Thermodynamics and Kinetics of γ-Al2O3 and AlOOH Transformations under Hydrothermal Conditions

Abstract

We have studied the kinetics of boehmite nanopowder formation during hydrothermal treatment of γ-Al₂O₃ nanopowder in a 1.5% HCl solution at 200, 170, and 150°C. The results demonstrate that the temperature-dependent reaction rate constant follows the Arrhenius equation. The E_a of the process has been determined to be 84 kJ/mol. The thermodynamics of γ-Al₂O₃ nanopowder conversion into boehmite during hydrothermal treatment at 150°C has been studied by differential scanning calorimetry. The heat of vaporization of water from a two-phase nanosystem (γ-Al₂O₃ + forming boehmite) has been determined to be 8, 16, and 22 kJ/mol H₂O, which points to an active role of water with a low heat of vaporization in the initial stages of the hydrothermal treatment of the γ-Al₂O₃ nanopowder. The heat effect of the АlООН → γ-Al₂O₃ conversion in the nanopowders is lower than the reference value by 7 kJ/mol AlOOH, which is attributable to the small particle size and low structural perfection of the synthesized boehmite (AlOOH).