A New Way to Spinnable Sols Derived from Modified Aluminumalkoxides

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 alpha-Al2O3 occurs at 1150 degrees C.