Influence of As2O3 on the Optical Properties of Ultrapure Multicomponent Silicate Glasses and Optical Fibers

To obtain low transmission loss optical fibers from ultrapure multicomponent silicate glasses, it is necessary to add small quantities of As₂O₃ (or Sb₂O₃). In optical fibers prepared from glasses without these agents, a significant increase in loss is observed. To investigate this effect, the influence of As₂O₃ (added to the batch and present in the glass as As₂O₅) on the optical properties of ultrapure silicate glasses was studied. These properties are the Rayleigh scattering loss coefficient, transition metal absorption, and position of the uv absorption edge. This study showed that the increase in loss of As₂O₃-free glass cannot be assigned to any of these contributions and was attributed to absorption by electrons, trapped in relatively shallow traps in the glass network. The As⁵⁺ ions serve as deep traps and therefore remove the additional absorption. The same phenomenon, although much more pronounced, was observed in optical fibers prepared from alkali borosilicate glasses.     

The Glass System SiO2-B2O3-Bap-Na2O for High-Numerical-Aperture Optical Fibers

The glass system SiO₂-B₂O₃-BaO-Na₂O was investigated to obtain high-refractive-index glasses for high-numerical-aperture (N.A.) optical fibers. Compositions having a mole ratio [B₂O₃]/[BaO+Na₂O]=2 have unique properties. They are both highly viscous and chemically durable despite the fact that they contain highly alkaline metals and alkaline-earth metals. Glass properties at this mole ratio are favorable for optical fibers. It is proposed that the composition for core glass of high-N. A. optical fibers be based on this mole ratio.     

Formation and Properties of GeSe2–Ga2Se3–PbI2 Novel Chalcohalide Glasses

The glass-forming region of the GeSe₂–Ga₂Se₃–PbI₂ system was determined and homogeneous glasses were prepared. The maximum dissolvable PbI₂ can be up to 50 mol%. The structures of glasses were characterized by Raman spectroscopy. The thermal, optical, and some basic physical properties of the glasses were investigated. The results show that GeSe₂–Ga₂Se₃–PbI₂ glasses have a wide region of transmission window (0.7–16 μm) and high refractive index (∼2.5) with the addition of PbI₂. The glasses have good glass-forming ability and high glass transition temperatures. Consequently, these novel glasses may be promising candidate materials for infrared optics and nonlinear optical field.     

Tensile Strengths of Se, As2S3, As2Se3, and Ge30As15Se55 Glass Fibers

The strengths of as-drawn, abraded, and pristine Se, As₂Se₃, As₂S₃, and Ge₃₀As₁₅Se₅₅ fibers are reported. Pristine strength values range from an average of 80 MPa for Se and Ge₃₀As₁₅Se₅₅ to 100 and 180 MPa for As₂Se₃ and As₂S₃, respectively. Although these values are considerably higher than those reported previously for bulk samples, in no case does the maximum observed strength reach more than about 6% of that expected from simple theoretial calculations. Several factors that can control the strength are discussed. The overall behavior is interpreted in terms of the glass structures which permit localized stress relaxation effects in regions of weak, nondirectional bonds. These effects occur at temperatures well below the glass-transition region.     

Multicomponent Glasses of GeO2 and Sb2O3 with Bi2O3, T12O, andlor PbO

Previous studies on glass formation involving GeO₂ with Bi₂O₃, TI₂O, and PbO were extended by the use of Sb₂O₃. Wide areas of glass formation occur in the systems GeO₂-PbO-Sb₂O₃ and GeO₂-Bi₂O₃-Sb₂O₃ at all but the lowest GeO₂ contents; the region of single-phase glasses in the system GeO₂-Tl₂O-Sb₂O₃ is severely restricted. Glasses were examined by powder X-ray diffraction, differential thermal analysis, thermomechanical analysis, and Archimedes'technique to obtain glass transition and crystallization exotherm temperatures, thermal expansion coefficients, and densities; these properties are presented in diagrams for the GeO₂-Sb₂O₃ binary and for two ternary systems. Based on calculated values of Δ_o,the waveleneth for zero material dispersion. and dM/dΔ . the material disiersion slope at Δ_o, compositions in these systems may be useful for the construction of ultralow-loss optical waveguides in the 3 to 4 μm region.     

Infrared-Transmitting Glasses in the System K2O-Sb2O3-Sb2S3

Glasses were discovered in the system K₂O-Sb₂O₃b₃ Raw materials used in the preparation of these glasses were potassium pyroantimonate, potassium hydroxide, potassium nitrate, antimony oxide, and antimony trisulfide. Details of the methods of preparing the glasses and the compositions investigated are given. A glass, prepared by melting a mixture of potassium pyroantimonate and antimony trisulfide in air, was investigated in some detail. It was found to have an average infrared transmission of 42% in the range 2 to 7 μ. The glass annealed at about 150°C. and softened at about 230°C. Its coefficient of linear thermal expansion, in the range 240° to 200°C., was 20 × 10⁻⁶ per °C. The glass had a specific gravity of 3.94, a modulus of elasticity of about 5 × 10⁶lb. per sq. in., a Knoop hardness of about 135, and was highly resistant to attack by atmospheric moisture.     

Effect of Sb2O3 on Thermal Properties of Glasses in Bi2O3–B2O3–SiO2 System

Glasses with compositions 50Bi₂O₃– x Sb₂O₃–10B₂O₃–(40– x ) SiO₂ ( x =0, 1, 3, 5, 8, 10) have been prepared by conventional melt quench technique. Substitution of Sb₂O₃ for SiO₂ exerted an obvious effect on properties of glasses, especially, increased glass transition temperature ( T _g) and crystalline temperature ( T _c) greatly. Results of infrared transmission spectra attributed the effect to the formation of new bridging bonds of Sb–O–B and Sb–O–Si in glass network.     

Phase Stability of CdF2-LiF-AIF3-PbF2 Glasses

The techniques of scanning electron microscopy, energy dispersive X-ray microanalysis, and dark-field transmission electron microscopy were combined to study the phase stability of CdF₂-LiF-AlF₃-PbF₂ glasses. The selected compositions, presumed to be exceptionally stable, exhibited a liquid-liquid immiscibility phase transition; this led to the formation of two amorphous phases consisting of a matrix near the original glass composition and an isolated spherical phase which was richer in CdF₂ and poorer in PbF₂ than the matrix. Subsequent secondary-phase separation and crystallization were observed following heat treatments near the glass transition temperature.     

Prediction of Immiscibility Boundaries of the Systems K2O-SiO2, K2O-Li20-SiO2, K20-Na2O-Si02, and K2O-BaO-SiO2

In earlier work, a prediction method of the immiscibility boundary of a ternary silicate glass system was developed involving two known binary immiscibility boundaries and a measured immiscibility temperature of one ternary glass composition. In the present work, the method is extended to the case where one of the two binary immiscibility boundaries is not known and is applied as an example to ternary silicate systems containing K₂O. First, the immiscibility boundary of the system K₂O-SiO₂ is estimated by measuring the immiscibility temperatures of three glasses in the system K₂O-Li₂O (or Na₂O)-SiO₂. Using this result the immiscibility boundaries of the systems K₂O-Li₂O-SiO₂, K₂O-Na₂O-SiO₂, and K₂O-BaO-SiO₂ are estimated. The results agree reasonably well with the experimentally determined immiscibility temperatures at selected compositions.     

Preparation and Characterization of High-Density PbO–Bi2O3–B2O3 Glasses

Transparent glasses with densities greater than 8 g/mL, which are resistant to nuclear radiation damage and can serve as a host for rare-earth scintillators, are being developed. Glasses in the PbO–Bi₂O₃ system are known to have some of the highest densities yet reported. In this study, a thorough reexamination of these glasses has been performed to examine their optical-transmission windows and densities. The observed glass-forming range found in this work agrees well with that reported in the literature. A minimum of ≅ 10 mol% B₂O₃ was required in some cases to vitrify the compositions. Glasses were examined in which the PbO:Bi₂O₃ ratios ranged from 10:90 to 90:10 with a maximum total B₂O₃ content of ≅50 mol%. Glasses with higher B₂O₃ contents were not examined because of the rapidly decreasing density with increasing B₂O₃ content. The densities of the glasses ranged from a low of 6.0 g/mL to a high of 8.1 g/mL. The highest densities were observed for glasses with the greatest PbO content. Ultraviolet/visible and infrared spectra were recorded for these glasses. The transmission window lies between ≅430 and 3850 nm. A systematic increase in the cutoff wavelength was found to occur with an increase in the density. Water-absorption peaks were found in the infrared spectra at ≅3000 nm.     

Characteristics of PbO–BiO1.5–GaO1.5 Glasses Melted in SnO2 Crucibles

PbO-BiO_1.5-GaO_1.5-based glasses are good candidates for optical applications, because of some of their interesting characteristics, such as high refraction indices and high transmission in the ultraviolet (UV), visible (VIS), and infrared (IR) regions. A limited stage in the processing of these glasses is the corrosion that is caused by the melt in all currently used conventional crucibles, such as noble metals (platinum or gold) and Al₂O₃. The absorption of crucible material by the glass composition may reduce the transmission level, the cutoff in the UV-VIS, and IR regions, and the thermal stability. In this study, a SnO₂ crucible has been tested for PbO-BiO_1.5-GaO_1.5 molten glass. Optical and thermal analyses show, in some cases, advantages over the use of platinum and Al₂O₃ crucibles. A visible cutoff value of 474 nm has been measured, and a longer melting time (850°C for 4 h) results in a significant reduction of the O-H absorption band at 3.2 μm.     

Optical Absorption of Na2O-WO3 Glass Containing Transition-Metal Ions

Several transition-metal ions are soluble in Na₂O-WO₃ glass (1:1.63 mole ratio); from their d-d spectra it is concluded that the sites these ions occupy in the glass are not necessarily the same as those occupied when the transition-metal ion is coordinated in heteropolytungstate anions. The tungstate glass appears to have coordinating properties similar to those of "discrete-anion" glasses (e.g. nitrate and acetate glasses) rather than to those of network-type glasses. In the glass, the tungstato-metal complexes apparently do not decompose readily; their stability is similar to that of phosphato-metal complexes in phosphate glasses.     

Preparation of SiO2-TiO2-ZrO2 Glasses from Alkoxides

Relatively large compact glass samples (∼5 mm in diameter) of 65SiO₂·20TiO₂·15ZrO₂ and other binary and ternary compositions were prepared by the alkoxide gel method. Prolonged storage of the gels in water before they were dried reduced the residual carbon content of the resulting glasses considerably. Optimal preparation conditions are given, and the microstructure of the gels and glasses obtained is discussed.     

Nucleation and Crystallization of NaNbO3 from Glasses in the Na2O-Nb2O5-SiO2 System

Transparent glass-ceramics, in which the major phase was NaNbO₃, were obtained by heat treatment of glasses in the Na₂O-Nb₂O₅-SiO₂ system. The structure of the glass and the changes occurring during crystallization as a function of temperature and heating rate were examined by X-ray diffraction, transmission and replication electron microscopy, density, and other measurements. On heating, a rather abrupt formation of uniformly dispersed particles was observed. In the early stages of crystallization, these particles contained NaNbO₃ as loose, radially grown dendrites of identical crystal orientation which became dense during later stages of crystallization. The particle sizes ranged from 200 to 10,000 A, depending on the SiO₂ content of the glass. Transparency of the crystallized material was dependent on the particle size rather than on the amount of NaNbO₃ formed. The temperature at which crystallization occurred increased with the heating rate whereas the viscosity at crystallization decreased. For a given value of the rate of crystal formation per °C of temperature increase, the product (viscosity)ⁿ× (heating rate) was constant. The nucleation and growth phenomena which occurred in these glasses was attributed to microheterogeneities of higher Nb₂O₅ content which formed part of the glass structure.     

Bioactivity of Na2O-CaO-SiO2 Glasses

Bioactivities of Na₂O-CaO-SiO₂ glasses were evaluated by examining the formation of bonelike apatite, which is responsible for their bonding to living bone, on their surfaces in a simulated body fluid, using thin-film X-ray diffraction and Fourier-transform infrared reflection spectroscopy. It was found that glasses in a wide compositional region in the P₂O₅-free Na₂O-CaO-SiO₂ system can show bioactivity, as those in the P₂O₅-containing system. The rate of apatite formation on the surfaces of glasses varied largely with the composition of the glasses. Under a constant SiO₂ content of 50 mol%, a glass containing equimole of Na₂O and CaO showed the highest rate of the apatite formation. Variation in the rate of apatite formation with the glass composition corresponded well with the rate of increase in the degree of the supersaturation of the simulated body fluid with respect to the apatite due to dissolution of sodium and calcium ions from the glasses. Little difference was observed in the rates of ion dissolution and of apatite formation between P₂O₅-containing Bioglass 45S5-type and a corresponding P₂O₅-free Na₂O-CaO-SiO₂ glass. It is believed that P₂O_s-free Na₂O-CaO-SiO₂ glasses also show bioactivity as high as that of Bioglass.     

Seeding Effects on Crystallization of KAlSi3O8, RbAlSi3O8, and CsAlSi3O8 Gels and Glasses

Crystallization of stoichiometric KAlSi₃O₈, RbAlSi₃O₈, and CsAlSi₃O₈ gels (single-phase and multiphasic gels) and glasses with and without seeding has been investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive spectrometry (EDS). The pure gels of K-, Rb-, and Cs-feldspar compositions crystallized mainly to leucite (KAlSi₂O₆), a Rb analogue of leucite (RbAlSi₂O₃), and pollucite (CsAlSi₂O₆), respectively. The KAlSi₃O₈ glass also yielded leucite. No feldspar phases crystallized in the temperature region studied. The leucite crystallization temperature was lowered by using multiphasic gels. The crystallization sequence of the KAlSi₃O₈ glasses and single-phase gels did not change upon seeding with isostructural feldspar crystals. No significant crystallization effects were detected with the use of RbAlSi₃O₈ and CsAlSi₃O₈ multiphasic gels. However, K-feldspar (sanidine) was crystallized by using both compositionally and structurally different gels of KAlSi₃O₈, i.e., multiphasic gels seeded With feldspar crystals. The microstructure of oriented sanidine crystals around the seeds indicated an epitaxial crystallization mechanism.     

The Influence of Sb2O3 Addition on the Properties of Low-melting ZnO–P2O5 Glasses

The influence of 0–16 mol% Sb₂O₃ substitution for P₂O₅ on the properties of ZnO–P₂O₅ glasses has been investigated. It was shown that Sb₂O₃ could participate in the glass network and thermal stability of the glasses decreased with increasing Sb₂O₃ content. Glass transition temperature T _g, softening temperature T _s, and water durability all decreased firstly (up to 6 mol% Sb₂O₃ added) and then increased. Substitution of 12 mol% Sb₂O₃ led to a 16°C decrease in T _g and 30°C decrease in T _s, and weight loss of the glass was only 0.42 mg/cm², which is ∼11 times lower than that of the glass without Sb₂O₃ after immersion in deionized water at 90°C for 1 day. The glass containing 12 mol% Sb₂O₃ might be a substitute for Pb-based glasses in some applications.     

Preparation and Properties of Quenched Li2O-BaO-Nb2O5 Glasses

Glasses were prepared in the wide variety of compositions in the system Li₂O-BaO-Nb₂O₅, which contains no "glass-former," by the twin-roller quenching technique. The crystallization temperature ranges from 500° to 700°C and increases as Li₂O is replaced by BaO. The dielectric constant increases steeply with temperature, reaching an anomalously large value (10⁴) in glasses which contain a large amount of Li₂O. Such a temperature dependence of dielectric constant is very similar to that of conductivity in each glass, indicating that the dielectric behavior is caused by polarization due to the ionic motion in glass. The conductivity at 500 K ranges from 10⁻¹³ to 10⁻⁵Ω⁻¹·cm⁻¹ and the activation energy for conduction from 120 to 40 kJ/mol. The concentration of Li⁺ ions mainly controls the conductivity and the addition of Ba²⁺ ions slightly lowers it.     

Structural and Thermophysical Properties of (PbO)0.5(SiO2)0.5 Glasses: Effect of SnO2 Incorporation

¹¹⁹Sn and ²⁹Si solid-state nuclear magnetic resonance studies on lead silicate glasses containing different amounts of SnO₂ confirmed that tin exists in the glass as distorted SnO₆ polyhedra and there is no direct interaction between tin and silicon structural units. Transmission electron microscopic studies have established that tin structural units are uniformly distributed in the glass. Significant changes in the values of glass transition temperature, microhardness, and thermal expansion coefficient with SnO₂ incorporation into the glass have been attributed to the increased rigidity of the glass network brought about by the replacement of weaker Pb–O linkages with stronger Sn–O linkages.     

Effect of Small Additions of Al2O3 and Ga2O3 on the Immiscibility Temperature of Na2O-SiO2 Glasses

Alumina and gallia were substituted separately for Na₂O in amounts of 0.2, 0.5, 1.0, 1.5, 2.0, and 3.0 wt% in three Na₂O-SiO₂ glass compositions (82, 84, and 86 wt% SiO₂) within the immiscibility region. The immiscibility regions for each system extend to ∼1.5 mol% of the added oxide. In general, the addition reduced the immiscibility temperature ( T _m), but at the edge of the immiscibility region (82% SiO₂) the Na₂O loss effect initially increased T _m. A structural model of the miscibility of Al₂O₃ added to silicate glasses is presented.