Sodium Aluminosilicate Glasses Research Articles

Strength Increase of Alumina Foams by a Sodium Aluminosilicate Glass Coating with Subsequent Na+ ↔ K+ Ion Exchange (Gorilla Glass Coating)

Reticulated alumina ceramic foams manufactured by the Schwartzwalder technique are coated with a sodium aluminosilicate glass using an aqueous precursor containing alumina particles and sodium silicate. After a heat treatment, a well‐adhering glass layer with a thickness between 10 and 120 μm is obtained. Besides the strut surface, the glass phase also penetrates the hollow strut cavities as well as strut cracks. The total porosity of the glass‐coated foams is between 88% and 90%, and the open cellular structure is not negatively affected by the glass coating. The compressive strength increases by a factor of two under consideration of the decrease in total porosity; a compressive strength in the order of magnitude of 2 MPa is feasible. An ion exchange of Na+ by K+ into the glass coating layer (chemical strengthening) is successfully demonstrated, but does not result in an additional improvement of the compressive strength.

Investigating cerium redox changes between aluminosilicate glass and melt: A multispectroscopic approach.

Redox control of glasses is paramount both to their fusion process and to obtaining the desired properties of high technological glasses. However, the link between melting parameters, such as temperature, furnace atmosphere, or quenching rate, and the redox state of the final products is poorly understood. In this work, in situ x-ray absorption near-edge structure (XANES) data at Ce L3-edge data were acquired at high temperatures on cerium-containing sodium aluminosilicate glasses, allowing the determination of thermodynamic constants necessary to predict the cerium redox state over a wide temperature range (900-1500 °C). The results obtained were compared to the Raman spectra of samples quenched at different temperatures. Our findings demonstrate that the quench performed was fast enough to block the cerium oxidation state, meaning the redox measured at room temperature is representative of a high temperature state. This was further verified by room temperature Raman spectroscopy, where a relationship was found between the spectra and melting conditions. Wet chemical analysis, XANES at Ce L3-edge, Raman spectroscopy, and optical absorption spectroscopy were successfully used to determine the redox state of cerium in aluminosilicates.

Elastic wave velocity measurements of sodium aluminosilicate glass and melt at high pressure and temperature

The combination of ultrasonic technique with synchrotron X-ray diffraction and radiography in a multi-anvil apparatus was utilized to measure the elastic wave velocities of sodium aluminosilicate glass and melt with the partially depolymerized composition of Na3AlSi3O9 (NAS). The measurements were conducted at pressure and temperature of up to 7.3 GPa and at ambient temperature for glass and up to 4.3 GPa and 2120 K for melt, respectively. The compressional wave velocity (VP) of the NAS glass remained mostly constant up to 4 GPa; subsequently, it increased with increasing pressure. Additionally, the NAS glass exhibited a minimum shear wave velocity (VS) at 4–5 GPa. Alternatively, the VP of the NAS melt was smaller than that of the NAS glass, showing a velocity minimum at ∼2 GPa. The negative pressure dependence of VP of the NAS melt is completely different from the depolymerized diopside (Di) melt, which shows a monotonic increase in VP with pressure. The contrasting behavior of the NAS and Di melts is caused by the difference in their structure, characterized by their degree of polymerization. Natural magma found in the interior of the Earth, such as basalt, has a partially depolymerized composition. This study indicates that the magma can exhibit elastic properties with negative pressure dependence, similar to the NAS melt.

Effect of alkali and alkaline-earth metal oxides on the chemical strengthening properties of sodium alumino-silicate glasses

Silicate based alumino-sodium (SAS) glasses were fabricated with various alkali (Li2O and K2O) and alkaline-earth metal (MgO and CaO) oxides to study their influence on chemical strengthening characteristics such as surface compression stress (CS) and depth of layer (DOL) after ion exchange of Na+ with K+. Introducing Li2O instead of Na2O decreased DOL while increasing CS up to 5.0 mol. % of Li2O. In contrast, replacing Na2O content with K2O increased DOL while decreasing CS. When alkaline-earth oxides such as MgO and CaO were substituted for Na2O, both CS and DOL decreased. Micro-Raman spectroscopy was used to study structural changes induced by alkali and alkaline-earth oxides and their impact on ion exchange properties. The inter-diffusion coefficients of K+ ions were predicted by employing the Boltzmann-Matano equation to support the chemical strengthening effect of various alkali and alkaline-earth elements in SAS glasses.

Effects of Na/Al ratio on phonon sideband spectra and luminescent characteristics of Eu3+ doped sodium aluminosilicate glasses

In this work, sodium aluminosilicate (NAS) glass systems were fabricated via traditional melting technique with various Na/Al ratios. Structure and surface morphology of the fabricated glasses were investigated by X-ray diffractometer, Raman spectroscopy and SEM images. Optical characteristics of the fabricated glasses were inspected by photoluminescence (PL) and photoluminescence excitation (PLE) spectra, and the observations showed that intensity of the excitation peak of Eu3+ ions in the NAS glasses at 392 nm increases while one at 463 nm decreases with the increasing of Na/Al ratio. Analysis of the phonon sideband spectra shown a change of multiphonon relative rate (Wmp/W0) of the synthesized glasses relates to Na/Al ratio. By applying the Judd-Ofelt theory, Ωλ = 2,4,6 parameters were evaluated from the PL spectra and used these parameters to estimate the radiative parameters like calculated lifetime (τcal), effective line width (Δλeff), transition probability rate (A), emission cross-section (σp) and branching ratio (βR). Decay curves were measured to investigate luminescence quantum efficiency (η) of Eu3+ emission and η gets value in the 53%–65% region. The color coordinates (x, y) and correlated color temperature (CCT) were also estimated for the synthesized NAS glasses.

Viscous healing of Vickers indentation–induced cracks in glass

AbstractViscous healing of cracks induced by the Vickers indentation in a soda lime magnesium silicate, a soda borosilicate, and a soda aluminosilicate glass (NAS) was studied by laser scanning microscopy. Plots of the crack length, width, and depth normalized to the initial crack length versus time over viscosity merge into single master curves of each of these quantities for each glass. Despite glass properties do not differ strikingly from each other, however, these master curves strongly differ among the glasses. This finding was attributed to a different interplay of various crack healing phenomena. Lateral cracks were found to be responsible for the bulging of the sample surface around the Vickers imprint, which in turn promotes radial crack widening as the main cause of healing delay. The most rapid healing of lateral cracks was observed in NAS in which bulging and crack widening were least pronounced.

Temperature dependence of interfacial reactions of sodium aluminosilicate glasses from reactive molecular dynamics simulations

Understanding the interfacial reactions of sodium aluminosilicate (NAS) glass surfaces in aqueous environments is of great scientific and technological importance. This work investigates the impact of temperature on the kinetics and mechanisms of NAS glass-water interfacial reactionsby using molecular dynamics simulations with reactive potentials. The results show that the propagation depth of water molecules increases significantly with increasing temperature from 298 Kto 363 K. Higher temperatures also accelerate the formation of silanol groups. Importantly, it was found that the hydrolysis of Al-O-Al and Si-O-Al linkages are more facile than Si-O-Si linkages for all the tested temperatures, suggesting that the Si-O-Si linkages are the most stable in the network glass structures. Higher concentration of Al2O3and higher Al/Na ratio lead to a decrease in dissolved Na+ion concentrations and a lower solution’s pH values, suggesting higher chemical durability of the glasses with the addition of alumina. The temperature was also found to affect the Na+ion dissolution kinetics. At 298 K, the dissolved Na+concentration saturates atAl/Na ratio close 1, but at 363 K, it decreases with increasing Al/Na ratio. These results provide atomistic insights into interfacial reaction mechanisms and temperature dependent reaction kineticsof NAS glasses.

Composition Effect on Interfacial Reactions of Sodium Aluminosilicate Glasses in Aqueous Solution.

Understanding the underlying reaction mechanisms responsible for aluminosilicate glass dissolution in aqueous environments is crucial for designing glasses for technological applications ranging from architecture windows and touch screens to nuclear waste disposal. This study investigated the glass composition effect on the interfacial reactions of sodium aluminosilicate (NAS) glasses using molecular dynamics (MD) simulations with recently developed reactive potentials. Glass-water interfacial models of six NAS glasses with varying Al2O3/Na2O ratios were investigated for up to 4 nanoseconds (ns) to elucidate the interfacial reaction mechanisms at ambient temperature. The results showed that the coordination defects, such as undercoordinated Si and Al, as well as non-bridging oxygens (NBOs) accumulated at the glass surfaces, play a crucial role in the initial hydration reaction process of the glasses. They promote the formation of silanol (Si-OH) and aluminol (Al-OH) species together with the Na+⇔ H+ ion-exchange reactions. The z-density profiles of H2O and H+ ions affirmed the water/H+ propagation into the glass up to 2 nanometers after 4 ns reactions. The penetration depth depends on the composition and shows a nonlinear dependence, suggesting that the subsequent water penetration, particularly into the bulk glass, is supported by the availability of random channels. Aluminol formations, including Al-OH or Al-OH2 near the surface, were found to form mainly through the hydrolysis of Al-O-Al bonds and hydration of Al+-NBO- units. While water molecules are involved in initial interfacial reactions, water penetration into the bulk glass region is primarily achieved by proton transfer. Compared to highly mobile proton transfer involving silanol groups, proton transfer associated with [AlO4]- species is much more limited, particularly in the bulk glass region. These new insights into the role of aluminum in interfacial reactions of the NAS glasses can help to understand the initial dissolution mechanisms and in designing more durable glasses.

Composition Dependence of the Atomic Structures and Properties of Sodium Aluminosilicate Glasses: Molecular Dynamics Simulations with Reactive and Nonreactive Potentials.

Understanding the composition-structure-property relations of glass materials is essential for their technological applications. In this study, the structures and properties of a series of sodium aluminosilicate glasses with varying Al2O3/Na2O ratios ((35 - x)Na2O-xAl2O3-65SiO2, x = 0, 5, 10, 15, 17.5, 20) covering peralkaline to peraluminous compositions, have been studied by using molecular dynamics simulations with two types of interatomic potentials: a fixed partial charge pairwise potential (Teter) and a reactive diffusive charge reactive potential (DCRP). The short and medium structural features such as bond lengths, coordination numbers, Qn distributions, and ring size distributions were obtained and compared with experimental data. It was found that silicon remained fourfold-coordinated throughout the compositional range, while a noticeable amount of fivefold-coordinated aluminum together with oxygen triclusters (TBO) are present in compositions with higher Al2O3 contents (RAl/Na > 1). In addition, the simulation results from both potentials show a certain level of violation of the Al avoidance rule by exhibiting a non-negligible amount of [AlOx]-[AlOx] polyhedral connections. Neutron and X-ray diffraction structure factors of the simulated glasses were calculated and compared with available experimental data. The mechanical properties, including Bulk, Shear, and Young's modulus, were calculated and found to increase with increasing RAl/Na, in good agreement with the experiments. Correlations of the properties with glass structures as a function of glass compositions and the advantages as well as potential issues of the two sets of potentials in modeling sodium aluminosilicate glasses are discussed in the context of features of glass structures and the prospect of future simulations of glass-water reactions.

Influence of interatomic potential and simulation procedures on the structures and properties of sodium aluminosilicate glasses from molecular dynamics simulations

The effects of various simulation parameters such as interatomic potential, cooling rate, system size, and glass-formation procedures on the short and medium range structures of sodium aluminosilicate glasses were investigated using molecular dynamics simulations. Two widely used interatomic potentials: a fixed-charge pair-wise potential and a diffusive charge reactive potential (DCRP) were investigated. To provide validation of the simulation results, high energy X-ray and neutron diffraction studies of the sodium aluminosilicate glasses were performed. The results show that the reactive potential provides reasonable structures consistent with those from the fixed charge potentials and experiments. But the fixed charge potential is more robust in various glass forming procedures such as constant pressure, constant volume, and the QSQ method, while DCRP is more sensitive to the ensemble choice and thermal history. The DCRP potential, however, has the advantage to allow study glass-water interactions and interfacial behaviors.

Molecular modeling of the thermal poling of sodium aluminosilicate glasses

Thermal poling is a process by which network modifiers are depleted from the surfaces of oxide glasses through the application of an electric field at moderate temperatures. Several kinetic and thermodynamic questions regarding the glass structure within the depleted layers as well as the process by which they are created remain unanswered. In this study, we develop a Molecular Dynamics (MD) simulation method to create Na-depleted layers in sodium aluminosilicate glasses. We observe that as the ratio of Al2O3 to SiO2 concentration increases, all other conditions being equal, the thickness of the Na-depleted layer decreases. Detailed structural analysis of the Na-depleted layer reveals a decrease in the fraction of 4-coordinated Al and an increase in the fraction of higher (5 or 6)-coordinated Al. This re-distribution of Al coordination is also accompanied by a reduction in Non-Bridging Oxygen (NBO) and an increase in Oxygen Tri-Coordinated (OTC). Overall, our results agree with previous experimental studies and suggest that MD can be an effective tool to gain insights into the significant structural re-arrangements that occur in oxide glasses during thermal poling.

Judd-Ofelt analysis of Eu3+ and adjustable emission in Eu3+/Eu2+ co-doped sodium aluminosilicate glasses

Europium-doped sodium aluminosilicate glasses were synthesized by using the melt quenching technique. X-ray diffraction, photoluminescence spectra and luminescence decay of Eu3+ ions in glasses were investigated to estimate structural and optical properties of the prepared glasses. Phonon energies, Judd-Ofelt (JO) intensity parameters Ωλ (λ = 2, 4, 6) and radiative properties such as transition probability (A), radiative lifetime (τ), and branching ratio (βR) of Eu3+ ions in the prepared glasses were determined and Eu3+ emission may be suggested for suitable laser applications because of its high value of βR = 70.8%. The adjustable emission of Eu3+/Eu2+ from red light to blue light can be reached by heating the prepared glasses in H2 gas with various temperature and heating time. The reduction process from Eu3+ to Eu2+ ions in the glasses increases and maximum of Eu2+ emission shifts to the long wavelength with the increasing of temperature and heating time, that indicated the increase of the crystal field of sodium aluminosilicate heated in H2 gas.

Leaching and Reactivity at the Sodium Aluminosilicate Glass–Water Interface: Insights from a ReaxFF Molecular Dynamics Study

In this study, we used ReaxFF reactive force field molecular dynamics (MD) simulations to investigate the dynamics associated with reactivity at the sodium aluminosilicate (NAS) glass–water interface. By combining van Hove correlation functions and visual analysis of individual trajectories, we found that when a Na+ ion leaves its initial position at the glass surface under the effect of water, it can be replaced either by a H+ ion or by another diffused Na+, resulting in a (Na+ ⇌ H+) ion exchange or (Na+ ⇌ Na+) ion exchange, respectively. These rearrangements at the NAS glass–water interface take place through many events such as the formation of oxygen-bearing functional groups (silanol Si(OH), germinal silanol Si(OH)2, and Al(OH)) and the agglomeration of Na+ ions on the glass surface. The high affinity between water and Na+ ions leads to two events, namely, the penetration of the water molecule into the first glass layer and the release of Na+ ions into the bulk water. The release of sodium ions into bulk water takes place via several successive steps: (1) leaving their original position to an area more exposed to bulk water, (2) diffusion to the surface of the glass, (3) leaving the surface toward the solution, and (4) coming back to the glass surface. Statistical analysis shows that oxygen-bearing functional group formation occurs both by protonation of the nonbridging oxygen (NBO) site and by filling defects such as SiIII, AlIII, and AlIV by OH– resulting from the dissociation of water molecules, while in the bulk, they could be produced by the proton jumps between two adjacent NBO sites and dissociation of the water diffused in deep layers of glass. Germinal silanol groups (Si(OH)2) are present in small amounts in the first layer of the glass after the protonation of two NBOs from a single SiIV. This process is accompanied by the conversion of AlIII and AlIV units into AlV units and SiIII units into SiIV units. By comparing the networks of Si and Al, we found that Al is more impacted by the occurrence of water molecules than Si, which is explained by an increase in the diffusion coefficient of Al compared with Si when these units become protonated (Si(OH) and Al(OH)).

Surface damage resistance and yielding of chemically strengthened silicate glasses: From normal indentation to scratch loading

AbstractWe report on surface elasticity, plastic deformation and crack initiation of chemically strengthened soda‐lime silicate and sodium aluminosilicate glasses during lateral indentation and scratch testing. Instrumented indentation using a normal indenter set‐up corroborated previous findings on the effects of chemical strengthening on surface Young's modulus, hardness, and indentation cracking. Using lateral indentation in the elastic‐plastic regime, we find a pronounced increase in the scratch hardness as a result of chemical strengthening, manifest in higher work of deformation required for creating the scratch groove. Thereby, the glass composition is found to play a stronger role than the absolute magnitude of surface compressive stress. Using a blunt conical stylus for instrumented scratch testing reveals three distinct modes of scratch‐induced surface fracture, which occur during scratching or after unloading. Occasional micro‐cracking caused by pre‐existing surface flaws at low scratching load can be completely suppressed through chemical strengthening. The intrinsic defect resistance to microcracking is reduced as a result of ion stuffing, depending on the initial glass composition, whereas the resistance to abrasive yielding is enhanced by several hundred MPa.

Structure and crystallization behavior of phosphorus-containing nepheline (NaAlSiO4) based sodium aluminosilicate glasses

The study aims at understanding the structural role of P2O5 in meta- and per-aluminous sodium aluminosilicate glasses, followed by its correlation with their crystallization behavior. Experimental results suggest an increase in the degree of polymerization of the phosphate network and a change in the aluminum environment in the glasses from Al(OSi)4 to Al(OP)4 with an increasing P2O5/SiO2 ratio. The substitution of SiO2–by–P2O5 in the amount varying between 10 – 20 mol.% suppresses the crystallization of nepheline. This has been attributed to the unavailability of Al3+ (to form Si–O–Al linkages) due to the formation of Al–O–P linkages in the glass structure. An increase in P2O5 content (>20 mol.%) in peraluminous glasses results in the crystallization of AlPO4 as the primary phase. The results have been discussed in the light of various models developed to predict the compositional dependence of nepheline crystallization in Hanford's high-level waste glasses.

Chemical Strengthening of Sodium Aluminosilicate Glasses Containing P2O5 and B2O3

Sodium alumino-silicate (SAS) glasses were synthesized with varying P2O5 and B2O3 contents, and their effect on chemical strengthening properties such as surface compressive stress (CS) and depth of layer (DOL) was examined. When P2O5 replaced SiO2, CS decreased, while DOL increased with P2O5 content. In contrast, B2O3 improved CS at the expense of DOL. The simultaneous addition of P2O5 and B2O3 with varying ratios also changed CS and DOL depending on the P2O5 and B2O3 content. The interdiffusion coefficients of K+ ions in SAS glasses were estimated using the Boltzmann–Matano equation and supported the observed effects of P2O5 and B2O3. Structural modifications related to changes in chemical strengthening properties were monitored by Raman spectroscopy and discussed.

A modified random network model for P2O5-Na2O-Al2O3-SiO2 glass studied by molecular dynamics simulations.

We investigated the short- and medium-range structural features of sodium aluminosilicate glasses with various P2O5 (0–7 mol%) content and Al/Na ratios ranging from 0.667 to 2.000 by using molecular dynamics simulations. The local environment evolution of network former cations (Si, Al, P) and the extent of clustering behavior of modifiers (Na+) is determined through pair distribution function (PDF), total correlation function (TDF), coordination number (CN), Qxn distribution and oxygen speciation analysis. We show that Al–O–P and Si–O–Al linkage is preferred over other connections as compared to a random model and that Si–O–Si linkage is promoted by the P2O5 addition, which is related to structural heterogeneity and generates well-separated silicon-rich and aluminum–phosphorus-rich regions. Meanwhile, due to the relatively high propensity of Al to both Si and P, heterogeneity can be partly overcome with high Al content. A small amount of Si–O–P linkages have been detected at the interface of separated regions. Clustering of Na+ is also observed and intensified with the addition of P2O5. Based on the simulated structural information, a modified random network model for P2O5-bearing sodium aluminosilicate glass has been proposed, which could be useful to optimize the mobility of sodium ions and design novel functional glass compositions.

Transition in deformation mechanism of aluminosilicate glass at high pressure and room temperature

AbstractDeformation experiments for 20(MgO or Na2O)‐20Al2O3‐60SiO2 glasses were performed in simple shear geometry at 1.5‐5 GPa and room temperature. An abrupt change in the thinning rate and the turning of the birefringence azimuth at a shear strain of γ = 1‐2 indicate a transition of deformation mechanism from uniaxial compression aided by densification to shear flow in the glasses. The high‐dense magnesium aluminosilicate glass showed strain softening controlled by the rearrangement of the tetrahedral network. On the other hand, low‐dense sodium aluminosilicate glass deformed by packing‐induced flow associated with densification and via the rearrangement of the tetrahedral network at lower and higher strains, respectively. The transition of the deformation mechanism was triggered by the limitations of the densification of the tetrahedral network. The difference of deformation mechanism brought about higher strain in magnesium aluminosilicate glass than sodium aluminosilicate glass at the same stress condition. Easiness of remarkable deformation, which relaxed residual stress, and high deformability contributed to the high ductility of the MgO‐aluminosilicate glass.

Investigation the effect of weathering on chemically strengthened flat glasses

Present work discusses weathering behavior of chemically strengthened flat glasses. With this aim, different soda-lime silicate and sodium aluminosilicate glasses were subjected to weathering tests before and after chemical strengthening to simulate possible scenarios that toughened glass products face and effect of weathering on topographical, optical, structural and mechanical properties were investigated. Topographical evaluations were made through roughness measurements and topography images using white light interferometery and atomic force microscopy techniques. Depth profiling was accomplished by time of flight secondary ion mass spectroscopy. Optical transmittance spectra were recorded with ultraviolet-visible-near infrared spectrophotometer. Structural properties were analzyed by Fourier-transform infrared spectroscopy. Mechanical testing was realized by applying biaxial bending and Vickers indentation tests. Experimental results revealed that soda-lime silicate glasses are more prone to corrosion when weathering takes place after chemical strengthening due to formation of alteration layers. This behavior can be altered by increasing alumina content in the glass composition.

Stress in ion exchanged soda‐lime silicate and sodium aluminosilicate glasses: Experimental and theoretical comparison

AbstractGlass samples of two different chemical compositions were strengthened by ion exchange. Residual stress profiles were experimentally determined by differential surface refractometry. The experimental results were compared with values theoretically predicted by a formalized viscoelastic mathematical model incorporating both stress buildup and stress relaxation contributions. The comparison exhibited a remarkable agreement both in terms of strengthening characteristics and stress profiles curves between experimentally measured and theoretically predicted values. The mathematical model incorporated terms directly linked to selected relaxation mechanisms either isochoric shear stress driven and fast relaxation. The comparison demonstrated the relevance of the stress relaxation mechanisms for the different glass chemical compositions. The approach presented in this study will allow the prediction of the mechanical behavior of chemically strengthened glass starting from its chemical composition together with the ion exchange process parameters.