Cations In Glasses Research Articles

Structural features and crystallization of Na2O-Cs2O-B2O3-SiO2 glasses for radioactive waste immobilization

Borosilicate glasses have long been the preferred form for immobilizing high-level radioactive wastes. However, a significant drawback of glass-matrices involves the low rate of loading with radionuclides. One of the approaches to solving this problem envisages a multiphase glass system with crystalline inclusions. The present work aims to study model borosilicate glasses and glass-ceramics containing Cs atoms serving as a radionuclide simulator. Two approaches for the synthesis of glass-ceramics were used: directed crystallization, and pressing followed by annealing. The structure of initial borosilicate glasses and glass-ceramic samples obtained by these means was studied using Raman spectroscopy. An X-ray diffraction analysis was applied to identify crystalline phases. The morphology and composition of the crystalline phase was evaluated using scanning electron microscopy. The obtained results showed that the structure and properties of the synthesized glass-ceramic material is determined by the composition of initial glasses. Due to the ratio of modifying cations in glasses at a constant boron-to-silicon ratio, the crystalline phases identified in glass-ceramics are significantly affected by the anionic structure. The formation and growth of crystals was also established to be dependent on the technological scheme of synthesis.

Spectroscopic studies of mobile cations in glass

Spectroscopic studies of mobile cations in glass

Ion conduction in beryllium-alumino-silicate glasses doped with sodium or sodium and lithium ions

Electrical properties of beryllium-alumino-silicate glasses containing sodium ions or sodium and lithium ions were studied with impedance spectroscopy technique over a frequency range from 10 mHz to 1 MHz and at temperature range from 213 to 473 K. The frequency- and temperature-dependent conductivity spectra of individual single alkali glasses were superimposed by means of the Summerfield scaling. Mixed-alkali glasses do not overlap into a single master curve. Glasses doped with sodium ions exhibit significantly higher values of D.C. conductivity and lower activation energy (~0.63 eV) than glasses doped with both sodium and lithium ions (~0.95 eV). The observed mixed-alkali effect can be described by the dynamic structure model (DSM). The conductivity pre-exponential factors and activation energy follow the Meyer-Neldel rule in both glass series. It was observed that the replacement of SiO2 by BeO in single cation glasses resulted in decrease in activation energy and pre-exponential factor σ0. In mixed cations glasses similar effect found for D.C. conduction process parameters was assigned to influence of both oxides BeO and Al2O3.

The structure of potassium germanate glasses as revealed by Raman and IR spectroscopy

Raman and infrared spectroscopy were used to determine the structure of glasses for compositions хK2O-(100-х)GeO2, where х = 0, 10, 20, 30 и 40 mol%. Curve-fitting was applied to both medium- and high-frequency regions of the Raman spectra, and the main structural species formed in the system were defined. It was shown that the maximum of Ge(IV) → Ge(VI) conversion occurs at a composition of about 20 mol% K2O. A further increase of modifier cation in glasses results in a decrease in the coordination number of Ge atoms. At the same time, there is a depolymerisation of the three-dimensional disordered network and formation of tetrahedra [GeO4] with one and two non-bridging oxygen atoms.

Effect of Gd2O3 doping on structure and boron volatility of borosilicate glass sealants in solid oxide fuel cells—A study on the La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) cathode

Boron volatility is one of the most important properties of borosilicate-based glass sealants in solid oxide fuel cells (SOFCs), as boron contaminants react with lanthanum-containing cathodes, forming LaBO3 and degrading the activity of SOFCs. Here, we report that the reaction between the volatile boron and a La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) cathode during polarization can be significantly reduced by doping aluminoborosilicate glass with Gd2O3. Specifically, the Gd cations in glass with 2 mol.% Gd2O3 dissolve preferentially in the borate-rich environment to form more Gd-metaborate structures and promote the formation of calcium metaborate (CaB2O4); they also condense the B–O network after heat treatment, which suppresses poisoning by boron contaminants on the LSCF cathode. The results provide insights into design and development of a reliable sealing glass for SOFC applications.

Label-Free, LC-MS-Based Assays to Quantitate Small-Molecule Antagonist Binding to the Mammalian BLT1 Receptor

We have developed and validated label-free, liquid chromatography–mass spectrometry (LC-MS)-based equilibrium direct and competition binding assays to quantitate small-molecule antagonist binding to recombinant human and mouse BLT1 receptors expressed in HEK 293 cell membranes. Procedurally, these binding assays involve (1) equilibration of the BLT1 receptor and probe ligand, with or without a competitor; (2) vacuum filtration through cationic glass fiber filters to separate receptor-bound from free probe ligand; and (3) LC-MS analysis in selected reaction monitoring mode for bound probe ligand quantitation. Two novel, optimized probe ligands, compounds 1 and 2, were identified by screening 20 unlabeled BLT1 antagonists for direct binding. Saturation direct binding studies confirmed the high affinity, and dissociation studies established the rapid binding kinetics of probe ligands 1 and 2. Competition binding assays were established using both probe ligands, and the affinities of structurally diverse BLT1 antagonists were measured. Both binding assay formats can be executed with high specificity and sensitivity and moderate throughput (96-well plate format) using these approaches. This highly versatile, label-free method for studying ligand binding to membrane-associated receptors should find broad application as an alternative to traditional methods using labeled ligands.

Transition and post-transition metal ions in borate glasses: Borate ligand speciation, cluster formation, and their effect on glass transition and mechanical properties.

A series of transition and post-transition metal ion (Mn, Cu, Zn, Pb, Bi) binary borate glasses was studied with special consideration of the cations impact on the borate structure, the cations cross-linking capacity, and more generally, structure-property correlations. Infrared (IR) and Raman spectroscopies were used for the structural characterization. These complementary techniques are sensitive to the short-range order as in the differentiation of tetrahedral and trigonal borate units or regarding the number of non-bridging oxygen ions per unit. Moreover, vibrational spectroscopy is also sensitive to the intermediate-range order and to the presence of superstructural units, such as rings and chains, or the combination of rings. In order to clarify band assignments for the various borate entities, examples are given from pure vitreous B2O3 to meta-, pyro-, ortho-, and even overmodified borate glass compositions. For binary metaborate glasses, the impact of the modifier cation on the borate speciation is shown. High field strength cations such as Zn2+ enhance the disproportionation of metaborate to polyborate and pyroborate units. Pb2+ and Bi3+ induce cluster formation, resulting in PbOn- and BiOn-pseudophases. Both lead and bismuth borate glasses show also a tendency to stabilize very large superstructural units in the form of diborate polyanions. Far-IR spectra reflect on the bonding states of modifier cations in glasses. The frequency of the measured cation-site vibration band was used to obtain the average force constant for the metal-oxygen bonding, FM-O. A linear correlation between glass transition temperature (Tg) and FM-O was shown for the metaborate glass series. The mechanical properties of the glasses also correlate with the force constant FM-O, though for cations of similar force constant the fraction of tetrahedral borate units (N4) strongly affects the thermal and mechanical properties. For paramagnetic Cu- and Mn-borate glasses, N4 was determined from the IR spectra after deducing the relative absorption coefficient of boron tetrahedral versus boron trigonal units, α = α4/α3, using NMR literature data of the diamagnetic glasses.

Short and Intermediate Range Ordering in Fast Cation Glasses for Battery Applications

Lithium batteries provide the highest energy density which makes them ideal candidates for future generations of portable electronics (laptops, cellular, tablets, etc.) and hybrid electric vehicles for the time being. However, the increasing demand for lithium batteries will be limited by the fact that lithium is not an abundant material and its cost is expected to increase considerably in the coming years. In contrast, sodium resources are unlimited (fourth most abundant element in Earth’s crust) and from economic point of view, sodium batteries appear as good alternative to lithium devices, particularly for large-scale stationary applications. The ionic conductivity of chalcogenide and chalcohalide glasses is 2 to 3 orders of magnitude higher than that of oxide glasses with the same mobile ion content. This makes chalcogenide systems suitable for applications in power rechargeable systems. Our studies are focused on the development of new Na+ion-conducting chalcohalide glasses combining sodium halides and sulfide-based glass network. Cation local environment and intermediate-range ordering in glasses are critically important to achieve fast ionic conduction. Usual structural hypothesis related to superionic glasses containing metal halides MY = LiI, NaBr, AgI, etc., implies the absence of chemical interactions between the host glass and metal halide. An expansion of the host network caused by large anions (I, Br) and related increase of the available free volume for fast cations, forming preferential conduction pathways, was considered to be the key parameter for glassy superionics. Nevertheless, recent studies of AgY and CuY crystalline coordination polymers show chemical interaction between metal halide and chalcogenide backbone giving rise to mixed M-centered polyhedra. The polyhedral connectivity was also found to be different, starting from isolated units and dimers and finishing by chains, 2D layers and tubes. Some characteristic types of MY-subnetwork are given in Fig. 1(a,b). Using pulsed neutron and high-energy x-ray diffraction combined with Reverse Monte Carlo modelling, we examine cation local and intermediate range ordering in two glassy systems containing either silver iodide or sodium halides. Sodium chalcogenide glasses exhibit high ionic conductivity and seem to be promising for battery applications. Figure 1

Structure and ionic diffusion of alkaline-earth ions in mixed cation glasses A2O–2MO–4SiO2 with molecular dynamics simulations

A series of mixed cation silicate glasses of the composition A2O–2MO–4SiO2, with A=Li, Na, K and M=Ca, Sr, Ba has been investigated by means of molecular dynamics simulations in order to understand the effect of the nature of the cations on the mobility of the alkaline-earth ions within the glass network. The size of the alkaline-earth cation was found to affect the inter-atomic distances, the coordination number distributions and the bond angle distributions, whereas the medium-range order was almost unaffected by the type of the cation. All the alkaline-earth cations contribute to lower vibrational frequencies but it is observed that there is a shift to smaller frequencies and the vibrational density of states distribution gets narrower as the size of the alkaline-earth increases. The results from our modeling for the ionic diffusion of the alkaline-earth cations are in a qualitative agreement with the experimental observations in that there is a distinct correlation between the activation energy for diffusion of alkaline earth-ions and the cation radius ratio. An asymmetrical linear behavior in the diffusion activation energy with increasing size difference is observed. The results can be described on the basis of a theoretical model that relates the diffusion activation energy to the electrostatic interactions of the cations with the oxygens and the elastic deformation of the silicate network.

Fabrication of amorphous calcium carbonate composite particles‐polymer multilayer films by a layer‐by‐layer method

Organic–inorganic hybrid multilayer films were prepared on a precoated cationic glass substrate by using a layer‐by‐layer (LbL) electrostatic self‐assembly technique with poly(diallyldimethylammonium chloride) as a polycation and submicron‐sized stable amorphous calcium carbonate (ACC) composite particles. The ACC composite particles (ACP) stabilized with poly(acrylic acid) were obtained by a carbonate controlled‐addition method. The average particles size of ACP was (1.8 ± 0.4) × 102 nm. An ethanolic dispersion of ACP was used for the LbL electrostatic self‐assembly technique on the precoated substrate due to instability of ACP in water. The deposition of the particles was confirmed by SEM analysis. The film thickness of the multilayer assembly increased from 230 to 710 nm with increasing the deposition layers. The FTIR spectra of scratched multilayer samples showed characteristic broaden peaks of ACC. The amorphous phase was stable after the LbL assembly process as well as after 2 months in a dry film state. POLYM. COMPOS., 36:330–335, 2015. © 2014 Society of Plastics Engineers

The Structural Properties of Cations in Nuclear Glasses

The structure of nuclear glasses and of simplified surrogates has been investigated using complementary diffraction and spectroscopic methods, together with numerical modeling. The diversity of structural surroundings of cations in glasses is reviewed at various scales. Cations usually occur in smaller sites in glasses than in crystals, with unusual site geometries such as 5-coordination. These sites may correspond to different structural positions. Network forming and networking situations illustrate the existence of a well-defined relationship with the glassy network, with cations improving glass stability. The complementary charge-compensation may sometimes give rise to a competition between cations. In that case, the cation may lose its stabilizing character and become a nucleating agent, as observed for “chameleon” elements, the coordination of which and hence the structural properties may change as a function of glass composition. Eventually, at the mesoscale, the heterogeneous distribution of cations has been recently visualized, providing keys to understand the nucleation processes in glasses.

Controls of host rock mineralogy and H2O content on the nature of pseudotachylyte melts: Evidence from Pan-African faulting in the foreland of the Gariep Belt, South Africa

Abstract Late-orogenic Pan-African tectonics formed an 8 km long fault-fracture zone in the shallow foreland crust of the Gariep Orogen in Mesoproterozoic granitoid basement. Pseudotachylyte was locally formed during a single seismic event that caused brittle failure in cohesive quartz-diorite, granodiorite and granitic gneiss. 40Ar/39Ar laser spot analysis provides an age of 512.5 ± 7.5 Ma for this seismic event. The depth of the hypocentre between 1700 and 5300 m is inferred from the likely thickness of the overlying rock at that time. Abundant quartz melting in conjunction with low host rock temperature indicates a minimum seismic temperature rise exceeding 1030 °C but in some samples dry quartz melting at temperatures exceeding 1700 °C might have been possible. The abundance of hydrous phases in the host rock controlled the volume of melt produced in a given host rock type. Different types of primary melt were formed by the fusion of batches of host rock with different relative proportions of plagioclase, alkali feldspar, quartz, biotite, and, where present, amphibole or garnet. The chemical and physical interaction between these melts depended on contrasting melt mobility and viscosity. In quartz-diorite, glasses of variable composition are well preserved and show the distribution of primary melt species at the time of quenching. These different melt species had limited tendency of mixing, unless mixing was assisted by syn-seismic shearing. In granodiorite, which has a low proportion of hydrous phases, low-viscosity melt was formed at high temperatures, eliminating most host rock fragments and leading to extensive melting of quartz. The low melt viscosity, probably further decreased by the dissolution of free H2O, permitted effective melt homogenisation in such veins. Still in the liquid state these melts segregated, effectively separating secondary melts of sodic–calcic and of K–Mg–Fe-rich composition. After quenching the solid state diffusion of cations in glass was comparatively insignificant.

Cation diffusion in mixed cation silicate glasses under non-equilibrium conditions

Diffusion of alkali (A) and calcium ions (Ca) in mixed cation glasses of the composition A2O⋅2CaO⋅4SiO2 was investigated by impedance measurements and radiotracer diffusion under reducing forming gas atmosphere and x-ray irradiation below the respective glass transition temperatures. Under reducing atmosphere the mobility of the alkali ions is hampered by the presence of additional hydrogen, which gives rise to an effect comparable to the mixed alkali effect. The lower alkali ion diffusivity leads to a reduced alkali ion assisted enhancement of calcium diffusion and thus to lower calcium mobilities in Na2O⋅2CaO⋅4SiO2 and K2O⋅2CaO⋅4SiO2 glasses. However, in Li2O⋅2CaO⋅4SiO2 an enhancement in calcium diffusion is observed, which is explained by electrostatic and elastic forces. X-ray irradiation enhances the sodium mobility in Na2O⋅2CaO⋅4SiO2 at lower temperatures. The irradiation induces additional defects in the glass and causes breaking of sodium–oxygen bonds. However, the temperatures at which the x-ray irradiation affects the cation diffusion are too low to observe a measurable impact on the calcium mobility.

Fundamental and applied electrochemistry at an industrial glass laboratory—an overview

This paper is a review of the author’s work at the SCHOTT Electrochemical Laboratory from 1965 to 1995. Special emphasis is given to the elucidation of the functioning of the glass electrode, mobility of cations in glasses, and to the research on the electrochemistry of glass melts.

Structure and Properties of Mixed Strontium−Manganese Metaphosphate Glasses

Structural, optical, and physical properties of glasses prepared by melt reduction in the mixed Sr−Mn metaphosphate system xMnO−(1 − x)SrO−P2O5, 0 ≤ x ≤ 1, have been investigated by vibrational, optical, EPR, and thermal techniques. Mn ions were found mostly in the +2 oxidation state and in sites of octahedral symmetry. Such sites are formed by neighboring Mn−oxygen polyhedra, where the covalent character of Mn−O bonding increases with cation mixing. The phosphate structure was found to consist predominantly of metaphosphate tetrahedral species (Q2) with a minority of pyrophosphate (Q1) and neutral (Q3) phosphate tetrahedra, whose relative abundance changes nonlinearly with MnO content. The symmetric stretching vibration of terminal PO2− units in Q2 species was employed to probe the influence of mixed Sr/Mn environments on phosphate structure, and the results suggested a deviation from the homogeneous distribution of metal cations. This was attributed to the coordination numbers of Sr and Mn ions (i.e., 8 and 6, respectively) which exceed the available number of terminal oxygen atoms per metal ion, M (i.e., 4), and thus require the formation of neighboring M−oxygen polyhedra which are connected by P−O−M−O−M−O−P linkages. Nevertheless, each metal ion was found to form its own M−O site and to retain the identity of its site in both single and mixed cation glasses. While density and molar volume follow a linear decrease with MnO content, glass transition temperature Tg, thermal expansion coefficient, refractive index, and optical dispersion exhibit clear deviations from additivity. The increasing trend of Tg with cation mixing was attributed to a combination of the different cross-linking abilities by P−O−M−O−M−O−P bridges of the Sr and Mn ions with the relative proportion of metaphosphate Q2 units. The composition dependence of optical dispersion, as expressed by the Abbe number, was correlated with the average electronic band gap obtained from refractive-index dispersion data using the Wemple−DiDomenico single oscillator model. While all glasses in the Sr−Mn system were found to exhibit low optical dispersion, cation mixing was shown to increase dispersion because of increased covalency in Mn−O bonding.

Alkaline-Earth Diffusion in Mixed Cation Glasses

Diffusion of alkaline-earth ions in mixed cation glasses of the composition xA2O•(3-x)MO•4SiO2 (x = 0.0, 0.1, 0.3, 0.4 and 1.0; A = Na, K; M = Ca, Ba) was investigated by means of the radiotracer diffusion technique below the respective glass transition temperatures. The mobility of alkaline-earth ions increases with the alkali content in all analyzed glass systems with no decrease in the diffusion activation energy, but a raise in the pre-exponential factor. A distinct dependency of the activation energy of the alkaline-earth ions on the type and content of the alkali ions in the glass is observed. Additional experiments with thin glass films derived by the sol-gel technique reveal an analogous diffusion behaviour. This demonstrates that the dynamic of alkaline-earth ions in mixed cation glasses does not depend on the way of glass preparation.

Leachability of Iron Ions from Binary and Ternary Phosphate Glasses

With a view to using glasses as a source of iron, which is one of the micronutrients required by plants, a systematic study on leachability of iron ions from binary and ternary phosphate glasses having molar composition (40+X)FeO.(60-X)P2O5 and (55-X)FeO. XR2O.45P2O5 (where X = 0–9 mol% and R = Li, Na, K) was carried out. Leaching of iron ions has been studied as a function of pH and the results show that leaching increases with increasing pH of the solutions. The concentration of iron ions in the leachate decreases with increasing bond strength between non-bridging oxygen ions and the cations in glasses. The leaching of iron ions enhances with increase in leaching time as well as an increase in the concentration of P2O5 in the glass. It decreases further with an increase in particle size of glasses.

EELS studies of nano-precipitates in borosilicate glasses

The sequence of precipitation in five different alkali-borosilicate glasses is studied by HREM, HAADF-STEM and EELS. The glasses are doped or supersaturated with 4 mol% of CeO2, and have varying concentrations of other dopant oxides, such as Fe2O3, Nd2O3, Cr2O3, and Ag2O. The shape and distribution of precipitates range from amorphous droplet shape to dendritic crystals. Oxidation states of Ce and other cations in glass and precipitates are measured by ELNES. It is found that Ce in glass preferentially adopts +IV valence in Ce-crystal-free glasses while it adopts +III valence in glass nanocomposites that contain Ce(+IV)O2 nanocrystals.

Electro-diffusion equations of monovalent cations in glass under charge neutrality approximation for optical waveguide fabrication

Two improvements of the usual three-dimensional partial differential equations that model ion-exchanged optical devices in glass under charge neutrality approximation are proposed. First, they are rigorously generalised for both non-ideal cation behaviour and concentration-dependent self-diffusion coefficients. Secondly, the Faraday equation is imposed in the derivation instead of the Ohm law. Accordingly, the current density distribution is not governed by the electric field but by the gradient of an effective electrical potential instead. On the other hand, the boundary conditions of those equations are obtained from standard electrolyte theory, which results in contact potentials at interfaces between glass and molten salt, silver film or metallic cathode. Therefore, typical arrangements for field-assisted ion exchange must be considered as electrochemical cells, and thus a correction term must be added to the applied voltage to get a proper modelling. This term can be neglected in some typical cases but it must be retained in others. Finally, it is predicted that the electrochemical cell effect can be used to diffuse cations from a silver film without need for an external applied field. This suggests a new simple method to fabricate integrated optical components by ion exchange in glass.

Effect of aluminum ions on intrinsic sub-critical crack growth in metaphosphate glasses

Sub-critical crack growth in various kinds of metaphosphate glasses was investigated by using DCDC (Double Cleavage Drilled Compression) technique. The crack growth measurements were only being made in Region III, or in an inert environment. In order to evaluate intrinsic crack growth behaviors in Region III, crack propagation tests were performed in dehydrated heptane, and the crack velocity, v, was plotted as a function of the stress intensity factor, K I. Fracture toughness of glass was also estimated from a stress intensity factor at a given crack velocity. For binary metaphosphate glasses (50MO · 50P 2O 5, M = Zn, Mg, Ca, Ba), fracture toughness increases in the order of Mg > Ca > Zn > Ba. However, the slope of K I– v curve is almost unchanged. In the case of aluminum containing metaphosphate glasses, with increasing aluminum content, fracture toughness increases and the slope of K I– v curve becomes smaller, regardless of the type of divalent cations in glass. It is concluded that an addition of aluminum ions into metaphosphate glass results in both high toughness and easy fatigue. In addition, the structural role of aluminum ions on the intrinsic sub-critical crack growth is discussed in terms of the models of atomistic bond rupture.