ABSTRACT
The controlled addition of water is not important; one can use excess water for the hydrolysis of tetraethyl orthosilicate as an additional advantage. Achieving the control to promote simultaneous hydrolysis of two alkoxides and homogeneous copolymerization is a rather difficult task. Direct formation of mullite from an amorphous precursor: The sprayed powder synthesized by Kanzaki et al. was amorphous to X-ray. However, XRD analysis of the powder after the completion of this peak showed the crystallization of both pseudotetragonal mullite and a small quantity of the spinel phase. A dried xerogel was synthesized by the slow coprecipitation of two components of the said solution mixture during in situ generation of ammonia by the thermal hydrolysis of urea, followed by the filtration and washing of the ammonium nitrate formed during neutralization of nitrate ions with ammonia. The morphology was retained after crystallization, as shown in an SEM photograph.
