Sol–gel dry spinning of mullite fibers from AN/TEOS/AIP system

Continuous mullite ceramic fibers were fabricated by a sol–gel dry-spinning technique. The sol was prepared from an aqueous solution of aluminum nitrate, aluminum isopropoxide and tetraethylorthosilicate. The sol–gel transition was investigated by measuring the volume, the solid content, the viscosity and the rheological properties of the solution. Shear viscosity η of the mullite sol varied dynamically with concentrating time and temperature of the sol. Combined with size analysis of sol particles and TEM analysis, the growth characteristics of sol particle agglomeration and its structural evolution were examined. By adjusting the temperature, the gelation degree could be stabilized at a certain value, and the sol–gel transition could be transferred to the spinning line. Continuous fibers were obtained from such sols using a laboratory dry-spinning apparatus. Sintering of the precursor fibers at 1100 °C yielded crack-free mullite ceramic fibers when the solid content of spinnable sol was above 50%.