Thermal Transformation of Transition Aluminas

This paper records conventional (CTEM) and scanning (STEM) microstructural examination of four transition aluminas (γ, δ, χ and κ) prepared from beohmite and hydrargillite. Bright and dark field images, and diffraction on a selected area (3 nm), show that the hydrargillite sequence transforms at 500°C, to ϰ alumina formed from a collection of slightly misoriented 6 to 8 nm microdomains. A very fast sintering to 100 nm microcrystals is observed upon heating at 950°C