Structure of High Alumina Content Al₂O₃−SiO₂ Composition Glasses

Abstract

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 approximately 1600 degrees C s(1-) 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 degrees between an Al ion and the adjoining cation via a bridging oxygen. We propose that the structure of the glass is a "transition state" between the alumina-rich liquid and the equilibrium mullite phase that are dominated by 4- and 6-coordinated aluminum ions, respectively.

27Al NMR Studies of Aluminosilicate Glasses

“…Sato et al [141,284] provided evidence for a strong dependence of the precise {AlO p } speciation on the quench-rate utilized in the glass preparation, claiming that all {Al [4] , Al [5] , Al [6] } species exist only for very fast cooling rates (10 5 À10 6 K/s), whereas for "normal" rates (10 2 À10 3 K/s), only AlO 4 and AlO 6 moieties are observed. However, their conclusions were also questioned in subsequent work [282,283] that overall supported the results of Risbud and coworkers. For a series of Al 2 O 3 -SiO 2 glasses with variable compositions, Sen and Youngman [282] concluded from 27 Al and 27 O MAS/3QMAS NMR that O ½3 T species are responsible for charge balancing the AlO 4 groups in glasses incorporating ≲0.6 mol% Al 2 O 3 , whereas all three Al [p] coordinations coexist when the Al 2 O 3 content is increased, with the AlO 4 /AlO 6 and AlO 4 /AlO 5 pairs of polyhedra dominating in the ranges of %0.6-4 mol% and ≳ 4 mol% Al 2 O 3 , respectively [282].…”

“…[281,282]) and $60-67 mol% Al 2 O 3 (Refs. [141,283]), whereas outside of these ranges, phase-separation occurs into Si-rich and Al-rich domains [141,281].…”

“…Asterisks mark spinning sidebands. The spectra were reproduced from Sen and Youngman [282] (left panel) and Weber et al [283] (right panel) with permission from The American Chemical Society. manifested by the structural fragment of Fig.…”

Ultrahigh-pressure acoustic wave velocities of SiO2-Al2O3 glasses up to 200 GPa

“…The SiO 2 -Al 2 O 3 system is the simplest from among the aluminous silicate systems. A number of previous studies have reported structural features at ambient pressure, as inferred by Raman scattering (Kato 1976;McMillan and Piriou 1982), infrared absorption (Poe et al 1992a;Okuno et al 2005), X-ray diffraction (Morikawa et al 1982;Okuno et al 2005), nuclear magnetic resonance (NMR) spectroscopic techniques (Risbud et al 1987;Sato et al 1991;Poe et al 1992a, b;Sen and Youngman 2004;Weber et al 2008), and by molecular dynamics (MD) computer simulations (Poe et al 1992a, b;Linh and Hoang 2007).…”

The alum-processing mechanism attenuating toxicity of Araceae Pinellia ternata and Pinellia pedatisecta

“…Instrument operation parameters were as follows: Spectral width was 31,152.6 Hz, sampling time was 0.70 s, advance and delay Fig. 1 Influence of the rabbit eye irritation induced by raphides before and after processed with the alum (x AE s, n = 6) was 6.0 ls, relaxation delay was 2.0 s, pulse width was 2.3 ls, and pulse angle was 30° (Weber et al 2008). …”