Yu. K. Startsev

Electrical conductivity and structure of glasses in the Na2O-Na2S-P2O5 and Na2S-P2S5 systems

The glasses, in which oxygen was partially replaced with sulfur, have been synthesized in the Na2O-P2O5-Na2S system. The chemical and chromatographic analyses of the glasses synthesized have been performed. The temperature-concentration dependences of electrical conductivity of the glasses have been studied over a wide temperature range; the glass transition temperatures and the nature of charge carriers have been determined. The IR spectra and Raman spectra have been recorded at room temperature; the density and microhardness of the glasses and ultrasound velocity have been measured. A comparison of the electrical conductivities of the investigated glasses with those of the earlier studied glasses in the Na2O-P2O5 system has shown their fair coincidence. The introduction of sodium sulfide into the Na2O-P2O5 system is accompanied by an approximately threefold increase in electrical conductivity, although the concentrations of charge carriers (sodium ions) in the glasses amount to ∼17 and ∼26 mmol/cm3, respectively. The rise in electrical conductivity has been assumed to be caused by the increase in the degree of dissociation of polar structural chemical units including sulfide ions and by the higher mobility of sodium ions in the oxygen-free matrix.

Specific Features of Changes in the Properties of One- and Two-Alkali Borate Glasses Containing Water: I. Viscosity, Thermal Expansion, and Kinetics of Structural Relaxation in Binary Alkali Borate Glasses

Alkali borate glasses with different contents of residual water are prepared by varying the synthesis conditions. The temperature dependences of the viscosity and thermal expansion of glasses are obtained. The structural relaxation parameters are calculated from the hysteresis dilatometric curves measured. The water content is determined using the IR absorption spectra in the range of stretching vibrations of hydroxyl groups at room temperature. It is found that an increase in the water concentration in alkali borate glasses leads to a decrease in the viscosity. The character of variations in the viscosity logarithm with a change in the water content depends on the alkali cation concentration. The glass transition temperatures determined from the dilatometric curves for all the studied glasses decrease with an increase in the water content. As the water concentration increases, the thermal expansion coefficient (above and below the glass transition range) and the degree of fragility decrease for glasses containing 25 mol % Na2O, increase for glasses with an alkali oxide content of 15 mol %, and remain virtually unchanged for glasses involving 5.5 mol % Na2O. A change in the water content in the concentration range under investigation does not affect the structural relaxation parameters.

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.

Specific Features of Changes in the Properties of One- and Two-Alkali Borate Glasses Containing Water: III. Thermal Expansion and the Structural and Mechanical Relaxation Parameters of Two-Alkali Borate Glasses

The thermal expansion and stress relaxation in mixed alkali borate glasses containing lithium, sodium, and potassium oxides with a total alkali oxide content of 15 mol % are measured on an inclined quartz dilatometer and a relaxometer. The experimental data obtained are used to determine the thermal expansion coefficients and the structural and mechanical relaxation parameters. No deviations from the additivity are found in the concentration dependences of the thermal expansion coefficient and the calculated parameters determining the width of the spectra of the structural and stress relaxation times. The IR absorption spectra of the studied glasses are recorded in the range of stretching vibrations of hydroxyl groups. Analysis of the IR spectra makes it possible to assume that the content of residual water in the structure of borate glasses affects the manifestation of the mixed alkali effect in the properties of these glasses.

Specific Features of Changes in the Properties of One- and Two-Alkali Borate Glasses Containing Water: II. Viscosity of Mixed Alkali Borate Glasses

The temperature dependences of the viscosity for mixed alkali borate glasses containing lithium, sodium, and potassium oxides with a total alkali oxide content of 15 mol % are measured by the central rod bending method in the temperature range corresponding to a change in the viscosity from 1010 to 1013 dPa s. Analysis of the results obtained and the data available in the literature demonstrates that the content of residual structural water affects the manifestation of the mixed alkali effect in the viscosity of borate glasses. No significant change in the degree of fragility is found upon replacement of one alkali oxide by another alkali oxide in the studied glasses.

Modeling the Combined Effect of Temperature and Composition on the Properties of a Glass Plate

The alkali-metal-ion exchange between glass surfaces and molten salts, widely used to strengthen glass and produce graded materials, is analyzed in terms of relaxation theory. A model is proposed which adequately describes stress development and relaxation in the glass during ion exchange and subsequent heat treatment. The model calculations are compared with the present and earlier experimental data. The model is shown to reflect the salient features of the temperature dependences and depth profiles of glass properties in the modified surface layer, in spite of the relatively small number of model parameters, some of which are derived from experiment.

Influence of Residual Water in a Glass on Its Rheological and Relaxation Properties (by the Example of a 5Na2O · 95B2O3Glass)

Glasses of the 5Na2O · 95B2O3(mol %) composition synthesized at a temperature of 1100°C for 180 and 20 min are studied. The temperature dependences of the viscosity and the thermal expansion of glasses are obtained. The thermal expansion coefficients and glass transition temperatures of the studied glasses are determined, and the parameters of structural relaxation (the constant characterizing the width of the spectrum of relaxation times, the relaxation modulus equal to the ratio of the viscosity to the relaxation time, and the relaxation time at zero reciprocal temperature) are calculated from the dilatometric curves measured at temperatures close to the glass transition range. The water content in the studied glasses is estimated by comparing the obtained dependence of the viscosity on the water content with the data available in the literature for glasses of a similar composition. The assumption is made that the structural relaxation time in sodium borate glass decreases with an increase in the water content.

Specific Features in the Investigation of Stress Relaxation Kinetics in Glasses with a Relaxometer

An improved experimental technique of investigating the mechanical relaxation in inorganic glasses is described. The temperature and concentration dependences of the stress relaxation times and their spectra are analyzed for commercial glasses. It is demonstrated that the results obtained make it possible to simulate stresses in glasses and their seals with other materials, including other glasses. The kinetics of stress relaxation in commercial sheet glasses is examined. It is emphasized that the results obtained can be affected by the composition of the gas mixture used for preparing samples in the flame of a burner.

A check of applicability of the relaxation model of annealing to calculation of stresses in low-temperature annealing of a glass-molybdenum seal

The previously developed relaxation model for annealing of glass seals with other materials has been applied widely. It remains unclear whether there are a specific low temperature and very long-term isothermal treatments at which this simple model ceases to work correctly and requires complication or even revision. With the aim to determine the minimum fictive temperature at which the relaxation model of annealing of glass seal with an elastic material is still applicable, the stresses in the sandwich S52-2 glass–molybdenum seals are measured at different stabilization temperatures. The experimental temperature–time dependences of the stresses are compared with those calculated using the relaxation model of seal annealing. The use of this relatively simple model leads to a quite satisfactory agreement (even if not identical at all the temperatures) in the range from the glass transition temperature to 380°C for stabilization durations as long as 81 days. This treatment duration makes it possible to reach a structural temperature of 434°C, which is considerably lower than the structural temperature (525°C) obtained upon simple cooling of glass at a rate of 3 K/min.

Strength of display glass

The strength of dual-display glass surfaces 0.64 mm (Corning 1737 glass) and 0.70 mm (Eagle2000 glass) thick is measured in the initial state and after annealing. Large dispersion of the strength of the glass before and after annealing is found. It is suggested that the low values of the strength are caused by the adverse conditions of storing and handling glass samples.