Identification of Float Glass Surfaces

Methods for identifying the lower (contacting with tin melt) and the upper (contacting with gaseous atmosphere) surfaces of float glass are considered.     

Adhesion of Nanoparticles Fouling Glass Surfaces

The fouling of glass surfaces by nanoparticles formed from corroding iron was studied. Simple experiments demonstrated that adherent films of nanoparticles were deposited by corrosion of iron particles on a glass surface and by flowing water past corroding particles and then onto a glass surface. The water collected from this experiment was found to contain about 2 parts per million (ppm) of particles 500 nm in diameter when tested by photon correlation spectroscopy. However, electron micrographs showed that the primary particles in the fouling film were 20 nm in diameter. This discrepancy was explained by a new theory of nucleation of the fouling films. The theory was confirmed by measuring the particle size of ferric hydroxide dispersions as a function of concentration and pH. It was shown that the 20 nm primary nanoparticles nucleated much larger stable aggregates (defined as nucleags), which were sensitive both to pH and to magnetic fields. In particular, as the pH rose above 6, flocculation occurred, and large unstable agglomerates were observed. The conclusion was that three types of particle could exist in the corrosion product of iron and water: nanoparticles, nucleags, and flocs.     

Structure of Sodium Aluminosilicate Glass Surfaces

Sodium aluminosilicate (NAS) glass surfaces with compositions containing approximately 63% SiO₂ and Al/Na ratios, R , of 0.25 R 2.0 were simulated using the molecular dynamics technique with a multibody interaction potential. There were changes to the surface structure and composition in comparison to bulk NAS glasses. The changes included an increased concentration of sodium and oxygen and the formation of nonbridging oxygen at the outermost surfaces, although the increases were smaller with increased Al concentration. In addition, the formation of small-membered rings and three-coordinated aluminum occurred in the subsurface regions. These changes were accompanied by a change in the ratio of Al/Na in the region extending to 4 Å below the surface.     

Optical Scattering from Nanostructured Glass Surfaces

Nanostructured glass surfaces enable new and innovative applications for glass substrates. These nanostructures enable trapping as well as extraction of light. They affect the propagation of light such that it scatters and is trapped or extracted based on the index of the propagation media. The diffusive scattering component as opposed to the specular component is what enables the trapping and extraction. Often smooth surfaces are required for growing semiconductor thin films. Scattering sites beneath these surfaces can significantly enhance the optical performance of these films. Example devices utilizing these substrates include organic light-emitting diodes (OLED) displays, OLED lighting components, and microelectromechanical systems reflective displays. We demonstrate methods to fabricate these substrates using nanoparticle deposition processes. Important parameters of these nanoparticles and their agglomerates include both size and refractive index. We characterize these substrates using atomic force microscopy and scanning electron microscopy microscopy, and we simulate their optical properties using optical scattering models.     

Ion Beam Effects on Glass Surfaces

X-ray photoelectron spectroscopy has been used to show that 4 keV Ar ⁺ bombardment of glass results in a drastic alteration of the sample surface. Field-induced migration of sodium ions and preferential sputtering account for these changes. The sputter yield is directly related to the binding energy of the ejected particles, in accordance with the linear collision cascade theory.     

Morphology of Fractures in Polished Glass Surfaces

A moisture-condensation technique previously described was utilized in a study of the effect of polishing on fracture patterns in glass surfaces. The experiments show that the apparent controversy concerning the polishing out or "bridging over" of surface fractures may be resolved on the basis of crack dimensions. If the fracture width is less than 1/4 λ, it may be sealed over by polishing, even though the depth may be 1 mm. or more. A modified condensation chamber was devised to show in detail the effect of aging and fracture growth in polished surfaces.     

Fluorine Treatments of Soda-Lime Silicate Glass Surfaces

A series of soda-lime silicate glasses was treated for varied times at different temperatures with 1, 1-difluoroethane. Sodium and calcium fluorides formed on the surface of the treated glasses. Formation of NaF is proportional to the square root of time, implying a diffusion-controlled reaction. Structural relaxation decreases the rate of bloom formation at high temperatures .     

Elastic Indentation Response of Float Glass Surfaces

Instrumented Hertzian indentation was used to evaluate the reduced elastic modulus and cone-crack initiation forces for the as-received surfaces of commercial float glasses. Custom-built indentation equipment with the capability of acoustic emission detection was used to monitor continuously the load and depth of penetration at the microscopic scale for forces up to 1 kN. Equipment verification was performed using a reference material, GE 124. The air and tin surfaces of commercial soda–lime–silica and borosilicate float glasses were tested to determine any difference in indentation response for the elastic and fracture behavior of as-received surfaces. Information obtained from the analysis of the load–displacement curves and from the visual inspection of the indentation sites was used to determine the elastic modulus, and the conditions for the onset of cone cracking as a function of surface roughness. The reduced modulus results were verified using additional equipment that allowed the in situ observation of the contact area during loading and unloading. The results showed that there was no difference in the reduced modulus data for the air and tin surfaces for the range of surface displacements studied. The same conclusions were found for cone-cracking loads on as-received surfaces but tests on abraded surfaces showed that the tin surfaces had slightly more resistance to cone cracking than the air surfaces.     

Crystallization of Silica on Polished Glass Surfaces

Polished surfaces of different optical glasses leached with diluted nitric acid exhibited (1) fine lines showing against the uniform background of a thin colored film, (2) macroscopic cracking with or without the production of flakes, (3) holes or grooves of Werent forms and sizes, and (4) numerous crystals of different forms of silica on the inside of lines and grooves and spread over the glass surface. The interpretation of such observations may help in the understanding of the nature of polished glass surfaces.     

Capillarity-Induced Smoothing of Glass Surfaces by Viscous Flow

A theoretical and experimental study of the smoothing rates of corrugations on glass surfaces demonstrated that the decay in amplitude of periodic surface perturbations having wavelengths from 5 to 14 μm occurs because of the action of capillarity forces and that the rate of smoothing is controlled by viscous flow. This technique allows determination of the viscosity of glasses from 10⁵ to 10¹² P. Also, a theoretical analysis of the decay of an isolated V-shaped groove by viscous flow is presented.     

Alkali Attack of Glass Surfaces by Molten Salts

The surface reaction of soda-lime-silica, sodium borosilicate, soda-zirconia-silica, and soda-alumina-silica glasses with pure molten sodium hydroxide and potassium hydroxide was investigated at 350° and 425°C, respectively. Chemical durability of these glasses is assessed in terms of an acid-base concept in which the glass network forms the acid function. Use of a mixture of sodium hydroxide in sodium nitrate resulted in a tenfold increase in the zirconia-silica glass durability at concentrations up to 60 mole % sodium hydroxide.     

Diffusion-Controlled Attack of Glass Surfaces by Aqueous Solutions

Simple binary alkali oxide silica glasses and some ternary glasses derived from the binary compositions by substituting alkaline earth oxides for silica were subjected to the action of water and various aqueous solutions (pH 1.4 to 10.9) and the kinetics of the reactions were studied. In every case a root-time relation of extraction, suggesting an ion-exchange controlled diffusion mechanism, was observed, followed by a time relation of extraction. The rate and duration of diffusion depended on the pH of the solution and the reaction temperature. Above a critical pH the hydrogen ion concentration of the attacking solution was so low that the surface sites began to be occupied preferentially by alkali ions, increasing their concentration at the leached layer-solution boundary and slowing the diffusion process. For potassium glasses only, where alkali ion distribution in the leached layer was exponential, the diffusion coefficients calculated from the concentration profiles agreed well with those calculated from the extraction of potassium ions by a diffusion mechanism.     

Strengthening of Glass Surfaces by Sulfur Trioxide Treatment

Removal of soda from a glass surface at high temperature can, on cooling, give appreciable strengthening due to lowering of the expansion coefficient at the surface. Soda depletion has been accomplished previously by treating a high-expansion soda-lime glass with SO₂ in the presence of oxygen and water. The depletion rate can be doubled by using dispersed platinum to catalyze the oxidation of SO₂ to SO₃ before the gas reacts with soda from the glass. The data are consistent with the soda depletion being Fickian both with and without the catalyst. Alumina in the glass composition markedly increases the strength which can be attained by sulfur oxide treatment. Although the percentage of soda retained in the leached layer increases, the total amount of soda removed from the glass also increases as alumina increases. It must follow that the depth of the layer is increased.     

Structural Implications of the Electron Microscopy of Glass Surfaces

Electron microscopy of fractured and polished surfaces of commercial silicate glasses by the preshadowed carbon replica technique reveals the presence of inhomogeneities in the glass ranging in size from 30 to 150 a.u. in diameter. Experiments were carried out to prove that the observed features resulted neither from the experimental technique used nor from the reaction of the glasses with atmospheric moisture. It is probable that these inhomogeneities are related to the bulk structure of the glass.     

Study of Glass Surfaces by Generation of Electrostatic Charges

A reproducible method for developing electrostatic charges by rubbing glass surfaces with a platinum electrode was developed as a quantitative approach to the study of glass surfaces. The charge-producing characteristics of glass surfaces were correlated with glass compositions as well as with the conditions of formation of the glass surfaces and their subsequent histories. The sign and magnitude of charges generated on glass surfaces arose primarily from the ions removed from the surface films. The charge development characteristics of glass interfaces seem to yield some indications of the atomic arrangements at glass interfaces.     

Hydroxylation and Dehydroxylation Behavior of Silica Glass Fracture Surfaces

The hydroxylation and dehydroxylation behavior of amorphous silica fracture surfaces was studied using temperature-programmed static SIMS. The results show that vacuum heat treatments result in more extensive condensation of silanol groups on the silica glass fracture surface as compared to fumed silica (Cabosil). This is attributed to differences in the distribution of silanol groups on the two silica surfaces. The rehydration kinetics of the dehydroxylated silica fracture surfaces showed two distinct reaction rates—an initial rapid increase in the silanol concentration, followed by a slower rehydration for longer dosing times. The slower rehydration reaction was shown to follow first-order reaction kinetics with the reaction rate constant, suggesting hydrolysis of strained siloxane bonds on three-membered silicate ring structures. The much faster initial rehydration is attributed to the hydrolysis of extremely strained siloxane bonds in two-membered, edge-shared tetrahedral rings. The effect of the dehydration time and temperature (i.e., thermal history of the surface) on the rehydration kinetics is also discussed.     

Study of Moisture-Condensation Patterns on Glass and Crystalline Surfaces

A method was devised whereby moisture-condensation patterns on glass and crystalline surfaces could be examined under the microscope and photographed. The characteristics of the condensation films were markedly influenced by the fracture patterns and by the structure of the underlying surface. The technique was applied in a detailed study of minute surface fracture patterns and Griffith flaws. Experiments were made showing the type of fracture patterns produced on glass by various mechanical means. Variations in the surface structure produced by polishing, etching, and other treatments were also studied by this method.