CHARACTERIZATION OF SOL-GEL MULLITE POWDERS

Using tetraethyl orthosilicate and aluminum tri-sec-butoxide as raw ma terials, two series of mullite gels were prepared, one involving a che mical modification of aluminum alkoxide by ethylacetoacetate, the othe r one by reacting both alkoxides in a non-homologous alcohol, i.e. iso propyl alcohol or 2-methoxyethanol. For the first route the excess wat er 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 isopropan ol as solvent. The sample preparation strongly influences the ceramic densifications that can vary from 70 to 93% of the theoretical value a fter 1200 degrees C calcination.