Glass formation in the MoO3–Nd2O3–La2O3–B2O3 system

In MoO₃–Nd₂O₃–B₂O₃ and MoO₃–Nd₂O₃–La₂O₃–B₂O₃ systems, glasses were obtained in the region between 20 and 30 mol% Ln₂O₃. A liquid-phase separation region was observed near the MoO₃–B₂O₃ side up to 20 mol% Ln₂O₃ (La, Nd). The amorphous phases were characterized by X-ray diffraction (XRD), differential thermal analysis (DTA), UV–VIS and infrared spectroscopy (IR). According to DTA data B₂O₃-rich glasses are stable up to 630 °C while glasses rich in MoO₃ are stable up to 430 °C. The glasses are transparent in the visible region. Structural models for the glasses network were suggested on the basis of IR spectral investigations. It was established that BO₃ (1380 cm⁻¹), BO₄ (1100–950 cm⁻¹) and MoO₄ (860 cm⁻¹) groups build up the glass network. MoO₆ units (band at 880 cm⁻¹) together with BO₃ units participate in the formation of the glass network with a high MoO₃ content (80–90 mol%).     

Study of electrical properties of MoO3–Fe2O3–P2O5 and SrO–Fe2O3–P2O5 glasses by impedance spectroscopy. II

The electrical and dielectric properties for three series of MoO₃–Fe₂O₃–P₂O₅ and one series of SrO–Fe₂O₃–P₂O₅ glasses were measured by impedance spectroscopy in the frequency range from 0.01 Hz to 3 MHz and over the temperature range from 303 to 473 K. It was shown in Part I that the MoO₃ is incorporated into phosphate network and the structure/properties are strongly influenced by the overall O/P ratio. The Fe₂O₃ content and Fe(II)/Fe_tot ratio in these glasses have significant effects on the electrical conductivity and dielectric permittivity. With decreasing Fe₂O₃ content in MoO₃–Fe₂O₃–P₂O₅ glasses with O/P at 3.5 the dc conductivity, σ_dc(ω) decreases for two orders of magnitude, which indicates that the conductivity for these glasses depends on Fe₂O₃ and is independent of the MoO₃ content. Also, the dielectric properties such as ^′(ω), ^″(ω) and σ_ac(ω) and their variation with frequency and temperature indicates a decrease in relaxation intensity with increase in the concentration of MoO₃. On the other hand, the dc conductivity for MoO₃–Fe₂O₃–P₂O₅ glasses with O/P > 3.5 increases with the substitution of MoO₃ which has been explained by an increase in the number of non-bridging oxygens and formation of Fe–O–P bonds that are responsible for formation of small polarons. The increase in the dielectric permittivity, ^′(ω) with increasing MoO₃ content is attributed to the increase in the deformation of glass network with increasing bonding defects. For SrO–Fe₂O₃–P₂O₅ glasses the conductivity and dielectric permittivity remained constant with increasing SrO.     

Thermodynamic modeling of the Al2O3–B2O3–SiO2 system

A complete literature review, critical evaluation, and thermodynamic modeling of the phase diagrams and thermodynamic properties of all oxide phases in the ternary Al₂O₃–B₂O₃–SiO₂ system at 1 bar pressure are presented. The molten oxide phase is described by the Modified Quasichemical Model and the Gibbs energy of the mullite solid solution is modeled using the Compound Energy Formalism. A set of optimized internally consistent thermodynamic functions for all the phases is presented. With the thermodynamic dataset, all available and reliable thermodynamic and phase equilibrium data can be reproduced within experimental error limits from 25 °C to above the liquidus temperatures. In addition, the reasonable predictions obtained for phase relations in the experimentally unexplored composition ranges suggest that the thermodynamic database can be used along with appropriate Gibbs energy minimization routines to calculate thermodynamic properties, phase equilibria, and phase diagrams of interest.     

Characterisation of semiconducting V2O5–Bi2O3–TeO2 glasses through ultrasonic measurements

Tellurite containing vanadate (50−x)V₂O₅–xBi₂O₃–50TeO₂ glasses with different bismuth (x=0, 5, 10, 15, 20 and 25 wt%) contents have been prepared by rapid quenching method. Ultrasonic velocities (both longitudinal and shear) and attenuation (for longitudinal waves only) measurements have been made using a transducer operated at the fundamental frequency of 5 MHz in the temperature range from 150 to 480 K. The elastic moduli, Debye temperature, and Poisson’s ratio have been obtained both as a function of temperature and Bi₂O₃ content. The room temperature study on ultrasonic velocities, attenuation, elastic moduli, Poisson’s ratio, Debye temperature and glass transition temperature show the absence of any anomalies with addition of Bi₂O₃ content. The observed results confirm that the addition of Bi₂O₃ modifier changes the rigid formula character of TeO₂ to a matrix of regular TeO₃ and ionic behaviour bonds (NBOs). A monotonic decrease in velocities and elastic moduli, and an increase in attenuation and acoustic loss as a function of temperature in all the glass samples reveal the loose packing structure, which is attributed to the instability of TeO₄ trigonal bipyramid units in the network as temperature increases. It is also inferred that the glasses with low Bi₂O₃ content are more stable than with high Bi₂O₃ content.     

Solidification of superalloy in a SiO2–ZrO2–B2O3 coating mould

The preparation of glass-lined coating mould from gels in the ternary system of SiO₂–ZrO₂–B₂O₃ has been investigated. The crystallization characterization and high temperature structure stability of this coating mould are demonstrated. We can find that the crystallization of t-ZrO₂ as well as the tetragonal to monoclinic phase transformation are, respectively, retarded and impeded owing to the encasement of SiO₂ matrix. While the inhibitive effect of B₂O₃ on crystallization of the SiO₂–ZrO₂–B₂O₃ coating mould is explained. Finally, DD3 single crystal superalloy melt can realize highly undercooled rapid solidification by adopting this coating mould, which further evinces that SiO₂–ZrO₂–B₂O₃ coating mould has an ideal nucleation inhibition for superalloy.     

Electrical and dielectric properties of Sb2O3–V2O5–K2O glasses

Electric measurements, including temperature dependencies of direct electrical conductivity and temperature dependencies of complex electrical modulus, have been implemented using Sb₂O₃–V₂O₅–K₂O glass samples. These glasses absorb ambient humidity but their resistance to water attack depends on composition. The significant decrease of conductivity up to 100 °C can arise from water desorption. Cycling measurements of direct electrical conductivity versus temperature were also implemented. They show that the 30Sb₂O₃–30V₂O₅–40K₂O and 70Sb₂O₃–30K₂O glasses are irreversibly damaged with the formation of the hydrated layer. In addition, it was observed that the evolution of DC conductivity is ruled by Arrhenius relation, while activation energy decreases as Sb₂O₃ concentration increases.     

Two-photon absorption in binary Bi2O3–B2O3 glass at 532 nm

Measurements of two-photon absorption (TPA) coefficients β at 532 nm in binary Bi₂O₃:B₂O₃ glasses are reported. The β obtained ranges from 12.9 to 16.4 cm/GW with the larger value observed in higher Bi₂O₃ glass. The relationship between β and glass composition is discussed in terms of the electronic structure of glasses: β can be scaled with optical band gap.     

Characteristics of ZnO–B2O3–CaO–Na2O–P2O5 glass powders prepared by spray pyrolysis

Fine-sized ZnO–B₂O₃–CaO–Na₂O–P₂O₅ glass powders with spherical shape were directly prepared by high temperature spray pyrolysis. The ZnO–B₂O₃–CaO–Na₂O–P₂O₅ powders prepared by spray pyrolysis at temperatures above 1200 °C had broad peaks at around 30° in the XRD patterns. The glass transition temperatures (T_g) of the glass powders obtained by spray pyrolysis at preparation temperatures between 900 °C and 1400 °C were near 480 °C regardless of the preparation temperatures. The dielectric layers formed from the glass powders prepared by spray pyrolysis at preparation temperatures above 1300 °C had clean surface and dense inner structure at the firing temperature of 580 °C. The transmittance of the dielectric layer formed from the glass powders obtained by spray pyrolysis at preparation temperature of 1400 °C was 90% at the firing temperature of 580 °C, in which the thickness of the dielectric layer was 13 μm. The UV cutoff edges gradually shift towards longer wavelength with increasing the preparation temperature of glass powders and the firing temperature of dielectric layers.     

Solubility of Ag2O into the Na2O–B2O3–Al2O3 system

The solubility of Ag₂O was measured for the Na₂O–B₂O₃ and Na₂O–B₂O₃–Al₂O₃ system with the rotating crucible method and static method, respectively, under air atmosphere at temperatures ranging from 1273 to 1423 K. The contamination of melts from crucibles could be avoided by the rotating crucible method, with which it became possible to measure the solubility of Ag₂O for the Na₂O–B₂O₃ system above the melting point of Ag for the first time. It was found that the addition of Na₂O decreases the solubility of Ag₂O while the addition of Al₂O₃ had little effect on the solubility. The effect of Na₂O and Al₂O₃ on the solubility of Ag₂O is expressed by interaction coefficients and is analyzed in terms of the basicity of melts. The solubility of Ag₂O in Na₂O–B₂O₃–Al₂O₃ melts increased with increased temperature. This phenomena was explained by a small enthalpy change in oxidation of silver.     

Glass formation in the PbBr2–PbCl2–PbF2–PbO–P2O5 system

New glasses in the PbBr₂–PbCl₂–PbF₂–PbO–P₂O₅ system have been prepared and characterized. The glass-forming regions have been explored and the stability of the glasses against crystallization studied. Results show that the PbBr₂–PbCl₂–P₂O₅ ternary system has a broad glass-forming region which extends to 30 mol% P₂O₅. Most of the glasses in this system show strong stability against crystallization and some have glass transition temperatures as low as 146°C. When 5% PbO or 5% PbF₂ is introduced into the PbBr₂–PbCl₂–P₂O₅ system, the glass-forming region becomes smaller and the glass transition temperatures increase. However, the introduction of 2.5% PbF₂ and 2.5% PbO into the ternary system increases the glass transition temperature and broadens the glass-forming region. The introduction of PbF₂ alone improves the glass-forming ability of the system while the introduction of PbO alone lowers the glass-forming ability.     

Nano-crystallization in LaF3–Na2O–Al2O3–SiO2 glass

Aiming at tailoring optical properties, the precipitation of LaF₃ nano-crystals in LaF₃–Na₂O–Al₂O₃–SiO₂ glass-ceramics is studied thoroughly on the nano-scale using advanced transmission electron microscopic techniques. Nano-sized phase-separation droplets enriched in lanthanum and silicon are formed already in the base glass. Within these less than 20 nm large droplets, LaF₃ crystallizes upon heat treatment. The nano-crystallization mechanism revealed is self-limited since growth is restricted by the size of the droplets. An average crystallite size of around 12 nm is achieved with a narrow size distribution since the phase-separation droplets also contain silicon not incorporated into the growing crystal. Instead, excess silicon relocated to the periphery of the pre-existing phase-separation droplets forms a diffusion barrier around the LaF₃ nano-crystals preventing further crystal growth and/or ripening.     

Magnetic behaviour of 20Fe2O380[3B2O3(1−χ)PbOχAs2O3] glasses

The results of magnetic measurements performed on 20Fe₂O₃80[3B₂O₃(1?χ)PbOχAs₂O₃] glasses, in the temperature range 4.2 to 300 K are reported. By decreasing the temperature a downward curvature of reciprocal susceptibility is observed for T<50 K. The composition dependence of the paramagnetic Curie temperatures and Curie constants is discussed.     

Supercritical fluctuations in the B2O3PbOAl2O3 system

A small-angle X-ray diffraction study of the supercritical region of the B₂O₃PbOAl₂O₃ immiscibility surface is presented. This is the first time that diffraction methods have been applied to the study of critical opalescence in a system of oxides at high temperatures. Debye's theory is shown to be applicable and, from the spectra correlation lengths and the range of molecular interactions l is calculated. The topography of the supercritical region is determined and the relationship between l and the main interatomic distances in the melt discussed.     

Effect of CaO on the surface morphology and strength of water soaked Na2O–B2O3–Al2O3–SiO2 vitrified bond

The surface morphology of Na₂O–B₂O₃–Al₂O₃–SiO₂ vitrified bond with and without calcium oxide was studied by soaking vitrified bonded microcrystalline alumina composites in water. The content of water introduced to the vitrified bond was determined by thermal gravity analysis, and the effects of water and calcium on the phase separation and nucleation of the vitrified bond were investigated using scanning electron microscope and energy-dispersive X-ray spectrometer. Soaked in water for 72 h, the Na₂O–B₂O₃–Al₂O₃–SiO₂ vitrified bond presented a porous surface, and its bending strength declined with increasing sintering temperature. However, the Na₂O–CaO–B₂O₃–Al₂O₃–SiO₂ vitrified bond was more durable against aqueous coolant even needle-shape crystals were found clustered on the surface of the vitrified bond. The crystals were enriched with aluminosilicate tested by energy-dispersive X-ray spectrums. The appearance of crystals lessened the dissolution of the vitrified bond and made the bending strength increase in the sintering temperature region between 870 °C and 930 °C.     

Raman and ESR study of sol–gel materials from ZnO–TiO2–B2O3 system

The paper studies the materials from ZnO–TiO₂–B₂O₃ ternary system, obtained by sol–gel method [1] and [2], starting from organic and inorganic precursors. The obtained samples are investigated by FTIR and Raman spectroscopy, which provide structural information, at molecular level. FTIR absorption maxima are identified and discussed according to literature data. Raman spectra are acquired by a Raman Jasco NRS-3100 spectrometer, at 532 nm wavelength and put in evidence characteristic vibration modes for all three oxide components. ESR spectra were plotted with the aid of a JES-FA 100-JEOL Japan spectrometer and titanium surrounding is investigated.     

Retarded elasticity in B2O3GeO2 glasses

The retarded elasticity was investigated for B₂O₃GeO₂ glasses having network structure in the glass transition range by using a compressive method. The compliance (J_∞) determined at the final stage of each measurement displayed a maximum for roughly constant viscosity (η ? 10¹⁴ P) in all the B₂O₃GeO₂ glasses and was simulated by the same equation applied for AsS glasses reported in a previous paper [1].

$\text{J}{}_{\mathrm{\infty }}\text{=(1?k}{}_2\text{keta;}{}_{\mathrm{G}}\text{keta;}\text{)[?}{}_1\text{(}\text{k}{}_1\text{keta;}\text{)+?}{}_2\text{(}\text{nk}{}_1\text{keta;}\text{)]}$

, where $\text{K}{}_1\text{, k}{}_2\text{, ?}{}_1\text{, ?}{}_2\text{and}\text{n}$ are parameters and η_G is the viscosity related to the retarded elasticity. The terms (k₁/η) and (nk₁/η) are assumed to be equal to one for all their values exceeding one. For B₂O₃GeO₂ glasses, the deformation due to the retarded elasticity could be alloted to two structural elements: the first element related to the term $\text{?}{}_1\text{(k}{}_1\text{/η)}$ and the second element related to the term $\text{?}{}_2\text{(nk}{}_1\text{/η)}$. The values of $\text{?}{}_1$ showed almost no variance with the glass composition, but $\text{?}{}_2$ had a minimum at the composition of 50 mol% GeO₂. These data suggest that the contribution of the second element is the smallest at B₂O₃/GeO₂ = 1. The values of k₂ were close to that of As₂S₃ glass having the network structure. k₁ and n (or nk₁) were almost constant regardless of the composition, respectively. These data suggest that the inhibition due to the viscosity starts at an approximately constant viscosity in B₂O₃GeO₂ glasses.     

Structural investigations of copper doped B2O3-Bi2O3 glasses with high bismuth oxide content

Raman and infrared spectroscopy have been employed to investigate the 99.5%[xB₂O₃(1−x)Bi₂O₃]0.5%CuO glasses with different Bi/B nominal ratios (0.07?x?0.625) in order to obtain information about the competitive role of B₂O₃ and Bi₂O₃ in the formation of the glass network. The glass samples have been prepared by melting at 1100 °C and rapidly cooling at room temperature. In order to relax the structure, to improve the local order and to develop crystalline phases the glass samples were kept at 575 °C for 10 h. The influence of both Bi₂O₃ and CuO on the vitreous B₂O₃ network as well as the local order changes around bismuth and boron atoms in as prepared and heat treated samples was studied. Structural modifications occurring in heat treated samples compared to the untreated glasses have been observed.     

Phase relations around langasite (La3Ga5SiO14) in the system La2O3–Ga2O3–SiO2 in air

Phase relations around langasite (LGS, La₃Ga₅SiO₁₄) were studied on the basis of phase assemblage observed during calcination and crystallization process of samples of various compositions in the ternary system La₂O₃–Ga₂O₃–SiO₂. A ternary compound of apatite structure, La₁₄Ga_xSi_9–xO_39–x/2 was found for the first time. Crystallization of this compound was observed in the cooling process of molten samples of stoichiometric LGS as well as LGS single crystal, demonstrating that LGS is an incongruent-melting compound. A phase diagram was established primarily based on the crystallization sequence in the cooling process.     

Cation site occupation by Ag/Na ion-exchange in R2O–Al2O3–SiO2 glasses

Ag⁺/Na⁺ ion-exchanged R₂O–Al₂O₃–SiO₂ glasses with uniform concentration profile of Ag⁺ and Na⁺ were prepared by heat treatment in molten silver salt followed by holding at the same temperature in an ambient atmosphere. Their glass transition temperature (T_g) and thermal expansion coefficient (TEC) were measured and structures were investigated using ²⁹Si-MAS NMR, ²⁷Al-MAS NMR, IR and Raman spectroscopies. Both T_g and TEC decreased with increase of the exchange ratio, but T_g was still above the ion-exchange temperature of 400°C even for the fully exchanged sample. The ²⁹Si- and ²⁷Al-MAS NMR spectra were mostly unchanged and no sign of the structural alteration of the glass network was observed. On the other hand, the vibrational spectra showed remarkable peak shifts depending on the exchange ratio. From these structural results, it was found that when the exchange ratio was low, the introduced Ag⁺ ions were stabilized at the non-bridging oxygen (NBO) site, and then Na⁺ ions in AlØ₄ site were exchanged by Ag⁺ ions after full replacement of NBO sites, where Ø represents the bridging oxygen.     

Densities of Li2O–B2O3 melts

The densities have been systematically measured in xLi₂O–(1−x)B₂O₃ melts of different compositions with Li₂O content varying from x=0 to 0.68 from their respective melting points up to about 1450 K with a modified Archimedean method. The density decreased with increasing temperature for all the melts measured in this work. When x<0.15, the plot of temperature versus density could be well fitted by a quadratic polynomial function, and when x0.15, density decreased linearly with increasing temperature. At a fixed temperature, the density of the melts increased rapidly with Li₂O content, went through a maximum at about x=0.333 (Li₂O–2B₂O₃), and then decreased slowly as Li₂O content was further increased. In addition, the volume expansion coefficient (β) was calculated based on the densities measured in this work, and it was found that a maximum value appeared in the dependence of β on the molar ratio of Li₂O at about x=0.333.