Sodium Transport in the Na2O-H2O-SiO2 Glass System

The variation with water content of dc conductivity and Na diffusion coefficient for the Na₂O · 4siO₂ and Na₂O · 2SiO₂ glass systems was found to be similar to that of the Na₂O.3SiO₂ series reported earlier. The conductivity was estimated for the ternary system Na₂O-H₂O-SiO₂ by combining the present results with the previous data on the Na₂O · 3SiO₂ system. When the conductivity of those glasses with a constant [Na₂O] + [H₂O] content was plotted against water content, a pronounced mixed "alkali" effect was demonstrated. The Haven ratio, calculated by comparison of the dc conductivity to the Na diffusion coefficient at 100°C for each of the three glass systems, was found to increase toward unity with increasing water content. This suggests that the addition of water reduces the number of sodium charge carriers. The subsequent increase in conductivity beyond the minimum with the introduction of larger amounts of water is, probably, due to an increase in the mobility of the Na⁺ ions.     

Effect of Water Content on the Electrical Conductivity of Na2O≅3SiO2 Glass

Na₂O–3SiO₂ glasses with up to ≅12 wt% water were prepared under high-pressure, hydrothermal conditions and their electrical conductivities were measured. The conductivity (σ) was found to depend on H₂O content in a manner similar to the "mixed-alkali" effect. At constant temperature, σ decreased initially with increasing H₂O content to a minimum at 3≅4 wt% H₂O and increased with further increase in water content. Infrared spectroanalysis of these glasses was made to determine the type of water present in the glass and the results were interpreted in the context of the measured activation energy and preexponential factor of dc conductivity. The sodium ion diffusion coefficient for a glass containing 0.76 wt% H₂O was less than that of water-free glass and in agreement with the electrical conductivity results.     

Infrared Spectra of a Water-Containing Glass

Infrared absorption was measured on an NajO-K₂O-ZnO-Al₂O₃-SiO₂ glass with up to ∼11 wt% water. Fundamental and overtone-combination bands were observed at 1.41, 1.91, 2.22, 2.87, and 6.1 μm. Molar absorptivities were determined for the hydrated glass for H₂O and OH levels using the molar absorptivity calculated for the 2.22-μm band in the as-melted glass. By this procedure the concentration of molecular water and OH groups could be determined separately. These results show that the OH content of the hydrated glass, as determined from the 2.22-μm band, is constant at >7 wt% H₂O; additional H₂O is attributed to molecular water only. Good agreement was found between these data and H₂O/OH molecular ratios obtained from NMR.     

Structure and Properties of Silver Borate Glasses

Clear glasses form in the system Ag₂O-B₂O₃ up to about 35 mol% (65 wt%) Ag₂O. Infrared absorption, thermal expansion, and density data indicated an analogy to the Na₂O-B₂O₃ system. Pentaborate-triborate group pairs appear to be formed on addition of Ag₂O to B₂O₃ up to 20 mol% Ag₂O and diborate groups from 20 to 33 mol% Ag₂O. This interpretation is supported by the comparison of the infrared absorption spectra of quenched and crystallized glasses. One crystallization product, Ag₂O-4B₂O₃, was identified previously. A new compound starts to appear at 28 mol% Ag₂O. The theory that silver is generally present as a network modifier like sodium was substantiated by the comparison of the molar volume of sodium and silver borate glasses. Above 27 mol% Ag₂O some atomic silver is assumed to be present; below 15 mol%, exploratory studies indicate a two-phase structure within an immiscibility gap. A low-temperature internal friction peak in the glasses up to 28 mol% Ag₂O corresponds to the alkali peak in other glasses; a high temperature peak appearing in the 34 mol% Ag₂O glass is associated with the appearance of nonbridging oxygen in the system.     

Visible Spectroscopy of Irradiated High-Alkali Borate and Mixed-Alkali Phosphate Glasses

Expectations of increased stability for trapped electrons in high-alkali glasses, based on extrapolations from observations on low-alkali borate glasses, are not borne out. In 69Na₂O-31B₂O₃ glass, electron centers have approximately the same thermal stability as in Na₂O·2B₂O₃ glass. In Na₂Oplus;P₂O₅ glasses the lifetimes, 3 · 0.5 μS, of transiently trapped electrons as well as their absorption spectra prove to be independent of increase of Na₂O content from 50 to 60 mol%. The same composition change destabilizes "permanent" hole centers. Exchange of Na₂O with K₂O in the metaphosphate glass also has no effect on the trapped electron lifetime. Small linear shifts in the trapped-hole absorption peak wavelengths are observed in the latter case. The most important positive finding in the phosphate glasses is a pronounced mixed-alkali effect on the yield of transiently trapped electrons and holes and of permanently trapped holes. The yield is a minimum at Na:K=1:1, due either to the elimination of trap sites or to the reduction of alkali ion mobilities which play a role in trap formation.     

Corrosion of Lead Glasses in Acid Media: I, Leaching Kinetics

The leaching kinetics of lead glasses (25 to 35 mol% PbO-75 to 65 mol% SiO₂; some with K₂O and A1₂O₃, additions) were determined in 10% acetic acid. Except for a ternary glass (SiO₂-PbO-K₂O) which had a linear dependence on time, all compositions exhibited a linear dependence on the square root of time for the amount of Pb and K removed. Increasing the SiO₂: PbO ratio or the Al₂O₃ content improved the durability whereas adding K₂O to a binary PbO-Si0₂ glass greatly increased the corrosion rate. Activation energies for the rates of Pb and K removal were determined for three compositions and it was deduced that the diffusion of H⁺ controlled the leaching for binary and 4-component glasses whereas dissolution of the silica network was rate-controlling for the ternary.     

Influence of Al2O3, ZnO, and K2O on the Opacity of Fluoride-Opacified Glasses

In the glass SiO₂ 71, Na₂O 17, CaO 12% with 7.5 parts per hundred of fluorine added to the batch, substitution of up to 6% ZnO for CaO produced a great increase in the opacity; substitution of Al₂O₃ for SiO₂ or of K₂O for Na₂O produced much smaller effects, which were dependent on the composition and were inappreciable in the presence of 6% ZnO. Despite the differences in opacity, no differences in fluorine content were detected. No support was found for the belief that Al₂O₃ is essential to the successful opacification of a glass by means of fluorides.     

Leaching of Glasses with Molar Composition 20Na2O · 10RO ·x Al2O3· (70-x)SiO2

Sodium depth profiles were determined in water-leached glass samples with molar composition 20Na₂O · 10RO · x Al₂O₃· (70 - x)SiO₂ (RO = CaO, MgO, and ZnO) using secondary ion mass spectrometry. The leaching of sodium ions decreases with increasing Al₂O₃ content in all three glass systems. For x = 0 the leaching is hardly affected by the nature of the divalent cation. For x = 5 and 10 the corrosion resistance is highest for the glass containing ZnO, and for the glasses containing ZnO and MgO, respectively. These glasses correspond to those with the smallest fraction of NBOs. From all these results it is concluded that the nonbridging oxygen atoms play an important role in promoting the leaching of a glass.     

Effects of Water Content on the Properties of Sodium Aluminosilicate Glasses

Sodium aluminosilicate glasses of the general formula 25Na₂O. x Al₂O₃.(75 – x )SiO₂ were prepared with a range of hydroxyl contents. Both the glass transformation and isokom temperatures decrease as the hydroxyl content increases. The magnitude of the decrease in each property is a function of the alumina content of the glass, with the largest effects occurring for the glass containing 25 mol% Al₂O₃. The magnitude of the effect of water as a function of alumina content reflects the decrease in the concentration of nonbridging oxygens in the glass with increasing Al₂O₃ content, since the effect of the terminal hydroxyl species on the connectivity of the glass is enhanced by the elimination of nonbridging oxygens. The results indicate that the large effect of water content on the properties of these glasses must be considered when discussing the role of alumina in glasses.     

Volume Relations in Na2O·B2O3 and Na2O·SiO2 B2O3, Melts at 1300·C

Density (and some viscosity) data are presented for binary sodium borate melts containing as much as 60 mole % Na₂O and for ternary sodium silicoborate melts with B/Si <2.0 between 1000°C and 1300°C. The high-temperature partial molar volume analysis of the binary sodium borate melts reveals about 50% BO₄ tetrahedra at the 40 mole % Na₂O composition, in agreement with recent NMR estimates for the binary glasses. No "boron anomaly" was found near 18 mole % Na₂O at high temperature. The synthetic partial molar volume model that agrees best with experiment for all ternary melts studied involves the presence of some BO₄ tetrahedra, the percentage of which varies with composition. This ternary model involves a high degree of internal consistency. No tendency toward extensive micro-immiscibility was observed for ternary melts near the SiO₂·B₂O₃ binary.     

Molybdenum Phosphate Glasses Containing Ag2O or K2O

Glasses in the systems MoO₃-P₂O₅-Ag₂O and MoO₃-P₂O₅-K₂O were investigated and general areas of composition for good glass formation were determined by X-ray diffraction methods. Temperature coefficients of electrical resistivity and linear expansion were determined for the glasses along with density, durability, and other thermal characteristics. Resistivity of the glasses was effectively reduced by the addition of Ag₂O.     

Conductivity Activation Energy Relations in High-Sodium-Content Borate and Aluminoborate Glasses

Glasses were prepared having compositions x Na₂O + (1 − x )B₂O₃ and x Na₂O + (1 − x )( n B₂O₃·Al₂O₃) where n = 4.0 and 6.7, and their conductivities and activation energies were determined up to 70 mol% Na₂O. Below 50 mol% Na₂O, the conductivity activation energy decreases with Na₂O content, which is attributed to a decreasing cation jump distance. Above 50 mol% Na₂O, however, the activation energy increases with Na₂O content. These measurements are the first to clearly show a conductivity activation energy increasing with alkali oxide content, an effect which is not yet explained by any of the current models of ionic conduction in glass.     

Properties and Structure of Glasses in the Binary Systems Alkali—TiO2

Glasses corresponding to mole formulas R₂TiO₃ and R₂Ti₂O₅ were prepared in 1- to 5-g quantities by quenching in a platinum crucible. K₂O, Rb₂O, and Cs₂O formed fairly stable glasses with TiO₂. On heat treatment, these glasses nucleated readily and formed opal-like glasses. Li₂O and Na₂O, however, did not form glasses with TiO₂ in 1-g quantities. Hygroscopicity increased with the alkali content and decreased with the increase in TiO₂ concentration. The refractive indices of the glasses ranged from 1.66 to 1.90. These facts indicate that TiO₂ is a glass former in its own right and that Ti⁴⁺ exists in sixfold coordination in these glasses.     

Solubility of Water Vapor in Alkali Borate Melts

The solubility of water vapor at 750° to 1050°C was determined for alkali borate melts containing 0 to 40 mole % Li₂O, Na₂O, or K₂O. In all cases the solubility in these melts is linearly proportional to the square root of the H₂O partial pressure. At p H₂O = 1 atm and T = 900°C, o.5 to 2.2 mole % H₂O are dissolved in the melts in equilibrium. In the potassium borate melts a minimum of solubility was observed at about 25 mole % K₂O; in the sodium borate melts the minimum was at 35 to 40 mole % Na₂O. In the lithium borate melts a minimum of solubility was not reached in the range of compositions investigated. These results are discussed in terms of a concept for the acid-base properties of melts and glasses in which the position of the solubility minimum corresponds to the "neutral point" of an acidity-basicity scale. Some corroborating qualitative observations concerning the evaporation of components from the glass melts and the chemical resistivity of the corresponding solid glasses are discussed.     

Nano-Blast Synthesis of Nano-size CeO2–Gd2O3 Powders

CeCl₃·7H₂O and GdCl₃·6H₂O that were dissolved in water were precipitated with urea (NH₂CONH₂) to produce matrix agglomerates for three-component nano-reactors. Mixing hexamethylenetetramine with dilute nitric acid resulted in the formation of well-dispersed nano-particles of cyclotrimetilene trinitramine (C₃H₆N₆O₆) (RDX) in the solvent. Nano-reactors were produced by impregnating the nano-C₃H₆N₆O₆ into the matrix agglomerates of an intermediate complex of cerium and gadolinium compounds. Blast initiation of the C₃H₆N₆O₆ resulted in extremely rapid detonation and gaseous products formation at temperatures of 2000°–5000°C, which were compressed into a volume nearly equal to the initial volume of each RDX nano-particle. Multiple "nano-blasts" occurred in the volume of each nano-reactor. The impact of the blast waves led to fragmentation of the surrounding matter. The evolution of a large volume of gaseous products dissipated the heat of the process and limited temperature increase, thus reducing the possibility of local sintering among the primary particles. The short-term high temperature generated during the blasts enhanced the solid solubility of the metal oxides. Uniform aggregates of 22∼74 nm consisting of 6∼14 nm crystallites of gadolinia in ceria solid solution were synthesized.     

Properties and Structure of Glasses in the System Bi2O3-SiO2-GeO2

In the system Bi₂O₃-SiO₂-GeO₂, good glasses can be formed only from limited compositional regions consisting of 2 narrow strips along the lines x Bi₂O₃-(100-:t) GeO₂ ( x ≤40) and 40Bi₂O₃ y SiO₂ (60- y )GeO₂ (mol%); such glass is dark brown. Compositions from a large region (Bi₂O₃ content <40 mol%) showed immiscibility. In the binary system Bi₂O₃-GeO₂, density and refractive index vary linearly with composition (mol%). Negative deviations of molar volume from ideality suggest that the coordination of a significant number of Ge ions is changing from 4-fold to 6-fold. Thermal expansion and electrical resistivity data are also reported.     

Glass Transition and Infrared Spectra of Low-Alkali, Anhydrous Lithium Phosphate Glasses

Anhydrous glasses in the series x Li₂O + (1 - x )P₂O₅ have been prepared and characterized in the range 0 ≤ x ≤ 0.5. FT-IR spectroscopy and glass transition temperature measurements have been used to explore the structure and a key physical property of the low-alkali phosphate glasses. The structure of v -P₂O₅ is proposed to consist of a 3-D network of trigonally connected tetrahedra decorated with a P=O unit. Contrary to what has long been proposed for these glasses, the addition of alkali degrades the 3-D network through the generation of nonbridging oxygens rather than strengthen the network through the proposed alkali ion bridging. The T _g of v -P₂O₅ is ∼653 K and decreases some 130 K with the addition of 10 mol% Li₂O. T _g then reaches a minimum value at 20 mol% Li₂O and increases with further Li₂O additions. The increase in T _g, even though the fraction of nonbridging oxygens is still increasing, is interpreted in terms of an increasing entanglement of long-chain PO₂ groups in the glass. Such a structural transition from a 3-D network of interconnected PO₄ groups for P₂O₅ to a 1-D chain structure for LiPO₃ is one of the first examples of the importance of intermediate-range order in governing the properties of glass.     

Densification and Phase Development of Spodumene–Cordierite Glass Powder Mixtures

The sintering and crystallization of spodumene-cordierite glass-ceramics that are made from mixtures of Li₂O-Al₂O₃-SiO₂ (LAS) and MgO-Al₂O₃-SiO₂(MAS) glass powders were investigated. Pure LAS and MAS powders have good sinterability. However, the densification of LAS was drastically reduced when small amounts of MAS were added. When larger amounts of MAS were added, the amount of densification further increased. The decrease in the Li₂O content in the LAS glass promoted the densification of the mixed glass samples. The above-mentioned results can be explained by examining the crystallization temperature, which is influenced by the interactions between the LAS and MAS glass particles. The lower the temperature of crystallization, the less sintering occurred. For the sintered samples, the phase that crystallized from the MAS glass was alpha-cordierite, and that which crystallized from the LAS glass was ß-spodumene or high-quartz solid solution, depending on the Li₂O content in the LAS glass.     

Compatibility of Hydrated Sodium MetasiIicate Glasses with Inorganic and Organic Compounds

By dehydrating crystalline Na₂SiO₃·9H₂O, a very low melting glass of the approximate composition Na₂SiO₃·3H₂O was obtained. The compatibility of selected inorganic compounds with this molten glass was found to be related to the nature of the cation or anion present in each compound. The behavior of organic indicator dyes in the glass melt provided further information on the nature of the molten glass, whereas the infrared spectrum of the glass gave an inconclusive result.     

Effect of Poling Temperature on Optical Second-Harmonic Intensity of Lithium Sodium Tellurite Glass

Second-harmonic generation has been observed in poled 10Li₂O10Na₂O80TeO₂ glass. The effect of poling temperature on the second-harmonic intensity has been examined. The second-harmonic intensity increases, attains a maximum, and then decreases as the poling temperature increases. In other words, an optimum poling temperature that results in a maximum second-harmonic intensity exists. The optimum poling temperature linearly increases as the glass-transition temperature increases for several types of tellurite glasses, including the present 10Li₂O10Na₂O80TeO₂ glass. This fact suggests that the process to create a polarization that results in the second-harmonic generation is affected by the structural relaxation at the glass-transition range. The thermal stability of 10Li₂O10Na₂O80TeO₂ glass is higher than that of 18Na₂O82TeO₂ (30NaO_1/270TeO₂) glass, as revealed via differential scanning calorimetry. As a result, the temperature range within which the poling is effective is wider for the former glass.