Preparation of Boehmite by the Hydrothermal Method and Analysis of its Dehydration Kinetics

Boehmite (AlOOH), due to its porous structure, excellent adsorption properties and high thermal stability, is widely used in various areas, including petrochemistry, biology and medicine (catalysts, flame retardants, functional ceramics, etc.). We propose replacing traditional Al salts (or Al alkoxides) with industrial-grade aluminium hydroxide Al(OH)₃ as the precursor and using a hydrothermal method to synthesise phase-pure boehmite powder. The phase transition from gibbsite to boehmite can be achieved by adjusting the hydrothermal temperature using industrial-grade aluminum hydroxide (Al(OH)₃) as the starting material. Based on this, the study investigated the influence of hydrothermal reaction temperature on the crystal structure and microscopic morphology of boehmite. The samples were characterized using a variety of analytical methods, including XRD, SEM, TEM, HRTEM, particle size distribution, and TG–DSC, to comprehensively analyze the phase, microscopic morphology, and phase transition process. Results demonstrate that pure-phase boehmite powder with a square plate-like morphology can be obtained at hydrothermal temperatures above 180°C. The square plates exhibit smooth surfaces, clear boundaries, and an average particle size of approximately 0.88 μm. Dehydration kinetics analysis using the Popescu method confirms that the synthesized boehmite has a thermal decomposition temperature above 700K and a dehydration weight loss of 17%. The dehydration process follows a model mechanism function of f(α) = 2(1 – α)^1/2, indicating a two-dimensional phase boundary reaction of shrinking cylindrical bodies. The average activation energy (E_a) for the dehydration process is determined to be 211.40 kJ/mol, the average pre-exponential factor (A) is 5.05 · 10¹³ min^–1, and the average correlation coefficient (R²) is 0.9939.