An alumina–YAG nanostructured fiber prepared from an aqueous sol–gel precursor: Preparation, rheological behavior and spinnability

Continuous-fiber development is needed for high-performance and high-temperature composites. Various methods have been used to make ceramic fibers. In this research, composite fibers (YAG/Al2O3) were synthesized from an aqueous solution of aluminum powder, aluminum chloride hexahydrate and yttrium oxide by the sol–gel method. Transparent fibrous gels were obtained by immersing a thin wire into the viscous sol, then pulling it out by hand. Rheological measurements suggested that the sols exhibited spinning when they were viscous and Newtonian or near Newtonian to the time of gelation. The sols became non-spinnable when thixotropic flow behavior was observed. It was observed that the time of hydrolysis–condensation, drawing, gelation and length of the gel fibers decreased with increasing the amounts of either acid or yttrium oxide. The time of hydrolysis–condensation and gelation decreased with increase in the amount of aluminum powder, whereas the time of drawing and spinnability increased. The desired viscosity of the sols for spinning was between 2000 and 5000 P. The dried gel fibers had a smooth surface with diameter ranging from 20 to 200 μm. The composite fiber showed fine-grained microstructure (100–200 nm) after heat treatment at 1400 °C.