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
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.
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
