Preparation of nanocrystalline aluminum hydroxide and alumina by thermal and vapor heat treatments of reaction products of terephthalic acid and aluminum hydroxide

Abstract

We have studied the behavior of terephthalic acid (TPA) particles in sodium aluminate solutions. The results demonstrate that the addition of TPA to a solution at room temperature leads to appreciable TPA particle growth and the formation of amorphous aluminum hydroxide on the surface of the crystalline TPA floccules. With increasing initial aluminum concentration in solution, the interface displaces toward the central part of the floccules and an almost complete extraction of the dissolved aluminum is reached. The aluminate ion incorporation into the structure of TPA causes its conversion to an ionized form. In the resultant structure of amorphous aluminum hydroxide in TPA, the aluminum hydroxide crystallizes over time to form bayerite. Autoclaving in water vapor at 420°C produced boehmite ranging in crystallite size from 300 to 700 nm. Heat treatment in air for 2 h at 800°C leads to the formation of γ-Al2O3 in the form of spheres with a fiber length on the order of 300 nm and a thickness of 50–100 nm.