Last period we mainly introduced the amorphous refractory fibers. This period we will introduce polycrystalline refractory fibers.

     Polycrystalline refractory fibers are mainly mullite fiber with A12 03 content of about 70%, alumina fiber and zirconia fiber with A12 03 content of about 95%.

     Such fibers are microcrystalline structures with a grain size of several hundred angstroms. The method for producing polycrystalline refractory fibers is colloidal method and precursor method.

     The colloidal process can be used to produce mullite fibers, alumina fibers, and zirconia fibers. For example, mullite fiber is produced by adding aluminum powder to an aqueous alumina solution, heating and dissolving, then adding a silicon solution and other additives, and evaporating and concentrating to a colloid which has a certain viscosity, and blowing it with compressed air in an environment controlling humidity and temperature. Or use spun method to fibrillate the colloid, and the fiber body is subjected to high temperature treatment. The precursor method is using organic fiber such as viscose, cloth or the like as a molding medium.

     Take producing zirconia fiber as an example, the molding medium is immersed in an zirconium salt aqueous solution containing stabilizer, the zirconium salt is infiltrated into the organic fiber, and then the solution adhered to the surface of the organic fiber is removed by centrifugation or extrusion, and dried. After heating in a specific atmosphere with a certain heating system, the organic molding medium is decomposed and volatilized, and then heat-treated to obtain zirconia fibers or cloth.

     Above is the introduction of refractory fibers. Hope this can bring help to furnace builders.