Dissolution behavior of ZnO–P2O5 glasses in water

Bulk binary ZnO–P₂O₅ glasses with 50–70 mol% ZnO were immersed in distilled water at 30–90 °C for up to 72 h. The immersed samples were characterized by weight loss, the change in solution pH, X-ray diffraction (XRD) analysis, scanning electron microscopy and Raman spectroscopy. Weight loss decreased with ZnO concentration for all immersion temperatures. Dissolution behavior was classified into two types in terms of weight loss and macroscopic appearance. Type I was primarily recognized in 50–60 mol% ZnO glasses. In type I, the weight loss for 72 h was relatively large (>1.0 × 10⁻⁷ kg mm⁻², >10% of initial sample weight). Raman spectra of the type I glasses indicated that the depolymerization of phosphate glass network occurred during the dissolution process. Crystalline Zn₂P₂O₇ · 3H₂O was precipitated in the water solution after immersion. Type II dissolution behavior was recognized in the 65 and 70 mol% ZnO glasses except for the 65ZnO–35P₂O₅ glass immersed at 90 °C. In the type II behavior, the weight loss for 72 h was relatively-small (<1.0 × 10⁻⁸ kg mm⁻², <1% of initial sample weight). The microstructure of the type II glass indicated selective dissolution. The dissolution process of the type II glass is discussed.     

Monte Carlo simulations of the dissolution of borosilicate glasses in near-equilibrium conditions

Monte Carlo simulations were performed to investigate the mechanisms of glass dissolution as equilibrium conditions are approached in both static and flow-through conditions. The glasses studied are borosilicate glasses in the compositional range (80 ? x)% SiO₂ (10 + x / 2)% B₂O₃ (10 + x / 2)% Na₂O, where 5 < x < 30%. In static conditions, dissolution/condensation reactions lead to the formation, for all compositions studied, of a blocking layer composed of polymerized Si sites with principally 4 connections to nearest Si sites. This layer forms atop the altered glass layer and shows similar composition and density for all glass compositions considered. In flow-through conditions, three main dissolution regimes are observed: at high flow rates, the dissolving glass exhibits a thin alteration layer and congruent dissolution; at low flow rates, a blocking layer is formed as in static conditions but the simulations show that water can occasionally break through the blocking layer causing the corrosion process to resume; and, at intermediate flow rates, the glasses dissolve incongruently with an increasingly deepening altered layer. The simulation results suggest that, in geological disposal environments, small perturbations or slow flows could be enough to prevent the formation of a permanent blocking layer. Finally, a comparison between predictions of the linear rate law and the Monte Carlo simulation results indicates that, in flow-through conditions, the linear rate law is applicable at high flow rates and deviations from the linear rate law occur under low flow rates (e.g., at near-saturated conditions with respect to amorphous silica). This effect is associated with the complex dynamics of Si dissolution/condensation processes at the glass–water interface.     

Structure and properties of NaPO3–ZnO–Nb2O5–Al2O3 glasses

In an effort to design low-melting, durable, transparent glasses, two series of glasses have been prepared in the NaPO₃–ZnO–Nb₂O₅–Al₂O₃ system with ZnO/Nb₂O₅ ratio of 2 and 1. The addition of ZnO and Nb₂O₅ to the sodium aluminophosphate matrix yields a linear increase of properties such as glass transition temperature, density, refractive index and elastic moduli. The chemical durability is also significantly, but nonlinearly, improved. The glass with the highest niobium concentration, 55NaPO₃–20ZnO–20Nb₂O₅–5Al₂O₃ was found to have a dissolution rate of 4.5 × 10^? 8 g cm^? 2 min^? 1, comparable to window glass. Structural models of the glasses were developed using Raman spectroscopy and nuclear magnetic resonance spectroscopy, and the models were correlated with the compositional dependence of the properties.     

Spectroscopic studies of tungsten ions in PbO–PbF2–SiO2 glasses

40PbO–(10 ? x)PbF₂–50 SiO₂:xWO₃ (where x = 1 to 7 mol%) glasses are prepared in the glass forming region. Spectroscopic studies (UV–Vis absorption, ESR, IR) are carried out for these glasses. Interesting changes are observed in the spectroscopic parameters of these glasses when the concentration of WO₃ is changing in the glass matrix. Two absorption bands are observed around at 830 and 620 nm. ESR signal are measured at room temperature for these glasses, the strength of the signal is increased and hyperfine splitting is resolved with increasing the concentration of WO₃ in the glass matrix. IR transmission gives valuable information about the nature of bonds in the glass matrix. The physical parameters along with spectroscopic parameters are measured.     

Manufacturing of porous niobium phosphate glasses

Niobium phosphate glasses with composition 33P₂O₅ · 27K₂O · 40Nb₂O₅ are usually very stable with regard to crystallization resistance, with a relatively high glass transition temperature (T_g ∼ 750 °C), and are potentially suitable for nuclear waste immobilization. Porous niobium phosphate glasses were prepared by the replication method. The porous glasses were produced via the dip-coating of an aqueous slurry containing 20 wt% powdered glass into commercial polyurethane foams. The infiltrated foams were oxidized at 600 °C for 30 min to decompose the polymeric chains and to burn out the carbon, leading to a fragile glass skeleton. Subsequent heating above the glass transition temperature in the range of 780–790 °C for 1 h, finally resulted in mechanically stable glass foams, which maintained the original interconnected pore structure of the polyurethane foam. The struts showed the neck formation between particles, evidencing the initial stage of sintering. The open and interconnected porosity of the glassy foams lies in the range of 85–90 vol.%. It was concluded that porous niobium phosphate glasses are potential candidates for immobilizing liquid nuclear waste.     

Synthesis and properties of cerium aluminosilicophosphate glasses

Cerium oxide is commonly added to silicate glasses as an optical property modifier. In particular, UV absorption, decoloration via redox coupling, and resistance to radiation-induced darkening are influenced by the addition of this rare-earth oxide. However, the limited solubility and visible color of rare-earth oxides in silicate glasses prevent any further beneficial enhancement of properties which might result from increasing the CeO₂ content. In contrast, rare-earth oxides are extremely soluble in phosphate glasses; for example, a binary cerium phosphate glass can incorporate up to 40 mol% CeO₂. Moreover, since the UV absorption edge of the phosphate network is blue-shifted compared to the silicate network, the effect of the Ce³⁺ absorption band tail on yellow coloration can be minimized.In this study, glasses in the cerium aluminosilicophosphate system were synthesized and a variety of physical and optical properties were measured including: density, refractive index, glass transition temperature, hardness, fracture toughness, and the location of the UV absorption edge. At ～9 mol% CeO₂, these cerium aluminosilicophosphate glasses exhibit similar coloration to commercially available silicate glasses which contain ～0.4 mol% CeO₂. Semi-quantitative photoemission analysis of the Ce oxidation states showed insignificant differences in the Ce³⁺/Ce⁴⁺ ratio between the phosphate and silicate glass systems.     

Luminescence properties and energy transfer of Eu/Tb ions codoped aluminoborosilicate glasses

Eu/Tb codoped aluminoborosilicate glasses were fabricated by high temperature melting-quenched technique and their luminescence properties were investigated by excitation and emission spectra. Under 376 nm excitation, blue, green and red emission bands were simultaneously observed at 425 nm, 485 nm, 540 nm and 611 nm, respectively. The broad blue emission band centered at 425 nm was originated from the reduced Eu²⁺ ions, which were reduced from Eu³⁺ ions at high temperature in an ambient atmosphere and the reduction process may be related with the optical basicity of glass matrix. A complex bright white light emission was obtained for 0.5 mol% Eu₂O₃, 0.5 mol% Tb₂O₃ codoped aluminoborosilicate glass with CIE-X = 0.31 and CIE-Y = 0.33. The energy transfer among Eu³⁺, Eu²⁺ and Tb³⁺ ions was also discussed.     

Electronic states of SnO-ZnO–P2O5 glasses and photoluminescence properties

SnO–ZnO–P₂O₅ glasses with 30 and 40 mol% P₂O₅ were prepared by a melting process in an air atmosphere. The glass transition temperature, refractive index, and photoluminescence of the glasses were investigated. The electronic states of Sn(II) and Sn(IV) were determined by Mössbauer spectroscopy. The PO₄ units were investigated by Raman spectroscopy. The glass transition temperature was lower than 450 °C, and decreased as the Sn concentrations increased, so that the minimum was about 250 °C. The refractive index increased as the Sn concentration increased. The emission spectra of the glasses peaked at around 2.0–3.0 eV and depended on the glass compositions.     

Electrical characterizations of silver chalcogenide glasses

We present a study of the electrical properties of silver chalcogenide glasses ‘40AgI’–30Ag₂S–30GeS₂, 45AgI–27.5Ag₂S–27.5GeS₂ and 50AgI–25Ag₂S–25GeS₂ in the 77–400 K temperature and the 20 Hz to 1 MHz frequency ranges. In our temperature range, a large variation of the real permittivity is observed, in relation with an electrodes polarization effect. As the amount of silver iodide increases in the Ag₂S–GeS₂ matrix, the glass transition temperature and the activation energies decrease, the electrical conductivity increases and reaches 4 Ω⁻¹ m⁻¹ at room temperature for the glass with 50% AgI. The study of the conductivity shows a behavior due to a high ionic conductivity, thermally activated with E_dc = 0.21 eV, E₁ = 0.075 eV (40AgI–30Ag₂S–30GeS₂, 45AgI–27.5Ag₂S–27.5GeS₂), E_dc = 0.17 eV, E₁ = 0.055 eV for 50AgI–25Ag₂S–25GeS₂. For these glasses, we have seen three conductivity regimes. The first two terms are thermally activated. The third term cannot be actually clearly identified because either it is thermally activated with a very low activation energy and frequency dependent, or it is almost non-thermally activated and frequency dependent.     

Phosphate speciation in sodium borosilicate glasses studied by nuclear magnetic resonance

The structure of RNa₂O · B₂O₃ · KSiO₂ · xP₂O₅ (0.5 < R < 2; 0.86 < K < 3) borosilicate glasses has been studied by nuclear magnetic resonance (NMR). ³¹P magic angle spinning (MAS), double quantum-magic angle spinning (DQ-MAS) and ³¹P–¹¹B transfer of populations under double resonance magic angle spinning (TRAPDOR MAS) NMR were used to determine the phosphate speciation in the glasses and their connectivity with the borosilicate network. The structure of the glass network was characterized with ¹¹B, ²⁹Si and ²³Na MAS NMR. Ab initio calculations of the ³¹P chemical shielding were carried out in order to confirm the connectivity between phosphorus and the structural units of the borosilicate glass network. Na₃PO₄ (monophosphate), Na₄P₂O₇ (diphosphate) and P–O–B species (mono- and diphosphate groups with borate units as the next nearest neighbors) are found all along the compositional range studied. The proportion of the P–O–B groups increases as the glass optical basicity decreases, while the proportions of mono- and diphosphate species decrease. The change in the glass transition temperature of the phospho-borosilicate glasses with respect to that of the borosilicate ones is discussed in terms of the structural characterization. The formation of phosphate species gives rise to the increase in T_g, which is attributed to the re-polymerization of the silicate network, while the formation of P–O–B bonds weakens the glass network and produces a decrease in the glass transition temperature.     

Kinetic fragility of hydrous soda-lime-silica glasses

The effect of hydration on the kinetic fragility of soda-lime-silica glasses was investigated by viscometry in the glass transition range. Water-bearing glasses were prepared from industrial float glass (FG) and a ternary model glass (NCS = 16Na₂O 10CaO 74SiO₂ in mol%) by bubbling steam through the melt at 1480 °C and up to 7 bar. Additionally, a sodium borosilicate glass (NBS = 16Na₂O 10B₂O₃ 74SiO₂ in mol%) was hydrated under equal conditions. As detected by infrared spectroscopy water dissolves in the glasses exclusively as OH-groups. The hydration resulted in a total water content C_W up to ≈ 0.2 wt% for FG, NCS and NBS glasses. Kinetic fragility, expressed by the steepness index m, was determined from the temperature dependence of η at the glass transition. Viscosity data from previous studies on hydrous float glasses (C_W > 1 wt%) were surveyed together with literature data on the (H₂O)–Na₂O–CaO–SiO₂, (H₂O)–Na₂O–SiO₂ and (H₂O)–SiO₂ systems to expand the range of water concentration and bulk composition. We could demonstrate that m decreases for all glasses although water is dissolved as OH and should depolymerize the network. An empirical equation of the general type m = a ? b logC_W where a, b are fitting parameters, enables m to be predicted, for each glass series as function of the water content C_W. The enlarged data base shows that the parameter B of the Arrhenius viscosity-temperature relation decreases much stronger than the isokom temperature at the glass transition.     

Heterophase inclusions and dissolved impurities in Ge25Sb10S65 glass

The impurity content and microhomogeneity of Ge₂₅Sb₁₀S₆₅ glass samples, prepared by direct synthesis from elements, were investigated. It was shown that the increase in temperature of synthesis of the glass-forming melt resulted in the increase of the content of impurities of H, Na, Al, Si, K, Ca and transition metals in the prepared glasses. The glasses from the melt, subjected to chemical-distillation purification, were characterized by the low content of gas-forming impurities and the increased content of Al, Si and Cl. The glasses contained heterophase impurity inclusions mainly consisting of SiO₂, and their concentration and size depended on the conditions of glass preparation. The impurity content in the purest glasses was as follows: oxygen – <0.5 ppm wt, carbon – <5 ppm wt, hydrogen – 0.1 ppm wt, Si – <1 ppm wt, transition metals – <0.25 ppm wt, heterophase impurity inclusions with sizes larger than 80 nm – <10² cm³. It was shown that heterophase impurity inclusions behaved as the centers of glass crystallization.     

Molar volume,glass-transition temperature,and ionic conductivity of Na- and Rb-borate glasses in comparison with mixed Na–Rb borate glasses

Mass densities, molar volumes, glass-transition temperatures, and ionic conductivities are measured in series of YNa₂O · (1 − Y)B₂O₃ glasses, with Y = 0.00, 0.04, 0.08, 0.12, 0.16, 0.20, 0.25, 0.30 and YRb₂O · (1 − Y)B₂O₃ glasses, with Y = 0.00, 0.12, 0.16, 0.20, 0.25, 0.30. Measurements of the molar volumes indicate that the incorporation of rubidium ions leads to a considerable expansion of the network, which is not observed for sodium ions. The glass-transition temperature increases with increasing alkali content and reaches a maximum near Y = 0.25 for both glass systems. These trends are attributed to changes in the glass network. For each glass composition an Arrhenius-activated increase of the product of dc conductivity and temperature is observed. The activation enthalpy decreases with increasing number density of ions. A comparison between the binary sodium- and rubidium-borate glasses from this work, with the ternary sodium–rubidium borate glasses studied earlier in our laboratory, provides interesting insights in the influence of the glass structure on ionic transport processes and the mixed-alkali effect.     

Compositional effects on fluorescence lifetime of Dy3+ ions embedded in chalcogenide Ge–As–S glasses containing very small amount of Ga and CsBr

We have investigated the fluorescence lifetimes of Dy³⁺: 1.3 μm emission in the chalcogenide Ge–As–S glasses with different compositions but identically containing 0.5 mol% Ga and 0.5 mol% CsBr. The measured lifetimes turn out to be sensitive not only to the concentrations of Ga and CsBr but also to compositional variations in the Ge–As–S host glasses. The lifetime is enhanced conspicuously in glass of the S-sufficient compositions, relative to the stoichiometric GeS₂–As₂S₃ composition, while this effect is not significant in the S-exact and S-deficient compositions. We employ Ga K-edge EXAFS analysis to support that the local structural environments of Ga in the modified chalcogenide glasses are closely correlated with the lifetime enhancement effect.     

Chromium phase behavior in a multi-component borosilicate glass melt

This paper reports the phase behavior of a multi-component borosilicate glass melt with 0–3 mass% Cr₂O₃ at 800–1500 °C in equilibrium with air. Both upper and lower liquidus temperatures were observed. When the temperature was between the upper and lower liquidus temperatures, eskolaite (Cr₂O₃) formed in melts with >2 mass% Cr₂O₃. Below the lower liquidus temperature, a dispersed chromate phase appeared in the melt that eventually became macroscopically segregated. The chemical durability of the glasses was virtually unaffected by chromium concentration. The particular glass studied was prototypic for vitrifying high-Cr high-level radioactive wastes stored in underground tanks at the Hanford site. The results suggest a significant potential cost benefit for Hanford tank waste cleanup through increased waste solubility in glass.     

The electrical switching and thermal behavior of bulk Ge15Te85 − xSnx and Ge17Te83 − xSnx glasses

Bulk Ge₁₅Te_85 ? xSn_x and Ge₁₇Te_83 ? xSn_x glasses, are found to exhibit memory type electrical switching. The switching voltages (V_t) and thermal stability of Ge₁₅Te_85 ? xSn_x and Ge₁₇Te_83 ? xSn_x glasses are found to decrease with Sn content. The composition dependence of V_t has been understood on the basis of the decrease in the OFF state resistance and thermal stability of these glasses with tin addition. X-ray diffraction studies reveal that no elemental Sn or Sn compounds with Te or Ge are present in thermally crystallized Ge–Te–Sn samples. This indicates that Sn atoms do not interact with the host matrix and form a phase separated network of its own, which remains in the parent glass matrix as an inclusion. Consequently, there is no enhancement of network connectivity and rigidity. The thickness dependence of switching voltages of Ge₁₅Te_85 ? xSn_x and Ge₁₇Te_83 ? xSn_x glasses is found to be linear, in agreement with the memory switching behavior shown by these glasses.     

Electron paramagnetic resonance and thermal behavior of vanadyl-doped mixed alkali bismuth borate glasses

Glasses with composition 15 Li₂O15K₂O10Bi₂O₃(60 ? x) B₂O₃: xV₂O₅ where x = 1, 3, 5, 7, and 9 mol% are prepared by normal melt-quench technique. Characterization of the prepared samples is done using X-ray diffraction, density and differential scanning calorimetry. The density and molar volume are found to increase with increasing x whereas the glass transition temperature decreases. Electron paramagnetic resonance spectra of the prepared samples are recorded using EPR-spectrometer operating in the X-band frequency. The resonance spectra are well resolved for x ≥ 5 mol% and the intensity of the resonance peak is found to increase with increasing x. The values of spin-Hamiltonian parameters (SHP) and molecular orbital coefficients are evaluated. From the values of SHPs it is concluded that V⁴⁺ ions in the present glass system exist as vanadyl ions in octahedral co-ordination with tetragonal compression. It is observed that the SPHs depend slightly on the relative concentration of V₂O₅. Further, the theoretical optical basicity of the glasses has also been evaluated and it is observed that the changes in optical basicity values are in accordance with the changes in SHPs.     

Preparation of lithium ion conducting glasses and glass–ceramics for all-solid-state batteries

Highly lithium ion conducting glasses and glass–ceramics were prepared by a mechanical milling technique in the Li₂S-based sulfide and oxysulfide systems. The Li₂S–P₂S₅ glass–ceramics showed ionic conductivity as high as 3.2 × 10^?3 S cm^?1 at room temperature. All-solid-state batteries using these sulfide-based materials as a solid electrolyte showed excellent charge–discharge performance with high capacity and high cycleability. The cells with the combination of the SnS–P₂S₅ glassy electrode and the Li₂S–P₂S₅ glass–ceramic electrolyte worked as a secondary battery, which was a first step of glassy monolithic cells with a common glass network.     

Structural evolution of Fe33Zr67 and Fe90Zr10 metallic glasses

We report on the structural evolution of melt-spun Fe₃₃Zr₆₇ and Fe₉₀Zr₁₀ glasses. These glasses are subjected to isothermal annealing over a wide temperature range, varying from the onset of crystallization up to near the melting point, for 20–300 min. Over 733–1223 K, the phase evolution sequence of the Fe₃₃Zr₆₇ glass follows: fcc FeZr₂ → fcc FeZr₂ + bct FeZr₂ → bct FeZr₂. In contrast, annealing of the Fe₉₀Zr₁₀ glass over 903–1173 K leads to a mixture of α-Fe, Fe₃Zr and Fe₂Zr phases. Some Fe₂Zr crystals are not developed perfectly, showing a special twin lamellar structure. The annealing temperature and alloy composition dependence of grain size in the present Fe–Zr system is discussed.     

Glass formation in and structural investigation of Li2S + GeS2 + GeO2 composition using Raman and IR spectroscopy

Li₂S + GeS₂ + GeO₂ ternary glasses have been prepared and a wide glass-forming range was obtained. The glass transition temperatures increase with the GeO₂ concentration in the glasses. The vibrational modes of both bridging (Ge–S–Ge) and non-bridging (Ge–S⁻) sulfurs are observed in Raman and IR spectra of binary Li₂S + GeS₂ glasses. Additions of GeO₂ to this binary glass increase the bridging oxygen band (Ge–O–Ge) at the expense of decreasing the bridging sulfur band (Ge–S–Ge), whereas the bands associated with the non-bridging sulfurs (Ge–S⁻) remain constant in intensity up to high GeO₂ concentrations. At higher concentrations of GeO₂ (⩾60%), the non-bridging oxygen band, which is not observed at low and intermediate GeO₂ concentrations, appears and grows stronger. From these observations, it is suggested that the added lithium ions favor the non-bridging sulfur sites over the oxygen sites to form non-bridging sulfurs, whereas the added oxygen prefers the higher field strength Ge⁴⁺ cation to form bridging Ge–O–Ge bonds. The structural groups in the Li₂S + GeS₂ + GeO₂ glasses that are consistent with results of Raman and IR spectra are described and are used to develop a structural model of these glasses.