The impact of nanocrystallite size and shape on phase transformation:Application to the boehmite/alumina transformation

International audienceThe thermal activation of oxyhydroxides is a key industrial process in preparing oxide materials. Whendealing with nanoparticles, the phase transition properties are drastically modified. By preparing sizeandshape-controlled boehmite nanoparticles, we demonstrate that the transformation temperature intoc-alumina is significantly altered. Rhombus crystallites were obtained from boehmite precipitated atbasic pH, whereas crystallites precipitated at pH 4.5 were hexagonal. For the same crystallite size (ca.4.5 nm), the transition temperature of the hexagonal crystallites was 315 C whereas that of the rhombusones was only 270 C. A thermodynamic model was developed to rationalize these observations: thetransition temperature results from a compromise between the crystallite size and the ratio of the lateraland basal surfaces. Consequently, the as-determined kinetic data could be a powerful tool for developingnew efficient calcination processes and optimizing alumina properties