The oriented growth behavior of α-Al2O3 grains in alumina-mullite biphasic fibers

Understanding the mechanism of the oriented growth in multi-component alumina-based fibers and inhibiting its progression is crucial for enhancing their thermal stability. In this study, a novel diphasic fiber composed of lamellar alpha-Al2O3 and mosaic-like mullite grains was prepared. We discussed the oriented growth behavior of lamellar alpha-Al2O3 grains and the diffusion phenomenon of the Al element in SiO2 substrate under the combined addition of iron sol and La2O3, proposing a new mechanism for oriented growth in diphasic fibers. The diffusion of the Si element to the tips of alumina grains contributed to a significant increase in the mobility of non-basal planes, resulting in (0001) surface growth of alpha-Al2O3 grains. Furthermore, the La segregation at grain boundaries significantly impeded the oriented growth of alpha-Al2O3 grains, which was critical for improving the thermal stability of multiphase alumina-based fibers.