EPR and Kinetic Studies of Hydrogen Centers in Aluminoborate Glasses

Barium aluminoborate glasses containing hydrogen as an impurity, irradiated at 77 K with X rays, show the characteristic doublet of atomic hydrogen in the EPR spectra when measured at T<200 K. The hfs constant of the H^o_i center is smaller than that of free atomic hydrogen, indicating that the attractive van der Waals interaction is more important than the repulsive Pauli exclusion forces in that glassy matrix. It is suggested on the basis of isochronal and isothermal annealing experiments that there are at least three different sites for hydrogen, each one contributing with Ist-order decay kinetics. The activation energies found in 30 mol% BaO, 60 B₂O₃, 10 Al₂O₃ glass are, respectively, equal to E₁=(0.5±0.1), E₂=(0.24±0.03), and E₃=(0.16±0.03)×lO⁻¹⁹ J.     

Structural and Luminescence Studies on Barium Sodium Borosilicate Glasses Containing Uranium Oxides

Barium sodium borosilicate glasses containing different amounts of uranium oxides were prepared by conventional melt quench method and investigated for their structural aspects by ²⁹Si and ¹¹B MAS NMR technique combined with steady‐state luminescence and lifetime measurements. Based on MAS NMR studies, it is confirmed that uranium ions act as network modifier up to 15 wt% and beyond which a separate uranium containing phase is formed. From the luminescence studies, it is inferred that uranyl species is in a highly distorted environment. For more than 15 wt% uranium oxide incorporation, weaker U–O–U linkages are formed at the expense stronger U–O–Si/B linkages, as suggested by the excited state lifetime value of the uranyl species as well as red shift in emission peak maximum. For glass samples containing more than 25 wt% uranium oxides, crystalline barium uranium silicate gets phase separated from glass matrix as confirmed by XRD studies.     

Dependence of the Dilatometric Properties of Glasses on Their Structure: I. Borate,Aluminoborate, and Lead-Containing Glasses

The dependences of the dilatometric properties on the hypothetical structure for a number of borate, aluminoborate, and lead-containing glasses are analyzed over a wide range of compositions. Special attention is focused on the specific features observed in the behavior of the structural temperature coefficient of linear expansion. It is demonstrated that the revealed regularities allow the justified inferences regarding the structural transformations of glasses with variations in their composition.     

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.     

Color Centers in Sulfur-Doped Silica Glasses: Spectroscopic Manifestations of an SO2 Interstitial Molecule

The photoluminescence spectra of sulfur-doped silica glass upon excitation into the absorption band at 203 nm and a temperature of 10 K are investigated. It is revealed that the photoluminescence band with a maximum at about 420 nm and the photoluminescence excitation band have a resolved vibrational structure. A model is proposed according to which the bands of absorption at 203 nm and luminescence at 420 nm are assigned to SO₂ interstitial molecules that are weakly bound to the glass network (the transitions X ^~1 A ₁ C ^~1 B ₂ and a ^~3 B ₁ X ^~1 A ₁, respectively).     

Effect of Different Treatments on Decay of Radiation-Induced Color Centers in Potassium Lead Silicate Glass

The influence of short-term heating or cooling and exposure to visible light on the bleaching of a gamma-irradiated glass stored at 20°C is investigated by photometry. The decay of radiation-induced color centers is retarded under the action of heating and gradually regains its initial rate after the heating ceases. The transient stage can be described as relaxation. It is revealed that isothermal photobleaching does not exhibit a similar aftereffect.     

Properties of Aluminoborate Glasses of Group II Metal Oxides: I, Glass Formation and Thermal Expansion

The glass formation of the aluminoborates of Group II metal oxides depends on the atomic weight of the oxide and on the electronic configuration of the metal ion. The participation of zinc, cadmium, and magnesium ions as network formers in the glass is shown from measurements of thermal expansion. The linear thermal expansion of the alkaline-earth aluminoborates varies from 4.7 × 10⁻⁶ to 16 × 10⁻⁶ per °C.     

Color Centers in Sulfur-Doped Silica Glasses: Spectroscopic Manifestations of an S 2 + Interstitial Molecular Ion

The absorption spectra of sulfur-doped silica glass are investigated under different external actions (laser irradiation, saturation of samples in a hydrogen atmosphere, and thermal annealing). It is found that the absorption band at 400 nm has a vibrational structure. A correlation between changes in the intensities of the absorption bands at 237 and 400 nm under different actions is revealed. Reasoning from analysis of the results obtained, a model is proposed according to which these bands are assigned to an S⁺ ₂ interstitial molecular ion. It is demonstrated that none of the optical centers considered in this work is responsible for the observed ESR signal.     

The Influence of Aluminum Oxide on the Thermal Expansion, Glass Transition Temperature, and Viscosity of Lithium and Sodium Aluminoborate Glasses

The glass transition temperatures and thermal expansion coefficients below and above the glass transition range are determined for lithium and sodium aluminoborate glasses over a wide range of concentrations. The temperature dependences of the viscosity for sodium aluminoborate and certain lithium aluminoborate glasses are studied in the viscosity range 10^10.5–10⁵ P. The data obtained are compared with the results of earlier investigations into the properties of barium aluminoborate glasses. The composition dependences of the properties studied are interpreted in the context of possible changes in the boron and aluminum coordination.     

Flame Spectrophotometric Analysis of Glasses: II, Calcium, Magnesium, and Barium, Including the Alkalis

The amount of calcium, magnesium, and barium, as well as of the alkali elements, in many glass compositions can be rapidly estimated with a flame spectrophotometer. Since the flame emission of the alkaline-earth elements is altered by such glass constituents as aluminum, iron, titanium, phosphorus, and zirconium, these elements should be removed, before flame analysis, by precipitation with ammonium hydroxide. With the elimination of the hydrous oxides and with corrections for the background interferences in the flame emission of the alkaline earths by the elements remaining, satisfactory flame analyses can be obtained. The mean difference between chemical and flame results for a series of 27 glasses of widely varying composition is approximately 0.15% for each element determined.     

Cerium Containing Al- and Zr-Pillared Clays: Promoting Effect of Cerium (III) Ions on Structural and Catalytic Properties

Ce³⁺ containing Al- and Zr-pillared clays were prepared by co-hydrolysis and co-intercalation methods, respectively. The materials were characterized by XRD, IR and near IR techniques. The expansion in the clay lattice as a result of pillaring was confirmed from X-ray diffraction study. The basal spacing for the pillared clay materials was observed typically in the range of 18–23 Å. The IR and near IR studies were employed to show the presence of acidic and non-acidic hydroxyl groups in the pillared clays. The IR peak at 3630 cm⁻¹ corresponding to the structural hydroxyl groups was more intense in pillared clays than in the parent clay. This peak is retained even after calcination at 500^∘C. Various overtone and combination bands were observed in the NIR range of 1200–2500 nm for the pillared clay materials. Pillaring with Al- and Zr-inorganic polycations enhanced the catalytic activity of the parent clays for dehydration of cyclohexanol. The presence of Ce³⁺ ions in the pillared clays was found to influence catalytic activity and stability of the Brønsted acidic sites. The stabilizing effect of cerium ion in the pillared clays is attributed to the competitive site occupancy and prevention of octahedral migration of the catalytically active protons.     

Internal Friction of Simple Alkali Silicate Glasses Containing Alkaline-Earth Oxides: II, Interpretation and Discussion

The results of internal friction measurements on simple three-component glasses that were reported in Part I of this paper are discussed. From a consideration of the basic equations governing internal friction and examination of the results of other investigators, a basis of interpretation is developed. It is shown that changes in peak-temperature position can be explained by changes in the activation energy of the process causing the peak. A change in peak height not accompanied by a change in the shape of the peak is shown to be due to a change in the concentration of the relaxation mechanisms. Using this information the changes in the peaks due to composition variations are explained on a structural basis. A mechanism is also suggested to explain the new high-temperature peak. A critical examination of the measurements on alkali-free and phosphate glasses leads to the conclusion that it may be necessary to re-evaluate some of the concepts concerning the low-temperature peak in alkali silicate glasses.     

Studies on conductivity of the system: Barium soap-water and propanol-1

The conductivity behavior of barium soap solutions in water-propanol-1 mixtures is exhibted by an equation: where A and B are constants, C is concentration of barium soap in q, moles/litre and μ is molecular conductivity. The values of the constant B are independent of the chain length of the soap below 50% propanol-1 concentration whereas above 50%, the values increase with the increase in the number of carbon atoms in the soap. The values of constant A also show a transition at 50% propanol-1 concentration. The results confirm that the change in the behavior takes place at about 50% propanol-1 concentration.     

Studies on surface tension of the system: Barium soap-water and propanol-1

The surface tension results of the barium soap solutions in water-propanol-1 mixtures have been explained on the basis of Szyszkowski’s empirical equation:γ =γ _o (1 + X ln Y) - Xγ _o ln C. The values of the constants X and Y of the equation have been calculated for various soap systems. The constant X is found to be almost independent of the composition of the solvent mixture but it depends to some extent on the chain length of the soap. The values of Y show a marked increase at 50% propanol-1 concentration which confirms that the transition in the nature of the micelles takes place at about 50% propanol-1 concentration. The values of X and Y are suggestive of the size and nature of the micelles, respectively.     

Specific Features of Changes in the Properties of One- and Two-Alkali Borate Glasses Containing Water: I. Viscosity, Thermal Expansion, and Kinetics of Structural Relaxation in Binary Alkali Borate Glasses

Alkali borate glasses with different contents of residual water are prepared by varying the synthesis conditions. The temperature dependences of the viscosity and thermal expansion of glasses are obtained. The structural relaxation parameters are calculated from the hysteresis dilatometric curves measured. The water content is determined using the IR absorption spectra in the range of stretching vibrations of hydroxyl groups at room temperature. It is found that an increase in the water concentration in alkali borate glasses leads to a decrease in the viscosity. The character of variations in the viscosity logarithm with a change in the water content depends on the alkali cation concentration. The glass transition temperatures determined from the dilatometric curves for all the studied glasses decrease with an increase in the water content. As the water concentration increases, the thermal expansion coefficient (above and below the glass transition range) and the degree of fragility decrease for glasses containing 25 mol % Na₂O, increase for glasses with an alkali oxide content of 15 mol %, and remain virtually unchanged for glasses involving 5.5 mol % Na₂O. A change in the water content in the concentration range under investigation does not affect the structural relaxation parameters.     

Specific Features of Changes in the Properties of One- and Two-Alkali Borate Glasses Containing Water: II. Viscosity of Mixed Alkali Borate Glasses

The temperature dependences of the viscosity for mixed alkali borate glasses containing lithium, sodium, and potassium oxides with a total alkali oxide content of 15 mol % are measured by the central rod bending method in the temperature range corresponding to a change in the viscosity from 10¹⁰ to 10¹³ dPa s. Analysis of the results obtained and the data available in the literature demonstrates that the content of residual structural water affects the manifestation of the mixed alkali effect in the viscosity of borate glasses. No significant change in the degree of fragility is found upon replacement of one alkali oxide by another alkali oxide in the studied glasses.     

Investigation of Glasses Using Surface Profiling by Spectrochemical Analysis of Sputter-Induced Radiation: II, Field-Driven Formation and Electrochemical Properties of Protonated Glasses Containing Various Proton Concentrations

The ion-sputtering technique for measuring concentration profiles in glass surfaces provides a method for studying ionic transport in solids. Simultaneous field-driven lithium ion and proton transfer from solutions into, and migration of these ions within, several lithium silicate glasses was investigated quantitatively. This work leads to the new field of protonated glasses which are distinguished by the availability of all sites to both cationic species. Conductivity and mobilities reported as a function of concentration (50°C) do not exhibit the typical features of the mixed-alkali effect. Mechanisms are proposed for ionic transfer across solution-glass interfaces and for migration of ions within protonated glasses. Small proton mobilities at low proton concentrations are explained in terms of specific sites which function as proton traps and are identified by infrared spectroscopy. The condition for stability of boundaries between migrating ions is discussed.