NOVEL FUNCTIONAL AND HIGH TEMPERATURE APPLICATIONS OF NANOCRYSTALLINE RARE EARTH PHOSPHATE COATINGS AND COMPOSITES

摘要

The range of rare earth phosphates has been identified for their high temperature phase stability and high melting points. Non reactivity with certain other ceramic materials such as alumina, use of the rare earth phosphate as an interface in alumina matrix composites, machinability of the alumina-rare earth composites, possible applications as catalysts and the luminescent and optical properties have been subject of investigation over the last decade. Synthesis and characterization of nanocrystalline rare earth phosphate has been of recent interest in view of the wide possibilities of this range of materials for various applications. The present work relates to the synthesis of 30-50 nm size particles of lanthanum and cerium phosphates by sol-gel colloidal technique starting from respective nitrates. The gel to phosphate transformation, the high temperature stability, densification characteristics at as low temperatures as 1300 ℃ are presented. The electrical properties of these phosphates indicate low dielectric constant and loss factors. Lanthanum phosphate coatings on various substrates have been developed and certain features of such coatings have also been investigated. The paper covers an overview of the novel characteristics of the rare earth phosphates. Experimental details of synthesis of nanocrystalline phosphate by sol-gel process are presented. The possibility of practical applications of this range of materials for a variety of applications is highlighted.