Heat Capacities of Heavy-Metal Fluoride Glasses

The heat capacities of a series of heavy-metal fluoride glasses were measured by differential scanning calorimetry from −23°C to above the glass transition. On a per mole of atoms basis all the heat capacities, C_p, at ambient temperature were ∼22 J/mol·K and near the glass transition they approached the Dulong-Petit limit of 3R. The differences, ΔC_p between liquid and glass heat capacities per mole of atoms at the glass transition were large compared to those for oxide glasses.     

Sol-Gel Synthesis of High-Quality Heavy-Metal Fluoride Glasses

Fluoride glasses are excellent laser hosts and are very well suited for a broad spectrum of optical applications. However, current fluoride glass synthesis is expensive. The solgel method is an affordable alternative for producing highperformance, optical-quality heavy-metal fluoride glasses. The method involves forming a hydrous oxide gel of the constituent metal alkoxides and salts, polymerizing the solution to form a gel, fluorinating the gel with anhydrous HF, melting the amorphous material in an oxidizing atmosphere of SF₆, and casting the melt into desired shapes. ZBLA (57ZrF₄·36BaF₂·4LaF₃·3AlF₃, in mol%) and Nd-doped (0.3 mol%) ZBLA glass rods were prepared by this process and their properties were measured. The solgel-based glasses had thermal and optical properties similar to those found in the literature for conventionally prepared fluorides.     

Micro-Raman Analysis of Carbon Inclusions in Heavy-Metal Fluoride Glasses

While vitreous carbon crucibles can be used to produce high-quality heavy-metal fluoride glasses using low concentrations of SF₆ gas (15%), pure SF₆ gas produces low-quality and high-scattering glasses. This has been attributed to contamination by vitreous carbon particles by a fallback mechanism due to reaction of SF₆ gas with the crucible walls above the melt. The detrimental effect of carbon particles is further highlighted by their high scattering efficiency factor which indicates that only 37 particles of 1-μm diameter can be tolerated in an optical fiber for attaining 0.01 dB/km loss.     

Preparation of Beryllium Fluoride Glasses Containing Xenon(VI) and/or Thallium (I)

The dissolution of CsXeF₇ in molten alkali fluoroberyllate glasses between 250° and 500°C is described. The apparent small solubility of Xe(VI) in these ionic glass-forming melts (about 1 to 2 wt% or less) may be related to retention of a molecular configuration by XeF₆ that is caused by its strong fluoride ion donor properties and/or to the nonmelting behavior of numerous MF-XeF₆ salts when they are heated. Rather low-softening (about 100°C) glasses were also prepared in the TIHF₂-NaHF₂-BeF₂ system, whereas TlHF₂ has a relatively low melting point (about 85°C). Contrary to expectations, Xe(VI) appears to oxidize TI⁺ in these molten glass environments at 250°C.     

Infrared Spectroscopic Studies of the Hydrolysis Reaction During Leaching of Heavy-Metal Fluoride Glasses

In this work, the interfacial reactions of heavy-metal fluoride glasses with water have been investigated by Fourier transform infrared spectroscopy. High dilution and stirring conditions were maintained to prevent any influence of pH drift and reprecipitation. From comparisons of the integrated absorption peak areas for the O-H stretching and H-O-H bending vibrations in the glass with those for molecular water, the contributions of metal hydroxyls formed in the corrosion layer can be separated from the total O-H band. The comparison between the infrared spectra for leached samples and hydroxides of the glass components show the presence of Zr-OH and La-OH groups in ZrF₄-based glasses after leaching and drying and of Th-OH groups in ThF₄ glass, indicating the existence of F.^-/OH^- ion exchange between the glass surface and water.     

Structural and Optical Properties of Erbium and Ytterbium Codoped Germanoniobophosphate Glasses

A series of glasses with compositions of 20Na₂O–30Nb₂O₅–(5?y?z)Al₂O₃–30P₂O₅–(15?x)TiO₂–xGeO₂–yEr₂O₃–zYb₂O₃, where x = (0; 5; 10; 15), y = (0; 1), z = (0; 2) mol%, were investigated with respect to their structural, optical, and luminescence properties. The coordination of the germanium(IV) ion is normally reported as being mainly tetrahedral. However, results of this study suggest that the germanium(IV) ion may have an octahedral coordination and that TiO₂ is substituted. This proposition can be done mainly by ³¹P MAS‐NMR spectroscopy, which spectra show predominantly pyrophosphate chains in the different glasses, without changes in their polymerization after substitution. A similar coordination of germanium can also be identified by the photoluminescence behavior of the different codoped samples, which shows similar erbium(III) emission decay lifetimes (5 ms), and Judd–Ofelt intensity parameters. It was found that the upconversion emission process involved 1.5 photons. Regarding the thermal behavior, it is noted that the glasses containing higher proportions of GeO₂ exhibit higher thermal stability and are therefore more resistant to devitrification when compared to compositions containing more TiO₂.     

Corrosion Studies of Various Heavy-Metal Fluoride Glasses in Liquid Water: Application to Fluoride-Ion-Selective Electrode

The leaching rates of various heavy-metal fluoride (HMF) glasses have been investigated in pH-buffered solutions. Measurements of weight losses and fluoride-ion and heavy-metal concentrations in solution have been performed. The agreement between the different experimental methods suggests a congruent dissolution although different time dependencies are observed between the investigated glasses. Their use as a membrane in a test fluoride-ion-selective electrode (fluoride-ISE) clearly demonstrates the existence of anion exchange between F^– ions on the glass surface and OH^– ions in the water solution.     

氟化铟玻璃若干性质研究

一、引言 自70年代中期Poulain等人发现氟锆酸盐玻璃后,在最近十几年中,相继出现了氟铪、氟钍和氟铝等为基础的氟化物玻璃形成系统。许多科学工作者为改善玻璃的析晶性能、化学稳定性和光学性能,在理论上和实用上做了大量的工作,对玻璃的形成、结构、性质及相互间的关系也进行了深入的研究,取得了一定的进展。与此同时,为了获得性能更为优良的玻璃,人们也在进一步探索新的形成系统。氟化铟玻璃系统是最新一代的氟化物玻璃。国     

Preparation of CdS-doped Glasses from Gels Containing Diethyldithiocarbamatocadmium

CdS-doped SiO₂ glasses were prepared via silica gels containing diethyldithiocarbamatocadmium Cd(S₂CN(C₂H₅)₂)₂. Heat treatment of the gels gave transparent yellow SiO₂glasses doped with hexagonal CdS crystals. In optical absorption and fluorescence spectra, the optical absorption edge and the emission peak clearly exhibited a blue shift, which was attributed to the quantum size effect of the carrier confinement, as the CdS content was decreased. In the fluorescence spectra of the CdS-doped silica glasses, the emission peak was observed only near 500 nm and not observed at longer wavelengths which were known to be present if there were sulfur vacancies.     

Preparation and Mechanical Properties of Mg-Al-Si-O-N Glasses

A three-component glass system (Mg–Al–Si) was nitrided by adding amorphous and crystalline Si₃N₄. Glasses with varying amounts of nitrogen were melted, and their mechanical properties were measured. Density, hardness, Young's elastic modulus, and fracture toughness increased with increasing nitrogen content.     

Preparation and Properties of Silver Borate Glasses

Silver borate Basses containing 0 to 30 mol% Ag₂O were formed. Properties measured include density, thermal expansion coefficient, glass transformation and dilatometric softening temperatures, transformation-range viscosity, dc electrical conductivity, and helium permeability and diffusivity. Optical spectroscopy revealed that the color of these glasses results from absorption bands at ∼407, ∼310, and ∼250 nm. Each band increased in intensity as the silver oxide content of the glass was increased. The properties of these glasses were consistent with the structural model currently used to describe the structure of alkali borate glasses. No evidence for the existence of phase separation was found for the conditions of the present study.     

Preparation and Properties of Nitrogen-Doped Phosphate Glasses

Techniques for preparation and the properties of phosphorus oxynitride glasses produced from sodium metaphosphate and nitride compounds are reported. Properties reported include nitrogen content, dissolution rate in water, thermal expansion coefficient, softening point, glass transformation temperature, density, refractive index, microhardness, and infrared absorption.     

Preparation and Properties of Yttrium-Silicon-Aluminum Oxynitride Glasses

Glasses containing up to 7 at.% nitrogen were prepared in the system Y-Si-Al-O-N. The glass transition temperature, hardness, and relative fracture toughness increase and the thermal expansion coefficient decreases with increasing nitrogen content. Weight losses after 350 h in 95°C distilled water are not simply related to nitrogen content, but for some compositions they are half that reported for fused silica. The electrical conductivity at 548°C and 10 kHz is 7.8×10⁻¹⁰ (Ω·cm)⁻¹ for one composition. Fourier transform ir spectroscopic analysis indicates the presence of Si-N bonds in the glasses. The data suggest that nitrogen substitutes for oxygen in the glass network to produce a more highly cross-linked structure.     

Physical and Optical Properties of Borobismuthate Glasses Containing Vanadium Oxide

Glasses with compositions 20BaO · 10Bi2O3 · (70 – x)B2O3 · xV2O5 with x = 0, 0.2, 0.4, 0.6, 0.8 and 1 mol % were prepared by melt quenching technique. The amorphous nature was established by X-ray diffraction studies. Fourier transform infrared studies carried out for samples and it exhibit absorption bands for oxides in various structural units. Physical parameters viz., density, molar volume, molar refraction, dielectric constant, electro negativity, polaron radius and oxygen packing density were calculated. Theoretical optical basicity was estimated and is increasing with vanadium content shows increasing polarizability of samples. Metallization criterion decreases shows the metallic nature of samples, this implies that prepared glass samples can be used as amorphous semiconductors and could be used in electronics and memory switching devices. Using UV-vis spectra optical band gap energy (Eopt) calculated and is decreased from 2.998–2.453 eV, linear refractive index is measured from Eopt. Increase in Urbach energy (Eu) with vanadium component is observed.     

Optical Properties and Effect of Gamma Irradiation on Bismuth Silicate Glasses Containing SrO, BaO or PbO

Optical and FT Infrared spectroscopic measurements have been utilized to investigate and characterize binary bismuth silicate glass together with derived samples by replacements of parts of the Bi₂O₃ by SrO, BaO, or PbO. This study aims to justify and compare the spectral and shielding behavior of the studied glasses containing heavy metal ions towards gamma irradiation. The study also aims to measure or calculate the optical energy band gap of these glasses. The replacements of parts of Bi₂O₃ by SrO, BaO or PbO caused some changes within the optical and infrared absorption spectra due to the different housing positions and physical properties of the respective divalent Sr2+, Ba2+, Pb2+ ions. The stability of both the optical and infrared spectra of the studied bismuth silicate glass and related samples towards gamma irradiation confirm some shielding behavior of the studied glasses and their suitability as radiation shielding candidates.     

Preparation and Faraday Effect of Fluoroaluminate Glasses Containing Divalent Europium Ions

Fluoroaluminate glasses containing various concentrations of Eu²⁺ were prepared under a reducing atmosphere for the present study, and the wavelength dependence of the Faraday rotation angle was examined. The magnitude of the Verdet constant (V_c) increased as the concentration of Eu²⁺ increased. In addition, the Verdet constant of glasses containing 5 cat.% Eu²⁺ was larger than that of fluoroaluminate glasses containing the same concentration of Tb³⁺ in the wavelength region from 400 to 600 nm. The effective transition wavelength, λ_t, for glasses containing Eu²+ as well as those containing Tb³+ was evaluated based on the Van Vleck and Hebb theory. Factors dominating the Verdet constant of those glasses are discussed in this report.     

Heterogeneous Plantinum Nucleation and Crystallization of a Heavy-Metal Fluoride Glass

The effect of controlled heterogeneous nucleation by platinum on the crystallization of a ZrF₄-BaF₂-LaF₃-AlF₃-NaF (ZBLAN) glass was studied. Various levels of platinum were incorporated into this glass by a combination of PtCl₂-doping and melting-atmosphere variation. The effect of doping levels and melting conditions on the incorporation of platinum and the subsequent nucleation of crystals was studied by optical microscopy, scanning electron microscopy, differential scanning calorimetry (DSC), and X-ray diffraction. Increased platinum in the glass resulted in an increased number of nucleation sites for the growth of β-ZrF₄-BaF₂ crystals. Analysis of isothermal and ramp-rate DSC measurements indicated that the crystallization of this glass changed from surface controlled to bulk controlled with an increased number of nuclei. This was confirmed by optical microscopy. In addition, Avrami analysis of the isothermal crystallization data gave an accurate approximation of the number of nuclei in the glass.     

Mechanical and Thermal Properties of Lead Borate Glasses Containing CaO and NaF

Glasses with the chemical composition 39PbO - 1NaF - (60-x){0.667B₂O_3-0.333Na₂O \(\}\)– x CaO (x \(=\) 0, 5, 10, 15, 20, and 25 mol %), were prepared by the usual melt quenching technique, and analyzed by using X-ray diffraction, density, differential thermal analysis (DTA), optical properties and mechanical properties. The structural variations due to the increase of the [BO₄] at the expense of [BO₃] structural units increase the ultrasonic velocity and the elastic moduli along with an increase of the density. The Makishima–Mackenzie model was applied successfully on the prepared glasses. The elastic moduli according to this model increase, which was due to the increase of CaO content. The increase of the glass transition temperature (T _g) according to DTA confirmed this behavior.     

Effect of Gamma Radiation on Optical and EPR Absorption Spectra of Phosphate and Fluoride Glasses Containing Lead

The induced optical and EPR absorption spectra of phosphate and fluoride glasses containing lead are investigated. It is revealed that exposure to gamma radiation leads to the formation of radiation-induced defects responsible for the induced absorption band with a maximum at 12500–13500 cm⁻¹ and the EPR signal in the form of an almost symmetric line with a g factor of 1.999 and a linewidth of ≈26 Oe. Analysis of the intensities of the absorption bands and the EPR signals in the spectra of glasses with low terbium, tin, and carbon contents and the study of their thermal bleaching demonstrate that the color centers are electron traps, whereas the paramagnetic centers are hole-trapping centers. Examination of the change in the parameters of the absorption bands in the spectra of glasses with different R ₂O contents (R = Na, K, Rb, Cs) makes it possible to determine the location of the color centers associated with the Pb⁺ ions in the structure. It is established that the glasses under investigation are characterized by the nonlinear absorption of radiation at a wavelength of 1.06 μm. The mechanism of formation of radiation-induced defects is considered. Original Russian Text Copyright ? 2005 by Fizika i Khimiya Stekla, Bocharova, Karapetyan.     

Preparation of High-Silica Glasses from Colloidal Gels: I, Preparation for Sintering and Properties of Sintered Glasses

A new method for preparing fused silica and high-silica glasses through the sougel process is described. Ordinarily, fused silica is formed by fusion of silica at 1900° to 2000°C. The method described consists of preparation of a porous body by mixing colloidal silica with water, drying, redispersion, molding by casting, followed by gelation, drying, and sintering at 1450° to 1500°C. The sintering is facilitated by addition of 3 to 5 wt% B₂O₃. The process of dispersion-drying-redispersion (so-called "double process") results in formation of a two-mode pore structure which permits drying of cast tubes and rods without breakage. The preparation of the porous bodies, study of pore structure, and properties of resulting glasses are described in Part I, the sintering is considered in Part II, and the mechanism of gel formation is interpreted from infrared spectroscopy studies in Part III.