Synthesis and characterization of sol–gel derived continuous spinning alumina based fibers with silica nano-powders

Silica nano-powders were used as the Si source to substitute acidic silica sol in the SiO2–Al2O3 sol mixture for benefiting the sintering of the fibers at 1250 °C. With the increase of nano-silica, grain diameter and porosity of the fibers decreased firstly and increased subsequently, a minimum value of 35.86 nm and 0.86% was exhibited at the nano-silica content of 20%. The solid content, linear growth model and homogeneity of the precursor sol were not affected by the presence of nano-silica, although the continuous spinning length became low. NMR Analysis of 27Al indicated that polymerization degree of the sol was enhanced by nano-silica. The nano-particle contributed to the reduced intermolecular distance of gel, so the appropriate content existed for resulting the reduced grain size and compact structure of the fibers.