Cation Field Strength Effects on Boron Coordination in Binary Borate Glasses

The field strength of modifier cations in boron‐containing oxide glasses has important but complex effects on boron coordination, and has long been known to have major effects on glass and liquid properties. With well‐constrained compositional and fictive temperature information in three binary borate glass series, we report how different modifier cations (Na⁺, Ba²⁺, Ca²⁺) affect boron coordination (¹¹B MAS NMR), as well as glass transition temperatures and configurational heat capacities (DSC). Using estimated reaction enthalpies for converting a ^[4]B to a ^[3]B with an NBO from previous studies, we compare boron coordinations in glasses with different modifier cations on an isothermal basis. Temperature and modifier cation effects can thus be isolated. At low modifier contents [R = (Na₂,Ca,Ba)O/B₂O₃<0.45], N₄ is systematically higher in the order Na>Ba>Ca, suggesting the enhanced stabilization of NBO for the divalent cations, especially for the smaller Ca²⁺. At higher R values, N₄ for Na borates drops below values for Ca and Ba borates. The trend in N₄ with modifier field strength reverses at high R values (~ R > 0.7), with Ca > Ba > Na. The transition may be related to the enhanced stabilization of ^[4]B‐O‐^[4]B groups by higher field strength cations in NBO‐rich glasses in which boron is the primary network component.     

Structure-property relations in crack-resistant alkaline-earth aluminoborosilicate glasses studied by solid state NMR

The effect of the average ionic potential ξ = Ze/r of the network modifier cations on crack initiation resistance (CR) and Young's modulus E has been measured for a series of alkaline-earth aluminoborosilicate glasses with the compositions 60SiO₂–10Al₂O₃–10B₂O₃–(20−x)M₍₂₎O–xM’O (0 ≤ x ≤ 20; M, M’ = Mg, Ca, Sr, Ba, Na). Systematic trends indicating an increase of CR with increasing ionic potential, ξ, have been correlated with structural properties deduced from the NMR interaction parameters in ²⁹Si, ²⁷Al, ²³Na, and ¹¹B solid state NMR. ²⁷Al NMR spectra indicate that the aluminum atoms in these glasses are essentially all four-coordinated, however, the average quadrupolar coupling constant <C_Q> extracted from lineshape analysis increases linearly with increasing average ion potential computed from the cation composition. A similar linear correlation is observed for the average ²⁹Si chemical shift, whereas the fraction of four-coordinate boron decreases linearly with increasing ξ. Altogether the results indicate that in pure alkaline-earth boroaluminosilicate glasses the crack resistance/E-modulus trade-off can be tailored by the alkaline-earth oxide inventory. In contrast, the situation looks more complicated in glasses containing both Na₂O and the alkaline-earth oxides MgO, CaO, SrO, and BaO. For 60SiO₂–10Al₂O₃–10B₂O₃–10MgO–10Na₂O glass, the NMR parameters, interpreted in the context of their correlations with ionic potentials, are consistent with a partial network former role of the MgO component, enhancing crack resistance. Altogether the presence of MgO in aluminoborosilicate glasses helps overcome the trade-off issue between high crack resistance and high elasticity modulus present in borosilicate glasses, thereby offering additional opportunities for the design of glasses that are both very rigid and very crack resistant.     

Effects of Al:Si and (Al + Na):Si ratios on the properties of the international simple glass,part II: Structure

High-alumina containing high-level waste (HLW) will be vitrified at the Waste Treatment Plant at the Hanford Site. The resulting glasses, high in alumina, will have distinct composition-structure-property (C-S-P) relationships compared to previously studied HLW glasses. These C-S-P relationships determine the processability and product durability of glasses and therefore must be understood. The main purpose of this study is to understand the detailed structural changes caused by Al:Si and (Al + Na):Si substitutions in a simplified nuclear waste model glass (ISG, international simple glass) by combining experimental structural characterizations and molecular dynamics (MD) simulations. The structures of these two series of glasses were characterized by neutron total scattering and ²⁷Al, ²³Na, ²⁹Si, and ¹¹B solid-state nuclear magnetic resonance (NMR) spectroscopy. Additionally, MD simulations were used to generate atomistic structural models of the borosilicate glasses and simulation results were validated by the experimental structural data. Short-range (eg, bond distance, coordination number, etc) and medium-range (eg, oxygen speciation, network connectivity, polyhedral linkages) structural features of the borosilicate glasses were systematically investigated as a function of the degree of substitution. The results show that bond distance and coordination number of the cation-oxygen pairs are relatively insensitive to Al:Si and (Al + Na):Si substitutions with the exception of the B-O pair. Additionally, the Al:Si substitution results in an increase in tri-bridging oxygen species, whereas (Al + Na):Si substitution creates nonbridging oxygen species. Charge compensator preferences were found for Si-[NBO] (Na⁺), ^[3]B-[NBO] (Na⁺), ^[4]B (mostly Ca²⁺), ^[4]Al (nearly equally split Na⁺ and Ca²⁺), and ^[6]Zr (mostly Ca²⁺). The network former-BO-network former linkages preferences were also tabulated; Si-O-Al and Al-O-Al were preferred at the expense of lower Si-O-^[3]B and ^[3]B-O-^[3]B linkages. These results provide insights on the structural origins of property changes such as glass-transition temperature caused by the substitutions, providing a basis for future improvements of theoretical and computer simulation models.     

Effect of alkali and alkaline earth metal ion as glass modifiers on the spectroscopic characteristics of Er3+-ion doped lead silicate glasses

The spectroscopic characteristics of Er-doped lead silicate glasses were investigated with respect to the effects of glass modifiers (Li⁺, Na⁺, K⁺, Mg²⁺, Ca²⁺, Sr²⁺, and Ba²⁺) with various optical basicities. Using the absorption spectra of the glasses, the Judd–Ofelt parameters of the glasses were calculated and examined, with an emphasis on the glass emission intensity ratio at 1572 nm. The spectra of the samples at low temperatures were examined, and the Stark splitting of Er3+ was investigated. The McCumber method was used to determine the emission cross sections of glasses. The SPM glass exhibited high values of full width at half maximum (51.24 nm) and the emission cross section at 1572 nm (1.908 × 10⁻²¹ cm²), with potential applications for guiding component design of 1.5-μm fiber lasers and amplifiers.     

Properties and vibrational spectra of magnesium phosphate glasses for nuclear waste immobilization

The leaching behavior and structure of magnesium phosphate glasses containing 45–55 mol% MgO incorporated with simulated high level nuclear wastes (HLW) were studied. The leach rate of the waste glasses decrease with increasing of the simulated HLW content. The gross leach rate of the glass waste form containing 50 mol% MgO and 45 mass% simulated HLW is of the order of 10⁻⁶ g/cm² day at 90 °C, which is small enough as compared with the corresponding release from a currently used borosilicate glass waste form. The isolated ions such as dimeric (P₂O₇)⁴⁻ and monomeric (PO₄)³⁻ ions increase upon as increasing the incorporating amount of the simulated HLW. The changes in properties can be attributed to the structure changes owing to the incorporation of the simulated HLW.     

Mixed alkaline‐earth effect on the mechanical and rheological properties of Ca–Mg silicate glasses

In this article, we investigate the mixed alkaline‐earth effect in a silicate glass series with varying the molar ratio of [MgO]/([CaO]+[MgO]). This effect manifests itself as a minimum in Vickers microhardness (H_V), coefficient of thermal expansion (CTE), and isokom temperatures at 10¹²(T_g) and 10² Pa·s, and as a maximum in liquid fragility. To probe the structural origin of the mixed alkaline‐earth effect in CTE and H_v, we conducted the Raman measurements. In contrast to the aluminosilicate glasses, the present glass series exhibit a negative deviation of shift of peak position at ~1100 cm^?1 from a linear additivity, indicating the role of the aluminum speciation in affecting the vibration modes. By fitting the Vogel–Fulcher–Tamann equation to the high‐temperature viscosity data, we found a near‐linear increase of the fractional free volume with the gradual substitution of Ca by Mg, confirming the dynamic structural mismatch model describing the mixed modifier effect. This work gives insight into the mixed modifier effect in glassy systems.     

The Effect of Bivalent Cations on the Physicochemical Properties and Structure of Borosilicate Glasses

The effect of modifier oxides (MgO, CaO, SrO, BaO, and ZnO) introduced instead of SiO₂ into borosilicate glass on glass properties is investigated. It is established that the physicochemical properties (TCLE, softening temperature, mircohardness, density, water resistance) of glasses are determined mainly by structure and phase composition and, to a lesser extent, depend on the type of modifier oxide.     

The influence of the mixed alkaline earth effect on the structure and properties of (Ca,Mg)–Si–Al–O–N glasses

Alkaline earth oxynitride glasses of (Ca, Mg)–Si–Al–O–N with different CaO/(CaO + MgO) molar ratios (0, 0.25, 0.5, 0.75, and 1) were successfully prepared using the sol-gel method, and their structural compositions were characterised by Raman and FT-IR techniques. The glass dynamic properties of thermal expansion coefficient, glass transition temperature (T_g), and static properties of density, molar volume, Vickers hardness and compressive strength were systematically measured and analysed. The results showed that the static properties exhibited an overall regular change as the CaO/(CaO + MgO) ratio gradually increased, while the dynamic properties had an obvious mixed alkaline earth effect, which represented the appearance of an extreme value point in CaO/(CaO + MgO) mole ratios of 0.25 and 0.75, respectively. The typical thermal expansion coefficient and T_g of mixed alkaline earth oxynitride glasses deviated far from the linear connection between single alkaline earth oxynitride glasses. Raman spectra and infrared spectra revealed that the ratio value of the Q³/(Q²+Q⁴) decreased (Qⁿ: n = no. of bridging anions joining SiO₄ tetrahedra) in the mixed alkaline earth oxynitride glasses with increasing the amount of Ca, confirming that Ca decreased the crosslinking between individual tetrahedra via the transformation of Q³ species into Q² and Q⁴ species.     

The dissolution behavior in alkaline solutions of a borosilicate glass with and without P2O5

There are a variety of applications for glasses in alkaline environments, including glass fibers and glass‐coated steel to reinforce concrete structures. To understand how a simple glass reacts in such environments, the dissolution behavior of a 25Na₂O–25B₂O₃–50SiO₂ (mol%) glass, doped with and without 3 mol% P₂O₅, in pH 12 KOH and pH 12 KOH saturated with Ca²⁺ ions was studied. Ca²⁺ ions in the solution significantly reduce the glass dissolution rate by forming a passivating calcium silicate hydrate (C–S–H) gel layer on the glass surface. When these corroded glasses were then exposed to Ca‐free KOH, the C–S–H layer redissolves into the undersaturated solution and the glass dissolution rate increases. For phosphate‐doped borosilicate glass, PO₄^3? units released from the dissolving glass react with Ca²⁺ ions in saturated solutions to form crystalline hydroxylapatite on the glass surface, but this layer does not protect the glass from corrosion as well as the C–S–H does. The nature of the C–S–H layer was characterized by Raman spectroscopy, which reveals a gel layer constituted mainly of silicate anions.     

Tunable colors and applications of Dy3+/Eu3+ co-doped CaO-B2O3-SiO2 glasses

A series of Dy³⁺/Eu³⁺ single- and co-doped calcium borosilicate luminescent glasses were prepared by the conventional high temperature melt-quenching method. A compact glass structure is obtained by the addition of Dy³⁺/Eu³⁺ ions, which is verified by the physical properties of synthetic glasses. As network modifiers, Dy³⁺/Eu³⁺ fill in the interspaces of glass network and contribute to the conversion of [BO₃] to [BO₄]. Dy³⁺/Eu³⁺ co-doped calcium borosilicate glasses can emit white light, which consists of blue, yellow, and red light under 387 nm excitation. The emission spectra and decay curves of the white-emitting glasses have proved the existence of energy transfer. The average lifetime of Dy³⁺ decreases from 0.251 to 0.165 ms with the increasing Eu³⁺ concentration. Changing rare earth ions concentration, CIE color coordinates of Dy³⁺/Eu³⁺ co-doped glass shifts from cyan to white with increasing excitation wavelength. A white-light emission is obtained when the concentration of Dy³⁺ and Eu³⁺ equals to 4% and 2%, respectively. Moreover, the Dy³⁺/Eu³⁺ co-doped calcium borosilicate glass shows high-thermal stability and it may be applicable for high-quality white LEDs based on high power near ultraviolet (n-UV) LED chip in the future.     

Cation field-strength effects on ion irradiation-induced mechanical property changes of borosilicate glass structures

We examine the impact of the glass network-modifier cation field strength (CFS) on ion irradiation-induced mechanical property changes in borosilicate (BS) glasses for the ternary M₂O–B₂O₃–SiO₂ systems with M = {Na, K, Rb} and the quaternary [0.5M₍₂₎O–0.5Na₂O]–B₂O₃–SiO₂ systems with M = {Li, Na, K, Rb Mg, Ca, Sr, Ba}. ¹¹B nuclear magnetic resonance (NMR) experiments on the as-prepared BS glasses yielded the fractional population of four-coordinated B species (B^[4]) out of all {B^[3], B^[4]} groups in the glass network, along with the fraction of B^[4]–O–Si linkages out of all B^[4]–O–Si/B bonds. Both parameters correlated linearly with the (average) CFS of the M⁺ and/or {M⁽²⁾⁺, Na⁺} cations. Both the nanoindentation-derived hardness and Young's modulus values of the glasses reduced upon their irradiation by Si²⁺ ions, with the property deterioration decreasing linearly with increasing M^z+ CFS, that is, for higher M^z+⋅⋅⋅O interaction strength. The irradiation damage of the glass network also increased linearly with the fraction of B^[4]–O–Si linkages, which are the second weakest in the structure after the M^z+⋅⋅⋅O bonds. Our results underscore the advantages of employing BS glasses with high-CFS cations for enhancing the radiation resistance for nuclear waste storage.     

Kinetics and Mechanism of the Interaction of Alkali Calcium Silicate Glasses with Salt Melts in the KNO3–Pb(NO3)2 System

The interaction of alkali calcium silicate glasses with salt melts in the KNO₃–Pb(NO₃)₂ system is investigated at temperatures of 420–520°C. The chemical composition of crystalline coatings formed upon treatment contains both components of the initial glass (SiO₂, 9–12 wt %; CaO, 0.8–1.2 wt %) and components of the salt melt (PbO, 82–89 wt %). The treatment temperature is the main factor affecting the structure of the modified surface layer. The mechanism of the interaction of alkali calcium silicate glasses with salt melts is analyzed. According to this mechanism, the interaction involves the ion exchange (with the participation of Na⁺, K⁺, Ca²⁺, and Pb²⁺ ions), crystallization of modified surface layers, and incorporation of Pb _x O _y nanoparticles (formed in the salt melt) into the coating structure.     

Crystallization,spectroscopic and dielectric properties of CuO-added magnesium aluminosilicate-based glasses

In this work, CuO-doped MgO-Al₂O₃-SiO₂ based glasses have been synthesized successfully through conventional melt quenching method, and the effect of CuO content on the structure and properties of the glasses was investigated. The results revealed that CuO could act as a glass modifier to depolymerize the silicate network and its effect was superior to that of MgO. In addition, the main crystalline phase was α-cordierite (Mg₂Al₄Si₅O₁₈), indicating that copper ions did not participate in the formation of the crystalline phase, and still existed in the interstitial position. The characteristic absorption band around 750 nm owing to the ²B_1g→²B_2g transition of Cu²⁺ ions appeared on the optical transmittance spectra, which confirmed the existence of Cu²⁺ ions in the tetragonally distorted octahedral sites. The luminescence center was caused by Cu⁺ ions, and the luminescence lifetime decreased with the addition of CuO. The dielectric constant and dielectric loss increased with the increase of CuO content, indicating an increase in the insulation performance. Finally, the obtained chromaticity coordinate parameters indicate that the prepared CuO-doped magnesium aluminosilicate-based glasses can be applied in optical and electrical fields.     

Thermal behavior,structure, crystallization and solubility of the melt-derived SiO2–P2O5–Na2O–F-MO (M = Ca,Sr, Zn) glasses

In this work, phospho-silicate glasses with SiO₂–P₂O₅–Na₂O–F-MO (M = Ca, Sr, Zn) composition were prepared by using the conventional melt quenching technology. Structural, physical, and chemical property tests were used to analyze the effects of different SrO and ZnO content on the structure and properties of the glasses. The results showed that the glass stability varied nonlinearly as CaO was replaced by SrO, which was mainly related to the different positions of Sr²⁺ and Ca²⁺ ions breaking the network connection in the network structure, and the substitution of ZnO for CaO led to a continuous decrease in the stability of the glasses. The immersion experiment showed that SrO doping was more feasible than ZnO doping to improve the biological activity of the glasses, and the doping of ZnO promoted the dissolution of ions in the glasses. The obtained results indicated that the glass samples prepared in this paper have potential biological activity, which has potential applications in dental treatment.     

Characterization of immiscibility in calcium borosilicates used for the immobilization of Mo6+ under Au-irradiation

The aim of this paper was to assess factors affecting primary and secondary phase separation in simplified calcium borosilicate glasses studied for nuclear waste applications. Several glasses with varying [MoO₃] and [B₂O₃] were synthesized and exposed to Au-irradiation to examine compositional effects on glass structure and domain size of separated phases induced by accumulated radiation damage resulting from α-decay over a ~1000 year timeframe. The produced glasses fell within the immiscibility dome of CaO−SiO₂−B₂O₃ and showed a unique microstructure of embedded immiscibility with three identifiable amorphous phases according to electron microscopy, Raman spectroscopy, and diffraction. These glasses were then bombarded with 7 MeV Au³⁺ ions to a dose of 3 × 10¹⁴ ions/cm² creating an estimated ~1 dpa of damage. Several changes to the morphology, spatial distribution, and size of secondary phases were observed, indicative of significant structural reorganization and changes to the chemical composition of each phase. A general mechanism of coalescence to form larger particles was observed for [MoO₃] < 2.5 mol%, whereas segregation to form smaller more evenly distributed particles was seen for [B₂O₃] ≤ 15 mol% and [MoO₃] ≥ 2.5 mol%. These microscopic changes were concurrent to surface-bulk diffusion of Ca and/or Mo ions, where the direction of diffusion was dependent on [B₂O₃] with a barrier identified at ~20 mol%, as well as cross-phase diffusion of said ions. These modifications occurred in part through the formation of distorted ring structures within the borosilicate network, which enabled the increased dissolution of isolated (MoO₄)²⁻ units. Au-irradiation was therefore able to increase the solubility of molybdenum and alter the structure and composition of secondary phases with the extent of modification varying with [MoO₃] and [B₂O₃]/[SiO₂], though glasses notably remained heterogeneous. The collective results suggest that radiation and composition can both be used as design tools to modulate the domain size and distribution of separated phases in heterogeneous glasses.     

Selective preparation of Ag species on photoluminescence of Sm3+ in borosilicate glass via Ag+-Na+ ion exchange

Photoluminescence (PL) of rare earth ion-doped glasses could be enhanced by diverse Ag species such as Ag⁺ ions, Ag⁺-Ag⁺ pairs, Ag nano-clusters (NCs), and Ag nanoparticles (NPs). Selective preparation of silver species in rare earth ion-doped glasses is a crucial step to obtain the luminescence enhancement of rare earth ions caused by the different silver species. In this work, Ag⁺ ions and Ag NCs were selectively prepared in the Sm³⁺-doped borosilicate glass via the Ag⁺-Na⁺ ion exchange. The influence of AgNO₃/NaNO₃ ratio in the molten salt on the Ag existing states was investigated. The results demonstrate that the isolated Ag⁺ ions exist in the Sm³⁺-doped borosilicate glass when the ratio of AgNO₃/NaNO₃ is 1/1000. The Ag NCs are formed in the Sm³⁺-doped borosilicate glass when the AgNO₃/NaNO₃ ratio is 1/10. The influence of Ag⁺ ions or Ag NCs on the PL of Sm³⁺ was systematically investigated. The results show that the PL of Sm³⁺ was enhanced by the energy transfer from Ag⁺ ions or Ag NCs to Sm³⁺.     

Role of Al3+ on tuning optical properties of Ce3+‐activated borosilicate scintillating glasses prepared in air

A colorless Ce³⁺‐activated borosilicate scintillating glass enriched with Gd₂O₃ is successfully synthesized in air atmosphere for the first time. The full replacement of 10 mol% BaO by Al₂O₃, and the partial substitution of 3 mol% SiO₂ by Si₃N₄ in the designed glass composition are crucial for this success. The role of Al³⁺ on tuning the optical properties of Ce³⁺‐activated borosilicate scintillating glass synthesized in air are analyzed by optical transmittance, X‐ray absorption near edge spectroscopy (XANES) spectra, photoluminescence (PL) and radioluminescence (RL) spectra. The results suggest that the stable Ce⁴⁺ ions can be effectively reduced to stable Ce³⁺ ions by the full replacement of BaO by Al₂O₃, and both the PL andRL intensity of the designed borosilicate scintillating glass are enhanced by a factor of 6.7 and 5.2, respectively. The integral RL intensity of the synthesized Ce³⁺‐activated borosilicate scintillating glass is ~17.2%BGO, with a light output of about 1180 ph/MeV. The strategy of substituting BaO by Al₂O₃ will trigger more scientific and technological considerations in designing novel fast scintillating glasses.     

Inward Migration of Glass‐Modifier Cations During Heat Treatment Under an N2 Atmosphere

An Na⁺/Ca²⁺‐deficient layer is observed to form on the glass surface region up to a depth of hundreds of nanometers when a soda‐lime‐silicate glass is heat treated under an N₂ atmosphere near its glass‐transition temperature. The measurements were performed using X‐ray photoelectron spectroscopy with C₆₀‐ion sputtering (C₆₀‐XPS) and dynamic secondary‐ion mass spectrometry (D‐SIMS) with consideration of the mass and charge balances. The increase in the amount of hydrogen is substantially less than the decrease in the total charge due to the loss of modifier cations in the Na⁺/Ca²⁺‐deficient layer; furthermore, the oxygen concentration in this layer is lower than the bulk value, suggesting that the silanol groups in the surface layer of the glass are dehydrated. A high‐concentration layer of Ca²⁺ is also confirmed in the dehydration layer of the glass heat treated under an N₂ atmosphere, suggesting that Na⁺ and Ca²⁺ ions migrate inward into the glass via an ion‐exchange reaction with protons, which migrate toward the surface from the bulk. We also confirmed that a thicker Na⁺/Ca²⁺‐deficient layer is formed on glass surfaces with higher water content. Our results suggest that the dehydration of the silanol groups is the driving force of the inward migration of Na⁺ and Ca²⁺ ions.     

Effect of CeO2 on the Glass Structure of Sodium Germanate Glasses

Germanate glasses have potential applications as optical fibers. Materials doped with rare earth ions are good candidates for optical, lasing, and magnetic applications. Based on the ternary system, CeO₂–Na₂O–GeO₂ a series of six glasses were fabricated using powder fusion, and varying the Na₂O content from 0 to 45 mol%, and a CeO₂ content constant at 3 mol%. The glasses were analyzed by FT‐IR, Raman and X‐ray photoelectron (XPS) spectroscopies to obtain information about the glass structure, cerium oxidation's state and how it is introduced in the glass network. FT‐IR and Raman spectra revealed the presence of GeO₆ and GeO₄ groups as well as Q² and Q³ units in the glasses with alkali low content. XPS spectra analysis revealed that the cerium ions were reduced from Ce⁴⁺ to Ce³⁺. The nonbonding to total oxygen ratio was estimated from the curve fitting of the O 1s core level spectra. Density and elastic parameters showed a nonlineal tendency in the change of the physical properties as a function of Na₂O content. Finally, photoluminescence spectroscopy confirmed the presence of Ce³⁺ ions. The characteristic 4f → 5d electronic transitions at 360 nm were detected, when a 280 nm excitation line of pulsed laser was used as excitation source.