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.     

Attack of Glass by Chelating Agents

The chemical attack of a soda-lime glass by the combined action of ethylene diamine tetraacetic acid and ortho-dihydroxy benzene (catechol) in dilute aqueous solution is reported u a function of pH. A pronounced maximum occurs in the rate of attack at a pH value determined by the anionic species present. The effects are ascribed to the chelation of the protective cations A1³⁺, Ca²⁺, and Mg²⁺ by ethylene diamine tetraacetic acid and to the chelation of Si⁴⁺ by catechol.     

Adsorption of Tagged Phosphute Ions on Glass Surfaces as Related to Alkaline Attack

A preliminary investigation has been made of various factors involved in the sorption of phosphate ions on glass surfaces, particularly with reference to a possible utilization of phosphate sorption as an indicator of alkaline attack of the surface. Sorption has been measured by means of a tracer technique using radioactive phosphorus as trisodium phosphate, and tests have been made with two types of soft glass and with Pyrex-brand glass, with and without alkaline pretreatments. Radioautographs have been prepared to determine the distribution of sorbed phosphate on soft-glass specimens treated in various ways. The sorption of phosphate ions from dilute alkaline solutions at room temperature on fused soft glass and Pyrex-brand glass has been found to be very slight, on the order of one-thousandth of a μ gm. per sq. in. (roughly equivalent to a thousandth of a monomolecular layer on the macrosurface). Treatment of soft glass for a few minutes in sodium hydroxide solution at 80°C. results in a multifold increase in subsequent sorption of phosphate ions at room temperature. A much longer alkaline pretreatment is required in the case of Pyrex-brand glass, but a similar increase in sorption is found. The different results obtained with soda-lime and borosilicate glasses may be explained on the basis of different types of nonadsorbing surface films. Zinc ions in the alkaline pretreatment solution appear to cause an increase in subsequent sorption, and it is proposed that adsorption of polyvalent cations facilitates the adsorption of phosphate ions.     

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.     

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.     

Investigation of Apatite Deposition onto Charged Surfaces in Aqueous Solutions Using a Quartz-Crystal Microbalance

Hydroxyapatite (HAp) deposition onto positively charged surfaces (i.e., self-assembled monolayers (SAMs) terminated with NH₂ head groups) and negatively charged surfaces (i.e., OH-SAMs (weak) and COOH-SAMs (strong)) soaked at 50°C in aqueous supersaturated solutions (1.5 SBF, pH 7.0–7.6; SBF = simulated body fluid) was investigated using a quartz-crystal microbalance. The results revealed that the solution conditions greatly influenced the formation of HAp on the charged surfaces. In a stable supersaturated solution of simulated body fluid (1.5 SBF, pH <7.4), more strongly negative surfaces had a more powerful induction capability for the heterogeneous nucleation of HAp (COOH > OH), whereas nucleation was obviously prohibited on a positive surface (NH₂-SAM). On the other hand, after the calcium phosphate particles had nucleated homogeneously in an unstable soaking solution (1.5 SBF, pH ≧7.4), adhesion of the HAp microparticles to the NH₂-SAM was observed. A two-step interaction is conceivable to describe the formation of HAp on the positive NH₂-SAM: At the first stage, electrostatic interaction dominates the adhesion of HAp microparticles; at the second stage, hydrogen bonds possibly form between the HAp microparticles and the amino head groups of the NH₂-SAM, for a firm bonding with the substrate, and the microparticles grow progressively into a thin film. The electrophoretic behaviors of the HAp microparticles confirmed this hypothesis.     

Contact Angle of Ethanol and n‐Propanol Aqueous Solutions on Metal Surfaces

The contact angles of the aqueous solution of ethanol and that of n‐propanol on copper, aluminum, and stainless steel surfaces are reported. The contact angles were measured under atmospheric conditions, and then under vapor‐liquid equilibrium conditions at 1 atm and different temperatures. The results showed the variations of the contact angles with the concentrations of aqueous solutions on different metal material surfaces with different roughness. Some unstable behavior of the wetting ability around the azeotropic point of a binary solution is reported. Influences of concentration, kind of materials, and the surface roughness on the wetting ability are discussed. The model for predicting the contact angle of alcohol aqueous solutions on metal surfaces under atmospheric and vapor‐liquid two‐phase equilibrium conditions at 1 atm is derived from the Young equation.     

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.     

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.     

Study of Composition of Leached Glass Surfaces by Photoelectron Spectroscopy

The effects of water attack on the surfaces of 2 bulk glasses, including changes with time of exposure to air after water exposure, were determined using X-ray photoelectron spectroscopy. Although the layer explored was extremely thin (∼30 Å), this nondestructive technique has potential for quantitative analysis. The results obtained for an industrial glass and an experimental nonresistant one are compared, i.e. the rapidity of ion exchange at the glass-water interface, fluctuation of Na content in the glass surface during water exposure, migration of Na through the SiO₂ surface layer, and nonmigration of Ca under the same conditions. The present results agree with those obtained by other workers from solution analysis and other surface-sensitive physical techniques. The surface of lead crystal glass exposed to dilute acetic acid was also studied.     

Dyes Adsorption from Aqueous Solutions by Chitosan

In this study the ability of chitosan to remove acid, basic, reactive, and direct dyestuffs by adsorption was studied. The effect of several factors influencing dye adsorption such as dye concentration, grain size, pH, and temperature were investigated. Desorption of dyes at different pH was also examined. It was shown that the adsorption capacities of chitosan were comparatively high for acid and direct dyes and that the adsorption was controlled by the acidity of the solution. The kinetics of adsorption were found to be of pseudo second order. Batch isotherm studies showed that adsorption of dyes from aqueous solution by chitosan was described by the Langmuir equation.     

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.     

The Heterogeneity of Glass Surfaces Revealed by Temperature Programmed Desorption

Adsorption of butanol and pyridine on E‐glass fibers with three different compositions, as well as on powders of silica and the crushed fibers, was studied by temperature programmed desorption (TPD) with a mass‐sensitive detector. In the case of butanol, there are two types of desorbing molecules: at lower temperatures butanol desorbs, but in the range 450°C–600°C, 1‐butene desorption is also observed. It is shown that 1‐butene desorption is due to thermal decomposition of butanol chemisorbed to OH groups on both the glass and silica surfaces. The binding energy distributions of adsorption sites for butanol and pyridine are similar on all three glass compositions, but they are much more heterogeneous compared to silica; this difference is most evident for pyridine and is attributed to the presence Al and B in the glasses. The decomposition temperature of chemisorbed butanol is highest for silica and depends on glass composition for the fibers and powders. Interestingly, the glass which does not contain boron shows a well‐defined peak for the decomposition of chemisorbed butanol, suggestive of unique adsorption sites on this boron‐free surface; but they are much less temperature stable than the chemisorption sites on silica. In situ exposure to water vapor increased the number of active sites for chemisorption.     

Removal of Detergents from Aqueous Solutions by Foaming

Abstract

The anionic (sodium tetrapropylenebenzenesulfonate, Nansa HS-55) and nonionic (polyethoxylated alkylphenol, Alfenol) detergents were removed by the foaming method. It was found that there is a possibility of improving the foaming effect of a nonionic detergent by the introduction of a feeding solution into the foam phase. As far as an anionic detergent is concerned, the influence of the kind of feeding was minor in the case of aqueous solutions as well as with those containing sodium chloride. A simple graphic method is presented for the determination of the number of the foaming processes or the number of columns which are to be used in order to obtain the required detergent removal effect.     

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.     

Deformation of Interparticle Necks by Diffusion-Controlled Creep

The deformation of a neck between two spherical particles of the same size by coupled grain-boundary and surface diffusion has been simulated numerically through the finite-difference method. In the case of pure sintering where there is no applied stress, the results agree quite well with simple analytical models. When a force is applied, it is found that they do not deform as truncated spheres, even when surface diffusion is much faster than grain-boundary diffusion. Expressions are given representing the rate of approach of the particles and the rate of growth of the neck as a function of the current neck radius and the applied stress.