Thermal conversion of the hydrous aluminosilicate LiAlSiO3(OH)2 into γ-eucryptite

Alisa Gordeeva,Ulrich Häussermann,Olga Yu Vekilova,Istvan Z Jenei,Kristina Spektor

doi:10.1515/znb-2021-0095

Alisa Gordeeva, Ulrich Häussermann + Show 3 more

Open Access

https://doi.org/10.1515/znb-2021-0095

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Abstract

Abstract LiAlSiO3(OH)2 is a dense hydrous aluminosilicate which is formed from LiAlSiO4 glass in hydrothermal environments at pressures around 5 GPa. The OH groups are part of the octahedral Al and Li coordination. We studied the dehydration behavior of LiAlSiO3(OH)2 by a combination of TEM and multi-temperature PXRD experiments. Dehydration takes place in the temperature interval 350–400 °C. Above 700 °C LiAlSiO3(OH)2 is converted via a transient and possibly still slightly hydrous phase into γ-eucryptite which is a metastable and rarely observed polymorph of LiAlSiO4. Its monoclinic structure is built from corner-sharing LiO4, AlO4 and SiO4 tetrahedra. The ordered framework of AlO4 and SiO4 tetrahedra is topologically equivalent to that of cristobalite.

Highlights

Crystalline phases with LiAlSiO4 composition include a zeolite, Li-ABW, as well as α- and β-eucryptite
Gordeeva et al.: Thermal conversion of LiAlO3(OH)2 to γ-eucryptite showed that the dehydration of LiAlSiO3(OH)2 takes place in the temperature interval 350–500 °C, with the associated weight loss in very good agreement with the stoichiometric amount of water (12.5%)
We studied the evolution of the dehydration on individual LiAlSiO3(OH)2 crystals in the transmission electron microscope (TEM, Figure 2d–f)

Summary

Introduction

Crystalline phases with LiAlSiO4 composition include a zeolite, Li-ABW, as well as α- and β-eucryptite. They are all built from corner-sharing AlO4 and SiO4 tetrahedra (observing strict Si–Al ordering) with Li+ ions being exclusively in a tetrahedral coordination. The orthorhombic zeolite Li-ABW (LiAlSiO4·H2O) is formed during hydrothermal treatment of glass or gels (made e.g. of LiOH, Al(OH) and SiO2) with Li2O·Al2O3·2SiO2 composition at temperatures below 350 °C, whereas higher temperatures afford rhombohedral α-eucryptite [6, 7]. Li ions coordinate to three framework O atoms (involving three different tetrahedra) and the water molecule. Water loss leads first to anhydrous Li-ABW (at around T = 300 °C) with narrowed, elongated, 8-ring channels in which Li+ is four-coordinated by framework O atoms, and (at around T = 600 °C) to monoclinic, cristobalite-like, γ-LiAlSiO4.

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