ISSN 0862-5468 (Print), ISSN 1804-5847 (online) 

Ceramics-Silikáty 49, (1) 34 - 39 (2005)


THE INFLUENCE OF THE PREFERRED ORIENTATION OF BOEHMITE CRYSTALLITES ON α-Al₂O₃ CRYSTALLIZATION
 
Bodišová Katarína, Pach Ladislav, Kovár Vladimir
 
Faculty of Chemical and Food Technology, Slovak University of Technology, Radlinského 9, 81237 Bratislava, Slovakia

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

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 α-Al₂O₃ nucleation. Spread of SiO₂ on the surface of α-Al₂O₃ particles inhibits α-Al₂O₃ crystallization up to 1350°C.


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