Adaptation of the GRAAL model of Glass Reactivity to accommodate non-linear diffusivity
Not Available
Rieke, Peter C.↗
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Results for “Glass”
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Correlation between Antimicrobial Activity and Bioactivity of Na-Mica and Na-Mica/Fluorapatite Glass and Glass-Ceramics and Their Corrosion Protection of Titanium in Simulated Body Fluid
The improvement in bioactivity of titanium (Ti) surface was achieved via coating it with Na-mica and Na-mica/fluorapatite glass and glass-ceramic using the low-cost electrophoretic deposition technique. Two compositions from pure Na-mica (M) and 80 Na-mica/20 fluorapatite glasses (MF) were prepared in the system SiO{sub 2}-Al{sub 2}O{sub 3}-MgO-MgF{sub 2}-Na{sub 2}O-B{sub 2}O{sub 3} using melting–quenching technique. Characterization of the as-prepared glasses and their counterpart glass-ceramics was studied using differential thermal analysis (DTA), x-ray diffraction (XRD), Scanning Electron Microscopy (SEM) and Fourier Transform-IR (FTIR) spectroscopy techniques. The bioactivity behavior was proved by studying the XRD, FTIR and SEM after immersing both glass and glass-ceramic samples in simulated body fluid (SBF). Both M and MF glasses and glass-ceramics showed high microhardness measurements and good antibacterial behavior. In vitro biodegradation was studied by using electrochemical corrosion behavior of the prepared glass- and glass-ceramic-coated Ti in SBF. The prepared coated Ti showed good corrosion resistance in SBF at 37 °C using potentiodynamic polarization technique, and the impedance data fitting explained the structure of the coating and the adsorption of SBF ions on the Ti surface. The MFGC provides the best corrosion-resistant coating, especially after sintering it.
36 MATERIALS SCIENCE↗
First principles study of the structural, electronic, and optical properties of Sn 2+ -doped ZnO–P 2 O 5 glasses [First principles study of the structural, electronic and optical properties of Sn-doped ZnO-P2O5 glasses]
The atomic-structural, electronic, and optical properties of Sn-doped ZnO–P 2 O 5 glasses are examined using combined semi-empirical and density functional theory calculations. From model structures for two different ZnO–P 2 O 5 glass compositions, it is found that these glasses consist of nearly ideal tetrahedral PO 4 unit and largely distorted ZnO 4 and ZnO 5 units. The concentration of ZnO 5 units is calculated to increase and exceed that of ZnO 4 as the amount of ZnO in the glass is increased. Also, the concentration of terminal oxygen atoms shared by two Zn neighbors is largely increased for 70ZnO:30P 2 O 5 (70:30) glass compared to 60:40 glass, which can be rationalized by electrostatic bond strength calculations. Regarding medium-range order, calculations show that Q 1 and Q 2 structures (where Q n refers to structures containing n bridging oxygen atoms on PO 4 tetrahedra) are dominant for the 60:40 glass, while Q 0 and Q 1 prevail for the 70:30 glass, in good agreement with experimental observations. For the Sn-doped ZnO–P 2 O 5 glass, various Sn coordination geometries are found, with trigonal pyramidal SnO 3 and largely distorted pyramidal SnO 4 configurations being dominant and a small fraction of two-fold and five-fold coordinated Sn configurations also present. From combined cluster and glass model calculations, two-fold coordinated Sn are found to exhibit slightly smaller optical transition energy than three-fold and four-fold coordinated Sn. However, local variations in coordination structures throughout the glass likely result in a broad singlet transition (S 0 →S 1 ) around 5.4 eV for all the different Sn configurations. Finally, a triplet transition (S 0 →T 1 ) driven by spin-orbit coupling can occur around 4.5 – 4.8 eV, but the magnitude of this transition is predicted to be much smaller than the spin-allowed singlet transition.
36 MATERIALS SCIENCE↗
Evaluation of GlassNet for physics-informed machine learning of glass stability and glass-forming ability
Glassy materials form the basis of many modern applications, including nuclear waste immobilization, touch-screen displays, and optical fibers, and also hold great potential for future medical and environmental applications. However, their structural complexity and large composition space make design and optimization challenging for certain applications. Of particular importance for glass processing and design is an estimate of a given composition's glass-forming ability (GFA). However, there remain many open questions regarding the underlying physical mechanisms of glass formation, especially in oxide glasses. It is apparent that a proxy for GFA would be highly useful in glass processing and design, but identifying such a surrogate property has proven itself to be difficult. While glass stability (GS) parameters have historically been used as a GFA surrogate, recent research has demonstrated that most of these parameters are not accurate predictors of the GFA of oxide glasses. Here, in this work, we explore the application of an open-source pre-trained neural network model, GlassNet, that can predict the characteristic temperatures necessary to compute GS with reasonable performance and assess the feasibility of using these physics-informed machine learning (PIML)-predicted GS parameters to estimate GFA. In doing so, we track the uncertainties at each step of the computation—from the original ML prediction errors to the compounding of errors during GS estimation, and finally to the final estimation of GFA. While GlassNet exhibits reasonable accuracy on all individual properties, we observe a large compounding of error in the combination of these individual predictions for the PIML prediction of GS, finding that random forest models offer similar accuracy to GlassNet. We also break down the performance of GlassNet on different glass families and find that the error in GS prediction is correlated with the error in crystallization peak temperature prediction. Lastly, we utilize this finding to assess the relationship between top-performing GS parameters and GFA for two ternary glass systems: sodium borosilicate and sodium iron phosphate glasses. We conclude that to obtain true ML predictive capability of GFA, significantly more data needs to be collected.
36 MATERIALS SCIENCE↗
Nepheline crystallization in boron-rich alumino-silicate glasses as investigated by multi-nuclear NMR, Raman, & Mössbauer spectroscopies
Not Available
McCloy, John (ORCID:0000000174767771)↗
Iron phosphate glasses: Bulk properties and atomic scale structure
Bulk properties such as glass transition temperature, density and thermal expansion of iron phosphate glass compositions, with replacement of Cs by Ba, are investigated as a surrogate for the transmutation of 137Cs to 137Ba, relevant to the immobilisation of Cs in glass. These studies are required to establish the appropriate incorporation rate of 137Cs in iron phosphate glass. Density and glass transition temperature increases with the addition of BaO indicating the shrinkage and reticulation of the iron phosphate glass network. The average thermal expansion coefficient reduces from 19.8 × 10-6 K-1 to 13.4 × 10-6 K-1, when 25 wt. % of Cs2O was replaced by 25 wt. % of BaO in caesium loaded iron phosphate glass. In addition to the above bulk properties, the role of Ba as a network modifier in the structure of iron phosphate glass is examined using various spectroscopic techniques. The FeII content and average coordination number of iron in the glass network was estimated using Mössbauer spectroscopy. The FeII content in the un-doped iron phosphate glass and barium doped iron phosphate glasses was 20, 21 and 22 ± 1% respectively and the average Fe coordination varied from 5.3 ± 0.2 to 5.7 ± 0.2 with increasing Ba content. The atomic scale structure was further probed by Fe K-edge X-ray absorption spectroscopy. The average coordination number provided by extended X-ray absorption fine structure spectroscopy and X-ray absorption near edge structure was in good agreement with that given by the Mössbauer data.
36 MATERIALS SCIENCE↗
Effects of optical dopants and laser wavelength on atom probe tomography analyses of borosilicate glasses
Atom probe tomography (APT) is a novel analytical microscopy method that provides three dimensional elemental mapping with sub-nanometer spatial resolution and has only recently been applied to insulating glass and ceramic samples. In this paper, we have studied the influence of the optical absorption in glass samples on APT characterization by introducing different transition metal optical dopants to a model borosilicate nuclear waste glass (international simple glass). A systematic comparison is presented of the glass optical properties and the resulting APT data quality in terms of compositional accuracy and the mass spectra quality for two APT systems: one with a green laser (532 nm, LEAP 3000X HR) and one with a UV laser (355 nm, LEAP 4000X HR). These data were also compared to the study of a more complex borosilicate glass (SON68). The results show that the analysis data quality such as compositional accuracy and total ions collected, was clearly linked to optical absorption when using a green laser, while for the UV laser optical doping aided in improving data yield but did not have a significant effect on compositional accuracy. Comparisons of data between the LEAP systems suggest that the smaller laser spot size of the LEAP 4000X HR played a more critical role for optimum performance than the optical dopants themselves. The smaller spot size resulted in more accurate composition measurements due to a reduced background level independent of the material’s optical properties.
Environmental Molecular Sciences Laboratory↗
Predicting nepheline precipitation in waste glasses using ternary submixture model and machine learning
Nepheline precipitation in nuclear waste glasses during vitrification can be detrimental due to its negative effect on chemical durability. Developing models to accurately predict nepheline precipitation from compositions is important to increase waste loading since existing models can be overly conservative. In this study, an expanded dataset containing 955 glasses was compiled from literature data, where 355 glasses are for high-level waste (HLW). Previously developed submixture models were refitted using the new dataset, where a misclassification rate of 7.8% was achieved. Nine machine learning (ML) algorithms (e.g., k-nearest neighbor, Gaussian process regression, artificial neural network, support vector machine, decision tree, etc.) were applied to evaluate their ability of predicting nepheline precipitation from compositions. Model accuracy, precision, recall/sensitivity, and F1 score were systemically compared between different ML algorithms and modeling protocols. Good model prediction with an accuracy ~0.9 (misclassification rate of ~10%) was observed with different algorithms under certain protocol. This study evaluated various ML models to predict nepheline precipitations in waste glasses, highlighting the importance of data preparation, modeling protocol, and their effect on model stability and reproducibility. The results provide insights into applying ML to predict glass properties and suggest areas for future research on modeling nepheline precipitations.
Lu, Xiaonan↗
Microscopic insight into the origin of enhanced glass-forming ability of metallic melts on micro-alloying
Extensive efforts have been made to develop metallic-glasses with large casting diameter. Such efforts were hindered by the poor understanding of glass formation mechanisms and the origin of the glass-forming ability (GFA) in metallic glass-forming systems. In this work, we have investigated relaxation dynamics of a model bulk glass-forming alloy system that shows the enhanced at first and then diminished GFA on increasing the percentage of micro-alloying. The micro-alloying did not have any significant impact on the thermodynamic properties. The GFA increasing on micro-alloying in this system cannot be explained by the present theoretical knowledge. Our results indicate that atomic caging is the primary factor that influences the GFA. The composition dependence of the atomic caging time or residence time is found to be well correlated with GFA of the system.
36 MATERIALS SCIENCE↗
Conversion of Nuclear Waste to Molten Glass: Cold-Cap Reactions in Crucible Tests
The feed-to-glass conversion, which comprises complex chemical reactions and phase transitions, occurs in the cold-cap zone during nuclear waste vitrification. Knowledge of the chemistry and physics of feed-to-glass conversion will help us control the conversion path by changing the melter feed makeup to maximize the glass production rate. To investigate the conversion process, we analyzed heat-treated samples of a simulated high-level waste feed using X-ray diffraction, electron probe microanalysis – wavelength dispersive X-ray spectroscopy, leaching tests, and residual anion analysis. Feed dehydration, gas evolution, and borate phase formation occurred at temperatures below 700 °C before the emerging glass-forming melt was completely connected. Above 800 °C, intermediate aluminosilicate phases and quartz particles were gradually dissolving in the continuous borosilicate melt, which expanded into transient foam. Knowledge of the chemistry and physics of feed-to-glass conversion will help us control the conversion path by changing the melter feed makeup to maximize the glass production rate.
Cold-cap↗
Modelling the sulfate capacity of simulated radioactive waste borosilicate glasses
The capacity of simulated high-level radioactive waste borosilicate glasses to incorporate sulfate has been studied as a function of glass composition. Combined Raman, 57 Fe Mössbauer and literature evidence supports the attribution of coordination numbers and oxidation states of constituent cations for the purposes of modelling, and results confirm the validity of correlating sulfate incorporation in multicomponent borosilicate radioactive waste glasses with different models. A strong compositional dependency is observed and this can be described by an inverse linear relationship between incorporated sulfate (mol% SO 4 2- ) and total cation field strength index of the glass, Σ(z/a 2 ), with a high goodness-of-fit (R 2 ≈ 0.950). Similar relationships are also obtained if theoretical optical basicity, Λ th (R 2 ≈ 0.930) or non-bridging oxygen per tetrahedron ratio, NBO/T (R 2 ≈ 0.919), are used. Results support the application of these models, and in particular Σ(z/a 2 ), as predictive tools to aid the development of new glass compositions with enhanced sulfate capacities.
36 MATERIALS SCIENCE↗
Impacts of glass composition, pH, and temperature on glass forward dissolution rate
Nuclear waste glasses dissolve at the forward dissolution rate (r f ) in very dilute aqueous solutions, which can isolate the impact of the glass composition from solution feedback and alteration product effects. While it has long been known that pH and temperature (T) strongly impact r f , the impacts of glass composition have remained uncertain. In this work, r f data from 19 nuclear waste glasses were used with the aim of identifying the effect of glass composition on r f . The r f values were modeled as: r f = k 0 10 –ηpH exp(-E a /RT), with k 0 , η, E a , and R, respectively, being the intrinsic rate constant, pH coefficient, apparent activation energy, and gas constant. However, no predictive correlation could be established between the individual model parameters (log[k 0 ], η, and E a ) and glass composition for the glasses considered in this study, an outcome that was attributed to the strong positive correlation between the log[$k_0$] and E a parameters. Therefore, a model was fitted directly to the combined r f from all 19 glasses. This approach showed that 90% of the variation in r f data could be accounted for solely by T and pH effects. Therefore, any composition effects must be relatively small. After normalizing for differences in pH and T, the only notable differences in r f between the glasses were found to correlate with variations in the fraction of glass forming tetrahedra contributed by tetrahedral boron, $f$([ 4 ]B), with an abrupt threshold at a high value of $f$([ 4 ]B) (~0.22), where higher r f are predicted with no discernable composition effects below the threshold.
36 MATERIALS SCIENCE↗
Structure–property relations of sodium iron phosphate nuclear waste glasses: Effects of iron redox ratio and glass composition
Iron phosphate glasses, known for their exceptional chemical durability and potential applicability in nuclear waste management, have gained significant attention over the years. The structures of these glasses are complicated by the coexistence of Fe 3+ and Fe 2+ , which plays a crucial role in determining their structures and properties. Here, this work uses molecular dynamics simulations to study the structural changes in Na 2 O–Fe 2 O 3 –P 2 O 5 glasses with varying glass composition and Fe 2+ /Fe 3+ redox ratio. It was found that the redox ratio and modifier contents significantly affected the short-range and medium-range orders in the glasses. Significant changes in the local environments around P 5+ and Fe 3+ were observed, as reflected by the bond distances and coordination numbers. Na + cations are found to preferentially associate with Fe 3+ (rather than Fe 2+ ), whereas Fe 2+ has stronger association with P 5+ than Na + , confirming the structural role of Fe 2+ as a glass modifier. The disruptions in P–O–P linkages upon increasing FeO suggest that FeO causes glass depolymerization. These glasses achieved higher connectivity with increasing Fe 3+ / (Fe 3+ + Fe 2+ ) ratios, conerting phosphorous Q 2 to Q 3 units and iron Q 5 units to Q 4 units. The decrease of nonbridging oxygen fractions with increasing Fe 3+ / (Fe 3+ + Fe 2+ ) ratios, through creating P–O–Fe linkages, is the main reason of enhanced network connectivity. Quantitative structure–property relationship analyses with different structural descriptors were used to correlate with measured properties. The analyses provided valuable insights into structure–property relationships, emphasizing the importance of choosing relevant energy parameters and defining glass network connectivity, particularly in F net descriptors. It was found the Fe–O–P linkage density exhibits strong correlations to measured dissolution rates, supporting the importance of these linkages in improving the chemical durability in iron phosphate glasses.
12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
Durability testing of actual Hanford waste glasses and their non-radioactive simulant glasses
The low-activity waste (LAW) fraction of Hanford tank waste will be converted to glass at the Waste Treatment and Immobilization Plant (WTP) and disposed on the Hanford site. The chemical durability of LAW glasses has been researched for decades to satisfy contract requirements. Most LAW glass durability data has been generated on non-radioactive simulant glasses fabricated via crucible melts. These non-radioactive glasses were chosen due to safety and cost reasons with confidence that radioactive waste glasses would exhibit similar behavior. To reduce the risk of significant differences in laboratory test response data between WTP melter waste glass and simulant glass, Product Consistency Tests (PCT, i.e., ASTM C1285-21) and Environmental Protection Agency (EPA) 1313 durability tests were performed on actual and simulant LAW glasses fabricated using laboratory-scaled melters. Actual and simulant glass durability test results are presented and statistically compared. Finally, differences in test responses were found to be within experimental uncertainty.
12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
Chemical Composition Analysis and Product Consistency Tests to Support Enhanced Hanford Waste Glass Models: Results for the January, March, and April 2015 LAW Glasses
In this report, the Savannah River National Laboratory provides chemical analyses and Product Consistency Test (PCT) results for several simulated low activity waste (LAW) glasses (designated as the January, March, and April 2015 LAW glasses) fabricated by the Pacific Northwest National Laboratory. The results of these analyses will be used as part of efforts to revise or extend the validation regions of the current Hanford Waste Treatment and Immobilization Plant glass property models to cover a broader span of waste compositions. The measured chemical composition data are reported and compared with the targeted values for each component for each glass. All of the measured sums of oxides for the study glasses fall within the interval of 97.9 to 100.7 wt %, indicating recovery of all components. The Al 2 O 3 concentration of glass EWG-LAW-ORP-LD1-3 is about 45% higher than the targeted value. The concentrations of other major oxides in this glass are below their targeted values, indicating that excess Al 2 O 3 may have been added to the batch for EWG-LAW-ORP-LD1-3. The PCT results were normalized to both the targeted and measured compositions of the study glasses. Several of the study glasses have normalized concentration values that are higher than the WTP contract limit of 4.0 g/L for both the quenched and CCC heat treatments. These results can be combined with additional characterization, including X-ray diffraction, to determine the cause of the higher releases. It is recommended that a more complete review of the influence of composition and heat treatment on the PCT responses of the glasses described in this report, as well as those described in a previous report, be performed in order to draw further conclusions.
12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
Development of High Alumina Glass Property Data for Hanford High-Level Waste Glass Models - 16231
Roughly half of the projected Hanford high-level waste batches will have waste loadings limited by relatively high concentration of Al{sub 2}O{sub 3}. Individual glasses have been formulated and tested to demonstrate that it is possible to increase the loading of these high-Al{sub 2}O{sub 3} wastes in glass by as much as 50%. To implement such increases in waste loading in the Hanford Tank Waste Treatment and Immobilization Plant, the impact of composition on the properties of high-Al{sub 2}O{sub 3} waste glasses must be quantified in the form of validated glass property-composition models. To collect the data necessary for glass property-composition models, a multi-phase experimental approach was developed. In the first phase of the study, a set of 46 glass compositions were statistically designed to most efficiently backfill existing data in the composition region for high-Al{sub 2}O{sub 3} (15 to 30 wt%) waste glasses. The glasses were fabricated and key glass properties were tested: - Product Consistency Test (PCT) on quench (Q) and canister centerline cooled (CCC) samples - Toxicity Characteristic Leaching Procedure (TCLP) on Q and CCC samples - Crystallinity as a function of temperature (T) at equilibrium and of CCC samples - Viscosity and electrical conductivity as a function of T The measured properties of these glasses were compared to predictions from previously existing models developed over lower Al{sub 2}O{sub 3} concentration ranges. Areas requiring additional testing and modeling were highlighted. (authors)
12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
In situ measurement of ferric iron in lunar glass beads using Fe-XAS
Through use of a new X-ray Absorption Spectroscopy (XAS) calibration for Fe3+ analysis in silicate glasses, the first direct measurements of ferric iron in natural lunar picritic glasses are presented. Lunar glass beads from the Apollo sample collection contain up to 60.0% Fe3+. No correlation with melt chemical properties, such as Mg# or weight % TiO2, or physical properties, such as bead diameter, was observed. Fe3+/ΣFe is negatively correlated with NBO/T. These elevated Fe3+/ΣFe values reflect eruption and post-eruption oxidation due to magmatic degassing of H or OH. Glass beads observed to be zoned to lower Fe3+/ΣFe rims may represent a subsequent reduction in the lunar vacuum prior to cooling through the glass transition temperature
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Foaming during Nuclear Waste Melter Feeds Conversion to Glass: Application of Evolved Gas Analysis
During the final stages of batch-to-glass conversion in a waste-glass melter, gases evolving in the cold cap produce primary foam, the formation and collapse of which control the glass production rate via its effect on heat transfer to the reacting batch. We performed quantitative evolved gas analysis (EGA) for several HLW melter feeds with temperatures ranging from 100 °C to 1150 °C, the whole temperature span in a cold cap. EGA results were supplemented with visual observation of batch-to-glass transition using the feed expansion tests. Upon heating, most of the gases—mainly H2O, CO2, NO, NO2, N2 and O2—evolve at temperatures below 700 °C and escape directly to the atmosphere through open porosity. However, as open porosity closes when enough glass-forming melt appears at 720 °C, the residual gas evolution leads to the formation of primary foam. We found that primary foaming is mostly caused by the decomposition of residual carbonates, though oxygen evolution from iron-redox reaction can also play a role. We also show that the gas evolution shifts to a higher temperature when the heating rate increases. The implications for the mathematical modeling of foam layer in the cold cap are presented.
Hujova, Miroslava↗