A layered double hydroxide (LDH) with chemical composition LiAl2(OH)7 ·2H2O was prepared via a wet chemical route of gel to crystallite (G–C) conversion at 80 °C involving the reaction of hydrated alumina gel, Al2O3 ·yH2O (80<y<120) with LiOH (Li2O/Al2O3 ≥0.5) in presence of hydrophilic solvents such as ethanol under refluxing conditions. The hydrothermal synthesis was carried out using the same reactants by heating to ≤140 °C in a Teflon-lined autoclave under autogenerated pressure (≤20 MPa). Transmission electron microscopy showed needle-shaped aggregates of size 0.04–0.1 µm for the gel to crystallite conversion product, whereas the hydrothermal products consisted of individual lamellar crystallites of size 0.2–0.5 µm with hexagonal morphology. The LDH prepared through the gel to crystallite conversion could be converted into LiAl(OH)4 ·H2O or LiAl(OH)3NO3 ·H2O by imbibition of LiOH or LiNO3 , respectively, under hydrothermal conditions. Thermal decomposition of LDH above 1400 °C gave rise to LiAl5O8 accompanied by the evaporation of Li2O. LiAl(OH)4 ·H2O and LiAl(OH)3NO3 ·H2O decomposed in the temperature range 400–1000 °C to α- or β-LiAlO2 . The compositional dependence of the product, the intermediate phases formed during the heat treatment and the possible reactions involved are described in detail.
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Journal of Materials Chemistry
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