Ceramics-Silikáty 49 (1) 34-39 (2005)

THE INFLUENCE OF THE PREFERRED ORIENTATION OF BOEHMITE CRYSTALLITES ON a-Al₂O₃ CRYSTALLIZATION

K. Bodišová, L. Pach, V. Kovár

Monolithic boehmite gels were prepared from commercial peptizable Condea product. The gels were modified by nanoparticle SiO₂ addition. Preferred orientation of boehmite crystallites in the gels and phase composition of sintered samples was observed by XRD analysis. To determine the effect of gel structure and eventually of SiO₂ addition on sintering and crystallization DTA, SEM and bulk density measurement were used. Boehmite crystallites align themselves spontaneously during gelation into preferred orientation state that can be avoided by ultrasonication or by the nanoparticle SiO₂ addition. The ordered or disordered gel microstructure has only marginal influence on high-temperature processes (crystallization, sintering). These processes are significantly influenced by addition of foreign SiO₂ nanoparticles, which decrease coordination of boehmite particles suppressing thus a-Al₂O₃ nucleation. Spread of SiO₂ on the surface of Al₂O₃ particles inhibits a-Al₂O₃ crystallization up to 1350°C.

Keywords: Sol-gel, Boehmite, Silica, Particle arrangement, a-Al₂O₃, Crystallization