural vibrations of the clusters, whereas the temperature behavior of the thermal conductivity coefficient is governed by the temperature evolution of the widths of the vibrational lines. With due regard for the results of investigations into the broadening of the vibrational lines, the temperature dependence of the thermal conductivity coefficient is calculated in the range 10–500 K. The calculated curve is in good agreement with the experimental data. The proposed model accounts for the low thermal conductivity of glasses in the temperature range under consideration.     

Measurement of Stress-Optical Coefficient and Rate of Stress Release in Commercial Soda-Lime Glasses

A method is described for measuring the stress-birefringence properties of soda-lime glasses in the range 23° to 650°C. Data on three glasses show that the stress-optical coefficient increases slowly with temperature, reaching a definite maximum in the range 570° to 590°C. The same apparatus was used to measure the rate of stress release in two of these glasses. Data obtained under thermal equilibrium conditions can be represented by equations that suggest that two or more concurrent mechanisms are involved in stress release in these glasses within the viscosity range log 12 to log 14.5 (a rapid one of 0.4 to 10 minutes in duration and a slow one of 2 to 60 minutes).     

Thermal Expansion and Glass Transition Temperature of Calcium Borate and Calcium Aluminoborate Glasses

The thermal expansion (the temperature coefficients of linear expansion for solid glasses and the structural temperature coefficients of linear expansion) and the glass transition temperatures are studied for glasses in the CaO–B₂O₃ and CaO–B₂O₃–Al₂O₃ systems. The results obtained are compared with the available data for barium borate and barium aluminoborate glasses. The revealed dependences are interpreted within the concepts of the borate glass structure.     

Dependence of Sodium Ion Mobility upon Melt Atmosphere in GeO2 Glasses

Sodium ion mobilities in high-purity GeO₂ glasses were examined for glasses melted under varying oxygen partial pressure. Increased oxygen partial pressure during melting increases the sodium ion mobility for glasses melted at the same temperature. This effect is attributed to the effect of oxygen partial pressure upon intrinsic defect concentrations within the glass.     

Substructure Classification of Silicate Glasses

It is proposed that silicate glasses be classified in terms of substructures uniquely identified with primary crystallization phases. All glasses having compositions within the ranges or areas covered by a given primary crystallization phase field should constitute a separate glass type or class. This classification is definitive for properties determined principally by the silica frameworks or substructures. Such composition-property relations can be reproduced by independent investigators if the properties are measured under temperature equilibrium conditions.     

Glass Formation and Polyamorphism in Rare-Earth Oxide–Aluminum Oxide Compositions

We report formation of single- and two-phase glasses from rare-earth oxide–alumina materials. Liquids with the Y₃Al₅O₁₂ and Er₃Al₅O₁₂ compositions underwent a liquid–liquid phase transition which resulted in glasses with a cloudy appearance due to spheroids of one glass in a matrix of a second glass. The two glasses were isocompositional within the limits of experimental error. Clear, brilliant, single-phase glasses were obtained from La₃Al₅O₁₂, ErLaYAl₅O₁₂, and compositions containing ≥5 mol% La₂O₃ substituted for the other rare-earth oxides. Formation of two glasses is attributed to nucleation and growth of the second liquid at a temperature below the equilibrium liquid–liquid transition temperature. Addition of lanthanum depresses the phase transition temperature below the glass transition temperature and the liquid–liquid phase transition is not observed. The results are discussed in the context of first-order liquid–liquid phase transitions (polyamorphism) and formation of single-phase glass from liquids that contain a high proportion of 4-coordinate aluminum ions.     

Electrical conductivity of CuI-Cu<Subscript>2</Subscript>Se-As<Subscript>2</Subscript>Se<Subscript>3</Subscript> chalcogenide films prepared by chemical deposition

The electrical conductivity of CuI-Cu₂Se-As₂Se₃ chalcogenide semiconductor films prepared through the chemical deposition from an organic solvent has been investigated as a function of the temperature and composition of the films. It has been established that the electrical properties of the chalcogenide glasses and related films are characterized by the same values within the limits of the experimental error. This result is in agreement with the model of dissolution of vitreous semiconductors in organic bases (amines), according to which the main properties of bulk (cast) chalcogenide glasses are retained in films prepared from these glasses.     

Formation of surface structures in thermally polished glasses (a review)

Present-day views are analyzed on the types of structural groupings present on the surface of commerical glasses manufactured by the float process on a tin melt. Consideration is given to the changes that occur in the qualitative and quantitative composition of the structural groups on the surface when the just-drawn glass is cooled within the drawing and annealing temperature, ranges, and upon further cooling to room temperature. The results reported in the paper can be used in developing optimal methods to identify the surface structure of commercial glasses with various reagents. Translated from Steklo i Keramika, No. 2, pp. 8–12, February, 1997.     

Nonexponential Dynamics in Porous Glasses

The dielectric relaxation properties of porous glasses prepared from sodium borosilicate glasses are studied by dielectric spectroscopy over a wide range of frequencies (20 Hz–1 MHz) and temperatures (–100–300°C). The dielectric behavior reflecting the geometric disorder is analyzed within the models describing the non-Debye slowly damped dynamics. It is found that the dielectric response is very sensitive to microstructural and mesostructural features of the porous matrix and the properties of a material filling pores. The response contains information on the dynamics of water molecules in pores, which accounts for the interaction of these molecules with the pore surface.     

Lead Galliate Glasses

Glasses have been formed in the binary system PbO–Ga₂O₃ within the compositional range extending from 60 to 80 mol% PbO. These glasses exhibit infrared cutoff values near 7.75 μm. The glasses are orange-red as a result of a cutoff in visible transmission near 500 nm. The glass transformation temperature decreases with increasing PbO concentration, whereas the thermal-expansion coefficient and density increase with increasing PbO content. Glasses containing 70 to 75 mol% PbO are good glass formers, with little tendency to crystallize, and exhibit good weathering behavior on exposure to normal atmosphere.     

Thermopower of Semiconducting Glasses in the V2O5-P2O5 and V2O5-CdS-P2O5 Systems

Vanadium phosphate and cadmium sulfide-doped vanadium phosphate glasses containing up to 50–80 mol % V₂O₅ are prepared. The thermopower of these glasses is measured in the temperature range 303–473 K. The activation energies are determined from the linear dependences of the thermopower S and the logarithm of the conductivity logσ on the reciprocal of the temperature 1/T. It is demonstrated that the activation energies obtained by two methods differ from each other. The difference between the activation energies is referred to as the hopping energy Δ. The possibility of an Anderson metal-insulator transition occurring is examined. It is revealed that similar transitions are not observed in the glasses under investigation. The data obtained are analyzed within the small-polaron hopping model describing the electron conduction. It is established that hopping conduction proceeds over localized states in the tail of the density of states. All the glasses are characterized by electron conduction. Original Russian Text Copyright ? 2005 by Fizika i Khimiya Stekla, Khairnar, Yawale, Pakade.     

Mössbauer Spectroscopy of Borate Glasses Containing Divalent Europium Ions

Borate glasses containing 0.99–30.0 mol% EuO have been prepared under a reducing atmosphere and ¹⁵¹Eu Mössbauer effect measurements have been carried out at room temperature in order to examine the chemical state of Eu²⁺ ions in these glasses. Mössbauer spectra indicate that most of the europium ions are present as the divalent oxidation state. In dilute Eu²⁺-containing borate glasses, spectra are split due to paramagnetic hyperfine interactions in the glasses with low and high sodium contents. In concentrated Eu²⁺-containing borate glasses, line broadening results from the contribution of quadrupole splitting due to asymmetrical oxygen coordination around Eu²⁺ and the contribution of inhomogeneous broadening due to site-to-site variation. The compositional dependence of isomer shift and quadrupole interaction parameter can be related to the structural changes in the borate glass. The variation of the isomer shift has a good correlation with the optical basicity of glass, and the trend can be explained in terms of the covalent admixture with 6 s character. The Eu-O bond in the borate glasses is more ionic than that in EuTiO₃ and EuZrO₃, where the oxygen coordination number for Eu²⁺ is 12. The average coordination number for Eu²⁺ is found to be 12 in all of the present glasses.     

A METHOD FOR MEASURING THE SOFTENING TEMPERATURE OF GLASSES1

For the purpose of measurement the softening point of glasses is defined as that temperature at which a uniform thread of glass .65 mm to 1 mm in diameter suspended in a vertical position in an electric furnace of specified characteristic will elongate at the rate of 1 mm per minute. The measurements on a given glass are reproducible to within 1 to 2°C. This method has been found useful as control of glass composition in melting units as well as a point of reference to distinguish between different glasses. Data are given showing the variation in softening point of a tank glass and a pot glass over an interval of time.     

Dissolution Rates of Silicate Glasses in Water at pH 7

Dissolution rates of different glasses in buffered solutions of constant pH of 7 were measured by weight change, profilometry, and ion implantation with Rutherford backscattering. Rates with different techniques agreed within experimental error. Natural obsidian glass dissolved most slowly, at a rate comparable with those of quartz and crystalline aluminosilicate minerals. Commercial soda–lime glass containing alumina dissolved slowly, at about the same rate as vitreous silica; soda–lime silicate glasses both commercial and laboratory without alumina dissolved much more rapidly. Pyrex borosilicate glass dissolved at a rate intermediate between those of soda–lime silicate glasses with and without alumina; at room temperature Pyrex borosilicate glass dissolved about 100 times faster than a commercial soda–lime glass containing alumina. We suggest that surface structure is the main factor determining the relative dissolution rates of silicate glasses. Glasses with transformed surface layers caused by hydration dissolve most rapidly; phase separation and openness of the glass structure are also important factors.     

VISCOSITY OF RECENT CONTAINER GLASS*

A high-temperature, concentric cylinder viscometer has been constructed and calibrated. The calibration checks within 1% that obtained by Lillie for a similar apparatus and provides further evidence of the high degree of reliability of this type of measurement. The contention of Washburn and Shelton that the calibration in such instruments is a function of the viscosity is shown to be false. Because four independent investigations have been unable to check this contention, it may now be regarded as spurious. A medium temperature-range fiber viscometer for measuring the viscosity of glass in the annealing range has also been constructed. It is shown that the Fulcher equation, log η=−A+B/T−T₀, fits the data obtained on the two instruments to within 0.5% for commercial soda-lime glasses. Complete viscosity data as a function of temperature are given for sixteen commercial container glasses, and the analyses are also included. These glasses show a wide range of viscosity.     

Effects of Viscosity and Stress Level on Rates of Stress Release in Soda-Lime, Potash-Barium, and Borosilicate Glasses

Previous work has suggested that two concurrent mechanisms act to relieve stresses in soda-lime commercial glasses in the viscosity range log 12 to log 14.5. The data were found to be best represented by a relation which indicated that the release of stress is the result of at least two distinct, but not necessarily independent, rate processes. The present paper shows stress release and viscosity data on two other types of glasses, namely, a potash-barium glass and a borosilicate. The data show that all three types of glass can be represented by similar equations and that the release of stress in glasses is related to both equilibrium temperature viscosities and delayed elasticity within the annealing zone.     

Technique for measuring the electric conductivity of glasses and melts over a wide temperature range covering the glass transition region

The technique for measuring the electric conductivity of glass-forming melts and glasses over a wide temperature range covering the glass transltion region is described in detail. The technique is based on the application of small-sized electrodes that provide the retention of their mutual arrangement in melts and glasses and prevent the appearance of mechanical stresses exceeding the ultimate strength of glasses. The potentialities of the proposed technique are illustrated by the measurement of the electric conductivity for several standard glasses. The coefficients of equations describing the temperature dependences of the electric conductivity above and below the glass transltion range are determined. The technique makes it possible to obtain the hysteresis loops of the electric conductivity at constant rates of cooling and the subsequent heating and also the temperature dependences of the first and second derivatives of the electric conductivity with respect to temperature.