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Now showing items 17 - 32 of 11966

  • Glass Science in the United States: Current Status and Future Directions

    Mauro, John C.   Philip, Charles S.   Vaughn, Daniel J.   Pambianchi, Michael S.  

    We review the current state of academic research in glass science in the United States. Our analysis is based on an evaluation of the number of journal articles published across the major segments of glass research. While the great majority of commercial opportunity is in silicate glasses and glass ceramics, together these represent less than one-quarter of publication activity. Academic research activity in glass ceramics is essentially nonexistent in the United States, while the attention given to metallic and chalcogenide glasses is disproportionately larger than the current industrial value for such glasses. We identify areas of glass research that are presently less explored, yet highly promising in terms of both industrial application and training students for future careers in industry.
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  • Topology of alkali phosphate glass networks

    Fu, Anna I.   Mauro, John C.  

    The glass transition temperature of alkali phosphate glasses shows anomalous extremum points that are evidence of an unusual physical trend with chemical composition. In this paper, we develop a topological model for the glass transition temperature of binary alkali phosphate systems that helps elucidate the underlying structural and topological origins of this phenomenon. The topological model is analytically derived accounting for a hierarchy of temperature-dependent constraints and is shown to give an accurate prediction of the scaling of glass transition temperature with composition. We also discuss the general implications of the model, including the relationship between network rigidity and the distinguishability of particles at the glass transition. (C) 2012 Elsevier B.V. All rights reserved.
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  • A note on compacted networks

    Boolchand, Punit   Mauro, John C.   Phillips, J. C.  

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  • Glass: The Nanotechnology Connection

    Mauro, John C.   Ellison, Adam J.   Pye, L. David  

    Nanoscale science and engineering, or nanotechnology as it is commonly known, has been a fundamental component of glass technology for hundreds if not thousands of years. Numerous examples can be found where our understanding of glass at the nanoscale level has proved transformational in the fabrication and application of this material. Among these are band theory, photosensitivity, ligand field theory, glass structure, microcrack theory, amorphous phase separation, controlled crystallization, and surface modification. Modern applications of glass in such diverse fields as energy, medicine, electronics, photonics, and communications are critically dependent on our awareness and appreciation of the intrinsic connections between glass and nanotechnology. Starting at the low end of the nanoscale, we review fundamental aspects of these connections with the intent of drawing attention to their role in both contemporary and future glass science and engineering. We argue that many of the most useful and interesting behaviors of glass are born at the nanoscale, even when we initially do not notice it.
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  • Are the dynamics of a glass embedded in its elastic properties?

    Potuzak, Marcel   Guo, Xiaoju   Smedskjaer, Morten M.   Mauro, John C.  

    The low temperature dynamics of glass are critically important for many high-tech applications. According to the elastic theory of the glass transition, the dynamics of glass are controlled by the evolution of shear modulus. In particular, the elastic shoving model expresses dynamics in terms of an activation energy required to shove aside the surrounding atoms. Here, we present a thorough test of the shoving model for predicting the low temperature dynamics of an oxide glass system. We show that the nonequilibrium viscosity of glass is governed by additional factors beyond changes in shear modulus. (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4730525]
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  • Principles of Pyrex(A (R)) glass chemistry: structure-property relationships

    Smedskjaer, Morten M.   Youngman, Randall E.   Mauro, John C.  

    Pyrex(A (R)) glass was one of the first commercial boroaluminosilicate glass compositions, selected in 1915 from thousands of compositions due to its ability to sustain mechanical and thermal shock. While the microscopic structure of Pyrex(A (R)) glass has recently been investigated, the microscopic origins of its macroscopic properties are not well understood, i.e., the atomic scale foundation of the original empirical invention of Pyrex(A (R)) glass has yet to be established. In this work, we have tackled this problem by investigating the effects of varying Si/Al and Na/B ratios on the boron and aluminum speciation and a range of physical and rheological properties in the Pyrex(A (R)) glass family. We show that the canonical Pyrex(A (R)) boroaluminosilicate composition is indeed optimal for attaining relatively high values of glass transition temperature and elastic moduli and a low coefficient of thermal expansion, while simultaneously maintaining a high glass-forming ability.
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  • Topological Model for the Viscosity of Multicomponent Glass-Forming Liquids

    Mauro, John C.   Ellison, Adam J.   Allan, Douglas C.   Smedskjaer, Morten M.  

    Topological constraint theory holds the key to understanding the temperature and composition dependence of the dynamics of glass-forming liquids. Unfortunately, existing analytical models currently do not apply to multicomponent industrial glasses. Moreover, models that are strictly empirical in nature fail to provide insight into the underlying physical trends and cannot extrapolate beyond the compositional ranges used for fitting of their parameters. In this paper, we present a phenomenological model offering an improved description of the composition and temperature dependence of the shear viscosity of multicomponent liquids. The model has a clear physical foundation based on the temperature dependence of the network constraints with only two empirical fitting parameters per oxide component. The model predicts the isokom temperatures of 7141 viscosity measurements for 760 different compositions with a root-mean-square error of only 6.55K.
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  • Glass-forming ability of soda lime borate liquids RID H-1313-2011

    Zheng, Qiuju   Mauro, John C.   Smedskjaer, Morten M.   Youngman, Randall E.   Potuzak, Marcel   Yue, Yuanzheng  

    We investigate the composition dependence of glass-forming ability (GFA) of a series of iron-containing soda lime borate liquids by substituting Na2O for B2O3. We have characterized GFA by measuring the glass stability against crystallization using a differential scanning calorimeter (DSC). The results show that the GFA decreases when substituting Na2O for B2O3. Moreover, we find that there is no direct link between the kinetic fragility and GFA for the soda lime borate series studied herein. We have also discovered and clarified a striking thermal history dependence of the glass stability against crystallization. In particular, the two glasses containing 20 and 25 Na2O mol% do not exhibit crystallization exotherms during the second DSC upscan at 10 and 20 K/min following prior slow (10 and 20 K/min) downscans. This indicates that the glass stability of these compositions can be enhanced by cooling their melts to the glassy state slowly, before any reheating. We explain this phenomenon in terms of the thermal history dependence of boron speciation. (C) 2011 Elsevier B.V. All rights reserved.
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  • Achieving long time scale simulations of glass-forming systems

    Mauro, John C.   Du, Jincheng  

    Glass-forming systems have posed an especial challenge for atomistic simualtions given their complicated non-crystalline structure and the long time scales involved with glass transition and relaxation phenomena. In this article, we review two recent techniques for extending the time scales of these simulations. First, we describe the enthalpy landscape approach, which uses inherent structure and transition point mapping to develop a set of coarse-grained master equations for computing long time dynamics. Accounting for the broken ergodic nature of glass, these master equations can be solved on any arbitrary time scale. Second. we discuss the Kinetic Monte Carlo method and its application to glassy systems. Kinetic Monte Carlo provides an effective means of sampling rare events without losing the detailed atomistic description of the glass structure. (C) 2011 Elsevier B.V. All rights reserved.
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  • Minimalist landscape model of glass relaxation

    Mauro, John C.   Smedskjaer, Morten M.  

    The relaxation behavior of glass is of great scientific and technological importance. However, prediction of glass relaxation behavior using direct first principles techniques is currently infeasible for realistic laboratory time scales. The enthalpy landscape approach has proven to be successful in overcoming this time scale constraint and providing insights into the fundamental physics governing glass transition and relaxation behavior. However, it is still too computationally intensive to calculate representative enthalpy landscapes for multicomponent glasses of industrial interest. It is thus interesting to consider a simplified enthalpy landscape that captures the essential features of glass relaxation and can be solved analytically. Here, we present the analytical solution for such a "minimalist landscape" model that is complicated enough to capture both primary (alpha) and secondary (beta) relaxation processes, yet simple enough to offer a closed-form solution. Using this minimalist landscape, we perform model calculations to illustrate the relative impact of activation barriers and entropy on glass relaxation behavior. The results of our model show that alpha and beta relaxation processes are largely decoupled, in agreement with recently published experimental results. (C) 2012 Elsevier B.V. All rights reserved.
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  • A model for phosphate glass topology considering the modifying ion sub-network

    Hermansen, Christian   Mauro, John C.   Yue, Yuanzheng  

    In the present paper we establish a temperature dependent constraint model of alkali phosphate glasses considering the structural and topological role of the modifying ion sub-network constituted by alkali ions and their non-bonding oxygen coordination spheres. The model is consistent with available structural data by NMR and molecular dynamics simulations and with dynamic data such glass transition temperature (T-g) and liquid fragility (m). Alkali phosphate glasses are exemplary systems for developing constraint model since the modifying cation network plays an important role besides the primary phosphate network. The proposed topological model predicts the changing trend of the T-g and m with increasing alkali oxide content for alkali phosphate glasses, including an anomalous minimum at around 20 mol.% alkali oxide content. We find that the minimum in T-g and m is caused by increased connectivity of the modifying ion sub-network, as the alkali ions must share non-bonding oxygen to satisfy their coordination requirements at higher alkali oxide contents. We argue that the systematically decreasing the T-g values of alkali phosphate glasses from Li2O to Na2O to Cs2O could be caused by a weakening of the modifying ion sub-network and can be accounted for by lower constraint onset temperatures. (C) 2014 AIP Publishing LLC.
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  • Topological origin of stretched exponential relaxation in glass

    Potuzak, Marcel   Welch, Roger C.   Mauro, John C.  

    The physical origin of stretched exponential relaxation is considered by many as one of the oldest unsolved problems in science. The functional form for stretched exponential relaxation can be deduced from the axiomatic diffusion-trap model of Phillips. The model predicts a topological origin for the dimensionless stretching exponent, with two "magic" values emerging: beta =3D 3/5 arising from short-range molecular relaxation pathways and beta =3D 3/7 for relaxation dominated by longer-range interactions. In this paper, we report experimental confirmation of these values using microscopically homogeneous silicate glass specimens. Our results reveal a bifurcation of the stretching exponent, with beta =3D 3/5 for stress relaxation and beta =3D 3/7 for structural relaxation, both on macroscopic length scales. These results point to two fundamentally different mechanisms governing stress relaxation versus structural relaxation, corresponding to different effective dimensionalities in configuration space during the relaxation process. (C) 2011 American Institute of Physics. [doi:10.1063/1.3664744]
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  • Liquid Fragility Determination of Oxide Glass-Formers Using Temperature-Modulated DSC

    Bechgaard, Tobias K.   Gulbiten, Ozgur   Mauro, John C.   Yue, Yuanzheng   Bauchy, Mathieu   Smedskjaer, Morten M.  

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  • Origin of dynamical heterogeneities in calcium aluminosilicate liquids

    Vargheese, K. Deenamma   Tandia, Adama   Mauro, John C.  

    We investigate the heterogeneous dynamics of calcium aluminosilicate liquids across both the peraluminous and peralkaline regimes. Using the isoconfigurational ensemble method we find a clear correlation between dynamical heterogeneities and concentration fluctuations. Regions of high dynamic propensity have higher concentrations of both calcium and aluminum, whereas low propensity regions are silica rich. The isoconfigurational ensemble is found to be a powerful tool for studying the origin of heterogeneous dynamics of industrially relevant glass-forming liquids. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3429880]
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  • Sodium diffusion in boroaluminosilicate glasses RID A-7944-2011 RID H-1313-2011

    Smedskjaer, Morten M.   Zheng, Qiuju   Mauro, John C.   Potuzak, Marcel   Morup, Steen   Yue, Yuanzheng  

    Understanding the fundamentals of alkali diffusion in boroaluminosilicate (BAS) glasses is of critical importance for advanced glass applications, e.g., the production of chemically strengthened glass covers for personal electronic devices. Here, we investigate the composition dependence of isothermal sodium diffusion in BAS glasses by ion exchange, inward diffusion, and tracer diffusion experiments. By varying the [SiO(2)]/[Al(2)O(3)] ratio of the glasses, different structural regimes of sodium behavior are accessed. We show that the mobility of the sodium ions decreases with increasing [SiO(2)]/[Al(2)O(3)] ratio, revealing that sodium is more mobile when it acts as a charge compensator to stabilize network formers than when it acts as a creator of non-bridging oxygens on tetrahedrally-coordinated silicon and trigonal boron. The impacts of both the addition of iron and its redox state on the sodium diffusivity are explored in terms of the structural role of ferric and ferrous ions. By comparing the results obtained by the three approaches, we observe that both the tracer Na diffusion and the Na-K interdiffusion are significantly faster than the Na inward diffusion. The origin of this discrepancy could be attributed to the fact that for sodium inward diffusion, the charge compensation for electron holes is a rather slow process that limits the rate of diffusion. (C) 2011 Elsevier B.V. All rights reserved.
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  • Nonequilibrium viscosity of glass

    Mauro, John C.   Allan, Douglas C.   Potuzak, Marcel  

    Since glass is a nonequilibrium material, its properties depend on both composition and thermal history. While most prior studies have focused on equilibrium liquid viscosity, an accurate description of nonequilibrium viscosity is essential for understanding the low temperature dynamics of glass. Departure from equilibrium occurs as a glass-forming system is cooled through the glass transition range. The glass transition involves a continuous breakdown of ergodicity as the system gradually becomes trapped in a subset of the available configurational phase space. At very low temperatures a glass is perfectly nonergodic (or "isostructural"), and the viscosity is described well by an Arrhenius form. However, the behavior of viscosity during the glass transition range itself is not yet understood. In this paper, we address the problem of glass viscosity using the enthalpy landscape model of Mauro and Loucks [Phys. Rev. B 76, 174202 (2007)] for selenium, an elemental glass former. To study a wide range of thermal histories, we compute nonequilibrium viscosity with cooling rates from 10(-12) to 10(12) K/s. Based on these detailed landscape calculations, we propose a simplified phenomenological model capturing the essential physics of glass viscosity. The phenomenological model incorporates an ergodicity parameter that accounts for the continuous breakdown of ergodicity at the glass transition. We show a direct relationship between the nonequilibrium viscosity parameters and the fragility of the supercooled liquid. The nonequilibrium viscosity model is validated against experimental measurements of Corning EAGLE XG (TM) glass. The measurements are performed using a specially designed beam-bending apparatus capable of accurate nonequilibrium viscosity measurements up to 10(16) Pa s. Using a common set of parameters, the phenomenological model provides an accurate description of EAGLE XG (TM) viscosity over the full range of measured temperatures and fictive temperatures.
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