Glass Dissolution Rate Research Articles

Compositional dependency on dissolution rate and cytocompatibility of phosphate-based glasses: Effect of B2O3 and Fe2O3 addition

The unique property of phosphate-based glasses and fibres to be completely dissolved in aqueous media is largely dependent on the glass composition. This article focuses on investigating the effect of replacing Na2O with 3 and 5 mol% Fe2O3 on cytocompatibility, thermal and dissolution properties of P2O5–CaO–Na2O–MgO–B2O3 glass system, where P2O5 content was fixed at 45 mol%. The effect of increasing Fe2O3 from 3 to 5 mol% on P2O5–CaO–Na2O–MgO glasses was also evaluated. The glass transition temperature, onset of crystallisation temperature and liquidus temperature were found to decrease with increasing Fe2O3 content and the addition of B2O3, while the thermal expansion values were found to decrease. The density of the glasses decreased with increasing Fe2O3 content. However, an increase in the density was observed by the addition of 5 mol% B2O3. The dissolution properties and mode of bulk glass and fibres were also examined which were found to decrease with increasing B2O3 and Fe2O3. However, it was found that the dissolution properties of the glasses containing both B2O3 and Fe2O3 were lower than only Fe2O3 containing glasses. The in vitro cell culture studies using human osteoblast like (MG63) cell lines revealed that the glasses containing both B2O3 and Fe2O3 maintained and showed higher cell viability as compared to the only Fe2O3 containing glasses. Glasses containing both B2O3 and Fe2O3 showed a pronounced effect on the dissolution rate of the glasses, which eventually improved the cytocompatibility properties of the glasses investigated.

Reactive Surface of Glass Particles Under Aqueous Corrosion

Glass dissolution rates are normalized to the glass surface area in contact with solution, and experiments are very often carried out using crushed and sieved materials whose size is narrowed between an upper and a lower value. Surface area of such particles could be determined by gas adsorption or geometric considerations. Although crushed particles cannot be assimilated with simple geometric shapes, rates normalized with—spheres of the same size—geometric surface area are underestimated but are close to those found for polished monoliths. Overestimation of the reactive surface when using gas adsorption measurements is discussed.

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.

Effect of low dose electron beam irradiation on the alteration layer formed during nuclear glass leaching

This investigation concerns borosilicate glass leaching mechanisms and the evolution of alteration layer under electron beam irradiation. A simple glass doped with rare earth elements was selected in order to access mechanistic and structural information and better evaluate the effects of irradiation. It was fully leached in initially pure water at 90 °C and at high glass surface area to solution volume ratio (S/V = 20 000 m−1) in static conditions. Under these conditions, the system quickly reaches the residual alteration rate regime. A small particle size fraction (2–5 μm) was sampled in order to obtain a fairly homogeneous altered material enabling the use of bulk characterization methods. External irradiations with 10 MeV electrons up to a dose of 10 MGy were performed either before or after leaching, to investigate respectively the effect of initial glass irradiation on its alteration behavior and the irradiation stability of the alteration layer. Glass dissolution rate was analyzed by regular leachate samplings and the alteration layer structure was characterized by Raman, luminescence (continuous or time-resolved), and 29Si MAS NMR and EPR spectroscopy.It was shown that the small initial glass evolutions under irradiation did not induce any modification of the leaching kinetic nor of the structure of the alteration layer. The alteration process seemed to “smooth over” the created defects. Otherwise, the alteration layer and initial glass appeared to have different behaviors under irradiation. No Eu3+ reduction was detected in the alteration layer after irradiation and the defect creation efficiency was much lower than for initial glass. This can possibly be explained by the protective role of pore water contained in the altered material (∼20%). Moreover, a slight depolymerization of the silicon network of the altered glass under irradiation with electrons was evidenced, whereas in the initial glass it typically repolymerizes.

The controversial role of inter-diffusion in glass alteration

Current kinetic models for nuclear waste glasses (e.g. GM2001, GRAAL) are based on a set of mechanisms that have been generally agreed upon within the international waste glass community. These mechanisms are: hydration and ion exchange reactions (the two processes are referred as inter-diffusion), hydrolysis of the silicate network, and condensation/precipitation of partly or completely hydrolyzed species that produces a porous and amorphous layer and crystalline phases on surface of the altered glass. Recently, a new idea with origins in the mineral dissolution community has been proposed that excludes inter-diffusion processes as a potential rate-limiting mechanism. To understand how the newly proposed interfacial dissolution/precipitation model can change the current understanding of glass corrosion, a key experiment used to account for this model was replicated to further revisit the interpretation. This experiment was performed far from saturation, at 50°C, with SON68 glass, in static mode, deionized water, and a S/V ratio of 10m−1 for 6months. Results were repeatable and showed that glass dissolution rate progressively dropped by ~1 order of magnitude compared to the forward rate, suggesting that a dense surface layer was under construction. According to previous and new solids characterizations, it is concluded that neither a simple inter-diffusion model nor the interfacial dissolution/precipitation model can account for the observed elemental profiles within the alteration layer. More generally, far-from- and close-to-saturation conditions must be distinguished. This argument is bolstered by literature where evidence shows that inter-diffusion takes place in acidic conditions and far from saturation. However, closer to saturation, when a sufficiently dense layer is formed, a new approach is proposed requiring a full description of chemical reactions taking place within the alteration layer and an accurate budget of hydrous species along the profile as it is thought that the access of a sufficient amount of water to the pristine glass is the rate-limiting process in these conditions.

Glass dissolution rate measurement and calculation revisited

Aqueous dissolution rate measurements of nuclear glasses are a key step in the long-term behavior study of such waste forms. These rates are routinely normalized to the glass surface area in contact with solution, and experiments are very often carried out using crushed materials. Various methods have been implemented to determine the surface area of such glass powders, leading to differing values, with the notion of the reactive surface area of crushed glass remaining vague. In this study, around forty initial dissolution rate measurements were conducted following static and flow rate (SPFT, MCFT) measurement protocols at 90 °C, pH 10. The international reference glass (ISG), in the forms of powders with different particle sizes and polished monoliths, and soda-lime glass beads were examined. Although crushed glass grains clearly cannot be assimilated with spheres, it is when using the samples geometric surface (Sgeo) that the rates measured on powders are closest to those found for monoliths. Overestimation of the reactive surface when using the BET model (SBET) may be due to small physical features at the atomic scale—contributing to BET surface area but not to AFM surface area. Such features are very small compared with the thickness of water ingress in glass (a few hundred nanometers) and should not be considered in rate calculations. With a SBET/Sgeo ratio of 2.5 ± 0.2 for ISG powders, it is shown here that rates measured on powders and normalized to Sgeo should be divided by 1.3 and rates normalized to SBET should be multiplied by 1.9 in order to be compared with rates measured on a monolith. The use of glass beads indicates that the geometric surface gives a good estimation of glass reactive surface if sample geometry can be precisely described. Although data clearly shows the repeatability of measurements, results must be given with a high uncertainty of approximately ±25%.

Antibiofilme effect and stem cell viability of bioactive SiO2-CaO-P2O5 gel-glass with different silica-content

Event Abstract Back to Event Antibiofilme effect and stem cell viability of bioactive SiO2−CaO−P2O5 gel-glass with different silica-content Renato Siqueira1, Natasha Maurmann2, Daniela Burguêz2, Daniela Pereira2, Alessandra Rastelli3, Oscar Peitl1, Patricia Pranke2, 4 and Edgar Zanotto1 1 Universidade Federal de São Carlos, PPG-CEM / Departamento de Engenharia de Materiais, Brazil 2 Universidade Federal do Rio Grande do Sul, Faculdade de Farmácia, Brazil 3 Universidade Estadual Paulista, Departamento de Odontologia Restauradora, Brazil 4 Instituto de Pesquisa com Células-tronco, Brazil Bioactive glass is a class of biomaterials that has the potential for application in medical and dental devices for replacement, regeneration and repair of hard and soft tissue [1, 2]. Due to some biological properties which show a strong relationship with the bioactive glass dissolution rate, ions release and pH environment, an evaluation was made in this study of the antibiofilm effect and stem cell viability of the 60%SiO2–36%CaO–4%P2O5 (A) and 80%SiO2–15%CaO–5%P2O5 (B) glass compositions (mol%). The glass was synthesized by the sol-gel method using stoichiometric amounts of tetraethoxysilane (Si(OC2H5)4), triethylphosphate (OP(OC2H5)3), and calcium nitrate tetrahydrate (Ca(NO3)2∙4H2O) under acidic conditions. Both samples were bioactive when immersed in simulated body fluid (SBF) but with different hydroxycarbonate apatite layer formation rates (more intense for glass A). Comparing the pH variation for all samples during this test, the most abrupt change occurred for glass A in the first few hours, justifying its higher antibiofilm effect against Streptococcus mutans (ATCC 25175). The lowest pH variation was observed for sample B, indicating that the solubility of this sample is lower than the other because the pH variation has a direct relationship with cation exchange from the glass with protons from the solution, such as calcium release from the sample to the media [3]. For in vitro viability testing, the mesenchymal stem cells obtained from the pulp of deciduous exfoliated teeth were cultivated with the bioactive glass at different concentrations (0 - 125 mg/mL) and cell viability was assessed by MTT assay. Glass B showed significantly higher cell viability in comparison with glass A at the concentrations of 0.125, 1.25 and 12.50 mg/mL for 2 days. These results indicate that the higher solubility of glass A favors the bioactivity and antibiofilm effect of the system but higher increases in the concentration of ions in the cell culture medium as a result of the degradation appear to inhibit cell proliferation. Therefore, by only varying the composition, it is possible to control the degradability and bioactivity levels of the glass, providing a more stable local microenvironment which is favorable for the cells. Financial support: CNPq, CAPES, FAPERGS, FAPESP (CeRTEV) and Stem Cell Research Institute

Transformation of acidic poorly water soluble drugs into ionic liquids

Poor water solubility of active pharmaceutical ingredients (API) is a major challenge in drug development impairing bioavailability and therapeutic benefit. This study is addressing the possibility to tailor pharmaceutical and physical properties of APIs by transforming these into tetrabutylphosphonium (TBP) salts, including the generation of ionic liquids (IL). Therefore, poorly water soluble acidic APIs (Diclofenac, Ibuprofen, Ketoprofen, Naproxen, Sulfadiazine, Sulfamethoxazole, and Tolbutamide) were converted into TBP ILs or low melting salts and compared to the corresponding sodium salts. Free acids and TBP salts were characterized by NMR and IR spectroscopy, DSC and XRPD, DVS and dissolution rate measurements, release profiles, and saturation concentration measurements. TBP salts had lower melting points and glass transition temperatures and dissolution rates were improved up to a factor of 1000 as compared to the corresponding free acid. An increase in dissolution rates was at the expense of increased hygroscopicity. In conclusion, the creation of TBP ionic liquids or solid salts from APIs is a valuable concept addressing dissolution and solubility challenges of poorly water soluble acidic compounds. The data suggested that tailor-made counterions may substantially expand the formulation scientist’s armamentarium to meet challenges of poorly water soluble drugs.

Dissolution rate of borosilicate glass SON68: A method of quantification based upon interferometry and implications for experimental and natural weathering rates of glass

Rates of glass dissolution from laboratory and field studies are often considered to be irreconcilable, although potential causes for the difference, such as solution saturation state and increasing surface area from progressive weathering, have not been explored in depth. The dissolution rate of SON68 glass, the non-radioactive analog of the French R7T7 composition, was determined in a single-pass flow-through (SPFT) system at 90°C and pH 9 over a silica-saturation interval. Dissolution rates were determined on both powdered and monolithic specimens by assaying the concentration of elements released from glass to effluent solution. In addition, rates of 12 monolithic specimens were quantified using a Vertical Scanning Interferometry (VSI) method. The method entails measuring the difference in height between a reference and reaction surface. The height difference is proportional to the dissolution rate. By adjusting the relative position of the reacted surface to average surface roughness, the effects of surface area on the dissolution rate can be minimized. Values of the dissolution rate, based upon chemical assay of the effluent solution on the one hand, and VSI methods on the other, were compared. In general, rates determined by the two methods are within a factor of 2×. The difference in rates may be due to the presence of a reaction layer that develops on the glass surface, resulting in an underestimation of the height difference measurement. The dissolution rates of SON68 glass in silica-saturated solutions were then compared to rates previously determined on basalt glass in natural weathering environments (Gordon and Brady, 2002, Chem. Geol. 190, 113–122). When adjusted for differences in temperature and pH, the ranges of borosilicate and basalt glass dissolution rates overlap, indicating that laboratory and field rates can be reconciled and that the principal control on glass dissolution is solution saturation with respect to amorphous silica.

Enhanced dissolution of basaltic glass in brackish waters: Impact on biogeochemical cycles

In order to better constrain the geochemical budget of Si in the ocean, and potentially other elements released by the dissolution of silicates, the alteration of riverine particulate material in estuaries and seawater needs to be estimated. For this, a series of alteration experiments of basaltic glass were performed at various degrees of salinity (from 0 to 3.5 g L−1) in far-from-equilibrium conditions. The solution used is a filtered natural seawater standard from the Atlantic Ocean. The forward dissolution rates increase from 2.1⋅10−7 molSim−2s−1 (S=0 gL−1) to 7.7⋅10−7 molSim−2s−1 (S=3.5 gL−1) at 90 °C and were extrapolated at 16 °C (from 2.9⋅10−10 molSim−2s−1 at S=0 gL−1 to 1.1⋅10−9 molSim−2s−1 at S=3.5 gL−1). This positive relationship between glass dissolution rate and salinity degree is consistent with published investigations concerning the role of specific cations and ligands present in seawater, which can promote dissolution at the glass surface. These results illustrate the potential of river basaltic glass particles to dissolve quickly in the water column after entering into the brackish waters of estuaries, and before sinking on continental margins. Based on these dissolution rates and on assumptions on the particulate solid flux of fresh basaltic glass exported by rivers towards the ocean, the corresponding flux of dissolved Si is estimated to range between 2 and 8⋅1012 molSiyr−1. This is of the same order of magnitude as the estimated river dissolved Si flux, which represents therefore a significant input of Si into the ocean. Additionally, if the glass dissolution process remains congruent during the residence time of suspended particles into the water column, the K flux to the ocean could also be significantly affected.

A unified in vitro evaluation for apatite-forming ability of bioactive glasses and their variants

The aim of this study was to propose and validate a new unified method for testing dissolution rates of bioactive glasses and their variants, and the formation of calcium phosphate layer formation on their surface, which is an indicator of bioactivity. At present, comparison in the literature is difficult as many groups use different testing protocols. An ISO standard covers the use of simulated body fluid on standard shape materials but it does not take into account that bioactive glasses can have very different specific surface areas, as for glass powders. Validation of the proposed modified test was through round robin testing and comparison to the ISO standard where appropriate. The proposed test uses fixed mass per solution volume ratio and agitated solution. The round robin study showed differences in hydroxyapatite nucleation on glasses of different composition and between glasses of the same composition but different particle size. The results were reproducible between research facilities. Researchers should use this method when testing new glasses, or their variants, to enable comparison between the literature in the future.

Effect of Callovo-Oxfordian clay rock on the dissolution rate of the SON68 simulated nuclear waste glass

Long-term storage of high-level nuclear waste glass in France is expected to occur in an engineered barrier system (EBS) located in a subsurface Callovo-Oxfordian (COx) clay rock formation in the Paris Basin in northeastern France. Understanding the behavior of glass dissolution in the complex system is critical to be able to reliably model the performance of the glass in this complex environment. To simulate this multi-barrier repository scenario in the laboratory, several tests have been performed to measure glass dissolution rates of the simulated high-level nuclear waste glass, SON68, in the presence of COx claystone at 90°C. Experiments utilized a High-Performance Liquid Chromatography (HPLC) pump to pass simulated Bure site COx pore water through a reaction cell containing SON68 placed between two COx claystone cores for durations up to 200days. Silicon concentrations at the outlet were similar in all experiments, even the blank experiment with only the COx claystone (∼4mg/L at 25°C and ∼15mg/L at 90°C). The steady-state pH of the effluent, measured at room temperature, was roughly 7.1 for the blank and 7.3–7.6 for the glass-containing experiments demonstrating the pH buffering capacity of the COx claystone. Dissolution rates for SON68 in the presence of the claystone were elevated compared to those obtained from flow-through experiments conducted with SON68 without claystone in silica-saturated solutions at the same temperature and similar pH values. Additionally, through surface examination of the monoliths, the side of the monolith in direct contact with the claystone was seen to have a corrosion thickness 2.5× greater than the side in contact with the bulk glass powder. Results from one experiment containing 32Si-doped SON68 also suggest that the movement of Si through the claystone is controlled by a chemically coupled transport with a Si retention factor, Kd, of 900mL/g.

Glass Degradation in Performance Assessment Models1

ABSTRACTThe interface with reactive transport models used in performance assessment calculations is described to identify aspects of the glass waste form degradation model important to long-term predictions. These are primarily the conditions that trigger the change from the residual rate to the Stage 3 rate and the values of those rates. Although the processes triggering the change and controlling the Stage 3 rate are not yet understood mechanistically, neither appears related to an intrinsic property of the glass. The sudden and usually significant increase in the glass dissolution rate suggests the processes that trigger the increase are different than the processes controlling glass dissolution prior to that change. Application of a simple expression that was derived for mineral transformation to represent the kinetics of coupled glass dissolution and secondary phase precipitation reactions is shown to be consistent with experimental observations of Stage 3 and useful for modeling long-term glass dissolution in a complex disposal environment.

Uncertainty in the Surface Area of Crushed Glass in Rate Calculations

ABSTRACTSeries of 7-day Product Consistency Tests (PCTs) were conducted with ARM-1 glass using the -100+200 mesh size fraction and several sub-fractions to measure the sensitivity of the test response to the distribution of particle sizes. Separate samples were prepared for testing by dry sieving and wet sieving, and the particle size distributions and PCT responses were measured for each fraction. Triplicate tests were conducted at 90 °C using a water/glass mass ratio of 10.0 with each size fraction. Test results are evaluated regarding the sensitivity of the test response to the particle size distributions and, conversely, the uncertainty due to calculating the surface areas (and dissolution rates) by modeling the particles as spheres. These analyses show the solution feedback effects of dissolved glass constituents (i.e., the reaction affinity) counteract the effects of the glass surface areas provided by different particle size distributions on the test response. The opposing effects of the surface area on the amount of glass dissolved and on the glass dissolution rate moderate the sensitivity of the PCT response to the particle size distribution.

Structure and properties of hafnium iron borophosphate glass-ceramics

Effects of hafnium addition on the structure and properties of iron borophosphate glasses with nominal composition of xHfO2–yB2O3–[40–(x+y)]Fe2O3–60P2O5 (x=0–8, mol%) and xHfO2–yB2O3–[40–(x+y)][40Fe2O3–60P2O5] (x=2–6, mol%) have been investigated by XRD, DTA, IR, SEM and Mössbauer spectroscopy. There were some surface crystallizations on some of the samples containing high amounts of Hf and B. XRD spectra revealed that HfP2O7 crystallized in the glass matrix when HfO2 content was above 2mol% even when there was no surface crystallization and samples looked glassy. SEM-EDAX image-analyses supported the formation of the HfP2O7 phase. Dissolution rates of Hf-containing iron borophosphate glasses were in the 10−9–10−10g/cm2min range which shows that the existence of the crystalline HfP2O7 phase in the glass matrix has not degraded the aqueous chemical durability of these glasses. The band observed at ~984cm−1 in the IR spectra of Hf containing samples was attributed to the Hf–O–P bonds in HfP2O7. Iron existed in two valence states, i.e. Fe2+ and Fe3+ and Mössbauer hyperfine parameters indicated that both ions have octahedral coordinations in the samples studied.

Nuclear waste disposal: I. Laboratory simulation of repository properties

After more than 30years of research and development, there is a broad technical consensus that geologic disposal will provide for the safety of humankind, now and far into the future. Safety analyses have demonstrated that the risk, measured as the exposure to radiation, will be of little consequence. Still, there is not yet an operating geologic repository for highly radioactive waste, and there remains substantial public concern about the long-term safety of geologic disposal. In the two linked papers we argue for a stronger connection between the scientific data (this paper I) and the safety analysis, particularly in the context of societal expectations (paper II). In the present paper I, we use new experimental data on the properties of clay formations simulating geological disposal conditions to illustrate how one can understand the ability of clay to isolate radionuclides. The data include percolation tests on various intact clay–rock cores with different calcite contents. For the first time, hydrodynamic parameters (anion and cation accessible porosities, permeability, dispersion and diffusion coefficients), as well as retention parameters (sorption behavior of iodine, cesium) and materials interaction parameters (glass dissolution rates, etc.) have been obtained for a series of clay–rock samples of varying mineralogy. Increased calcite content leads to lower permeability and porosity, but the difference between anion and cation accessible porosity diminished. The data confirm very slow radionuclide migration, and a direct extrapolation to repository geometry yields isolation times, for a 70m clay–rock formation, of many hundreds of thousands of years, even for the most mobile radionuclides such as iodine-129 and chlorine 36 and complete retention for the more radiotoxic, less mobile radionuclides such as the actinides or cesium-137.In order to assess the meaning of the technical results and derived models for long-term safety, paper II addresses model validity and credibility not only from a technical perspective, but in a much broader historical, epistemological and societal context. Safety analysis is treated in its social and temporal dimensions. This approach provides new insights into the societal dimension of scenarios and risk, and it shows that there is certainly no direct link between increased scientific understanding and a public position for or against different strategies of nuclear waste disposal.

Effects of alteration product precipitation on glass dissolution

Understanding the mechanisms that control the durability of nuclear waste glass is paramount if reliable models are to be constructed so that the glass dissolution rate in a given geological repository can be calculated. Presently, it is agreed that (boro)silicate glasses dissolve in water at a rate dependent on the solution concentration of orthosilicic acid (H4SiO4) with higher [H4SiO4] leading to lower dissolution rates. Once the reaction has slowed as a result of the buildup of H4SiO4, another increase in the rate has been observed that corresponds to the precipitation of certain silica-bearing alteration products. However, it has also been observed that the concentration of silica-bearing solution species does not significantly decrease, indicating saturation, while other glass tracer elements concentrations continue to increase, indicating that the glass is still dissolving. In this study, we have used the Geochemist’s Workbench code to investigate the relationship between glass dissolution rates and the precipitation rate of a representative zeolitic silica-bearing alteration product, analcime [Na(AlSi2O6)⋅H2O]. To simplify the calculations, we suppressed all alteration products except analcime, gibbsite (Al(OH)3), and amorphous silica. The pseudo-equilibrium-constant matrix for amorphous silica was substituted for the glass pseudo-equilibrium-constant matrix because it has been shown that silicate glasses act as a silica-only solid with respect to kinetic considerations. In this article, we present the results of our calculations of the glass dissolution rate at different values for the analcime precipitation rate constant and the effects of varying the glass dissolution rate constant at a constant analcime precipitation rate constant. From the simulations we conclude, firstly, that the rate of glass dissolution is dependent on the kinetics of formation of the zeolitic phase. Therefore, the kinetics of secondary phase formation is an important parameter that should be taken into account in future glass dissolution modeling efforts. Secondly, the results indicate that, in the absence of a gel layer, the glass dissolution rate controls the rate of analcime precipitation in the long term. The meaning of these results pertinent to long-term glass durability is discussed.

The Effect of Composition on Short- and Long-term Durability of UK HLW Glass

An understanding of the aqueous durability of glass is essential for determining the dissolution and release of radionuclides from vitrified nuclear waste in a geological disposal facility over short and long timescales. There are many factors that determine the rate of glass dissolution in aqueous solution, and environmental factors such as temperature and pH will be significant. However, in terms of glass properties, the composition has the biggest influence on aqueous durability.The majority of High Level Waste (HLW) worldwide has been immobilised using borosilicate glass, although within this family there are significant compositional variations between different countries depending on the composition of the waste being vitrified. For example, the French R7T7 HLW glass contains calcium, while the Magnox waste glass produced in the UK contains significant quantities of magnesium, which results in different dissolution behavior.This paper summarizes the main compositional variations in UK vitrified HLW and identifies the key similarities and differences in composition that affect short- and long-term glass durability in aqueous solution. The effect of a number of key elements is discussed along with the current state of the art understanding of how they impact on the glass dissolution mechanisms.

Micro-channel as a New Tool to Investigate Glass Dissolution Kinetics

A reliable modeling of the long-term dissolution of HLW glass requires sufficient evaluation of the glass dissolution kinetics including a sound understandings of reaction mechanism. For the evaluation of glass dissolution kinetics, we need much more data on the glass dissolution rate measured precisely, consistently and systematically under various well-constrained test conditions. The current standard test methods, unfortunately, cannot provide enough data for the kinetic evaluation. Therefore, we should improve or develop the test methods to provide precise and consitent data for the kinetic evaluation. In the present paper, therefore, major standard test methods currently applied to the measurement of glass dissolution are summarized with their advantages and disadvantages, and some newly developed test methods are introduced. In addition, problems to be solved are discussed to advance the kinetic evaluation.

Influence of SrO substitution for CaO on the properties of bioactive glass S53P4

Commercial melt-quenched bioactive glasses consist of the oxides of silicon, phosphorus, calcium and sodium. Doping of the glasses with oxides of some other elements is known to affect their capability to support hydroxyapatite formation and thus bone tissue healing but also to modify their high temperature processing parameters. In the present study, the influence of gradual substitution of SrO for CaO on the properties of the bioactive glass S53P4 was studied. Thermal analysis and hot stage microscopy were utilized to measure the thermal properties of the glasses. The in vitro bioactivity and solubility was measured by immersing the glasses in simulated body fluid for 6h to 1week. The formation of silica rich and hydroxyapatite layers was assessed from FTIR spectra analysis and SEM images of the glass surface. Increasing substitution of SrO for CaO decreased all characteristic temperatures and led to a slightly stronger glass network. The initial glass dissolution rate increased with SrO content. Hydroxyapatite layer was formed on all glasses but on the SrO containing glasses the layer was thinner and contained also strontium. The results suggest that substituting SrO for CaO in S53P4 glass retards the bioactivity. However, substitution greater than 10mol% allow for precipitation of a strontium substituted hydroxyapatite layer.