Influence de l'addition de cations sur les transformations successives gamma→delta→theta→alpha de l'alumine = Influence of addition of cations on the gamma→delta→theta→alpha successive transformations in alumina

National audienceA l'aide de résultats expérimentaux de mesure de surface spécifique et de diffraction des rayons X, les degrés d'avancement des transformations successives gamma-delta-théta-alpha de l'alumine peuvent être déterminés. L'application de cette méthode à des échantillons dopés par différents cations (Al3+, Mg2+, K+, Ca2+, ln3+, Zr+4, Th4+) permet de montrer l'influence des dopants sur chacune des transformations de l'alumine. // The influence of additives on the transformation of the intermediate phases of alumina through the sequence gamma-delta-theta-alpha Al2O3 was investigated by obtaining the kinetic curves of each transformation. The content in theta and alpha Al2O3 phases was measured by X-ray diffraction for samples calcinated at numerous intervals during a 30 hour period. On the other hand the observed change in surface area associated to the gamma-delta Al2O3 phase transformation allows to determine the corresponding rate of transformation. The influence of additives was followed by adding Al3+, Mg2+, K+, Ca2+, ln3+, Zr+4, Th4+ cations by a dry impregnation method using nitrate salts. By comparison with a sample modified by a nitric acid solution, the effects of added cations are determined for each step of the gamma-delta-theta-alpha Al2O3 sequence