Results of Vertical Scanning Interferometry (VSI) of Dissolved Borosilicate Glass: Evidence for Variable Surface Features and Global Surface Retreat

2002 ◽  
Vol 757 ◽  
Author(s):  
Icenhower J.P. ◽  
Lüttge A. ◽  
McGrail B.P. ◽  
Beig M.S. ◽  
Arvidson R.S. ◽  
...  
Keyword(s):  
Reaction Mechanisms ◽  
State Theory ◽  
Dissolution Rates ◽  
Surface Features ◽  
Glass Dissolution ◽  
Variable Surface ◽  
Competing Models ◽  
A New Technique ◽  
Vertical Scanning Interferometry ◽  
Glass Compositions

ABSTRACTTwo disparate reaction mechanisms have been invoked to explain the reactivity of glass in contact with aqueous solution. One model is based on arguments from Transition State Theory (TST), which postulates that glass dissolution rates are surface reaction controlled. Alternatively, the second model argues that release of elements from glass to solution is governed by diffusion through an altered layer that forms on the surface of glass. Vertical Scanning Interferometry (VSI) is a new technique that allows one to observe surface features of specimens exposed to solution and may, potentially, be used to distinguish between competing models. We performed a series of dissolution experiments with a suite of glass compositions from chemically simple (sodium borosilicate) to complex (sixteen component borosilicate). Dissolution rates were determined using single-pass flow-through (SPFT) apparatus at 90°C and pH = 9 and over a solution saturation interval. Upon termination of the experiments, glass coupons were examined by VSI techniques. Effluent chemistry and VSI measurements indicate a nearly constant rate of 2.2 to 3.4 g m-2 d-1 over the solution interval; rates calculated from both methods are identical within experimental uncertainty. We argue that this glass is phase separated, and propose a model for dissolution based on the relative rates of dissolution of the two glass compositions. The data are consistent with a modified version of TST and indicate the potency of VSI methods to elucidate glass reaction mechanisms.

Investigating first-year undergraduate chemistry students’ reasoning with reaction coordinate diagrams when choosing among particulate-level reaction mechanisms

2021 ◽  
Author(s):  
Molly B. Atkinson ◽  
Michael Croisant ◽  
Stacey Lowery Bretz
Keyword(s):  
Reaction Mechanism ◽  
Reaction Mechanisms ◽  
Peak Height ◽  
Student Thinking ◽  
Reaction Coordinate ◽  
First Year ◽  
Phase Reaction ◽  
Structured Interviews ◽  
Surface Features ◽  
Undergraduate Chemistry

Reaction coordinate diagrams (RCDs) are an important tool used to visualize the energetics of a chemical reaction. RCDs provide information about the kinetics of the reaction, the mechanism by which the reaction occurs, and the relative thermodynamic stability of the molecules in a reaction. Previous research studies have characterized student thinking about chemical kinetics, including their confusion in distinguishing between kinetics and thermodynamics. Semi-structured interviews were conducted with 44 students enrolled in a second-semester, first-year undergraduate chemistry course to elicit students’ ideas about surface features of RCDs and to examine how students connect those surface features to features of particulate-level reaction mechanisms. Students were provided both a gas-phase reaction and its accompanying RCD, and then they were asked to choose the particulate-level reaction mechanism that best corresponded to both the reaction and the RCD from among several possible particulate-level reaction mechanisms. Students were asked to explain their reasoning throughout the interview. Findings include students who chose the correct mechanism with appropriate reasoning, as well as students who chose the correct mechanism yet still expressed inaccurate ideas related to the surface features of RCDs and the concepts encoded within them. Students struggled to explain and reason with surface features such as peaks, valleys, and peak height. Moreover, students frequently found it difficult to identify meaningful connections between these surface features, the stoichiometry of the reaction, and the steps in a reaction mechanism. In addition, many students failed to mention important features of RCDs when describing their reasoning about the connections between particulate-level reaction mechanisms and RCDs. The implications for incorporating these research findings into teaching practices in first-year undergraduate chemistry contexts are discussed.

scholarly journals The initial dissolution rates of simulated UK Magnox–ThORP blend nuclear waste glass as a function of pH, temperature and waste loading

2015 ◽  
Vol 79 (6) ◽  
pp. 1529-1542 ◽  
Author(s):  
N. Cassingham ◽  
C.L. Corkhill ◽  
D.J. Backhouse ◽  
R.J. Hand ◽  
J.V. Ryan ◽  
...  
Keyword(s):  
Dissolution Kinetics ◽  
Intrinsic Rate ◽  
Waste Glass ◽  
High Level Waste ◽  
Dissolution Mechanism ◽  
Dissolution Rates ◽  
Forward Rates ◽  
Glass Dissolution ◽  
High Level ◽  
Kinetics Of

AbstractThe first comprehensive assessment of the dissolution kinetics of simulant Magnox–ThORP blended UK high-level waste glass, obtained by performing a range of single-pass flow-through experiments, is reported here. Inherent forward rates of glass dissolution were determined over a temperature range of 23 to 70°C and an alkaline pH range of 8.0 to 12.0. Linear regression techniques were applied to the TST kinetic rate law to obtain fundamental parameters necessary to model the dissolution kinetics of UK high-level waste glass (the activation energy (Ea), pH power law coefficient (η) and the intrinsic rate constant (k0)), which is of importance to the post-closure safety case for the geological disposal of vitreous products. The activation energies based on B release ranged from 55 ± 3 to 83 ± 9 kJ mol–1, indicating that Magnox–THORP blend glass dissolution has a surface-controlled mechanism, similar to that of other high-level waste simulant glass compositions such as the French SON68 and LAW in the US. Forward dissolution rates, based on Si, B and Na release, suggested that the dissolution mechanism under dilute conditions, and pH and temperature ranges of this study, was not sensitive to composition as defined by HLW-incorporation rate.

scholarly journals Nanodusty plasma chemistry: a mechanistic and variational transition state theory study of the initial steps of silyl anion–silane and silylene anion–silane polymerization reactions

2015 ◽  
Vol 17 (24) ◽  
pp. 15928-15935 ◽  
Author(s):  
Junwei Lucas Bao ◽  
Prasenjit Seal ◽  
Donald G. Truhlar
Keyword(s):  
Transition State ◽  
Reaction Mechanisms ◽  
Transition State Theory ◽  
Plasma Chemistry ◽  
State Theory ◽  
Variational Transition State Theory ◽  
Variational Transition State

The aim of the present work is to understand the detailed reaction mechanisms in the growth of nanodusty particles, which is critical in plasma chemistry, physics and engineering.

The effect of aqueous sulphate on basaltic glass dissolution rates

2008 ◽  
Vol 72 (1) ◽  
pp. 39-41 ◽  
Author(s):  
T. K. Flaathen ◽  
E. H. Oelkers ◽  
S. Gislason
Keyword(s):  
Steady State ◽  
Rate Equation ◽  
Rate Increase ◽  
Basaltic Glass ◽  
Mixed Flow ◽  
Dissolution Rates ◽  
Flow Reactors ◽  
Glass Dissolution ◽  
Sulphate Concentration

AbstractSteady-state dissolution rates of basaltic glass were measured in mixed-flow reactors at 50ºC at pH 3 and 4 as a function of aqueous sulphate concentration. Dissolution rates in the presence of 0.1 moles/kg SO42- were found to be ~3 times greater than those in corresponding SO42- free solutions. This rate increase is found to be approximately consistent with that calculated using a rate equation previously proposed by Gislason and Oelkers (2003). These results suggest that the addition of sulphate to injected CO2 may facilitate CO2 sequestration in basalts by accelerating basaltic glass dissolution rates thus more rapidly releasing aqueous Ca and Mg to solution.

Dissolution Kinetics of a Simple Analogue Nuclear Waste Glass as a Function of Ph, Time and Temperature

1989 ◽  
Vol 176 ◽  
Author(s):  
Kevin G. Knauss ◽  
William L. Bourcier ◽  
Kevin D. McKeegan ◽  
Celia I. Merzbacher ◽  
Son N. Nguyen ◽  
...  
Keyword(s):  
Dissolution Rate ◽  
Rate Constant ◽  
Rate Constants ◽  
Dissolution Kinetics ◽  
State Theory ◽  
Alkaline Solutions ◽  
Glass Dissolution ◽  
Constant Ph ◽  
Transport Control ◽  
Dissolution Rate Constants

ABSTRACTWe have measured the dissolution rate of a simple five-component borosilicate glass (Na2O, CaO, Al2O3, B2O3, SiO2) using a flow-through system. The experiments were designed to measure the dissolution rate constant over the interval pH 1 through pH 13 at 3 temperatures (25°, 50° and 70°C). Dilute buffers were used to maintain a constant pH. Analyses of solutions and solid surfaces provided information that is used to develop a kinetic model for glass dissolution.Under all conditions we eventually observed linear dissolution kinetics. In strongly acidic solutions (pH 1 to pH 3) all components but Si were released in their stoichiometric proportions and a thick, Si-rich gel was formed. In mildly acidic to neutral solutions the gel was thinner and was both Si- and Al-rich, while the other components were released to solution in stoichiometric proportions. In mildly to strongly alkaline solutions all components were released to solution in stoichiometric proportions. By varying the flow rate at each pH we demonstrated a lack of transport control of the dissolution rate.The dissolution rates were found to be lowest at near-neutral pH and to increase at both low and high pH. A rate equation based on transition-state theory (TST) was used to calculate dissolution rate constants and reaction order with respect to pH over two pH intervals at each temperature. At 250C between pH 1 and pH 7 based on the Si release rate the log rate constant for glass dissolution (g glass/m20d) was −0.77 and the order with respect to pH was −0.48. Between pH 7 and pH 13 the log rate constant for glass dissolution was −8.1 and the order with respect to pH was +0.51. The measured simple glass dissolution rate constants compare very well with constants estimated by fitting the same TST equation to experimental results obtained for SRL-165 glass and to dissolution rate estimates made for synthetic basaltic glasses.

scholarly journals A Kinetic Model for Borosilicate Glass Dissolution Based on the Dissolution Affinity of a Surface Alteration Layer

1989 ◽  
Vol 176 ◽  
Author(s):  
William L. Bourcier ◽  
Dennis W. Peiffer ◽  
Kevin G. Knauss ◽  
Kevin D. McKeegan ◽  
David K. Smith
Keyword(s):  
Kinetic Model ◽  
Dissolution Rate ◽  
Borosilicate Glass ◽  
Geochemical Modeling ◽  
Secondary Phases ◽  
Dissolution Rates ◽  
Ion Concentrations ◽  
Glass Dissolution ◽  
Gel Layer ◽  
Amorphous Surface

ABSTRACTA kinetic model for the dissolution of borosilicate glass, incorporated into the EQ3/6 geochemical modeling code, is used to predict the dissolution rate of a nuclear waste glass. In the model, the glass dissolution rate is controlled by the rate of dissolution of an alkalidepleted amorphous surface (gel) layer. Assuming that the gel layer dissolution affinity controls glass dissolution rates is similar to the silica saturation concept of Grambow [1] except that our model predicts that all components concentrated in the surface layer, not just silica, affect glass dissolution rates. The good agreement between predicted and observed elemental dissolution rates suggests that the dissolution rate of the gel layer limits the overall rate of glass dissolution. The model predicts that the long-term rate of glass dissolution will depend mainly on ion concentrations in solution, and therefore on the secondary phases which precipitate and control ion concentrations.

scholarly journals Dissolution Rates of DWPF Glasses from Long-Term PCT

1996 ◽  
Vol 465 ◽  
Author(s):  
W. L. Ebert ◽  
S.-W. Tam
Keyword(s):  
Dissolution Rate ◽  
Surface Area ◽  
Spherical Particles ◽  
Dissolution Rates ◽  
Glass Dissolution ◽  
Dissolution Tests ◽  
Dissolution Model ◽  
Advanced Stages ◽  
Radionuclide Release

ABSTRACTWe have characterized the corrosion behavior of several Defense Waste Processing Facility (DWPF) reference waste glasses by conducting static dissolution tests with crushed glasses. Glass dissolution rates were calculated from measured B concentrations in tests conducted for up to five years. The dissolution rates of all glasses increased significantly after certain alteration phases precipitated. Calculation of the dissolution rates was complicated by the decrease in the available surface area as the glass dissolves. We took the loss of surface area into account by modeling the particles to be spheres, then extracting from the short-term test results the dissolution rate corresponding to a linear decrease in the radius of spherical particles. The measured extent of dissolution in tests conducted for longer times was less than predicted with this linear dissolution model. This indicates that advanced stages of corrosion are affected by another process besides dissolution, which we believe to be associated with a decrease in the precipitation rate of the alteration phases. These results show that the dissolution rate measured soon after the formation of certain alteration phases provides an upper limit for the long-term dissolution rate, and can be used to determine a bounding value for the source term for radionuclide release from waste glasses. The long-term dissolution rates measured in tests at 20,000 m−1 at 90°C in tuff groundwater at pH values near 12 are about 0.2,0.07, and 0.04 g/(m2•d) for the Environmental Assessment glass and glasses made with SRL 131 and SRL 202 frits, respectively.

scholarly journals A Statistical Approach for Analysis of Dissolution Rates Including Surface Morphology

Minerals ◽  
2019 ◽  
Vol 9 (8) ◽  
pp. 458 ◽  
Author(s):  
Elisabete Trindade Pedrosa ◽  
Inna Kurganskaya ◽  
Cornelius Fischer ◽  
Andreas Luttge
Keyword(s):  
Mineral Dissolution ◽  
Etch Pits ◽  
Dissolution Rates ◽  
Calcite Dissolution ◽  
Crystal Dissolution ◽  
Vertical Scanning Interferometry ◽  
Surface Morphologies ◽  
Micrometer Scale ◽  
Flow Experiments

Understanding mineral dissolution is relevant for natural and industrial processes that involve the interaction of crystalline solids and fluids. The dissolution of slow dissolving minerals is typically surface controlled as opposed to diffusion/transport controlled. At these conditions, the dissolution rate is no longer constant in time or space, an outcome observed in rate maps and correspondent rate spectra. The contribution and statistical prevalence of different dissolution mechanisms is not known. Aiming to contribute to close this gap, we present a statistical analysis of the variability of calcite dissolution rates at the nano- to micrometer scale. A calcite-cemented sandstone was used to perform flow experiments. Dissolution of the calcite-filled rock pores was measured using vertical scanning interferometry. The resultant types of surface morphologies influenced the outcome of dissolution. We provide a statistical description of these morphologies and show their temporal evolution as an alternative to the lack of rate spatial variability in rate constants. Crystal size impacts dissolution rates most probably due to the contribution of the crystal edges. We propose a new methodology to analyze the highest rates (tales of rate spectra) that represent the formation of deeper etch pits. These results have application to the parametrization and upscaling of geochemical kinetic models, the characterization of industrial solid materials and the fundamental understanding of crystal dissolution.

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