Crystalline yttrium aluminate and process for making

Details Crystalline yttrium aluminate and process for making Crystalline yttrium aluminate and process for making

1992-10-30

1995-01-03

Bell, Mark L.

Compositions: ceramic

Ceramic compositions

Refractory

501152, 501153, 501 86, 501 12, 501127, 423600, 423263, C04B 3550, C04B 3510

Patent

active

053786653

ABSTRACT:
Ceramic yttrium aluminate fibers are produced by processes that result in the formation of a microcrystalline ceramic oxide structure. In one process, a stoichiometric amount of a yttrium alkoxide is mixed with an aluminum alkoxide to produce a homogeneous mixture in an alcohol solvent. Following the addition of an alkoxide precursor of ZrO.sub.2 or of HfO.sub.2, the optional addition of an alkoxide precursor of MgO, and the subsequent addition of an organic acid, hydrolytic condensation to produce a suitable sol is accomplished by adding water. A slight excess of yttrium alkoxide can be used instead of the MgO precursor. The viscosity of the sol is adjusted to form a tractable gel that is spun into fibers which, after curing and firing, are shown to be microcrystalline in form, the resulting fibers having a submicron average grain size. Strength and stability result from the presence of solid particles of partially stabilized zirconia or hafnia at the grain boundaries and the triple points. The fibers exhibit good tensile strength at high temperatures and can be employed to make ceramic composites having excellent resistance to high-temperature creep.

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