Microwave Hybrid Post-Heat Treatment of Reaction Sintered Alumina/Lanthanum Hexaaluminate Composite Ceramics

• Published in: Advanced engineering materials 2010-03, Vol.12 (3), p.216-221
• Main Authors: Negahdari, Zahra, Willert-Porada, Monika
• Format: Article
• Language: English
• Subjects: Aluminum oxide; Ceramics; Densification; Heat treatment; Lanthanum; Microwaves; Particulate composites; Sintering
• ISSN: 1438-1656; 1527-2648
• DOI: 10.1002/adem.200900319

One of the main problems in development of in situ reaction sintered alumina/lanthanum hexaaluminate composite ceramics is achievement of simultaneous densification and in situ formation of lanthanum hexaaluminate (LHA) platelets inside the matrix. Microwave hybrid post‐sintering was investigated as a method to enhance the solid‐state reaction of LHA formation and the densification of composite ceramics with 2.8–80 vol% LHA. Comparison of the conventionally and microwave assisted sintered alumina/lanthanum hexaaluminate composite ceramics revealed that utilization of microwave heating in second stage of sintering could enhance the solid‐state reaction, the densification, and the anisotropic grain growth of the LHA platelets in ceramics containing more than 20 vol% LHA and for heat treatment at 1500 °C. Lanthanum hexaaluminate (LHA) is a defective compound. With increase in the LHA content the defect concentration increases in alumina/LHA composite ceramics. The net result is that in microwave electric fields the migration of charged defects can produce a near‐surface depletion or accumulation. This constitutes a nonlinear driving force for diffusional flows of defects and ions within the material which enhance LHA in situ formation and sintering of composite ceramics.