The formation of core-sheath structure and its effects on thermal decomposition and crystallization of alumina fibers

Thermal decomposition is a critical process for fabricating alumina fibers using sol-gel methods. In this work, effects of preheating time on microstructure of prepared alumina fibers were studied. Results showed that core-sheath structure formed in the fibers when holding time exceeded 2 h at 400 °C. The fibers having core-sheath structure after thermal decomposition showed more residues, smaller crystal grain size and lower density. Thermal decomposition and densification of fibers were investigated. Results showed that core-sheath structure formed because fiber surface and core underwent different decomposition reactions due to the reduction in the number of gas channels on the fiber surface. This work provides a comprehensive study of thermal decomposition of precursor fibers and provides guidelines for developing appropriate calcination schedules.