Effect of Magnesia Addition on Microstructure and Mechanical Properties of Low Soda Alumina.

Abstract

The effect of magnesia addition on the microstructural development and the mechanical properties of commercial low-soda alumina was investigated in the context of sintered bodies highly toughened by plate-like abnormal grains. Magnesia addition did not affect sinterability and final density. The alumina bodies, with and without magnesia, sintered at just below the temperature for which fully dense materials are obtained with high bending strength (i.e., exceeding 600MPa). Very large plate-like grains were formed at higher sintering temperature in the sample without magnesia. These large plate-like grains are the reason of both a lowered bending strength and an extremely high increase in fracture toughness. Fracture toughness of more than 7MPa·m1/2 and bending strength of 200MPa were achieved in a sample sintered at 1800°C without magnesia addition. The small amount of magnesia effectively inhibited abnormal grain growth in low soda alumina and even the sample sintered at 1800°C showed a bending strength higher than 300MPa and 5MPa·m1/2 fracture toughness. The high fracture toughness obtained in these samples is attributed to crack bridging mechanism.