Preparation And Properties Of The Alumina Fibers And Fiber Boards Via A Sol-gel Method

Alumina fiber is one kind of the important high performance inorganic ceramic materials with excellent tensile strength and modulus, which is broadly applied to high temperature insulation material, catalyst support and the reinforcement of metal or ceramic matrix composites. Various methods for the alumina and mullite fibers synthesis are reviewed and a series of researches about alumina fibers prepared by sol-gel method are particularly discussed. Different kinds of influential factors like starting materials, preparation of precursor sols and heat treatment process determine the properties of the final materials. Polycrystalline alumina continuous fibers were synthesized via a sol-gel centrifugal spinning technique using anhydrous aluminum chloride, aluminum powder and acetic acid or lactic acid as starting materials. FT-IR, TG-DTA, XRD and SEM analysis were characterized the properties of the gel and alumina fibers. The effects of different spinning additives on the sol and fiber phase transformation were discussed. The result displays that, the precursor sol has the longest gelation time as 10wt% acetic acid added. When the gel fibers were sintered at 840℃ for 2 h, γ-alumina was the only phase present and transformed to phase a-alumina at 1100℃. The fibers hold the grain coarsening and were powdered seriously, explaining the pure alumina fibers have a poor creep resistance at 1400℃. The addition of SiO2 second phase particles inhibits the grain growth at high temperature and the fiber properties with different amounts of silica are studied. The influence of colloidal viscosity, spinning machine rotation speed, hot air temperature and other parameters on the fiber performance are also investigated. Mullite is the only stable combination of Al2O3-SiO2 from medium up to high temperatures at ambient pressure and the phase transformation of mullite fibers is illustrated at high temperature. The mullite fiber morphology doped with a small amount of oxide second phases at high temperatures is discussed as well. At last, the applications of alumina fibers are introduced simply, mainly to conduct the alumina fiber boards for high temperature heat insulation.