Hydrothermal Synthesis of Submicrometer α‐Alumina from Seeded Tetraethylammonium Hydroxide‐Peptized Aluminum Hydroxide

Abstract

Submicrometer α‐alumina powder was successfully synthesized from seeded aluminum hydroxide peptized with tetraethylammonium hydroxide (TENOH) and hydrothermally treated at 200°C, using α‐alumina particles as seeds. The powders were characterized by XRD, SEM, DTA‐TG, and BET analyses. Results showed that seeding could greatly enhance the transition to α‐alumina at 200°C without formation of other transient alumina phases. α‐Alumina with some amount of boehmite formed in the seeded samples, whereas boehmite was the exclusive phase formed in the nonseeded sample. The morphology of α‐alumina embedded in the boehmite matrix for the seeded samples suggests a direct transition from aluminum hydroxide to α‐alumina without the formation of transient alumina phases. The formation of α‐alumina in the seeded samples at temperatures as low as 200°C could be attributed to a favored nucleation in the TENOH‐peptized aluminum hydroxide and to the subsequent hydrothermal treatment that supplies the necessary activation energy for crystal growth. Transition of boehmite to α‐alumina in the hydrothermally treated samples with low‐seed contents was significantly promoted by heat‐treating the samples at 500°C.