Physical aging effect on the boson peak and heterogeneous nanostructure of a silicate glass

The effect of physical aging on a silicate glass has been investigated by low-frequency Raman scattering. It was observed that the low-frequency side of the excess of Raman scattering, or boson peak, due to harmonic vibration modes decreases in intensity with the thermal annealing (aging) at a temperature lower than the glass transition temperature (T_g), after quenching (rejuvenation) from a temperature higher than T_g. Moreover, it was found that the lowering of the very low-frequency scattering mainly due to anharmonic modes becomes more pronounced when the aging temperature is decreased. These observations are interpreted in the frame of the energy landscape, and by considering the model of the glass heterogeneous cohesion at the nanometric scale.     

X-ray irradiation-induced coloration of manganese in soda-lime silicate glass

Coloration of Mn in soda-lime silicate glass by X-ray irradiation was investigated as a coloration method suitable for glass recycling. Mn was initially reduced to Mn²⁺ with the addition of Fe, Sn or carbon, and the resultant colorless or near-colorless glasses containing no Mn³⁺ were studied. These glasses turned violet after X-ray irradiation and heat treatment at 200 °C due to formation of Mn³⁺. The color was stable at room temperature and decoloration occurred with heat treatment at 600 °C. The addition of Fe or Sn increased the optical absorption by Mn³⁺ ions. ESR measurement suggests that Mn photo-oxidation occurred through charge transfer from photo-induced hole centers.     

Acid-base properties of glass surfaces

The adhesion of polymers to inorganic oxides such as glass is very dependent on acid-base interactions between the acidic or basic surface sites of the glass and the basic or acidic functional sites of the polymer. This paper reviews the principles of such interactions, methods of measuring the acidity or basicity of surface sites, and the enhanced mechanical properties of glass-reinforced polymer composites resulting from interfacial acid-base complexation. A new study is presented of the acid-base properties of fiberglass and of surface treatments with silane coupling agents and polyvinyl acetate. It illustrates calorimetric titration methods for assessing surface acidity and basicity, and correlates these findings with angular-dependent X-ray photoelectron spectroscopy (ADXPS).     

Stress corrosion of silicate glass: a review

In the first section of the present paper, some examples, from the field, of the manifestations or consequences of the fatigue of silicate glass are briefly presented. In the second section, the interpretation of fatigue in terms of stress corrosion is reviewed: the role of ambient molecular water is well established. Whatever the details of the mechanism of action of water, it takes place very efficiently in the highly strained material close to the tip of a surface crack. This enables its sub-critical growth to be explained. But it does not explain many other observed effects of the environment on the mechanical behavior of silicate glass, and, in the last section, questions and issues are presented, which would still need to be investigated.     

Evidence of structural anisotropies in silicate glass fibres by ESR

The ESR spectra of Cr³⁺ and Cr⁵⁺ in soda-lime-silicate glass fibres were investigated with respect to defined parameters of the fibre drawing process from a nozzle. The following results concerning the structure of the fibres were obtained: Although the short-range order of the Cr³⁺ and Cr⁵⁺ ions is identical in the structure of the bulk glass as well as in the fibre glass, changes of the covalent portion of the bonds between the Cr⁵⁺ ion and its oxygen ligands were observed. The fibre glass structure is a frozen-in deformed or orientated (this depends on definition) silicate glass network, which influences the bonds in the square bipyramidal [Cr⁵⁺O₆] ⁷⁻ complexes in the following manner: the σ-bonds between Cr⁵⁺ and the four oxygens in the square plane of the bipyramid are more covalent in the fibre than in the bulk glass. They are also orientation-dependent: more covalent for those of the randomly distributed complexes with their c-axes perpendicular to the fibre axis than parallel to it. The π-bond of the CrO³⁺ oxygen is less covalent in the fibre than in the bulk glass and is also orientation-dependent: more covalent for those complexes with their c-axes parallel to the fibre axis than perpendicular to it.

The ability of the glass network to form [Cr⁵⁺O₆] ⁷⁻ or CrO³⁺ complexes increases with the following increasing parameters of the fibre drawing process: melting temperature, oxygen partial pressure, mean cooling rate, and tensile stress. This fact is primarily a consequence of the shift of the redox-equilibrium and of the difficulty for the structural change from an octahedral symmetry of the Cr³⁺ and Cr⁵⁺ to a tetrahedral symmetry of the Cr⁶⁺ and vice versa during the fibre drawing process. The [Cr⁵⁺O₆] ⁷⁻ complex is highly unstable and is an intermediate state.     

Spectroscopic properties and simulation of white-light in Dy-doped silicate glass

Spectroscopic properties of various concentrations Dy³⁺-doped silicate glasses were characterized by excitation and emission spectra. The optimal doping concentration of Dy³⁺ ions was found to be 3.0 wt%, and the nature of resonance energy transfer was confirmed to be electric dipole-dipole interaction according to Huang’s rule. Simulation of white-light for these glasses was also performed by varying the excitation wavelength. The results show that the white-light luminescence color could be tuned to various wavelength excitations, and the present silicate glass is more suitable for generation of white-light for blue LED chips.     

Stress relaxation of a soda lime silicate glass below the glass transition temperature

Stress relaxation is an important effect in the ion-exchange procedure of glasses, as it controls the stress profile and the strength. Creep and stress relaxation tests have been performed to study the viscoelastic behavior of soda-lime silicate glass at typical ion-exchange temperatures. The experimental data of these tests can be fitted well by the Burger model and a comparison between the viscosity data from both tests was made. The strain and temperature dependences of the stress relaxation process were studied and the glass exhibited a non-linear viscoelastic behavior and an anomalous temperature dependence. In addition, it was found there is a relationship between the glass density and the stress relaxation behavior.     

Memory effect in the glass transition region of silicate glass based on light scattering data

The experimental results of the changes of the visible light scattered intensity after temperature jumps in the glass transition region of silicate glass were presented. The influence of the thermal prehistory on the height and location of the scattered intensity maximum was studied. The conditions corresponding to the maximum value of the scattered intensity were determined. The non-monotone character of the dependence of the limit height of the maximum as a function of the stabilization temperature was obtained. It was shown that the relaxation times of the increasing of the intensity considerably exceeded the structural relaxation times. These features were similar to the results obtained for the phosphate glass earlier. The universal character of the non-linear coupling of the laser irradiation with the glass structure formed in the process of development of the maximum intensity was found.     

Structural changes between soda-lime silicate glass and melt

Neutron diffraction has been used to study the structure of a glass and melt of composition 75SiO₂-15Na₂O-10CaO. RMC modeling of the neutron and X-ray diffraction data for the glass allowed the determination of the Na and Ca environment. The structure has been investigated at 300K, just below the glass transition at 823 K and in the melt at 1273 K. The short range order does not present important modifications with temperature while significant reorganization appears at the medium range order. These latter changes can be associated with the Si and O pairs and indicate the relaxation of the silicate network. This indicates that the glass formation involved structural rearrangement during cooling.     

Chemical characteristics of float glass surfaces

The regions near the top and bottom surfaces of float glass are chemically different from the bulk glass composition. In addition to the presence of tin oxide at the bottom surface and to a lesser extent at the top surface, differences are found in SiO₂, Na₂O, CaO, SO₃ and Fe₂O₃. The concentrations of Na₂O, CaO and SO₃ are lower at the top surface than in the bulk glass, while SiO₂ is higher. In the case of tin at the bottom surface and iron at both top and bottom surfaces, the components exist in complex concentration gradients. In addition, there are variations in oxidation state for tin, iron and sulfur. Tin appears to exist in both stannous and stannic states near the bottom surface. So far it has been found that iron at the top surface and sulfur at the bottom are largely in reduced states. Some consequences of these effects have been observed in physical and chemical behavior of the surface.     

Surface compositional studies of heat reduced lead silicate glass

SIMS and AES compositional analysis of the surface layer for a lead silicate glass reduced at three different temperatures was carried out and the depth distribution for some components to a depth of 120 nm was obtained. It was found that by increasing the reduction temperature the layer located just below the surface becomes rich in silicon oxides, a potassium accumulation takes place on the surface and the depth distribution of the other chemical components exhibits a maximum, the location of which depends on the reduction temperature.     

Volume fluctuations in potassium silicate glass studied by molecular dynamics

Potassium-silicate glass, 0.05K₂O·0.95SiO₂, was prepared by molecular dynamics under three different regimes (cooling rates, simulating box sizes) to study their influence to temperature regimes of volume fluctuations. Partial volume fluctuations (VF) were introduced with the help of Voronoi polyhedra tessellation. Dynamic and static fluctuations were suggested as a measure for time- and space-related fluctuations. Separation of the dynamic and static VFs anticipates glass transition. The glass transition was related with the change of the temperature course of the static VFs. The dynamic VFs changed their temperature regimes well below the glass transition and the transition temperature was related with the change of the transport regime. Glass transition cages the atoms but Voronoi polyhedra are definitely shaped well below the glass transition temperature.     

Water and the glass transition temperature of silicate melts

Literature data on the effect of water on the glass transition in silicate melts are gathered for a broad range of total water content c_w from 3 × 10⁻⁴ to 27 wt%. In terms of a reduced glass transition temperature T_g^*=T_g/T_g^GN, where T_g^GN is T_g of the melt containing c_w≈0.02 wt% total water, a uniform dependence of T_g^* on total water content (c_w) is evident for silicate melts. T_g^* decreases steadily with increasing water content, most strongly at the lowest water content where H₂O is dominantly dissolved as OH. For water-rich melts, the variation of T_g^* is less pronounced, but it does not vanish even at the largest water contents reported (≈27 wt%). T_g^* vs. c_w is fitted by a three-component model. This approach accounts for different transition temperatures of the dry glass, hydroxyl and molecular water predicting T_g^* as a weighted linear combination of these temperatures. The required but mostly unknown water speciation in the glasses was estimated using IR-spectroscopy data for hydrous sodium trisilicate and rhyolite.     

Nanosized gold clusters formation in selected areas of soda-lime silicate glass

Nanosized gold clusters were developed in a gold-doped soda-lime silicate glass after X-ray irradiation followed by annealing, which provided an alternative way of forming metallic nanoclusters in glass to ion implantation. The formation of gold nanoclusters can be controlled by irradiation time or annealing time.     

Determination of light-scattering properties of glass surfaces

Glass surfaces were damaged in a defined manner by sandblasting with an adjustable sand blasting machine and subsequent etching with HF. Investigations with the scanning electron microscope (SEM) showed surface defects with an ellipsoidal shape. A quantitative evaluation of the exact profile of these defects was made using mathematical evaluation of stereographic pairs. A new method is described for characterizing surfaces with optical light scattering. In contrast to the usual method of a fixed specimen and a photocell moving on a circle around it, here the specimen revolves on an axis perpendicular to a laser beam and rotates on an axis parallel to it in order to average the scattering over a large area of the surface, thus preventing interferences of the coherent laser beam with surface defects. A theory is described which enables a numerical estimation of roughness parameters using a distribution function of angles of small mirrors to the average surface. In this special case the theory was extended for the special type of defects having an ellipsoidal shape. The results are discussed with respect to creation of surface defects by sandblasting, which are accompanied by subsurface cracks.     

Local fluctuations and FDR violations in aging glass

Dipolar fluctuations were measured in both macroscopic samples, and locally in mesoscopic volumes of polymer glass. Following a temperature quench, the macroscopic measurements revealed fluctuation–dissipation-relation (FDR) violations with a complex dependence on aging time and measurement frequency. New results on imaging mesoscopic spatio-temporal fluctuations, and the possibility of using this technique to study the heterogeneity of aging and local FDR violations will be discussed.     

Phase evolution on heat treatment of sodium silicate water glass

Heat treatment of sodium silicate water glass of the nominal composition Na₂O/SiO₂ = 1:3 was carried out from 100 °C up to 800 °C and the advancement of the resulting phases was followed up by powder X-ray diffraction, scanning electron microscopy and thermogravimetry along with differential thermal analysis. The water glass, initially being an amorphous solid, starts to form crystals of β-Na₂Si₂O₅ at about 400 °C and crystallizes the SiO₂ modification cristobalite at about 600 °C that coexists along with β-Na₂Si₂O₅ up to 700 °C. At 750 °C Na₆Si₈O₁₉ appears as a separate phase and beyond 800 °C, the system turns into a liquid.     

Dealkalization of glass surfaces utilizing HCI gas

Surfaces of silicatee glasses can be dealkalized when exposed to SO₂⁻, chlorine- and fluorine-containing gases. The chemically modified near-surface regions display properties which are different from those of the bulk. Emphasis will be placed on the deakalization mechanism and the improvement of specific surface properties of various industrial glasses.