Fragile Glass Research Articles

Mapping and classification of ionic liquids in terms of glass transition and fragility

Mapping and classification of ionic liquids in terms of glass transition and fragility

Crystallization Study of Pb Additive Se-Te-Ge Nanostructured Alloys using Non-isothermal Differential Scanning Calorimetry

Nanotechnology started a new era in research and continuous escalations due to its potential applications. In modern optoelectronics, Pb additive nano-chalcogenides are becoming promising materials. For a memory and switching material, the thermal stability and glass-forming ability are vital, and the glass should be thermally stable from a technological point of view. This research article investigates the thermal behaviour of bulk (Se80Te20)94-xGe6Pbx (x = 0, 2, 4 and 6) samples synthesized using the melt quench procedure non-isothermal differential scanning calorimetry at four heating rates from 5 to 20°Cmin-1. Further, the overall crystallization study, which includes thermal stability, ease of glass formation, fragility, glass relaxation and glass-crystallization transformation kinetics of investigated alloys using different empirical formalisms, is reported and discussed. Compositional and heating rate dependence of recorded characteristic temperatures and other deduced parameters of reheated alloys are also discussed. The correlation between deduced parameters is also established to define the utility of these materials in practical applications.

Glass transition kinetics and fragility of ZrCuAlNi(Nb) metallic glasses

The kinetics of glass transition and the fragility of Zr55Cu30Al10Ni5 and (Zr55Cu30Al10Ni5)98Nb2 metallic glasses were investigated by the calorimetric measurements. The Nb minor addition narrows the width of glass transition, accelerates the relaxation process during glass transition, and decreases the energy barrier of glass transition. In addition, the fragility was evaluated in terms of the kinetic fragility index. While both alloys can be classified as intermediate glass formers, the Nb minor addition remarkably decreases the fragility and a stronger glass is achieved by the microalloying process. The lower fragility in the Nb-containing alloy is accompanied by higher degree of short-range ordering inferred from structural characterizations, formation of nanoscale chemical heterogeneities evidenced from the energy-dispersive X-ray spectroscopy (EDS) results, and deteriorated plasticity evaluated from the bending experiments. Our results highlight positive correlations between the fragility and the plasticity of the studied glasses.

Glass formation, thermal stability and fragility minimum in Ge-Te-Se glasses

Tellurium based chalcogenide glasses are known to transmit IR light over a wide wavelength range but are difficult glass formers. For practical applications, the glass should have high glass forming ability and high thermal stability. GexTeySe(100-x-y) glasses with x between 10 and 40 have been prepared by melt quenching method. The chosen compositions are found to have excellent glass forming ability with high thermal stability. Glass transition temperature shows an increasing trend indicating a continuous polymerization of the network. The fragility index varies between 20 and 35 indicating that the melts of these glasses are strong and the fragility is minimum. The structural, thermal, optical properties are mainly dictated by the Ge/Se ratio and the concentration of Te. The high glass forming ability and high thermal stability of these glasses may be useful for many applications particularly for making IR lenses and optical fibres.

Surface diffusion of a glassy discotic organic semiconductor and the surface mobility gradient of molecular glasses.

Surface diffusion has been measured in the glass of an organic semiconductor, MTDATA, using the method of surface grating decay. The decay rate was measured as a function of temperature and grating wavelength, and the results indicate that the decay mechanism is viscous flow at high temperatures and surface diffusion at low temperatures. Surface diffusion in MTDATA is enhanced by 4 orders of magnitude relative to bulk diffusion when compared at the glass transition temperature Tg. The result on MTDATA has been analyzed along with the results on other molecular glasses without extensive hydrogen bonds. In total, these systems cover a wide range of molecular geometries from rod-like to quasi-spherical to discotic and their surface diffusion coefficients vary by 9 orders of magnitude. We find that the variation is well explained by the existence of a steep surface mobility gradient and the anchoring of surface molecules at different depths. Quantitative analysis of these results supports a recently proposed double-exponential form for the mobility gradient: log D(T, z) = log Dv(T) + [log D0 - log Dv(T)]exp(-z/ξ), where D(T, z) is the depth-dependent diffusion coefficient, Dv(T) is the bulk diffusion coefficient, D0 ≈ 10-8m2/s, and ξ ≈ 1.5nm. Assuming representative bulk diffusion coefficients for these fragile glass formers, the model reproduces the presently known surface diffusion rates within 0.6 decade. Our result provides a general way to predict the surface diffusion rates in molecular glasses.

Compositional trends in surface enhanced diffusion in lead silicate glasses

In this work, we use molecular dynamics simulations to study the enhancement of surface over bulk diffusion (surface enhanced diffusion) in (PbO)x(SiO2)1-x glasses. This work is motivated to better understand surface diffusion in glasses and its connection to fragility, and to enhance surface diffusion in silica and related glasses for greater thermodynamic stability during vapor-deposition. By adding PbO to silica, the fragility of glass increases continuously for 10% ≤ x ≤ 70% during experiments. The increase in fragility may correspond to an increase in surface enhanced diffusion, as fragility and surface diffusion are correlated. We observe that for the silicates investigated, while surface enhanced diffusion increases with fragility, the enhancement is quite small. The slower diffusing Si and O atoms have higher enhancements, which could allow for some surface stabilization effects. We demonstrate that there are only small changes in atomic arrangements, consistent with the similar diffusion rates, at the surface as compared to bulk. Finally, we examine the trend of bulk versus surface diffusion in view of previous observations in organic and metallic glasses and found that in oxides, fragility increase may not be strongly linked to enhanced surface diffusion.

Surface Diffusion Is Controlled by Bulk Fragility across All Glass Types.

Surface diffusion is vastly faster than bulk diffusion in some glasses, but only moderately enhanced in others. We show that this variation is closely linked to bulk fragility, a common measure of how quickly dynamics is excited when a glass is heated to become a liquid. In fragile molecular glasses, surface diffusion can be a factor of 10^{8} faster than bulk diffusion at the glass transition temperature, while in the strong system SiO_{2}, the enhancement is a factor of 10. Between these two extremes lie systems of intermediate fragility, including metallic glasses and amorphous selenium and silicon. This indicates that stronger liquids have greater resistance to dynamic excitation from bulk to surface and enables prediction of surface diffusion, surface crystallization, and formation of stable glasses by vapor deposition.

Structure and Fragility of Zn-phosphate glasses: Results from multinuclear NMR spectroscopy and calorimetry

The structure of (ZnO)x(P2O5)100-x glasses with 35≤x ≤ 67 is investigated using 31P and ultra-high field 67Zn NMR spectroscopy. The 31P NMR results confirm a nearly binary Q-species distribution. The progressive decrease in the connectivity of the phosphate network upon addition of ZnO is manifested in a monotonic drop in Tg in the composition range 35≤x ≤ 55. The 67Zn NMR spectra indicate that the average Zn-O coordination number varies between 4 and 6 and increases progressively with increasing Zn content. The resulting increase in the connectivity of the Zn-O-P network compensates for the depolymerization of the P-O-P network, which is reflected in a reversal in the compositional trend in Tg for x > 55. In contrast to Tg, the fragility index m shows negligible composition dependence until x∼50, beyond which it increases rapidly with increasing Zn content in response to the progressive shortening of the Q2 chains.

Viscosity and transport in a model fragile metallic glass

How thermally activated structural excitations quantitatively mediate transport and microplasticity in a model binary glass at the microsecond timescale is revealed using atomistic simulation. These local excitations, involving a stringlike sequence of atomic displacements, admit a far-field shear-stress signature and underlie the transport of free-volume and bond geometry. Such transport is found to correspond to the evolution of a disclination network describing the spatial connectivity of topologically distinct bonding environments, demonstrating the important role of geometrical frustration in both glass structure and its underlying dynamics.

An All Solid State Electrochemical pH Sensor Based on Niobium Modified Electrode

pH is an important chemical index. The measurement of pH is widely used in various fields. At present, the most common pH meter on the market is the glass electrode pH meter, which has many advantages, such as high accuracy, short response time and so on. However, when industrial wastewater and environmental water samples need long-time real-time monitoring, such as using glass electrode pH meter will lead to leakage of internal liquid, fragile glass and sodium difference. Therefore, it is urgent to design and develop a new type of pH meter with all solid, simple structure and no nanodeviation. In this study, an all solid state electrochemical modified pH electrode was developed based on the adsorption and storage of hydrogen by niobium. Hydrogen in hydrochloric acid was adsorbed and stored in niobium electrode by constant potential electrolysis. The results showed that the detection linear range was pH1-pH13, the response slope was −56.4 mV dec <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−1</sup> , and the response time was 5 seconds. In the actual sample detection, the detection results are consistent with the glass electrode pH meter. In addition, cyclic voltammetry and electron microscopy were used to study the response mechanism.

Stress hyperuniformity and transient oscillatory-exponential correlation decay as signatures of strength vs fragility in glasses.

We examine and compare the local stress autocorrelation in the inherent states of a fragile and a strong glass: the Kob-Andersen (KA) binary mixture and the Beest-Kramer-Santen model of silica. For both systems, local (domain-averaged) stress fluctuations asymptotically reach the normal inverse-volume decay in the large domain limit; accordingly, the real-space stress autocorrelation presents long-range power law tails. However, in the case of silica, local stress fluctuations display a high degree of hyperuniformity, i.e., their asymptotic (normal) decay is disproportionately smaller than their bond level amplitude. This property causes the asymptotic power law tails of the real-space stress autocorrelation to be swamped, up to very large distances (several nanometers), by an intermediate oscillatory-exponential decay regime. Similar contributions exist in the KA stress autocorrelation, but they never can be considered as dominating the power law decay and fully disappear when stress is coarse-grained beyond one interatomic distance. Our observations document that the relevance of power-law stress correlation may constitute a key discriminating feature between strong and fragile glasses. Meanwhile, they highlight that the notion of local stress in atomistic systems involves by necessity a choice of observation (coarse-graining) scale, the relevant value of which depends, in principle, on both the model and the phenomenon studied.

Cold-crystallization and physical stability of glassy carbamazepine

Physical stability as well as isothermal and non-isothermal cold-crystallization of quench-cooled drug carbamazepine (CBZ) was studied using powder X-ray diffraction (XRD), differential scanning calorimetry (DSC) and Fourier-transform infrared spectroscopy (FT-IR). Three phase transitions on heating were reported: glass softening (∼329 K), cold-crystallization (∼389 K) and melting (∼463 K). XRD results and evaluation of DSC data using Adam-Gibbs model extended to the glassy state revealed, that the amorphous sample of CBZ remains physically stable for 8 h at room temperature (i.e. about 30 K below glass transition temperature). Isothermal XRD measurements showed that amorphous CBZ is prone to rapid nucleation even about 50 K below the glass transition, but crystal growth is considerably slowed down in such conditions. Fragility parameter m was calculated and quench-cooled CBZ was identified as moderately fragile glass. FT-IR measurements coupled with moving-window two-dimensional correlation spectroscopy proved that changes in vibrational dynamics accompanied all phase transitions. Considerable strengthening of hydrogen bonding was observed during cold crystallization.

Advances in the study of supercooled water.

In this review, we report recent progress in the field of supercooled water. Due to its uniqueness, water presents numerous anomalies with respect to most simple liquids, showing polyamorphism both in the liquid and in the glassy state. We first describe the thermodynamic scenarios hypothesized for the supercooled region and in particular among them the liquid-liquid critical point scenario that has so far received more experimental evidence. We then review the most recent structural indicators, the two-state model picture of water, and the importance of cooperative effects related to the fact that water is a hydrogen-bonded network liquid. We show throughout the review that water's peculiar properties come into play also when water is in solution, confined, and close to biological molecules. Concerning dynamics, upon mild supercooling water behaves as a fragile glass former following the mode coupling theory, and it turns into a strong glass former upon further cooling. Connections between the slow dynamics and the thermodynamics are discussed. The translational relaxation times of density fluctuations show in fact the fragile-to-strong crossover connected to the thermodynamics arising from the existence of two liquids. When considering also rotations, additional crossovers come to play. Mobility-viscosity decoupling is also discussed in supercooled water and aqueous solutions. Finally, the polyamorphism of glassy water is considered through experimental and simulation results both in bulk and in salty aqueous solutions. Grains and grain boundaries are also discussed.

Kovacs effect in glass with material memory revealed in non-equilibrium particle interactions

The Kovacs effect is a remarkable feature of the ageing dynamics of glass forming liquids near the glass transition temperature. It consists in a non-monotonous evolution of the volume/enthalpy after a succession of two abrupt temperature changes: first from a high initial temperature T i to a much lower annealing temperature T a followed by a smaller second jump back to a slightly higher final temperature T f. The second change is performed when the instantaneous value of the volume/enthalpy coincides with the equilibrium one at the final temperature. While this protocol might be expected to yield equilibrium dynamics right after the second temperature change, one observes the so-called Kovacs hump in glassy systems. In this paper we apply such thermal protocol to the distinguishable particles lattice model for a wide range of fragility of the system. We study the Kovacs hump based on energy relaxation and all main experimental features are captured. Results are compared to general predictions based on a master equation approach in the linear response limit. We trace the origin of the Kovacs hump to the non-equilibrium nature of the probability distribution of particle interaction energies after the annealing and find that its difference with respect to the final equilibrium distribution is non-vanishing with two isolated zeros. This allows Kovacs’ condition of equilibrium total energy to be met out-of-equilibrium, thus representing the memory content of the system. Furthermore, the hump is taller and occurs at a larger overlap with the system initial configuration for more fragile systems. The dynamics of a structural temperature for the mobile regions strongly depends on the glass fragility while for the immobile ones only a weak dependence is found.

Interpretation of the apparent activation energy of glass transition

The temperature dependence of the viscosity of glass is a major concern in glass research. The apparent activation energies obtained from Arrhenius plots often show unusual values larger than bond energies, which makes the interpretation of the activation energy difficult. In this study, a reasonable interpretation of the apparent activation energy is obtained along similar lines as those adopted in solid state physics and chemistry. In contrast to the widely held view that the transition occurs at the reference temperature T 0 according to the Vogel–Fulcher–Tammann formula, in this work the structural change observed at the calorimetric temperature T g is considered as a transition from the liquid to solid phases. The energy barrier for atom rearrangements significantly changes in the transition range with width ΔT g . This change in the energy barrier alters the manner in which the apparent activation energy constitutes the Arrhenius form. Analysis of available experimental data shows that the real value of energy barrier is significantly smaller than the apparent activation energy, and the obtained values are in the reasonable range of energy expected for chemical bonds. The overestimation of the apparent activation energy depends on the ratio T g /ΔT g , which is larger for fragile glasses than for strong glasses. Importantly, the linear term in the temperature dependence of the energy barrier does not appear in Arrhenius plots. This explains why the temperature dependence of viscosity for strong glasses obeys well the Arrhenius law, despite that the temperature dependence of energy barrier is expected for every glass.

Large heat-capacity jump in cooling-heating of fragile glass from kinetic Monte Carlo simulations based on a two-state picture.

The specific-heat capacity c_{v} of glass formers undergoes a hysteresis when subjected to a cooling-heating cycle, with a larger c_{v} and a more pronounced hysteresis for fragile glasses than for strong ones. Here we show that these experimental features, including the unusually large magnitude of c_{v} of fragile glasses, are well reproduced by kinetic Monte Carlo and equilibrium study of a distinguishable particle lattice model incorporating a two-state picture of particle interactions. The large c_{v} in fragile glasses is caused by a dramatic transfer of probabilistic weight from high-energy particle interactions to low-energy ones as temperature decreases.

Ice crystals that flex and bend

Ice—cold, rigid, brittle . . . bendy? Researchers are surprised to find that ice is flexible and elastic at a microscopic scale when grown as tiny, fiber-like crystals ( Science 2021, DOI: 10.1126/science.abh3754 ). Unlike naturally occurring ice, with air bubbles and cracks, the crystals in this study were nearly perfect and able to transmit light with less than 1% loss of intensity. Creating the crystals was tricky. The team, based at Zhejiang University and led by Xin Guo and Limin Tong, used an electric field in a freezing chamber to grow hexagonal crystals ranging from 10 μm down to less than 800 nm in diameter (shown). Most materials can bend when made very thin, like notoriously fragile glass fiber-optic cables. But these microfiber ice crystals can be bent into a minuscule radius of curvature, such that strains and stresses in the surface become incredibly high—almost the theoretical limit. “I

Glass-liquid and glass-gel transitions of soft-shell particles.

We study the structure and dynamics of colloidal particles with a spherical hard core and a thermo-responsive soft shell over the whole phase diagram by means of small-angle x-ray scattering and x-ray photon correlation spectroscopy. By changing the effective volume fraction by temperature and particle concentration, liquid, repulsive glass. and attractive gel phases are observed. The dynamics slow down with increasing volume fraction in the liquid phase and reflect a Vogel-Fulcher-Tamann behavior known for fragile glass formers. We find a liquid-glass transition above 50 vol.% that is independent of the particles' concentration and temperature. In an overpacked state at effective volume fractions above 1, the dispersion does not show a liquid phase but undergoes a gel-glass transition at an effective volume fraction of 34 vol.%. At the same concentration, extrema of subdiffusive dynamics are found in the liquid phase at lower weight fractions. We interpret this as dynamic precursors of the glass-gel transition.

DATA FUSION OF HISTORICAL PHOTOGRAPHS WITH MODERN 3D DATA FOR AN ARCHAEOLOGICAL EXCAVATION – CONCEPT AND FIRST RESULTS

Abstract. Through the destruction of war, most of the documents of an archaeological excavation from 1934 – 1939 of a megalithic tomb in north-west Germany have been destroyed irretrievably. Fortunately, more than 500 historical pictures have been preserved, which visually document the excavation situation at that time. Parts of the image collection are preserved on fragile glass plates that are difficult to preserve and have to be digitised urgendly. A method for digitising these glass plates will be presented first. With the help of the digitised historical images, the excavation situation at that time shall be reconstructed. Since a reconstruction based only on the historical images is not possible, the current state of the megalithic tombs has been recorded with modern measuring technology and a 3D model has been calculated. The aim is to fuse the historical images with the modern 3D model. For this purpose, different possibilities of linking the data are presented. As first results, point clouds calculated by Structure from Motion and the orientation of historical images in relation to the modern 3D model using direct linear transformation are shown. The hybrid model of historical and modern data will be used for archaeological interpretations of the excavation.

Про застосування титанової фольги в конструкціях паяних малогабаритних вікон для передачі променевої енергії

The aim of this work was to miniaturize the design of a brazed joint of a thin non-metallic disk with a hollow thin-walled metal cylinder for operation as part of a vacuum device in a wide temperature range. For brazing a non-metallic disk with a glass tube-shaped device body, when choosing a metal filler, the fragility of glass, its low mechanical strength in bending and tensile and a lower thermal coefficient of linear expansion than metal fillers must be taken into account. Therefore, the use of low-temperature plastic solders based on tin, indium, lead etc., which are alloyed with titanium, is preferable. However, the disadvantages of these fillers include a significant decrease in mechanical strength when the brazed unit is heated to relatively low temperatures, especially if there is a gas inside the device under excessive pressure. The option of brazing a leucosapphire disk with a glass tube was also considered. A design has been proposed to determine how a disk is connected to a titanium body. This design has increased the heat resistance of the leucosapphire lens, which is connected to the body of the product made of titanium alloy or covar. Such connection can be used as pyrometer windows installed directly in the body of an internal combustion engine or gas turbine engine. The main feature of this development was the creation of a brazed joint structure in which the shell covering the disk is made of non-metal, in this case of leucosapphire, made of titanium foil with a thickness of 100 and in some cases 50 μm. Brazing modes were set and brazed windows were made. Tests on the vacuum density after different modes of thermal cycling of brazed samples showed high performance of this structure of the brazed joint. It was shown that the use of titanium foil makes it possible to obtain high-quality heat-resistant brazed joints. The relatively small stresses that lead to plastic deformation of the foil make it possible to increase the inconsistency of the thermal coefficient of linear expansion (TCLE) of materials that were brazed. It shout be noted that the foil material can also be other metals which had chemical active towards non-metallic materials or their components, for example, zirconium, niobium, tantalum, etc. Keywords: structures of brazed joints, brazing of non-metals, non-metallic materials, leucosapphire, glass tube, adhesive-active filler metals, fillers, titanium.