Effect of different valence forms of iron on the properties of glasses in the SiO2 - Al2O3 - Fe x O y - CaO - MgO system

The effect of different valence forms of iron on the physicomechanical and crystallization properties of glasses in the SiO₂ - Al₂O₃ - Fe _x O _y - CaO - MgO system is described. It is established that the properties of the glasses improve with an increase in the fraction of bivalent iron. A mechanism of crystallization in the glasses is suggested and the effect of the redox synthesis medium on the process of devitrification of iron-containing glasses is substantiated.Translated from Steklo i Keramika, No. 9, pp. 3 – 5, September, 1996.     

Valence state and speciation of uranium ions in borosilicate glasses with a high iron and aluminum content

The valence state and the local environment of uranium ions in borosilicate glasses intended for immobilizing high-level wastes with high concentrations of iron and aluminum ions are investigated using X-ray absorption (XANES, EXAFS) spectroscopy. It is demonstrated that, in glasses predominantly containing iron oxides, at least 80% of the total uranium exists in a hexavalent form as uranyl ions. In high-alumina glasses, uranium is in hexavalent and pentavalent states; in this case, the fraction of the latter form increases with an increase of the uranium concentration and its local environment is similar to the configuration of an axially distorted tetrahedron.     

Effect of Oxidation State of Iron on Phase Separation in Sodium Silicate Glasses

The effect of the oxidation state of iron on the phase separation of x Na₂O·(100 – x )SiO₂ glasses, x = 18.56 and 13, containing 0.5 mol% Fe₂O₃ was studied. The oxidation state of iron in the glasses was varied by changing the melting conditions, such as melting temperature and melting atmosphere. The oxidation states of the iron ion were determined using colorimetric and UV–VIS–NIR spectrophotometric methods, and a comparison was made between the results obtained using these two methods. Immiscibility temperatures of the glasses were determined using opalescence and clearing methods. The immiscibility temperature of the sodium silicate binary glasses decreased ∼25°C with the addition of 0.5 mol% Fe₂O₃. The immiscibility temperature of the doped glasses increased slightly with increased concentration of Fe²⁺ ion in the glass. The prediction of immiscibility tendency on the addition of a minor amount of third component was made using models proposed by Tomozawa and Obara and Nakagawa and Izumitani. The Tomozawa and Obara model showed good agreement with measured immiscibility values.     

Color and Spectral Transmittance of Amber Bottle Glass

Because of increased interest in color uniformity among iron-sulfur amber bottle glasses, a study was undertaken of their color, their spectral transmittance, and the relationship of these properties. It was found that the psychophysical attributes of color (C.I.E. system) as computed from complete light-transmittance spectra can actually be estimated for iron-sulfur amber glasses with good accuracy from transmittance at only two suitable wave lengths, 550 and 650 mp. Transmittance at 550 mμ is closely correlated with brightness (C.I.E.) and thus is sufficient to characterize color intensity, which is the most important variable of color quality among commercial amber glasses. There is also fair correlation between transmittance at 550 mμ and transmittance in the ultraviolet. The latter is important in the avoidance of photochemical action on bottled products. Incidental to this work, the transmittances of a large number of glasses were compared with their iron and sulfur contents. Broadly speaking, it was found that transmittance at 550 mp decreases with increasing ferrous iron or with increasing sulfide content. However, this transmittance is affected substantially by other factors, such as gross composition, minor constituents like fluorine, and thermal history, of which no account was taken in the present work. Transmittance at 1050 mp can be correlated closely with ferrous iron content (as determined by chemical analysis) and absorbancy per unit concentration of ferrous iron in carbon-sulfur ambers is about the same as in green glasses containing no sulfur.     

Borate Glasses with Paramagnetic Dopants—A New Magnetooptic Material for the IR Spectral Range

The spectral, field, and temperature dependences of the magnetooptic Faraday effect and the optical absorption spectra in the IR range are measured for potassium aluminoborate glasses doped with iron, manganese, and diamagnetic metal oxides at low concentrations. It is found that the glasses are characterized by high magnitudes of the Faraday rotation and the magnetooptic figure of merit in the spectral range 1.3–1.5 m. The observed magnetooptic and optical properties of glasses are explained by the formation of magnetic-ordered nanosized particles that are similar to manganese ferrite in structure and properties.     

Electrode Properties of Fluorine-Containing Alkali Silicate Glasses

An attempt is made to change the electrode properties of alkali silicate glasses containing various glass-formers and modifiers by introducing fluorine components into their compositions. Model systems with the initial hydrogen and metallic electrode functions are investigated. The study is based on the assumption that new ionogenic structural units with a mixed-anion constituent are formed in the glass structure. Lithium, sodium, and potassium silicate glasses with different fluorine contents are synthesized. Their potentiometric properties are studied. It is shown that the introduction of fluorine exerts the strongest effect on the electrode properties of alkali aluminosilicate glasses. An indirect corroboration is obtained for the assumption that strongly acid groupings containing fluorine can be formed in the glass network. It is found that the technological properties of the electrode glasses are significantly improved and the chemical durability in the potassium-containing system also becomes much higher. From the results obtained, the inference is drawn about the prospects of fluorine introduction into electrode glasses.     

Total Heat-Transmission Coefficients of Amber and Green Glasses in Temperatures of Melting Range

Measurements of an over-all heat-transmission coefficient for several commercial amber glasses were carried out in a pilot-scale furnace at temperatures of the melting range. The data obtained were used in deciding depth and insulation of tank furnaces. It appears that the transmission of light of amber glasses in the near-infrared range gives a practical indication of these heat-transmission properties. The same pilot-scale furnace was used to investigate the effect of chromium oxide, nickel oxide, and iron oxide on the over-all heat-transmission coefficients of green glasses. An empirical equation was derived, relating the heat-transmission coefficient to the concentration of the coloring oxides. Of the three oxides, the effect of the nickel oxide on heat transmission is the strongest and the effect of the iron oxide is the weakest.     

An Overview of the Structure and Properties of Silicon-Based Oxynitride Glasses

The silicon oxynitride glasses take advantage of nitrogen bonding to attain high elastic modulus, increased softening temperatures and viscosities, greater slow crack growth resistance, and modest gains in fracture resistance. Of the oxynitride glasses, the Si–Y–Al-based oxynitride glasses have been most extensively studied and a degree of success has been achieved in understanding how changes in glass composition affect structural parameters and their relationship with properties. More recent studies have focused on the Si–RE–Me oxynitride glasses, where Me is primarily Al or Mg and rare earth (RE) includes most of the lanthanide series elements. These glasses possess a range of elastic, thermal, mechanical, and optical properties, which can be correlated with the strength of the RE bond in terms of the cationic field strength. However, such correlations require knowledge of not only the RE valence state but also its coordination with the anions. Herein, the current state-of-the-art understanding of the properties and structural parameters of oxynitride glasses and their interrelationships are reviewed.     

Properties of lead borosilicate glasses: The effect of the structure

A study of the structure and physicochemical properties of lead borosilicate glasses is reported. Consideration is given to the coordination transitions in the glasses and their effect on the properties. A pattern of changes is established in the properties depending on the chemical and phase composition of the glasses.     

Composition and properties of glass obtained from Early Cretaceous Sidi Aich sands (central Tunisia)

The present work describes the chemical–mineralogical characterization of Barremian sand deposits. These Sidi Aich sands are observed exclusively in central Tunisia; in the Central Atlas two major domains might be discriminated: north–south axis and southern Atlas. In the collected raw samples, quartz and potassic feldspars are depicted with percentages that reach 30 wt.%. The chemical and XRD analyses confirm the existence of K-feldspars. These compounds are known fluxing agents. Since the amount in heavy minerals (<0.36 wt.%) and Fe₂O₃ (<0.71 wt.%) is relatively low, their interest for glass manufacturing is high.In accordance, semi-industrial tests were carried out to produce glass. The obtained bodies were investigated by XRD, attempting to detect the crystalline phases that can appear and influence the technological behaviour of these glasses. Mechanical properties distinguished SMS and SAT glasses when the others are conditioned by microfractures that could be related to annealing stage. The investigation also concerned the colours exhibited by final products (green to amber). This aspect is dependent on the amount of iron and its redox states; ferrous (Fe²⁺)/ferric iron (Fe³⁺) which is here detected in UV–vis–NIR spectra of different tested glasses.     

Formation and Properties of Low-Melting Glasses in the Ternary Systems As—TI—S, As-TI-Se, and As—Se—S

Glass formation has been found to be extensive in the systems As-TI-S, As-Tl-Se, and As-Se-S. Glasses in these systems exhibit unique low-melting properties; some are highly fluid as low as 185OC. The marked effect of thallium in lowering the viscosity of binary As-S melts was found to be unique among all the metallic additives studied. The glasses are stable, covalent, chemically durable, and dielectric. They exhibit good wetting properties with respect to most metals, and the permeability of the seals formed as well as the volume permeability of the glasses themselves appears to be extremely low. Linear thermal expansion coefficients of some compositions are high, but associated thermal cracking problems are minimized to some extent by the low softening temperatures. The glasses can be evaporated and directly condensed (in uacuo) to form continuous, grain-free glassy films. The glasses are of considerable interest in the study of the nature of the vitreous state. In addition, their over-all properties make them potentially useful for hermetic sealing of semiconductor and other moisture-sensitive electronic components which might be damaged by high-temperature sealing processes.     

Acid-Base Reactions Between Components in Sodium-Aluminoborosilicate Glasses

The effect of coordination groups of boron, aluminum, and silicon on acid-base properties and specifics of the variation in the redox state of copper in boron-containing melts are investigated. An approximate evaluation of acid-base properties of industrial glasses synthesized in an alkaline-aluminoborosilicate system is implemented.     

Spectroscopic Inquiry of the Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>-role in Binary Sodium Borate,Sodium Silicate and Sodium Phosphate Glasses and Effects of Gamma Irradiation

Optical absorption spectral investigations have been carried out on Fe³⁺ ions doped sodium borate, sodium silicate and sodium phosphate glasses before and after gamma irradiation. The UV-visible absorption spectrum exhibits bands characteristic of Fe³⁺ ions coordination in each system. Interesting aspects of FT-IR spectra were found, and this gives information about the structure changes in the constituent units of these glass systems as a function of Fe₂O₃ concentration. All glasses reveal characteristic absorption bands due to the addition of different ratios of iron which explain the state of iron in each system in terms of its valence and coordination number. Results indicate that iron favors a higher oxidation state (tetrahedral coordination) in the case of sodium silicate glasses. The doping with progressive Fe₂O₃ additions (0.5?7.5 %) has some effect on the number and position of the characteristic bands due to formation of FeO₄ groups. The IR absorption spectra after irradiation reveal limited changes in the intensity which can be correlated with minor changes in bond angles and /or bond lengths within the structural units by irradiation.     

Co/Ce共掺杂高硅氧玻璃的制备和光谱性能

为开发新型电光源,研究了掺杂高硅氧玻璃的制备和光谱性能,首先制作多孔玻璃,通过掺杂溶液浸渍,制备掺Co和Ce高硅氧玻璃,并研究了在还原气氛下热处理玻璃的光谱性能,实验表明：合理的温度制度是制备掺杂高硅氧玻璃的关键,改进工艺条件可制成耐热性能优良的掺杂高硅氧玻璃,光谱测试表明,Co离子的价态较为稳定,通常以低价Co^2 离子形态存在于玻璃之中,Ce则主工以Ce^4 离子形态存在,在还原气氛下热处理,被还原成低价Ce^3 离子,玻璃的荧光光谱也证实了价态的变化。     

Indentation deformation and cracking behavior of hydrated aluminoborate glasses

Aluminoborate glasses have recently been found to feature high resistance to crack initiation during indentation due to a highly flexible network structure. In cesium aluminoborate glasses, it has been found that the use of a simple post-treatment, namely aging in a humid atmosphere, can further improve this resistance. To better understand the mechanical properties of this glass family upon humid aging, we here study the effect of aging conditions on the structure and mechanical properties of Li,K,Cs-aluminoborate glasses. As expected, we find that higher humidity and longer aging time cause more pronounced permeation of atmospheric water into the glasses. Due to their denser structure and stronger modifier-oxygen bonds, the humid aging has a relatively smaller effect on the mechanical properties of Li- and K-containing glasses relative to Cs-containing glasses, with the latter achieving an ultrahigh crack resistance. We find that the humid aging leads to the formation of a hydration layer in the Cs-aluminoborate glass surface, with a thickness of around 26 μm upon aging at 23 °C with 40% relative humidity for 7 days. Moreover, a remarkable indentation behavior, that is, the observation of μm-sized shear bands inside the imprint of the Cs-glass upon aging at 60% relative humidity is reported. Taken as a whole, the work provides guidelines for how to control the humid aging rate as a function of relative humidity and temperature to form a hydration layer and thus achieve improved crack resistance in such glasses.     

Influence of the content of a surrogate of iron aluminate high-level wastes on the phase composition and structure of glassy materials for their immobilization

Alkali borosilicate glassy materials with high iron and aluminum oxide concentrations, which simulate vitrified high-level wastes from the Savannah River Site (United States) at their content ranging from 50 to 70 wt %, have been investigated using X-ray powder diffraction, optical and electron microscopy, and infrared spectroscopy. Quenched and slowly cooled samples containing 50 wt % wastes are glasses. Samples containing 60 and 70 wt % wastes, which were quenched on a metal slab, are predominantly glasses with an insignificant content of the spinel formed in a trevorite-magnetite solid solution. The slowly cooled samples also contain nepheline, and its amount increases with an increase in the waste content in the glassy materials.     

Oxynitride Glasses

Oxynitride glasses are grain boundary phases within silicon nitride ceramics. The desire to understand their nature led to various investigations on oxynitride glass formation, structure, properties, and crystallization. This paper provides a review of oxynitride glasses and outlines the effect of glass chemistry, including nitrogen contents and cation ratios, on properties such as glass transition temperature, Young's modulus, and viscosity and relates this to structural features within the glass. A short outline of crystallization of oxynitride glasses to form glass–ceramics is presented.     

Iron oxide nanoparticles supported on mesoporous MgO and CeO2: A comparative physicochemical and catalytic study

Iron (III) containing nanoparticles with superparamagnetic behaviour are prepared via deposition on various mesoporous supports (MgO, CeO₂ and SBA-15). XRD, TEM-EDX, N₂ physisorption, FTIR, and Moessbauer spectroscopy are used for their characterization. The reductive properties and catalytic behaviour in methanol decomposition of the materials are also studied. Depending on the chemical nature of the support, the predominant formation of: isolated iron species, strongly interacting with the support (for SBA-15), mixture of hematite and binary MgFe₂O₄ nanoparticles (for MgO) or almost homogeneously dispersed hematite particles (for CeO₂) are observed. The state of iron species strongly affects their catalytic properties. The favorable effect of the support mesoporosity on the catalytic activity is most pronounced for the iron modified CeO₂.     

Neutron diffraction study of antibacterial bioactive calcium silicate sol-gel glasses containing silver

Bioactive sol-gel calcia-silica glasses can regenerate damaged or diseased bones due to their ability to stimulate bone growth. This capability is related to the formation of a hydroxyapatite layer on the glass surface, which bonds with bone, and the release of soluble silica and calcium ions in the body fluid which accelerates bone growth. The addition of silver ions imbues the glass with antibacterial properties due to the release of antibacterial Ag⁺ ion. The antibacterial activity is therefore closely dependent on the dissolution properties of the glasses which in turn are related to their atomic-level structure. Structural characterization of the glasses at the atomic level is therefore essential in order to investigate and control the antibacterial properties of the glass. We have used neutron diffraction to investigate the structure of silver-containing calcia-silica sol-gel bioactive glasses with different Ag₂O loading (0, 2, 4, 6 mol%). The presence of the silver had little effect on the host glass structure, although some silver metal nanoparticles were present. Results agreed with previous computer simulations.