Characterization of fluorine-doped silica glasses

Fluorine-doped silica glasses containing up to 2 wt% were prepared by the vapour-phaseaxial-deposition (VAD) sintering process. The characteristics of these glasses were investigated by Raman spectroscopy, vacuum-ultraviolet-ultraviolet (v.u.v-u.v.) spectroscopy, and viscosity measurements. From the Raman spectroscopic investigation, it has been shown that the Si-F bond structure in the fibres is the same as that in bulk glass and is not affected by codoped additives such as B₂O₃. From the u.v.-v.u.v, spectroscopic investigation, it has been shown that the absorption band at 7.6 eV in high-purity silica glass is removed with the addition of fluorine. This addition produces a silica glass with most excellent transparency in u.v. and v.u.v. regions. Also it was observed that the optimum addition is around 1 wt%. This fact proves that fluorine incorporation in glass prevents the generation of defects related to optical loss in fibres. From the viscosity study, it was found that the viscosity decreases with an increase of the fluorine content in glass and the activation energy also decreases with increasing fluorine content.     

Characterization of lead, barium and strontium leachability from foam glasses elaborated using waste cathode ray-tube glasses

Foam glass manufacture is a promising mode for re-using cathode ray tube (CRT) glasses. Nevertheless, because CRTs employ glasses containing heavy metals such as lead, barium and strontium, the leaching behaviour of foam glasses fabricated from CRTs must be understood. Using the AFNOR X 31-210 leaching assessment procedure, the degree of element inertization in foam glasses synthesized from waste CRT glasses (funnel and panel glasses, containing lead and barium/strontium respectively) were determined. The amount of leached lead from foam glasses prepared from funnel glass depends on the nature and concentration of the reducing agent. The effects of the reducing agents on the generation of cellular structure in the fabrication of foam glass were studied. The fraction of lead released from foam glass was less than those extracted from funnel glass and was lower than the statutory limit. Leached concentrations of barium and strontium were found to be approximately constant in various tests and were also below regulatory limits.     

Characterization of heterophase inclusions in glasses opaque in the visible range

We have designed an apparatus and developed a nondestructive laser ultramicroscopy technique involving digital detection of the 0.98-μm radiation scattered by individual inclusions for determining the concentration and size of submicron heterophase inclusions in high-purity glasses opaque in the visible range. The capabilities of the technique have been illustrated by analyzing several test systems. The detection limit for the inclusion size is shown to be n × (10–100) nm, depending on the refractive indices n of the inclusions and glass. The working range of inclusion concentrations is 10² to 10⁹ cm^?3, and the maximum scan depth is ～1 cm. The technique has been used to assess the microinhomogeneity of selenium and As-S-Se glass samples.     

Characterization and modeling of breaking-induced spontaneous nanoscale periodic stripes in metallic glasses

Stripes with a period of 87 nm appear in the mirror region of the fracture surface of metallic glasses. Two competing failure mechanisms of immediate meniscus instability and cavitation mechanism near the crack tip control the fracture process of metallic glasses and the formation process of nanostripes.     

Characterization of B2O3-SiO2 glasses prepared via sol-gel

B₂O₃-SiO₂ glasses were prepared by the sol-gel method from boron and silicon alkoxides. The gels were densified by several heat-treatments at temperatures above 800° C. The gel-glass transition was studied with the data obtained from differential thermal analysis, dilatometry and thermal evolution of density. The structural features of the glassy materials prepared were analysed by means of infrared (IR) and near-infrared (NIR) spectroscopy. The IR spectra indicated the existence of mixed Si-O-B bonds, preferential located at the outside of the material particles. The NIR spectra, recorded from gels heat-treated at low temperatures, demonstrated the existence of a great number of OH^– groups varying in nature, as well as their evolution and their positional changes on the silica particle surface as a function of the heat-treatment.     

Characterization of corrosion products on old protective glass,especially daguerreotype cover glasses

The method of casing objects using a protective cover glass bound to the object using a tape or frame promotes glass corrosion on the inside surface of the cover glass in preference to the outside surface. The characterization of some of the corrosion products found on these glasses is discussed especially as it applied to cased daguerreotypes. The geometry of these packages is responsible for the corrosion phenomenom. The types of corrosion products and the severity of the corrosion is a function of the bulk composition of individual cover glasses.     

Characterization of gas components and deposits in bubbles in silicate glasses prepared with sodium sulphate

The gas contents and surface deposits in bubbles that were formed at various temperatures in sodium calcium silicate glasses using sodium sulphate as a starting material were investigated by means of Raman microprobe and scanning microscopic techniques. Either elemental sulphur or sodium sulphate could be readily detected in the deposits, depending on treatment conditions for the glass. Higher amounts of elemental sulphur were found as deposits on bubble surfaces for glasses prepared using both carbon and sodium sulphate. SO₂ or CO₂ could be detected as gas components in various bubbles.     

Characterization of Fe<Superscript>3+</Superscript>-doped silver phosphate glasses

The relationship among the composition, structure and selected properties for five series of silver phosphate glasses containing 0, 5, 10, 15 and 20 wt% Fe₂O₃ has been investigated. The synthesized glasses have been characterized using different experimental techniques. X-ray diffraction studies revealed that the glasses are amorphous in nature. IR spectral studies have shown the presence of characteristic P–O–P linkages of linear phosphate chains, presence of O–P–O units in the phosphate tetrahedral and the formation of P–O–Fe bonds in the doped glass. It is also confirmed that due to doping of Fe₂O₃, loosening of glassy structure occurred and the glass became more disordered. Differential scanning calorimetric (DSC) studies revealed that glass transition temperature increased with Fe₂O₃ concentration. Scanning electron microscopic studies have shown that Fe₂O₃ doping modifies the microstructures of the glass and at lower concentration of dopant, a nanostructure is obtained. Electrical conductivity measurements from 303 to 373 K in a frequency range from 100 Hz to 5 MHz have indicated that all glasses are ionic conductors with Ag⁺ ions as the charge carrier. Fe₂O₃ doping in silver phosphate glass increased the electrical conductivities. Results have shown that dielectric constants increased with the increase of temperature at all the frequencies; a.c. and d.c. conductivities have been separated and a Cole–Cole plot is also drawn. Dielectric losses in all the glasses decreased with frequency at a particular temperature. It is found that Ag₂O–P₂O₅ glass doped with 5 wt% Fe₂O₃ gives high OCV value and the doped glass can be used as an electrolyte for solid-state batteries.     

Micro-machining of optical glasses — A review of diamond-cutting glasses

In order to diamond-turn optical glasses to a nanometric surface finish, it is critical to determine the transition point from brittle mode to ductile mode. This paper presents various experimental techniques to study this transition and discusses the mechanism of the surface generation. It has been recognized that tool wear is a serious issue in diamond turning of glasses. Thus, research in future should be concentrated on this field to enable the technology to be applied in commercial production.     

Infrared glasses

Driven by applications in hot fields such as optical communications, lasers, sensors, etc. infrared glasses have to be considered as key components in the development of devices for telecom signal amplification, fibre-laser emission as well as for passive functions related to IR remote spectroscopy or thermal imaging. Stable vitreous materials with low-phonon energies are found in the family of fluorides and chalcogenides glasses; they offer the advantage of excellent transparency in the mid-IR and weak nonradiative relaxation when doped with rare earth elements. Despite the number of candidates only a very limited number of glass compositions can be shaped into good optical waveguides such as channel or fibre. When possible, this led to remarkable amplification in the 1.3 μm region and lasing emission in the blue or mid-IR. Non-linear optical properties of chalcogen-based glasses are also of special interest for fast all optical switching and photo-induced effects.     

Conducting glasses

Ion-conducting tellurite glasses are built from trigonal bipyramidal TeO₄ units. Neutron diffraction as well as Raman and IR spectroscopic studies have shown that there is a continuous transition from TeO₄ → TeO₃₊₁ → TeO₃ as the alkali oxide content is progressively increased, non-bridging oxygens being created in the process. Electrical conduction in both single and mixed alkali tellurite glasses is satisfactorily explained by the interchange transport mechanism, based on the site-memory effect exhibited by the glass network.     

Nitrate glasses

A large number of new nitrate glasses have been prepared. Their formation depends upon a balance in anion to cation ratio as influenced by anionic cluster size and cation field strengths. Vitreous combinations of M⁺, M²⁺, M³⁺ and/or M⁴⁺ nitrates, save for M⁺-M⁺ combinations, have been obtained.     

Fluoride glasses

A new family of vitreous materials based on the glass forming ability of some specific fluorides is presented. Conditions of formation, stability against devitrification, chemical durability, and structural models are examined in comparison with the traditional oxide glasses. The ZrF₄-based glasses and some other multicomponent materials are examined in depth in view of their promising optical properties, which arise from their broad transmission range from ultraviolet to mid infrared and their potential as ultratransparent materials for long distance repeaterless optical fibre. Other active optical applications of doped glasses, such as lasers and their electrical and magnetic properties, are also discussed.     

Metallic glasses

Metallic glasses are a new class of materials produced by rapidly quenching the melts at rates often exceeding a million deg/sec. These have been found to display an optimum combination of properties such as high strength, good bend ductility, improved corrosion resistance and excellent soft magnetic properties. Thus, metallic glasses are emerging as economically viable competitors to conventional engineering materials. A clear understanding of the atomic structure of metallic glasses and its change during annealing are of prime importance. Although techniques such as field-ion microscopy (fim) x-ray diffraction and small angle x-ray scattering have been employed for this purpose, high resolution electron microscopic (hrem) investigations conducted during the last few years aided greatly in deriving information on the atomic scale. Availability of high-voltage high-resolution electron microscopes has been mainly responsible for this happy situation. Studies on several metallic glasses have revealed thathrem images contain well-defined pattern of fringes over local regions, even though the diffraction pattern is that of a typical amorphous structure. The details of structure in the early stages of crystallization derived throughhrem, fim and analytical microscopic techniques are presented and discussed.     

Cadmium halide glasses. II. - Chloride glasses

New chloride glasses based on CdCl₂ have been discovered in the binary composition (Cd_0.5Ba_0.5)Cl₂ and in the two ternary systems CdCl₂-BaCl₂-KCl and CdCl₂-BaCl₂-NaCl within the limits in mole percent: 30–60 CdCl₂, 15–50 BaCl₂, 0–35 KCl or NaCl. Other chlorides such as LiCl, CsCl₂, ZnCl₂, PbCl₂, SrCl₂, AgCl may be included in the glass composition. Only thin samples may be obtained by quenching the melt. Although less hygroscopic than ZnCl₂ glasses, they undergo a surface attack by atmospheric water. For a representative glass Cd_0.5Ba_0.3K_0.2Cl_1.8, glassy transition occurs at 167° C, crystallization at 221 and melting at 363° C. Their optical transmission range lies continuously from the U.V.-visible spectrum to 16 μ in I.R. region. They appear thus as attractive new materials for infrared technology at 10.6 μ and for low-loss optical fibres. The structural discussion is based on the assumption of the 6-coordination of cadmium.     

Characterization and study of Na2O-B2O3-SiO2 glasses prepared by the sol-gel method

The sol-gel procedure has been used to prepare vitreous materials whose compositions are situated in the liquid-liquid immiscibility area of the Na₂O-B₂O₃ SiO₂ phase equilibrium diagram. Gels were prepared from different precursors and under different experimental conditions. After determining optimum conditions for gelling and heat-treatment, the gels were characterized with the aid of thermal analysis, X-ray diffraction, density and specific surface area measurements, as well as infrared and near-infrared spectroscopy. The textures of the samples and their microstructures were studied by means of scanning electron microscopy and transmission electron microscopy, respectively. The phase separation in the gels was compared to the same phenomenon in one of the glasses of identical composition, but prepared by conventional melting.     

Crystallization of fluorozirconate glasses

The crystallization of a number of glasses of the fluorozirconate family has been studied using powder X-ray diffraction and differential scanning calorimetry, as a function of time and temperature of heating. The main crystalline phases were β-BaZrF₆ and β-BaZr₂F₁₀. Stable and metastable transformations to the low temperature α phases were also investigated. The size of crystallites in fully devitrified glasses was calculated to be $\text{～ 600}\text{A}\text{?}$ from line broadening of the X-ray diffraction peaks.     

Fatigue of metallic glasses

The fatigue behaviour of Ni₄₉Fe₂₉P₁₄B₆Si₂, Ni₄₈Fe₂₉P₁₄B₆Al₃ and Pd_77.5Cu₆Si_16.5 metallic glasses is examined. In the finite lifetime regime the relationship between stress amplitude ( _a), fracture stress ( _f), mean stress ( _m) and cycles to failure (N _f) is _a=A( _f–_m) (2N _f) ^b , whereA andb are 16.9 and –0.40 respectively for reduced gauge section Ni₄₉ strips (for _m 140 kg mm^–2) and 27.0 and –0.44 for Pd base wires. These results are unusual in thatA 1. Consequently, a sharp discontinuity exists near _a( _f– _m) –1. In a simple tensile test failure occurs at _f(=_y) and 2N_f=1; for peak stresses only a percent or so less than _f the sample will withstand hundreds of cycles of stress. For uniform cross-section glassy metal filaments, a fatigue limit is observed at stress ratios ( _a/ _f) in the vicinity of 0.07 to 0.15. The fatigue limit for reduced section specimens is a factor of 2 higher. Fatigue failure of the Ni-Fe strips may occur under partially or fully plane stress or plane strain conditions, depending on sample thickness and stress. Final failure of the Pd_77.5Cu₆Si_16.5 wires always occurs by general yielding of the remaining section.