A new layered phase in the alumina-terephthalic acid-water system

Abstract

Reactions between aqueous solutions of aluminum salts and ammonium terephthalate at pH 6–8 lead to the formation of a previously unknown, weakly ordered phase. It has signs of a layered compound with a unit cell parameter of 1.072–1.073 nm. Its empirical composition can be represented by the formula Al2O3 · xC8H6O4 · yH2O · δ(NH3), where x = 0.7–1.2, y = 4.4–6.0, and δ = 0–0.4. It has good structural order across the layers, whereas the order along the layers is weaker and depends on synthesis conditions. Calcination at 120°C leads to partial dehydration and changes the order along the layers, whereas the order across the layers changes little, with a slight increase in lattice strain. Heat treatment at 400°C leads to almost complete dehydration and fully eliminates the order along the layers, whereas the order across the layers is partially retained. Firing at 800°C leads to the formation of γ-Al2O3. A structural model has been proposed for the new phase.