A catalyst-free approach for sol-gel synthesis of highly mixed ZrO2-SiO2 oxides

The synthesis of mixed ZrO2-SiO2 oxides has been carried out using a new non-acid-base alkoxide route. The chemical reactivity of zirconium n-propoxide (ZP) is first modified with the chelating agent acetylacetone (acac) before it is brought in contact with tetraethoxysilane (TEOS). It is found that the gelation rate of bi-component sols is much faster than those of the mono-components under similar preparation conditions. A self-catalytic effect of the resultant Zr-O-Si on Si-O-Si formation is thus identified. By employing FTIR/DTA/TGA/XRD techniques, the mixing level of the two oxides in terms of Zr-O-Si hetero-linkages has been investigated in detail. A linear relationship between the IR absorption band shift of Zr-O-Si linkages and the Zr content is established to indicate the amount of oxide mixing. Phase segregation and thermal decomposition of xerogels upon calcination are studied and factors responsible for good mixing are also discussed. Using this approach, a high level of mixing has been achieved for the ZrO2-SiO2 binary oxides (Zr up to 50 mol%) with an acac to ZP molar ratio in the range 0.2-0.4 in the absence of an acid or base catalyst. (C) 1999 Elsevier Science B.V. All rights reserved.