Chemical durability and leaching mechanisms of simulated radioactive glass waste forms for the early stage.

Structural origin of high bioactivity in zirconia containing bioactive glasses.

Abstract A detailed study of palagonitization in rocks from Deception Island—one of Antarctica's most active volcanoes—has been performed to advance our understanding of this alteration process. A detailed petrographic (optical and SEM), mineralogical (XRD), and mineral and glass spot geochemistry (EDS and EMP) characterization has been conducted on pyroclastic samples. Palagonitization occurred at 80–100°C and involved (a) initial glass to palagonite transformation by congruent glass dissolution and precipitation, followed by (b) palagonite maturation resulting in increasing crystallization into an assemblage of dominant smectite with minor illite, zeolites and Ti‐bearing oxides. During the first stage, an optically amorphous phase is formed with an estimated average density of 1.7–1.8 g/cm 3 and a very early mineralogical control on its composition indicating nucleation at the nm‐scale. Major elements are typically leached except for Ti, which behaves as immobile throughout palagonitization. Palagonite maturation occurs in an open system (variable element depletion and supply) and is controlled by an interplay between crystal nucleation and growth, overall mass balance, and local equilibration between crystals and fluid. Mass balances control palagonite porosity and density. Highly local physicochemical conditions (e.g., fluid chemistry or water‐rock ratio) play a major role in the chemical and mineralogical composition and evolution of palagonite. Variability of these controls at the microscale produces a large variability in palagonite characteristics even at the intraclast scale. Glass composition has not been observed to play a significant role. Textures observed in several samples indicate the contribution of microbial activity to glass alteration.

Rare-earth-doped chalcogenide films, as key materials for flexible optoelectronic integrated devices, have shown considerable potential in optical communications, precision metrology, and optical sensing. Herein, we address a persistent challenge in the dissolution of selenide glasses by developing an optimized ethylenediamine-based solvent system that enables exceptional solubility of As2Se3-up to 0.78 g/mL-in organic amine solvents. Leveraging this achievement, we engineered a highly uniform and reproducible spin-coating process for film fabrication. Through precise control of annealing temperature and Er3+ doping concentration, we demonstrate, for the first time, intense near-infrared (NIR) photoluminescence (PL) at 1.5 µm from Er3+-doped As2Se3 films, with optimal performance achieved at 3 mol% Er3+. Additionally, a source solution doping strategy was employed to tailor film composition, revealing the critical impact of introducing Se or As into the As2Se3 precursor solutions on the luminescence efficiency of Er3+-doped films. This work provides a robust and scalable approach for the fabrication of high-performance chalcogenide luminescent films, advancing their application in next-generation photonic devices.

Abstract This study investigates the controlled dissolution and ion release kinetics of multicomponent borate glasses within the borate anomaly, focusing on therapeutic ions such as calcium, zinc, and fluorine, which are critical in applications ranging from cancer therapy to bone regeneration and oral health. A Design of Mixtures (DoM) statistical modeling approach was employed to systematically evaluate the effects of glass composition on dissolution, ion release, and cytotoxicity. By synthesizing 23 glass formulations, the study demonstrates how statistical modeling enables precise prediction and control of material properties, revealing key interactions between components that are difficult to identify using traditional methods. Notably, higher ZnO content stabilized the glass network, reducing dissolution and ion release rates. The approach also uncovered complex synergies between zinc, titanium, and calcium, emphasizing the value of a multifactorial approach in optimizing glass performance. While higher ZnO concentrations (i.e., 16–20 mol%) correlated with increased cytotoxicity in human umbilical vein endothelial cells (HUVECs), several formulations exhibited no cytotoxic effects at a concentration of 0.2 g/mL, highlighting the need for careful compositional tuning. This research demonstrates how integrating experimental and computational methods can permit the design of glasses with tailored dissolution and ion release kinetics, enabling more effective, customizable, and personalized medical treatments.

Toward a better understanding of the mechanisms that control dissolution of calcium aluminosilicate glass

Abstract A new technique, termed the stirred‐reactor coupon analysis (SRCA) method, has been developed to measure the rate of glass dissolution in forward‐rate conditions. Monolithic glass coupons are partially masked with an inert material before placement in a large volume of well‐mixed solution with known chemistry and temperature for a predetermined duration. After the test, the mask is removed, and the difference in step height between the protected area and the exposed corroded portions of the sample coupon is measured to determine the extent of glass dissolution. The step height is converted to a rate measurement using the test duration and glass density. Test parameters such as sample surface preparation and test duration were evaluated to determine their effects on the measured rates. Additionally, results from an interlaboratory study (ILS) consisting of 12 laboratories from 11 different institutions are presented, where each laboratory performed 12 independent tests. When removing experimental outlier data, the 95% reproducibility limits for the SRCA method has no statistical difference with previously published standardized test methods used to determine the forward rate of glass dissolution. Overall, this paper describes steps necessary to perform the test method and provides the statistical calculations to evaluate test accuracy.

Digital optical and scanning electron microscopy (SEM) was used to study advance of incipient weathering of basaltic rock particles for two enhanced rock weathering (ERW) sites in Eastern Australia and three natural basalt sites (New Zealand and Eastern Australia). At the ERW sites, weathering of amended rock particles (up to 8 mm in diameter) induced a significant increase (1–1.5 pH unit) in shallow soil pH. After 14 months of incubation at the more recent site, 6–8 mm basalt particles showed dissolution of glass and olivine while pyroxene and plagioclase remained largely fresh. No secondary minerals were identified by SEM and high-quality X-ray diffraction analysis. Compared to the fresh, quarried basalt, the measured specific surface area (SSA) increased by 33%, suggesting microporosity formation via dissolution. At the >20 years ERW site, results were complex because of inconsistent application of basalt and greenschist facies ‘metabasalt’. Metamorphic rock particles showed negligible weathering while basalt particles could only be identified in the coarse (>6 mm) fraction of the shallowest (0–5 cm) soil. Within the finer particles in the deeper (5–10 cm) zone of elevated pH, potential ‘ghost’ basalt particles were identified by distribution patterns of ilmenite, suggesting near-complete basalt breakdown of mm-sized particles on decadal timescale. In variably weathered natural samples, dissolution also dominated over precipitation of secondary phases. Weathering progress in basaltic tephra deposited 150–600 years ago strongly depended on emplacement context. Tephra in free-draining >10 cm thick lapilli beds was only weakly altered, even where covered by soil, likely due to lacking connectivity of fracture networks for water access. In all studied incipiently weathered particles, we found sequential breakdown of glass and olivine before attack of pyroxene and plagioclase. Recognisable secondary mineral formation was minimal, but SSA increased over least weathered particles. The presence of interconnected glass and fracture networks apparently aids the rate of incipient weathering, increases microporosity and promotes particle disaggregation. This may permit application of relatively coarse (>5 mm) basalt for ERW but only for potential amendments where microscopic investigation and SSA have established suitable weathering fluid access networks.

Abstract The long‐term behavior of high‐level radioactive waste glass depends on the mineralogical and geochemical interactions between the various components of the multibarrier system, under geological repository conditions. The present study focuses on SON68 glass alteration in synthetic cement water and at 50°C and 70°C. While pH > 10, the glass dissolution rates were lower when contacting synthetic cement water than deionized water. This effect stems from the high Ca concentration and the presence of Si in the porewater. The initial dissolution rates at low reaction progress (3.4 ± 1.0 × 10−2 g m−2 d−1 at 50°C and 1.9 ± 0.8 × 10−2 g m−2 day−1 at 70°C) and the long‐term dissolution rates at high reaction progress (1.5 ± 0.5 × 10−5 g m−2 day−1 at 50°C and 6.7 ± 1.0 × 10−5 g m−2 day−1 at 70°C), were two times to one order of magnitude lower than the rates determined in deionized water. The cement water has a beneficial effect on glass dissolution rates which were dependent on pH, Si, and Ca concentrations.

Although models have been proposed to explain the mechanisms of bioglass (BG) dissolution and subsequent calcium phosphate (CaP) mineralization, open questions remain. The processes in which phase transition occurs in aqueous solutions and their dynamics remain underexplored partly because traditional instruments/techniques do not allow for direct observations at the adequate time and length scales at which such phase transformations occur. For instance, given the crucial role of the silica gel in CaP formation during BG dissolution, uncertainty exists about how such a silica gel forms on the BG surface. In the case of CaP formation driven by BG dissolution, questions can also be added, i.e., how CaP develops into an apatitic-like structure, how many transient phases there are, and, in general, phenomena occurring in the solid-liquid interface during BG dissolution. Several approaches were taken to study CaP mineralization driven by BG dissolution, mainly examining the solid-liquid interface and the BG after-reaction surface. This paper focuses on gaining insight into silica gel formation on the BG's surface during dissolution. Electron microscopy techniques were used, including scanning electron microscopy and focused ion beam cross sections. Other analysis techniques, such as time-of-flight secondary ion mass spectrometry, were utilized. Cross sections of reacted BG-blocks gave essential insights into the BG dissolution, particularly its strong dependency on experimental conditions, and tentative evidence has shown that soluble silica from BG dissolution may not reprecipitate/repolymerize on BG blocks' surface; thus, we wonder where it precipitates. Additionally, complementary analysis techniques determined that CaP, during BG dissolution, transitions from amorphous calcium phosphate to a calcium-deficient nanocrystalline apatitic structure with minimal contents of Si4+ and Na+ ions that may be molecularly part of CaP. The Hench model has been the core guide for BG dissolution and subsequent CaP formation for many years. However, this study shows tentative evidence that contributes to and somewhat differs from it.

Selecting appropriate buffers is crucial for evaluating the chemical durability of glass under controlled conditions such as in the EPA 1313 test designed to measure elemental release as a function of pH. The efficacy of two alkali-metal free buffers, TRIS (NH2C(CH2OH)3) and ammonium chloride—ammonia (NH3/NH4Cl), was investigated during EPA 1313 testing of a simulated Hanford low-activity waste borosilicate glass in the alkaline regime (pH 8.5–10.5) at varying temperatures (RT, 40 °C, and 60 °C). While both buffers maintained the desired pH at room temperature, and up to 40 °C, the effectiveness of TRIS decreased at elevated temperatures, particularly at pH 10.5. Although 11B NMR showed evidence of TRIS-B complexation, its effect on the rate of elemental release was found to be negligible under the test conditions. With ammonium buffer, the release of alkali cations was slightly elevated when compared to the same conditions with TRIS at early time points.

Simplified borosilicate glass powders were irradiated by 952 MeV 136Xe ions and then altered in a solution at a high S/V ratio at pH 9 and 90 °C for 33 days. Compared to the alteration of a non-irradiated sample, the irradiated sample altered 3–5 times more. Overall, both the gels had a similar structure as indicated by 29Si, 27Al, 23Na, and 17O NMR experiments. Nevertheless, according to 11B and 1H NMR experiments, differences were observed in the quantity and speciation of B retained in the gels. The results suggest that the glass alteration mechanisms responsible for passivation are not changed because of the irradiation-induced structural damages. However, the alteration kinetics, gel morphology related to porosity, and the degree of maturation are different. It seems that the gel formed on irradiated glass matures faster and retains B, which in turn influences the glass dissolution rate.

In situ γ-irradiated dissolution of the International Simple Glass (ISG) 1 & 2 and a UK high-level waste glass (post-operational-clean-out (POCO)) was investigated following a modified Product Consistency Test-B protocol for 158 d at 40 °C in ultra-high-quality water. Tests were conducted under atmospheric conditions and received a total dose of 21.6 MGy delivered at a rate of 0.137 MGy d–1. The normalised mass loss of B, Na, Ca and Mg were slightly higher in γ-irradiated tests when compared to non-irradiated tests whilst the normalised mass loss of Si was comparable or slightly lower. Boron-normalised mass losses of 0.87 ± 0.31, 0.60 ± 0.04 and 0.68 ± 0.07 g m–2 were calculated for γ-irradiated ISG-1, ISG-2 and POCO, respectively, whilst normalised mass losses in non-irradiated controls were 0.62 ± 0.01, 0.57 ± 0.01 and 0.41 ± 0.06 g m–2. The difference was tentatively attributed to acidification during irradiation.Graphical abstractIn situ γ-irradiation tests on HLW reference glasses

Boron isotope tracers of diffusion during glass dissolution

xFe2O3-(100 - x)P2O5 glasses were synthesized by melt quenching and structure-property correlation studies were carried. Glasses containing 25 to 40 mol% Fe2O3 were prepared while the sample with 50 mol% Fe2O3 formed a crystalline sample containing Fe3 2+Fe4 3+[PO4]6 3- and Fe2 2+[P2O7]4- phases on melt-quenching. Glass density increases from 2.98 to 3.20 g cm-3, ionic packing fraction is in the range of 0.63-0.65 and the glass transition temperature decreases from 500 °C to 493 °C on increasing Fe2O3 concentration from 25 to 40 mol%. Pair distribution function analysis and Reverse Monte Carlo simulations of neutron diffraction datasets were used to calculate the atomic pair distributions, interatomic distances and co-ordination environments. The P-O co-ordination is essentially tetrahedral and is in the range: 3.9-3.7 (±0.1), the Fe-O co-ordination number decreases steadily from 4.8 to 4.2 (±0.1) with an increase in Fe2O3 concentration in the phosphate network, while O-O co-ordination is in the range: 6.6-6.3(±0.1), the decrease in these co-ordination numbers are due to an increase in oxygen deficiency in the glass network with an increase in Fe2O3 mol%. Fe-O and P-O pair distributions are asymmetrical indicating short-range disorder due to the existence of a wide range of bond-lengths with maxima at 1.79 Å and in the range: 1.45-1.51 Å respectively. Mössbauer studies carried out at room temperature and 80 K found that Fe exists in 2+ and 3+ valence states, and the glass and crystalline samples contained Fe2+ at least at three different sites. Raman studies found that the meta and pyrophosphate structural units are dominant species up to 35 mol% Fe2O3 concentration, while the orthophosphate units are in majority at 40 mol% of Fe2O3. The crystalline sample is a two phase material and contained both orthophosphate and pyrophosphate units with the former being the dominant species. Leaching studies on two iron phosphate glasses carried out in purified water at 90 °C found that dissolution of glasses decreases and the chemical durability increases drastically with an increase in Fe2O3 mol%.

Bioactive glass particles have previously been found to stimulate new bone growth in vivo and have a long clinical track record. The effect of bioactive glasses on human bone marrow derived stromal cells (hBMSCs) has not been clearly ascertained previously. Recently, 3D printed scaffolds of the ICIE16 glass composition (49.46 mol% SiO2, 36.6 mol% CaO, 6.6 mol% Na2O, 6.6 mol% K2O, 1.07 mol% P2O5) were found to produce high quality bone ingrowth in vivo in a rabbit model. This composition was chosen because it can be sintered into scaffolds without crystallisation. Here, we cultured hBMSCs on the 3D printed ICIE16 scaffolds to determine whether the scaffolds can support cell growth and osteogenic differentiation in vitro, with and without the presence of osteogenic supplements. This was compared to a control of culture media containing dissolution products of the bioactive glass scaffold. Our hypothesis was that the cells cultured on the scaffolds would undergo more osteogenic differentiation than cells cultured in media containing only the dissolution ions of the scaffolds, even without osteogenic supplements. hBMSCs cultured on ICIE16 scaffolds significantly increased expression of osteogenic differentiation and matrix formation markers, including Runx 2, Col1a1, Osteopontin, Osteocalcin and Alkaline Phosphatase, in comparison to monolayer cultures in basal conditions with bioactive glass dissolution products, at all time points up to 6 weeks. Six weeks was chosen as it is the time scale for bone fracture healing. The presence of osteogenic supplements appeared to have synergetic effects with 3D scaffolds, especially during early stages of osteogenic differentiation (week 2 and 4). By week 6, there was no significant difference in the expression of osteogenic markers by hBMSCs cultured on ICE16 scaffolds with and without osteogenic supplements. These findings support our hypothesis and highlight that the 3D structure and the dissolution of ICIE16 bioactive glass ionic products both independently influence osteogenic differentiation of hBMSCs.Graphical

Bioactive glasses are one of the most promising materials for applications in bone tissue engineering. In this study, the focus was on borosilicate bioactive glasses with composition 47.12 SiO2 - 6.73 B2O3 - 21.77-x-y CaO - 22.65 Na2O - 1.72 P2O5 - x MgO - y SrO (mol%). These compositions are based on silicate S53P4 bioactive glass, from where 12.5% of SiO2 is replaced with B2O3, and additionally, part of CaO is substituted for MgO and/or SrO. The impact of ion release, both as extract and in direct contact, on human adipose-derived stem cells’ (hADSCs) viability, proliferation, ECM maturation, osteogenic commitment and endothelial marker expression was assessed. Osteogenic media supplements were utilized with the extracts, and in part of the direct cell/material culturing conditions. While it has been reported in other studies that boron release can induce cytotoxicity, the glasses in this study supported cells viability and proliferation. Moreover, borosilicate’s, especially with further Mg/Sr substitutions, upregulated several osteogenic markers (such as RUNX2a, OSTERIX, DLX5, OSTEOPONTIN), as well as angiogenic factors (e.g., vWF and PECAM-1). Furthermore, the studied glasses supported collagen-I production even in the absence of osteogenic supplements, when hADSCs were cultured in contact with the glasses, suggesting that while the bioactive glass degradation products are beneficial for osteogenesis, the glasses surface physico-chemical properties play a significant role on hADSCs differentiation. This study brings critical information on the impact of bioactive glass compositional modification to control glass dissolution and the subsequent influence on stem cells proliferation and differentiation. Furthermore, the role of the material surface chemistry on promoting cell differentiation is reported.Graphical

Aqueous dissolution rate of nuclear waste glasses as a function of aqueous Si concentration and pH

Phosphate glasses are materials that are expected to have a wide range of applications, including highly ion-conductive materials in fuel cells and biomaterials that supply therapeutic ions. Diffusion of ions in glasses plays an important role in designing glasses for these applications. The diffusion of protons is one of the most important properties of fuel cells, and the diffusion of network-modified cations such as Na+ and Ca2+ ions is closely related to glass dissolution and hydration reactions. In general, these diffusion properties are strongly dependent on the atomic-scale glass structure. We found that the difference in the morphology of PO4 tetrahedra (P-Qn : number of bridging oxygen) greatly affects the diffusion of protons and Na+ ions in phosphate glass, where these ions can diffuse much more easily near P-Q2 than near P-Q3 , and suggested that ionic conductivity and glass solubility can be designed by controlling the P-Qn distribution of phosphate glasses [1]. We also suggested that the P-Qn distribution can be controlled using 6-coordinated Si (6cSi), which is formed in phosphate glasses containing more than 40 mol% P2O5 [2]. However, the formation mechanism of 6cSi is not clear. In this study, we aim to elucidate the formation mechanism of 6cSi in phosphate glasses based on first-principles molecular dynamics (MD) simulations.The glass models for 55.0P2O5-21.3SiO2-23.7Na2O (mol%) were generated by quenching from the melt using classical MD simulations with the DL POLY [3] program. Subsequently, first-principles MD simulations using the SIESTA code [4] were performed to observe the reaction process from 4cSi to 5/6cSi. Atomic energies were calculated using orbital decomposition of the total energy by the OpenMX code [5]. For these electronic structure calculations, a localized basis with the GGA-PBE functional was used.In obtained models, atomic energies for non-bridging oxygen (NBO) are higher than those for bridging oxygen (BO). In the first-principles MD simulation, the formation of chemical reaction from "4cSi + P-Q2 " to " 5/6cSi + P-Q3 " was observed as shown in Fig. 1. The energy decreases by the change from a NBO in P-Q2 to a BO in P-Q3 is larger than the energy increase by the change for 4cSi to 5c/6cSi.It will be possible to design highly functional glasses by applying the 6cSi formation mechanism and controlling the amount of 6cSi formed.Reference:[1] K. Takada, T. Tamura, H. Maeda, and T. Kasuga, Phys. Chem. Chem. Phys. 23, 14580 (2021). [2] K. Takada, T. Tamura ,and T. Kasuga, RSC Adv. 12, 35043 (2022). [3]T. Todorov et al., J. Chem. 16, 1911 (2006). [4] J. Solar et al., J. Phys. Cond. Matt. 14, 2745 (2000). [5] T. Ozaki, Phys. Rev. B 67, 155108 (2003). Figure 1

Reactive transport model of the long-term geochemical evolution in a HLW repository in granite at the disposal cell scale: Variants, sensitivities, and model simplifications