Determination of Fictive Temperature of Soda-Lime Silicate Glass

Peak positions of silica structural bands, both in infrared absorption and reflection modes, were used earlier to measure the fictive temperature of silica glass. In the present study, the method was applied to determine the fictive temperatures of a soda-lime silicate glass. For the silicate glass, the IR absorption spectra produced a broad structural band which made the precise determination of peak position difficult, and only the IR reflection band was used. Equilibrium peak positions of ∼1056 cm⁻¹ IR band, due to Si-O stretching, were found to be directly correlated with the fictive temperature of the soda-lime silicate glass. The soda-lime glass exhibited an opposite dependence of the IR band position on the glass fictive temperature as compared to silica glass.     

Thermal Behavior of Silver in Ion-Exchanged Soda-Lime Glasses

The refractive index and the nonlinear optical properties of sodium silicate glass can be easily tailored by replacing the sodium with silver. However, the thermal responses of silver and the corresponding modifications of the silica (SiO₂) network in ion-exchanged glass under heating are still not clear. X-ray photoelectron spectroscopy has been used to study the in-situ behavior of silver and SiO₂networks on the surfaces of silver-ion-exchanged-content soda-lime glasses during heating and cooling processes under ultrahigh vacuum. Temperature-dependent concentration changes and oxidation states have been monitored. The results show that silver diffuses toward the surface, precipitates, and crystallizes during heating, and the total silver surface concentration is slowly increased during cooling. The concentration changes and binding-energy shifts of oxidized and neutral silver atoms, a new nonbridging oxygen species (NBO*), and a new silicon species (Si[a]) have been applied to deduce a disappropriation reaction mechanism of the Ag+ ion on the surface during annealing. The SiO2 network is modified at temperatures of <350°C to accommodate more silver on the surface and to balance the extra charge that is carried by the Ag+ ion. The fact that the SiO2 network polymerizes during annealing has been deduced from the results of the higher binding energies of Si 2_p and O 1s after annealing. This observation is of importance in optimizing the distribution of the ion-exchanged silver and in the formation of silver-metal colloids in glass networks.     

Indentation Behavior of Soda-Lime Silica Glass, Fused Silica, and Single-Crystal Quartz at Liquid Nitrogen Temperature

In an attempt to elucidate the processes involved in the formation of indentation impressions, Vickers hardness measurements have been made on soda-lime silica glass, fused silica, and crystalline quartz indented at room temperature and 77 K. The hardness of all three materials increases by a factor of ∼2.5 on cooling to liquid nitrogen temperature. High-magnification SEM photographs revealed that the deformation and cracking patterns of the glasses changed strikingly: no shear lines were observed within the indentations, and ring cracking occurred instead of radial/median cracking. In addition, cracking occurs at much higher loads than at room temperature. The hardness results have been explained in terms of volume flow (densification) rather than shear flow (viscous or plastic) for the glasses at low temperature. The quartz crystal, on the other hand, deformed plastically at both room temperature and 77 K. Cracking differences result from changes in both flow and water activity     

The Effect of Fictive Temperature on the Structural Environment of Fluorine in Silicate and Aluminosilicate Glasses

We have examined temperature-induced changes in the local structure of fluorine in silicate and aluminosilicate glasses through the application of ¹⁹F magic-angle spinning nuclear magnetic resonance to glasses synthesized with a wide range of fictive temperatures. We have observed an increase in Si–F bonding in binary silicates with increasing temperature, as well as a change in the degree of ordering in mixed modifier silicates. We have also observed an increase in F–Al bonding in aluminosilicates, although the degree of this change appears to be composition dependent. These results could help explain the significant changes in properties of melts on the addition of fluorine.     

Dynamic and Static Fatigue of Silicate Glasses

Fatigue of silicate glasses was studied using both static and dynamic tests. Static fatigue data for acid-etched soda-lime silicate glass determined at 74°F in 50 and 100% rh can be represented by a single universal fatigue curve (UFC). The UFC for acid-etched glass does not lie on the UFC of Mould and Southwick, which was determined for abraded soda-lime silicate glass; the acid-etched glass was less susceptible to static fatigue. The susceptibility of acid-etched soda-lime silicate glass to static fatigue differed little from that of pristine E-glass and fused SiO₂ fibers. Dynamic fatigue data for soda-lime, E, borosilicate, and fused quartz glasses agreed well qualitatively and quantitatively with fundamental crack velocity data for these glasses; the dynamic fatigue theory of Charles was used in the comparison. The theoretical implications of these results are discussed.     

Shrinkage Behavior of Knoop Indentations in Silica and Soda–Lime–Silica Glasses

The annealing characteristics of Knoop-indented silica and soda–lime–silica glasses were investigated. These glasses were indented using a Knoop indenter in water, and they were annealed at various temperatures below the glass transition temperature. The major diagonal length of the Knoop indentation was measured before and after annealing, and the change of the diagonal length was determined. The change of diagonal length in silica glass was much larger than that in soda–lime–silica glass. This was attributed to the occurrence of more densification around the Knoop indentation in the silica glass. The activation energy of the shrinkage of the Knoop indentation in the silica glass, estimated from the temperature dependence of the relaxation time, was 46 kJ/mol, which was much less than that of viscous flow in silica glass. This suggested that the shrinkage of the Knoop indentation was caused by the structural relaxation of densified glass around the Knoop indentation.     

Structural Relaxation Time of Bulk and Fiber Silica Glass as a Function of Fictive Temperature and Holding Temperature

The structural relaxation times of silica glass, both bulk glass and fiber glass at various fictive temperatures, were estimated at selected temperatures. The structural relaxation time of a glass is needed to estimate the rate of change of various glass properties in the glass transition temperature range. Traditionally, the Tool–Narayanaswamy model, in which activation energy of the relaxation time is divided into two parts, one representing the fictive temperature effect and the other representing the temperature effect, has been used. The model can explain the property changes of glass in the glass transition temperature range well when the change of the fictive temperature is small, but the model fails when the change of the fictive temperature is large, as was the case when a fiber sample was heat treated close to the glass transition temperature. The structural relaxation times estimated in the present work exhibited activation energies that varied with fictive temperature, unlike the assumption in the Tool–Narayanaswamy model. On the other hand, the relaxation time for both bulk glass and fiber glass exhibited the same temperature and fictive temperature dependence within experimental error. From these observations, one can see the source of discrepancy between the Tool–Narayanaswamy model and experimental data when the change in fictive temperature is large.     

Measurement and Prediction of the Dynamic Temperature Distributions in Soda-Lime Glass Plates

Experimental measurement of the dynamic internal temperature distribution in soda-lime glass plates using thermocouples fused in the glass has been carried out. Experimentally measured temperatures are compared to predictions obtained from the solution of the transient energy equation where the internal radiative transfer has been accounted for using rigorous radiative transfer theory. A discussion of the experimental method, the process used to fuse the thermocouples in the test plates and the rigorous formulation of the energy equation, for semitransparent materials is given. Predicted and measured instantaneous surface temperatures are compared and very good agreement is obtained. It is also concluded that the empriical equation for the phonon conductivity used in the analysis underpredicts the conductivity. A 20% increase in phonon conductivity is shown to significantly improve the agreement between measured and predicted centerline to surface temperature differences.     

Effect of Aluminum and Neodymium Admixtures on Devitrification of Silica Glasses

This investigation concerned the devitrification kinetics (in the temperature range 1100° to 1500°C) of silica glasses doped with aluminum oxide (0.1 and 1.0 mol%), neodymium oxide (0.08 and 0.25 mol%), and with aluminum and neodymium oxides simultaneously, at their mutual molar ratio close to 4. The glasses were obtained by electric melting of quartz under vacuum and by the sol/gel method. On the basis of the obtained results, conclusions have been drawn concerning the mode in which the admixtures become incorporated into the silica glasses as well as the structural differences between the melted and sol/gel glasses.     

Influence of Composition on Fatigue Behavior and Threshold Stress Intensity Factor of Borosilicate Glasses

Fatigue behavior of borosilicate glasses was studied using the analysis of subcritical propagation of Vickers indentation cracks. Glasses containing various amounts of glass-network modifiers, mainly soda, were considered. Cone and median/radial crack systems were observed, depending on glass composition, indenter geometry, and test environment. Indentation tests were performed in water, holding the maximum load for durations ranging from 15 s to 6 d. The analysis of the crack length as a function of dwell time allowed evaluation of the subcritical growth parameters and fatigue limit at crack arrest. The influence of composition on fatigue parameters and fatigue limit was discussed in terms of fourfold-coordinated boron atoms fraction compared with the content of glass-network modifier ions.     

Effect of Atmosphere and Temperature on the Equilibrium between Molten Tin and Soda-Lime Glass

The interaction of soda-lime glass with molten tin is of practical and scientific interest. Here the observation that the interfacial tin content of glass in contact with molten tin decreases with increasing temperature and increases with increasing oxygen pressure is confirmed and discussed.     

Effect of Enameling on the Strength and Dynamic Fatigue of Soda–Lime–Silica Float Glass

The effect of a glass enamel coating on the strength and fatigue behavior of float glass was investigated. Commercially available enamel that was comprised of Cu₂Cr₂O₄ pigment particles in a bismuth-zinc borosilicate glass matrix was applied to a soda–lime–silica float glass via screen printing, followed by fusion at elevated temperature. Strengths of the enameled specimens were evaluated in biaxial flexure using a ring-on-ring (ROR) test geometry, and the data were analyzed using a conventional two-parameter Weibull distribution. Enameling was found to significantly degrade the strength of the float glass. There was no statistical difference in the characteristic strengths of samples enameled on the air side (66 MPa) compared with samples enameled on the tin side (61 MPa) of the float glass. Fractographic analysis revealed that the failures in the enameled float glass samples initiated at pores and pigment aggregates in the enamel, whereas failures in float glass samples initiated solely from surface flaws. Dynamic fatigue tests were performed on enameled float glass and indented float glass samples to determine the effect of the enamel on the stress corrosion behavior of the enameled components. There was no statistically significant difference between the stress corrosion exponents for the float glass and enameled float glass specimens.     

Acoustic Characterization of Silica Glasses

Acoustic characterization of doped silica glasses with a GeO₂, P₂O₅, F, TiO₂, Al₂O₃, or B₂O₃ dopant having different concentrations is presented. Quantitative measurements were performed with a 225-MHz line-focus-beam scanning acoustic microscope. The acoustic velocity variation due to different dopant concentrations is given. It has been found that the Al₂O₃ dopant increases, but the other dopants decrease, the acoustic velocity as compared with that of the pure fused silica. We have also found that the fractional change in acoustic velocity is greater than that in refractive index for a given dopant concentration.