Glass Surface Area Research Articles

Surface layers on a borosilicate nuclear waste glass corroded in MgCl 2 solution

Surface layers on the French borosilicate nuclear waste glass, R7T7, corroded in MgCl 2 solution were studied to determine the composition, structure and stability of crystalline phases. The characteristics of the phases constituting the surface layer varied with the parameter S V × t , the glass surface area ( S) to solution volume ( V) ratio, times time ( t). At low S V × t values (< 360 days/m; ≤ 36 d) th surface layer was thin and contained mainly iron hydroxide particles and hydrotalcite crystals. At an intermediate S V × t value (2800 d/m; 5.5 y) the surface layer contained hydrotalcite-, chlorite- and saponite-type phases. At the highest S V × t value (10 7 d/m; 463 d) the major phases were saponite, powellite, barite and cerianite solid solutions. About 95% of the uranium and > 98% of the neodymium released from the glass were precipitated in the surface layer. In the 463 day experiment, 86% of the neodymium in the surface layer was in solid solution with powellite, the rest with saponite. Uranium was contained exclusively in saponite. High S V ratios, typical of disposal conditions for vitrified high-level radioactive waste, favor retention of actinides in fairly insoluble corrosion products. Observation of similar corrosion products on natural glasses as on nuclear waste glasses lend support to the hypothesis that the host phases for actinides observed in the laboratory are stable over geological periods of time.

Trapping of Radioactive Inert Gas Radon on an Oxide Glass: Scintillating Glass Fiber Bundle Method

Two macroporous fiber bundle radon sensors were developed by close-packing the 50 μm fibers drawn from scintillating oxide glass in the quartz tubes. Radon (222Rn) diffuses from the source, through these sensors in parallel or in series, to the end of the linear closed system filled with air under ambient temperature and pressure of 290.15 K ∼ 307.95 K and 760 Torr, respectively. The strategy is to provide radon atoms and alphas emitted from radon and its progeny with large accessible scintillating glass surface areas for efficient trapping and detection, respectively. The variations of count rates over 115 days indicate both the significant trapping of radon on the glass surfaces as well as the dependence of this trapping process on temperature.

Recent sediment accumulation and organic carbon burial in the North Sea sediment

cent labelled 16S ribosomal RNA probes, demonstrates the presence of both Archaea and Bacteria. Compared to the fresh glass, the spherical and vermicular bodies are invariably depleted in CaO and Na2O, generally depleted in SiO2 and MgO, whereas K2O is invariably strongly enriched. Preliminary data also show enrichment in P?O5. A12O3, FeO(t) and TiO2 show either depletion or enrichment. Particularly the generally extreme enrichment of K2O (up to 5 wt.% compared to 0.01 wt.% in the fresh glass) is a property that can be attributed to active cells. The carbon isotopic composition of disseminated carbonates from a large number of samples through the core, also indicates that glass samples were affected by microbial processes, but not those which are wholly crystalline. Thus, d'C values of the trace carbonates for the glassy material and the crystalline material show ranges from -15.5 to +0.2 (average -8.8) and -8.0 to +0.7 (average -4.8), respectively. Basaltic glass, represented by glass rims on pillows, comprise a substantial volume of the upper part of the oceanic crust. Further, the surface area of glass to which seawater has access, is enormous. Bacteria living on, and at the same time processing the glass by dissolution and precipitation, may thus have an important bearing on the geochemical balance between the upper part of the oceanic lithosphere and the ocean water. We believe that microbial attack on the glass margins of pillows takes place immediately after eruption, and continues at depth as new flows bury the older one. This process is probably most active at the relatively young stage of the ocean crust, when there is sufficient heat to drive the hydrothermal system.

Hydrogenation activity of benzenes on nickel catalysts supported on porous glass prepared from borosilicate glass with small amounts of metal oxides

The surface area and micropore distribution of the porous glass prepared from borosilicate glass were controlled by the addition of metal oxides. When alumina or zirconia was added to the borosilicate glass, the micropore size distribution was very sharp and the maximum of the distribution was located at 1–2 nm. The addition of manganese oxide or antimonial oxide did not produce a sharp micropore distribution in the porous glass. When the hydrogenation of benzenes, substituted with a different number of methyl groups, was carried out over nickel catalysts supported on the porous glass prepared from the borosilicate glass with zirconia, the hydrogenation rate decreased according to the number of methyl groups and the position of the groups. These results indicate that a shape-selective nickel catalyst can be prepared from the porous glass synthesized from the borosilicate glass with a small amount of metal oxide.

Colloid Formation During the Interaction of HLW Glass with Interstitial Clay Water

ABSTRACTDuring the reaction of HLW glass with interstitial clay water at different temperatures with various ratios of glass surface area to solution volume (SA/V) and durations, Eu released from the glass forms predominantly Eu-humate colloids (organic colloids) by a complexation reaction. The size distribution and stability of Eu-humate colloids have been characterized. It is likely that inorganic colloids which are mainly composed of Si, Al and Ca are generated from the corrosion of waste glass by a nucleation reaction.

A glass dissolution model for the effects of S/V on leachate pH

The observed relationship between the ratio of the glass surface area to the volume of the leachant (S/V) and the leachate pH is discussed in terms of a simple model of the glass dissolution process. Data from leach tests on several nuclear waste glass compositions at different S/V ratios show that the leachate pH increases with time and stabilizes at a nearly constant value beyond about 28 days. This stabilized pH increases systematically with the S/V ratio of the test. The model developed here reproduces the essential features of the data and suggests that a single parameter describing the intrinsic rate of alkali diffusion and ion exchange from the glass is sufficient to represent the major glass composition dependence. Interestingly, the results are essentially independent of the rate constant for matrix dissolution. This study suggests that the diffusion-ion exchange process is central in determining the solution pH and its dependence on S/V. Under static or low-flow-rate conditions, the rate of the matrix hydrolysis reaction slows to a long-term value that is determined by the (diffusional) rate of alkali release.

Experimental Investigation of Aqueous Corrosion of R7T7 Nuclear Glass at 90°C in the Presence of Humic Acids: a Kinetic Approach

ABSTRACTThe dissolution kinetics of the French “R7T7” nonradioactive LWR reference glass in solutions containing dissolved humic acids were investigated at 90°C during static tests with imposed or free pH. Experiments conducted in highly dilute media, with a glass-surface-area-to-solution-volume (SA/V) ratio of 5 m-1, showed that the glass dissolution surface reaction is catalyzed by humic acids. With higher degrees of reaction progress (SA/V = 100 m-1 and free pH) the humic acids impose pH modifications on the system compared with inorganic media; moreover, they directly or indirectly enhance the dissolution of certain alkali metals and transition elements, forming aqueous complexes with the latter. During experiments with an imposed pH of 8.5 (SA/V = 1300 and 5300 m-1), the humic acids appear to cause increased silica solubility that cannot be accounted for by the formation of silica complexes. A residual corrosion rate in the humic acid media exceeding the rate measured in inorganic media suggests that, in addition to silica, one or more element complexes formed by humic acids may be a kinetically limiting factor. This hypothesis must be confirmed, however, as the quantity of humic acids per unit glass surface area was too small in this experiment to allow unambiguous characterization of the phenomenon.

Issues affecting the prediction of glass reactivity in an unsaturated environment

Abstract Prior to the licensing of a high-level waste repository, the US Department of Energy (DOE) will seek to initiate hot startup of the high-level waste glass processing facilities at Savannah River and West Valley. To provide confidence that issues related to glass reactivity and disposal are evaluated prior to startup, the Environmental Restoration and Waste Management branch of DOE is studying important physical parameters that will affect glass reaction in a repository environment and is developing a modeling approach to predict glass performance. In this report, results are presented comparing the reactivity of fully radioactive glass with simulated glass of the same nominal composition. While differences in elemental releases between the glass types are observed, the differences are moderated with time and can be related to the dominant reaction mechanism. Additionally, the relationship between glass surface area and the volume of leachate ( SA/V) is evaluated. The reactivity at different SA/V is dominated by solution pH and reaction affinity, with an increase in reactivity observed at long reaction times. Finally, data are presented which provide necessary parameters for the application of predictive modeling. In particular, forward reaction rate constants are presented, for a 165-frit based glass and a simple analogue, and a list of secondary phases observed during glass reaction under a variety of conditions is compiled.

Effect of alumina content on surface area and micropore distribution of porous glass prepared from borosilicate glass

The surface area and micropore distribution of porous glass prepared from borosilicate glass were controlled by the addition of alumina up to 8 wt%. The surface area increased with increased alumina content in the range from 0 to 3 wt%, but it suddenly decreased when the percent alumina exceeded 4 wt%. The mean pore diameter and micropore volume also decreased with increased alumina content. When nickel ion was supported into the porous glass, the surface area decreased to about one-half that of the original glass. Since the amount of nickel supported on the porous glass increased directly with surface area, the silanol group was considered to be uniformly distributed on the glass. La surface specifique et la distribution de micropores de verre poreux prepare avec du verre de borosilicate. ont ete contro'lees par l'ajout d'alumine jusqu'a 8% en poids. La surface specifique augmente avec la teneur en alumine dans la gamme de 0 a 3% en poids, mais diminue soudainement lorsque ce taux excede 4% en poids. Le diametre moyen des pores et le volume de micropores diminuent egalement lorsque la teneur en alumine augmente. Lorsque du nickel ionique est depose sur du verre poreux, la surface specifique diminue environ de moitie par rapport a la surface originale. Etant donne que la quantite de nickel depose sur du verre poreux augmente directement avec la surface specifique, on considere que le groupe des silanols est distribue uniformement sur le verre.

The Thickness of Parison Layer Formed in Blow Method

In forming a glass container by the blow-blow method, parison is formed in a blank mold by air blow. It is then blown in a blow mold and inflated to form a bottle. Since the final shape of a bottle is designated from the beginning, the final wall thickness of a bottle is controlled by the shape and the wall thickness of an intermediate product parison. In this way the design of parison is important, but it is difficult to study how parison is formed as glass materials to be formed are extremely hot. With this in mind, the author used silicone oil in place of high-temperature glass and measured temperature at which parison is produced and the wall thickness of parison being produced. The author also studied, from the calculation of glass flow, the relationships between variations in equal temperature distribution and temperature of parison and the wall thickness of parison. In addition, the author studied causes of bottom wall thickness and waved faults and countermeasures to be taken. The result is that we have reached the following observations: (1) The wall thickness of parison from its mouth to gob line is closely related to the flow velocity of glass material and is nearly proportionate to the parison diameter. (2) Variations in the temperature distribution of parison according to glass temperature, mold temperature and the length of time during which glass stays in a blank mold cause the flow velocity of glass material to change which in turn affects the wall thickness of parison. (3) The wall thickness of the bottom below the gob line decreases or increases depending upon the length from the gob line to the bottom of parison (the surface area of glass in contact with the mold).

Does Fully Radioactive Glass Behave Differently than Simulated Waste Glass?

ABSTRACTStatic tests at SA/V (ratio of surface area of glass to solution volume) 20,000 m−1 on SRL 200 glass compositions show that, at long test periods, the simulated nuclear waste glass (nonradioactive) leaches faster than the corresponding radioactive glass by a factor of about 40, although comparative tests, done through 560 days, at lower SA/V, 2000 m−1, indicate little difference in the leach behavior of the two types of glasses. The similarity in leach behavior between radioactive and simulated glasses at SAN of 2000 m−1 or lower is also observed for SRL 165/42 and 131/11 compositions. The accelerated glass reaction with the simulated glass 200S is associated with the formation of crystalline phases such as clinoptilolite (or potassium feldspar), and a pH excursion. The radiation field generated by the fully radioactive glass reduces the solution pH. This lower pH, in turn, may retard the onset of increased reaction rate. The radiation field generated by the radioactive glasses does not directly affect the stability of the glass surface alteration layer under those conditions where the radioactive and simulated glasses react at the same rate. These results suggest that the fully radioactive nuclear waste glass 200R may maintain a much lower leach rate than the simulated 200S, if the lower pH in the 200R leachate can be sustained. Meaningful comparison tests between radioactive and simulated nuclear waste glasses should include long-term and high SA/V tests.

Analysis of high-level waste glass performance by the physical and geochemical simulation code STRAG4

A source term release analysis code for high-level waste glass has been developed for simulation of long-term dissolution behavior under repository conditions. The STRAG4 code consists of models for (a) element diffusion in both the bulk glass and surface layer, (b) glass dissolution kinetics at the interface between glass and water, and (c) geochemical reactions of dissolved elements in underground water. The simulations for various conditions of glass dissolution, including a static and dynamic system, show accordance with the experimental observations even in the relatively complicated case where bentonite is present. Long-term dissolution analyses of a borosilicate waste glass were carried out as preliminary study. The calculations were achieved by considering detrimental effects due to interactions between the glass and surrounded materials which are presumed to be in a repository environment (i.e., compacted bentonite, corrosion products from the iron overpack, and underground water). The environmental conditions such as temperature and geochemical reactions are also taken into account in the calculations. The results suggest the life of the waste glass would be more than 50,000 years even if the glass surface area increased by a factor of 10 due to crack formation.

The Long-Term Dissolution Behaviour of the Pamela Borosilicate Glass SM527 - Application of SA/V as Accelerating Parameter

ABSTRACTThe Al2O3 rich borosilicate glass SM527 was submitted to corrosion tests with glass surface area to solution volume ratios ranging from 10 to 10000 m-1. This latter condition would correspond with a 1000 fold acceleration relative to the reference MCCI condition. Powdered glass was used to reach SANV ratios of 500 m-1 and more. The leaching solutions were either distilled water or referred to Boom clay disposal conditions. The results based on the boron concentration in solution revealed a relatively linear dependence on SA/V.t0.5 in the pure solutions, on the longer term (DW and clay water). Diffusion is suggested to be the process governing the glass dissolution, although other processes should not be excluded. In a clay / clay water mixture (slurry), long term dissolution seems to be limited by saturation. Short term data for boron are largest in the clay slurry, but with time the boron concentrations converge to similar values in the three media considered. The use of SA/V as an accelerating factor is promising, but certainly requires additional research.

Time-Dependence of Volatilization of 137Cs and 106Ru Over High-Level Waste Glass in a Canister

ABSTRACTVolatility of 137Cs and 106Ru at 600ºC over high-level waste glass in a canister is numerically analyzed. The time-dependence of normalized concentrations of each radionuclide is traced by a differential equation based on a simple model consisting of competitive forward and backward steps. It is assumed that, as time proceeds, a surface layer forms on the glass and serves as a protective barrier against volatilization. It is found that the forward rate of volatilization for 137Cs is about 140 times greater than that of 106Ru at 600ºC. The effects of the glass surface area and plenum volume on the concentration excursion inside the canister are closely estimated by the differential equation.

Sediment and the settlement of larvae of the reef coralPocillopora damicornis

The larval settlement rate of the Indo-Pacific reef coral,Pocillopora damicornis, on bare glass was compared with the rate on glass covered with measured amounts and area of fine sediment. Larval settlement in all sediment treatments was significantly less than on bare glass. Sediment cover of 95% completely prevented settlement. There was no increase in settlement when sediment cover was reduced from 90% to 50% of the glass surface area. If planulae of many coral species behave in a similar fashion in nature, sedimentation at a level that only partially covers the substrate and that is not directly harmful to adult colonies could significantly reduce larval recruitment by inhibiting settlement.

The Role of Laboratory Analog Experiments in Assessing the Performance of Waste Package Materials

ABSTRACTThere is an immediate need to begin to validate models that can be used for assessing the performance of waste package materials in an unsaturated repository environment. This paper examines available testing information and testing approaches that could support validation of models for engineering barrier system (EBS) radionuclide release. The content is presented in the context of the general methodology that has been proposed for validating performance assessment models [1], Available experimental observations are used to test some of the EBS release rate modeling premises. These observations include evidence of fluid film formation on waste glass surfaces in isothermal humid environments, accelerated waste glass reaction rates under repository service conditions of large glass surface area to water volume ratio, and mobilization of radionuclides as solutes and colloids. It is concluded that some important modeling premises may not be consistent with available experimental Information. However, it is also concluded that future laboratory testing, which simulates the Integrated waste package system (i.e., laboratory analog testing), is needed to evaluate the significance of these Inconsistencies and to test the system level models. A small-scale apparatus which was developed and tested to examine the feasibility of laboratory analog testing for the unsaturated Yucca Mountain repository environment is described.

R7T7 Nuclear Waste Glass Behavior in Moist Clay: Role of the Clay Mass/Glass Surface Area Ratio

ABSTRACTR7T7 glass alteration was investigated in the presence of various moist clays. In contact with smectite 4a, selected in France as a potential engineered barrier material, the glass was significantly corroded: after 6 months the glass corrosion rate was practically the same as the initial alteration rate in double-distilled water. Substantially lower alteration was observed in contact with bentonite 6 activated by sodium carbonate.Smectite 4a consumes silicon released by glass corrosion, and thus retards the rise to high silicon concentrations in solution at which the glass corrosion rate diminishes. Glass can therefore in some cases be altered as much in moist clay as in water with high renewal rates. Other experiments with smaller quantities of smectite 4a showed that the phenomenon becomes less important in time: its duration is proportional to the ratio between the clay mass (C) and the glass surface area (SA). Comparing the results of studies at different C/SA ratios indicates that low glass corrosion rates are obtained more slowly at higher C/SA ratios.Tests with 239Pu-doped R7T7 glass also showed that the radionuclide retention factor in the alteration film at the glass surface is only 6, compared with a factor of nearly 50 in double-distilled water.

Effects of Surface Area-to-Solution Volume Ratio on Chemical Durability of Nuclear Waste Glasses

ABSTRACTWe report data on the relationship between nuclear waste glass durability, as measured by leachate concentrations and leach rates, and the ratio of glass surface area to solution volume, S/V. The study includes West Valley non-radioactive production glasses (SF6 and SF10), West Valley glasses containing U and Th designed at CUA (WVCM47, WVCM50, and WVCM59), Savannah River SRLTDS-131 glass, and Hanford waste glass HW-39 (for which existing literature data is used). While some of these glasses show departures of leachate concentrations from simple (S/V)t scaling others conform well. The departures are, in all cases, most evident at high values of S/V. It is therefore important, therefore to understand how glass composition determines which corrosion mechanism is dominant in order to assess the region of validity of extrapolations based on (S/V)t scaling. While leach rates show a general tendency to decrease with S/V and time, exceptions are evident for the less durable glasses which show minima and maxima in the S/V-dependence at fixed time.

Influence of Calcium Ion on Initial Alkali Corrosion Process of Zirconia Containing Glass

The influence of calcium ion on the initial alkali corrosion process of zirconia containing glass was investigated. Alkali-resistant glass fiber which contains about 15wt% zirconia was immersed in an alkali solution of pH 12.6 containing calcium ion ranging from 0 to 0.74mg/ml at 65°C. The amounts of Si dissolved, depth profiles of atomic ratios at near surface region by XPS analysis and morphology of glass surface by SEM varied with calcium ion concentration, immersion time and acid treatment. These changes showed that reaction process in the low calcium ion concentration region was different from that in the high concentration region. In the low concentration region, Si was dissolved and Zr-rich surface region was formed as in the case of NaOH immersion; however, surface reaction layer was formed by deposited Ca and decreased the reaction rate without showing any surface morphological change. In the high concentration region, calcium was deposited on surface despite little Zr-rich region formation. Thereafter the precipitates containing calcium began to encrust the surface reaction layer on the glass intermittently and this layer was corroded from the near site of these deposits. The concentration dividing these two regions was about 0.1mg/ml in case that surface area of the glass to soaking liquid volume ratio was about 5.75cm-1. Reaction between zirconia containing glass and cement extract solution was considered to be determined by calcium ion concentration per unit glass surface area. The effect of other ion such as sodium or potassium was not observed under these experimental conditions.

Adsorption of toluene vapor on glass plates and surface area estimation from the adsorption isotherm gradient at the linear portion

In order to evaluate a novel method for estimating solid surface areaas from the adsorption isotherm gradient at the linear portion of type II isotherms, the adsorption of toluene on glass plates having a geometrical surface area of 1152 cm 2 at 0° and 10°C was studied. The almost constant isotherm gradient value ( dv d ( P P s ), v : amount adsorbed) in a relative pressure ( P P s ) region from 0.15 to 0.45, as well as in the cases of aluminum foil and mica plates, showed a good fit with the monolayer capacity calculated using the average, proper molecular cross section of toluene. For various materials whose geometrical surface area were not known, the standard BET areas were compared with the areas estimated from the isotherm gradient of toluene adsorption and their reasonable agreement suggested the usefulness of the gradient method for the surface area estimation. Based on these results a theoretical basis and conditions for the use of the method were discussed by considering an alternative two-dimensional gas model on the low-energy adsorption surface. In addition, a small type B hysteresis found in the region of low relative pressure and at submonolayer adsorption on the glass plate sample pile was reported.