Fibrous composites including monazites and xenotimes

Abstract

Thermodynamically stable ceramic composites are provided for use in high temperature reactive environments. A phosphate selected from monazites and xenotimes functions as a weak bond material in the composite. Monazite comprises a family of minerals having the form MPO.sub.4, where M is selected from the larger trivalent rare earth elements of the lanthanide series (La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, and Tb) and coupled substituted divalents and tetravalents such as Ca or Sr with Zr or Th. Xenotimes are phosphates similar to monazite where M is selected from Sc, Y, and the smaller trivalent rare earth elements of the lanthanide series (Dy, Ho, Er, Tm, Yb, and Lu). High temperature ceramic composites that include monazite or xenotime and exhibit damage tolerant behavior or non-catastrophic fracture may be fabricated in a variety of material systems and reinforcement morphologies, including multilayered laminar composites; fiber, whisker, and particulate reinforced composites; hybrid laminar composites; and fabric or fiber preform composites. In preferred embodiments, the ceramic matrix comprises a material similar to the reinforcement to improve compatibility of the composite materials. The weak bond material allows debonding and 'frictional' sliding between the constituents of the composite and inhibits crack growth across the interface.