Thermally stable boron-containing mullite fibers derived from a monophasic mullite sol

Abstract

In this work, we reported the synthesis of monophasic boron-containing mullite (MBM) fibers using basic aluminum acetate (BAA) and tetraethyl orthosilicate (TEOS) as starting materials and performed a comparative study between our newly synthesized MBM and commercial Nextel™ 312 fibers. The morphology and the tensile strength are investigated for the new MBM fibers. Continuous and uniform green fibers with a smooth surface were produced via hand drawing method. After the pyrolysis process, amorphous inorganic MBM fibers with a tensile strength of 1.18 ± 0.17 GPa were obtained. After various heat treatment processes (1000–1400 °C for 1.5 h), we found the mullite formation temperature is within the temperature range from 1050 to 1075 °C for both MBM and Nextel™ 312 fibers. However, the results show that the MBM fibers fabricated in this study have a better thermal stability than Nextel™ 312 fibers despite the fact both have the same chemical composition. The improved stability of our MBM fibers is owing to their higher Al4B2O9 formation temperature and lower Al18B4O33 decomposition rate in comparison to those of Nextel™ 312 fibers. Moreover, the newly synthesized MBM fibers have more stable microstructure and less loss in tensile strength at elevated temperatures.