Novel insights into electrical transport mechanism in ionic‐polaronic glasses

Transformation of electrical transport from ionic to polaronic in glasses, which are a potential class of new cathode materials, has been investigated in four series containing WO₃/MoO₃ and Li⁺/Na⁺ ions, namely: xWO₃–(30?0.5x)Li₂O–(30?0.5x)ZnO–40P₂O₅, xWO₃–(30?0.5x)Na₂O–(30.5x)ZnO–40P₂O₅, xMoO₃–(30?0.5x)Li₂O–(30?0.5x)ZnO–40P₂O₅, and xMoO₃–(30?0.5x)Na₂O–(30?0.5x)ZnO–40P₂O₅, 0 ≤ x ≤ 60, (mol%). This study reports a detailed analysis of the role of structural modifications and its implications on the origin of electrical transport in these mixed ionic‐polaron glasses. Raman spectra show the clustering of WO₆ units by the formation of W–O–W bonds in glasses with high WO₃ content while the coexistence of MoO₄ and MoO₆ units is evidenced in glasses containing MoO₃ with no clustering of MoO₆ octahedra. Consequently, DC conductivity of tungstate glasses with either Li⁺ or Na⁺ exhibits a transition from ionic to polaronic showing a minimum at about 20‐30 mol% of WO₃ as a result of ion‐polaron interactions followed by a sharp increase for six orders of magnitude as WO₃ content increases. The formation of WO₆ clusters involved in W‐O‐W linkages for tungsten glasses plays a key role in significant increase in DC conductivity. On the other hand, DC conductivity is almost constant for glasses containing MoO₃ suggesting an independent ionic and polaronic transport pathways for glasses containing 10‐50 mol% of MoO₃.     

High Chrome Refractory Characterization: Part I. Impact of Melt Reduction/Oxidation on the Corrosion Mechanism

High Cr₂O₃ containing Monofrax^™ K-3 is a robust refractory that is used in the fiberglass industry and used in radioactive waste glass melters worldwide. Monofrax^™ K-3 is tolerant of transition metal oxides but contains highly reduced solid solutions of spinels, that is, (Mg,Fe²⁺)(Al,Cr)₂O₃. Conversely, many of the waste feeds being processed are highly oxidizing. The K-3 refractory corrosion was tested in sealed crucibles starting with slurried melter feed instead of prereacted glass called for by ASTM C621. Testing the refractory coupon during the feed-to-glass conversion exposes the refractory to the oxidizing and reducing species being released during vitrification, for example, NO₃⁻, NO₂⁻, CO₂, CO, O₂. Corrosion rates measured in highly oxidizing (high nitrate) feeds 3 3 Oxidized feeds give glass Fe⁺²/∑Fe of ~0.
were ~1.8–2.8 times higher than those determined using prereacted glass or reduced feeds. 4 4 Reduced feeds give glass Fe⁺²/∑Fe of > 0.09.
Confirmatory corrosion rates were measured on Monofrax^™ K-3 coupons immersed in oxidizing feed in a 1/100th-scale HLW pilot-scale melter. Corrosion is heterogeneous or incongruent as Ni and Fe in the waste glass exchange with Mg and Al in the refractory. An insoluble NiFe₂O₄ spinel corrosion product is formed that can build up a protective layer along the refractory walls or spall and settle to the melter floor depending on melt pool convection/agitation.     

Thermochemical investigation of lithium borate glasses and crystals

Lithium borate (LB) glasses and crystals with x = Li/(Li + B) = mole fraction of Li₂O of 0.2–0.5 have been synthesized by the quenching method. The thermodynamics of these materials were analyzed by high-temperature oxide melt solution calorimetry. The formation enthalpies from oxides of glasses range from −33.6 to −67.3 kJ/mol and those of crystals range from −42.1 to −77.4 kJ/mol, where compositions are given on the basis of one mole of (Li₂O + B₂O₃). The formation enthalpies of both glasses and crystals become more negative with increasing Li₂O mole fraction up to 0.5. The enthalpies of formation of glasses can be fit over the entire composition range (0 < x < 1) by a quadratic polynomial). The vitrification enthalpies were derived for x = 0.2 to 0.5 and ranged from 8.5 to 17.6 kJ/mol. The main factors controlling energetics are the strongly exothermic acid–base reaction between the network former (B₂O₃) and the network modifier (Li₂O) and the formation of tetrahedrally coordinated boron in the glasses and crystals.     

Crystallization behavior of iron- and boron-containing nepheline (Na2O·Al2O3·2SiO2) based model high-level nuclear waste glasses

This study focuses on understanding the relationship between iron redox, composition, and heat-treatment atmosphere in nepheline-based model high-level nuclear waste glasses. Glasses in the Na₂O–Al₂O₃–B₂O₃–Fe₂O₃–SiO₂ system with varying Al₂O₃/Fe₂O₃ and Na₂O/Fe₂O₃ ratios have been synthesized by melt-quench technique and studied for their crystallization behavior in different heating atmospheres—air, inert (N₂), and reducing (96%N₂–4%H₂). The compositional dependence of iron redox chemistry in glasses and the impact of heating environment and crystallization on iron coordination in glass-ceramics have been investigated by Mössbauer spectroscopy and vibrating sample magnetometry. While iron coordination in glasses and glass-ceramics changed as a function of glass chemistry, the heating atmosphere during crystallization exhibited minimal effect on iron redox. The change in heating atmosphere did not affect the phase assemblage but did affect the microstructural evolution. While glass-ceramics produced as a result of heat treatment in air and N₂ atmospheres developed a golden/brown colored iron-rich layer on their surface, those produced in a reducing atmosphere did not exhibit any such phenomenon. Furthermore, while this iron-rich layer was observed in glass-ceramics with varying Al₂O₃/Fe₂O₃ ratio, it was absent from glass-ceramics with varying Na₂O/Fe₂O₃ ratio. An explanation of these results has been provided on the basis of kinetics of diffusion of oxygen and network modifiers in the glasses under different thermodynamic conditions. The plausible implications of the formation of iron-rich layer on the surface of glass-ceramics on the chemical durability of high-level nuclear waste glasses have been discussed.     

Structural dependence of crystallization in phosphorus-containing sodium aluminoborosilicate glasses

The article reports on the structural dependence of crystallization in Na₂O–Al₂O₃–B₂O₃–P₂O₅–SiO₂-based glasses over a broad compositional space. The structure of melt-quenched glasses has been investigated using ¹¹B, ²⁷Al, ²⁹Si, and ³¹P magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy, while the crystallization behavior has been followed using X-ray diffraction and scanning electron microscopy combined with energy dispersive spectroscopy. In general, the integration of phosphate into the sodium aluminoborosilicate network is mainly accomplished via the formation of Al–O–P and B–O–P linkages with the possibility of formation of Si–O–P linkages playing only a minor role. In terms of crystallization, at low concentrations (≤5 mol.%), P₂O₅ promotes the crystallization of nepheline (NaAlSiO₄), while at higher concentrations (≥10 mol.%), it tends to suppress (completely or incompletely depending on the glass chemistry) the crystallization in glasses. When correlating the structure of glasses with their crystallization behavior, the MAS NMR results highlight the importance of the substitution/replacement of Si–O–Al linkages by Al–O–P, Si–O–B, and B–O–P linkages in the suppression of nepheline crystallization in glasses. The results have been discussed in the context of (1) the problem of nepheline crystallization in Hanford high-level waste glasses and (2) designing vitreous waste forms for the immobilization of phosphate-rich dehalogenated Echem salt waste.     

Elucidating the Effect of Iron Speciation (Fe2+/Fe3+) on Crystallization Kinetics of Sodium Aluminosilicate Glasses

We report on the influence of Fe₂O₃ on the crystallization kinetics of nepheline (Na₂O·Al₂O₃·2SiO₂)‐based sodium aluminosilicate glasses. A series of glasses with varying Al₂O₃/Fe₂O₃ content were synthesized in the system 25Na₂O–(25–x) Al₂O₃–xFe₂O₃–50SiO₂ (x varies between 0 and 5 mol%) through melt‐quench technique. A systematic set of experiments were performed to elucidate the influence of iron speciation (Fe²⁺/Fe³⁺) on the crystallization kinetics of these glasses including: (1) obtaining the details of nonisothermal crystallization kinetics by differential scanning calorimetry, (2) determining the influence of heat treatment on the structure and iron coordination in glasses by X‐ray photoelectron spectroscopy and wet chemistry, and (3) following the crystalline phase evolution in glasses in air and inert environments by X‐ray diffraction and scanning electron microscopy. The crystallization of two polymorphs of NaAlSiO₄—carnegieite (orthorhombic) and nepheline (hexagonal)—was observed in all the glasses, wherein the incorporation of iron promotes the formation of nepheline over carnegieite while shifting the crystallization mechanism from surface to volume. The influence of environment (air versus inert) and iron content on the crystallization kinetics of these glasses is contextualized from the perspective of the devitrification problem usually observed in sodium‐ and alumina‐rich high level nuclear waste glasses.     

Properties and Crystallization Behavior of Sodium Iron Phosphate Glasses

Ternary Na₂O–Fe₂O₃–P₂O₅ (NFP) glasses with varying Na₂O/Fe₂O₃, Na₂O/P₂O₅, and Fe₂O₃/P₂O₅ ratios were prepared. The properties and crystallization tendencies were systemically investigated. It is shown that both density and chemical stability of the glass increase with Fe₂O₃. In contrast the Na₂O/P₂O₅ ratio has little effect on the glass properties for a fixed Fe₂O₃ content. The crystallization behavior of the glasses was analyzed by DTA and XRD. Unlike Li₂O–Fe₂O₃–P₂O₅ glasses NFP glasses were found to be stable against crystallization. 15Na₂O–27Fe₂O₃–58P₂O₅ glass was found to have the highest chemical stability among the studied NFP samples; the influence of TiO₂, ZrO₂ on crystallization in this composition was studied. It is found that addition of 3.4 mol% TiO₂ or 2.2 mol% ZrO₂ had little effect on the crystallization behavior of this glass. However, when the amounts of TiO₂ or ZrO₂ were increased to 8.4 or 5.5 mol% respectively the glass readily devitrified. Furthermore the addition of fluorine (introduced by replacing Na₂CO₃ with NaF in the glass batch) leads to amorphous glasses which could be crystallized to form NaFeP₂O₇ upon controlled thermal treatment. With increasing NaF additions the activation emergy for crystallization decreased from 428 to 381 kJ/mol.     

Phosphate-based glasses and glass ceramics for immobilization of lanthanides and actinides

Borosilicate glasses used to be a choice to vitrify nuclear wastes in most of the countries. However, Russian HLW vitrification plant at the Mayak Production Association (Chelyabinsk Region, Urals) uses phosphate-based glasses. Initially, Russian HLW glasses were based on sodium-aluminophosphate with the following approximate composition (mol.%): 40 Na₂O_, 20 Al₂O₃, 40 P₂O₅. Recently we have modified this composition by replacing of up to 50% Al₂O₃ with Fe₂O₃. Such replacement increases chemical durability and resistance to devitrification and radiation of the glasses. The phase composition and structure of these glasses containing ~ 10?wt% RE oxides and ~ 10, ~ 50, and ~ 100?wt% UO₃ (over 100?wt%) were studied in details using XRD and FTIR. Glasses and glass-ceramics have high chemical durability. Thus, the glasses and glass ceramics on sodium-aluminum-iron-phosphate basis are good waste forms for lanthanide fraction of HLW generated at spent nuclear fuel pyroprocessing and minor actinides.     

Effect of small additions of Li2O on phase separation and crystallization of barium-silicate glasses

It is known that the addition of Li₂O to 33.3BaO-66.7SiO₂ glass, whose composition is the same as BaSi₂O₅, promotes crystallization of BaSi₂O₅. In this study, in order to clarify the effect of a smaller amount of Li₂O, xLi₂O-(30-x)BaO-70SiO₂[mol%] (x = 0, 0.2, 0.5) glasses were prepared. The main crystalline phases in the heat treatments near the maximum crystallization peak temperature, were high-BaSi₂O₅ and low-BaSi₂O₅ which transformed from high-BaSi₂O₅. It is found that the introduction of only 0.2 mol% and 0.5 mol% Li₂O significantly changes the crystallization behavior. In the composition without Li₂O, only high-BaSi₂O₅ was formed after heat treatment even for 24 h. For compositions containing Li₂O, low-BaSi₂O₅ was formed within 1 h of heat treatment. In these compositions, it is found that the addition of Li₂O enhances phase separation in the early stage of heat treatment, resulting in the formation of Si-rich droplet phases and Ba-rich phases. The composition of the Ba rich glass phase would be close to the stoichiometric composition of BaSi₂O₅, suggesting a significant change in crystallization behavior.     

Influence of Al2O3/SiO2 ratio in multicomponent LNAS glasses and glass-ceramics on the crystallization behavior,microstructure and mechanical performance

Transparent glass-ceramics containing eucryptite and nepheline crystalline phases were prepared from alkali (Li, Na) aluminosilicate glasses with various mole substitutions of Al₂O₃ for SiO₂. The relationships between glass network structure and crystallization behavior of Li₂O–Na₂O–Al₂O₃–SiO₂ (LNAS) glasses were investigated. It was found that the crystallization of the eucryptite and nepheline in LNAS glasses significantly depended on the concentration of Al₂O₃. LNAS glasses with the addition of Al₂O₃ from 16 to 18 mol% exhibited increasing Q⁴ (mAl) structural units confirmed by NMR and Raman spectroscopy, which promoted the formation of eucryptite and nepheline crystalline phases. With the Al₂O₃ content increasing to 19–20 mol%, the formation of highly disordered (Li, Na)₃PO₄ phase which can serve as nucleation sites was inhibited and the crystallization mechanism of glass became surface crystallization. Glass-ceramics containing 18 mol% Al₂O₃ showed high transparency ～84% at 550 nm. Moreover, the microhardness, elastic modulus and fracture toughness are 8.56 GPa, 95.7 GPa and 0.78 MPa m^1/2 respectively. The transparent glass-ceramics with good mechanical properties show high potential in the applications of protective cover of displays.     

Phase formation of Na+-beta-aluminas synthesized by double zeta process

Na⁺-beta-aluminas in the Na₂O–Al₂O₃–Li₂O ternary system were synthesized by double zeta process and the dependence of the crystal phase formation on the composition and the calcination temperature was studied. For the synthesis of Na⁺-β/β″-alumina, sodium aluminate varying compositions of [Na₂O]:[Al₂O₃] = 1:4–1:6 and lithium aluminate in the forms of Li₂O·5Al₂O₃ with different amounts of Li₂O (0.35–0.45 wt%) were well-mixed and calcined at temperatures ranging between 1300 and 1600 °C for 2 h. The β″-alumina fraction appeared to be approximately 10% higher compared to the conventional solid state reaction, showing around 70% of β″-alumina fraction. These values increased about 10–15% by additional heating near the binary eutectic temperature for a short time.     

Dual effect of ZrO2 on phase separation and crystallization in Li2O–Al2O3–SiO2–P2O5 glasses

ZrO₂ is an effective nucleation agent for low-expansion lithium–aluminum silicate (LAS) glass–ceramic (GC) with high Al₂O₃ content. However, the effect of ZrO₂ is still not fully understood in LAS glasses with low contents of Al₂O₃ and P₂O₅. In this work, the effect of ZrO₂ on the phase separation and crystallization of Li₂O–Al₂O₃–SiO₂–P₂O₅ glasses were investigated. The results revealed that ZrO₂ significantly increased T_g and the crystallization temperature of Li₂SiO₃ and Li₂Si₂O₅ crystals. Li₃PO₄ crystals precipitated preferentially in the glass containing 3.6-mol% ZrO₂, wherein Zr was stable in the network and no precipitation of ZrO₂ nanocrystals was observed. Moreover, the separation of phosphate-rich phases in the as-quenched glasses increased with the addition of ZrO₂. The findings of the study revealed a dual role of ZrO₂. First, ZrO₂ acted as a glass network former rather than a nucleation agent, increasing glass viscosity and the nucleation barrier of Li₂SiO₃ through its strong network connectivity. Second, as Zr preferentially combined with non-bridging oxygen to form Si–O–Zr linkages, a sufficient amount of charge-balancing Li⁺ ions existed in the network, which promoted the separation of phosphate-rich phases. It indicated that the incorporation of ZrO₂ contributes to the activation of the nucleation role of P₂O₅, thus contributing to the formation of nanocrystals and fine microstructure of GCs.     

Submixture model to predict nepheline precipitation in waste glasses

High-alumina high-level waste (HLW) glasses are prone to nepheline precipitation during canister-centerline cooling (CCC). If sufficient nepheline forms, the chemical durability of the glass will be significantly impacted. Overly conservative constraints have been developed and used to avoid the deleterious effects of nepheline formation in U.S. HLW glasses. The constraints used have been shown to significantly limit the loading of waste in glass at Hanford and therefore the cost and schedule of cleanup. A 90-glass study was performed to develop an improved understanding of the impacts of glass composition on the formation of nepheline during CCC. The CCC crystallinity data from these glasses were combined with 657 glasses found in the literature. The trends showed significant effects of Na₂O, Al₂O₃, SiO₂, B₂O₃, CaO, Li₂O, and potentially K₂O on the propensity for nepheline formation. A pseudo-ternary submixture model was proposed to identify the glass composition region prone to nepheline precipitation. This pseudo-ternary with axes of SiO₂ + 1.98B₂O₃, Na₂O + 0.653Li₂O + 0.158CaO, and Al₂O₃ was found to divide glasses that precipitate nepheline during CCC from those that do not. Application of this constraint is anticipated to increase the loading of Hanford high-alumina HLWs in glass by roughly one-third.     

Alkali metal tungsten bronze-doped energy-saving glasses for near-infrared shielding applications

Tungsten bronze has attracted global attention for its applications in near-infrared (NIR)-shielding windows. Here, alkali metal tungsten bronze (M_xWO₃, M = one or two types of Li, Na, and K)-doped glasses are prepared by a simple melt-quenching method. Their structure and properties were characterized by XRD, Raman spectroscopy, XPS and UV–Vis–NIR spectrophotometry. The effects of M on their structure and the NIR shielding performance are investigated. The LiF sample has the best NIR shielding performance, but its visible transmittance is sacrificed due to its low quality. The glasses containing mixed Li⁺ and K⁺ cooperate to form a high-quality Li⁺/K⁺-codoped tungsten bronze, while the glasses containing mixed Li⁺ and Na⁺ compete for limited tungsten resources to form Li⁺- and Na⁺-doped tungsten bronzes separately. The research here is helpful for understanding the role of different alkali metal ions in bulk energy-saving glass and is hugely significant for the guidance of the future applications of energy-saving glass without films.     

Structural dependence of crystallization in glasses along the nepheline (NaAlSiO4) ‐ eucryptite (LiAlSiO4) join

Lithium and sodium aluminosilicates are important glass‐forming systems for commercial glass‐ceramics, as well as being important model systems for ion transport in battery studies. In addition, uncontrolled crystallization of LiAlSiO₄ (eucryptite) in high‐Li₂O compositions, analogous to the more well‐known problem of NaAlSiO₄ (nepheline) crystallization, can cause concerns for long‐term chemical durability in nuclear waste glasses. To study the relationships between glass structure and crystallization, nine glasses were synthesized in the Li_xNa_1‐xAlSiO₄ series, from x = 0 to x = 1. Raman spectra, nuclear magnetic resonance (NMR) spectroscopy (Li‐7, Na‐23, Al‐27, Si‐29), and X‐ray diffraction were used to study the quenched and heat‐treated glasses. It was found that different LiAlSiO₄ and NaAlSiO₄ crystal phases crystallize from the glass depending on the Li/Na ratio. Raman and NMR spectra of quenched glasses suggest similar structures regardless of alkali substitution. Li‐7 and Na‐23 NMR spectra of the glass‐ceramics near the endmember compositions show evidence of several differentiable sites distinct from known Li_xNa_1‐xAlSiO₄ crystalline phases, suggesting that these measurements can reveal subtle chemical environment differences in mixed‐alkali systems, similar to what has been observed for zeolites.     

Investigation of the Electrode Properties of Glasses as a Method for Elucidating the Structural Role of Their Components: The 25Na2O–15TiO2–6ZrO2–4RxOy–50SiO2 System (R = Ca, Ba, Sr, La, Nb, and Ta)

Glass electrodes are fabricated from the title glasses, and the emf–pH curves are measured at room temperature. The structural role played by the glass components is elucidated from an analysis of the curves. The TiO₂, ZrO₂, Nb₂O₅, and Ta₂O₅ oxides are network-formers, and their effect on the electrode properties of glasses upon simultaneous introduction is summarized within the limits of the studied compositions, whereas the total acidity of the glass increases. The oxides of modifiers La, Ba, Sr, and Ca neutralize the acidic groups of the network-former (supposedly [ZrO_6/2]^2–). The tendency to neutralization decreases in the above order. The ionic electrode selectivity of glasses with an increased content of ZrO₂, which contain Nb₂O₅ and Ta₂O₅, is expressed by the series H⁺ Na⁺ > Li⁺ > K⁺.     

Toward Understanding the Effect of Low‐Activity Waste Glass Composition on Sulfur Solubility

The concentration of sulfur in Hanford low‐activity waste (LAW) glass melter feed will be maintained below the point where the salt accumulates on the melt surface. The allowable concentrations may range from near zero to over 2.05 wt% (of SO₃ on a calcined oxide basis) depending on the composition of the melter feed and processing conditions. If the amount of sulfur exceeds the melt tolerance level, a molten salt will accumulate which may upset melter operations and potentially shorten the useful life of the melter. At the Hanford site, relatively conservative limits have traditionally been placed on sulfur loading in melter feed, which in turn significantly increases the amount of LAW glass that will be produced. Crucible‐scale sulfur solubility data and scaled melter sulfur tolerance data have been collected on simulated Hanford waste glasses over the last 15 years. These data were compiled and analyzed. An empirical model was developed to predict the solubility of SO₃ in glass based on 253 simulated Hanford LAW glass compositions. This model represents the data well, accounting for over 85% of the variation in data, and was well validated. The model was also found to accurately predict the maximum amount of sulfur in melter feed that did not form a salt layer in 13 scaled melter tests of simulated LAW glasses. The model can be used to help estimate glass volumes and make informed decisions on process options (e.g., scale of supplemental LAW treatment facility, and pretreatment facility performance requirements). The model also gives quantitative estimates of component concentration effects on sulfur solubility. The components that increase sulfur solubility most are Li₂O > V₂O₅ > CaO ≈ P₂O₅ > Na₂O ≈ B₂O₃ > K₂O. The components that decrease sulfur solubility most are Cl > Cr₂O₃ > Al₂O₃ > ZrO₂ ≈ SnO₂ > Others (i.e., the sum of minor components) ≈SiO₂. The order of component effects is similar to previous literature data, in most cases.     

Effect of Al2O3 and K2O content on structure,properties and devitrification of glasses in the Li2O–SiO2 system

The effect of Al₂O₃ and K₂O content on structure, sintering and devitrification behaviour of glasses in the Li₂O–SiO₂ system along with the properties of the resultant glass–ceramics (GCs) was investigated. Glasses containing Al₂O₃ and K₂O and featuring SiO₂/Li₂O molar ratios (3.13–4.88) far beyond that of lithium disilicate (Li₂Si₂O₅) stoichiometry were produced by conventional melt-quenching technique along with a bicomponent glass with a composition 23Li₂O–77SiO₂ (mol.%) (L₂₃S₇₇). The GCs were produced through two different methods: (a) nucleation and crystallization of monolithic bulk glass, (b) sintering and crystallization of glass powder compacts.Scanning electron microscopy (SEM) examination of as cast non-annealed monolithic glasses revealed precipitation of nanosize droplet phase in glassy matrices suggesting the occurrence of phase separation in all investigated compositions. The extent of segregation, as judged from the mean droplet diameter and the packing density of droplet phase, decreased with increasing Al₂O₃ and K₂O content in the glasses. The crystallization of glasses richer in Al₂O₃ and K₂O was dominated by surface nucleation leading to crystallization of lithium metasilicate (Li₂SiO₃) within the temperature range of 550–900 °C. On the other hand, the glass with lowest amount of Al₂O₃ and K₂O and glass L₂₃S₇₇ were prone to volume nucleation and crystallization, resulting in formation of Li₂Si₂O₅ within the temperature interval of 650–800 °C.Sintering and crystallization behaviour of glass powders was followed by hot stage microscopy (HSM) and differential thermal analysis (DTA), respectively. GCs from composition L₂₃S₇₇ demonstrated high fragility along with low flexural strength and density. The addition of Al₂O₃ and K₂O to Li₂O–SiO₂ system resulted in improved densification and mechanical strength.     

Structural and Optical Properties of Erbium and Ytterbium Codoped Germanoniobophosphate Glasses

A series of glasses with compositions of 20Na₂O–30Nb₂O₅–(5?y?z)Al₂O₃–30P₂O₅–(15?x)TiO₂–xGeO₂–yEr₂O₃–zYb₂O₃, where x = (0; 5; 10; 15), y = (0; 1), z = (0; 2) mol%, were investigated with respect to their structural, optical, and luminescence properties. The coordination of the germanium(IV) ion is normally reported as being mainly tetrahedral. However, results of this study suggest that the germanium(IV) ion may have an octahedral coordination and that TiO₂ is substituted. This proposition can be done mainly by ³¹P MAS‐NMR spectroscopy, which spectra show predominantly pyrophosphate chains in the different glasses, without changes in their polymerization after substitution. A similar coordination of germanium can also be identified by the photoluminescence behavior of the different codoped samples, which shows similar erbium(III) emission decay lifetimes (5 ms), and Judd–Ofelt intensity parameters. It was found that the upconversion emission process involved 1.5 photons. Regarding the thermal behavior, it is noted that the glasses containing higher proportions of GeO₂ exhibit higher thermal stability and are therefore more resistant to devitrification when compared to compositions containing more TiO₂.     

Evaluation of novel composition (SiO2–CaO–Na2O–P2O5, SrO–CuO) degradable amorphous silicate glasses properties and comprehensive characterization of the thermal features

The current work presents and discusses the findings of a comprehensive study on the structural, chemical and thermal properties of SrO and CuO incorporated SiO₂–CaO–Na₂O–P₂O₅ amorphous silicate glass with a novel composition. Here, fundamental features (experimental density, oxygen density, and hardness) of all glasses were determined and chemical as well as phase composition of the glasses was verified with XRF and XRD, respectively. Moreover, the thermal behavior (viscos flow and crystallization kinetics) of amorphous silicate glass was investigated by non-isothermal methods using DTA analysis. The activation energies of glass transition (E_g) were calculated in the range of 546–1115 kJ/mol by Kissinger method, whereas the activation energies of crystallization (E_c) were calculated in the range of 164–270 kJ/mol by three different methods (Kissinger, Ozawa, Yinnon and Uhlmann). Avrami exponent (n) values ranged from 1.17 to 3.28 demonstrated that amorphous silicate glasses have different crystallization mechanism. Working temperature, which is one of the parameters indicating glass stability, increased with the incorporation of Sr and Cu from 187 °C to 245 °C. The initial dissolution measurement has been applied to study the degradability behavior of Sr and Cu incorporated amorphous glasses in vitro. Quantitative evaluation of Si⁴⁺ (0.156–0.373 kV), Ca²⁺ (0.043–0.332 kV), Na⁺ (0.044–0.329 kV), P⁵⁺ (0.057–0.289 kV), Sr²⁺ (0.134–0.385 kV), and Cu²⁺ (0.090–0.203 kV) depending on the ion activation energy (E_a-ion) and ion concentration at different temperature values (24, 37 and 55 °C) was performed in contact with Tris-HCl solution by ICP-OES analysis. The results revealed that investigated glasses were degradable and incorporation of Sr and Cu affected the glass initial dissolution. Overall, investigated glasses are suitable for various application such as hot-working production, glass-ceramic manufacturing, and glass or glass-ceramic scaffolds fabrication, due to wide working temperature ranges and high crystallization tendencies of the developed glasses.