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• Molecular dynamics simulations have been used to simulate sodium silicate and aluminosilicate glasses. • The effect of pressure during glass production on the final structure and mechanical properties has been investigated. • The distinct roles of aluminum and sodium has been unraveled. Aluminum strengthens glasses, while sodium acts differently, impacting structures as a compensator or modifier, shaping novel coordination environments. • Uniaxial tensile tests reveals that pre-densified glasses are more ductile than silicates thanks to the possibility of bond-switching during deformation. • Hydrostatic compression tests reveal that densification is largely reversible under varying pressure loads, with pre-treatment conditions significantly influencing residual densification. This study investigates the effects of pressure-induced densification on the structural and mechanical properties of albite-like (12.5 % Na 2 O·12.5 % Al 2 O 3 ·75 % SiO 2) and sodium silicate (12.5 % Na 2 O·87.5 % SiO 2) glasses using Molecular Dynamics simulations. Densification increased the coordination numbers of Al and Na, facilitated Al-O-Al clustering and formation of three-bridging oxygens, reduced T-O-T angles, and packed sodium ions in albite glass. Sodium silicate glass exhibited densification primarily through increased Na coordination, reduction of Si-O-Si angle and reduced Na-Na distances. Elastic modulus calculations revealed increased stiffness with densification due to enhanced atomic packing and glass reticulation. Uniaxial tensile tests showed densified glasses had higher ductility and strength than undensified counterparts, highlighting the positive effects of pressure-induced structural rearrangements. Hydrostatic compression tests demonstrated reversible densification under varying pressure loads, with pre-treatment conditions significantly affecting residual densification. [ABSTRACT FROM AUTHOR]

• A new molten-salt-bath-free ion exchange technique utilizing TiO 2 particles is proposed for ion exchange of silver. • Coloration and bactericide are verified for soda-lime-silicate and sodium-aluminosilicate glasses, respectively. • Glasses ion-exchanged using the TiO 2 -based slurry exhibit more uniform surfaces without any residues. In an effort to fully exploit the merits of molten-salt-bath-free ion exchange technique for alkali-containing glasses, in this study, TiO 2 -based slurry is employed in Na+ ↔ Ag+ reaction rather than the conventional kaolinite-based slurry. It is experimentally verified that both soda-lime-silica glass and sodium-aluminosilicate glass preserve their optical transmittance, without any residues on their surface and unwanted distortions after ion exchange using the TiO 2 -based slurry. A position-selective ion exchange is demonstrated by way of coloration due to presence of Ag0 particles in soda-lime-silica glass containing a small amount of Fe2+ ions. Antibacterial activity by Ag species is ascertained to be effective in the case of Fe-free sodium-aluminosilicate glass subjected to ion exchange adopting the TiO 2 -based slurry. Here, diffusion coefficient of Ag+ ions turns out to be tantamount to the corresponding diffusion coefficient values observed from the same category of glass ion-exchanged using a conventional molten-salt bath. The ion exchange technique proposed in this study would be more beneficial to applications where both optical clarity and morphological uniformity are more prioritized. [ABSTRACT FROM AUTHOR]

• Packing is a physical property that is directly related to atomic structure. • Lithium, zinc, lead, and bismuth borates were studied. • The fraction of four-coordinated boron is strongly correlated to packing in these borate glasses. • Lithium, lead, and bismuth silicate glasses were studied. • Changes in the numbers of non-bridging per silicon are related to packing trends in silicates. The densities of lead oxide and bismuth oxide modified glasses determined over a wide range of compositions were collected from the literature. Using these data as well as Shannon atomic radii and atomic masses, the glass systems' total packing fractions and oxygen packing fractions were computed. For borates, these fractions were correlated against the trend of the fraction of tetrahedral borate (N 4) units. This analysis was compared to that of lithium borate and silicate glasses and zinc borate glasses. The peak of the N 4 distribution versus R (= molar fraction of modifier/molar fraction B 2 O 3) corresponds well to the peak in oxygen packing in lithium and lead borate glasses but does not closely coincide with the peak in oxygen packing for zinc and bismuth glasses. In contrast to the borates, silicon in glassy silicate systems does not change coordination and the resulting packing trends change less than in the borates. Furthermore, the packing in the silicate systems is correlated to the change in Q n units. [ABSTRACT FROM AUTHOR]

Abstract Understanding and predicting the compositional dependence of the stiffness of silicate glasses is key for various technological applications. Here, we propose a new topological model for predicting the Young's modulus of silicate glasses. We show that the Young's modulus is governed by the volumetric density of bond-stretching and bond-bending topological constraints acting in the atomic network. The predicted Young's modulus values offer an excellent agreement with molecular dynamics and experimental data over a wide domain of compositions (the entire calcium aluminosilicate ternary system) and a large range of Young's modulus values (from around 80 to 160 GPa). Highlights • We present a new topological model for predicting the Young's modulus E of silicate glasses. • This model expressed E in terms of the volumetric densities of radial and angular constraints. • The model is tested to a large selection of calcium aluminosilicate glasses. • Our model shows an excellent agreement with simulated and experimental Young's modulus data. [ABSTRACT FROM AUTHOR]

Abstract The interaction of water with glass has a profound impact on its mechanical, chemical, and kinetic properties. Water can enter the glass network either as molecular form (H 2 O) or hydroxyl species (OH). The resulting impact of water on glass properties depends on the relative concentrations of hydroxyl to molecular species. While attenuated total reflection infrared (ATR-IR) spectroscopy can be used to determine the presence of these species in the subsurface region of glass, there is currently no approach to characterize their relative abundance in the glass surface. In this paper, we propose a calculating method for quantifying the ratio of hydroxyl to molecular water in silicate glasses based on a combination of ATR-IR spectroscopy and secondary ion mass spectrometry (SIMS). The technique is applied to leached soda lime silicate and sodium aluminosilicate glasses under a variety of process conditions. The method presented in this paper offers a new avenue for understanding the multiple roles of water in silicate glass network structure and topology. [ABSTRACT FROM AUTHOR]

Abstract The consistent development of the waste-minimisation and recycling-oriented technologies in the most resource- and energy-intensive industries is crucial for sustainable development. Chemical activation based on a non-fired or low-temperature approach for the production of binders from glassy aluminosilicates, including a wide range of wastes and by-products from different industries, is an intensively developing and promising clean technology that finds application in construction and building materials, management of hazardous and nuclear waste, etc. Blended binders are designed using a mixture of mineral materials as a tool, through the regulation of composition and structure, to obtain materials with controlled performance. The resulting materials in turn improve engineering performance and aid the valorisation of different types of wastes and by-products. This is one of the main trends in the development of the modern cement industry, including the alkali activation technology. Coal fly ash is one of the large-tonnage wastes that is effectively converted by alkali activation in binders and compatible with many mineral supplementary materials. This paper reviews (i) the supplementary mineral materials of natural and waste origin from different industries for alkali activated fly ash (class F) cements (AAFA); (ii) the composition, structure, and properties formation process of AAFA incorporated with blending and modifying materials, and (iii) the feasibility for improvement of the structures and properties of mixed AAFA. Highlights • Alkali activation is a clean technology minimising and recycling wastes and by-products. • Fly ash is compatible with many wastes and by-products of aluminosilicate nature. • Blending fly ash with supplementary materials improves alkali-activated cements performance. [ABSTRACT FROM AUTHOR]

Abstract The influences of boron on silicate glass dissolution behavior and crystallization have long been important in the nuclear waste glass and technical glass communities. Boron is a challenging component to model due to this ability to assume three- and four-fold coordinations with oxygen, as well as its ability to form complex structural units with silicate tetrahedra. Furthermore, the low atomic mass limits the available characterization techniques. In the present work, recent literature findings on the compositional influence on boron speciation are implemented to interpret new data on alkali boroaluminosilicate glasses studied with 11B nuclear magnetic resonance (NMR), synchrotron X-ray scattering (s-XRS), and chemical durability measurements. The purpose of this study is to understand the influence of boron on the crystallization behavior of sodium and lithium aluminosilicate systems, NaAl 1-x B x SiO 4 and LiAl 1-x B x SiO 4 , as applied to problems in nuclear waste vitrification. Comparisons are drawn between the alkali coordination number and crystallization behavior as a function of boron addition, as obtained through modeling of synchrotron X-ray total scattering using Empirical Potential Structural Refinement. Highlights • EPSR modeling of glasses with systematic boron addition and comparison to NMR. • N4 increases with increasing boron. • Crystallization propensity reduced with increasing alkali coordination. • Increase of glass corrosion at higher boron fractions due to greater interruption of glass network. [ABSTRACT FROM AUTHOR]

Abstract The relationship between the luminescence properties and the glass structure of Nd3+-doped CaO-Al 2 O 3 -(B 2 O 3 , SiO 2 , or Ga 2 O 3) glasses are investigated. The luminescence properties of CaO-Al 2 O 3 -B 2 O 3 system are twice as much as that of the CaO-Al 2 O 3 -(SiO 2 or Ga 2 O 3) system. The glass structure and the coordination environment of the Nd3+ ions were investigated using nuclear magnetic resonance, Raman and electron paramagnetic resonance spectroscopy. All Al, Ga, and Si atoms are four coordinated. The B atoms have three- and four-coordinated boron units, however, most of them are three coordinated. The hyperfine sublevel correlation spectra reveal that the Al and B nuclei are in the coordination sphere of Nd3+ ions for aluminoborate glasses; however, only 27Al signals could be observed for aluminosilicate and aluminogallate glasses. Owing to the increased number of AlO 4 -BO 3 connections and 11B nuclei around the Nd3+ ions, B has a significant effect on the luminescence properties of the Nd3+ ions. The increase in GaO 4 or SiO 4 does not change the three dimensional-tetrahedral network, and the coordination environment of Nd3+ ions varies slightly. Thus, the effect of Ga 2 O 3 and SiO 2 on the luminescence properties of the Nd3+ ions is not as great as that of B 2 O 3. Highlights • B has greater effect on the luminescence properties of Nd3+ ions than that of Si or Ga. • B changes the glass network greater than that of Si or Ga. • B has greater impact on the local environment of Nd3+ ions than that of Si or Ga. [ABSTRACT FROM AUTHOR]

Abstract Sixteen glasses of mixed keatite solid solution – cordierite stoichiometry, with 4 mol% TiO 2 as nucleating agent, were produced and ceramized to investigate their crystallization sequence. Employed analytical methods included differential scanning calorimetry, X-ray diffraction and scanning electron microscopy. Differences were identified already during the first ceramization stages: Al 2 O 3 /(Al 2 O 3 + SiO 2) and Li 2 O/(Li 2 O + MgO) ratios were crucial to determine which seed former phases would precipitate and the nucleation efficiency of each glass, reaching its maximum at Mg-free composition. Metastable formation of high quartz solid solution was observed in all samples; this phase was most persistent at Li 2 O/(Li 2 O + MgO) ratio equal to 0.33 and high SiO 2 -enrichment. Its destabilization led to the appearance of keatite solid solution and/or indialite, whose crystallization sequence and final relative amounts, as well as the microstructure of the glass-ceramics, were strongly influenced by the composition of the parent glasses. Highlights • Crystallization sequence of 16 glasses in the lithium-magnesium aluminosilicate system was studied. • Li 2 O/(Li 2 O + MgO) and Al 2 O 3 /(Al 2 O 3 + SiO 2) ratios influenced the nucleation mechanism and efficiency. • Metastable HQss crystals of different structural features decomposed into Kss and/or indialite. [ABSTRACT FROM AUTHOR]

Abstract A set of 12 glass compositions with distinct structural features have been designed over a broad composition space in the per-alkaline region of the Na 2 O – Al 2 O 3 – SiO 2 ternary system. As expected from a per-alkaline system, aluminum has been found to be tetrahedrally coordinated in all the glasses using 27Al magic angle spinning – nuclear magnetic resonance (MAS-NMR) spectroscopy and from structure models generated using molecular dynamic (MD) simulations. The physical properties of glasses, for example, density, coefficient of thermal expansion (CTE), glass transition, elastic moduli and Vickers hardness and brittleness have been measured experimentally and their trends have been explained based on the atomic structure of glasses, from both simulations and experiments. A reasonable agreement has been observed between the composition – structure – property relationship trends obtained experimentally when compared with those predicted by MD simulations. This demonstrates that MD simulation is a promising technique for predictive modeling and designing novel glass compositions for functional applications. [ABSTRACT FROM AUTHOR]

Geopolymers are new binders resulting from the activation of an aluminosilicate source by an alkaline solution. It is well-established that the precursors that are used affect geopolymer formation. This study focuses on how to control the geopolymer setting time with an alkaline silicate solution. To conduct this investigation, various geopolymer mixtures based on different alkaline silicate solutions were characterized in terms of viscosity and setting time. To understand the link between geopolymer formation and the properties of the solution, the ionic conductivity and the viscosity of the solutions were measured. The solutions were also characterized by Raman spectroscopy. The characterization of the geopolymer mixture shows that the properties of the alkaline silicate solution highly depend on the viscosity and setting time of the geopolymer. Therefore, the alkali molar concentration (3 < [M] < 10 mol·L −1 ) influenced the properties of the solution (silicate species, ionic conductivity, and viscosity). A relationship among the chemical composition, the silicate species of the solution and the geopolymer setting time is highlighted depending on the n si n Al + n M ratio. For example, a ratio of n si n Al + n M > 1.1 permits a slower geopolymerization reaction, and the setting time of the geopolymer mixture is higher. [ABSTRACT FROM AUTHOR]

Glasses and/or glass fibers of a new glass system, RE 2 O 3 (RE = Sc,Y, La)-MgO-CaO-Al 2 O 3 -SiO 2 , were studied in detail, covering rare earth (RE) effects on high temperature viscosity, liquidus temperature and crystalline phases, softening and glass transition temperature, and speciation reactions of aluminum (AlO x , x = 4, 5) and silicate network (Q n , n  = 4, 3, 2) using 27 Al and 29 Si MAS NMR and Raman spectroscopic methods. Rare earth oxides (RE 2 O 3 ) were shown to have a dual functionality, i.e., decreasing melt viscosity like a network modifier depolymerizing glass network, but increasing viscosity at low temperature, i.e., glass softening temperature (T soft ) and transition temperature (T g ), strengthening the glass network functioning like Al 2 O 3 . Liquidus temperature (T Liq ) was found to be sensitive to the type of RE 2 O 3 modifications in terms of their ionic field strength (IFS); Sc 3+ of the highest IFS increased, but La 3+ of the lowest IFS decreased T Liq . Effect of Y 3+ (intermediate IFS) on T Liq resembles Sc 3+ only at higher concentration. The overall results suggest that RE ions of different IFS have different “true” solubility limits in the host glass matrix, above which RE 2 Si 2 O 7 crystallizes. All of the glasses with and without RE 2 O 3 contained predominately four-fold coordinated aluminum, AlO 4 ; yet replacement of CaO by RE 2 O 3 increased AlO 5 according to 27 Al MQMAS NMR spectroscopic measurements. Raman spectroscopic results suggested that depolymerization of the silicate network. [ABSTRACT FROM AUTHOR]

The expanding raw materials base is one of the drivers for the further development of inorganic binders, including alkali-activated cements. This research focuses on studying marl with a high calcite/aluminosilicates ratio as a geopolymer precursor, and limestone as a mineral addition to this geopolymer. The calcination of marl at 800 °C resulting in the formation of reactive Si, Al, and Ca due to the dehydroxylation of clay minerals and decarbonation of calcite makes marl suitable for use as a geopolymer precursor. Calcined marl activated with sodium silicate and cured at ambient temperature had a 28-day compressive strength of 34 MPa. When incorporated with 50% limestone, the compressive strength became 39.2 MPa. XRD, TG/DSC, FTIR, optical and SEM have been used to investigate the reaction products, as well as the microstructure of the geopolymer hardened pastes. [ABSTRACT FROM AUTHOR]

The inherent brittleness and poor crack resistance of oxide glasses have always been among their main limitations for many advanced applications. As the formation of cracks leads to amplification of applied tensile stresses and ultimately catastrophic failure, there is an interest in understanding the compositional and structural dependence of crack initiation and growth. The resistance to cracking can conventionally be measured using instrumented indentation that mimics the real-life damage for certain applications. Wada introduced a method to evaluate the crack resistance by counting the number of initiated cracks as a function of the applied load. Experiments have shown that the environmental humidity and the time period between indentation and crack counting both affect the crack resistance value, but unfortunately these parameters are not always reported in literature studies. Here we perform a systematic study of the time and humidity dependence of crack initiation in calcium aluminosilicate glasses. Depending on the experimental conditions (time and humidity), the crack resistance of an aluminosilicate glass can vary by more than a factor of two. Furthermore, the observed radial/median cracks can initiate several hours after indentation. These results therefore indicate the need for a standardized procedure for determination of crack resistance to allow comparison of data from different research groups. We suggest including a sufficiently long waiting period (such as 24 h) between indentation and crack counting, as the majority of the crack initiation will then have occurred. [ABSTRACT FROM AUTHOR]

The elastic-plastic deformation in raw and ion-exchanged aluminosilicate glass is investigated by loading rate dependent nanoindentation. The nanohardness and Young's modulus of the raw and ion-exchanged glasses at different loading rate (100–20,000 μN.s −1 ) are explored up to a maximum load of 9000 μN. The nanoindentations are scanned with AFM to observe the morphology of the indents. The results show that Young's modulus of the aluminosilicate glass increases after ion exchange and that the nanohardness of the raw and ion-exchanged aluminosilicate glass increases linearly with the loading rate, when plotted on a double logarithmic axes. However, the nanohardness of the raw glass is more sensitive to the variation of loading rate. The compressive stress on the ion-exchanged glass can inhibit plastic deformation. These results are explained in terms of shear stress underneath the indenter and the number of the flow lines in the nanoindentations. These findings are useful for better understanding the dynamic contact-induced damage growth mechanisms of ion-exchanged glass. [ABSTRACT FROM AUTHOR]

The origin of the various manifestations of the mixed modifier effect in silicate glasses remains poorly understood. Here, based on molecular dynamics simulations, we investigate the origin of a negative deviation from linearity in the hardness of a series of mixed alkaline earth aluminosilicate glasses. The minimum of hardness is shown to arise from a maximum propensity for shear flow deformations in mixed compositions. We demonstrate that this anomalous behavior originates from the existence of local structural instabilities in mixed compositions arising from a mismatch between the modifiers and the rest of the silicate network. Overall, we suggest that the mixed modifier effect manifests itself as a competition between the thermodynamic driving force for structural relaxation and the kinetics thereof. [ABSTRACT FROM AUTHOR]

The present study aims to determine the influence of aluminum and calcium availability from two different aluminosilicate sources (COx argillite and sediment), thermally treated at 750 °C, on the formation, the structure and the working properties of the resulting alkali-activated materials. Despite their similar chemical composition, some differences in terms of aluminum coordination, amorphous phase and calcium availability were detected between the two studied aluminosilicate sources. Indeed, sediment sample exhibits higher reactive aluminum and lower reactive calcium compared to argillite sample. Moreover, FTIR spectroscopy has revealed that available calcium interacts with free silicon and aluminum and alkali cation in excess (sodium or potassium) leading to the formation of several networks (Si O Al and Si O Ca bonds). For both aluminosilicates, the calcium content (0.33 < Ca/Si < 0.36) seems to be not sufficient to produce C-S-H hydrated phases. It was also demonstrated that the low availability of aluminum in addition to the high availability of calcium favor the precipitation of secondary reaction products in the detriment of the geopolymer network. These products fill the voids inducing a decrease of the porosity and the pore size but also lead to higher heterogeneity that decreases the mechanical properties of the final material. However, the higher availability of aluminum and the lower availability of calcium in presence of high alkaline conditions favor the polycondensation reaction. [ABSTRACT FROM AUTHOR]

Alkali-free boro-aluminosilicate glasses were prepared by the melt quenching method. The effect of Al 2 O 3 replaced by different contents of Y 2 O 3 on the structure and various properties of alkali-free boro-aluminosilicate glasses was studied. The changes of glass structure with varying components were investigated by the Fourier transform infrared spectra. Simultaneously, the relationship between the glass structure and the coefficient of thermal expansion, density, vickers hardness, bending strength, glass transmittance and chemical stability was discussed. The results show that the coefficient of thermal expansion and the density of glass increase with the increase of Y 2 O 3 content. While, the chemical stability of the glass is reduced. The vickers hardness and bending strength decrease first and then increase with the Y 2 O 3 content increasing. All the glasses have excellent optical transmittance, reaching more than 85%. [ABSTRACT FROM AUTHOR]

The effects of alkaline earth metal oxides (RO) concentrations on the network structure and properties of non-alkali aluminoborosilicate glasses were studied. With the increasing of RO concentrations from 10 to 20 mol%, the number of Q 4 units decreased, while the number of Q 3 units increased. The [AlO 4 ] units always predominated in Al groups, and the fraction of [BO 4 ] among B groups increased from 2% to 10%. Meantime, the value of NBO/T increased from 0.48 to 0.70, indicating the weak network connectivity. The depolymerization of T-O-T network resulted in higher coefficient of thermal expansion, lower temperature of transition point, weaker durability in HF acid. While, the increasing in R 2 + cations and [BO 4 ] units led to the higher elastic modulus of glasses. The increasing in RO also enhanced the density, dielectric constant and durability in NaOH solution of glasses. [ABSTRACT FROM AUTHOR]

The bulk and surface structures, as well as physical properties such as ionic diffusion and mechanical moduli, of sodium borosilicate and boroaluminosilicate model nuclear waste glasses with composition similar to the international simplified glass (ISG) have been studied using molecular dynamics simulations with the recently developed partial charge composition dependent potentials. Short and medium range structures of these glasses were analyzed and it was found that, for glass former cations, silicon ion is all four-fold coordinated by oxygen, aluminum is also mainly four-fold coordinated, while boron exists in a mixture of 3- and 4-fold coordination, with the fraction of 4-fold coordinated B (N 4 value) close to but slightly higher than the experimental and theoretical values. The medium range structure features such as network former cation oxygen polyhedral connectivity, sodium distribution around the network formers, and network ring size distribution were characterized. The surface structure was generated from the simulated bulk glass structures and showed sodium enrichment on the glass surface. Addition of alumina to borosilicate glasses increased B N 4 value and overall glass network connectivity that led to improved mechanical properties. Ion diffusion properties, mechanical properties as well as surface characteristics for the simplified ISG have also been investigated with simulations and compared with available experimental data. This detailed atomic structure information provides insight of the physical properties of these glasses and a step further in understanding the chemical durability and dissolution behaviors. [ABSTRACT FROM AUTHOR]

Optical, structural properties and redox were studied for Ce-bearing silicate and aluminosilicate glasses and Ce-activated silica (SiO 2 ) fiber preforms, by X-ray Absorption, Raman and Photoluminescence Spectroscopy. The introduction of Al 2 O 3 in Ce-bearing silicate glass strongly stabilizes reduced species in agreement with the optical basicity concept and additionally induces modifications in the Ce 3 + surrounding. In Al-free silica preforms, depending on the collapsing conditions, the Ce 3 + /ΣCe ratio has the highest variability (Ce 3 + /ΣCe = 0.7–0.85 ± 0.07), whereas in Al-bearing fiber preforms, Al codoping induces a strong stabilization of Ce 3 + species, despite the collapsing atmosphere. Al presence induces modifications on Ce local environment, and thus variations of the distance between Ce 3 + and its ligands, and/or to variations of the covalency of the bonds. Absorption bands in the UV region, ascribed to Charge-transfer (CT) bands, in our samples, occur only for low amount of Ce 4 + (Ce 3 + /ΣCe > 0.85 ± 0.07). Indeed, in silicate and aluminosilicate glasses the higher amount of Ce 4 + does not give rise to UV absorption bands ascribed to CT processes, whereas, in fiber preforms, Ce 3 + species can induce the trapping of hole centers, and enhance the photoluminescence efficiency. More generally, these results enhance our understanding of REE structural and chemical roles in amorphous materials and increase our knowledge for technical applications. [ABSTRACT FROM AUTHOR]

The effect of low NiO doping (0–0.15 mol%) on the extinction coefficient of zinc aluminosilicate glass-ceramics prepared by five different two-stage heat treatments was studied experimentally. Extinction coefficient vs wavelength presented as a log-log plot was separated into scattering and absorption coefficients. The NiO addition drastically changes not only values of the scattering coefficient at a given wavelength of visible light (effect 1), but also the type of wavelength dependence of this coefficient (effect 2). These effects do not correlate with variation of sizes and volume fractions of nanocrystals determined by Rietveld refinement of X-ray diffraction data. They cannot be described in the model of independent Rayleigh scatterers. These effects are characteristic features of anomalous light scattering by inhomogeneous glasses and can be explained by interference of light scattered by different nanocrystals. To calculate interference effects, the detailed information on mutual arrangement of nanocrystals is required, which unlikely can be determined experimentally for multiphase polydisperse system of nanocrystals. Instead, simplified models for systems of nanocrystals in glass-ceramics can be considered. And finally, we cannot explain the mechanism of the effect of small NiO additions on light scattering and hence, on structure of glass-ceramics. [ABSTRACT FROM AUTHOR]

Brick clay mixtures are raw materials with the potential for use in geomaterials other than tiles or bricks. This study concerns the effect of mixed alkali cation solutions on the polycondensation reactions of geomaterials based on brick clay mixtures. To evidence the feasibility and the understanding of such effects, FTIR and Raman spectroscopy, thermal analyses and compressive tests were investigated to reveal the performance of the alkaline solution and aluminosilicate source. The various solutions used contained different siliceous species (rings, chains) that modified the polycondensation reactions and the Si-O-Ca bond formation. The effect of the polarizability of the alkaline and alkaline earth solutions must be controlled to enhance the final properties. Better mechanical properties were obtained with a low water content. [ABSTRACT FROM AUTHOR]

Silver ion-exchanged was employed to introduce silver into the surface layer of aluminosilicate glasses. Effects of salt composition and annealing conditions on the distribution, valence and clustering states of silver were investigated through emission and excitation spectra measurement. It was found that isolated Ag + ions, clusters of Ag 2 + and Ag 2 2 + , and other mixed species of Ag + ions and Ag 0 atoms were present in the ion-exchanged glasses. Upon UV excitation (250–400 nm), silver ion-exchanged glasses showed three distinct bands centers at 420 nm, 480 nm and 530 nm, exhibiting great potential for the UV light down-shifting. Using the silver ion-exchanged glass as cover, quantum efficiency of α-Si solar cell in the 280–318 nm spectral range was improved. [ABSTRACT FROM AUTHOR]

The energetics of structural mechanisms involving inter-conversions among oxygen species dictate structure and properties of oxide glasses. We explored the change in boron coordination as a function of fictive temperature in glasses containing Zr and/or Na. There was lower boron coordination in the Zr-containing glass, and there was less decrease in boron coordination with temperature. We relate this difference to changes in the energetics of Zr-O-Si and Na-O-Si linkages. Furthermore, we varied fictive temperature to explore the distribution of non-bridging oxygens (NBO) on Al and Si in a Ca aluminosilicate and a Y aluminosilicate. As temperature increased, Al-NBO% increased. We attribute this change with temperature to differences in the energetics of Si-NBO and Al-NBO, which result in a strong preference for Si-NBO that is predicted to persist over a wide temperature range. [ABSTRACT FROM AUTHOR]

The correlation between K + -Na + diffusion coefficient and mechanical properties of chemically tempered and hybridly tempered (thermally plus chemically tempered) aluminosilicate glass is investigated. First, the profile of the potassium ion concentration is experimentally measured, and the diffusion coefficient is calculated according to the Boltzmann-Matano approach. Second, the flexural strength and the Weibull modulus are determined using a method combining experimental (coaxial double ring) and finite element analysis. The results indicate that the flexural strength decreases with the diffusion coefficient of the air side for both types of glass samples, while there is no significant relationship between the diffusion coefficient and the Weibull modulus. The diffusion coefficient on the air side shows a higher value than that on the tin side. With the same diffusion coefficient, the flexural strength of chemically tempered glasses is found to be higher than that of hybridly tempered glasses. The effect of the diffusion coefficient on the modulus of rupture (MOR) for the hybridly tempered glass is more remarkable. These results would be useful for designing the glass strength and guiding the strengthening process by chemical or hybrid tempering. [ABSTRACT FROM AUTHOR]

In this work, thermal poling of ternary oxide glasses, including borosilicates and aluminosilicates, is studied using molecular dynamics. For the glass compositions simulated, results show that thermal poling lowers the Young's modulus of those ternary oxide glasses. Additionally, comparisons between the structures of as-melted and poled glasses, as well as comparisons with their binary as-melted counterparts of the same composition, reveal that the changes in elastic properties can be partially attributed to changes in void size distributions within those glass networks. Overall, this study shows that thermal poling can effectively be used to alter the elastic properties of oxide glasses. [ABSTRACT FROM AUTHOR]

Glasses with compositions SiO 2 -CaO-Al 2 O 3 -TiO 2 -Na 2 O were prepared by conventional melt quench technique. The dielectric properties of these glasses with a variation in alkali content over a frequency range from 20 Hz to 1 MHz and temperature variation of 30–280 °C have been investigated. The electric modulus representation has been used to provide comparative analysis of the ion transport properties in these glasses. The conductivity isotherms show a transition from frequency independent dc region to dispersive region where the conductivity continuously increases with increasing frequency. The present glasses exhibit conductivity in the range of 10 − 5 to 10 − 3 S/m which is higher than the alkali containing silicate glasses. Hysteresis loop observed at room temperature confirms the ferroelectric nature of glasses. [ABSTRACT FROM AUTHOR]

We have conducted a systematic analysis on dynamics and structure of aluminum-silicate melt at various pressures and at 3500 K. Firstly, the analysis with respect to network structure units reveals that the melt contains separate Si-O and Al-O subnets which evidences the micro-segregation of the liquid. We propose a model of solid-like particle to interpret the diffusivity for three types of atom. Secondly, from the analysis on the sets, immobile, mobile and random atoms we reveal the dynamics heterogeneity (DH) in the melt. Moreover the simulation also shows a clear correlation between DH and structural heterogeneity. Finally, the analysis with respect to O-simplex and T-simplex provides a new view on the structure of the melt. It was shown that there are not only T-clusters with one atom that form a simple network structure, but instead the melt contains a number of T-cluster with numerous atoms. The structure heterogeneity of silicate melt concerns two aspects: T-clusters and O-simplexes which contain extremely large number of atom. [ABSTRACT FROM AUTHOR]

Enabling accurate prediction of the properties of aluminosilicate glasses is important for the development of new glass compositions for high-tech applications. In this study, we use a combined topological and thermodynamic approach to connect the configurational heat capacity ( C p,conf ) with the liquid fragility ( m ) and glass transition temperature ( T g ) of calcium aluminosilicate glass-forming liquids. To study structural and dynamical features of these systems, we choose two representative glass composition series: one at the tectosilicate join with varying SiO 2 content and one with constant CaO content but varying Al 2 O 3 /SiO 2 ratio. C p,conf is determined using differential scanning calorimetry (DSC), while m and T g are determined through both DSC and viscosity measurements. The C p,conf model is found to predict the measured data well for most systems, but deviations between the modeled and measured C p,conf values appear for the "strongest" glasses in the tectosilicate series and for the most peraluminous glasses in the constant CaO series. We discuss the structural origins of these model-from-data deviations based on Raman spectroscopy measurements. [ABSTRACT FROM AUTHOR]

The incorporation of rare-earth (RE) elements into an aluminosilicate (AS) glass generally enhances its optical and mechanical properties. Atomistic molecular dynamics (MD) simulations were employed for probing the coordinations of Y 3 + and Sc 3 + in Y 2 O 3 –Al 2 O 3 –SiO 2 and Sc 2 O 3 –Al 2 O 3 –SiO 2 glasses of variable Si, Al, and RE contents. YO 6 and ScO 5 polyhedra are the most abundant RE species. We explore the trends in the distributions of the various (non)bridging oxygen species and Si/Al/RE cations in the first and second RE coordination spheres, respectively. The lowest RE [4] and RE [5] coordinations of both Y and Sc exhibit a strong preference for coordinating non-bridging O species, which gradually relaxes for increasing coordination number p . Clear deviations from a statistical Si/Al/RE distribution around the REO p polyhedra is observed, with preferences for RE–RE contacts relative to RE–Al and (notably) RE–Si. The extents of RE–RE associations are similar for Y and Sc and grow slightly for increasing Si content and/or glass network polymerization. The propensity for RE–Al contacts becomes emphasized in the Sc AS glasses, mainly at the expense of Sc–Si. The YO p and ScO p polyhedra connect to their Si/Al/RE neighbors primarily by sharing corners, but a significant extent of edge-sharing is also observed, which increases both with the RE [ p ] coordination number, and along the series Si

The effect of the variation in the Al 2 O 3 content on select physical properties of pristine and ion-exchanged glasses in the systems: (75 − x)SiO 2 mol%-25Na 2 O-xAl 2 O 3 and (75 − x)SiO 2 -15Na 2 O-10CaO-xAl 2 O 3 , are reported. The surface compressive stress, surface hardness and K + /Na + exchange ratio increase, while the depth of the interdiffusion distance decreases, with increasing Al 2 O 3 content. These trends are shown to be consistent with the compositional variation of the glass transition temperature and the molar volume, and their atomistic and thermodynamic bases are discussed. [ABSTRACT FROM AUTHOR]

The solubility of hafnium dioxide (HfO 2 ), used as a surrogate for tetravalent uranium, is measured in glass melts belonging to the CaO-Al 2 O 3 -SiO 2 and Na 2 O-CaO-Al 2 O 3 -SiO 2 systems, under oxidizing and reducing conditions. Two methods have been carried out to determine it and the kinetic factors controlling the HfO 2 dissolution in glass melt have been investigated in order to approach equilibrium. The solubility ranges from 3 to 6.5 mol% HfO 2 in aluminosilicate glasses at temperature between 1250 °C and 1400 °C, and is not affected by the redox conditions. Conversely, the solubility is modified by the melting temperature and the glass composition. The excess of alkalis or alkaline earths which are not involved in the charge balance of AlO 4 tetrahedrons in the silica network appears to play a significant role. Glass homogeneity is checked by scanning electron microscopy and X-ray diffraction. HfO 2 , HfSiO 4 , Ca 2 HfSi 4 O 12 , Na 4 Hf 2 (SiO 4 ) 3 and Na 2 HfSi 2 O 7 are metastable crystals observed in the glass melts. The stability of those crystalline phases mainly depends on the glass composition. [ABSTRACT FROM AUTHOR]

• Amorphous aluminosilicates have been prepared by coprecipitation at room temperature as low-cost ion exchangers. • Amorphous aluminosilicates show higher cation exchange capacity (CEC) than a synthetic mordenite and a natural zeolite. • The effect of the presence of K+ as competing cation on the ammonium removal efficiency was stronger than that of Na+. • Amorphous aluminosilicates can be regenerated with a KCl solution and reused for the ammonium removal. The efficient removal of ammonium cation, one of the main causes of the eutrophication of water sources, has been achieved by using amorphous aluminosilicates as low-cost ion exchangers. The materials with a Si/Al ratio that varied from 1 to 5 were prepared by the coprecipitation method just by mixing an acidic aluminium sulphate solution with a basic sodium silicate solution, and the products were characterized by XRD, SEM and 27Al MAS NMR spectroscopy. All the amorphous solids presented a higher cation exchange capacity (CEC) than a synthetic mordenite (Si/Al = 9.5) and a natural zeolite (Si/Al = 4.6). The ammonium uptake was investigated as a function of contact time and initial ammonium concentration; additionally, the presence of Na+ and K+ as coexisting cations in the solutions was also evaluated. Langmuir and Freundlich models were applied to describe the data obtained in the ammonium exchange isotherms. The amorphous aluminosilicate with Si/Al = 3 was regenerated with a KCl aqueous solution and was reused 5 times keeping a stable removal efficiency. The reusability of the amorphous aluminosilicate combined with the superior cation exchange capacity manifests the promising use of this type of materials as ion exchangers to remove ammonium cations from wastewater. [Display omitted] [ABSTRACT FROM AUTHOR]

• Novel SiOC/spodumene composites with tailorable CTE are obtained employing SPS. • Spodumene and SPS reduce the sintering temperature of the SiOC matrix at least 100 °C. • Spodumene promotes sintering of SiOC, then its phase separation and crystallization. • Low CTE (0.128 3 –1.902 × 10−6 K−1) is obtained at 1200 °C by the formation of β-spodumene. • The maximum values of h (11.5 GPa) and e (91 MPa) are reached at 1300 °C. Highly densified silicon oxycarbide (SiOC)/spodumene composites with low coefficient of thermal expansion (CTE) were obtained just selecting the spark plasma sintering temperature employed. For the first time we proposed the use of spodumene a cheap and natural available lithium aluminium silicate mineral as meltable/active filler for SiOC-derived composites, due to its powerful fluxing properties and also its very low CTE. SiOC/spodumene composites sintered at 1200 ⁰C display a very low CTE (0.128±0.004–1.902±0.002 × 10−6 K−1) due to the α,β-transformation of spodumene. At higher sintering temperatures the CTE increases to 3.288±0.004 × 10−6 and 4.516±0.006 × 10−6 K−1 (1300 and 1400 ⁰C) due to the β-SiC formation. In this range of temperature, spodumene promotes the phase separation of SiOC and subsequent crystallization of cristobalite and β-SiC. The maximum values of hardness (11.5 ± 0.5 GPa) and elastic modulus (91±4 MPa) are reached at 1300 ⁰C, where the SiOC/composite displays a neat densification and the lowest roughness (1.61±0.01 nm). [ABSTRACT FROM AUTHOR]

In this article, structural, thermal, and optical properties of zinc boro-aluminosilicate glasses with addition of different alkali (Li, Na, and K) and alkaline oxides (Mg, Ca, Sr, and Ba) have been reported. 10 mol% of alkali and alkaline oxides were incorporated into Zinc boro-aluminosilicate glasses and all these glasses possess high optical quality. Samples were characterized using X-ray diffraction (XRD), scanning electron microscopy and energy dispersive X-ray analysis (SEM-EDAX), attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy, Raman spectroscopy, thermo-gravimetric analysis (TGA), differential scanning calorimetry (DSC), and optical absorption spectroscopy. The XRD and SEM measurements demonstrated the amorphous origin for all the prepared glasses and EDAX confirms that all the elements are presented in the prepared glasses. The presence of various functional groups such as triangular and tetrahedral-borate (BO 3 and BO 4 ) was confirmed by ATR-FTIR and Raman spectra, and both of the ATR-FTIR and Raman spectra show lower phonon energy for H3 (K 2 O) in alkali series, and H7 (BaO) for alkaline. From TGA analysis we found a lower weight loss < 0.1% in K 2 O, MgO, and BaO; and from the DSC profiles the glass transition temperature (T g ), onset crystallization temperature (T x ), crystallization temperature (T c ), and melting temperature (T m ) were identified and related different thermal parameters are evaluated. Alkali and alkaline influenced Zinc boro-aluminosilicate glasses demonstrate excellent glass stability. From the optical absorption spectra, we calculated cut-off wavelength and it shows spectral shifting to longer wavelength with alkali (Li → Na → K), and alkaline (Mg → Ca → Sr → Ba) modifiers. We investigated optical band gap energy also for allowed transitions in UV–visible region using three methods; direct, indirect, and absorption spectrum fitting (ASF). [ABSTRACT FROM AUTHOR]

Viscosity and diffusivity of silicate melts and glasses are related to each other through relaxation timescales. The systematic is explored based on published data. Diffusion coefficients for Sr and Ba were measured in calcium aluminosilicate glasses at conditions near the glass/supercooled liquid boundary in temperature – time space making use of thin film technology and Rutherford Backscattering Spectroscopy (RBS) to measure concentration profiles on nanoscales. These data extend the range of published diffusion coefficients and combined with the systematic noted above allow the nature of change of diffusion coefficients across the glass transition region to be studied. Activation energies for diffusion in the glassy state (~ 360 kJ/mol) are higher than in the molten liquid (~ 213 kJ/mol). A defect based model of glass transition derived by Ojovan and coworkers, where attainment of a percolation threshold of configuron-type defects accounts for the glass – liquid transition, can explain the observed diffusion behaviour. Data treatment using this model yields a defect formation enthalpy of ~ 146 kJ/mol and a migration enthalpy of ~ 213 kJ/mol. The results of this study provide generalized expressions for the prediction of diffusion coefficients of cations in silicate melts for any composition at any temperature. [ABSTRACT FROM AUTHOR]

Understanding and controlling materials' resistance to fracture is critical for various applications. However, the structural origin of toughness, brittleness, and ductility remains poorly understood. Here, based on the experimental testing and atomistic simulations of a series of aluminosilicate glasses with varying thermal and pressure histories, we investigate the role of structure in controlling fracture toughness at fixed composition. We show that fracture toughness decreases with density, but strongly depends on the details of the temperature and pressure histories of the glass. This behavior is found to arise from a loss of nano-ductility rather than a loss of cohesion. Finally, we demonstrate that the propensity for nano-ductility is primarily controlled by the extent of angular flexibility between the rigid polytopes of the network. Tuning the extent of nano-ductility in silicate glasses would permit the design of ultra-tough glasses. [ABSTRACT FROM AUTHOR]

A set of empirical potentials have been developed to enable molecular dynamics simulations of oxide glasses with the most common glass formers: silica, boron and aluminum oxides. Built upon the recent borosilicate potentials, this set of partial charge effective potentials features composition dependent variable atomic charges and pairwise short range interactions that ensure high computational efficiency. They can correctly reproduce the short range structure features of boroaluminosilicate glasses including [SiO 4 ] tetrahedral network, aluminum coordination, and, importantly, the coordination change of boron as a function of composition. By using the newly developed potentials, a series of sodium boroaluminosilicate glasses were simulated and the structures analyzed in terms of bond distance, bond angle, and coordination number, which were compared with available theoretical, simulation and experimental results. Structural analysis such as polyhedral connectivity analysis, Q n analysis, and ring size distribution were obtained to investigate the medium range structure features of these glasses. Furthermore, mechanical properties such as Young's, shear and bulk moduli were calculated and were found to be in good agreement with experimental data. The vibrational density of states was also calculated and compared with previous MD and ab initio results. The results show [3] B and [4] B had distinctive spectra features and vibrational spectra were in good agreement with earlier ab initio studies. [ABSTRACT FROM AUTHOR]

Iron-calcium-aluminosilicate glasses with additions of different amounts of ZnO were prepared. The influence of ZnO on the structure, physical properties, crystallization and sintering of the glasses has been investigated. The FTIR spectroscopy reveals that the addition of ZnO leads to the increase of non-bridging oxygen. ZnO acts as a glass modifier, residing in the voids of the glass network, resulting in a linearly increase of the glass density with ZnO. Due to the increasing discontinuity of the glass network, the glass transition point decreases with ZnO, indicating the reduction of the glass viscosity, which facilitates the sintering of the glass with a high amount of ZnO. However, Zn 2 + also has aggregation effect on the glass network, leading to the decrease of the thermal expansion coefficient. All glasses show surface crystallization, however, the crystallization tendency decreases with ZnO. Ferroan wollastonite (Ca 2.87 Fe 0.13 (SiO 3 ) 3 and silicon oxide are mainly identified in the thermally treated samples. [ABSTRACT FROM AUTHOR]

We evaluate the fracture mechanism in the binary aluminosilicate glasses using molecular dynamics simulations. The simulations using two independent force fields reveal that increasing the alumina content promotes shear and suppresses fracture, thereby increasing the intrinsic ductility, in agreement with experimental observations. In indentation simulations, it is directly demonstrated that the deformation mechanism shifts from densification to shear flow with the increase in alumina content. The origin of this intrinsic ductility is that the Al atoms are more amenable to plastic flow and can reduce the creation of lower coordinated weak spots during deformation. [ABSTRACT FROM AUTHOR]

Rare earth oxide–aluminate–phosphate–silicate (REAPS) glasses are useful precursors for ceramic-matrix-composites (CMCs) with important thermal and mechanical properties. It is important to determine the glass structure, relaxation and crystallization properties for designing and controlling CMC formation. Transparent 3Al 2 O 3 ·2SiO 2 -LaPO 4 glasses containing 25–80 mol% mullite (3Al 2 O 3 ·2SiO 2 ) component were prepared by quenching from high temperature melts using a containerless technique. Glass transformation and crystallization behavior were examined by differential scanning calorimetry and X-ray diffraction. The glass transition onset increased from 845 to 906 °C with mullite content. The temperature interval between T g and crystallization was maximized at 200 °C for 50 mol% mullite glass. Below 40 mol% mullite, successive appearance of LaPO 4 (monazite) and mullite gave rise to two crystallization peaks, while at higher mullite content, only one combined exotherm was observed. A glass structure model constructed from 27 Al, 31 P and 29 Si magic angle spinning (MAS) NMR and Raman spectroscopy results indicated that Si 4 + and P 5 + remained tetrahedrally bonded while Al 3 + ions were predominantly in four-fold coordination with some five-coordinated sites. The presence of La 2 O 3 component resulted in an increased proportion of AlO 4 tetrahedra. The PO 4 polymerization state varied from Q 3 to Q 2 with increasing LaPO 4 content. The SiO 4 , AlO 4, and PO 4 units form a continuous network with PO 4 tetrahedra attached to aluminosilicate framework through two or three P–O–Al linkages. SiO 4 tetrahedra crosslink with AlO 4 tetrahedra to form Q 4 (4Al) and Q 4 (3Al) units. The glass structure model helps explain the crystallization sequence as a function of mullite content and the formation of different CMC textures. [ABSTRACT FROM AUTHOR]

The combination of neutron diffraction with aerodynamic levitation and laser heating, pioneered by Neville Greaves and co-workers about 15 years ago, is an important tool for studying the structure of liquid melts. Since the first work on liquid Al 2 O 3 published in 2001, the technique has been largely improved and experiments are now routinely performed at neutron sources, providing interesting structural information on various materials. In this paper, the structure of glass-forming compounds in the system CaO-Al 2 O 3 -SiO 2 was measured by applying neutron diffraction with aerodynamic levitation. Results obtained in the liquid state above the melting point and from the glass at room temperatures are presented. Various compositions were studied by increasing the silica content and by changing the ratio CaO/Al 2 O 3 . As observed using other methods, the main structural changes relate to modification of the Al-O short range order. [ABSTRACT FROM AUTHOR]

Co-doped Yb/Ce aluminosilicate fiber preforms with less than 1 Wt% fluorine were prepared by MCVD with organic chelate precursor doping technique at 1400 °C. Fluorine content characterized by electron probe microanalysis decreased with increasing SiF 4 flow and flow ratio of SiF 4 /SiCl 4 . Under maximum SiF 4 flow the concentrations of Yb 2 O 3 and CeO 2 in the perform core were only as much as 17% and 25% under minimum SiF 4 flow, respectively, but smaller refractive index change was only shown in fiber core. The reason was that the reaction of SiF 4 with Al 2 O 3 ,Yb 2 O 3 ,CeO 2 were intensified with increasing flow ratio of SiF 4 /SiCl 4 and then resulted in producing more exhaust gas such as AlF 3 , YbF 3 and CeF 4 . Raman spectra of core glasses with < 0.5 Wt% fluorine present different Raman shifts from F doped silica glass with 1–3.3 Wt% fluorine: 945 cm − 1 of Si F stretching bond was not observed, and with growth of fluorine content antisymmetric stretching vibrations of Si-O-Si linkages split from an envelope of 1188 cm − 1 into two peaks or three peaks shifted higher frequency. At the same time, Boson peak near 125 cm − 1 shifted to lower frequency. They were attributed to some minor changes of glass's network structure due to introducing lower fluorine into core glasses. On base of bonding energy measured by X-ray photoelectric spectroscopy, the plane graph describing the complex bonding distribution with F in core was supplied to in order to illustrate network structure change. [ABSTRACT FROM AUTHOR]

The main objective was to study the effect of reducing the phosphate content of the glass structures and the mechanical properties of the resultant cements. The effect of fluorine and soda content on the fluoride release was also investigated. A fluoro-aluminosilicate glass and its modified glass compositions were studied. The structures of the glasses were determined using X-ray diffraction (XRD), 27 Al, 19 F, and 31 P Magic Angle Spinning (MAS) NMR, and DSC. The mechanical properties and the fluoride release of the cements were also measured. Phosphorous forms Al-O-P linkages in the glass. The formation of Al-O-P groups inhibits the degradation of the Si-O-Al bond in the Si-O-Al-O-PO 3 3 − group. Reducing the phosphate content decreases the proportion of Al-O-P bonds, with a concomitant change in the mechanical properties. The fluoride release kinetics was observed to be different, but there was no significant difference in the total amount of the fluoride released at 56 days. The mechanical properties of the glass ionomer cements (GICs) increased by a simple reduction of the phosphate content. The compressive strengths of the cements were twice the ISO standard and were higher than the commercially available cements. Therefore, this study could be a basis to improve the properties of GICs. [ABSTRACT FROM AUTHOR]

Brillouin spectroscopy is used to investigate the elastic properties of XAlSiO 4 aluminosilicate glasses where X = Li, Na, K, Mg 0.5 , Ca 0.5 , Sr 0.5 , Ba 0.5 , and Zn 0.5 . The Brillouin frequency shifts obtained in two different scattering geometries allow the calculation of the refractive index, the two sound velocities and Poisson's ratio. Measurements of the mass density give in turn the elastic moduli and the Debye temperature. We find that the elastic properties scale with the atomic density of the glassy network or the charge-balancing cation field strength while they negatively correlate with the glass transition temperature. Further, Poisson's ratio depends on the nature of the non-framework cations in this glass series. [ABSTRACT FROM AUTHOR]

The main objective of this study was to investigate the physico-chemical and mechanical properties of ion-exchanged float aluminosilicate glasses deposited the Al 2 O 3 films. The concentration gradients of potassium (K), sodium (Na), aluminum (Al) and oxygen (O) elements near Al 2 O 3 film/ion-exchanged glass interface were analyzed by electron probe X-ray micro-analyser (EPMA). Compared with the ion-exchanged glasses, the peak of potassium concentration profile in the ion-exchanged glasses deposited Al 2 O 3 films decreases and moves from glass surface to the inner part. Potassium ion diffusion is accompanied by aluminum (Al) and oxygen (O) diffusion from Al 2 O 3 film into the ion-exchanged glass during deposition. In-depth analyses are performed using micro-Raman spectroscopy on sample cross sections in the aim to investigate the microstructure variation of the ion-exchanged glasses after deposited Al 2 O 3 film on it. The results show that the change of chemical composition throughout ion-exchanged glass surface region can cause a gradual change in microstructure and physical properties. [ABSTRACT FROM AUTHOR]

The mechanical properties of glasses are not only determined by their chemical composition, but also by their thermal history, i.e., fictive temperature. In this paper, we consider an alkaline earth aluminosilicate glass composition which has been annealed to exhibit a wide range of fictive temperatures (~ 130 K). Hardness and brittleness index have previously been shown to increase with decreasing fictive temperature, whereas the crack resistance decreases. Through quantification of the indentation depth before and after heat treatments, we show that these changes in micromechanical properties arise from an increased resistance to densification under the indenter when the glasses are annealed. We discuss these results in relation to the indentation size effect and the overall network compaction. [ABSTRACT FROM AUTHOR]

Clarifying the effect of pressure on the structure of aluminosilicate glasses is important for understanding the densification mechanism of these materials under pressure and the corresponding changes in macroscopic properties. In this study, we examine changes in density, network structure, indentation hardness, and crack resistance of sodium aluminosilicate glasses with varying Al/Si ratio and thus non-bridging oxygen (NBO) content before and after 1 GPa isostatic compression at elevated temperature. With increasing NBO content, the silicate network depolymerizes, resulting in higher atomic packing density, lower hardness, and higher crack resistance. The ability of the glasses to densify under isostatic compression is higher in the high-NBO glasses, and these glasses also exhibit more pronounced pressure-induced changes in mechanical properties. The 27 Al NMR data show a surprising presence of five-fold aluminum in the as-made high-NBO glasses, with additional formation upon compression. Our study therefore provides new insights into the complicated relationship between Al coordination and NBO content in aluminosilicate glasses and how it affects their densification behavior. [ABSTRACT FROM AUTHOR]

Bulk elastic properties, hardness and fatigue of calcium aluminosilicate (CAS) glasses in the technically relevant region of the ternary with intermediate-silica fraction were determined by combining results of Vickers indentation, ultrasonic echography and Archimedian buoyancy at room temperature. Of three studied compositional series, the first series was along the meta-aluminous join, while in the two other series the molar fraction of SiO 2 was kept constant. For the first series the elastic moduli and hardness show an almost linear increase with increasing SiO 2 fraction. In contrast, increasing the CaO/SiO 2 ratio at constant silica content results in a characteristic change when passing the meta-aluminous join. Elastic constants and hardness were lower at the percalcic than on the peraluminous side. Empirical models which relate bulk elastic moduli to internal energy, short-range inter-atomic forces and the packing density of their oxide constituents were found to be in agreement with the experimental data for meta-aluminous glasses, while deviations between the observed and predicted trends were evident for percalcic compositions. Empirical fatigue parameters such as the probability to initiate cracks after indentation reflect the bulk mechanical properties in the CAS system when conducted in inert atmosphere, but are otherwise clearly dominated by environmental effects. [ABSTRACT FROM AUTHOR]