Durability Of Glasses Research Articles

Study of the Effect of Calcium Substitution by Magnesium in the Vitreous System 3P2O5-2K2O-(1 - x) CaO-x MgO.

Phosphate glasses have potentially interesting properties that can be used in various applications. Recently, different studies are focusing on their dissolution behaviours that can be modified to suit some environmental applications, such as controlled-release fertilisers. In this work, magnesium had been suggested to improve the glass durability of 3P2O5-2K2O-(1 − x)CaO-xMgO glasses (0 ≤ x ≤ 1). Indeed, its effect on glass structure, thermal properties and most important dissolution behaviours were studied, in order to evaluate their suitability of being used as controlled-release fertilisers. Various compositions in which calcium was partially replaced by magnesium were prepared by melting at 800 °C. The samples were characterised by differential scanning calorimetry, density measurements, X-Ray diffraction, FTIR spectroscopy and Raman spectroscopy. The dissolution behaviours were investigated using inductively coupled plasma optical emission spectrometry ICP-OES, pH measurements and SEM. Substitution of calcium by magnesium reduced the glass density, owing to the lower atomic weight of magnesium compared to calcium, and caused an increase in glass transition and crystallisation temperatures. Magnesium substitution significantly improved the chemical durability of the glasses due to more covalent Mg–O bond than the Ca–O bond. This study demonstrated that 3P2O5-2K2O-0.3CaO-0.7MgO (x = 0.7) had a dissolution profile adequate to the criteria of controlled-release fertilisers and could be used to nourish the plants with phosphorus, potassium, calcium and magnesium.

Data-driven predictive models for chemical durability of oxide glass under different chemical conditions

We conducted a comprehensive study to investigate the performance of various machine-learning models in predicting the chemical durability of oxide glasses under different chemical conditions with glass composition as input features, by taking advantage of the large dataset (~1400 datapoints) we have collected. Two typical machine-learning tasks, weight loss regression, and surface appearance change rating classification, were conducted in the study. We successfully made Neural Networks delivered an excellent performance in predicting the weight loss, while Random Forest in classifying the surface appearance change rating. Additionally, feature importance analysis showed that SiO2, Na2O, P2O5 were the most dominate features for predicting the weight loss, while SiO2, ZrO2, CaO were the topmost features for classifying the surface appearance change rating, under acid, HF, and base testing conditions, respectively. We also realized that the trained models fall short of extrapolating data far from the training dataset space even though they exhibit outstanding interpolation performance in some cases. Topology constrained theory fed by structural information from molecular dynamics simulations seems to be a promising approach to address the challenge.

A data‐driven approach for predicting nepheline crystallization in high‐level waste glasses

AbstractHigh‐level waste (HLW) glasses with high alumina content are prone to nepheline crystallization during the slow canister cooling that is experienced during large‐scale production. Because of its detrimental effects on glass durability, nepheline (NaAlSiO4) precipitation must be avoided; however, developing robust, predictive models for nepheline crystallization behavior in compositionally complex HLW glasses is difficult. Using overly conservative constraints to predict nepheline formation can limit the waste loading to lower than the achievable capacity. In this study, a robust data‐driven model using five compositional features has been developed to predict nepheline formation. A new descriptor is introduced called the “difference based on correlation”, which has higher accuracy compared to previous descriptors and also has more balanced false positive and false negative rates. The analysis of the model and the data show an overlap, instead of a distinct compositional boundary, between glasses that form and do not form nepheline. As a result, the model's predictive accuracy is not the same throughout the feature space and instead is dependent on the location of the glass composition in the dimensionally reduced feature space.

Nepheline crystallization and the residual glass composition: Understanding waste glass durability

AbstractThe vast majority of High‐Level Waste (HLW) originating from defense nuclear programs is sequestered and immobilized in borosilicate glass. Borosilicate glass is universally accepted for immobilizing HLW, but its efficiency has limitations based on the compositional makeup of the waste stream. The chemical durability of the glass is the most important factor in determining the longevity and usefulness of the final glass waste form. The primary detriment to this durability in glasses containing high levels of aluminum is nepheline (NaAlSiO4) crystallization, as it is generally accompanied by a measurable decrease in the glass's chemical durability. This work seeks to understand nepheline crystallization, within the context of thermal history, and to elucidate the influence of compositional shifts in the residual glass (after crystallization) on the measured durability. The results presented within show a distinct deviation in leaching behavior as a function of structural makeup (calculated Q units). This understanding will provide practical information required for broadening glass compositional regions needed to more efficiently vitrify HLW.

Effect of V2O5 on crystallization tendency and chemical durability of Mo-bearing aluminoborosilicate glass

AbstactThe effect of V2O5 addition on molybdates crystallization tendency, glass structure and chemical durability of aluminoborosilicate glass belonging to SiO2-B2O3-CaO-Na2O-Al2O3-MoO3 system has been studied. The results confirm that V2O5 addition can effectively suppress the crystallization tendency of powellite and enhance the molybdenum solubility in the glass. The MoO3 solubility limit is found to be 2.8 mol% in the V2O5-containing aluminoborosilicate glass. Raman results reveal that V2O5 addition seems to modify the local structural environment of isolated MoO4 units and increase their chemical disorder in the glass, which is favored for molybdenum incorporation in the glass. The molar volume and glass transition temperature of samples are found to depend on V2O5 content. Product consistency test (PCT) results show that the normalized leaching rates of the V2O5-containing aluminoborosilicate glass maintain at a fairly low level compared with standard borosilicate glassy waste form.

Characterisation of co-mixed HIP wasteforms for Magnox sludge and clinoptilolite wastes

Co-mixed simulant wasteforms consisting of calcined Magnox sludge simulant and clinoptilolite, with additions of a glass forming frit and CeO2 or U3O8 were processed using Hot Isostatic Pressing (HIP). This enabled the production of high waste loaded materials, with the successful incorporation of both simulant and active material. These formed heterogeneous glass-ceramic products, with decomposition of raw materials and some vitreous phase formation. The aqueous durability of these materials was assessed over a 28-day period using a modified PCT test, and favourably compared to the durability of an international glass. Overall this verifies the potential for HIP technology to be used in wasteform production, with potential large reductions in waste volume, especially if co-mixed wastes are considered.

Network Structure and Chemical Durability of Non-alkali Aluminoborosilicate Glasses Containing ZnO

The structure and chemical durability of non-alkali aluminoborosilicate glasses with various contents of ZnO were investigated. As the replacement of MgO by ZnO increases from 0 to 3.2mol%, the average number of bridge oxygen per tetrahedron (BO/T) as a measure of network connectivity increases from 2.84 to 3.04, and the chemical durability improved. The weight loss ratio (WLR) of glass etched in 10vol% HF (20 °C, 20 min) solution decreased from 4.809 to 4.509, and in 5wt% NaOH (95 °C, 6 h) solution decreased from 1.201 to 0.994. The replacement of MgO by ZnO further increased to 6.4mol%, the value of BO/T decreased to 3.04 instead, and thus the chemical durability deteriorated. The WLR of HF-acid and NaOH-alkali corrosion increased to 6.683 and 1.994, respectively. The chemical durability shows strongly dependent on the network connectivity and exhibits mixed intermediate effects during the replacement of MgO by ZnO.

Atomistic understanding of surface wear process of sodium silicate glass in dry versus humid environments

AbstractUnderstanding surface reactions of silicate glass under interfacial shear is critical as it can provide physical insights needed for rational design of more durable glasses. Here, we performed reactive molecular dynamics (MD) simulations with ReaxFF potentials to study the mechanochemical wear of sodium silicate glass rubbed with amorphous silica in the absence and presence of interfacial water molecules. The effect of water molecules on the shear‐induced chemical reaction at the sliding interface was investigated. The dependence of wear on the number of interfacial water molecules in ReaxFF‐MD simulations was in reasonable agreement with the experimental data. Confirming this, the ReaxFF‐MD simulation was used to find further details of atomistic reaction dynamics that cannot be obtained from experimental investigations only. The simulation showed that the severe wear in the dry condition is due to the formation of interfacial Sisubstrate–O–Sicounter_surface bond that convey the interfacial shear stress to the subsurface and the presence of interfacial water reduces the interfacial bridging bond formation. The leachable sodium ions facilitate surface reactions with water‐producing hydroxyl groups and their key role in the hydrolysis reaction is discussed.

The Abrasion of Photovoltaic Glass: A Comparison of the Effects of Natural and Artificial Aging

Natural soiling and the subsequent requisite cleaning of photovoltaic (PV) modules result in abrasion damage to the cover glass. The durability of the front glass has important economic consequences, including determining the use of antireflective and/or antisoiling coatings as well as the method and frequency of operational maintenance (cleaning). The abrasion of coatings and glass has been explored in a field study, including the soiling-prone locations of Dubai (United Arab Emirates), Kuwait City (Kuwait), Mesa (Arizona), Mumbai (India), and Sacramento (California). Dry-brush-cleaned specimens will be compared with those subjected to artificial-brush testing. The characteristics of material integrity, surface energy, optical transmittance, surface roughness, and scratch size were examined using an optical microscope, contact goniometer (for water), spectrophotometer, interferometer, and atomic force microscope, respectively. The findings of this article will be used to provide feedback regarding the cleaning equipment, cleaning methods, and coatings used in the PV industry. The study here will also be used to aid in developing an abrasion standard for the PV industry.

The effect of mixed La-Y doping on water resistance of phosphate glass

In this work, the effect of mixed La-Y doping on the water resistance of xLa2O3–(16-x)Y2O3–8Al2O3–10Na2O–66P2O5 (x = 0, 4, 8, 12, 16 mol%) glasses was studied. The glass structure, glass transition temperature (Tg), dc conductivity (σdc) and water resistance of glass were respectively characterized by Fourier transform infrared spectroscopy (FTIR), differential scanning calorimeter (DSC), electrochemical workstation and water resistance test. The results show that with the gradual replacement of Y2O3 by La2O3, the value of Q(2) (Q2 content as a percentage of the sum of Q1 and Q2 contents in glass structure) and water resistance characterized by mass loss per unit surface area indicate strong “mixed rare earth effect”. It is obvious that the change of glass structure causes water resistance of glass to vary nonlinearly and exhibit a positive deviation from linearity. The results can provide some useful information for tailoring the chemical durability of glass by mixed rare earth doping.

Coupling Radioactive Waste Glass Dissolution Measurements in Generic Groundwaters With Reactive Transport Modeling of Repository Scenarios

AbstractThe reliable simulation of radionuclide migration away from the near field of a geological repository for safety analyses requires a fundamental understanding of processes in the near field. We focus this study on investigating the behavior of UK MW25 waste glass (a nonradioactive simulant of U.K. Magnox glass) and other near‐field components in a geological repository over long periods of time. The approach used involved a two‐step process: waste glass dissolution measurements and modeling in potential repository groundwaters, and reactive transport simulation of radionuclide release and transport in the near field. The Stage 1 rate of MW25 measured in lower‐strength‐sedimentary‐rock groundwater was found to be slightly higher than that measured in higher‐strength‐rock groundwater. Experimental results show the critical role of groundwater chemistry on waste glass dissolution kinetics. Reactive transport model parameterization was accomplished by coupling direct laboratory measurements and literature data with transport processes. The results revealed that 79Se, 99Tc, and 237Np are the radionuclides that will have the greatest impact on the environment at long times. The performance assessment results show that the improvement afforded by the addition of a copper canister in the waste package, as opposed to having only a steel canister, is marginal and higher strength rock would be a more effective barrier at long time than lower strength sedimentary rock in terms of restricting the transport of the radionuclides. Our model provides deep insights into the contribution of waste glass durability and other near‐field components in the containment and retardation of radionuclide transport.

Sol-Gel Synthesis and Characterization of Gels with Compositions Relevant to Hydrated Glass Alteration Layers.

During the processes associated with glass corrosion, porous hydrated glass alteration layers typically form upon exposure to aqueous conditions for extended time periods. The impacts of the alteration layer on glass durability have not been agreed upon in the glass science community. In particular, the formation mechanisms of hydrated glass alteration layers are still largely unknown and require further investigation, but these layers often require months to years to develop and are often too thin to adequately characterize. Meanwhile, sol–gel-derived silicate gels are relatively easy to synthesize in bulk with custom compositions relevant to hydrated glass alteration layers. If alteration layers and synthetic silicate gels demonstrate physical and chemical properties that are sufficiently similar, synthetic silicate gels could be used as analogues for hydrated glass alteration layers in future studies. However, synthetic gels must first be prepared and evaluated before comparisons between glass alteration layers and synthetic silicate gels can be made. This work focuses entirely on the synthesis and observed physical properties of synthetic silicate gels. A future work will compare the characteristics of synthetic gels described in this work with altered waste glass formed in similar pH environments. In this study, synthetic gels were made with custom compositions at various pH values to evaluate the effect of pH on gel structure and morphology. Several other variables were examined also, such as composition, drying, and aging. Gels were produced by sequential additions of organometallic precursors in a single container. Gels were analyzed with several techniques including small-angle X-ray scattering, gas adsorption, and He pycnometry to determine the effects of the variables on physical properties. Results show that gels prepared at pH 3 consistently contained fewer primary particles with diameters larger than 7.2 nm and fewer pores with diameters larger than 30 nm compared to gels synthesized at pH 7 and 9. Composition was shown to have no discernable effect on primary particle and pore sizes at any pH.

Relating Magnox and international waste glasses

Magnox and international radioactive waste glasses observe significantly different aqueous dissolution behaviours. Previously, the effects of Li on the kinetics of dissolution and B network of analogues of a complex Magnox waste glass were investigated (Li-Mg-EM). Here, an “International Simple Glass” with Li substituted for Na at two ratios (Li-ISG) was fabricated to compare the aqueous durability of Magnox and international glasses. 11B MAS-NMR, 23Na MAS-NMR, 6Li1H CP-NMR and SEM studies are presented. The IIIB/IVB ratio and the role of Na in the pristine glasses varied insignificantly with the Li:Na ratio. Further, the B network of Li-ISG was shown to leach congruently. Li, Na and Mg-containing secondary phases were present for Li-Mg-EM, whilst no precipitates were observed for Li-ISG. Li in ISG was shown to be detrimental but further substitution of Li improved long-term aqueous durability, which was attributed to a LiNa mixed alkali effect for Li-ISG but not Li-Mg-EM.

Influence of composition of nuclear waste glasses on vapor phase hydration

For the first time, the influence of glass composition on the vapor hydration kinetics of the French AVM nuclear waste glass simulants was investigated. Three complex borosilicate glasses (>20 oxides) along with three simplified Na/(Ca, Na)/(Mg, Na)-alumino-borosilicate glasses with four or five oxides were altered at 50 °C in water vapor (95% RH) for up to 557 days. The solid characterization of the altered samples (by SEM, TEM, XRD, ToF-SIMS, SAXS) revealed that the rate-controlling vapor hydration mechanism is composition dependent. The vapor hydration rate of the more durable glasses, whose molar ratio of Al2O3/(CaO or MgO) is ≥ 1, seems to be limited by network-hydrolysis, whereas the overall glass alteration rate of the less durable glasses, whose Al2O3/MgO ratio is < 1, seems to be driven by the precipitation of Mg-rich secondary phases. All the vapor hydrated glasses show the presence of a homogeneous gel layer of a few tens of nm thickness. The more durable glasses have a smaller quantity of secondary phases precipitated on their surface. The less durable glasses have a relatively significant quantity of secondary phases precipitated above the gel layer and irregularly shaped, scattered and highly porous altered zones formed beneath the gel layer. The overall alteration rate of the less durable glasses was 10–20 times faster than the more durable glasses. For all glasses, FTIR spectroscopy indicated an inflexion in the vapor hydration rate after 120–200 days of alteration, likely due to a passivating effect of the altered layer formed under unsaturated conditions. The average pore size of the altered layer in certain vapor hydrated glasses measured by SAXS is similar to the pore sizes of the gel layer formed in aqueous medium and varies very slightly with glass composition.

Mixed reactions: Glass durability and the mixed‐alkali effect

AbstractMultiple‐component oxide silicate glasses possess a complex network backbone, which results in manifolded composition property relationships. The relation between the chemical composition and durability of silicate glasses is not linear, however, this relation has always been considered somewhat relevant. Several contradicting observations on the mixed‐alkali effect and its relation with their chemical alteration have been reported. Here, laboratory results and historical evidence show that the often good state of preservation of aged mixed modifier glasses is in good agreement with the influence of a mixed‐modifier cation effect (MMCE) such as had been observed for other mobility‐ and bulk‐related properties. This concordance supports the proposals made through this work concerning pore closure and lower diffusivity of mobile species under the MMCE.

Determination of the effects of temperature changes on solar glass used in photovoltaic modules

Solar glass is one of the most important components of PV modules and it protects solar cells from harsh environmental conditions. Considering that the PV modules have around 25-year lifetime, it is preferred that the PV modules operate in stable conditions. This situation also changes the temperature of the solar glass due to environmental and operating conditions. The scope of this study is testing the durability of the solar glass used in PV panels in different environmental conditions. Two different types of solar glass, called type A and type B, will be examined in this study. In the measurement results for the A samples, values of the exergy efficiency change between 0.67% and 1.42%; while the ones for the samples B range from 0.66% to 1.49% in parallel with the solar radiation. From the same standpoint, energy and power conversion efficiency values have been determined for both solar glass types. Among different wavelength densities, the reflectance ratios of the samples used in the experimental study vary from 2% to 8% for the sample A and from 6% to 14% for sample B.

Structure and chemical durability of calcium iron phosphate glasses doped with La2O3 and CeO2

Calcium iron phosphate glasses doped with La2O3 and CeO2 have been prepared by the melting method. The structure and chemical resistance of the glasses were analyzed by XRD, FTIR and SEM. The XRD results showed that the glasses after aqueous corrosion were amorphous, while several crystals emerged after the alkali corrosion. FTIR analysis demonstrated an increase in non-bridging oxygens by adding rare earth oxides and the glass network depolymerized from Q1 to Q0 with the corrosion. Densities increased with increasing La2O3 and CeO2 content. SEM tests displayed that the smooth glass surface became rough with the corrosion time increasing and some cracks emerged at last. Comparing the values of the weight loss ratios of La-doped and Ce-doped glasses, the latter was more corrosion resistant. The least weight loss rate was 10.85% with 2.0 mol% CeO2 addition and the Ce-doped glass had the best alkali resistance in these two series. The addition of La2O3 and CeO2 significantly improved the water and alkali resistance of the glass specimens.

Tribochemical wear of silicon nitride against silicate and phosphate glasses

Using an environment-controlled ball-on-flat reciprocating tribometer, the effects of water on the wear of Si3N4 were investigated in various environments (dry air, humid air, and liquid water) when rubbing with two kinds of oxide glasses. The experimental results indicated that the wear of Si3N4 was very sensitive to the presence of water and the counter-surface it rubbed against. When rubbing against soda lime glass, the expected mechanical wear of Si3N4 was observed in dry air, and the normal tribochemical wear of Si3N4 occurred in the presence of water (humid air and liquid water). In contrast, when rubbing against phosphate glass, wearless behaviors were observed for Si3N4 surface in all tested environments (dry air, humid air, and liquid water). Moreover, when rubbing against phosphate glass, the abnormal wearless behaviors were also observed for other ceramic materials, such as alumina, zirconia, and silicon carbide. Analyses suggested that poor mechanochemical durability of phosphate glass and the phosphorus-containing compounds in the wear debris were mainly responsible for the wearless behavior of ceramic ball surfaces. Results in present paper could provide insights into the tribochemical wear mechanisms of Si3N4 materials in order to optimize their tribology design.

Investigation of the role of Mg and Ca in the structure and durability of aluminoborosilicate glass

The structure and dissolution behaviour of Na2O·CaO·(15–x)Al2O3·xB2O3·SiO2 and Na2O·MgO·(15–x)Al2O3·xB2O3·SiO2 glasses, relevant to compositions of UK nuclear waste glass, have been investigated using nuclear magnetic resonance (NMR) spectroscopy and static dissolution experiments using the PCT protocol. Structural data from 11B, 27Al and 29Si NMR analyses show that increasing the [B2O3]/([Al2O3] + [B2O3]) ratio of the alkali-alkaline-earth aluminoborosilicate glasses led to an overall decrease in the proportion of non-silicate tetrahedral species (IVAl + IVB) and a decrease in SiOX bonds (XB, Al). The Mg-containing glasses exhibited lower IVB fractions than their Ca-containing counterparts, which is thought to be due to the presence of IVMg tetrahedra in the network. The measured corrosion rates were similar for both Ca and Mg-containing glasses although unexpectedly some Ca-containing glasses exhibited higher corrosion losses than the Mg-containing ones for time periods up to 112 d. However, there was evidence of a greater tendency to rate resumption in the Mg containing than the Ca containing ones. Alteration products were found to contain Ca, Si and Al with the Ca containing glasses and Ca, Mg, Si and Al with the Mg containing glasses; Na was not detected in the alteration products although its presence cannot be ruled out based on the data obtained.

Improvement of Electrical Conductivity and Chemical Durability in Fe₂O₃ Doped V₂O5-B₂O₃-P₂O5 Glasses.

In this study, we verified the relationship among the electrical conductivity, chemical durability, and structure of conductive vanadate glass in which Fe2+-Fe3+ and V4+-V5+ systems simultaneously coexist. We prepared samples of iron vanadium borophosphate glass with various compositions given by 78V₂O5-15P₂O5-7B₂O₃-xFe₂O₃ (1, 5, 7.5 and 10 mol%) and analyzed the electrical conductivity, chemical durability, FTIR spectra, thermal properties, density, and molar volume. The results indicated that the addition of Fe₂O₃ improved the electrical conductivity, chemical durability, and thermal properties. The following conclusions could be drawn: Fe2+-O-P bonds or Fe3+-O-P bonds were generated in the glass structure, and Fe3+ and Fe2+ ions were located at tetrahedral and octahedral sites. Furthermore, V═O bonds were expected to be replaced with Fe-O-V and P-O-V bonds, which are stronger than double bonds, so that the complete glass structure was strong. The structural reinforcement of the glasses was additionally confirmed based on thermal and chemical properties and electrical conductivity.