Evolution of aluminosilicate structure and mullite crystallization from homogeneous nanoparticulate sol–gel precursor with organic additives

The influence of non-ionic polyethylene glycol and poly(vinylpyrrolidone) on monophasic-like nanoparticulate aluminosilicate with mullite bulk composition was investigated. The chemical homogeneity in the sol–gel state, as well as the evolution of the calcined aluminosilicate/mullite structures thereof, was studied by dynamic laser scattering, small angle X-ray scattering, nuclear magnetic resonance spectroscopy, X-ray diffraction, differential thermal analysis, dilatometry, N2 adsorption and Fourier transform infrared spectroscopy. The results show that the organic additives have virtually no influence on the chemical structure of the monophasic-like nanoparticles in the sol–gel state, and the overall homogeneity of monophasic gels in the fired ceramics was generally sustained, as judged by the Type I crystallization. The porosity was not due to the polymers directly acting as porogens, but due to voids formed during the restructuring of matter during heat treatment.