Flow Of Glass Research Articles

Numerical simulation of the Ge28Sb12Se60 fiber extrusion process

AbstractA computational fluid dynamics model of the glass fiber extrusion process is proposed and verified. The model describes the homogeneous non‐isothermal motion of a viscous glass melt and the surrounding air in an experimental setup, taking into account the interface between the media and the movement of the metal rod. The unclad Ge28Sb12Se60 glass fibers for sensor applications are fabricated by extrusion. The validation of the developed model is performed based on the experimental data, including pressure values, temperature field in extrusion setup, and extruded glass mass outflow. Based on the proposed model, the thermal and kinetic conditions for the flow of Ge28Sb12Se60 glass during extrusion are numerically studied. The presented model could be used as a tool for analyzing the hydrodynamic and thermal processes during fiber extrusion.

Thermodynamics description of startup flow of soft particles glasses.

Particle dynamics simulations are used to study the startup flow of jammed soft particle suspensions in shear flow from a thermodynamic perspective. This thermodynamic framework is established using the concept of the two-body excess entropy extracted from the transient pair distribution function and elastic energy of the suspension as a function of strain at different shear rates and suspension volume fractions. Although the evolution of the elastic energy in these soft particle glasses closely mimics the stress-strain behavior at different shear rates and volume fractions, there are several differences corresponding to their overshoots in terms of the broadness and location of the peaks. The transient excess entropy shows an anisotropic behavior due to the anisotropic distribution of contacts at high shear rates. The excess entropy at high shear rates increases as a function of the strain and attains a steady state. On the other hand, it is nearly constant and isotropic in the quasi-static regime, where the stress response is close to the dynamic yield stress. Using the transient elastic energy and excess entropy, a transient temperature is defined to establish a relationship between thermodynamics and the static yield stress data. This transient temperature increases with the strain and then diverges at strains close to the static yield point at high shear rates.

The Flow of Glasses and Glass-Liquid Transition under Electron Irradiation.

Recent discovery and investigation of the flow of glasses under the electron beams of transmission electron microscopes raised the question of eventual occurrence of such type effects in the vitrified highly radioactive nuclear waste (HLW). In connection to this, we analyse here the flow of glasses and glass-liquid transition in conditions of continuous electron irradiation such as under the e-beam of transmission electron microscopes (TEM) utilising the configuron (broken chemical bond) concept and configuron percolation theory (CPT) methods. It is shown that in such conditions, the fluidity of glasses always increases with a substantial decrease in activation energy of flow at low temperatures and that the main parameter that controls this behaviour is the dose rate of absorbed radiation in the glass. It is revealed that at high dose rates, the temperature of glass-liquid transition sharply drops, and the glass is fully fluidised. Numerical estimations show that the dose rates of TEM e-beams where the silicate glasses were fluidised are many orders of magnitude higher compared to the dose rates characteristic for currently vitrified HLW.

Area-Specific Positioning of Metallic Glass Nanowires on Si Substrate

This paper presents a novel technique to fabricate metallic nanowires in selective areas on a Si substrate. Thermoplastic drawing of viscous metallic glass from cavities etched in Si can produce metallic nanowires. The length and diameter of nanowires can be controlled by adjusting the drawing conditions without changing the Si mold. A thin metal shadow mask is stacked above the Si mold during thermoplastic drawing to fabricate the nanowires only in specific locations. The mask restricts the flow of metallic glass to predefined shapes on the mask, resulting in the formation of nanowires in selected areas on Si. An Al foil-based mask made by a benchtop vinyl cutter is used to demonstrate the proof-of-concept. Even a simple Al foil mask enables the positioning of metallic nanowires in selective areas as small as 200 µm on Si. The precision of the vinyl cutter limits the smallest dimensions of the patterned areas, which can be further improved by using laser-fabricated stencil masks. Results show that a single row of metallic glass nanowires can be patterned on Si using selective thermoplastic drawing. Controllable positioning of metallic nanowires on substrates can enable new applications and characterization techniques for nanostructures.

Investigation of flow dynamics of molten glass in different solar glass production units using radiotracer method

A radiotracer investigation was previously carried out to characterize the flow of the molten glass and to identify the cause of poor quality of the glass sheets produced in an industrial solar glass production unit (SGPU-1) (Pant et al., 2016). Based on the investigations, several flow abnormalities were identified and the design of the unit was modified to improve the quality of the product and meet the product specifications. Subsequently, the radiotracer investigation was repeated in the modified unit (SGPU-1m). The results of the study showed that the dead volume and homogenization time in the modified unit were significantly reduced with improvement in mixing of the molten glass as compared to the SGPU-1. Based on the results of the two investigations, a new glass production unit (SGPU-2) with enhanced capacity was designed, fabricated and commissioned. The radiotracer investigation was repeated in the newly designed unit with an objective to evaluate and validate its design. The results indicated that the performance of SGPU-2 was as per the design criteria and the quality of the glass sheets produced was as per the desired specifications.

The effects of distorted optic flow in multifocal glasses on self-motion perception

The effects of distorted optic flow in multifocal glasses on self-motion perception

Shear transformations in metallic glasses without excessive and predefinable defects

Plastic flow in metallic glasses (MGs) is known to be mediated by shear transformations (STs), which have been hypothesized to preferentially initiate from identifiable local "defect" regions with loose atomic packing. Here we show that the above idea is incorrect, i.e., STs do not arise from signature structural defects that can be recognized a priori. This conclusion is reached via a realistic MG model obtained by combining molecular dynamics (MD) and Monte Carlo simulations, achieving liquid solidification at an effective cooling rate as slow as 500 K/s to approach that typical in experiments for producing bulk MGs. At shear stresses before global yielding, only about 2% of the total atoms participate in STs, each event involving typically ~10 atoms. These observations rectify the excessive content of "liquid-like regions" retained from unrealistically fast quench in MD-produced glass models. Our findings also shed light on the indeterministic aspect of the ST sites/zones, which emerge with varying spatial locations and distribution depending on specific mechanical loading conditions.

Characterisation of a Complex CaZr0.9Ce0.1Ti2O7 Glass–Ceramic Produced by Hot Isostatic Pressing

The behaviour of Ce-containing zirconolites in hot isostatically pressed (HIPed) materials is complex, characterised by redox interactions between the metallic HIP canister that result in reduction of Ce4+ to Ce3+. In this work, a glass–ceramic of composition 70 wt.% CaZr0.9Ce0.1Ti2O7 ceramic in 30 wt.% Na2Al2Si6O16 glass was produced by HIP (approx. 170 cm3 canister) to examine the extent of the material–canister interaction. A complex material with six distinct regions was produced, with the extent of Ce reduction varying depending on the distance from the canister. Notably, the innermost bulk regions (those approximately 7 mm from the canister) contained only Ce4+, demonstrating that a production-scale HIPed glass–ceramic would indeed have a bulk region unaffected by the reducing environment induced by a ferrous HIP canister despite the flow of glass at the HIP temperature. Each of the six regions was characterised by XRD (including Rietveld method refinements), SEM/EDX and linear combination fitting of Ce L3-edge XANES spectra. Regions in the lower part of the canister were found to contain a significantly higher fraction of Ce4+ compared to the upper regions. Though zirconolite-2M was the major crystalline phase observed in all regions, the relative abundances of minor phases (including sphene, baddeleyite, rutile and perovskite) were higher in the outermost regions, which comprised a significantly reduced Ce inventory.

Indentation creep dynamics in metallic glasses under different structural states

In this study, the effects of the structural energy states (as-cast and relaxed) of Zr50Cu40Al10 metallic glass were investigated using depth-sensing nanoindentation. In terms of cooperative shear model, we performed experimental characterization of shear transformation zone for plastic flow of metallic glass. The shear transformation zone volume of the relaxed metallic glass is larger than that of as-cast one, while the strain rates sensitivity displays the opposite tendency. The plastic deformation in the creep stage of nanoindentation originates from the “delayed plasticity” inherited from the loading process. The creep depth shows strain rates and microstructural states dependence. The characteristic relaxation time and creep depth limit were determined by fitting the displacement versus time curves with Kelvin model are employed to characterize the creep dynamics of metallic glasses. It was found that the softening effects in the plastic deformation originates from the collective movements of the deformation carriers (shear transformation zones). The different softening behaviors were discussed from the perspective of soft zones in the framework of the free volume model. Our experimental as well as the theoretical analysis deepens the fundamental understanding of plasticity deformation mechanism in metallic glasses.

Selective-area fabrication of bulk metallic glass nanowires on silicon

• Metallic glass nanowires can be selectively patterned on silicon. • Inexpensive Al foil masks can generate wide range of nanopatterned areas. • Size and shape of nanostructures in selective areas can be readily tailored. • The approach has potential for nanowire-based microfluidic devices. We report a facile technique to fabricate metallic nanowires on selective areas on silicon. Nanowires are fabricated by thermoplastic drawing of bulk metallic glass from microscale cavities etched in silicon. The metallic nanowires are formed only on selective areas by using aluminum foil masks. The mask restricts the flow of bulk metallic glass to predefined openings during thermoplastic processing and enables the formation of nanowires on selective areas on silicon. We show that nanowires with different aspect-ratios can be formed by tailoring the drawing conditions without changing the silicon. Inexpensive aluminum masks can produce a wide range of nanopatterned areas in the size range of 200 µm and larger.

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 (Eg) were calculated in the range of 546–1115 kJ/mol by Kissinger method, whereas the activation energies of crystallization (Ec) 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 (Ea-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.

Mechanical size effect and serrated flow of various Zr-based bulk metallic glasses

Despite superior mechanical properties, the cross-scale mechanical properties of Zr-based bulk metallic glasses (BMGs) are urgent to be revealed. Depth-sensitive nanoindentation technique was employed to directly investigate the significant depth-dependent mechanical properties of three kinds of Zr-based BMGs. Specifically, the surface hardness H and elastic modulus E are verified to increase with the decrease of indentation depth while the fracture toughness KIC decreases with the indentation depth. The mechanical size effect is closely related to the evolution of shear bands at various indentation depths, which can be equivalently revealed by the distribution of serrated flow. Based on a relatively shallow indentation depth, the comparatively minor stress gradient established inside the micro-region underneath the indenter tip induces insufficient activation energy of shear bands, which prevents the nucleation of shear bands and further restricts plastic deformation, and ultimately results in enhanced surface hardness and elastic modulus but reduced fracture toughness. In addition, the shear band morphology of residual indentation and the stress distribution obtained from the finite element simulation provide integral evidence in support of the depth-induced mechanical size effect.

Sluggish dynamics of homogeneous flow in high-entropy metallic glasses

A comparative study of high-entropy metallic glasses and their reference counterparts was conducted via mechanical relaxation behavior and high-temperature deformation. We show that the high-entropy metallic glasses possess a relatively more homogeneous structure, which generates smaller activation volumes and sluggish free volume evolution during high-temperature deformation. A spectrum analysis that allows to delineate the deformation details of high-entropy metallic glasses were constructed. The core finding sheds important light on the structural heterogeneity and sluggish dynamics and provides an essential piece for understanding the deformation mechanism of high-entropy metallic glasses.

Uncovering the flow of metallic glass.

Uncovering the flow of metallic glass.

Softening in an ultrasonic-vibrated Pd-based metallic glass

The mechanical behavior of the Pd40Cu30P20Ni10 metallic glass after ultrasonic vibration was systematically investigated by nanoindentation. A notable softening after ultrasonic treatment was demonstrated by about 25% and 40% reduction of hardness and elastic modulus, respectively. The Maxwell-Voigt model was utilized to characterize the structure evolution during ultrasonic-assistant plastic deformation. Combined with differential scanning calorimeter experiments, it is found that the flow defects with shorter characteristic relaxation time activated under ultrasonic-frequency cycling loading benefits fast atomic diffusion with a low energy barrier, which eventually leads to the pronounced creep displacement, and thereby the large moldability at ambient temperature. This work might enlighten the structural origin for the plastic flow of metallic glasses under stress-assisted molding, imprinting as well as cold joining, which may help us in deeply understanding the defect activation mechanism in disordered systems.

Comparative Study of the Measured and Two Ideal Glass Transition Temperatures Corresponding to the Limit of Infinitely Slow Heating Rate and the Infinite Barriers with Respect to Flow in Metallic Glasses and Glass-Forming Liquids

Comparative Study of the Measured and Two Ideal Glass Transition Temperatures Corresponding to the Limit of Infinitely Slow Heating Rate and the Infinite Barriers with Respect to Flow in Metallic Glasses and Glass-Forming Liquids

Simulation and experimental study on CO2 laser polishing quartz glass

High quality surface can be quickly obtained by laser polishing quartz glass. With the improvement of application requirements of quartz glass, the combination of process parameters for optimizing CO2 laser polishing large area quartz glass sheet is proposed. The untreated quartz ground glass was scanned by CO2 laser. Taking the roughness as the research index value, the parameters affecting CO2 laser polishing were studied and analyzed. The transient model was established by COMSOL software to simulate the polishing process, predict the combination of polishing parameters, and obtain the temperature field change in the polishing process and the flow of quartz glass during melting. 300W continuous CO2 laser was used in the experiment. The effect of surface improvement was the best when the laser power was 300W, the scanning rate was 100~200mm/s. The micro area roughness can reach Ra=10.18nm. Then, the chemical corrosion was combined with CO2 laser polishing, and the quartz glass was corroded by hydrofluoric acid and sodium hydroxide solution, and then polished to obtain the average minimum roughness Ra=5.63nm. The research results can be put into practical industrial production, which is conducive to improving production efficiency and promote the development of laser polishing quartz glass technology.

Self-motion illusions from distorted optic flow in multifocal glasses

SummaryProgressive addition lenses (PALs) are ophthalmic lenses to correct presbyopia by providing improvements of near and far vision in different areas of the lens, but distorting the periphery of the wearer's field of view. Distortion-related difficulties reported by PAL wearers include unnatural self-motion perception. Visual self-motion perception is guided by optic flow, the pattern of retinal motion produced by self-motion. We tested the influence of PAL distortions on optic flow-based heading estimation using a model of heading perception and a virtual reality-based psychophysical experiment. The model predicted changes of heading estimation along a vertical axis, depending on visual field size and gaze direction. Consistent with this prediction, participants experienced upwards deviations of self-motion when gaze through the periphery of the lens was simulated, but not for gaze through the center. We conclude that PALs may lead to illusions of self-motion which could be remedied by a careful gaze strategy.

Rate-dependent inhomogeneous creep behavior in metallic glasses

Creep deformation can be classified as homogeneous flow and inhomogeneous flow in bulk metallic glass (BMG). In order to understand the conversion conditions of the two types of creep deformation, the effect of loading rate on the creep behavior of a Ti40Zr10Cu47Sn3 (at.%) BMG at ambient temperature was investigated using nanoindentation and molecular dynamic simulation. Results indicate that at low loading rates, many serrations appear in loading stage, leading to inhomogeneous serrated flow in the creep stage. When the loading rate is high enough, the creep deformation tends to be homogeneous. The related mechanism responsible for the rate-dependent creep behavior is attributed to the number of pre-existing major shear bands which is influenced significantly by the loading rate.

Atomic-scale homogeneous plastic flow beyond near-theoretical yield stress in a metallic glass

The onset of yielding and the related atomic-scale plastic flow behavior of bulk metallic glasses at room temperature have not been fully understood due to the difficulty in performing the atomic-scale plastic deformation experiments needed to gain direct insight into the underlying fundamental deformation mechanisms. Here we overcome these limitations by combining a unique sample preparation method with atomic force microscopy-based indentation, which allows study of the yield stress, onset of yielding, and atomic-scale plastic flow of a platinum-based bulk metallic glass in volumes containing as little as approximately 1000 atoms. Yield stresses markedly higher than in conventional nanoindentation testing were observed, surpassing predictions from current models that relate yield stress to tested volumes; subsequent flow was then established to be homogeneous without exhibiting collective shear localization or loading rate dependence. Overall, variations in glass properties due to fluctuations of free volume are found to be much smaller than previously suggested.