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 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.     

Preparation and Properties of Silver Borate Glasses

Silver borate Basses containing 0 to 30 mol% Ag₂O were formed. Properties measured include density, thermal expansion coefficient, glass transformation and dilatometric softening temperatures, transformation-range viscosity, dc electrical conductivity, and helium permeability and diffusivity. Optical spectroscopy revealed that the color of these glasses results from absorption bands at ∼407, ∼310, and ∼250 nm. Each band increased in intensity as the silver oxide content of the glass was increased. The properties of these glasses were consistent with the structural model currently used to describe the structure of alkali borate glasses. No evidence for the existence of phase separation was found for the conditions of the present study.     

Thermal Expansion of Alkali Borate Glasses

The thermal expansion behavior of lithium, sodium, potassium, and rubidium borate glasses was measured. The results indicate that the "borate anomaly" in the thermal expansion coefficient occurs at ∼20 mol% alkali oxide. A maximum in the glass transformation and dilatometric softening temperatures also occurs at ∼27 mol% alkali oxide. No evidence for phase separation was observed in this study. These effects are related to the structural changes reported for these glasses by Bray and coworkers.     

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.     

Viscosity and Thermal Expansion of Mixed-Alkali Borate Glasses

Transformation-range viscosity and thermal expansion measurements were made for five series (Li-Na, Li-K, Li-Cs, Na-Cs, and K-Rb) of mixed-alkali borate glasses containing 30 mol% total alkali oxide. In each case, negative deviations from additivity were observed in the isokom and glass transformation temperatures. Positive deviations from additivity were observed in the thermal expansion coefficients for the Li-Na, Li-K, and K-Rb glasses, while the Li-Cs and Na-Cs glasses exhibited negative deviations. Maximization of the deviation from additivity in the viscosity and glass transformation temperatures occurred when the radius ratio of the two alkali ions was approximately 1.7 to 1.8. Combination of the results of this study with those of earlier studies indicates that the deviations from additivity observed for these properties are independent of the identity of the glass former.     

Properties and Structure of Lanthanum Borate Glasses

Glass formation limits were determined for the lanthanum borate glasses. Stable immiscibility prevents the formation of clear glasses over the range 0 to 20 mol% La₂O₃, but excellent quality glasses could be formed between 20 and 28 mol% La₂O₃. Data are reported for the density, refractive index, thermal expansion coefficient, glass transformation and dilatometric softening temperatures, transformation range viscosity, helium permeability, and chemical durability of these glasses. A limited Raman and infrared spectroscopy study suggests that lanthanum plays a similar structural role in these glasses and in the related crystals.     

Viscosity and Thermal Expansion of Mixed-Alkali Sodium-Potassium Borate Glasses

The transformation-range viscosity and thermal expansion be-havior of sodium-potassium borate glasses were studied. The results indicate that negative deviations from additivity in the viscosity of these glasses are a function of the Na²O to K²O ratio and that the magnitude of these deviations increases with alkali oxide content. The thermal expansion coefficient exhibits a maximum deviation from additivity as a function of the Na²o to K²O ratio. The magnitude of this deviation increases with increasing total alkali oxide content. The results indicate that there is little, if any, interaction between the factors which lead to the mixed-alkali effect and the changes in the structure of the vitreous network which occur as the alkali oxide content of the glasses increases.     

Structural Interpretation of the Results of Investigations into the Influence of Residual Water on the Properties of One-Alkali Borate Glasses

The results obtained in earlier investigations into the influence of water on the viscosity, thermal expansion coefficients, structural relaxation parameters, and fragility parameters of one-alkali borate glasses are analyzed, and schemes of the interaction of water with the glass network are proposed. The variations observed in the properties of glasses are explained in terms of possible changes in the ratio between different borate groups in the structure of the glass with a change in its composition.     

Influence of water on the structure and kinetics of structural relaxation in sodium borate glasses

The influence of the water content on the microinhomogeneous structure of sodium borate glasses containing 2.5 and 5.0 mol % Na₂O and on the kinetics of structural relaxation in vitreous boron oxide and sodium borate glasses is studied by the small-angle X-ray scattering (SAXS) technique. It is demonstrated that an increase in the water content brings about an increase in the size of the inhomogeneity regions and a decrease in the mean square of the difference between the electron densities 〈(Δρ)²〉 for the microinhomogeneous structure. The inference is made that water has a catalytic effect on the aggregation of alkali borate structural units. The kinetic dependence of the intensity of small-angle X-ray scattering by thermal density fluctuations is described by the Kohlrausch equation. The exponent β in the Kohlrausch equation is close to 1.0 for “dry” glasses and decreases to 0.5 for glasses containing 0.7–1.0 mol % H₂O.     

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.     

Transformation Range Behavior of Lithium Galliosilicate Glasses

The transformation range viscosity and thermal expansion behavior of lithium galliosilicate glasses were studied. The glass transformation and dilatometric softening temperatures exhibit maxima at gallium to lithium ratios of somewhat greater than one. Similar behavior was observed for the transformation range viscosity. The effect of phase separation on the dilatometric softening temperature is discussed in detail. These results are compared with those obtained for lithium alumino-silicate glasses in other studies. The results are discussed in terms of the structural role of aluminum and gallium in the glass network.     

Structure of Borate Glasses

Anomalous thermal expansion and other properties of borate glasses have previously been given a structural explanation by Abe. This explanation is here reinterpreted and revised in terms of the structon theory of Huggins. In agreement with Warren, it is postulated that, in glasses containing, in addition to boric oxide, small relative amounts of an alkali or alkaline-earth oxide, some of the boron atoms are surrounded by four oxygen atoms and all the oxygen atoms bridge between two boron atoms. At concentrations beyond that of the thermal expansion minimum, some oxygens are assumed to have only one boron neighbor. These ideas are formulated quantitatively and are used to interpret pertinent experimental data. From the concentrations where the property-composition curves show breaks, conclusions may be drawn as to the average number of oxygens surrounding each metal atom.     

Structure-Property Relations in Barium Borate Glasses from Raman Scattering Data

Glasses in the xBaO-(100 ? x)B₂O₃ system (x = 16–50 mol %) are investigated by Raman spectroscopy. The spectral forms of stoichiometric groupings are separated from the experimental Raman spectra. The diagram of the content of these groupings in glasses is constructed. The diagram obtained makes it possible to calculate the densities, refractive indices, temperature coefficients of linear expansion, and fractions of four-fold-coordinated boron atoms with the use of the experimentally determined partial properties of the groupings. It is revealed that the dependences of the boson peak intensity, the boson peak frequency, and the glass transition temperature on the composition of glasses in the barium borate system correlate with each other.     

The influence of water on the structure and glass transition of sodium borate supercooled liquids from the small-angle X-ray scattering data

Sodium borate glasses containing 5.5, 15, and 25 mol % Na₂O are synthesized under different conditions (different temperatures and times of heat treatment, treatment under vacuum) and studied by the small-angle X-ray scattering (SAXS) technique. The temperatures of the glass transition and the transition from the supercooled liquid state to the noncrystalline solid state are determined from the temperature dependences of the SAXS intensity. It is revealed that a decrease in the water content leads to an increase in the glass transition temperatures and to an increase in the SAXS intensity in the case of glasses containing 15 and 25 mol %. It is assumed that this behavior can be associated with the increase in the isothermal compressibility.     

Dependence of the Dilatometric Properties of Glasses on Their Structure: I. Borate,Aluminoborate, and Lead-Containing Glasses

The dependences of the dilatometric properties on the hypothetical structure for a number of borate, aluminoborate, and lead-containing glasses are analyzed over a wide range of compositions. Special attention is focused on the specific features observed in the behavior of the structural temperature coefficient of linear expansion. It is demonstrated that the revealed regularities allow the justified inferences regarding the structural transformations of glasses with variations in their composition.     

Manganous-Manganic Equilibrium in Alkali Borate Glasses

The manganous-manganic equilibrium was studied in potassium, sodium, and lithium borate glasses. The glasses were analyzed chemically for total and trivalent manganese. The manganese equilibrium shifts more toward the oxidized state when the alkali concentration in the glass is increased and/or when the molar equivalent of lithia is replaced by soda and soda is replaced by potash. A linear relation between log (Mn³⁺/Mn²⁺) and mole percent alkali oxide was observed. Straight lines were obtained for lithium, sodium, and potassium borates. The disadvantages of using a concentration equilibrium constant where the glass composition is varied are discussed.     

On the Structure of Low-Alkali Rubidium and Cesium Borate Glasses and Melts

The structure of low-alkali rubidium and cesium borate glasses and melts at temperatures from the glass transition points of the initial glasses to 1000–1100°C is studied by the small-angle X-ray scattering (SAXS) technique. It is found that, over the entire temperature range under investigation, the melts have a microinhomogeneous structure. A decrease in the melt temperature leads to an increase in the sizes of inhomogeneity regions, which is caused by the Ostwald ripening. The sizes remain unchanged at temperatures in the vicinity of the liquidus temperature (in the range of approximately ±50 K). The temperature dependences of the inhomogeneity density are determined at low temperatures. It is demonstrated that, at temperatures close to the glass transition point of the inhomogeneity regions, their density decreases with a decrease in the temperature.     

Interaction of γ-rays with Some Alkali-Alkaline-Earth Borate Glasses Containing Chromium

The change in the visible spectra of some irradiated ternary borate glasses containing chromium has been studied by increasing the γ-ray doses with changing alkali content or increasing chromium concentration. In the glass without chromium, the γ-rays induce two absorption bands which are attributed to the formation of positive hole centers, whereas in the glass containing chromium at least three absorption bands are observed. The results showed that the visible absorption bands before and after γ-ray irradiation exhibited changes with the radiation dose and/or the chemical composition of the glass. The response of the glasses to γ irradiation is related to the creation of defect color centers, the approach of a saturation condition, and the possible photochemical effect on the transition metal.     

The effect of alkali metal oxide on the properties of borosilicate fireproof glass: Structure,thermal properties,viscosity, chemical stability

The purpose of the current work was to research the effect of alkali metal oxide on the structure, thermal properties, viscosity and chemical stability in the glass system (R₂O–CaO–B₂O₃–SiO₂) systematically. Because the glass would emulsify when Li₂O was added to the glass batch, this article did not discuss Li₂O. The results showed that when the amount of Na₂O was less than 4 mol.%, there was a higher interconnectivity of borate and silicate sub-networks in glass, as more mixed Si–O–B bonds were present in glass. The glass samples exhibited excellent thermal properties and chemical stabilities. As the amount of Na₂O exceeded 4 mol.%, the interconnectivity of borate and silicate sub-networks was weakened. The thermal properties and chemical stabilities of the glass samples were reduced. The connectivity of the silicate sub-network was weakened slightly as the Na/K ratio varied, and the coefficient of thermal expansion (CTE) of the glass samples gradually increased, and the resistance to thermal shock (RTS) value gradually decreased. Moreover, the viscosity of the glass samples decreased with the ratio of Na/Si and Na/K increased.