Characterization of sol-gel mullite powders

Using tetraethyl orthosilicate and aluminum tri-sec-butoxide as raw materials, two series of mullite gels were prepared, one involving a chemical modification of aluminum alkoxide by ethylacetoacetate, the other one by reacting both alkoxides in a non-homologous Alcohol, I.e. isopropyl alcohol or 2-methoxyethanol. For the first route the excess water or basic conditions promote the formation of nanosized powders that appear X-ray amorphous after the crystallization exotherm on the DTA trace. The same result is obtained for the second route with isopropanol as solvent. The sample preparation strongly influences the ceramic densifications that can vary from 70 to 93% of the theoretical value after 1200 °C calcination.