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Crystallization of Electrostatically Seeded Lanthanum Hexaluminate Films on Polycrystalline Oxide Fibers
Author(s) -
Saruhan Bilge,
Abothu Isaac Robin,
Komarneni Sridhar,
Loong ChunKeung
Publication year - 2000
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/j.1151-2916.2000.tb01700.x
Subject(s) - crystallization , materials science , lanthanum , crystallite , differential scanning calorimetry , dip coating , oxide , fiber , lanthanum oxide , composite material , coating , chemical engineering , phase (matter) , chemistry , metallurgy , inorganic chemistry , physics , organic chemistry , engineering , thermodynamics
Lanthanum hexaluminate (LaAl 11 O 18 ), 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 this material include the high crystallization temperature and the occurrence of an intermediate phase. This paper presents a method to overcome these difficulties by introducing crystalline seeds into the LaAl 11 O 18 sol during the fiber coating. Seed particles are deposited initially on the fibers via electrostatic forces. Then, the sol is dip‐coated on the preseeded fibers, and the final LaAl 11 O 18 coating is achieved via the use of heat treatments. The crystallization temperature can be reduced by at least 50°C, in comparison with that for the unseeded case, according to differential scanning calorimetry measurements, and no intermediate LaAlO 3 phase is formed. The estimated seed numbers are on the order of 10 9 seeds/cm 3 in the preseeded sol‐coated fiber surfaces and 10 11 seeds/cm 3 in the 4‐wt%‐seeded gels. The crystallization and structure of the La 1− x Al 12− y O 19− z MP phase in the 4‐wt%‐seeded gels that have been heated at 400° and 1200°C have been studied using powder neutron diffraction.