Continuous α-Al2O3 fibers grown by seeding with in-situ suspension

Abstract A highly stable α-Al2O3 suspension with average particle size of ~30 nm was prepared via selective corrosion of co-precipitated α-Fe2O3/α-Al2O3 mixture using hydrochloric acid solution. Using the in-situ α-Al2O3 suspension as a seeding agent, continuous α-Al2O3 fibers were achieved via sol-gel route. Effects of seeding and sintering on the densification behavior of the alumina fibers were investigated. Adding 1.5 wt.% of ultrafine α-Al2O3 seeds enabled α-Al2O3 to heterogeneously nucleate at a temperature as low as 700 °C, and the number of nucleation sites was high enough to eliminate the “vermicular” structures during the development of α-Al2O3 from transient phases. By calcination at 1200 °C, α-Al2O3 fiber with high density and equiaxed grains was directly obtained. A modified two-step sintering method could further result in α-Al2O3 fibers attaining almost full density with the finer grain size down to ~100 nm. Doping with trace amounts of silica was found to slow down the grain boundary migration and suppress the abnormal grain growth of α-Al2O3.