Effect of crystallite size on the thermal phase change and porous properties of boehmite

The effect of crystallite size on the thermal phase change and porous properties of boehmite was investigated using boehmites with crystallite sizes of 2.9 to 24.4 nm and boehmite gels prepared by precipitation and hydrothermal methods. The dehydroxylation temperature of boehmite increases, its phase transition temperature from γ- to θ-Al₂O₃ decreases and the θ- to α-Al₂O₃ transition temperature increases as the crystallite size of the boehmite increases. Boehmite with a crystallite size of ∼5 nm shows the highest specific surface area and greatest thermal stability. This boehmite contains pores of about 2-3 nm radius, suggested to be responsible for the superior porous properties and thermal stability.