Crystallization of electrostatically seeded lanthanum hexaluminate films on polycrystalline oxide fibers

Lanthanum hexaluminate (LaAl11O18), which features easily cleavable atomic planes in the magnetoplumbite (MP) structure, is a good candidate material for the fiber/matrix interface in oxide/oxide-fiber-reinforced composites. Difficulties that are encountered when using sol-gel synthesis to produce t his material include the high crystallization temperature and the occurrenc e of an intermediate phase. This paper presents a method to overcome these difficulties by introducing crystalline seeds into the LaAl11O18 sol during the fiber coating. Seed particles are deposited initially on the fibers vi a electrostatic forces, Then, the sol is dip-coated on the preseeded fibers , and the final LaAl11O18 coating is achieved,ia the use of heat treatments . The crystallization temperature can be reduced by at least 50 degreesC, i n comparison with that for the unseeded case, according to differential sca nning calorimetry measurements, and no intermediate LaAlO3 phase is formed. The estimated seed numbers are on the order of 10(9) seeds/cm(3) in the pr eseeded sol-coated fiber surfaces and 10(11) seeds/cm3 in the 4-wt%-seeded gels. The crystallization and structure of the La1-xAl12-yO19-z MP phase in the 4-wt%-seeded gels that have been heated at 400 degrees and 1200 degree sC have been studied using powder neutron diffraction.