Obtaining “hard” and “crack-resistant” glasses have always been of great important in glass science and glass technology. However, in most commercial glasses both properties are not compatible. In this work, colorless and transparent xAl2O3–(100–x)SiO2 glasses (30 ≤ x ≤ 60) were fabricated by the aerodynamic levitation technique. The elastic moduli and Vickers hardness monotonically increased with an increase in the atomic packing density as the Al2O3 content increased. Although a higher atomic packing density generally enhances crack formation in conventional oxide glasses, the indentation cracking resistance increased by approximately seven times with an increase in atomic packing density in binary Al2O3–SiO2 glasses. In particular, the composition of 60Al2O3•40SiO2 glass, which is identical to that of mullite, has extraordinary high cracking resistance with high elastic moduli and Vickers hardness. The results indicate that there exist aluminosilicate compositions that can produce hard and damage-tolerant glasses.

/pdf/crack-resistant-al2o3-sio2-glasses-38cfyx3rm9.pdf

Crack-resistant Al2O3-SiO2 glasses.

The study of disorder and nanocrystallinity in C-S-H, supplementary cementitious materials and geopolymers using pair distribution function analysis

Aluminosilicate glasses are of great geological and technological importance Significant efforts have been spent for enhancing the insight into their structures, where magic-angle-spinning (MAS) NMR that exploits the spin-5/2 27Al as probe nucleus constitutes one widely utilized option We review the application of basic 27Al NMR experimentation for studying primarily the short-range ( ≲ 03  nm) structure of aluminosilicate glasses, emphasizing practical aspects of performing MAS and triple-quantum MAS NMR experiments, as well as options for data analysis to extract 27Al NMR parameters and quantifying AlOp populations We illustrate the strengths and weaknesses of routine 27Al NMR for investigating aluminosilicate glasses, including its development over time While parts of the text apply generally to MAS NMR targeting half-integer spins as structural probes in crystalline as well as amorphous materials, the focus remains on 27Al NMR applications to aluminosilicate glasses, whose basic structural features are outlined together with a survey of the most central research problems in the field By providing both in-depth discussions about the building blocks of aluminosilicate glasses while assuming a modest background knowledge of the reader about MAS NMR and glass structure, we hope that the presentation will appeal to a broad audience, encompassing both experienced researchers in solid-state NMR or glass structures, as well as to beginners in either area

27Al NMR Studies of Aluminosilicate Glasses

This paper summarizes the scientific trends associated with the rapid development of the technique of high-energy X-ray diffraction over the past decade pertaining to the field of liquids, glasses, and amorphous materials. The measurement of high-quality X-ray structure factors out to large momentum transfers leads to high-resolution pair distribution functions which can be directly compared to theory or combined with data from other experimental techniques. The advantages of combining highly penetrating radiation with low angle scattering are outlined together with the data analysis procedure and formalism. Also included are advances in high-energy synchrotron beamline instrumentation, sample environment equipment, and an overview of the role of simulation and modeling for interpreting data from disordered materials. Several examples of recent trends in glass and liquid research are described. Finally, directions for future research are considered within the context of past and current developments in the field.

/pdf/a-review-of-high-energy-x-ray-diffraction-from-glasses-and-3pnf3mejvm.pdf

A Review of High-Energy X-Ray Diffraction from Glasses and Liquids

Liquid Al2O3 has been supercooled more than 500 K below its melting point (Tm = 2327 K) using aerodynamic levitation and laser heating techniques. High energy synchrotron x-ray measurements were performed over a temperature range of 1817 ≤ T (K) ≤ 2700 and stroboscopic neutron diffraction at 1984 K and 2587 K. The diffraction patterns have been fitted with Empirical Potential Structure Refinement (EPSR) models and compared to classical molecular dynamics (MD) simulation results. Both sets of models show similar trends, indicating the presence of high populations of AlO4 and AlO5 polyhedral units predominantly linked by triply shared oxygen atoms. EPSR reveals that the mean Al–O coordination number changes linearly with temperature with nAlO = 4.41 – [1.25 × 10-4] (T – Tm), with a 2.5 A cutoff. Both EPSR and MD simulations reveal a direction of the temperature dependence of the aluminate network structure which moves further away from the glass forming ideal i.e. towards nAlO = 3 during supercooling. Furthermore, we provide new experimental data and models for amorphous alumina grown by sequential infiltration synthesis of a polymer template. The amorphous solid form likely has a larger Al–O coordination number than the liquid, consistent with expectations for the hypothetical glass.

/pdf/the-structure-of-amorphous-and-deeply-supercooled-liquid-2esnzf6u3h.pdf

The structure of amorphous and deeply supercooled liquid alumina

The structure of binary aluminosilicate glasses containing 60−67 mol % Al2O3 were investigated using high-resolution 27Al NMR and X-ray and neutron diffraction. The glasses were made by aerodynamic levitation of molten oxides. The 67% alumina composition required a cooling rate of ∼1600 °C s1− to form glass from submillimeter sized samples. NMR results show that the glasses contain aluminum in 4-, 5-, and 6-fold coordination in the approximate ratio 4:5:1. The average Al coordination increases from 4.57 to 4.73 as the fraction of octahedral Al increases with alumina content. The diffraction results on the 67% composition are consistent with a disordered Al framework with Al ions in a range of coordination environments that are substantially different from those found in the equilibrium crystalline phases. Analysis of the neutron and X-ray structure factors yields an average bond angle of 125 ± 4° between an Al ion and the adjoining cation via a bridging oxygen. We propose that the structure of the glass i...

Structure of high alumina content Al2O3-SiO2 composition glasses.

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Structure of high alumina content Al2O3-SiO2 composition glasses.