Effect of thermal exposure on the microstructure and strength of an alumina-silica ceramic fiber

The microstructure and mechanical properties of an alumina-silica ceramic fiber after thermal exposure at 1100-1300 degrees C were investigated by X-ray diffraction, nuclear magnetic resonance, scanning electron microscopy, transmission electron microscopy analyses and room temperature tensile strength test. The results showed that the fiber was composed of gamma-A1(2)O(3) and amorphous SiO2. A phase reaction of gamma-A1(2)O(3) and amorphous SiO2 occurred when thermal exposure temperature exceeded 1150 degrees C, and a new mullite phase formed. The grain size of the newly formed mullite increased with the increase of exposure temperature. Both the phase transition and grain growth of mullite had a significant impact on the mechanical properties of the fiber. Tensile strength of the fiber decreased slightly when thermal exposure temperature was below 1150 degrees C, while the strength retention of the fiber decreased sharply to 65.36% as exposure temperature rose to 1200 degrees C. A higher dispersion of tensile strength was also observed at higher exposure temperatures, as revealed by the Weibull statistical model.