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.     

Spectroscopic Properties of Er3+-Doped Na2O–La2O3–Al2O3–SiO2 Glasses

Er³⁺-doped sodium lanthanum aluminosilicate glasses with compositions of (90− x )(0.7SiO₂·0.3Al₂O₃)· x Na₂O·8.2La₂O₃· 0.6Er₂O₃·0.2Yb₂O₃·1Sb₂O₃ (in mol%) ( x = 12, 20, 24, 40, 60 mol%) were prepared and their spectroscopic properties were investigated. Judd–Ofelt analysis was used to calculate spectroscopic properties of all glasses. The Judd–Ofelt intensity parameter Ω _t ( t = 2, 4, 6) decreases with increasing Na₂O. Ω₂ decreases rapidly with increasing Na₂O while Ω₄ and Ω₆ decrease slowly. Both the fluorescent lifetime and the radiative transition rate increase with increasing Na₂O. Fluorescence spectra of the ⁴ I _13/2 to ⁴ I _15/2 transition have been measured and the change with Na₂O content is discussed. It is found that the full width at half-maximum decreases with increasing Na₂O.     

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.     

Polymer Mixtures in Na2O.Sb2O3.GeO2 Glasses

Ternary Na₂O.Sb₂O₃.GeO₂ glasses (with various [Na]/[Na + Sb] ratios) that contained ≥65 mol% GeO₂ were prepared. Their densities (volumes), refractive indices, and infrared spectra were determined and their colors noted. The ternary glasses with ≥88 mol% GeO₂ exhibit nearly additive volumes, refractivities, and frequencies for the main Ge-O vibration. Ternary glasses with lesser amounts of GeO₂ exhibit a variety of behaviors, depending on the [Na]/[Na + Sb] ratio. Small amounts of Sb₂O₃ cause significant volume and refraction deviations, as well as changes in ν_Ge-O, that can be associated with gradual elimination of GeO₆ octahedra. All the information supports a model for the glasses with 65 to 88 mol% GeO₂ that involves a degree of depolymerization that is greater when Na₂O and Sb₂O₃ are present together than when either is present alone.     

Glass Formation and Properties of Glasses in the System Na2O-B2O3-SiO2-TiO2

An investigation was made of the effect of TiO₂ on the glassforming region and on the physical properties of glasses in the system Na₂O-B₂O₃-SiO₂TiO₂. Glasses containing up to 45 mole % TiO₂ may be formed with an alkali content of 30 mole %. At lower alkali contents (10 mole % Na₂O) glasses may be formed containing up to 22 mole % TiO₂. The way in which the coefficient of linear thermal expansion and the transformation and softening temperatures are affected by TiO₂ additions has been determined.     

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.     

Formation of Nepheline Glass-Ceramics Using Nb2O5 as a Nucleation Catalyst

The crystallization of several Nb₂O₅-catalyzed glasses in the Na₂O.Al₂O.SiO₂ system was studied using DTA, X-ray diffraction, and electron microscopy. The Nb₂O₅ was an effective nucleation catalyst; fine-grained body-nucleated glass-ceramic materials containing hexagonal nepheline and NaNbO₃ were obtained. The crystallization sequence and final crystalline phases in these compositions were quite different from those found in the equivalent TiO₂ analogs. The addition of small amounts of carbides and nitrides at the expense of oxides in the initial glass batch markedly affected the final crystalline phases.     

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.     

Elastic Properties of 0.98Li2O-1.0Al2O3-nSiO2 Glasses and Keatite-Phase Glass-Ceramics

Bulk physical properties such as elastic moduli, thermal expansions, and moduli of rupture were measured for a series of 0.98Li₂O-1.0ALO₃- n SiO₂ glasses and the corresponding keatite solid-solution-phase glass-ceramics. The SiO₂ content ranged from n =4 to 12. The magnitude of the elastic properties of the glasses changed monotonically with increasing SiO₂ content. The properties of keatite-phase glass-ceramics depended almost linearly on SiO₂ content, but their behavior differed qualitatively from that of the glasses.     

Growth of α-Al2O3 Crystals by Na2O Evaporation

A technique for growing α-Al₂O₃ crystals is described in which Na₂O·11Al₂O₃ is dissolved in a liquid of composition Na₂O·4TiO₂·3Al₂O₃. Alpha Al₂O₃ is precipitated as Na₂O evaporates from the system; Na₂O·11Al₂O₃ serves as a source of Al₂O₃, and Na₂O in the liquid. The content of solids in the mixture is always such that it does not melt completely. The size of the α-Al₂O₃ crystals grown is related to the Na₂O content of the composition. Crystals as large as 4000 by 3000 μm in the α-axis direction and 500 μm in the c -axis direction have been grown.     

Helium Migration in TiO2-SiO2 Glasses

Helium permeability, diffusivity, and solubility were measured for a series of TiO₂-SiO₂ glasses containing up to 10.3 mol% TiO₂. The activation energies for helium permeation and diffusion decrease with increasing TiO₂ concentration. The enthalpy of solution is independent of composition, as are the infinite-temperature values for the permeability, diffusivity, and solubility. It is concluded that the observed changes in activation energies result from changes in the strain energy necessary to distort the R-O-R'bond. The average diffusional jump distance appears to be essentially independent of composition, as would be expected from the small changes observed in the molar volume as TiO₂ replaces SiO₂ in these glasses.     

Phase Diagram of Na2O-B2O3-SiO2 System

The binary isopleth Na₂O.B₂O₃-SiO₂ of the Na₂O-B₂O₃ SiO₂ ternary system has been investigated. A phase diagram is presented based upon data from differential thermal analysis studies of prepared glasses and direct observation of the melting behavior using solid-state video imaging. Phase equilibria relations in the Na₂O-B₂O₃-SiO₂ ternary system have been reassessed by combining information from this study with existing data from the literature. A revised liquidus surface for the ternary is presented in which the form of the isotherms is updated.     

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.     

Effect of Na2O/K2O Ratio on Chemical Durability of Alkali-Lime-Silica Glasses

The chemical resistance of mixed-alkali glasses to water was measured by determining the sodium, potassium, calcium, and silicon ions extracted instead of evaluating it from the alkalinity of the mixed-alkali extracts. In glasses of the composition K₂O and Na₂O 18, CaO 10, and SiO₂ 72% the minimum extraction of alkali (maximum durability) occurred for a K₂O/-Na₂O ratio of 2.6/1.0 (by weight). Based on an ionic-composition analysis of the results, an empirical index is suggested for determining the relative degree of ion-exchange and network-breakdown modes of reactions that occur when such mixed-alkali glasses are attacked by water.     

Effect of Na2O Additions in the Crystallization of Barium Ferrite from a BaO-B2O3-Fe2O3 Glass

A glass crystallization method was utilized to synthesize nanosized BaO-6Fe₂O₃ platelets from a 0.412BaO-0.258B₂O₃-0.330Fe₂O₃ batch composition. Quenched ribbons were inhomogeneous, showing microclustering and ∼1 μm hematite crystals. Na₂O substitutions for BaO greatly enhanced the glass-forming tendency of quenched ribbons, though quenched-in ∼0.5 μm barium ferrite crystals were infrequently present. The improved homogeneity with Na₂O substitution was attributed to lower vapor pressure of BaO during batch melting, which increased its retention in the as-quenched ribbons. Quantities of BaO equal to or in excess of Fe₂O₃ allowed iron ions to adopt stable network positions in the glass melt. With Na₂O substitution, devitrification of dispersed ∼40 nm barium ferrite particles from phase-separated regions occurred after secondary heat treatment. 5 mol% Na₂O batch substitution showed the lowest crystallinity in the as-quenched ribbons, and the highest crystallinity after secondary heat treatment. After optimum devitrification, the maximum values of saturation magnetization and coercivity were 21.22 emu/g and 2.82 kOe, respectively.     

Direct Formation and Photocatalytic Performance of Anatase (TiO2)/Silica (SiO2) Composite Nanoparticles

Anatase (TiO₂)/silica (SiO₂: 23.9–27.7 mol%) composite nanoparticles were directly synthesized from (i) the reaction of titanyl sulfate (TiOSO₄) and sodium metasilicate (Na₂SiO₃) under mild hydrothermal conditions, (ii) the acidic precursor solutions of TiOSO₄ and tetraethylorthosilicate (TEOS) by thermal hydrolysis, and (iii) the metal alkoxides, i.e., tetraisopropoxide (TTIP) and TEOS, by the sol–gel method. Their photocatalytic activities were evaluated by measurements of the relative concentration of methylene blue after UV irradiation. The as-prepared TiO₂/SiO₂ composite nanoparticles showed far more improved photocatalytic activity than the pure anatase-type TiO₂. The composite nanoparticles formed from (i) TiOSO₄ and Na₂SiO₃ as well as those from (ii) TiOSO₄ and TEOS showed fairly good photocatalytic activity, and it was better than that of those synthesized from (iii) the metal alkoxides, which was suggested to be due to the difference in crystallinity of the anatase.     

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.     

Elastic Moduli and Refractive Indices of Aluminosilicate Glasses Containing Y2O3, La2O3, and TiO2

Glasses in the system Al₂O₃-Y₂O₃-SiO₂, containing TiO₂ and La₂O₃, were investigated. Glasses of high refractive index and elastic modulus were developed. The observed Young's and shear moduli of these glasses show good agreement with theoretical values. Agreement was also found between the observed and calculated values of refractive index when the Appen's empirical coefficients were used.     

Studies in Lithium Oxide Systems: VI, Progress Report on the System Li2O-SiO2-TiO2

Data on compatibility triangles and liquid immiscibility are presented for the portion of the ternary system bounded by SiO₂, Li₂O, SiO₂, Li₀O TiO₂, and TiO₂. X-ray data showed the ternary compound Li₂O. TiO₂. SiO₂ to be tetragonal with a = 6.41 a.u. and C = 4.40 a.u. The compound is uniaxial negative with 1.81 < < 1.82 and 1.83 < < 1.84. It melted to two liquids at 1207° 3°C. Seven joins were established by solid-state, fusion, and quenching methods. Using electron microscopy and petrographic microscope and quenching data, liquid immiscibility originating in the binary system SiO₂-TiO₂ was shown to extend over a substantial portion of the ternary system.     

Influence of TiO2 on Properties of Glasses in the System K2O–PbO–SiO2–TiO2 and Its Relation to Structure

By a progressive weight percent substitution of TiO₂ for SiO₂ at various rations of concentration of K₂O and PbO, the entire region of glass formation in the quaternary system K₂O–PbO–SiO₂–TiO₂ was covered with 51 glass compositions. The properties of these glasses were determined and studied with respect to the role of TiO₂ in the system. The results indicated that the dielectric constant increased progressively with increasing TiO₂ concentration whereas the dissipation factor showed an overall decrease, when measured at 1 Mc and 25°C. Density and the refractive index increased progressively with increasing TiO₂ concentration but deviated from the additive relation. Chemical durability, expansivity, and softening temperature vs. composition curves showed definite inflections. The effect of TiO₂ on oxygen packing indicated that Ti⁴⁺ strengthens the network in lower concentrations and weakens the network in higher concentrations in this system. It appears to be likely that Ti⁴⁺ changes its coordination number form 4 to 6.