THE STUDIES ON THE PREPARATION OF CERAMIC FIBERS .2. PREPARATION OF ALUMINA FIBERS BY PRECURSOR METHOD

Alumina fibers were prepared by the precursor methods based on the aqueous solutions of Al(OPr(i))3-AlCl3-Citric acid (Method A), Al(OPr(i))3-AlCl3 (Method B), Al(OPr(i))3-Al(NO3)3-Citric acid (Method C) and Al(OPr(i))3-Al(NO3)3 (Method D) at room temperature. The compositional regions of these precursor solutions for spinnability were as follows. For the method A and B, in the region of H2O mol/total Al mol > 20/1, 2/1 less-than-or-similar-to Al(OPr(i))3 mol/Al(NO3)3 mol or AlCl3 mol less-than-or-similar to 4/1 and total Al mol/citric acid mol = 10/1 fibers could be drawn. On the other hand, in the method C and D, the solutions having compositions of H2O mol/total Al mol > 20/1 and 2/1 less-than-or-similar-to Al(OPr(i))3 mol/Al(NO3)3 mol or AlCl3 mol < 3/1 was spinnable. The structure of Al-containing polymers (or chemical species) on concentration processes to make spinnable solutions was examined by Al-27-NMR spectra. The existence and its content of Al13(7+) polycation, and the bonding state in Al-polymers were found to be very important factors for spinnability. The structure and thermal decomposition behavior of precursor fibers were affected by the addition of citric acid, and by Cl- and NO3- ions.