Influence de l'addition de cations sur les transformations successives γ → δ → Θ → α de l'alumine

Département de Chimie-Physique des Processus Industriels, Ecole Nationale Supérieure des Mines, 158, Cours Fauriel, 42023 Saint-Etienne Cedex , France.

Résumé

A l'aide de résultats expérimentaux de mesure de surface spécifique et de diffraction des rayons X, les degrés d'avancement des transformations successives γ → δ → θ → α de l'alumine peuvent être déterminés. L'application de cette méthode à des échantillons dopés par différents cations (Al³⁺, Mg²⁺, K⁺, Ca²⁺, ln³⁺, La³⁺, Zr⁴⁺, Th⁴⁺) permet de montrer l’influence des dopants sur chacune des transformations de l'alumine.

Abstract

The influence of additives on the transformation of the intermediate phases of alumina through the sequence γ → δ → θ → α-Al₂O₃ was investigated by obtaining the kinetic curves of each transformation. The content in and á-AI2O₃ 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 γ → δ-Al₂O₃ phase transformation allows to determine the corresponding rate of transformation. The influence of additives was followed by adding Al³⁺, Mg²⁺, K⁺, Ca²⁺ , ln³⁺, La³⁺, Zr⁴⁺ and 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 γ → δ → θ → α-Al-Al₂O₃ sequence.