A new way to spinnable sols derived from modified aluminumalkoxides

Abstract

The preparation of spinnable sols has been developed to obtain a new type of sol-gel derived pure alumina fiber. The starting material was aluminum sec-butoxide, which was modified in a first step with glycolether, e.g., isopropoxyethanol. This leads to a partial replacement of alkoxy groups via alcoholysis and a change of the precursor structure from a trimeric to a tetrameric one. In the second step, carboxylation, the transformation to six-coordinated aluminum could be observed. Due to the formation of a sol with Newtonian flow behavior after hydrolysis, gel fibers up to several kilometers long could be drawn directly from the clear colorless sol with spinning velocities up to 200 m/min. The addition of an organic filament-forming polymer is not necessary. The sol is spinnable for periods up to one year. The transformation of the gel fiber to α-Al₂O₃ occurs at 1150° C.