Liquidus Viscosity Research Articles

Key melt properties for controlled synthesis of glass beads by aerodynamic levitation coupled to laser heating

AbstractBinary alkali silicate glasses were synthesized as beads by aerodynamic levitation coupled to laser heating to test the applicability of the method to this compositional range. While bubble‐free lithium disilicate beads could be easily obtained, sodium and potassium silicates proved more challenging to melt without significant alkali evaporation: the final samples contained bubbles and exhibited compositional drifts compared to the starting stoichiometry, especially at high SiO2content. The risk of volatilization from the melts was evaluated empirically: the volatility of each oxide component scaled to the ratio between its melting temperatureTmand theTmof the target composition (revap), while the difference between such ratios (Δevap) provided a qualitative estimation of the risk of differential evaporation. The formulated approach enables to evaluate the suitability of aerodynamic levitation synthesis for a given target glass composition: while low melting temperature and low liquidus viscosity (η < 100 Pa s) represent the primary optimal conditions, more viscous materials can still be prepared without major compositional drifts using a more careful melting procedure, especially ifrevapandΔevapare minimized.

The glass formation of sodium metaphosphate: Perspective from the correlation of thermodynamic and kinetic parameters

In this work, the glass-forming ability (GFA) of sodium metaphosphate (NaPO3) is focused, and the cooperative nature of its thermodynamics and kinetics is explored. The critical cooling rate (Rc) of this substance is determined, giving a value as low as ~ 0.5 K/s, and the fragility m-index of 83±3 is calculated based on the calorimetric measurements. Among oxide systems with a mixture of covalent-ionic bonds, the compatibility of relatively high fragility of NaPO3 and its good GFA seems an exception. The good GFA is ascribed to its impressive liquidus viscosity (ηL) and the low entropy of fusion normalized by the structural parameter 'beads' (ΔSm/beads). Strikingly, an extended survey of various glass formers delivers a correlation between ηL and ΔSm/beads, verifying the significance of low entropies of fusion for the glass formation. A critical liquidus viscosity (ηL ~ 0.01 Pa-s) is featured, below which this thermo-kinetic correlation cannot be detected.

Determining the liquidus viscosity of glass‐forming liquids through differential scanning calorimetry

AbstractViscosity at the liquidus temperature (TL), ηL, is a critical parameter for the design of new glasses, particularly for industrial glass production where crystallization must be suppressed. However, a direct viscometric determination of ηL for a glass‐forming system is difficult due to crystallization. Here we propose an alternative approach for determining ηL through differential scanning calorimetry (DSC). Specifically, DSC is used to measure both the viscosity curve and liquidus temperature of a glass‐forming system and then derive its ηL value. The ηL values determined using DSC are found to be in excellent agreement with those measured through viscometry. The DSC approach is applicable to various glass‐forming systems covering a wide range of fragilities and ηL values spanning over five orders of magnitude. Other advantages of this approach are its accuracy and small sample requirements.

Why does B2O3 suppress nepheline (NaAlSiO4) crystallization in sodium aluminosilicate glasses?

The uncontrolled growth of nepheline (NaAlSiO4) crystals during the manufacturing of sodium aluminosilicate glasses via the fusion draw or float techniques and during the vitrification of some of the sodium- and alumina-rich nuclear waste glasses is a well-known problem. The addition of B2O3 to suppress the crystallization in these glasses is well documented in the literature. Another advantage of B2O3 is that it lowers the viscosity of the glass melt and, if incorporated in its trigonal coordination state, will improve the intrinsic damage resistance of the final glass product. Hence, B2O3 has been an integral component of glass compositions for advanced industrial applications and for nuclear waste vitrification. However, one major disadvantage of adding B2O3 to alkali aluminosilicate based glasses is its adverse impact on their chemical durability due to the rapid hydrolysis of B[3,4]-O-B[3,4] bonds in comparison to (Si, Al)-O-(Si, Al) bonds. Therefore, designing a boron-containing alkali aluminosilicate based functional glass with minimal tendency towards crystallization and high chemical durability requires an in-depth fundamental understanding of the mechanism through which B2O3 tends to suppress crystallization in these glasses. There is no current consensus on the fundamental mechanism through which B2O3 tends to suppress nepheline crystallization in these glasses. Based on the mechanisms described and the questions raised in the preceding literature, the present study focuses on addressing the ongoing debate through a detailed structural and thermo-kinetic investigation of glasses designed in the Na2O-Al2O3-B2O3-SiO2 based quaternary system over a broad composition space. Using a combination of Raman and (1D and 2D) nuclear magnetic resonance spectroscopies along with equilibrium and non-equilibrium viscosity, and liquidus temperature measurements, it has been shown that the substitution of Si-O-Al by Si-O-B linkages in the glass structure results in a significant increase in the glass forming ability as well as an increase in the liquidus viscosity (slower diffusivity), thereby suppressing the nepheline crystallization.

Fiber spinnability of glass melts

AbstractFiber spinnability is the ability of a glass‐forming melt to be steadily stretched and spun into defect‐free fiber filaments. However, its quantification has not been well established owing to many controlling factors such as melt fragility, melt strength, surface tension, liquidus temperature, liquidus viscosity, and crystallization. To understand and quantify the fiber spinnability of a glass melt, we consider two key aspects: fiberizing viscosity window and melt stability. The fiberizing viscosity window is defined by the upper and lower viscosity limits. Fibers rupture above the upper viscosity limit, whereas a stable melt stream cannot form below the lower limit (ηlow). We introduce a simple parameter to quantify fiber spinnability, namely, Kfib=ηL/ηlow, where ηL is the viscosity at liquidus temperature (TL). A fiber can only form if Kfib>1. To quantify melt stability we propose the parameter of S=(TL‐TC)/(TL‐Tg), where TL and TC are the liquidus temperature, and the onset temperature of melt crystallization during cooling, respectively. Both parameters (Kfib and S) are important for a rational design of glass fiber compositions, and fiberizing process. We use two basalt melts as examples of this study to demonstrate the high sensitivity of fiber spinnability to a minor variation in chemical composition of melts.

Bioactive Glass Innovations Through Academia‐Industry Collaboration

Since the discovery of 45S5 bioactive glass by Hench in 1969, numerous studies have been conducted on the use of bioactive glasses for the repair of hard and soft tissues. However, limited progress has been achieved in the commercialization of bioactive glass as medical products, with the most successful ones being 45S5‐based Perioglas®, Novabone®, and NovaMin®. This indicates that a gap exists between academic research and industrial scale‐up. Our work attempts to provide a preliminary study on the two well‐known bioactive glasses, 45S5 and 13‐93, to evaluate their suitability for mass production in an industrial platform. Glass properties including strain, annealing, and softening points, thermal expansion, density, and liquidus temperature are characterized. Our results show that both glasses have a substantially lower liquidus viscosity than soda lime silicate (SLS) glass, suggesting that melting and forming them in an industrial continuous‐unit melting system could be challenging. Innovations in bioactive glass compositions by delving into literature, referencing relevant phase diagrams, conducting design of experiments (DOE), and utilizing modeling tools are needed. Furthermore, joint research between academia and industry on the development of new forming techniques is critical to meet the increasing demand for bioactive glass in a variety of sizes and shapes.

Chemically Strengthened Low Crystallinity Black Glass‐Ceramics with High Liquidus Viscosities

Strong, black materials are needed for electronic device backs and appliance facings. While glass‐ceramics have good strength and toughness, their liquidus viscosity is too low to enable economical forming of these devices by the fusion or slot draw methods. Thus, we invented a new class of low crystallinity glass‐ceramics with 10–20 nm crystallites in the Fe2O3‐TiO2‐MgO system. These materials were formed into transparent glasses and then heat treated to make black opaque glass‐ceramics containing magnetite, pseudobrookite, and/or ε‐Fe2O3. The ε‐Fe2O3 phase exhibited extensive solid solution (ss) between Fe2O3 and MgTiO3. The blackness and opacity of the ε‐Fe2O3 glass‐ceramics peaked at a ceram temperature of 750°C where the Fe2+ in the crystallites was maximized, resulting in peak Fe2+‐Ti4+ charge transfer absorption. The liquidus viscosity was increased to more than 100 kPa*s by optimizing the base glass composition and minimizing the amount of crystallinity, thereby enabling fusion formability. These fusion formable glass‐ceramics had strengths exceeding the best commercially available glasses after ion exchange. This work provides a new class of low crystallinity fusion formable glass‐ceramics with high strength.

The relationship between viscosity and glass forming ability of Al-(Ni)-Yb alloy systems

The dynamic viscosity of Al-Yb and Al-Ni-Yb superheated melts was measured using a torsional oscillation viscometer. The results show that the temperature dependence of viscosity fits the Arrhenius law well and the fitting factors are calculated. The amorphous ribbons of these alloys were produced by the melt spinning technique and the thermal properties were characterized by using a differential scanning calorimetry (DSC). E (the activation energy for viscous flow), which reflects the change rate of viscosity, has a good negative relation with the GFA in both Al-Yb and Al-Ni-Yb systems. However, there is no direct relation between liquidus viscosity (ηL) and GFA. The superheated fragility M can predict GFA in Al-Yb or Al-Ni-Yb alloy system.

Liquid and magma viscosity in the anorthite‐forsterite‐diopside‐quartz system and implications for the viscosity‐temperature paths of cooling magmas

We measured the viscosity of 17 liquids in the systems anorthite‐forsterite‐quartz and anorthite‐diopside‐forsterite, representing analogs of dacitic, basaltic andesitic, and basaltic magmas. The three series lie in the anorthite liquidus fields and represent liquid lines of descent. The viscosity of evolving basaltic and basaltic andesite liquids changes little during cooling because the viscosity decrease associated with removal of polymerized anorthite component from the melt offsets the viscosity increase associated with cooling. A minimum liquidus viscosity in the basaltic system is encountered in the anorthite stability field. In contrast, dacitic liquids appear insensitive to the compositional changes during anorthite crystallization, and liquidus viscosity increases monotonically between anorthite and the anorthite‐forsterite‐quartz eutectic. Using the Einstein‐Roscoe equation to calculate the rheological effect of crystals, we show that magma viscosity always increases during crystallization for closed systems and that crystallinity is the dominant control on the viscosity of all three magma series. We introduce the concept of viscosity paths, which may approach one of four end‐members: (1) equilibrium crystallization (closed system) and (2) perfect fractional crystallization (open system) are both associated with changing residual liquid compositions; (3) supercooling without crystal growth maintains constant liquid composition, while (4) increasing crystallinity at constant liquid composition is only permissible for eutectic starting compositions. Because of the dependence of crystal‐liquid segregation rates on liquid viscosity and crystal buoyancy, feedback relations exist between evolving liquid composition, crystallinity, and magma viscosity. Crystal‐liquid segregation rates may increase or decrease during progressive cooling and crystallization of basaltic liquids.

Glass formation and crystallization in Li2ONa2OK2OSiO2

Glass-forming regions in the Li2ONa2OmSiO2 (m = 2 or 1.5) and Li2ONa2OK2OmSiO2 (m = 2 or 1.5) systems were determined with various cooling rates. Viscosity and liquidus temperature were measured. Eutectics were observed in these systems. The critical cooling rate shows a minimum and the liquidus viscosity shows a maximum. It was found that Li2ONa2OmSiO2 showed more extensive glass-forming ability than Li2OmSiO2, Na2OmSiO2 or K2OmSiO2. Li2ONa2OK2OmSiO2 shows an even larger glass-forming ability than Li2ONa2OmSiO2. The significant role of mixing entropy or liquidus viscosity in the glass-forming kinetics of mixed alkali silicate systems is recognized.

多成分系無アルカリガラスの粘性特性と結晶化挙動

Critical cooling rate Q* for glass formation was determined by means of DTA method for a non-alkali multicomponent system of 39.8SiO2·10.1Al2O3·24.4CaO·12.6ZnO·11.1TiO2·2.0B2O3mol% composition. Q* was found to be 1.5×10-2°C/sec. Viscosity of the system was measured by the beambending and the counter balancing method. The liquidus temperature T1 of the system was determined by DTA method. From the viscosity and T1 data, the Liquidus viscosity η1 was obtained (logη1/PaS=0.94). The Q*-η1 relationship of the non-alkali system was compared with those of alkali silicate and alkali borate systems.It was found that the present non-alkali system has a critical cooling rate equivalent to 94SiO2·6Li2O, 75B2O3·25Li2O or 85B2O3·15Na2O glass. The fusion entropy ΔSf was calculated from eq. (2) using the values of liquid parameters of the non-alkali system. It became apparent that the non-alkali system has a considerably high ΔSf value compared with the alkali borate or alkali silicate system. This was regarded to indicate that the present system is composed of various polyhedra, including SiO4, AlO4 or TiO4 tetrahedra, thus easing a glass formation of a SiO2 poor melt.

Glass-forming tendency in the NaPO 3-MnCl 2 system

Glass-forming regions were determined by quenching 10g melts at various cooling rates in the NaPO 3 -MnCl 2 system. The critical cooling rate for glass formation exhibited a minimum at 85 mol% NaPO 2 . Melt viscosity was measured and the liquidus viscosity was calculated according to the liquidus temperatures. The glass-forming tendency was discussed in relation to the kinetic parameters based on the crystallization theory.

希土類含有高融点酸化物ガラスの作製とその二，三の物性

Thermal image furnace melting and twin-roller quenching were used to prepare glasses containing large amounts of rare earth oxides in Ln2O3-MXOY systems (Ln2O3=La2O3, Nd2O3, Y2O3; MXOY=SiO2, Al2O3, TiO2, Nb2O5).The glass-forming regions were found at the following compositions close to the eutectic points of the phase diagrams: (20-30)Ln2O3-(70-80)SiO2, 60Ln2O3-40SiO2, 20Ln2O3-80Al2O3, 20Ln2O3-80 TiO2, (20-30)Ln2O3-(70-80)Nb2O5 and 60Ln2O3-40Nb2O5. The glass transition temperature Tg was determined by DTA. All the glasses showed high glass transition temperatures over 700°C. Although Tg increased or decreased with Ln2O3 content depending upon the system, the change was linear with Ln2O3 content around the eutectic compositions. This seems to indicate that there is no peculiar behavior of viscosity itself at the eutectic compositions. The liquidus viscosity becomes the maximum at the eutectic compositions due to low liquidus temperatures, which makes glass-formation easier at the eutectic compositions.A glass model consisting of four-coordinated aluminum units was proposed for Ln2O3-Al2O3 glasses based on the results of IR spectra and observed AlKα chemical shifts. On the other hand IR spectra of Ln2O3-TiO2 glasses showed a mixture of six- and four-coordinated titanium units.Visible and ultraviolet absoption spectra of Nd3+ were studied on Nd2O3-MXOY glasses. The peak positions of these absorption bands moved towards lower wave numbers linearly with increasing compositional basicity of the glasses. Their color changed from purple-like blue to green-like blue, as the absorption bands shifted towards lower wave numbers.

Glass Formation by Rapid Quenching in Lithium Silicates Containing Large Amounts of Li<sub>2</sub>O

The rapid-quenching technique extended the glass-forming region in the system Li2O-SiO2 toward the composition with high Li2O content. The ratio of the glass transition temperature Tg to the liquidus one T1 deviates largely from the so-called “two thirds rule” (Tg/T1=2/3) in the glasses containing large amounts of Li2O. The deviation was observed only in the glasses prepared by rapid quenching and it can be attributed to their high liquidus viscosity or small temperature variation of viscosity. The relation between the deviation from the “two thirds rule” and the glass-forming ability was discussed on the basis of the temperature and time variation curves of viscosity.

融液冷却法によるＢ２Ｏ３‐Ｎａ２Ｏ２成分系ガラスの生成に対する粘度の役割

The glass-forming region in the B2O3-Na2O system was tried to interpret on the basis of an assumption concerning the glass-forming ability of a substance that higher viscosity melts will make a glass when quenched at an appropriately rapid rate, while lower viscosity melts will not. Ten grams of B2O3-Na2O melts were water-quenched at a rate of 7°C/sec, and two glass-forming regions were determined. The upper glass region was 100∼61 mole per cent B2O3 and the lower glass region was 32∼28 mole per cent B2O3. Viscosity was measured by a counter-balanced viscometer at elevated temperatures above the liquidus temperature, and the liquidus viscosity log ηl was obtained for the compositions of 100∼25 mole per cent B2O3. The liquidus viscosity curve plotted as a function of B2O3 content for the B2O3-Na2O system exhibited two maxima and two minima in viscosity. It was found that the glass regions, 100∼61 and 32∼28 mole per cent B2O3, corresponded quite closely with the regions where the liquidus viscosity was higher than log ηl (poise)=0∼0.1. The single-bond strength BM-O and the Rawson's parameter BM-O/Tl for glass formation were calculated and were compared with the glass-forming regions of this system. These parameters were found unsatisfactory to explain the glass-forming ability of the lower glass region. But the liquidus viscosity described rather quantitatively the existence of the separate glass regions in the B2O3-Na2O system.