Borosilicate Glass Samples Research Articles

Contribution of atom-probe tomography to a better understanding of glass alteration mechanisms: Application to a nuclear glass specimen altered 25 years in a granitic environment

We report and discuss results of atom probe tomography (APT) and energy-filtered transmission electron microscopy (EFTEM) applied to a borosilicate glass sample of nuclear interest altered for 25.75years at 90°C in a confined granitic medium in order to better understand the rate-limiting mechanisms under conditions representative of a deep geological repository for vitrified radioactive waste. The APT technique allows the 3D reconstruction of the elemental distribution at the reactive interphase with sub-nanometer precision. Profiles of the B distribution at pristine glass/hydrated glass interface obtained by different techniques are compared to show the challenge of accurate measurements of diffusion profiles at this buried interface on the nanometer length scale. Our results show that 1) Li from the glass and hydrogen from the solution exhibit anti-correlated 15nm wide gradients located between the pristine glass and the hydrated glass layer, and 2) boron exhibits an unexpectedly sharp profile (~3nm width) located just outside of the Li/H interdiffusion layer; this sharp profile is more consistent with a dissolution front than a diffusion-controlled release of boron. The resulting apparent diffusion coefficients derived from the Li and H profiles are DLi=1.5×10−22m2·s−1 and DH=6.8×10−23m2·s−1. These values are around two orders of magnitude lower than those observed at the very beginning of the alteration process, which suggests that interdiffusion is slowed at high reaction progress by local conditions that could be related to the porous structure of the interphase. As a result, the accessibility of water to the pristine glass could be the rate-limiting step in these conditions. More generally, these findings strongly support the importance of interdiffusion coupled with hydrolysis reactions of the silicate network on the long-term dissolution rate, contrary to what has been suggested by recent interfacial dissolution–precipitation models for silicate minerals.

Dynamic Impact Absorption Behaviour of Glass Coated with Carbon Nanotubes

Boro-silicate glass samples were coated with chemically treated multi-walled carbon nanotubes (MWCNTs) to study the resistance offered by the coatings under the high strain rate impact. Impact testing of these glass samples was performed on Split Hopkinson Pressure Bar (SHPB), where strain rates were varied from 500/s to 3300/s. However, the comparisons were limited to samples subjected to a strain rate of 2300/s to 3000/s so that the effect of only variable deposits of coatings on the stress-strain behavior of glass can be studied. Variable deposits (0.1 mg to 0.8 mg) of MWCNTs were coated uniformly on glass samples having a disc shape with a fixed surface area (79 mm2) to observe the effect of the coating on the impact absorption capacity of glass. It was observed that the small thickness of about 25 μm formed due to the fact that 0.2 mg of MWCNTs deposit spread over the surface increased the impact absorption capacity of the glass pieces by nearly 70%. However, beyond this amount when the deposit was increased to 0.4 mg, the coating thickness got doubled to nearly 49 μm and this led to a fall in absorption capacity which remained static till 0.8 mg deposit. However, even this decrease in capacity was able to absorb 30% more impact than offered by pure glass sample.

Synthesis and Optical Investigations on (Ba,Sr)TiO<sub>3</sub> Borosilicate Glasses Doped with La<sub>2</sub>O<sub>3</sub>

In this research paper we are reporting synthesis, structural and optical investigations of barium strontium titanate borosilicate glasses with addition of La2O3. Glasses were synthesized by conventional rapid melt quench method. Infrared absorption spectra, for various (Ba,Sr)TiO3 borosilicate glass samples having glass system 64[(Ba1-xSrx)TiO3]-35[2SiO2-B2O3]-5[K2O]-1[La2O3] (x = 0.3, 0.5, 0.6, 0.8 and 1.0), were recorded over a continous spectral range from 450 - 4000 cm-1. IR spectra were analyzed to determine and differentiate the various vibrational modes in the structural changes. Raman spectroscopy of all glass samples were also carried out wavenumber range form 200 - 1500 cm-1. These two complementary spectroscopic techniques revealed that the network structure of the studied glasses is mainly based on BO3, pentaborate groups linked to BO4 tetrahedra and units placed in different structural groups, the BO3 units are dominanting. The recorded IR and Raman spectra of different glasses are used to clarify the optical properties of the prepared glass samples correlating with their structure and compositions. UV-Vis spectroscopy was carried out in range of 200 - 800 nm. The optical band gap was found between 2.023 - 3.320 eV.

Graded porous glasses for antireflective applications formed by chemical treatment

Porous glass surface can be achieved by the neutral-solution etch process, which has been reported to be effective in suppressing light reflection from glasses. Samples of a commercial borosilicate glass were submitted to a static aqueous corrosion at 87°C for several hours for introducing porosity on glass surface. Morphology, composition and optical properties of the surface, which were analyzed by scanning electron microscope (SEM), energy dispersive spectrum (EDS) and spectrometer, can be controlled by changing both the neutral-solution concentration and etching time. The results show that the transmittance of glass substrate can be improved after chemical treatment, and the laser-induced damage threshold of graded porous glass is much higher than that of antireflective coatings. The SEM and EDS results revealed a significant corrosion process in the solution, and determined the relationship between the graded porosity and refractive index of glasses.

Application of particle induced gamma-ray emission for non-destructive determination of fluorine in barium borosilicate glass samples

Barium borosilicate glass (BaBSG) is proposed as a potential candidate for vitrification of nuclear waste generated from thoria based nuclear reactors. Along with fission products, activation products and many inactive chemicals, like fluorine in the form of HF are expected to be present in the dissolver solution with nuclear waste. As vitrification occurs at high temperature, it is important to quantify fluorine in BaBSG. Due to its complex matrix, most of the wet chemical and nuclear analytical methods encounter problems in the estimation of fluorine. Particle induced γ-ray emission (PIGE) method has been standardized for non-destructive determination of fluorine contents in BaBSG samples utilizing measurement of prompt gamma-rays from 19F (p, p’γ) 19F reaction. Experiments have been carried out with thick pellet targets prepared in cellulose matrix using 4 MeV proton beam from the folded tandem ion accelerator at BARC, Mumbai. For obtaining current normalized count rate of interest, beam current variation was monitored by the Rutherford backscattering spectrometry (RBS) method as well as by the in situ approach using an externally added element sensitive to PIGE. In this paper standardization of PIGE methods for F determination, validation of methods using synthetic samples, and application to BaBSG samples are reported.

Nuclear Glass Durability: New Insight into Alteration Layer Properties

We have performed TEM, Raman microspectroscopy, and NanoSIMS characterization of borosilicate glass samples altered for nearly 26 years at 90 °C in a confined granitic medium in order to better understand the rate-limiting mechanisms under conditions representative of a deep geological repository for vitrified radioactive waste. For the first time, we show a thick interphase that behaves like a diffusion barrier between the pristine glass and the other alteration products (porous gel and crystalline phases). Our findings indicate that the glass undergoes two distinct irreversible reactions: (i) hydration of the pristine glass controlled by water diffusion with a diffusion coefficient of 2 × 10–21 m2/s and (ii) transformation of the hydrated glass into a macroporous gel with major structural changes. Both materials are nonstoichiometric and metastable. A final reversible reaction leads to the formation of crystalline phases that consume elements forming the gel layer and the hydrated glass. All these react...

Elastic properties investigation of gamma-radiated barium lead borosilicate glass using ultrasonic technique

The ultrasonic velocities were measured in barium lead borosilicate glass samples of different compositions before and after irradiation with γ-rays. Measurements were carried out at room temperature and 4 MHz frequency using ultrasonic technique. The ultrasonic velocities data of glass samples have been used to find the elastic modulus and micro-hardness. Densities of glass samples were measured by Archimedes’s principle using n-hexane as immersion liquid. It was found that ultrasonic velocity, elastic modulus and micro-hardness increase with increasing barium oxide content and increasing γ-radiation dose.

Thermal and crystallization kinetics of yttrium and lanthanum calcium silicate glass sealants for solid oxide fuel cells

The crystallization kinetics of glass sealants is an essential parameter to check the suitability of glass as a sealant. The crystallization kinetic behavior of calcium borosilicate glasses were studied by Differential thermal analysis (DTA), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). These glasses were exposed for different heat treatment durations in oxidizing atmosphere at 800 and 900 °C. XRD results indicate the presence of La2SiO5 crystalline phase which increases the thermal expansion of the glasses. However, yttria doped calcium borosilicate glass (CaY) sample could not form any crystalline phase even after 10 h heat treatment at 900 °C. Moreover, the thermal expansion coefficient (TEC), viscosity values and fragility index of the glasses indicate that lanthanum doped calcium borosilicate glass (CaLa) might be a better glass sealant for solid oxide fuel cell as compared to CaY glass.

Permeability and elastic properties of cracked glass under pressure

[1] Fluid flow in rocks is allowed through networks of cracks and fractures at all scales. In fact, cracks are of high importance in various applications ranging from rock elastic and transport properties to nuclear waste disposal. The present work aims at investigating thermomechanical cracking effects on elastic wave velocities, mechanical strength, and permeability of cracked glass under pressure. We performed the experiments on a triaxial cell at room temperature which allows for independent controls of the confining pressure, the axial stress, and pore pressure. We produced cracks in original borosilicate glass samples with a reproducible method (thermal treatment with a thermal shock of 300°C). The evolution of the elastic and transport properties have been monitored using elastic wave velocity sensors, strain gage, and flow measurements. The results obtained evidence for (1) a crack family with identified average aspect ratio and crack aperture, (2) a very small permeability which decreases as a power (exponential) function of pressure, and depends on (3) the crack aperture cube. We also show that permeability behavior of a cracked elastic brittle solid is reversible and independent of the fluid nature. Two independent methods (permeability and elastic wave velocity measurements) give these consistent results. This study provides data on the mechanical and transport properties of an almost ideal elastic brittle solid in which a crack population has been introduced. Comparisons with similar data on rocks allow for drawing interesting conclusions. Over the timescale of our experiments, our results do not provide any data on stress corrosion, which should be considered in further study.

Application to temperature sensor based on Er<sup>3 +</sup>-doped barium borosilicate glasses at visible band

The process of preparing Er 3+ -doped barium borosilicate glass samples with different dopant concentrations using a high-temperature sintering technique is discussed. Under a 978-nm semiconductor laser excitation, the energy transfer from 2 H11/2 to 4 I15/2 and 4 S3/2 to 4 I15/2 caused by the transitions of Er 3+ ions yields a 534- and a 549-nm green fluorescence. The relationship between the absolute temperature T and the fluorescence intensity ratio R of these two up-conversion photo- luminescence spectra is discussed and fitted to the exponential func- tion R = 1.782exp(−328/T) in the temperature range of 298 to 698 K. The sensitivity of the samples descends monotonously from 0.00219 to 0.00075 K −1 with the temperature increase from 298 to 698 K. The data are of undoubted repeatability, and the proposed doped glass is suitable for sensitive, high-temperature measurement. C 2011 Society of Photo-Optical

Cosmochemistry of thorium, samarium, and cesium in the substance of ordinary chondrites and problem of disposal of actinide and fission product concentrates in the Earth crust

The hydrothermal treatment of the substance of unequilibrated Krymka chondrite is studied. This substance is a sample of the oldest basalts of the Earth group planets and is considered as a natural analog of matrices for immobilization of Th, Sm, and Cs. It is shown that Th and Sm are mainly fixed in phosphates, whereas Cs becomes a scattered element. In equilibrated chondrites, Cs is found in feldspars. A sol-gel synthesis procedure was developed, and tests were performed for ferro(alumino)silicophosphate matrices for immobilization of actinides and fission products. The corrosion resistance of the matrices with respect to Cs leaching appeared to be higher by an order of magnitude than that of the best samples of borosilicate glass. Suggestions are made on optimizing the isolation from the biosphere of concentrates of long-lived high-level nuclear wastes.

Composition effects on synthetic glass alteration mechanisms: Part 1. Experiments

Alteration of nuclear waste glasses and silicate minerals is governed by complex processes regulated by several coupled mechanisms. Among these processes is reactive mass transfer through the amorphous gel layer (known as the passivating reactive interphase (PRI) in case of a rate-limiting effect) located between the pristine glass and the bulk solution. In order to assess the influence of the glass composition and the pH on the properties of the PRI, and thus on the nuclear glass durability, an experimental leaching study was performed on borosilicate glass samples with or without Ca, Al, and Zr. Experiments were conducted to understand the influence of the pH and glass composition on the solvated cation diffusion coefficient within the PRI and to generate data for calibration of a PRI solubility model (not presented here). All the experiments were carried out at high S/ V ratios so that silicon rapidly reached apparent saturated conditions and the PRI could form: in such conditions glass alteration is controlled only by diffusion of water and dissolved species through the PRI and by precipitation of crystallized secondary phases. The constituents in the PRI and the crystallized secondary phases depend to a large extent on the glass composition and pH. Alkali metal (Na) or preferentially alkaline earth (Ca) elements are retained in the PRI for charge compensation of Al and Zr. The apparent diffusion coefficient calculated from the release of boron, a good tracer, varies with the pH from less than 4 × 10 −22 to 9 × 10 -18 m 2 s −1 in the studied glasses. These very low diffusion coefficients decrease as the pH increases. Concerning the PRI composition we show that Si, Al, Ca and Zr have strong interactions and thus major consequences on the glass durability. Our findings indicate that the SiO 2aq activity is relatively constant and independent of the pH below pH 9, followed by a drop at pH 10. In addition, the activity of SiO 2aq is affected by the glass composition, and especially by aluminum and zirconium. As soon as dissolved silicon reaches steady state in solution the aluminum and zirconium concentrations start to decrease, probably due to silicon, aluminum and zirconium interactions with retention in the PRI. The formation of crystallized secondary phases is observed at pH 10 for aluminum-free glasses, which diminishes the saturation state of amorphous silica in solution. In these glasses the saturation index indicates that the solution is oversaturated with respect to calcium silicate hydrates (ex: tobermorite, gyrolite). Moreover, the formation of crystallized secondary phases causes dissolution of the PRI and the glass, which sustains renewed alteration. This study leads to the conclusion that modeling nuclear glass dissolution kinetics over a wide pH range (typically from pH 7 to pH 10) must take into account (1) PRI composition variations and relations between the PRI composition and properties (solubility, diffusion coefficient); and (2) crystallized secondary phases that can consume elements from the PRI. Applying PRI modeling concepts to other kinds of natural glasses or even multi-oxide minerals might prove useful for enhancing our understanding of alteration mechanisms.

Emission and energy relaxation of excitons in quantum dots with disordered interfaces grown in a low-permittivity matrix

Samples of borosilicate glasses doped by CdS with concentrations smaller than 1% are studied. It is shown that, due to a disorder at interfaces of quantum dots, the main channels of emission of excitons by quantum dots are the annihilation of excitons in quantum and localized surface states, while the efficiency of interaction between the channels largely depends on the radius of quantum dots. It is found for the first time that states that form the second emission channel are not discrete energy levels in the band gap, as is usually assumed in some experimental and theoretical works, but rather form a quasi-continuous tail of the density of localized states. These localized states appear as a result of dangling bonds of outer atoms of quantum dots. Energy relaxation of carriers via localized states is the reason for a long response time of these structures to an external action and can be enhanced due to a polarization effect caused by different dielectric constants of materials of quantum dots and matrix.

Barium borosilicate glass as a matrix for the uptake of dyes

Barium borosilicate (BBS) and sodium borosilicate (SBS) glass samples, prepared by the conventional melt-quench method, were used for the uptake of Rhodamine 6G dye from aqueous solution. The experimental conditions were optimized to get maximum uptake and was found to be 0.4 mg of dye per gram of BBS glass sample. For the same network former to modifier ratio, barium borosilicate glasses are found to have improved extent of uptake for the dye molecules from aqueous solutions compared to sodium borosilicate glasses. Based on 29Si MAS NMR studies on these glasses, it is inferred that significantly higher number of non-bridging oxygen atoms present in barium borosilicate glasses compared to sodium borosilicate glasses is responsible for its improved uptake of Rhodamine 6G dye. 11B MAS NMR studies have confirmed the simultaneous existence of boron in BO 3 and BO 4 configurations in both barium borosilicate and sodium borosilicate glasses. The luminescence studies have established that the dye molecule is incorporated into the glass matrix through ion exchange mechanism by replacing the exchangeable ions like Na +/Ba 2+ attached with the non-bridging oxygen atoms present in the glass.

Radiative heat transfer in enhanced hydrogen outgassing of glass

This paper explores the physical mechanisms responsible for experimental observations that led to the definition of photo-induced hydrogen outgassing of glass . Doped borosilicate glass samples were placed inside an evacuated silica tube and heated in a furnace or by an incandescent lamp. It was observed that hydrogen release from the glass sample was faster and stronger when heated by an incandescent lamp than within a furnace. Here, sample and silica tube were modeled as plane-parallel slabs exposed to furnace or to lamp thermal radiation. Combined conduction, radiation, and mass transfer were accounted for by solving the one-dimensional transient mass and energy conservation equations along with the steady-state radiative transfer equation. All properties were found in the literature. The experimental observations can be qualitatively explained based on conventional thermally activated gas diffusion and by carefully accounting for the participation of the silica tube to radiation transfer along with the spectral properties of the silica tube and the glass samples. In brief, the radiation emitted by the incandescent lamp is concentrated between 0.5 and 3.0 μm and reaches directly the sample since the silica tube is nearly transparent for wavelengths up to 3.5 μm. On the contrary, for furnace heating at 400°C, the silica tube absorbs a large fraction of the incident radiation which reduces the heating rate and the H2 release rate. However, between 0.8 and 3.2 μm undoped borosilicate does not absorb significantly. Coincidentally, Fe3O4 doping increases the absorption coefficient and also reacts with H2 to form ferrous ions which increase the absorption coefficient of the sample by two orders of magnitude. Thus, doped and reacted samples heat up much faster when exposed to the heating lamp resulting in the observed faster response time and larger H2 release rate.

Prompt gamma-ray neutron activation analysis methodology for determination of boron from trace to major contents

Prompt gamma ray neutron activation analysis methodologies were standardized using a reflected neutron beam and Compton suppressed γ-ray spectrometer to quantify boron from trace to major concentrations. Neutron self-shielding correction factors for higher boron contents (0.2–10 mg) in samples were obtained from the sensitivity of chlorine by irradiating KCl with and without boron. This method was validated by determining boron concentrations in six boron compounds and applied to three borosilicate glass samples with boron contents in the range of 1–10 mg. Low concentrations of boron (10–58 mg kg−1) were also determined in two samples and five reference materials from NIST and IAEA.

INTENSIFICATION OF NANOPOROUS GLASS PRODUCING BY POWERFUL ULTRASONIC FIELDS

ABSTRACT Nanoporous inorganic glasses are promising materials for many practical applications. Unfortunately the leaching-based technology allows the formation of pores at not more than 3 mm depth. The study is aimed at searching paths to intensify the ultrasonic (US) technology of nanoporous glass manufacturing. Two series of experiments were carried out on samples of sodium borosilicate glass. First series of experiments included the etching of glass samples without US field. The second series included the application of US field. One can conclude that effect of powerful US vibrations on the etching process grows up with the depth of micro channels. Seems the mostly presumable reasons of this phenomenon are: influence of “sound capillary” effect, cavitation and acoustic flows.

Role of Sulfate in Structural Modifications of Sodium Barium Borosilicate Glasses Developed for Nuclear Waste Immobilization

A sodium barium borosilicate glass matrix with a higher solubility of sulfate has been developed recently at Bhabha Atomic Research Centre for vitrification of sulfate bearing high‐level nuclear waste. We report here the studies carried out to understand the influence of sulfate ion on the three‐dimensional borosilicate network. Experiments were carried out with sodium barium borosilicate base glass samples loaded with varying amounts of SO42− (0–5 mol%). Phase separation studies on the samples revealed that as much as 3 mol% of SO42− can be loaded within the base glass without any phase separation, however, beyond this limit BaSO4 (barite) crystallizes within the matrix. Thermal analyses of the samples indicated a shift in glass transition temperature from 534° (0 mol% SO42−) to 495°C (3 mol% SO42−) and it remained more or less unaltered afterwards even with high SO42− loading. A similar observation of structure stabilization was obtained from 29Si MAS–NMR studies also, which showed that with 2 mol% of SO42− loading, the Q2:Q3 ratio changed from 59:41 (for samples with 0 mol% SO42− loading) to 62:38 and it remained almost the same afterwards even with higher SO42− loading. 11B MAS NMR patterns of the glass samples, however, remained unchanged with SO42− loading ([BO4]:[BO3]=38:62). Based on 29Si and 11B MAS NMR studies, the authors propose two different ways of interaction of SO42− ions with the borosilicate network: (i) the network modifying action of SO42− ions with ‐Si–O–Si‐ linkages, at low SO42− ion concentration (<2 mol%) and (ii) the preferential interaction of SO42− with the Ba2+ ions at high SO42− concentration (>2 mol%).

SAXS study of barium borosilicate glasses containing ThO2

Abstract Barium borosilicate (BBS) glass samples incorporated with 6.8–28 wt.% of ThO 2 have been characterized by small angle X-ray scattering (SAXS) technique. The samples contain smaller crystallites of average radius in the range 9–14 nm. Variation of the crystallite size with dopant concentration shows a significant increase in the value beyond about 23 wt.% of ThO 2 and a maximum in the polydispersity. This increase in sizes is probably due to the agglomeration of smaller particles occurring leading to the phase separation of crystallites from BBS matrix noticed in the earlier study.

Quantitative AFM analysis of phase separated borosilicate glass surfaces

Phase separated borosilicate glass samples were prepared by applying various heat treatments. Using selective chemical etching we performed AFM measurement on the phase separated glass surfaces. A quantitative roughness analysis allowed us to measure precisely the dependence of the characteristic size of the phase domains on heating time and temperature. The experimental measurements are very well described by the theoretically expected scaling laws. Interdiffusion coefficients and activation energy are estimated from this analysis and are consistent with literature data.