Calcium Aluminosilicate Glasses Research Articles

Investigation on radiation shielding potentials of barium calcium aluminosilicate glass material using silicon carbide nanotubes reinforcement

This work investigated the gamma ray attenuation power of barium calcium aluminosilicate glass by using silicon carbide nanotube modifiers. Shielding efficiency of BaO–15CaO–5Al2O3–10B2O3–35SiO2 was investigated by adding different concentrations of silicon carbide nanotubes (10, 15, 20, 25 mol %). Amorphous and fine characteristics of the prepared glass materials were analyzed using XRD and FTIR techniques. In the results obtained, absence of sharp peaks in the XRD pattern revealed that the prepared glass was amorphous. Analysis of the radiation shielding properties was tested against gamma radiation by using PHY-X/PSD software. Various shielding parameters such as linear attenuation coefficient, mass attenuation coefficient, half value layer, tenth value layer, mean free path, and effective atomic number were determined to access the radiation shielding strength of the prepared samples. From the obtained results, composites of barium calcium aluminosilicate and silicon carbide nanotubes (sample 1) with higher values of mass attenuation coefficient (32.92 cm2/g) and effective atomic number (52.02) provided superior gamma ray attenuation. Results also revealed that the density and chemical composition of the prepared glass samples strongly influence photon interactions and weakly influence electronic interactions during the photon attenuation process. The results demonstrated that increasing the weight fractions of silicon carbide nanotubes in the glass samples increases the shielding properties.

Transformations to the aluminum coordination environment and network polymerization in amorphous aluminosilicates under pressure.

The structure of calcium aluminosilicate glasses (CaO)x(Al2O3)y(SiO2)1-x-y with the near tectosilicate compositions x ≃ 0.19 and 1 - x - y ≃ 0.61 or x ≃ 0.26 and 1 - x - y ≃ 0.49 was investigated by in situ high-pressure neutron diffraction and 27Al nuclear magnetic resonance (NMR) spectroscopy. The results show three distinct pressure regimes for the transformation of the aluminum coordination environment from tetrahedral to octahedral, which map onto the deformations observed in the production of permanently densified materials. The oxygen packing fraction serves as a marker for signaling a change to the coordination number of the network forming motifs. For a wide variety of permanently densified aluminosilicates, the aluminum speciation shares a common dependence on the reduced density ρ' = ρ/ρ0, where ρ is the density and ρ0 is its value for the uncompressed material. The observed increase in the Al-O coordination number with ρ' originates primarily from the formation of six-coordinated aluminum Al(VI) species, the fraction of which increases rapidly beyond a threshold ρthr'∼ 1.1. The findings are combined to produce a self-consistent model for pressure-induced structural change. Provided the glass network is depolymerized, one-coordinated non-bridging oxygen atoms are consumed to produce two-coordinated bridging oxygen atoms, thus increasing the network connectivity in accordance with the results from 17O NMR experiments. Otherwise, three-coordinated oxygen atoms or triclusters appear, and their fraction is quantified by reference to the mean coordination number of the silicon plus aluminum species. The impact of treating Al(VI) as a network modifier is discussed.

Geoenvironmental characteristics of ferroniobium slag from the saint Lawrence columbium mine, Oka, Québec, Canada

Niobium (Nb) is a critical metal usually hosted in pyrochlore and mined from carbonatite deposits. The aluminothermic reduction of pyrochlore concentrate yields ferroniobium (FeNb) alloy and a slag waste. This study presents results from mineralogical, geochemical, and radiochemical investigations of FeNb slag found at the former Saint Lawrence Columbium mine in Oka, Québec, Canada. Slag casts exhibit a vertical zonation resulting from fractional crystallization and differentiation in the melt. Sampling of the slag was designed to characterize resulting chemical and mineralogical variations within casts. The median bulk composition of samples (n = 14) is dominated by Al2O3 (47%) and CaO (16%) from process reagents. The slag also contains significant TiO2 (4%) and trace elements including Zr (6763 ppm), U (601 ppm), and Th (1371 ppm) from pyrochlore that partition preferentially from concentrate to the slag. Based on radiochemical analyses of daughter products and assuming secular equilibrium, median (n = 3) activity concentrations for U and Th decay series are 213 and 111 Bq/g, respectively. A field spectral radiometric survey of the slag disposal area found median (n = 37) equivalent U and Th concentrations of 1069 and 2101 ppm, respectively. The primary mineralogy of the top and middle of slag casts is dominated by hibonite, grossite, and perovskite. Most of the U and Th is hosted by perovskite. The bottom of slag casts is an assemblage of mainly gehlenite, ferri-gehlenite, hercynite, grossite, and anorthite. The casts also contain a (Na,F,Ce) calcium-aluminate glass decreasing in abundance from top to bottom, and a (Na,F,Ce,Ti,Zr) calcium-aluminosilicate glass in the cast bottoms. The (Na,F,Ce) calcium-aluminate glass, grossite, and hibonite are the phases most susceptible to weathering. Perovskite, gehlenite, and hercynite show little or no signs of alteration. A leach test was performed on three columns filled with material from the top, middle, and bottom of casts. In the field, a parallel leach experiment was conducted with three barrels filled with undifferentiated slag material and open to atmospheric conditions. Column leachate was found to be highly alkaline, with pH in the top column reaching 13.2. Median pH values in column and barrel leachate were 10.4 and 9.2, respectively. The maximum U concentration in column leachate was 13 μg/L whereas in barrel leachate it was 65 μg/L. Maximum Th concentrations in column and barrel leachates were 7.65 and 0.2 μg/L, respectively. Median Al concentrations in column and barrel leachates were 74.9 and 3.9 mg/L, respectively. Slag from the production of FeNb is readily weathered and represents a technologically enhanced naturally occurring radioactive material (TENORM) requiring environmental management because of its radioactivity and the alkaline nature of its leachate.

Mechanisms and energetics of calcium aluminosilicate glass dissolution through ab initio molecular dynamics-metadynamics simulations

The dissolution of silicate glasses has implications in diverse fields ranging from the immobilization of radioactive waste to the development of sustainable alternatives to Portland cement. Here, we used ab initio molecular dynamics simulations biased with well-tempered metadynamics to study Si-O-T bridge dissociation in calcium aluminosilicate glasses, crucial for understanding their dissolution. In a departure from the conventional Michalske-Freiman model, our findings reveal a nucleophilic substitution reaction mechanism characterized by a short-lived, 5-fold coordinated Si intermediate or transition state, depending on the Si bridge coordination, with a near-trigonal bipyramidal geometry. We find that the reorganization required for reaching this state causes the activation energy barriers to be dependent on the Si bridge coordination, with Si Q3 species serving as the rate-limiting step in the dissolution reaction. Our findings not only challenge long-standing theoretical models but also pave the way for more accurate and comprehensive frameworks for understanding the dissolution of silicate glasses in various applications.

Radiation shielding properties of 35-XBaO-15CaO-5Al2O3-10B2O3-35SiO2-XBNNT (X=5, 10, 15, 20) glass reinforced with boron nitride nanotubes

Glass composite materials are the most widely used radiation shielding materials. Barium aluminosilicate glass have versatile properties which make them very useful for applications in industries. In the present study, the mass attenuation coefficient, effective atomic numbers as well as effective electron densities of barium calcium aluminosilicate glass (BCAS) were studied by adding boron nitride nanotubes in various concentrations. Analysis were conducted using phy-x/PSD simulation codes. It as was found that MAC and δa decrease with increasing photon energy in consistent with previous works. It was also found that attenuation parameters such as MAC, LAC, HVL and Zeff were all influenced by change in density of BCAS/BNNT glass. The present study found BCAS/BNNT1 glass as best for gamma radiation protection.

The first demonstration of wavelength-tunable Yb3+-doped low silica calcium aluminosilicate (LSCAS) glass lasers

We report on the first demonstration of diode-pumped wavelength-tunable Yb3+-doped low silica calcium aluminosilicate (LSCAS) glass lasers. Using a 976 nm diode laser as pump source, a Yb:LSCAS laser has been successfully achieved with a maximum output power of about 0.28 W. Using an MgF2 thin plate as birefringence filter, we have found that the lasing wavelength can be tuned with a range of about 60 nm. We have also analyzed the intracavity round-trip loss of the current laser cavity, and related it to the optical quality of the used Yb glass. This sheds light on the path of the development of upcoming Yb3+ glass lasers in the future since it has many advantages, and after improving the optical quality, the wide and smooth emission spectrum of Yb:LSCAS will be very conducive to obtaining femtosecond pulse lasers.

High pressure-driven effects on the structural and spectroscopic attributes of Eu3+-doped amorphous silicates

The present study focuses on synthesizing and investigating the structure of Eu3+-doped sodium calcium silicate and calcium alumino silicate glasses under extreme high-pressure conditions. For a thorough understanding of glassy systems in extreme conditions, we conducted in-situ micro-luminescence experiments using a diamond anvil cell, reaching pressures up to 16 GPa. Hydrostatic pressure demonstrated a notable impact on luminescence, attributed to the nephelauxetic effect causing the contraction of central-ion-ligand distances. The band transitions of Eu3+ from the 5D0 to 7F1,2 states revealed pronounced pressure-induced splitting, highlighting the pressure influence on crystal-field properties. The energy shifts for the 5D0 → 7F1 transitions were determined to be 0.14 nmGPa−1 and 0.20 nmGPa−1 for sodium calcium silicate and calcium alumino silicate, respectively. These distinct slope differences indicated a lower structural adaptability of the former glass, resulting in reduced deformability under high-pressure conditions. Furthermore, as pressure increased, the asymmetry ratio of the 5D0 → 7F2/1 transitions decreased, though it consistently maintains levels higher than unity, reflecting the highly asymmetric environment surrounding Eu3+ ions. The estimated elastic limit for both samples was approximately 7 GPa. To assess pressure-induced changes in the local environment, Judd-Ofelt intensity parameters were employed for the calcium alumino silicate glass. The trends observed throughout compression revealed that Ω2 > Ω4 up to 6.8 GPa, while Ω2 < Ω4 for higher pressures, indicating higher covalency between Eu3+ ions and ligands in the elastic domain compared to the plastic domain. The observed increase in Si and Al coordination in the plastic domain was found to play a role in these parameters.

Atomistic simulations of calcium aluminosilicate interfaced with liquid water.

The dissolution behavior of calcium aluminosilicate based glass fibers, such as stone wool fibers, is an important consideration in mineral wool applications for both the longevity of the mineral wool products in humid environments and limiting the health impacts of released and inhaled fibers from the mineral wool product. Balancing these factors requires a molecular-level understanding of calcium aluminosilicate glass dissolution mechanisms, details that are challenging to resolve with experiment alone. Molecular dynamics simulations are a powerful tool capable of providing complementary atomistic insights regarding dissolution; however, they require force fields capable of describing not-only the calcium aluminosilicate surface structure but also the interactions relevant to dissolution phenomena. Here, a new force field capable of describing amorphous calcium aluminosilicate surfaces interfaced with liquid water is developed by fitting parameters to experimental and first principles simulation data of the relevant oxide-water interfaces, including abinitio molecular dynamics simulations performed for this work for the wüstite and periclase interfaces. Simulations of a calcium aluminosilicate surface interfaced with liquid water were used to test this new force field, suggesting moderate ingress of water into the porous glass interface. This design of the force field opens a new avenue for the further study of calcium and network-modifier dissolution phenomena in calcium aluminosilicate glasses and stone wool fibers at liquid water interfaces.

Prediction of the surface chemistry of calcium aluminosilicate glasses

We have used a combination of density functional theory, the implicit solvent model COSMO-RS and molecular dynamics simulations to predict the pKa of surface groups on calcium aluminosilicate glasses. We found that the average of pKa for deprotonation and protonation for silanols agrees well with the point of zero charge for pure silica materials. Similarly, the average of pKa for deprotonation and protonation for aluminols agrees well with the point of zero charge for pure alumina. We identified trends in the pKa related to the hydrogen bonding of the surface groups, as well as the influence of tri-briding oxygen defects.

Insights from molecular dynamics into the chemistry-structure relationships of calcium aluminosilicate glasses

Calcium aluminosilicate (CAS) glasses are ubiquitous in nature and play an important role in diverse technological applications ranging from structural glasses to sustainable cementitious materials. Understanding the relationship between the chemical composition and the structure of CAS glasses is an essential step towards optimizing their properties for different uses in the future. Here, we use extensive molecular dynamics (MD) simulations to characterize the multiscale structure of CAS glasses over the full compositional range. Analysis of the short and medium range order of the glasses reveals that Lowenstein's rule is widely violated, that silica is more susceptible than alumina to the depolymerizing effects of calcium, and that high-silica glasses favor calcium in lower oxygen coordination states, while the opposite is true for high-alumina ones. We also find the presence of highly coordinated aluminum and tricluster oxygens in high-alumina glasses, which form as a charge compensation mechanism. We find that current theoretical models used to predict oxygen species, oxygen bridge types, or tetrahedral coordination, while overall qualitatively reasonable, simplify the complex interplay between the different oxides which results in inaccurate predictions, particularly for glasses in intermediate compositional regions. Our analysis of the cluster, chain, and ring topological structures in the aluminosilicate network reveals a sharp transition from a connected to a disconnected graph which depends not only on the calcium content of the glass, but also on the ratio of silica to alumina. Glasses in the compositional region corresponding to such transition display the largest ring and longest chain structures of any glass studied.

Downconversion luminescence in Ce3+, Yb2+, and Yb3+ co-doped low silica calcium aluminosilicate glasses: Potential for spectral conversion in solar cell technology

Yb–Ce co-doped LSCAS glasses melted under a vacuum atmosphere are free of OH− radicals presenting downconversion luminescence of interest for solar cell application. Absorption spectra showed an ultraviolet–visible broad band related to the 2F5/2, 2F7/2 → 5d transitions of the Ce3+. Time-resolved luminescence evidenced energy transfer from Ce3+ to Yb3+, and the contour maps spectra showed a decrease in Ce3+ emission with the increase of Yb concentration. Thermal lens results evidenced an increase in heat generation, suggesting the occurrence of nonradiative transitions due to the formation of Yb2+ or Ce4+ ions. The observed emissions are attributed to energy transfer from Ce3+ or Yb2+ to two Yb3+ ions by quantum cutting mechanism, emission from Ce3+ at 520 nm, and predominantly, a phonon-assisted energy transfer from Ce3+ or Yb2+ to one Yb3+ ion.

Role of Zn in aluminosilicate glasses used as supplementary cementitious materials

The cement industry relies on the use of supplementary cementitious materials (SCM) to lower the related CO2 emission. SCM are often amorphous materials containing minor elements, which is why it is important to study the impact of these materials on cement reactivity. Two calcium aluminosilicate glass series as model substances of SCM were synthesized and investigated. In both series Ca was partially replaced by Zn, Sr and Mg in different ratios. Moreover, four cement blends made with CEM I 52.5 R and aqueous solutions of Mg(NO3)2·6H2O, Zn(NO3)2·6H2O and Sr(NO3)2 were investigated. Zn retards the reactivity of both glasses and cements system. This retardation effect is suggested to be related both to the formation of the calcium hydroxozincate hydrate, which affects the portlandite formation and, thus, the pH of the system, and to the formation of surface complexes which retards the dissolution and so the reactivity of the glasses.

Mechanisms of microstructural deformation governing Vickers hardness in phase‐separated calcium aluminosilicate glasses

AbstractThe impact of microstructure on hardness in phase‐separated calcium aluminosilicate glasses is investigated. Changes in hardness are governed by microstructure deformations that occur during indentation. Phase separation leads to decreased hardness due to the incongruent yielding of the droplet and matrix phases. Moreover, the deformation of microstructures possessing dilute, spherical droplets did not have a significant impact on hardness. Microstructures characterized by concentrated, acicular droplets were found to deform through a process of droplet coalescence. This process absorbs additional energy during yielding and results in glasses that deform through droplet coalescence possessing improved hardness.

The changes in the reaction kinetics and phase assemblage of sodium silicate-activated CaO-MgO-Al2O3-SiO2 glasses induced by the Al replacement by Mg

Although intensive research was done on the impact of slag chemistry on the reaction kinetics of alkali-activated materials, its role remains unclear due to the slag's uncontrolled oxides variations. This research investigated the role of the Al replacement by Mg on the reaction kinetics and phase assemblage of sodium silicate-activated calcium‑magnesium-aluminosilicate (CMAS) glasses by a novel approach. The calcium-aluminosilicate (CAS) glass reacted faster than the CMAS ones. Also, increasing the replacement level in the CMAS glasses slightly accelerated the reaction but considerably increased the total heat. Katoite and strätlingite precipitated at high Al2O3 wt% of 20 and 25, respectively. A decrease in the total volume of the hydrates was predicted by thermodynamic modelling and further supported by gas adsorption measurements. The paper's outcomes aid in providing a fundamental understating of the effect of Al and Mg which could help with customising the mix design for enhanced performance of alkali-activated binders.

Broadband downconversion in Eu2+,3+/Yb3+ doped calcium aluminosilicate glasses for solar cells applications

Novel Eu2+,3+/Yb3+ co-doping calcium aluminosilicate glasses prepared under a vacuum atmosphere were developed and characterized from the spectroscopic point of view, as a potential spectral converter for application in solar cells. The emission of near-infrared photons by downconversion due to cooperative energy transfer (ET) from Eu2+ and Eu3+ to Yb3+ in these glasses was reported. Absorption, excitation, emission, and fluorescence decay measurements were performed to examine the ET processes. The occurrence of cooperative energy transfer from Eu2+ and/or Eu3+ to Yb3+ ions was discussed in detail. The obtained samples have high efficiency and broad absorption in the ultraviolet and visible regions. Under 325 nm excitation, the samples achieve intense near-infrared emission, which increases with Yb2O3 concentration (0 &amp;lt; Yb2O3 &amp;lt; 1.38 mol. %). The energy transfer efficiency from Eu2+,3+ to Yb3+ was evaluated, and a maximum efficiency of ∼85% was obtained (Yb2O3 = 1.38 mol. %).

The Effect of Glass Structure on the Luminescence Spectra of Sm3+-Doped Aluminosilicate Glasses.

Peralkaline Sm3+-doped aluminosilicate glasses with different network modifier ions (Mg2+, Ca2+, Sr2+, Ba2+, Zn2+) were investigated to clarify the effect of glass composition and glass structure on the optical properties of the doped Sm3+ ions. For this purpose, the Sm3+ luminescence emission spectra were correlated with the molecular structure of the glasses derived by molecular dynamics (MD) simulations. The different network modifier ions have a clear and systematic effect on the peak area ratio of the Sm3+ emission peaks which correlates with the average rare earth site symmetry in the glasses. The highest site symmetry is found for the calcium aluminosilicate glass. Glasses with network modifier ions of lower and higher ionic radii show a notably lower average site symmetry. The symmetry could be correlated to the rare earth coordination number with oxygen atoms derived by MD simulations. A coordination number of 6 seems to offer the highest average site symmetry. Higher rare earth coordination probabilities with non-bridging oxygen result in an increased splitting of the emission peaks and a notable broadening of the peaks. The zinc containing glass seems to play a special role. The Zn2+ ions notably modify the glass structure and especially the rare earth coordination in comparison to the other network modifier ions in the other investigated glasses. The knowledge on how glass structure affects the optical properties of doped rare earth ions can be used to tailor the rare earth absorption and emission spectra for specific applications.

Influences of Mn2+ ions, and Mn2+–Yb3+ dimer on the optical band gaps and bandwidth flatness of near-infrared emissions of Ho3+/Tm3+, Ho3+/Tm3+/Yb3+ co-doped calcium aluminosilicate glasses

We investigate and report the influences of Mn2+−Yb3+ dimer on the optical band gaps and bandwidth flatness of near-infrared (NIR) emission spectra of Ho3+/Tm3+, and Ho3+/Tm3+/Yb3+ co-doped CaO–Al2O3–SiO2 (CAS) calcium aluminosilicate glasses. Differential thermal analysis (DTA) and Energy dispersive X-ray spectroscopy (EDS) analyzes were performed to determine temperature values for heat treatment and elemental composition existing in the glass materials, respectively. NIR emission spectra of Ho3+/Tm3+/Yb3+ co-doped CAS glasses with a bandwidth of ∼450 nm using a 980 nm laser diode (LD) as the excitation resource was identified. Influences of Mn2+ ions and Mn2+–Yb3+ dimer on the direct/indirect optical band gaps, and bandwidth flatness of NIR emission of Ho3+/Tm3+/Yb3+ co-doped were investigated. At the same time, we determined the optimal Mn2+:Yb3+concentration ratio for the best flatness of the bandwidth NIR emission of Ho3+/Tm3+/Yb3+ co-doped CAS glasses.

Quantification of the resonant energy transfer processes in Er3+/Yb3+ co-doped Ca3Al2Si3O12 glasses

The resonant cross relaxation processes between Yb3+ and Er3+ ions in calcium alumino-silicate glasses have been quantified under selective Er3+ excitation. The infrared emission spectra, measured under steady state conditions (CW excitation to the 4I9/2 erbium level), have allowed to obtain an experimental relationship linking the transfer (Yb3+ → Er3+) and back transfer (Er3+ → Yb3+) parameters. These measurements combined with the dynamics of the main emitting levels, measured under pulsed excitation to the 2H11/2 erbium level, have allowed the fully quantification of the energy transfer parameters. The obtained values, C25=5.5×10−18cm3s−1 (Yb3+ → Er3+), C52=1.5×10−18cm3s−1 (Er3+ → Yb3+) and C27=7.6×10−18cm3s−1 (up-conversion mechanism, estimated from the Judd-Ofelt analysis previously reported), can be used to predict the temporal evolution of the main luminescent emission bands.

Modeling Oxygen Tricluster Formation in Calcium Aluminosilicate Supercooled Liquids and Glasses.

Calcium aluminosilicate glasses have technological importance for a variety of industrial applications. However, the short-range structure of this glass system remains widely debated regarding the formation of oxygen triclusters. It is argued that triclusters are observed in high percentages within molecular dynamics simulations because of the high melting temperatures and correspondingly high fictive temperatures. This work explores the formation of such structural units by first simulating various compositions at different liquid temperatures to understand thermodynamic factors affecting the formation of such species. Structural results are then implemented into a statistical mechanical model which can predict the formation of triclusters at a given fictive temperature. Results show temperature and composition dependence of these structures, with aluminum charge modification favored in the peraluminous regime. It is concluded that oxygen triclusters are the preferred method of charge compensation even when extrapolating to laboratory fictive temperatures, indicating that triclusters are not a byproduct of simulation timescales.

Passivation of Mid-Gap Electronic States at Calcium Aluminosilicate Glass Surfaces upon Water Exposure: An Ab Initio Study.

When a clean glass surface is exposed to humid air, a thin water layer forms on the hydrophilic surface. Using ab initio molecular dynamics, we simulate the changes in the electronic structure of a CaO-Al2O3-SiO2 glass model upon vacuum fracture and subsequent exposure to H2O. When the glass is fractured, dangling bonds form, which lower the band gap of the surface by ∼1.8 eV compared to the bulk value due to mid-gap surface states. When H2O adsorbs onto the vacuum-fractured surface, the band gap increases to a value closer to that of the bulk band gap. Using two different hydroxylation methods, we find that the calculated band gap of the glass surface depends on the hydroxylation state. Surfaces with ∼4.5 OH/nm2 have smaller band gaps due to unfilled surface states, and surfaces with ∼2.5 OH/nm2 have larger band gaps with no apparent unfilled surface states. The resulting changes in the electronic structure, quantified by electron affinity and work function values, are hypothesized to play an important role in the electrostatic charge transfer based on the principles of surface state theory, which posit that the density of electronic surface states determines the amount of electronic charge transfer to or from material surfaces.