Viscosity and Fragility of Alkaline‐Earth Sodium Boroaluminosilicate Liquids

Understanding the composition and temperature dependence of viscosity of silicate liquids is of the highest importance not only for geological processes but also for production of industrial glass. In this work, we have determined the temperature dependence of equilibrium liquid viscosity of 36 alkaline‐earth sodium boroaluminosilicate liquids as a function of the Si/Al ratio and the type of alkaline‐earth oxide (MgO, CaO, SrO, or BaO). We demonstrate that the isokom temperature at 10¹² Pa s (i.e., the glass transition temperature) generally increases with increasing Si/Al ratio, whereas the isokom temperatures at 10⁴ and 10^1.5 Pa s exhibit a decrease with increasing [Al₂O₃] in the peraluminous regime. The isokom temperatures decrease with increasing alkaline‐earth size in the peralkaline regime, whereas they increase with increasing alkaline‐earth size in the peraluminous regime. The liquid fragility index m exhibits a minimum value at an intermediate Si/Al ratio, with the position of the minimum increasing to a higher value of [Al₂O₃] with increasing alkaline‐earth size. We have discussed our findings in terms of the underlying structural and topological changes as a function of composition and temperature.     

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.     

Structural and emission properties of Eu3+‐doped alkaline earth zinc‐phosphate glasses for white LED applications

Quaternary alkaline earth zinc‐phosphate glasses in molar composition (40 ? x)ZnO – 35P₂O₅ – 20RO – 5TiO₂ – xEu₂O₃ (where x=1 and R=Mg, Ca, Sr, and Ba) were prepared by melt quenching technique. These glasses were studied with respect to their thermal, structural, and photoluminescent properties. The maximum value of the glass transition temperature (T_g) was observed for BaO network modifier mixed glass and minimum was observed for MgO network modifier glass. All the glasses were found to be amorphous in nature. The FT‐IR suggested the glasses to be in pyrophosphate structure, which matches with the theoretical estimation of O/P atomic ratio and the maximum depolymerization was observed for glass mixed with BaO network modifier. The intense emission peak was observed at 613 nm (⁵D₀→⁷F₂) under excitation of 392 nm, which matches well with excitation of commercial n‐UV LED chips. The highest emission intensity and quantum efficiency was observed for the glass mixed with BaO network modifier. Based on these results, another set of glass samples was prepared with molar composition (40 ? x)ZnO – 35P₂O₅ – 20BaO – 5TiO₂ – xEu₂O₃ (x=3, 5, 7, and 9) to investigate the optimized emission intensity in these glasses. The glasses exhibited crystalline features along with amorphous nature and a drastic variation in asymmetric ratio at higher concentration (7 and 9 mol%) of Eu₂O₃. The color of emission also shifted from red to reddish orange with increase in the concentration of Eu₂O₃. These glasses are potential candidates to use as a red photoluminsecent component in the field of solid‐state lighting devices.     

Chemical durability of borosilicate pharmaceutical glasses: Mixed alkaline earth effect with varying [MgO]/[CaO] ratio

Glass for pharmaceutical packaging requires high chemical durability for the safe storage and distribution of newly developed medicines. In borosilicate pharmaceutical glasses which typically contain a mixture of different modifier ions (alkali or alkaline earth), the dependence of the chemical durability on alkaline earth oxide concentrations is not well understood. Here, we have designed a series of borosilicate glasses with systematic substitutions of CaO with MgO while keeping their total concentrations at 13 mol% and a fixed Na₂O concentration of 12.7 mol%. We used these glasses to investigate the influence of R = [MgO]/([MgO] + [CaO]) on the resistance to aqueous corrosion at 80°C for 40 days. It was found that this type of borosilicate glass undergoes both leaching of modifier ions through an ion exchange process and etching of the glass network, leading to dissolution of the glass surface. Based on the concentration analysis of the Si and B species dissolved into the solution phase, the dissolved layer thickness was found to increase from ~100 to ~170 nm as R increases from 0 to 1. The depth profiling analysis of the glasses retrieved from the solution showed that the concentration of modifier ions (Na⁺, Ca²⁺, and Mg²⁺) at the interface between the solution and the corroded glass surface decreased to around 40%–60% of the corresponding bulk concentrations, regardless of R and the leaching of modifier cations resulted in a silica-rich layer in the surface. The leaching of Ca²⁺ and Mg²⁺ ions occurred within ~50 and <25 nm, respectively, from the glass surface and this thickness was not a strong function of R. The leaching of Na⁺ ions varied monotonically; the thickness of the Na⁺ depletion layer increased from ~100 nm at R = 0 to ~200 nm at R = 1. Vibrational spectroscopy analysis suggested that the partial depletion of the ions may have caused some degree of the network re-arrangement or re-polymerization in the corroded layer. Overall, these results suggested that for the borosilicate glass, replacing [CaO] with [MgO] deteriorates the chemical durability in aqueous solution.     

Effect of the Glass Structure on Emission of Rare‐Earth‐Doped Borate Glasses

A series of glasses composed of xB₂O₃–8Al₂O₃‐(90?x)Na₂O–R₂O₃ (x = 65, 70, 75, 80, 85; R = Dy³⁺, Tb³⁺, Sm³⁺) were prepared through melt‐quenching. Structural evolution was induced by varying the glass composition. Increasing the glass network former B₂O₃ enhanced the luminescence of rare‐earth ions, as observed in the emission spectra. The mechanism of the glass structural evolution was investigated by the NMR spectra analysis. The dispersant effect of the glass structure was believed to promote the better distribution of the rare‐earth ions in the matrix and reduced the concentration quenching between them. The relationship between the glass structure and its optical properties was established.     

Viscosity-structure relationship of alkaline earth silicate melts containing manganese oxide and calcium fluoride

The effect of CaF₂ on the viscosities of the MO-SiO₂-xMnO-yCaF₂ melts (M[=Ca or Ba]O/SiO₂ = 0.4-0.5, x = 10[±1] or 40[±2] mol%, y = 0-15 mol%) have been studied at high temperatures. At MnO = 40[±2] mol%, the viscosity of Ba-Mn-silicate melts is lower than that of Ca-Mn-silicate melts because Mn²⁺ is a strong network modifier in the former system. However, the viscosities of both alkaline earth silicate melts with MnO = 10[±1] mol% are not affected by cation type because MnO activity is too low to affect the viscosity of the melts. The CaF₂ addition decreases the viscosities of the Ba-Mn-silicate melts with low-MnO contents, while it has less impact on the viscosities of the melts with high-MnO contents. The effect of CaF₂ on the relationship between viscosity and the structure of the silicate melts is quantitatively analyzed using the micro-Raman spectra of quenched glass samples. The NBO/Si ratio of alkaline earth silicate melts, which indicates the degree of polymerization of the silicate networks, has a linear relationship with the activation energy for the viscous flow of the melts.     

Ionic Conductivity in Sodium–Alkaline Earth–Aluminosilicate Glasses

The effect of alkaline‐earth ions on Na transport in aluminosilicate glasses was studied by measuring ionic conductivity for a systematic compositional series of Na₂O–RO–Al₂O₃–SiO₂ glasses (R=Mg, Ca, Sr, Ba). The Na transport in aluminosilicate glass could be affected by compositional changes in aluminum coordination and nonbridging oxygen as well as physical properties such as dielectric constant, shear modulus, and ionic packing factor. Through careful experimental designs and measurements, the main determinants among these parameters were identified. ²⁷Al MAS‐NMR indicated that all aluminum species contained in these glasses are four‐coordinated. The activation energy for ion conductivity decreased with increasing aluminum content and decreasing ionic radii of the alkaline‐earth ion in the region where [Al] < [Na]. When the aluminum content exceeded the sodium content ([Al] > [Na]), the composition dependence of the activation energy depended on the specific alkaline earth. These results are explained based on variations in free volume and dielectric constant caused by structural changes around the AlO₄ charge compensation sites. These structure changes occur in response to the smaller size and higher field strength of the alkaline‐earth ions, and are most prevalent in the compositions which require bridging of two AlO₄ sites by the alkaline‐earth ion for charge compensation.     

Reduction‐Induced Inward Diffusion and Crystal Growth on the Surfaces of Iron‐Bearing Silicate Glasses

We investigate the sodium inward diffusion (i.e., sodium diffusion from surface toward interior) in iron containing alkaline‐earth silicate glasses under reducing conditions around T_g and the induced surface crystallization. The surface crystallization is caused by formation of a silicate‐gel layer first and then the growth of silica crystals on the glass surface. The type of alkaline‐earth cations has a strong impact on both the glass transition and the surface crystallization. In the Mg‐containing glass, a quartz layer forms on the glass surface. This could be attributed to the fact that Mg²⁺ ions have stronger bonds to oxygen and lower coordination number (4–5) than Ca²⁺, Sr²⁺, and Ba²⁺ ions. In contrast, a cristobalite layer forms in Ca‐, Sr‐, and Ba‐containing glasses.     

Mixed modifier effect in lithium‐calcium borosilicate glasses

The mixed modifier effect (MME) in the lithium‐calcium borosilicate glasses, which have a composition of 0.4[(1?x)Li₂O–xCaO]–0.6[(1?y)B₂O₃–ySiO₂] with x in the range of 0~1 and y in the range of 0.33~0.83, is investigated. The MME manifests itself as a positive deviation from linearity in the activation energy of electrical conductivity (Ea^σ) and as a negative deviation from linearity in the fraction of four‐coordinated boron (N₄), glass transition temperature (T_g), dilatometric softening temperature (T_d), Vickers microhardness (H_v), dielectric constant (ε), and dielectric loss (tanδ). Moreover, the deviation, which exhibits a maximum at [CaO]/([CaO]+[Li₂O])=0.5, is enhanced with increasing [SiO₂]/[B₂O₃] ratio in the glass network. The observed MME in T_g, T_d, and H_v are attributed to the bond weakening in the network; however, the MME in ε, tanδ, and Ea^σ are caused by the obstruction of modifier transport in the glass network.     

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.     

Chemical Processes During Energy‐Saving Preparation of Lightweight Ceramics

Lightweight glass‐ceramic material similar to foam glass was obtained at 700°C–800°C directly from alkali‐activated silica clay and zeolitized tuff without preliminary glass preparation. It was characterized by low bulk density of 100–250 kg/m³ and high pore size homogeneity. Chemical processes occurring in alkali‐activated silica clay and zeolitized tuff were studied using X‐ray diffraction, thermal gravimetry, IR‐spectroscopy, and scanning electron microscopy. Pore formation in both compositions is caused by dehydration of hydrated sodium polysilicates (Na₂O·mSiO₂·nH₂O), formed during alkali activation. Additional pore‐forming gas source in alkali‐activated zeolitized tuff is trona, Na₃(CO₃)(HCO₃)·2H₂O, formed during interaction between unbound NaOH and CO₂ and H₂O from air. Influence of mechanical activation of raw materials on chemical processes occurring in alkaline compositions was also studied.     

Structural impact of nitrogen incorporation on properties of alkali germanophosphate glasses

The structure, atomic packing density, calorimetric glass transition, and hardness of mixed sodium–lithium germanophosphate oxynitride glasses with varying Ge/P and N/P ratios were investigated. The combined influences of nitridation and mixed network former effect (MNFE) on the glass structure were analyzed using Raman spectroscopy, X‐ray photoelectron spectroscopy (XPS), and ³¹P nuclear magnetic resonance (NMR) spectroscopy. Evidence for the existence of germanium in a higher coordination state, i.e., five‐ or sixfold coordination, was obtained by performing XPS analysis of the oxide glasses, with indication of conversion to tetrahedral coordination upon nitridation. Raman spectroscopy measurements implied that the germanate network was modified upon nitridation, including the removal of ring‐like germanate structures and P–O–Ge mixed linkages. The partial anionic N‐for‐O substitution gave rise to the linear dependence of the glass transition temperature (T_g) and hardness (H_V) on nitrogen content (expressed as N/P ratio), especially for lower Ge/P ratio. However, nitridation also caused an unexpected increase in liquid fragility and decrease in density. This suggests that the governing structural parameter for property evolution in such LiNaGePON glasses is not only the increased degree of cross‐linking of the phosphate chains, but rather the short‐ and intermediate‐range structural modifications within the germanate component of the oxynitride glasses.     

Effect of crystalline fraction on upconversion luminescence in Er3+/Yb3+ Co-doped NaYF4 oxyfluoride glass-ceramics

The crystalline fraction were adjusted MgO concentration and the corresponding effect on upconversion (UC) luminescence in Er³⁺/Yb³⁺ co-doped NaYF₄ oxyfluorode glass-ceramics was investigated. With increase of MgO and the content of Na₂O reduced, the internal network structure of the glass became compact, which made the size of NaYF₄ nanocrystals unchanged, while the average distance between the nanocrystals increased significantly. Crystal growth is limited with the glass network, keeping the crystal size not changed. SNM-1 glass ceramics samples show a predominant red up-conversion emission under near infrared excitation at 980 nm, while a predominant green emission is observed in the SNM-3 samples. In this paper, it was indicated that it changed the effect of glass network modifier MgO in the glass structure. The possible mechanism responsible for the color variation of UC in Er³⁺/Yb³⁺ co-doped was discussed.     

Field strength effect on structure,hardness, and crack resistance in single modifier aluminoborosilicate glasses

Although the interactions among glass formers and modifiers, for example, connectivity and charge distribution, have been studied extensively in oxide glasses, the impact of a particular modifier species on the mechanical performance of aluminoborosilicate (ABS) glasses is not well understood. This work compares the indentation properties of six ABS glasses, each of which contains a different network modifier (NWM) with varying field strength (FS). Three alkali and three alkaline earth ABS glasses were designed with low NWM content and [NWM] ≈ [Al₂O₃], to test the modifier FS effect at low concentrations and to maximize three-coordinated boron. It has been found that both hardness and crack resistance increase with increasing FS in these ABS systems, which is surprising in the context of historical reports. Using ¹¹B, ²⁷Al, and ²⁹Si solid-state nuclear magnetic resonance, this work provides evidence of how charge distributions differ as a function of NWM species, and how this relates to the observed indentation behaviors.     

Optically transparent aromatic poly(ester imide)s with low coefficients of thermal expansion. 2: Effect of the introduction of alkyl‐substituted p‐biphenylene units

A series of ester‐linked tetracarboxylic dianhydrides (TA‐X) were synthesized from trimellitic anhydride chloride and 4,4′‐biphenol analogs containing different numbers and positions of methyl substituents. Aromatic poly(ester imide)s (PEsIs) were polymerized from TA‐Xs and 2,2′‐bis(trifluoromethyl)benzidine to investigate the film properties systematically. A significant substituent effect on the target properties (T_g, optical transparency, the linear coefficient of thermal expansion (CTE) and ductility) was observed. A PEsI containing 2,2′,3,3′,5,5′‐hexamethyl‐substituted p‐biphenylene units was chemically imidized in a homogeneous state. It was highly soluble at room temperature, even in less hygroscopic non‐amide solvents such as cyclopentanone (CPN), and provided a stable CPN solution with a high solid content. The CPN‐cast PEsI film was almost colorless as suggested from the rather low yellowness index (3.2), high light transmittance at 400 nm (71.5%) and very low haze (1.15%). This PEsI film also had a high T_g (294 °C, determined by thermomechanical analysis) in addition to a low CTE (21.7 ppm K^?1), moderate film ductility and very low water uptake. A structural modification of the PEsI by copolymerization with a tetracarboxylic dianhydride with a rigid/linear structure was effective in further reducing the CTE while maintaining the other excellent target properties. Thus, some of the PEsIs developed in this work are promising candidates as novel plastic substrates for use in image display devices. © 2017 Society of Chemical Industry     

Enhanced Up‐Conversion Luminescence in Er3+‐Doped 25GeS2·35Ga2S3·40CsCl Chalcogenide Glass–Ceramics

Enhanced luminescence in rare‐earth‐doped chalcogenide glass–ceramics is of great interest for the potential integrated optoelectronic devices. However, fundamental mechanism on the enhancement of luminescence upon crystallization remains largely unknown. We report the fabrication and characterization of wide transmission chalcogenide glass and glass–ceramics based on the 25GeS₂·35Ga₂S₃·40CsCl:0.3Er glass composition, and discuss the mechanism of enhanced luminescence. By monitoring the ⁴I_9/2–⁴I_15/2 of Er³⁺ transition, up‐conversion luminescence of 12 times higher was observed in glass–ceramics compared with that in base glass. Electron paramagnetic resonance (EPR) and Raman scattering spectroscopies were employed to obtain the information of selective environment of Er³⁺ ions and microstructural evolution with the crystallization progress. Both of them evidenced that the enhanced up‐conversion luminescence was mainly related to the local environmental evolution from a mixed chlorine‐sulfur coordination to a low phonon energy chlorine coordination in the residual glassy matrix of glass–ceramics.     

Incorporating bis‐benzimidazole into polyimide chains for effectively improving thermal resistance and dimensional stability

Heteroaromatic 6,6′‐bis[2‐(4‐aminobenzene)benzimidazole] and its corresponding copolyimides were synthesized to produce high temperature resistant polyimides (PIs). Due to the rigidity and aromaticity of heterocyclic bis‐benzimidazole, and the increased hydrogen bonding interactions, these PIs were found to have a high glass transition temperature (T_g) over 457 °C, which also guarantees a better dimensional stability with a coefficient of thermal expansion (CTE) lower than 10 ppm K^?1 in a wider temperature range of 50–400 °C. In addition, the PIs exhibit excellent thermal stability (5% weight loss temperature higher than 559 °C) along with outstanding mechanical properties. This study demonstrates the viability to access PIs with ultrahigh T_g and low CTE in a wider range of temperature by the incorporation of bis‐benzimidazole moieties. © 2019 Society of Chemical Industry     

Effect of pressure and temperature on viscosity of a borosilicate glass

During industrial glass production processes, the actual distribution of stress components in the glass during scribing remains, to date, poorly quantified, and thus continues to be challenging to model numerically. In this work, we experimentally quantified the effect of pressure and temperature on the viscosity of SCHOTT N‐BK7^® glass, by performing in situ deformation experiments at temperatures between 550 and 595°C and confining pressures between 100 and 300 MPa. Experiments were performed at constant displacement rates to produce almost constant strain rates between 9.70 × 10^?6 and 4.98 × 10^?5 s^?1. The resulting net axial stresses range from 81 to 802 MPa, and the finite strains range from 1.4% to 8.9%. The mechanical results show that the SCHOTT N‐BK7^® glass is viscoelastic near the glass transition temperature at 300 MPa of confining pressure. To elucidate the data, we incorporated both 1‐element and 2‐element generalized Maxwell viscoelastic models in an inversion approach, for which we provide MATLAB scrips. Results show that the 2‐element Maxwell model fits the experimental data well. The stress decreases with increasing temperature at 300 MPa and the temperature dependence yields a similar activation energy (601 ± 10 kJ mol^?1 or ?H/R = 7.2 × 10⁴ K) to a previously reported value at 1‐atm (615 kJ mol^?1 or ?H/R = 7.4 × 10⁴ K). The SCHOTT N‐BK7^® glass shows a limited linear increase in viscosity with increasing pressure of ~0.1 log₁₀ (Pa·s)/100 MPa, which is in agreement with the most recent 2‐internal‐parameter relaxation model (based on experiments).     

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.     

Spectral Properties of Pr3+‐Doped Transparent‐Glass‐Ceramic Containing Ca5(PO4)3F Nanocrystals

A Pr³⁺‐doped transparent oxyfluoride glass‐ceramic containing Ca₅(PO₄)₃F nanocrystals was prepared by melt quenching and subsequent thermal treatment. The crystallization phase and morphology of the Ca₅(PO₄)₃F nanocrystals were investigated by X‐ray diffraction and transmission electron microscope, respectively. The volume fraction of the Ca₅(PO₄)₃F nanocrystals in the glass‐ceramic is about 10% and the fraction of Pr³⁺ ions incorporated into the Ca₅(PO₄)₃F nanocrystals is about 22%. The peak absorption cross sections at 435 and 574 nm increase up to 128% and 132% after crystallization, respectively. The peak stimulated emission cross sections of the ³P₀→³H₄ blue laser channel and ³P₀→³F₂ red laser channel for the glass‐ceramic are 4.95 × 10^?20 and 29.8 × 10^?20 cm², respectively. The spectral properties indicate that the glass‐ceramic is a potential visible laser material.