Effect of the alumina and silica source mixing procedure on the microstructural evolution of alumina-mullite composite fibers prepared by sol–gel method

The preparation of precursor sol is the first and crucial step in fabricating oxide fibers by the sol–gel method. In this study, different aluminum-silica sols were prepared by adjusting the alumina and silica source mixing procedure using aluminum carboxylate sol and tetraethoxysilane (TEOS) as the aluminum source and silicon source, respectively. Continuous alumina-mullite precursor fibers were obtained by dry spinning and the effects of alumina and silica source mixing procedure on the phase transition and microstructure evolution of alumina-mullite composite fibers were investigated. The results showed that the mullite formation temperature in the fibers obtained by adding TEOS during the preparation of aluminum carboxylate sol was about 1300 °C, while it was 800 °C in the fibers obtained by mixing aluminum carboxylate sol and TEOS. In addition, the grain size of the fibers obtained by adding TEOS during the preparation of aluminum carboxylate sol was significantly smaller than that obtained by mixing aluminum carboxylate sol and TEOS. The mechanism of this difference was that the aluminum-silica sol obtained by adding TEOS during the preparation of aluminum carboxylate sol was a diphasic sol, while the aluminum-silica sol obtained by adding TEOS in the prepared aluminum carboxylate sol was a monophasic sol.