Dissolution Of Glass Matrix Research Articles

Do Different Application Modes Improve the Bonding Performance of Self-etching Ceramic Primer to Lithium Disilicate and Feldspathic Ceramics?

To evaluate the effect of different application modes of a recently introduced self-etching ceramic primer on the microshear bond strength (μSBS) and ceramic surface-etching pattern of two glass-ceramic surfaces. Twenty-two CAD/CAM blocks of lithium disilicate (LD) and feldspathic glass ceramic (VTR) were each cut into 4 rectangular sections (n = 88 for ceramic surface). The LD and VTR specimens were divided into one control group (hydrofluoric acid + silane coupling agent [HF+SII]), and 10 experimental groups using Monobond Etch and Prime (MEP) applied for a combination of scrubbing times (5, 10, 20, 40, and 60 s) and reaction times (20 or 40 s). After each treatment, Tygon matrices (n = 8) were filled with a resin cement and light cured for each ceramic specimen. The specimens were stored in water at 37°C for 24 h and subjected to the μSBS test. The failure pattern and μSBS were statistically evaluated (α = 0.05). In addition, the ceramic surface etching pattern was analyzed using scanning electron microscopy. For the LD groups, the application of MEP 60/40 resulted in a higher mean μSBS compared to HF+SI (p < 0.05). Groups 5/40, 10/40, and 20/40 resulted in mean μSBS similar to that obtained by HF+SI (p > 0.05). For VTR, no significant difference was observed among the groups (p = 0.32). Compared with MEP, HF better promoted the dissolution of glass matrix for both ceramics. However, prolonged MEP scrubbing or reaction caused significant dissolution of the glass matrix for both evaluated ceramics. Active and prolonged application of MEP may be a viable alternative to HF+SI for increasing the bond strength to LD.

Development of performance assessment models for glass dissolution

ABSTRACTNUMO and JAEA have been conducting a joint research since FY2011, which is aimed to enhance the methodology of repository design and performance assessment in preliminary investigation stage for the deep geological disposal of high-level radioactive waste. As a part of this joint research, we have been developing glass dissolution models which include various processes derived from glass-overpack-bentonite buffer interaction, considering the precipitation of Fe-silicates associated with steel overpack corrosion, and Si transport through altered layer of glass. The objective of this modeling work is to show comprehensively the lifetime of the vitrified waste due to glass matrix dissolution timescales through sensitivity analysis, and to identify the feature/process that most strongly influences the lifetime, and to identify future R&amp;D issues that would help to improve the nuclide transport analysis with confidential value and the safety case in future. The sensitivity analysis suggested that the duration of the glass dissolution might be predicted in the ranges from 3.8×103 to 1.9×105 years. Also, the results indicated that the precipitation of Fe–silicate has the strongest influence on the long-team behavior of vitrified waste.

Key Phenomena Governing HLW Glass Behavior in the French Deep Geological Disposal

ABSTRACTAccording to the Planning Act of 28th June 2006, Andra is in charge of ensuring the sustainable management of all radioactive waste generated in France, especially the high-level and long-lived vitrified waste produced from spent fuel recycling.Since 2006, all the studies and research related to the components of HLW cells have been incorporated into a broader R&amp;D program which aims at characterizing and modeling (i) the glass matrix dissolution, (ii) the corrosion of the overpack and the lining, and (iii) the claystone evolution in the near field, considering all the interactions between these surrounding materials. This program, coordinated by Andra, has involved up to eighteen laboratories.After closure of disposal cells and overpack failure, glass alteration is expected to begin in partially saturated conditions due to hydrogen production resulting from carbon steel corrosion in anoxic conditions. Therefore, the glass should at least partially be hydrated by water vapor during thousands of years until complete saturation. A part of the studies aimed to determine the glass behavior in such conditions, the influence of the main parameters (temperature, relative humidity) and consequences of vapor hydration on subsequent radionuclides release by water leaching.In addition, the major part of the work focused on the influence of the environment on glass alteration. The effect of clay pore water on glass alteration rates (initial rate, rate drop and residual rate) was determined and particularly that of pH and magnesium. The nature of steel corrosion products and their interactions with glass alteration were also investigated. All these studies relied on experiments in surface laboratories, in Andra’s underground laboratory, together with natural or archeological analogs and modeling studies.

ICONE23-1463 IDENTIFYING RESEARCH ISSUES ON DISSOLUTION BEHAVIOR OF RADIONUCLIDES FROM THE VITRIFIED HIGH-LEVEL RADIOACTIVE WASTE IN JAPAN

The vitrified high-level radioactive waste from reprocessing spent fuels is planned to be disposed of within a stable geological environment at least 300m below ground surface. The evaluation of the individual dose rate caused by the waste to the biosphere is the primary issue for evaluating the safety of geological disposal. The radionuclide dissolution behavior from the vitrified waste is an especially critical processes for calculating the dose rate. The dissolution model proposed by Japan Nuclear Fuel Cycle (JNC, now JAEA) in the second progress report (H12 report)(JNC, 1999) has been used in Japan. However, various dissolution models have been proposed by researchers and implementers since the H12 report. This paper presents the recent progress of the glass matrix dissolution research and identifies four issues of the dissolution behavior of radionuclides. The four issues are as follows: A) "Identification of alteration rate acceleration mechanism and conditions", B) "Investigation into the protective nature of glass alteration layers", C) "Model development for potential disposal environments", and D) "Investigation into the effective surface area".

Functionalization of Sol Gel Bioactive Glasses Carrying Au Nanoparticles: Selective Au Affinity for Amino and Thiol Ligand Groups

It is demonstrated here that bioactive glasses containing Au nanoparticles (AuNPs) can be selectively functionalized with small molecules carrying either amino or thiol groups by simply varying the temperature and pH of the functionalization batch. The results evidence the following. (i) At room temperature (RT), no functionalization of Au-free glass occurs, whereas in the case of glasses containing AuNPs, stable linkages form only with amino groups, as in this condition Au does not bind with either thiol or hydroxyl groups. The RT functionalization with cysteine and cystine confirms the preferential functionalization through the amino groups, while the -SH groups are oxidized to S-S bridges. (ii) The functionalization with cysteine and cystine, compared at pH = 5, 9, and 12, is shown not to take place at pH = 5 and to be hindered by the glass matrix dissolution at pH = 12 (with consequent release of AuNPs), while the best results are obtained at pH = 9. (iii) For the effect of reaction temperature, at 4 °C it is possible to obtain a strong Au-S interaction, whereas at RT, a weak Au-N linkage is formed. These results should allow production, in a selective way, of different bonds exhibiting different strengths and, consequently, different release times in solution, with a wide range of possible applications (for instance, weak Au-N bonds in the case of drug delivery, strong Au-S bonds in protein immobilization).

Impact of Silicon Migration Through Buffer Material on the Lifetime of Vitrified Waste

AbstractA sensitivity analysis was conducted to evaluate the impact of silicon migration through buffer material on the lifetime of vitrified waste. The results indicate that the lifetime depends on a combination of the dissolved glass fraction in the non-steady-state phase controlled by the silicon pore diffusion coefficient (Dp) and the silicon distribution coefficient (Kd) in the buffer material and the steady-state dissolution rate defined by Dp and the groundwater flow rate (Q) in the excavation disturbed zone. In the case where the glass dissolution rate reaches the steady-state dissolution rate, the sensitivity of the lifetime to Dp and Q varies according to the magnitude relationship between Dp and Q. We also discuss the impact on the lifetime of glass hydration, which proceeds simultaneously with glass matrix dissolution. The results show that glass hydration is less important for the lifetime than glass matrix dissolution in an open system and it can be concluded that silicon migration through the buffer material will be an important process for estimating the lifetime of the vitrified waste. A preliminary calculation of the long-term waste behavior with realistic assumptions indicates the importance of the silicon migration parameters Kd and Dp, which control the dissolution behavior of the vitrified waste in the non-steady-state phase, for evaluating radionuclide release.

AFM and SEM study of the effects of etching on IPS-Empress 2 TM dental ceramic

The aim of this study was to investigate the effects of increasing etching time on the surface of the new dental material, IPS-Empress 2 TM glass ceramic. Twenty one IPS-Empress 2 TM glass ceramic samples were made from IPS-Empress 2 TM ingots through lost-wax, hot-pressed ceramic fabrication technology. All samples were highly polished and cleaned ultrasonically for 5 min in acetone before and after etching with 9.6% hydrofluoric acid gel. The etching times were 0, 10, 20, 30, 60, 90 and 120 s respectively. Microstructure was analysed by scanning electron microscopy (SEM) and atomic force microscopy (AFM) was used to evaluate the surface roughness and topography. Observations with SEM showed that etching with hydrofluoric acid resulted in preferential dissolution of glass matrix, and that partially supported crystals within the glass matrix were lost with increasing etching time. AFM measurements indicated that etching increased the surface roughness of the glass-ceramic. A simple least-squares linear regression was used to establish a relationship between surface roughness parameters ( R a, RMS), and etching time, for which r 2>0.94. This study demonstrates the benefits of combining two microscopic methods for a better understanding of the surface. SEM showed the mode of action of hydrofluoric acid on the ceramic and AFM provided valuable data regarding the extent of surface degradation relative to etching time.

A natural analogue of nuclear waste glass in compacted bentonite

A marine based argillaceous rock containing volcanic glass shards has been investigated to infer the long-term durability of vitrified nuclear waste in compacted bentonite, which is a candidate for buffer material constituting the engineered barrier system for nuclear waste disposal. Fission track ages indicate that the volcanic glass shards, andesitic scoria, have been buried in the argillaceous rock for about 1 Ma. Neither glass matrix dissolution nor precipitation on the surface was seen under an optical microscope. Little leaching of any element has been recognized by analyses using an electron microprobe analyzer. Secondary ion mass spectrometry analysis, however, indicates significant hydration which may dominantly be a permeation of molecular water. As an indicator of durability of glass against groundwater a normalized mass loss of Si (NL Si) has been evaluated for the volcanic glass based on free energy for hydration. The difference between estimated NL Si of the volcanic glass and that of a simulated waste glass is within one order so that the volcanic glass may be analogous to a waste glass with respect to durability to water. The argillaceous rock is analogous to the compacted bentonite with respect to physical properties such as dry-density, unconfined compression strength, porosity, and hydraulic conductivity. The ambient physical and chemical conditions surrounding the volcanic glass have been also investigated: temperature was in the range from 4 to 30°C due to the burial history of the volcanic glass. Over most of the past 1 Ma the volcanic glass has been in contact with groundwater originating from seawater. Thermodynamic calculations indicate (1) pH (=7.74–7.94) of the groundwater has mainly been controlled by dissolution of carbonate minerals, (2) the redox potential (Eh=−34–−73 mV) of the groundwater has dominantly been controlled by decomposition of organic materials to produce CH 4(g), and (3) activity of aqueous silica of the groundwater was in equilibrium with SiO 2 amorphous. Because of the equilibrium between aqueous silica and SiO 2 amorphous, the volcanic glass did not dissolve during the burial. Vitrified nuclear waste sealed in compacted bentonite, therefore, will not dissolve significantly if buried in an environment as mentioned above.

Water–rock interaction and hydrothermal mineral equilibria in the Tendaho geothermal system

The Tendaho geothermal system occurs within a NW–SE-trending rift basin filled with Quaternary volcanics (mainly basalts) and fluvio-lacustrine sediments. Three deep (TD-1, TD-2 and TD-3) and one shallow (TD-4) geothermal wells have been drilled. The waters of productive wells TD-1, TD-2 and TD-4 are typical Na–Cl geothermal waters with reservoir temperature ranging between 220 and 270°C. Chemical analysis of core samples (altered basalts) shows increased Ca, Fe, Mg, Al content (owing to the dissolution of plagioclase and femics and the precipitation of wairakite, laumontite, epidote, garnet, calcite and clay minerals) and decreased Na, K, Si and Ti (owing mostly to the dissolution of glass matrix). Petrographic study of cuttings and core samples shows: (1) evidence of an early stage of calcite, zeolite (wairakite or laumontite) and quartz crystallization, while calcite underwent different stages of dissolution/precipitation, possibly due to abrupt changes in pH and CO 2 partial pressure; (2) that epidote, garnet, prehnite, pyroxene and amphibole crystallization occurred after wairakite or laumontite. Chlorite is the main layered silicate in the basaltic rocks in wells TD-1 and TD-2, temperatures beyond the stability of smectite and chlorite/smectite (C/S) interlayers must have been reached. The smectites and C/S interlayers in association with chlorite in well TD-3 indicate that this well has had a more complex thermal history, with variable temperatures. The smectites occur at temperatures above 120°C, which is considered to be the threshold for the transformation of smectite to illite. No evidence of disequilibrium conditions of smectites has been found at reservoir temperatures currently present at Tendaho. Fluid inclusion data indicate heating in the well TD-1, and thermal conditions similar to the ones measured in the deepest part of well TD-2, while the uppermost part of this latter has undergone cooling. Intense cooling has affected well TD-3, drilled far from the upflow zone of the field, probably in an area characterized by self-sealing, cooling and very low permeability.

Kinetics of glass corrosion in acid solutions

AbstractThe interaction of simulated nuclear waste borosilicate glass with acid solutions (pH = 2, pH = 4) was studied under static conditions (i.e. without refreshment of corroding solution) at 30, 60 and 90°C. Tests with stirred and unstirred solution were compared. The rate of glass dissolution (given by the rate of SiO2 transfer into the solution) and the rate of glass leaching (represented by the rate of sodium transfer into the solution) were significantly higher at lower pH and in stirred solution. The first phenomenon can be explained by the more extensive opening of glass structure at lower pH. The second phenomenon can be caused by the creation of thin solution layer adjacent to the glass surface in the case of unstirred corroding media. The SiO2 and sodium concentration in this layer are then higher in comparison to the bulk solution. Due to this fact the driving force of glass matrix dissolution and sodium leaching are lower than in the case of stirred solution. The temperature dependencies of the initial rate of glass matrix dissolution and of the sodium diffusion coefficient can be described using equations of Arrhenius' type.

Corrosion behavior of a powdered simulated nuclear waste glass: A corrosion model including diffusion process

Static corrosion tests were performed with a powdered simulated waste glass in deionized water at 90°C for periods of up to 130 days. It was observed that normalized elemental mass loss (NL) values for soluble elements (Li, B, Na and Mo) were larger than those for Si by a factor of three and continued to increase after saturation of Si. A corrosion model (diffusion-combined model), where a diffusion model is combined with a dissolution/precipitation model (reaction path model), was developed and applied to the analysis of experimental results. In the diffusion-combined model, it is assumed that less-soluble elements dissolve into the solution congruently with the silica glass matrix (glass matrix dissolution). On the other hand, it is assumed that soluble elements diffuse through the glass to the surface and dissolve into the solution, in addition to the glass matrix dissolution. The diffusion-combined model can explain the experimental results well, and it is found that the diffusion coefficient is the most effective parameter determining the corrosion behavior.

Remaining Uncertainties in Predicting Long-Term Performance of Nuclear Waste Glass From Experiments

ABSTRACTThe current knowledge on the glass dissolution mechanism and the representation of glass dissolution concepts within overall repository performance assessment models are briefly summarized and uncertainties related to mechanism, radionuclide chemistry and parameters are discussed. Understanding of the major glass dissolution processes has been significantly increased in recent years. Long-term glass stability is related to the long-term maintenance of silica saturated conditions. The behavior of individual radionuclides in the presence of a dissolving glass has not been sufficiently and results do not yet allow meaningful predictions. Conservative long-term predictions of glass matrix dissolution as upper limit for radionuclide release can be made with sufficient confidence, however these estimations generally result in a situation were the barrier function of the glass is masked by the efficiency of the geologic barrier. Realistic long-term predictions may show that the borosilicate waste glass contributes to overall repository safety to a much larger extent than indicated by overconservatism. Today realistic predictions remain highly uncertain and much more research work is necessary. In particular the long-term rate under silica saturated conditions needs to be understood and the behavior of individual radionuclides in the presence of a dissolving glass deserves more systematic investigations.