Ceramic Composites of Monazite and Alumina

Abstract

A new family of high-temperature, oxidation-resistant, ceramic composites, with (La)-monazite (LaPO,) serving as a weakly bonded interphase, is proposed. Monazite is stable and phase-compatible with alumina at temperatures at least as high as 1750°C in air. Especially important for use in high-toughness composites, the monazite-alumina interface is shown to be sufficiently weak that interfacial debonding prevents cracks from growing from monazite into alumina. Observations of fracture responses of fibrous and laminar reinforcements are presented.

(1 2 0) and (1 2 2̄) monazite deformation twins

“…It is stable with many common structural oxide ceramics [6). The weakness of monazite relative to other refractory oxides in both the brittle and ductile field makes it interesting for various structural applications [4,5,[7][8][9][10][11][12][13]. As before [1|.…”

“…Monazite (I.aP0 4 ) is refractory (mp 2072 °C), relatively soft (5 GPa), and machinable [4,5]. It is stable with many common structural oxide ceramics [6).…”

Preparation and Fracture Behavior of Alumina Platelet Reinforced Alumina-Monazite Composites

“…[8][9][10][11] Also, monazite was introduced as a weak interphase to cause cracks to propagate intergranularly during fracture, based on the results of the previous researchers. 12,13) In Fig. 2, white phase is monazite.…”

“…9) But they did not investigate what mechanism operated to enhance the fracture toughness in the textured alumina. A few years ago, Morgan and Marshall, 12) and Mawdsley et al 13) have studied damage-tolerant alumina ceramic matrix composites, in which crack deflection and delamination occurred between the alumina matrix and reinforcement material during fracture, by placing LaPO 4 (monazite) as an weak interphase to promote debonding between the matrix and reinforcement. From their results, LaPO 4 /Al 2 O 3 interface is sufficiently weak to promote debonding.…”

Thermal characterization of nanocrystalline porous CePO4ceramics

“…In recent years, rare earth phosphates have become increasingly important for several applications, which include ceramic materials, catalysts, photoluminescence materials, dielectric substrates, metal surface treatment agents, optical materials, etc. [3][4][5][6]. Other potential applications of these materials include host matrices for immobilization of actinide radio-nuclear wastes, solid protonic conductors and weak fiber matrix interfaces in ceramic-ceramic composites or thermal protection coatings [7][8][9][10].…”