Mullite crystallization using fully hydrolyzed silica sol: the gelation temperature influence

作者：Campos Tiago M B; Cividanes Luciana S^*; Machado Joao Paulo B; Simonetti Evelyn A N; Rodrigues Liana A; Thim Gilmar P

来源：Journal of Sol-Gel Science and Technology, 2014, 72(2): 219-226.

DOI：10.1007/s10971-014-3285-9

• Mullite
• Sol-gel
• Ethylene glycol
• Crystallization

Mullite is an aluminosilicate widely used as a structural material for high temperature applications. This paper studies the effect of the gelation temperature on the synthesis of two mullite precursors: polymeric and colloidal silica, using both in fully-hydrolyzed silica sol, derived from sodium silicate. The gels were synthesized using aqueous silicic acid and aluminum nitrate. Ethylene glycol was added into polymeric gels. Two gelation temperatures were used: 80 and 100 degrees C. In the polymeric precursor, the increasing of the gelation temperature caused an increase in the silica incorporation inside the mullite crystalline lattice at 1,000 degrees C, and it also generated an increase in the reaction extent at all calcination temperatures. In the colloidal precursors, these effects were more intense than in the polymeric precursors in terms of yield. Colloidal samples calcined at 1,250 degrees C crystallized cristobalite and alpha alumina in addition to mullite when they were previously gelled at 80 degrees C. On the other hand, the same sample gelled at 100 degrees C led to only crystallized mullite. The reaction extent increased by more than 20 % for colloidal samples gelled at 100 degrees C compared to colloidal samples gelled at 80 degrees C (calcined at 1,250 degrees C). This increase was due to the almost total incorporation of alumina and silica in the crystalline lattice of mullite.

• 出版日期2014-11