Sol-gel based extrusion of alumina fibers

Alumina fibers were prepared by sol-gel method using an in-house fabricated extruder. The starting material used for the preparation of alumina sol was aluminium-tri-isopropoxide. A suitable binder was added to the sol and aged at room temperature for gelation to occur. When the sol became a paste appropriate for extrusion, the fibers were drawn through the extruder and dried at room temperature and subsequently sintered at 1200 degrees, 1400 degrees, and 1600 degrees C in air. It was found that regardless of sintering temperature, the XRD traces indicated that the only phase present in sintered fibers was alpha-Al2O3. Thermogravimetric analysis of the extruded fibers indicated that most of the volatile compounds were burned out at 500 degrees C. The DTA and FTIR studies confirmed the phase transition to alpha-Al2O3 and this was in good agreement with the XRD analysis. The SEM investigation revealed that a dense microstructure formed when fibers sintered at 1600 degrees C. In addition, the SEM micrograph revealed that an intergranular fracture was the predominant fracture mode. Mechanical tests indicated that the optimum tensile strength was achieved for fibers sintered at 1600 degrees C.