Polycrystalline alumina fibers can be manufactured by precursor method and colloidal method.

However, colloidal fiber forming process is generally used in large-scale industrial production. In colloidal production, the transparent "mother liquor" is prepared by heating the aqueous solution of aluminum chloride and aluminum powder. After filtration, add an appropriate amount of silica sol (containing sio223% -26%), boric acid, phosphoric acid and stabilizer, heat and concentrate to a colloidal solution with appropriate viscosity, and spray it into a fiber "embryo" within the range of 20-50 degrees. After drying, heat treatment is carried out at 800-1300 ℃, and the amorphous alumina is gradually transformed into stable alumina.