ESCA examination of tin oxide coatings on glass surfaces

ESCA analysis was carried out on glass surfaces which had been treated with SnCl₄ vapour or with SnCl₄/butyl acetate spray at temperatures of 450–650°C. Two forms of stannic tin werer indentified, one assigned to SnO₂ and the other to Sn in association with one or more of the glass elements. Varying proportions of each form of stannic were obtained, depending on type and temperature of treatment. Two forms of carbon were also found, one due to normal hydrocarbon contamination in the instrument, the other apparently associated with the treatment layer.     

Particulate erosion of glass surfaces at subsonic velocities

The erosion of borosilicate glass plates through multiple collisions with 70–290 μm glass beads and 1.8 mm water drops is described. The basic element for the initiation of erosion damage by rounded solid particles is the cone fracture. The diameter of the ring and penetration of the conical fracture surface extending into the glass specimens have been measured for various impact conditions. The material removal process near the velocity threshold for cone fracture formation is dependent on the radius of the impacting particle. At intermediate velocities in the subsonic range the damage due to a single water drop impact is much more difficult to identify compared to solid-particle impingement. The observed damage is not coherent and fracture surfaces approximating circular arcs only begin to become evident at velocities considerably higher than that required for preferential erosion of the specimen's surface.     

Corrosion and crystallization at the inner surfaces of glass bricks

Glass bricks are important transparent building materials. They are produced by joining two halves of glass pressings at 600–700 °C. During this production process alkali oxides evaporate and are redeposited at the cooler inner front surfaces of the bricks. This surface layer reacts with H₂O and CO₂ from the residual brick atmosphere, leading to the formation of an alkali-rich silicate-hydrate layer of ?50 nm thickness, which could be evidenced leading to a reduced nano-hardness of similar thickness, and from which NaHCO₃ crystals can finally grow. Climate chamber experiments (repeated cooling between at ?8 and ?14 °C and reheating to 0 to 15 °C) resulted in reversible NaHCO₃ crystallization and redissolution, presumably influenced by water evaporation or condensation and driven by the NaHCO₃ supersaturation of the silicate-hydrate layer. Depending on the time–temperature schedule, different crystal morphologies became visible in this closed system, e.g. isolated spherical crystals, crystals arranged in chains and in double-chains, respectively, which can limit already the transmittance of the glass bricks. When a crack occurs or the brick is opened, the hygroscopic NaHCO₃ crystals take up more H₂O from the ambient, react irreversibly with the glass surface, finally leading to a total loss of transmittance.     

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).     

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.     

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.     

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.     

Exafs for studying corrosion of glass surfaces

The technique of glancing angle EXAFS is introduced and applied to the study of aqueous corrosion at the surface of sodium borosilicate glass. In particular, the structural roles of iron and uranium are compared at loadings typical for nuclear waste disposal. The structural chemistry observed at the surface is rich in detail and adds considerably to the qualitative picture for the leaching of oxide glasses obtained from conventional surface analytical probes. Both metald migrate to the surface as corrosion progresses, iron more rapidly than uranium. There is evidence for mineralisation of the modifiers at the surface following leaching and, in the case of uranium, as a result of polishing. Indeed the uranyl configuration of U⁶⁺ is particularly sensitive to changes just beyond the oxygen ligand. Wet and dry surfaces can be distinguished and square planar clustering can be identified. The sequence of events is interpreted in terms of ion migration and water infusion taking place along percolation channels within the borosilicate network.     

Tensile strength of boric oxide glass in vacuum and at very low humidities

The tensile strength of a glass fiber of pure boric oxide was measured at low humidities and in vacuum. The strength increased from 60 kg/mm² in a relative humidity (RH) range of 7% to 120 kg/mm² at 0.4% RH, levelling off to 0.02% RH which was the lower limit of humidity in this experiment. At relative humidities higher than 0.4% weathering and stress corrosion were observed, while at relative humidities lower than 0.4%, weathering was not observed but the decrease of the strength with a dynamic loading duration was observed, although the behavior was somewhat different from the typical stress corrosion. The strength measured in vacuum was almost equal to that measured at relative humidities lower than 0.4%, although the data were more scattered. The strength of boric oxide glass was much lower than that of silica glass, even when weathering and stress corrosion were depressed to the extreme. This weakness of boric oxide glass may be attributed to its layer structure.     

The effect of a small amount of oxide additives on the wetting behavior of glass on metal

The wetting behavior of glass on ferronickel alloy, with the separate addition in the glass of a small amount of the oxide of some fourth period and VIB group elements, has been studied. The factors affecting the wetting process, and the reaction mechanism due to additives, have been studied.     

Novel solution routes of synthesis of metal oxide and hybrid metal oxide nanocrystals

Novel solution routes covering a wide range of processes like hydrothermal, solvothermal and supercritical techniques have been described in detail with reference to the processing of a wide range of advanced inorganic nanocrystalline materials and organic-inorganic hybrid nanocrystalline materials. The significance of the thermochemical calculations, in situ surface modification and the experimental parameters has been discussed. One step in situ fabrication of advanced functional nanocrystalline materials by soft solution processing has also been discussed briefly. Synthesis of nanocrystals of metal oxides and hybrid nanocrystals and also processing several nanocomposites like carbon nanotubes: metal oxide, activated carbon: metal oxide, etc. has been reviewed in relation to various process parameters. The effect of doping, size, shape and quality on the properties of nanocrystalline materials has been discussed in relation to the photoluminescence and photocatalytic characteristics.     

Characterization of organic adsorbates on model glass surfaces

Model silicate glasses in planar thin film structures are prepared using sol/gel techniques. A typical structure consists of 3.0–12.0 nm of glass on vapor deposited Ag. In this study, a pure silica and a 50/50 binary alumina-silica films are examined. Poly(methyl methacrylate) (PMMA) is adsorbed from chlorobenzene solution onto the surfaces. Infrared reflection (IR) spectroscopy, ellipsometry and quartz oscillator microgravimetry (QOM) are applied to characterize the PMMA/silicate glass interfaces formed. The QOM and IR data show that PMMA adsorption on the pure silica surface is irreversible with respect to removal by pure solvent rinse while on the binary glass surface and on a pure alumina surface, solvent rinses remove the initially adsorbed polymer. These results are interpreted in terms of Bronsted acid-base interactions involving the basic properties of the PMMA C=O group, the acidic nature of the silica and the more basic nature of the alumina containing surfaces. Further evidence for this interpretation is given by the IR spectral data which show broadening of the C=O stretching mode to lower frequencies for the irreversible adsorbed polymer on silica as compared with simulated spectra of non-surface bonding PMMA thin films. This spectral perturbation is interpreted as evidence for a hydrogen bonding interaction between OH groups on the silica surface and the C=O groups. The overall conclusion is that the surface of a 50/50 binary alumina-silica composition is dominated by the basic nature of alumina.     

Vibrational spectroscopic studies of some lead silicate glasses

Results are presented of measurements on the infrared and laser Raman spectra of some lead silicate glasses of general formula (PbO)_x(SiO₂)_y.For the infrared spectra, the frequency dependence of the imaginary component of the complex dielectric constant was determined from a Kramers-Krönig analysis of the reflectance spectra of the glasses at normal incidence. Apparently the addition of small amounts of PbO to vitreous silica serves to modify the continuous three-dimensional silica network; whereas in those glasses with a high lead content, the influence of the cation, Pb²⁺, appears to lie between that of network former and network modifier.     

Viscoelastic behaviour of an oxide glass near the glass transition temperature

The dynamical properties of an industrial oxide glass have been measured using new equipment consisting of a very low frequency torsion pendulum and the “METRAVIB” viscoelasticimeter. The internal friction of the glass has thus been investigated in a temperature range of 200°C near T_g and a frequency range from 10^?3 to 10⁺³ Hz. Starting from the results, a contribution to the knowledge of the physical mechanisms which cause internal friction has been made. So the shortcomings of the time-temperature superposition principle are illustrated and a simple rheological model suitable for the experimental results is given.     

Novel properties of glass–metal nanocomposites

Nanoparticles of silver and copper were grown at the glass–crystal interfaces within a silicate glass by reducing the ion-exchanged glass–ceramic concerned. By controlling the reduction treatment a wide range of surface resistivity e.g., from 0.2 to 10¹⁰ Ω/sq. could be generated. Silver nanowires of diameter ∼40 nm were grown within the pores of a silica gel. They exhibited single electron tunneling as evidenced by conductance maxima at definite intervals of the applied voltage. Silver nanowires of diameter 0.5 nm were grown within the crystal channels of fluorophlogopite mica which were first precipitated in a silicate glass. The nanowires when broken gave giant dielectric permittivity (∼10⁷) to the composite. Copper core–copper oxide shell and iron core–iron oxide shell nanostructures respectively were generated within a silica gel. The core–shell structure exhibited electrical conductivity several orders of magnitude higher than that of the precursor gel. An interfacial amorphous phase contributed to this increase in electrical conductivity. Glass–ceramics containing BaTiO₃ and nanoparticles of silver showed a five order of magnitude decrease in electrical resistance as the relative humidity was changed from 25% to 75%. Arrays of metal nanoparticles (silver or copper) grown within a silicate glass exhibited a diode-like behavior. This was explained as arising due to formation of metal–semiconductor nanojunctions – metal particles smaller than 3 nm behaving like a semiconductor. The examples reviewed here show that exploiting the void spaces available in an oxide glass nanophases of a wide variety could be grown within and novel properties generated. This approach could be promising in imparting new functionality to conventional glasses.     

Interdiffusion of hydrogen and alkali ions in glass surfaces

The Boksay-Doremus theory on the interdiffusion of hydrogen and alkali ions in glasses was extended by taking into account the association of hydrogen ions and non-bridging oxygen ions. In the derivation of the interdiffusion coefficient the bulk composition of the glass is taken into account. Theoretical concentration profiles were compared with experimental data, reported in literature, of alkali-alkaline earth-silicate glasses and of a sodium-aluminium-silicate glass. An essential feature of this extended B-D theory is, that the relative order of chemical durability of alkaline earth containing glasses is found by this theory without assuming excessive changes in individual diffusion coefficients.     

Quantitative AFM analysis of phase separated borosilicate glass surfaces

Phase separated borosilicate glass samples were prepared by applying various heat treatments. Using selective chemical etching we performed AFM measurement on the phase separated glass surfaces. A quantitative roughness analysis allowed us to measure precisely the dependence of the characteristic size of the phase domains on heating time and temperature. The experimental measurements are very well described by the theoretically expected scaling laws. Interdiffusion coefficients and activation energy are estimated from this analysis and are consistent with literature data.     

Adsorption/desorption of water on glass fiber surfaces

The interaction of water with glasses and ceramics has a profound effect on their properties. For many samples, standard analytical techniques are inappropriate or insufficiently sensitive for the detection of associated water. A thermodesorption method with an electrolytic detector is described which permits the measurement of minute quantities of water associated with such samples. Because of the sensitivity of the method, the surface water present on low specific area substrates can be measured. A simple and rapid method for obtaining water adsorption isotherms at low pressures is described. A preliminary investigation of single mode optical fibers demonstrates their substantial adsorptive capacity for water, due to the cladding used. Adsorbed water is also shown to differ on two glasses of similar bulk composition, presumably due to large differences in glass surface composition.