ABSTRACT
Synthesis of precursors like monophasic gels/polymeric gels/Type I, colloidal gels/coprecipitated gels/Type III, diphasic gels/colloidal gels/Type II, and spray-pyrolyzed samples. According to Engelhadt and Michel, the silica tetrahedra in a solid silicate have been classified into five species on the basis of the number of bridging oxygen atoms forming Si–O–Si bonds. Risbud et al. presented Si MAS-NMR spectra of silica glasses with a wide range of compositions showing a wide range of chemical shifts and demonstrating a range of local structural environments. To attain stable mullite, calcination needs to be done far above 1100 C. 9.2.2 MAS-NMR studies of the coprecipitated sample of mullite gel were done by Nishu et al. Komarneni and Roy measured the Al MAS-NMR spectra of the diphasic mullite gel heated to 1010 C and showed that the tetrahedral to octahedral ratio of aluminum was 0.45. MAS-NMR studies of these diphasic gels will be discussed in the following paragraphs.
