Oxide Borosilicate Glass Research Articles

Effect of structural disorder induced by external irradiation with heavy ions on the alteration of a four oxide borosilicate glass

The irradiation of glass by heavy ions induces structural damage, generally leading to a decrease in its chemical durability whose amplitude strongly depends on the glass chemical composition. Here, we investigate the effects of irradiation by 7 MeV Au ions (simulating the main ballistic effects induced by self-irradiation in nuclear glass) on the behavior of a 4-oxide borosilicate glass in both the initial and residual dissolution regimes. The comparison between irradiated and non-irradiated glasses provides insights into the predominant atomic mechanisms governing glass alteration processes. The most pronounced effect is observed on interdiffusion in acidic conditions, with the rate increased by more than an order of magnitude for the irradiated glass. We show that both the interdiffusion regime and the residual regime are controlled by the hydrolysis of the B—O—Si linkages, whereas under initial dissolution rate regime in basic conditions the rate-limiting step becomes the hydrolysis of Si—O—Si linkages. Overall, the observations suggest structural disorder due to external irradiation by Au ions primarily affects the kinetics of glass alteration without changing the fundamental nature of the limiting reactions.

Role of Bi2O3 in altering the structural, optical, mechanical, radiation shielding and thermoluminescence properties of heavy metal oxide borosilicate glasses

With the main intention of developing a transparent radiation shielding as well as a gamma dosimetric material, a series a heavy metal oxide borosilicate glass of composition (60-x) B2O3- 20SiO2- xBi2O3- 10ZnO- 10BaO with x = 0, 5, 10, 15 mol% was prepared by melt- quench technique. The glasses obtained were all transparent, except Bi-15 sample which is opaque and black in colour. The darkening is due to thermal reduction of Bi3+ ions, which is clearly indicated by absorption band around 377nm. XRD patterns showed the absence of crystalline peaks even in the opaque Bi-15 sample, confirming the glassy nature of all glasses. Furthermore, the structural changes in the glasses were confirmed with density measurement and FTIR studies. The Vickers hardness test done on transparent samples proved their higher mechanical strength, along with the theoretical calculation of elastic constants. The detailed analysis of gamma and neutron radiation shielding parameters for all the glasses was done using Photon Shielding and Dosimetry (PSD) software. The results suggested that the ϒ-ray shielding capacity increased, whereas the neutron attenuation ability decreased with the successive addition of Bi2O3. The opacity of Bi-15 can create problem in certain applications where transparency is needed. In order to assess the possibility of transparent glasses to be used as gamma dosimeter, they were irradiated with gamma rays of 1.25 MeV and thermoluminescence (TL) glow curves were recorded. An interesting behaviour of quenching of TL intensity for initial addition and enhancement of TL intensity for further addition of Bi2O3 was observed. The linearity of the dose- response curve for Bi-10 sample in two regions of gamma doses 100 Gy-3 kGy and 5- 50 kGy, showcased the chances of Bi-10 sample to be used as TL dosimeter for both low and high doses.

Alteration of synthetic basaltic glass in silica saturated conditions: Analogy with nuclear glass

This study investigates the analogy between basaltic and borosilicate glasses of nuclear interest, by focusing on mechanisms controlling glass dissolution under silica saturation conditions. These conditions are representative of a non- or slowly renewed contacting solution, favouring the formation of a potentially passivating silica rich gel layer and secondary phases. Laboratory batch experiments were performed with synthetic basaltic glass altered at 90 °C, at pH 7 in a saturated 29Si-doped aqueous solution for more than 600 days. Using elemental and isotopic solution analysis and solid characterizations by SEM, TEM and ToF-SIMS, we show that basaltic glass corrodes at an unexpectedly high and constant dissolution rate of 4 × 10−3 g m−2 d−1 associated with the absence of passivating gel. Our results highlight the fact that the dissolution rate is controlled by the hydrolysis of the glassy network, sustained by the precipitation of clay-type minerals and amorphous silica. When tested in similar conditions, the International Simple Glass (ISG), a six oxide borosilicate glasses of nuclear interest displays a much lower rate limited by water diffusion through a passivating layer. The different behavior of the two glasses is explained by their ability to form secondary crystalline phases at the expense of an amorphous passivating film.

The Effect of TiO2 on the Optical and Mechanical Properties of Heavy Metal Oxide Borosilicate Glasses

The density, the molar volume, the rigidity, the UV reflectance and the glass transition temperatures of the x TiO2 – 20Na2B4O7 – 30PbO – 20SiO2 – (30-x) Bi2O3 glass system were determined. These physical parameters were acquired by using the DTA, ultrasonic and UV techniques to explore the effect of TiO2. The replacement of Bi2O3 by TiO2 decreased these physical parameters, which suggested the glass modifier role of TiO2. This attitude can be attributed to the smaller ionic radii, the density and the polarizability of TiO2 than that of Bi2O3. Moreover, according to the FTIR, TiO2 created non-bridging oxygens in the network that decreased the bond strength of the glass system. The decreases of the rigidity, the glass transition temperature and the optical band gap are sensitive to the decrease of the bond strength and the created non-bridging oxygens in the lead alkali borosilicate network. The obtained results were discussed in relation to the role of TiO2 in the lead borosilicate glass system.

Various effects of magnetite on international simple glass (ISG) dissolution: implications for the long-term durability of nuclear glasses

Understanding the effect of near-field materials, such as iron corrosion products, on the alteration of vitreous nuclear waste is essential for modeling long-term stability of these waste forms in a geological repository. This work presents experimental results for which monoliths of International Simple Glass—a six oxide borosilicate glass–, with polished and unpolished cut sides, were aged for 70 days under oxic conditions at 90 °C in a solution initially saturated in 29SiO2 at pH 7; then magnetite was added to the leaching environment. Solution and solid analyses were performed to correlate the changes in the surface features and dissolution kinetics. It was found that magnetite primarily influences the mechanically constrained surface of the non-polished sides of the monoliths, with little to no effect on the polished surfaces. This work highlights the importance of the unique chemistry within surface cracks that invokes a drastic change in alteration of glass in environments containing iron corrosion products.

Atom-Probe Tomography, TEM and ToF-SIMS study of borosilicate glass alteration rim: A multiscale approach to investigating rate-limiting mechanisms

Significant efforts have been made into understanding the dissolution of silicate glasses and minerals, but there is still debate about the formation processes and the properties of surface layers. Here, we investigate glass coupons of ISG glass – a 6 oxide borosilicate glass of nuclear interest – altered at 90°C in conditions close to saturation and for durations ranging from 1 to 875days. Altered glass coupons were characterized from atomic to macroscopic levels to better understand how surface layers become protective. With this approach, it was shown that a rough interface, whose physical characteristics have been modeled, formed in a few days and then propagated into the pristine material at a rate controlled by the reactive transport of water within the growing alteration layer. Several observations such as stiff interfacial B, Na, and Ca profiles and damped profiles within the rest of the alteration layer are not consistent with the classical inter-diffusion model, or with the interfacial dissolution-precipitation model. A new paradigm is proposed to explain these features. Inter-diffusion, a process based on water ingress into the glass and ion-exchange, may only explain the formation of the rough interface in the early stage of glass corrosion. A thin layer of altered glass is formed by this process, and as the layer grows, the accessibility of water to the reactive interface becomes rate-limiting. As a consequence, only the most easily accessible species are dissolved. The others remain undissolved in the alteration layer, probably fixed in highly hydrolysis resistant clusters. A new estimation of water diffusivity in the glass when covered by the passivating layer was determined from the shift between B and H profiles, and was 10−23m2.s−1, i.e. approximately 3 orders of magnitude lower than water diffusivity in the pristine material. Overall, in the absence of secondary crystalline phases that could consume the major components of the alteration layer (Si, Al), it is assumed that the glass dissolution rate continuously decreases due to the growth of the transport limiting alteration layer, in good agreement with residual rates reported in the literature for this glass. According to our results it can be expected that new kinetic models should emerge from an accurate time dependent budget of water within the nanoporous alteration layer.

Surface and bulk electron irradiation effects in simple and complex glasses

A three oxide sodium borosilicate (BS3) and a complex, thirty oxide borosilicate glass (SON68) were irradiated with 2.3MeV electrons to doses ranging from 0.15GGy to 4.6GGy at 350K. The irradiated glasses were characterized using Raman and NMR spectroscopies, ToF-SIMS, AFM and microhardness to understand surface and bulk irradiation effects. Glass surfaces were observed to be depleted of the alkali atoms. The depletion depth depended on the dose and glass composition, reaching 660nm and 500nm on any vacuum facing surface for BS3 and SON68 at 4.6GGy respectively. The alkali-depleted region was enriched in molecular oxygen and showed characteristics of phase separated glasses. In the bulk of the glass, Raman and NMR spectroscopies showed a silica network depolymerisation, a transformation of 4 to 3-coordinated boron and formation of non-bridging oxygen atoms on silicon and boron atoms. The hardness of the depolymerized glasses decreased by 20% (BS3) and 10% (SON68). Based on the experiments and theory, it is shown that electron stimulated desorption is the dominant surface depletion mechanism. These results show that the surfaces behave differently than the bulk of the glass. Therefore, surface related phenomena are expected to be dominant in TEM and other in-situ and ex-situ surface characterizations having depth resolution of a few hundred nanometers. Thus, sample size plays an important role in evaluating the radiation damage and one must be careful in extending the conclusions drawn from surface sensitive techniques to bulk irradiation effects in electron irradiated glasses.

The fate of silicon during glass corrosion under alkaline conditions: A mechanistic and kinetic study with the International Simple Glass

International Simple Glass – a six oxide borosilicate glass selected by the international nuclear glass community to improve the understanding of glass corrosion mechanisms and kinetics – was altered at 90°C in a solution initially saturated with respect to amorphous 29SiO2. The pH90°C, was fixed at 9 at the start of the experiment and raised to 11.5 after 209d by the addition of KOH. Isotope sensitive analytical techniques were used to analyze the solution and altered glass samples, helping to understand the driving forces and rate limiting processes controlling long-term glass alteration. At pH 9, the corrosion rate continuously drops and the glass slowly transforms into a uniform, homogeneous amorphous alteration layer. The mechanisms responsible for this transformation are water penetration through the growing alteration layer and ion exchange. We demonstrate that this amorphous alteration layer is not a precipitate resulting from the hydrolysis of the silicate network; it is mostly inherited from the glass structure from which the most weakly bonded cations (Na, Ca and B) have been released. At pH 11.5, the alteration process is very different: the high solubility of glass network formers (Si, Al, Zr) triggers the rapid and complete dissolution of the glass (dissolution becomes congruent) and precipitation of amorphous and crystalline phases. Unlike at pH 9 where glass corrosion rate decreased by 3 orders of magnitude likely due to the retroaction of the alteration layer on water dynamics/reactivity at the reaction front, the rate at pH 11.5 is maintained at a value close to the forward rate due to both the hydrolysis of the silicate network promoted by OH− and the precipitation of CSH and zeolites. This study provides key information for a unified model for glass dissolution.

Release of uranium from candidate wasteforms

AbstractLarge volumes of depleted natural and low-enriched uranium exist in the UK waste inventory. This work reports on initial investigations of the leaching performance of candidate glass and cement encapsulation matrices containing UO3 powder as well as that of uranium oxide powders. The surface areas of UO3 powder and the monolith samples of UO3 conditioned in the glass and cement matrices were very different making leaching comparisons difficult. The results showed that for both types of monolith conditioned samples a steady increase of uranium concentration in solution with time was generally not observed. The wt.% of uranium leached from UO3 conditioned in the lead borosilicate glass wasteform was approximately five orders of magnitude less than that leached from UO3 powder. Similarly, the quantities of uranium leached from UO3 conditioned in composite cement made with ordinary Portland cement, and from magnesium phosphate cement, were approximately four and three orders of magnitude, respectively, less than that leached from UO3 powder. The performance of a mixed oxide borosilicate glass wasteform was only slightly better than that of UO3 powder. This work shows that wasteforms based on encapsulation in lead borosilicate glass and cement matrices have the greatest potential for further development.

Role of aluminium oxide in the structure of heavy metal oxide borosilicate glasses

AbstractLead borosilicate and bismuth borosilicate glasses with and without aluminium oxide of varying compositions were prepared by conventional melt‐quench method. Raman spectroscopy was used to analyze the influence of Al2O3 incorporation in the heavy metal oxide borosilicate glass network. The compositions of glasses were chosen in a way that Al2O3 is added at expenses of PbO and Bi2O3 in lead borosilicate and bismuth borosilicate glasses, respectively.

The hydrolytic durability of two high-level waste oxide borosilicate glasses (GP [formula omitted] and GP [formula omitted

Two glasses containing 15 wt.% simulated high-level liquid waste (HLLW) oxides were leached several times in distilled water, Asse rock salt brine, and carnallite-containing quinary solution at normal pressure (Soxhlet: 100 °C) and at 130 bars (autoclave: 100, 150 and 200 °C). The leach rates are relatively high during the first few days, but decrease rapidly, and after 10 to 15 days approach a constant value. The leach rates increase with temperature and show only a slight difference between water and brine but a decrease in the case of quinary solution. Leaching at elevated pressure and 100 °C is less than at normal pressure and the same temperature. The crystallization of the glass products (annealing time 100 days at 750 °C) has no effect on the leach resistance as determined in Soxhlet tests.