Ion Depletion of Glass at a Blocking Anode: II, Properties of Ion-Depleted Glasses

The application of an electric field to an ion-conducting glass at high temperatures will cause depletion of mobile ions beneath a blocking anode. The present study extends the investigation of ion depletion to several types of ion-conducting glass and presents new data for the physical and chemical properties of depleted surfaces. Ion-scattering spectrometry and electron microprobe analysis show that all positive monovalent and divalent ions are removed from the vicinity of the anode. The less mobile ion species are observed to pile up beneath the depleted region. Experimental data indicate that the removal of ions from the vicinity of the anode creates a microporous region that densifies at a rate determined by glass composition, temperature, and voltage. Ion-depleted surfaces display a lower refractive index and an increased electrical resistivity compared to untreated glass. Ion depletion also imparts an enhanced chemical durability to glass surfaces and increases the breaking strength of some glasses.     

Internal Friction of Simple Alkali Silicate Glasses Containing Alkaline-Earth Oxides: I, Experimental Results

The internal friction of simple alkali silicate glasses to which systematic alkaline-earth oxide additions were made was investigated. These additions produced two significant results: (1) The two peaks previously reported in alkali silicate glasses were shifted to higher temperatures and decreased in height and (2) a third peak was found in some glasses which became more pronounced with increasing alkaline-earth oxide content. Internal friction measurements of alkali-free silicate and phosphate glasses also are described. In these glasses, peaks were present which closely resembled those found in glasses containing alkali.     

Physical Properties and Structure of Silicate Glasses: I, Additive Relations in Alkali Binary Glasses

Correlations between certain physical properties, P , and all eighteen compositional ratios between the five ionic parameters of the system were studied with a computer for the five alkali silicates. Linear relations were found between P and the alkali/silica, alkali/oxygen, and silica/alkali ratios for certain regions of the glass field when the P's are expressed in proper molar terms. Specific volume and heat of formation data indicate three linear regions with two sharp break points between. The log electrical resistivity and the volatilization loss show two such regions and only the second break point. The break points, while structural in origin, must therefore occur for different reasons. The break points are the same for all P's and coincide with the eutectics. The constants of the linear relations are the partial molar quantities associated with P. Break points are not found in the molar refractivity data, so that no change in ligancy for these systems is indicated.     

Mechanical Relaxations in Mixed-Alkali Silicate Glasses: I, Results

The internal friction of silicate glasses containing mixtures of Li-Na, Li-K, Li-Rb, Li-Cs, Na-K, Na-Rb, Na-Cs, and K-Rb was measured from -180° to 500°C at a frequency of 0.4 Hz. Values for the density, index of refraction, and dynamic shear modulus are also reported. With small additions of a second alkali, a new internal friction peak was observed in addition to the two peaks originally present in the glasses containing only one alkali. The magnitude of this new peak was especially sensitive to small amounts (less than 1 mol%) of a second alkali. Activation energies are given for the alkali peak in Li-Cs glasses and for the new internal friction peak in Li-Na glasses.     

Compressibility of Binary Alkali Borate and Silicate Glasses at High Pressures

Isothermal compressibility data at 21°C. at pressures between 1000 and 10,000 atmospheres are reported for the binary alkali borate and silicate glass systems. In general, a decreasing compressibility is noted with increasing alkali content in both silicates and borates, the effect being much greater in the borates in the range of compositions studied. A maximum compressibility appears to be indicated for the potassium silicates at low potassium concentrations. In silicates and at high alkali contents in the borates, the order of compressibility is K > Na > Li. At low alkali contents in the borates, this order appears to be reversed. Possible interpretations of these data are discussed in terms of the concepts of the structura of glasses.     

Colors and Magnetic Properties of Iron in Glasses of Various Types and Their Implications Concerning Structure: I, High Alkali Silicate Glasses

The effect of increase of alkali and the replacement of soda by potash and lithia was studied in glasses containing iron and melted under strongly reducing conditions. An increase of alkali in these glasses causes an increase in the absorption throughout the visible spectrum; this is attributed, from magnetic and optical measurements, to Fe2+04 incorporated in the molecular network of the glass structure and having a very low magnetic susceptibility as found in some black spinels (hercynite).     

Mechanical Relaxations in Mixed Alkali Silicate Glasses: II,Discussion*

The internal friction of mixed Li-Na, Li-K, Li-Rb, Li-Cs, Na-K, Na-Rb, Na-Cs, and K-Rb silicate glasses is interpreted on the basis of the various explanations proposed for the mixed alkali effect. A direct correlation was found between the mechanical loss peak due to the stress-induced movement of the alkali ions, i.e. the alkali peak, and the electrical loss properties. The large mechanical loss peak appearing when the alkalis are mixed was attributed to an interaction between dissimilar alkali ions such that an elastic dipole is formed. The absence of a comparable electrical loss peak was interpreted as indicating that the elastic dipole is electrically inactive. In glasses containing equimolar quantities of two alkalis, the activation energy and height of the new loss peak, i.e. the mixed peak, were more closely related to the size difference than to the mass difference of the alkali ions.     

Short-Range and Medium-Range Order in Lithium Silicate Glasses, Part I: Diffraction Experiments and Results

Silicate glasses of the composition (Li₂O) _x (SiO₂)_100−x ( x = 0, 20, 33.3, and 40) have been prepared and characterized by X-ray and neutron diffraction experiments using the technique of isotopic substitution. Thus, at each composition, a set of independent diffraction patterns allows the discussion of the short-range and medium-range structure. For the short-range structure, average coordination numbers and atomic-pair distances are obtained from the pairdistribution functions. For the medium-range structure, i.e., for atomic-pair distances >0.5 nm, an increase of the amplitudes of the oscillations in the pair-distribution function is observed with increases in the Li₂O content.     

Copper ⇌ Alkali Ion Exchange of Alkali Aluminosillcate Glasses in Copper-Containing Molten Salt: I, Monovalent Copper Salt, CuCl

Cu⁺⇌ R⁺ (R = Li, Na, and K) ion exchange experiments were conducted for 20R₂O·10Al₂O₃·70SiO₂ glasses in molten CuCl at 550°C in air and nitrogen atmospheres. The depth profiles of the copper incorporated into glasses were determined with an electron microprobe X-ray analyzer. The total amount of diffusing copper, M _t, strongly depended on the type of alkali ion in the glass and the ion-exchange atmosphere; i.e., M _t increased with increasing cationic size in the order Li < Na < K and M _t was greater in air than in nitrogen. The Cu ⇌ R⁺ ion exchange kinetics are discussed in detail.     

Physical and Mechanical Properties of Barium Alkali Silicate Glasses for SOFC Sealing Applications

The physical and mechanical properties of two barium alkali silicate glasses were determined as a function of temperature. Their Young's modulus and Poisson's ratio were determined by resonant ultrasound spectroscopy; their viscosity, thermal expansion, and glass transition temperature were determined using a thermomechanical analyzer. The wetting behavior of the two glasses on alumina and 8 mol% yttria stabilized zirconia (8YSZ) substrates was determined by measuring contact angles in air as a function of temperature and time. Values of Young's modulus for both glasses were in good agreement with those predicted by the Makishima and MacKenzie model. The physical and mechanical properties of these glasses are discussed in the context of their potential use for sealing applications in solid-oxide fuel cells.     

Relation of Alkali Mobility and Mechanical Relaxation in Mixed-Alkali Silicate Glasses

Internal friction and Na and K self-diffusion coefficients for (I–X)Na₂OXK₂O-3SiO₂ glasses were measured. Alkali diffusion was measured between 300° and 500°C using radioactive isotopes and a thin-sectioning technique; internal friction was determined at room temperature to 500°C at 0.1 to 2000 Hz. Comparison of the data for alkali diffusion and internal friction in Na-K glasses with those for other mixed-alkali glasses shows that the mixed-alkali peak is related to alkali mobility. It is concluded that the mechanism of mixed-alkali internal friction is cooperative rearrangement of dissimilar alkali ions, with the slower-moving ion controlling the rate of reorientation.     

Sodium Diffusion in Glass: I, Single-Alkali Silicate

The isotope effect for ²²Na/²⁴Na diffusion was measured for three 25-mol% alkali-silicate glasses. A multiple diffusion mechanism wherein the Na ions diffuse both singly (vacancy mechanism) and in pairs (interstitialcy mechanism) provided the best agreement with the experimental data. According to this tentative model, diffusion by Na ion pairs predominates at low temperatures, and the fraction of Na ions diffusing singly increases with increasing temperature. In the glasses investigated, nearly all of the Na ions diffuse singly in the vicinity of the transformation range.     

A Model of Fluctuation Free Volume and the Valence-Configurational Theory of Viscous Flow of Alkali Silicate Glasses

The activation volume and the free activation energy of viscous flow of alkali silicate glasses at the glass transition temperature are estimated in the framework of the fluctuation free volume theory. The results are in agreement with the data obtained in terms of the valence-configurational theory of viscous flow. The interrelation between the parameters of these theories is discussed.     

Internal Friction of Simple Alkali Silicate Glasses Containing Alkaline-Earth Oxides: II, Interpretation and Discussion

The results of internal friction measurements on simple three-component glasses that were reported in Part I of this paper are discussed. From a consideration of the basic equations governing internal friction and examination of the results of other investigators, a basis of interpretation is developed. It is shown that changes in peak-temperature position can be explained by changes in the activation energy of the process causing the peak. A change in peak height not accompanied by a change in the shape of the peak is shown to be due to a change in the concentration of the relaxation mechanisms. Using this information the changes in the peaks due to composition variations are explained on a structural basis. A mechanism is also suggested to explain the new high-temperature peak. A critical examination of the measurements on alkali-free and phosphate glasses leads to the conclusion that it may be necessary to re-evaluate some of the concepts concerning the low-temperature peak in alkali silicate glasses.     

Sintering of Low-Density Glasses: I, Theory

An analysis is presented which describes the rate at which a cubic array of cylinders densifies by viscous flow driven by surface energy reduction. The cubic array is proposed as a model for the microstructure of low-density, open-pore materials such as gels and flame-hydrolysis preforms. The parameters of the model structure (cylinder length and radius) can be deduced from Hg penetration porosimetry.     

Spontaneous Bubble Formation in Silicate Melts at High Temperatures: II, Effect of Wet Atmospheres and Behavior of Mixed Alkali Glasses

Earlier work with alkali silicates was extended. Time and temperature for originally melting the glass had little influence on bubble or foam formation. Water vapor in the furnace atmosphere lowered foaming temperature considerably. Mixed alkali glasses showed complex and unexpected behavior. Nucleation and growth of foam bubbles as well as foam stability are discussed.     

Pulsed Cathodoluminescence and Vibrational Structure of Localized Electronic States in Alkali Silicate Glasses

The cathodoluminescence of localized electronic states (L intrinsic centers) in glasses of the composition (mol %) 22Me ₂O · 3CaO · 75SiO₂ and Me ₂O · 3SiO₂ (Me = Li, Na, K) is investigated upon excitation with a pulsed electron beam (180 keV, 700 A/cm², 2 ns). The luminescence spectra recorded in a pulsed periodic mode contain bands of L centers of two types whose occurrence reflects the formation of fragments with different degrees of atomic ordering in the microstructure of glasses. The line spectra with separations between the lines ₀ = 820 cm^-1 and ₁ = 520-640 cm^-1 are measured in a single-pulse mode. The effect revealed is attributed to the manifestation of the vibronic interactions during radiative relaxation of the triplet state of L centers. It is demonstrated that, according to the mechanism of cathodoluminescence, electronic excitations interact with local vibrations of nonbridging oxygen atoms and phonon modes of the glass network. The corresponding interactions are classified as vibronic(₀) and electron-phonon (₁) interactions.     

Infrared Absorption of Some Alkali Borate and Alkali Silicate Glasses Containing Nickel &amp; Iron Oxides

This work has been carried out to investigate the infrared absorption spectra, of a number of alkali borate and alkali silicate glasses containing nickel oxide and/or iron oxide to investigate the structure of theses glasses. All glasses studied were melted in platinum 2 % rhodium crucibles in an electrically heated furnace at different temperature (1000 – 1400) ⁰C for two hours. The results are explained on the basis that the nickel and ferric ions exist in glass as divalent nickel and trivalent ferric ions respectively in two different states, i.e., octahedral and tetrahedral coordinations.     

Ion Diffusion in Oxide Glasses and Melts: I. Bibliography

The first part of the review generalizes the basic results and the bibliography of experimental works on the self-diffusion and heterodiffusion of different-type ions in oxide glasses and glass-forming melts.