Effect of magnesia addition on microstructure and mechanical properties oflow soda alumina

The effect of magnesia addition on the microstructural development and the mechanical properties of commercial low-soda alumina was investigated in th e context of sintered bodies highly toughened by plate-like abnormal grains . Magnesia addition did not affect sinterability and final density. The alu mina bodies, with and without magnesia, sintered at just below the temperat ure for which fully dense materials are obtained with high bending strength (i.e., exceeding 600 MPa), Very large plate-like grains were formed at hig her sintering temperature in the sample without magnesia, These large plate -like grains are the reason of both a lowered bending strength and an extre mely high increase in fracture toughness, Fracture toughness of more than 7 MPa.m(1/2) and bending strength of 200 MPa were achieved in a sample sinte red at 1800 degrees C without magnesia addition, The small amount of magnes ia effectively inhibited abnormal grain growth in low soda alumina and even the sample sintered at 1800 degrees C showed a bending strength higher tha n 300 MPa and 5 MPa m(1/2) fracture toughness, The high fracture toughness obtained in these samples is attributed to crack bridging mechanism.