Strengthening of Alumina by Formation of a Mullite/Glass Layer on the Surface

• Published in: Journal of the American Ceramic Society Vol. 80; no. 7; pp. 1877 - 1880
• Main Authors: Kim, Hyoun-Ee, Moorhead, A. J., Kim, Sang-Hak
• Format: Journal Article Conference Proceeding
• Language: English
• Published: Oxford, UK Blackwell Publishing Ltd 01.07.1997; Blackwell; Wiley Subscription Services, Inc
• Subjects: Applied sciences; Building materials. Ceramics. Glasses; Ceramic industries; Chemical industry and chemicals; Exact sciences and technology; Structural ceramics; Technical ceramics; Strengthening; Aluminium Silicates; Surface layer; Glass; Mechanical properties; Mullite; Experimental study; Alumina; Oxide ceramics; Structural ceramic
• ISSN: 0002-7820; 1551-2916
• DOI: 10.1111/j.1151-2916.1997.tb03064.x

A layer composed of mullite and silicate glass was caused to form on the surface of a high‐purity alumina ceramic in order to enhance the strength of the material. The layer was formed by exposing the specimens above a bed of SiC platelets at 1400°3C to a flowing H2 atmosphere containing ∼0.1% H2O. A reaction between the SiC platelets and the H2O in the environment resulted in the generation of SiO gas. Some of the SiO gas subsequently reacted with ambient H2O in the atmosphere, forming SiO2“smoke” which was deposited on, and reacted with, the alumina substrate. The strength of the ceramic was significantly improved by the reaction layer, which was found to be comprised of mullite and silicate glass. The increases in strength (about 60% above that of the material in the “as‐polished” condition) was attributed to the blunting of surface cracks. A similar strengthening effect was observed in samples of the material which had been ground with a 220‐grit diamond abrasive wheel (as had all of the samples) but not polished.