Formation of sol-gel nanostructured mullite by additions of fluoride ion

• Published in: Journal of thermal analysis and calorimetry 2005-02, Vol.79 (3), p.487-492
• Main Authors: Simendic, B, Radonjic, Lj
• Format: Article
• Language: English
• ISSN: 1388-6150; 1572-8943
• DOI: 10.1007/s10973-005-0567-z

Mullite has received much attention as a matrix material for high temperature composite development, as a substrate in multilayer packing in eletronics, and as an infrared-transparent window, especially for high temperature applications. The subject of this study was to investigate the effect of fluoride ions addition on the temperature of sol gel mullite formation based on the hypotheses that the presence of fluoride ions can decrease the temperature of mullite formation (in respect to common 980DGC, in sol-gel processing). Polymeric sols were prepared by mixing TEOS and aluminum nitrate nanohydrate and by adding fluoride ions (from 2 to 5 mass%). DTA, TG, XRD and SEM were used for characterisation of mullite gel and crystalline mullite. The experimental results confirmed that the addition of fluoride ions decrease the temperature of mullite formation up to 890DGC for the fluorine concentration of 3.5 mass%. Experimental results showed that the temperature of mullite formation is not a simple function of the fluoride ion content. The mechanism of fluorine effect was discussed in terms of the gelling process, gel structure and the phase separation before the mullite formation.