Interdiffusion and Phase-Boundary Reaction Between Silicate Glass Surface and Aqueous CsCl Solution

Technical silicate glass samples with fresh fracture surfaces or HF-etched surfaces were treated in aqueous CsCl at 90°C for 10 to 85 min. Reaction profiles were determined quantitatively using a SIMS technique. The Cs₂O concentration at the glass surface increased with increasing time, followed by penetration of Cs⁺ ions into the glass. The profiles can be described assuming a model which contains both a surface phase-boundary process and an interdiffusion process in the glass for which D=5.10⁻¹⁷ cm² s⁻¹.     

Measurement of ion concentration profiles in surface layers of leached (“swollen”) glass electrode membranes by means of luminescence excited by ion sputtering

A new method is described of measuring concentration profiles of luminous ions in glass surface layers. The method is applied to so-called “swollen surface layers” of lithium ion containing electrode membrane glass after treatment (“swelling”) in solutions of different pH containing various alkali metal ions. Thickness (up to 300 Å) and lithium concentration profile of the layers are a function of pH and Li⁺-concentration of the solutions. The results are discussed in terms of ion-exchange equilibria. The layers are defined as “leached layers”.     

Glass Surface Layer Density by Neutron Depth Profiling

Several lithium-disilicate ( Li₂O∙2SiO₂ ) glass samples were synthesized, polished and subjected to static leach tests for varying periods of time in an HCl solution (pH 4) at 90°C. The presence of an alteration layer on the leached specimens was independently confirmed using infrared spectroscopy. These samples were then analyzed with neutron depth profiling (NDP), and for all exposure times between 1 and 20 h, a leached layer was detected by NDP. The residual concentration of ⁶Li in the alteration layer was observed to be approximately 10% of the bulk glass value. The 7.5 h and 17.5 h samples were cross-sectioned using focused ion beam milling, and the thickness of the alteration layer on the samples was measured directly using scanning electron microscopy to be 9.8 and 22.9 μm, respectively. The areal density of the gel layers — determined by deconvolution of the NDP spectra — was coupled with the SEM measurement to give densities of 1.46 ± 0.08 g/cm³ for the 7.5 h specimen and 1.46 ± 0.05 g/cm³ for the 17.5 h specimen. This preliminary work shows that NDP can be used to determine the average density of gel layers formed owing to leaching of alkali-silicate glass.     

IR spectroscopic investigation of interaction between sodium aluminosilicate electrode glasses and aqueous solutions

The effect of introduction of aluminum oxide into the composition of sodium silicate glasses has been studied by IR absorption and reflection spectroscopy. The change in the spectroscopic characteristics of glasses after their treatment with HNO₃ and AgNO₃ aqueous solutions is analyzed. The concentration profiles of Na₊ and Ag₊ ions in the surface layers of these glasses are determined by the HF-sectioning technique. It is found that silver ions predominantly interact with the [AlO_4/2]^- groups in the glass. The leaching of sodium ions, formation of amorphous silica in the surface layers of the treated glass samples, and exchange of sodium ions by hydrogen ions are revealed from changes in the spectra.     

IR spectroscopic investigation of interaction between sodium aluminosilicate electrode glasses and aqueous solutions

The effect of introduction of aluminum oxide into the composition of sodium silicate glasses has been studied by IR absorption and reflection spectroscopy. The change in the spectroscopic characteristics of glasses after their treatment with HNO₃ and AgNO₃ aqueous solutions is analyzed. The concentration profiles of Na₊ and Ag₊ ions in the surface layers of these glasses are determined by the HF-sectioning technique. It is found that silver ions predominantly interact with the [AlO_4/2]^- groups in the glass. The leaching of sodium ions, formation of amorphous silica in the surface layers of the treated glass samples, and exchange of sodium ions by hydrogen ions are revealed from changes in the spectra.     

Effect of Heat Treatment on the Composition of Surface Layers in Lithium Silicate Glass Exposed to Acid and Salt Solutions

The concentration distribution of lithium ions in the surface layers of the 27Li₂O–73SiO₂ (mol %) glass samples subjected and unsubjected to heat treatment under different conditions after exposure to 0.1 M HCl + y M LiCl (y = 0, 1.0, 5.0, and 10) solutions is studied by the HF-sectioning technique. It is found that the specific (molded) layer formed on the glass surface upon pouring of a glass melt into a cooled mold affects the leaching processes in both the initial and phase-separated glasses. In the absence of the molded layer, the leaching rate of the initial glass in the acid is lower than that of the phase-separated glass and higher than that of the crystallized glass. The leaching rate of the phase-separated and crystallized samples in the acid with an salt additive is higher than that of the initial salt. Chlorine ions in the acid solution bring about a weakening of the silicon–oxygen network. The profiles of the dissolution rate of glass in a 1% HF solution correlate with the concentration profiles of lithium.     

Investigation of Glasses Using Surface Profiling by Spectrochemical Analysis of Sputter-Induced Radiation: II, Field-Driven Formation and Electrochemical Properties of Protonated Glasses Containing Various Proton Concentrations

The ion-sputtering technique for measuring concentration profiles in glass surfaces provides a method for studying ionic transport in solids. Simultaneous field-driven lithium ion and proton transfer from solutions into, and migration of these ions within, several lithium silicate glasses was investigated quantitatively. This work leads to the new field of protonated glasses which are distinguished by the availability of all sites to both cationic species. Conductivity and mobilities reported as a function of concentration (50°C) do not exhibit the typical features of the mixed-alkali effect. Mechanisms are proposed for ionic transfer across solution-glass interfaces and for migration of ions within protonated glasses. Small proton mobilities at low proton concentrations are explained in terms of specific sites which function as proton traps and are identified by infrared spectroscopy. The condition for stability of boundaries between migrating ions is discussed.     

Influence of Feed Composition and Drying Parameters on the Surface Composition of a Spray-Dried Multicomponent Particle

Surface properties of multicomponent particles produced in spray drying can be controlled by selective accumulation of specific components, which are present in the liquid feed, on the particle surface. Such modification of the surface composition can take place only before a solid shell forms on the particle surface. In this contribution, the influence of the concentration of surface active component on modifications of the surface composition is discussed. Based on results of single-droplet drying simulations, changes in the concentration of the surface active component at the solution-air interface are related to the composition of spray-dried particles.     

Analysis of Design Parameters in Anode‐Supported Solid Oxide Fuel Cells Using Response Surface Methodology

Achieving high performance from a solid oxide fuel cell (SOFC) requires optimal design based on parametric analysis. In this paper, design parameters, including anode support porosity, thicknesses of electrolyte, anode support, and cathode functional layers of a single, intermediate temperature, anode‐supported planar SOFC, are analyzed. The response surface methodology (RSM) technique based on an artificial neural network (ANN) model is used. The effects of the cell parameters on its performance are calculated to determine the significant design factors and interaction effects. The obtained optimum parameters are adopted to manufacture the single units of an SOFC through tape casting and screen‐printing processes. The cell is tested and its electrochemical characteristics, which show a satisfactory performance, are discussed. The measured maximum power density (MPD) of the fabricated SOFC displays a promising performance of 1.39 W cm^–2. The manufacturing process planned to fabricate the SOFC can be used for industrial production purposes.     

Surface Tension of Molten Glass from Drop Profile. Application to the Characterization of the Interface in Glass/Polymer Blends

A modified drop shape method has been developed to allow the simple determination of the surface free energy of a mineral glass. Our approach is based on the study of the profile of a large sessile drop of glass. The drop is formed by heating a glass cylinder settled on a horizontal solid plane.

The experimental parameters, in particular the size of the glass drop, leading to the accurate characterization of the surface free energy, have been determined by using mercury as a model of a high surface free energy liquid. It has been shown that the ratio between the diameter of the drop and the capillary length, (γ/ρμ)^1/2, must be of the order of 10.

In this paper, practical details and results of measurements are presented for a series of four different glasses. A clear relationship between glass composition and surface free energy is observed. In particular, tin oxide reduces significantly the surface free energy of zinc phosphate glass. The coalescence of glass particles is probably related to glass surface and glass/polymer interfacial free energies. A discussion on how this may impact glass/polymer blend processability is presented.     

Low‐Energy Ion‐Scattering Spectroscopy of Modified Silicate Glasses

Low‐Energy Ion‐Scattering (LEIS) spectroscopy is a technique with a unique sensitivity to the elemental composition of the top atomic layer of a solid surface. LEIS measurements of ternary silicate glasses modified with Na₂O, Cs₂O, CaO, and BaO show that the compositions of the as‐cast (melt) surface and the in‐vacuum fracture surface often differ. While the as‐cast surface is usually depleted of alkali ions (Na⁺ or Cs⁺) compared to the nominal (batch) glass composition, there is often strong accumulation of the same mobile cations on the fresh fracture surface. Depth profiles obtained by sputter etching reveal elemental concentration gradients normal to the glass surface. The final concentrations often fail to reach the nominal glass composition, suggesting the likely presence of preferential sputtering effects and thereby the distortion of the measured concentration gradient. At present, the lack of reliable standards and preferential sputtering effects in the LEIS of multicomponent glasses limit somewhat the absolute chemical composition and structural information that can be obtained with this otherwise unique and powerful method of surface analysis.     

Application of the SIMS Method in Studies of Cr Segregation in Cr-Doped CoO: I, Aspects of Quantitative Analysis

Aspects of calibration of intensities of SIMS secondary ions vs concentration as well as sputtering time vs depth are considered for Cr-doped CoO. Advantages and limitations of the SIMS method in quantitative analysis of segregation-induced concentration profiles in oxide crystals are discussed. The studies indicate a substantial effect due to charging the surface during sputtering. The depth calibration was performed by using the Ta₂O₅/Ta system as a standard. Good depth resolution was revealed. The calibration dependence of Cr intensities on concentration is characterized by a wide scatter of data caused by charging the surface. Very good shape reproducibility of the intensity ratio vs depth profiles was revealed. Therefore, normalized intensity ratios can be used for calibration.     

Surface textures induced by convection in thin films of polymeric and polymerizable fluids

Thin liquid layers of polymer solutions, oligomers and monomers, and oligomer–monomer bilayers were used as model systems to explore the mechanism of formation of surface textures in solid coatings and films. It was shown that under particular conditions vertical temperature gradients imposed on these fluid layers induce in them various types of convection. We demonstrated that hexagonal patterns with a high degree of order and symmetry are generated in fluid films undergoing surface tension-driven convection. Various non-equilibrium textures have been trapped in the solid state either by vitrification induced by solvent evaporation from the fluid layer, or by carefully performed polymerization of monomers and oligomers. Finally, we demonstrated that convection patterns can be replicated in convection-passive fluids by bringing them in contact with a fluid layer undergoing convection.     

Surface conductivity of nitrogen-doped diamond

Synthetic type Ib diamond crystals with (001) surfaces that expose growth sectors of different nitrogen content have been used to study the phenomenon of p-type surface conductivity upon plasma hydrogenation and upon overgrowth with thin epitaxial CVD diamond layers. We found that an unbiased microwave-driven hydrogen plasma leads to surface conductivity only on well-defined regions on the substrates that correlate with growth sectors of low nitrogen content; whereas no conductive layer is found on top of growth sectors with higher nitrogen concentrations in the range of 200 ppm. After growing a homoepitaxial intrinsic diamond layer of only 20 nm on top of the nitrogen doped diamond, these differences are no longer observed and surface conductivity is established homogeneously over the whole sample. The same effect can be achieved by exposing the Ib substrates to a pure hydrogen plasma provided the sample is biased with an additional DC voltage of −250 V. Both results can be understood in the framework of the surface transfer doping model suggested earlier by Maier and colleagues when the compensation of nitrogen donors by surface acceptors and their passivation by hydrogen is taken into account. The quantitative discussion shows that the doping capability of the surface acceptors is exhausted at lateral concentrations of approximately 1×10¹³ cm⁻², which also corresponds to the maximum hole concentration usually observed in hydrogen-induced p-type conductive layers.     

A solid–solid extraction

When a vessel containing two equal-sized particle species is subjected to vibration with an acceleration significantly greater than 1g, the particle bed sometimes separates into two clear-cut layers, the bottom layer consisting only of the lighter particles. This paper shows that the above inverse density segregation can be used to perform a solid–solid extraction. A mixture of equal-sized glass and steel beads (1290 μm in mean diameter) did not separate into two layers under vibration. However, when equal-sized lead beads were added to the mixture and the three-component mixture was subjected to vibration the bed separated into two clear-cut layers, the top layer being the mixture of the three components, the bottom layer consisting only of glass beads. The scale effect and the underlying mechanisms of this solid–solid extraction are discussed.     

Elemental Depth Profiling of Nuclear Waste Glasses after Two-Years Burial in a Salt Geology

Detailed surface compositional analysis has been conducted on 12 simulated nuclear waste forms leached for two years in the brine environment of the Waste Isolation Pilot Plant (WIPP). Secondary ion mass spectrometry (SIMS) of both cations and anions has identified characteristic leaching and precipitation zones within the leached layers on all specimens. The thickness of the leached layers is found to range from approximately 0.3 to 2.7 μm and the total element loss from 80 to 625 mmol/m², indicating that durability in brine differs by less than an order of magnitude between the different glasses. The in-depth profiles of anionic elements indicate the significant roles of carbon, fluorine, and chlorine in the formation of surface phases. Also recorded and discussed are elemental SIMS images of sputter crater tapers, providing additional documentation of leaching subzones.     

Surface Energy and Crystallization Phenomena of Ammonium Dinitramide

Ammonium dinitramide (ADN) was characterized during recrystallization from the melt. The surface tension of molten ADN at 97 °C was measured to be 89 mN/m. The wetting angles between molten ADN and different solid surfaces (polytetrafluoroethylene, glass, steel, and aluminum) were determined. The wettability depends on the surface tension of molten ADN, the free surface energy of the solid surfaces and the interfacial tension between the solid and liquid. Observations of the recrystallization behavior of molten ADN showed that nucleation does not occur, even at super cooling rates of 70 K. Crystallization can be initiated by the application of seed crystals.     

Surface profilometric study of the kinetics of the intercalation of graphite

The kinetics of the intercalation of graphite was investigated by measuring the c-face surface profiles during the intercalation of Br₂ into highly-oriented pyrolytic graphite cylindrical discs at room temperature. A sharp intercalate front was observed to advance while the surface profile evolved from a bucket-shape to a V-shape, as predicted by the model of interface-controlled intercalation proposed by the authors [11]. The average magnitude of the steady velocity of the front was ~ 15 Å/see; the initial period was marked by a larger velocity attributed to an edge effect. The same behavior was observed during ICI intercalation at room temperature. During desorption, inverted surface profiles were obtained, indicating that desorption may be the reverse of intercalation. In the case of HNO₃ intercalation at room temperature, bowl-shaped surface profiles were observed. Preliminary profile measurements were made during ICI intercalation at 50°C, at which the intercalate layers are known to be disordered.     

Surface shear stress relaxation of silica glass

A constant angle of twist was applied to silica glass rods in order to produce a torsional shear strain and a reduction in torque representative of the stress state in the glass was measured as a function of time when rods were heat-treated in air at temperatures, 550-700°C, far below the glass transition temperature. The monotonic decrease of torque with time was explained by surface stress relaxation, which can be described by a relaxation of stress at the surface of glass which is promoted by water. The obtained surface stress relaxation diffusion coefficients were consistent with those obtained earlier from silica glass fiber bending under a similar water vapor pressure. The observed relaxation in torsion supports the mechanism of surface stress relaxation over the swelling-based mechanism for applications including glass fiber strengthening.     

Characterization of Glass Beads Surface Modified with Ionic Surfactants

Knowledge of the wetting characteristic of mineral surfaces is very important in enhancing the efficiency of separation of valuable minerals from gangue using froth flotation or oil agglomeration. In this paper a capillary rise technique was used to characterize the glass beads surface modified with cationic surfactant. The glass microspheres were used as model particles with a spherical shape and smooth surface to eliminate the roughness effect. The value of the contact angle for water was found to be 21.5 for unmodified beads, and 61.8, 89.7, 68.4 for 0.1, 1.0, 10 mg/g_solid of CTAB, and 39.8, 68.6, 87.9 for 0.1, 1.0, 10 mg/g_solid of DDAHCl, respectively. Data revealed that the adsorption of surfactant onto glass beads decreased the value of the electron donor component, γ-, which defines the hydrophobicity of the surface. Also, the property of the surface was investigated by flotation and oil agglomeration experiments. It was observed that particles with low value of contact angle for water and high for 1-bromonaphthalene and low value of γ- were floated with a recovery equal to 91.1 and 83.1% for CTAB and DDAHCl, respectively, and effectively agglomerated. This indicates that the capillary rise method can be successfully used to predict the wetting properties of solid particles in mineral processing.